JP2006171123A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which can prevent temperature fall of a fixing belt, as much as possible, even during the rotation stop of the belt and can delay printing start and avert the occurrence of fixing unevenness, and to provide an image forming apparatus. <P>SOLUTION: The fixing device heat fixes the toner sticking onto a recording material by the fixing belt 21, supported rotatably by a heating roller 25 and a fixing roller 27. Heat auxiliary members 41, 42 installed to face the fixing belt 21 are held at positions where the members separate from the fixing belt 21, while the belt 21 rotates. The members are switched to the positions, where the members come into contact or proximity to the fixing belt 21 while the belt 21 is held stopped. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly, to a fixing device that heats and fixes toner adhered on a recording material by a fixing belt, and an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus including the fixing device.

  Conventionally, in an electrophotographic image forming apparatus, a fixing device using a fixing belt is used as a fixing member for heat-fixing toner transferred onto a sheet. In this type of fixing device, the fixing belt is normally held rotatably by two tension members (support rollers), and a pressure roller is brought into pressure contact with the first tension member, thereby the first belt. By arranging an elastic material such as rubber on the outer peripheral surface of the tension member and the pressure roller, a large nip portion for sandwiching the sheet for fixing the toner is secured. Therefore, the heating source for heating the fixing belt is built in the second stretching member that is located away from the first stretching member.

  By the way, since the fixing belt is not driven to rotate when the machine is in a standby state, the temperature of the fixing nip portion away from the heating source is lowered, and even if the machine is in an operation state based on the print start signal, the fixing nip portion Until the temperature rises and stabilizes, the fixing operation is not performed, and the printing start is delayed. If the fixing operation is started before the temperature of the fixing nip is stabilized, uneven fixing will occur.

Therefore, conventionally, as disclosed in Patent Documents 1 to 4, it is proposed that the fixing heating source is turned on and the fixing belt is rotationally driven to compensate for the temperature decrease of the fixing belt even in the machine standby state. Has been. However, rotationally driving the fixing belt even in the machine standby state leads to early deterioration of the fixing belt and the like.
JP 2003-307963 A JP 2002-287543 A JP 2003-295684 A Japanese Patent Laid-Open No. 11-222404

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device and an image forming apparatus that can prevent a temperature drop as much as possible even when the fixing belt is stopped from rotating, delay the start of printing, and avoid occurrence of uneven fixing. It is in.

  In order to achieve the above object, the fixing device according to the present invention is a fixing device that heats and fixes toner adhered on a recording material by a fixing belt rotatably supported by two or more stretching members. At least one heat auxiliary member installed opposite to the belt, distance switching means for changing the distance of the heat auxiliary member to the fixing belt, and control means for controlling the distance switching means according to rotation and stop of the fixing belt It is characterized by comprising. Further, an image forming apparatus according to the present invention includes the fixing device.

  According to the fixing device and the image forming apparatus of the present invention, the temperature reduction of the fixing belt is compensated as much as possible by the heat auxiliary member even in the machine standby state. Therefore, it is not necessary to rotate the fixing belt while waiting for the machine, and there is no need to delay the start of printing. Further, it is possible to obtain a good quality image without causing uneven fixing.

  In the fixing device according to the present invention, the control means is arranged such that the heat auxiliary member is separated from the fixing belt when the fixing belt is rotating, and the heat auxiliary member is the fixing belt when the fixing belt is stopped. It is preferable to control the distance switching means so as to be in contact with or in proximity to.

  The heat auxiliary member may be a heating plate provided with a metal base layer and a heating resistor layer that generates heat when energized. The heat auxiliary member may be disposed on the fixing surface side of the fixing belt, and may be switched to a position for guiding the recording material fed to the fixing device when the heat auxiliary member is separated from the fixing belt.

  Hereinafter, embodiments of a fixing device and an image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus, see FIG. 1)
An image forming apparatus 10 shown in FIG. 1 is an electrophotographic copying machine or printer, and is generally configured around a photosensitive drum 11, and the rotation direction (see arrow A) around the photosensitive drum 11. A charging charger 12, a laser scanning optical unit 13 that exposes an image with a laser beam, a developing device 14, a transfer charger 15, a separation charger 16, a residual toner cleaning device 17, and a residual charge eraser lamp 18 are arranged. Yes. The process of forming an image by an electrophotographic method using such an image forming element is well known, and the description thereof is omitted.

