JP2005321511A - Image forming apparatus and fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure safety by preventing an excessive increase in the temperature of a fixing device being in an abnormal state when released from pressure, the fixing device using a fixing member having an elastic layer suitable for a color image forming apparatus. <P>SOLUTION: The image forming apparatus includes: a fixing section in which a recording material with an image held thereon is heated and fixed while conveyed by being held in a nip between the first fixing member having the elastic layer 101 and a second fixing member 102 disposed opposite the first fixing member; a pressure mechanism 107 for applying pressure to the first fixing member and the second fixing member; pressure release mechanisms 108 and 109 for releasing the first fixing member and the second fixing member from the pressure for separation; an M2; and a switch 110 for detecting separation between the first fixing member and the second fixing member by the pressure release mechanism. In response to a switch 110 when the first and second fixing members are separated, the image forming apparatus forcibly shuts off power supplied to the heat generating part of the fixing member. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to protection of the fixing device.

  In recent years, colorization has progressed in image forming apparatuses such as printers and copiers. As a fixing device used in such a color image forming apparatus, a heat fixing roller having an elastic layer on a fixing member is well known. An example of a fixing device using a fixing roller having such an elastic layer is shown in FIG.

  In this fixing device, unfixed at the contact nip portion (fixing nip portion) N of the two heating rollers, which is composed of a fixing roller 801 and a pressure roller 802, which are rotationally driven in the direction of the arrow and adjusted to a predetermined fixing temperature. The recording material P on which the toner image t is placed is configured to pass therethrough.

  When the unfixed toner image t passes through the nip portion N, it is heated and pressed by the fixing roller 801 and the pressure roller 802 and fixed on the recording material P as a completed image (permanently fixed image).

  Each of the rollers 801 and 802 is provided with a halogen heater H in the center, and the radiant energy generated from the heater H is absorbed by the aluminum cores 801a and 802a inside each roller and heated. The thermistors 803 and 804 are elastically brought into contact with the surfaces of the rollers 801 and 802, and the rollers 801 and 802 correspond to the halogen heater H based on the temperature detected by the thermistors 803 and 804. Power supply is controlled and temperature adjustment is performed.

  Elastic layers 801b and 802b made of silicone rubber having a thickness of 2 mm are provided around the aluminum cores 801a and 802a of the rollers 801 and 802, respectively. PFA (tetrafluoroethylene / perfluoroalkyl ether copolymer / tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin), FEP (tetrafluoroethylene / hexafluoropropylene copolymer) to prevent paper dust and the like from sticking Coating layers 801c and 802c made of a resin having good releasability and heat resistance, such as a coalescence / tetrafluoroethylene / hexafluoropropylene copolymer resin) are provided.

  The reason why the elastic layer 801b is provided on the side of the fixing roller 801 that is a fixing member in