  The paper P is conveyed one by one from a paper feeding unit (not shown) in the direction of arrow B, and after the toner image is transferred from the photosensitive drum 11, it is sent to the fixing device 20 where the toner is heated and fixed. The driving and temperature of the fixing device 20 are controlled by the CPU 5 which is a central control unit of the device 10, and the fixing temperature, rotation / stop of the fixing belt, position switching of the heat auxiliary member and the temperature described below are also controlled by the CPU 5. Be controlled.

(Fixing device, see FIGS. 2 to 7)
Hereinafter, first to fifth embodiments of the fixing device 20 will be described. In addition, in each Example, the same code | symbol is attached | subjected regarding the same components and parts, and the overlapping description is abbreviate | omitted.

(See the first embodiment, FIG. 2)
As shown in FIG. 2, the fixing device 20 according to the first embodiment stretches the fixing belt 21 between the heating roller 25 and the fixing roller 27, and the pressure roller 31 is disposed at a position facing the fixing roller 27. Is. The heating roller 25 and the pressure roller 31 incorporate halogen heaters 26 and 32 as heating sources, respectively. As the heating source, a resistance heating element, electromagnetic induction means for generating eddy current, and the like can be used.

  The fixing belt 21 is heated to a predetermined temperature from the halogen heater 26 via the heating roller 25. In order to increase the efficiency of heat conduction, the heating roller 25 is configured as a thin metal roller such as aluminum or iron.

  The fixing roller 27 has a metal shaft portion covered with an elastic material (silicon rubber, fluorine rubber, etc.), and the pressure roller 31 has a metal core metal surface covered with an elastic material (silicon rubber, fluorine rubber, etc.). ing. Then, by pressing the pressure roller 31 toward the fixing roller 27 with a pressure mechanism (not shown), a fixing nip portion 30 having a predetermined width is formed at the pressure contact portion between the fixing roller 27 and the pressure roller 31 by elastic deformation. Yes. The sheet is conveyed from the direction of arrow B to the fixing nip portion 30 with unfixed toner on the fixing roller 27 side.

  A driving mechanism (not shown) for rotating the roller 31 in the direction of arrow a is connected to the pressure roller 31. The fixing belt 21 is driven to rotate in the direction of the arrow b by the frictional force with the pressure roller 31, and the rollers 25 and 27 are also driven to rotate.

  A temperature detection sensor (not shown) is installed at an appropriate location in the fixing device 20, and the voltage applied to the halogen heater 26 is adjusted based on the detection result of the sensor, whereby the fixing nip portion 30. The temperature is controlled to maintain a predetermined value.

  Conventionally, a spring member, a cam mechanism, or the like has been used as the pressure mechanism of the pressure roller 31, and a pressure release mechanism and a pressure change / control unit can be used together as necessary. .

  Further, it is preferable to control the rotational drive, particularly the rotational speed, with respect to the pressure roller 31 according to fixing conditions, paper type, paper transport speed, environmental state, machine state, paper passing state, and the like.

  Since the fixing belt 21 is used while being deformed around the rollers 25 and 27 by driven rotation, toughness is required, and a thin metal such as nickel or stainless steel or a heat resistant resin material such as polyimide is used as a base material. . Further, in order to ensure releasability with the toner, a releasable layer such as polytetrafluoroethylene perfluoroalkyl vinyl ether (PFA) or polytetrafluoroethylene (PTFE) is provided on the surface. In order to improve the image quality of the fixed toner image, an elastic layer may be interposed between the base material and the release layer.

  Further, in order to maintain the temperature of the fixing belt 21, heat assisting members 41 and 42 are installed facing the surface (fixing surface) of the belt 21. The heat auxiliary members 41 and 42 have at least the same width as the fixing belt 21 and are separated from the surface of the fixing belt 21 at a first position (the position shown in FIG. 2, about 5 mm from the surface of the fixing belt 21. Distance switching means (not shown) is provided for moving between the second position and the second position in contact with or close to the surface of the belt 21. As such a distance switching means, a known drive mechanism such as a cam mechanism, a gear mechanism, or a cylinder can be employed.

  The fixing belt 21 is driven to rotate during the printing operation by the image forming apparatus 10 and is controlled to stop rotating during standby. The heat auxiliary members 41 and 42 are set at the first separated positions when the fixing belt 21 is in a rotating state, and the belts when the fixing belt 21 is in a rotation stopped state such as when the image forming apparatus 10 is on standby. The second position is set in contact with or close to the surface of 21. Here, the standby state means a state from the printing instruction to the end of the printing operation, and does not include the time of the sheet passing interval during continuous printing.

  Although the heat auxiliary members 41 and 42 may be heat storage members, it is preferable to include a heat generating resistor that generates heat when energized, and at least when the device 10 is in a standby state (second position), a predetermined temperature ( 100-200 ° C).

  Specifically, the heat auxiliary members 41 and 42 can be configured as shown in FIGS. In the heat auxiliary member shown in FIG. 7A, a heating resistor layer 53 such as stainless steel is provided on a metal base material 51 such as aluminum via an insulating layer 52 such as PFA, and further an insulating layer 54 such as PFA is coated. It is a thing.

  In the heat auxiliary member shown in FIG. 7B, a heating resistor layer 63 such as stainless steel is provided on the lower surface of a metal base 61 such as aluminum via an insulating layer 62 such as PFA, and an insulating layer such as PFA is provided therebelow. 64, and an insulating layer 65 such as PFA is coated on the metal substrate 61.

  Since the heat auxiliary member shown in FIG. 7A conducts heat to the fixing belt 21 only through the insulating layer 54 coated with the heating resistor layer 53, the heat conduction efficiency is good. The heat assisting member shown in FIG. 7B conducts heat from the heating resistor layer 63 to the fixing belt 21 via the metal base 61, so that the heat conduction efficiency is slightly reduced, but the heat conduction is planarly uniform. Excellent in properties.

  In addition, as a heating source of the heat auxiliary member, a heating element using induction heating can be used instead of the heating resistor. This type of heating element has better heating efficiency than a heating source using radiant heat such as a halogen heater.

  A method of supplying power to the heat auxiliary members 41, 42 continuously or intermittently such that the temperature is constant with respect to the heat capacity of the members 41, 42, or thermistor, etc. It is possible to adopt a method of providing a temperature sensor and controlling the temperature to a constant temperature or controlling the hysteresis temperature.

  In the first embodiment, the fixing belt 21 stops rotating in the standby state of the apparatus 10, the portion wound around the heating roller 25 is heated by heat transfer from the roller 25, and the fixing nip portion 30 is pressurized. Heat is conducted from the roller 31. Further, the flat portion of the fixing belt 21 is transferred with heat assisting members 41 and 42 in contact with or close to each other to compensate for a decrease in temperature as much as possible. Accordingly, it is not necessary to rotationally drive the fixing belt 21 during the standby of the apparatus 10 to compensate the temperature, and it is not necessary to delay the start of printing. Further, it is possible to obtain a good quality image without causing uneven fixing.

  Further, the heat auxiliary members 41 and 42 are arranged to face the flat portion of the fixing belt 21, that is, the portion not wound around the rollers 25 and 27. This flat portion is a portion where heat is not supplied when the fixing belt 21 is stopped, and the temperature reduction is effectively compensated by the heat auxiliary members 41 and 42.

  On the other hand, when the fixing belt 21 is in the rotating state, the heat auxiliary members 41 and 42 are switched to the first position separated from the belt 21. Since heat conduction is sufficient while the belt 21 is rotating, heat conduction from the heat auxiliary members 41 and 42 is not necessarily required, and the risk of the belt 21 being in contact with the heat auxiliary members 41 and 42 and being damaged is avoided. Because.

  The heat auxiliary members 41 and 42 may be brought into contact / close proximity to the inner surface side of the belt 21. However, as in the first embodiment, the temperature compensation effect is better when the belt 21 is brought into contact with / close to the fixing surface side.

  By the way, when the heat auxiliary members 41 and 42 are brought into contact with the fixing belt 21 in a fixed position, the position of the flat portion is unstable, so that the contact pressure varies greatly and it is difficult to obtain a stable heat auxiliary effect. Therefore, the heat auxiliary members 41 and 42 are preferably brought into elastic contact with the fixing belt 21 by a spring or the like.

  The elastic contact pressure may be set to about 100 to 1000 gf. If the contact pressure is too small, the contact becomes unstable. If the contact pressure is too large, the elastic layers of the fixing belt 21 and the fixing roller 27 are greatly deformed, which may cause deterioration.

  Further, when the rotation of the fixing belt 21 is stopped, the heat auxiliary members 41 and 42 may be brought close to the belt 21 instead of being in contact with each other to obtain an effective heat auxiliary effect. The fixing belt 21 immediately after completion of the fixing operation is as high as about 150 to 200 ° C., and the heat assisting by the heat assisting members 41 and 42 is not required at that temperature. Accordingly, when the heat auxiliary members 41 and 42 are brought into contact with the belt 21 in spite of the fact that the auxiliary heating is unnecessary, the heat is taken away from the belt 21. In consideration of such circumstances, it is preferable that the heat auxiliary members 41 and 42 are simply brought close to each other. The proximity distance is 2 mm or less.

  Further, the temperature of the heat auxiliary members 41 and 42 may be detected, and the heat auxiliary members 41 and 42 may be brought into contact with the fixing belt 21 on condition that the temperature is equal to or higher than a predetermined temperature. Further, the heat auxiliary members 41 and 42 are brought into contact with the fixing belt 21 after the elapse of a predetermined time after the apparatus 10 enters the standby state, or on the condition that the temperature of the fixing belt 21 is detected and lowered to a predetermined temperature or less. It is also possible to adopt a control to be performed.

  Furthermore, control using both contact and proximity is also possible. For example, the heat auxiliary members 41 and 42 may be brought close to each other until a certain time has elapsed after the apparatus 10 enters the standby state, and then switched to a position where the heat auxiliary members 41 and 42 come into contact with each other in two stages.

  In addition, the heat auxiliary members 41 and 42 may be configured separately, and contact and proximity may be individually controlled. For example, the heat auxiliary member 41 arranged on the upper side can be brought into contact with the fixing belt 21 as having no heat generation function, and the heat auxiliary member 42 arranged on the lower side can be used having a heat generation function. . The upper heat auxiliary member 41 does not have a heat generation function due to heat conduction from the heating roller 25 by contact with the fixing belt 21 and heat transfer by convection of air heated by the lower heat auxiliary member 42. However, it is warmed to some extent and exhibits a heat assist effect for the fixing belt 21.

  By the way, in the fixing device 20, in order to achieve space saving and increase the width of the fixing nip portion 30, it is necessary to reduce the surface hardness of the elastic body of the fixing roller 27 and increase the pressure deformation thereof. For this reason, it is preferable that the elastic material covering the surface of the fixing roller 27 has an Asker C hardness of 30 to 70 degrees.

  In order to efficiently heat the entire belt while the fixing belt 21 is rotating, it is preferable to increase the ratio of the length of the belt 21 that is hung on the rollers 25 and 27 to the circumferential length of the belt 21. It is also effective in terms of space.

(Refer to the second embodiment, FIG. 3)
As shown in FIG. 3, the fixing device 20 according to the second embodiment is configured such that the heat auxiliary members 41 and 42 are longer than the first embodiment and one end of the heat auxiliary members 41 and 42 is also hung on the heating roller 25. Yes. Further, the other end portion of the heat auxiliary member 41 is configured to hang on the fixing roller 27.

  Since the heating roller 25 has a built-in halogen heater 26 as a heating source, the heat from the heater 26 is conducted to the flat portion of the fixing belt 21 whose rotation is stopped via the heat assisting members 41 and 42, and the heat assisting. It can be performed.

  Therefore, it is not always necessary for the heat auxiliary members 41 and 42 used in the second embodiment to incorporate a heating resistor as shown in FIGS. 7A and 7B, and a good heat conductor such as aluminum and its surface. And a material having a low emissivity (for example, a resin material such as Teflon (registered trademark)).

(Refer to the third embodiment, FIG. 4)
As shown in FIG. 4, the fixing device 20 according to the third embodiment is obtained by adding a roller 28 as a stretching member. The roller 28 functions as a control roller for preventing the fixing belt 21 from meandering and an auxiliary roller for applying / recovering the lubricant to the fixing belt 21. In the third embodiment, the upper heat auxiliary member 41 is bent along the moving path of the fixing belt 21 due to the addition of the roller 28.

(Refer to the fourth embodiment, FIG. 5)
As shown in FIG. 5, the fixing device 20 according to the fourth embodiment is provided with a roller 28 as in the third embodiment. The roller 28 includes a halogen heater 29 as a heating source. The temperature stability of the fixing belt 21 is improved. The upper heat assisting member 41 is divided into two parts, which are arranged along the moving path of the fixing belt 21 due to the addition of the rollers 28.

(Refer to the fifth embodiment, FIG. 6)
As shown in FIG. 6, the fixing device 20 according to the fifth embodiment has the same configuration as that of the first embodiment, and the first position of the heat auxiliary member 42, that is, the position separated from the fixing belt 21. The sheet is conveyed to the fixing nip portion 30 from the direction indicated by the arrow B and is set to a position for guiding the sheet.

  By causing the heat auxiliary member 42 to function as a paper guide, the paper immediately before entering the fixing nip 30 is preliminarily heated by the heat stored in the heat auxiliary member 42 or the heat from the internal heating resistor. Therefore, the toner fixing property is improved.

  In this case, the heat auxiliary member 42 is controlled to an optimum temperature when it is in the first position that functions as a guide and when it is in the second position that functions as the heat auxiliary member of the fixing belt 21. It is preferable.

  Further, it is preferable that the heat auxiliary member 42 that also functions as a paper guide adopt the configuration shown in FIG. This is because the heat from the heating resistor layer 63 is conducted to the paper through the metal substrate 61 while maintaining planar uniformity.

(Other examples)
The fixing device and the image forming apparatus according to the present invention are not limited to the above-described embodiments, and can be variously modified within the scope of the gist.

  In particular, the present invention is not limited to the image forming apparatus 10 shown in the above embodiment, but various image forming apparatuses such as a color / monochrome printer, a color / monochrome copying machine, and a facsimile machine, or a halogen lamp or LED not limited to a laser beam. The present invention can be applied to an image forming apparatus using an exposure light source.

  Further, the configuration of the heat auxiliary member, the details of the shape, the configuration of the fixing belt and the stretch member, the stretch form, and the like are arbitrary.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus. 1 is a cross-sectional view illustrating a first embodiment of a fixing device according to the present invention. FIG. 6 is a cross-sectional view illustrating a second embodiment of the fixing device according to the present invention. FIG. 6 is a cross-sectional view showing a third embodiment of the fixing device according to the present invention. FIG. 6 is a cross-sectional view showing a fourth embodiment of the fixing device according to the present invention. FIG. 7 is a cross-sectional view showing a fifth embodiment of the fixing device according to the present invention. It is sectional drawing which shows the structure of a heat auxiliary member.

Explanation of symbols

5 ... CPU
DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 20 ... Fixing apparatus 21 ... Fixing belt 25, 27, 28, 31 ... Stretch member (roller)
41, 42 ... heat auxiliary member 51, 61 ... metal base material 53, 63 ... heating resistor layer

Claims (6)

In a fixing device that heats and fixes toner adhered on a recording material by a fixing belt rotatably supported by two or more stretching members,
At least one heat assisting member installed opposite to the fixing belt;
Distance switching means for changing the distance of the heat auxiliary member to the fixing belt;
Control means for controlling the distance switching means according to rotation and stop of the fixing belt;
A fixing device comprising:   The control unit controls the distance switching unit so that the heat auxiliary member is separated from the fixing belt when the fixing belt is rotating, and the heat auxiliary member is operated when the fixing belt is stopped. The fixing device according to claim 1, wherein the distance switching unit is controlled so as to contact or approach the fixing belt.   The fixing device according to claim 1, wherein the heat auxiliary member is a heating plate including a metal base layer and a heating resistor layer that generates heat when energized.   The fixing device according to claim 1, wherein the heat auxiliary member is disposed on a fixing surface side of the fixing belt.   5. The fixing device according to claim 1, wherein when the heat auxiliary member is separated from the fixing belt, the heat auxiliary member is switched to a position for guiding a recording material fed into the fixing device. An image forming apparatus comprising the fixing device according to claim 1.

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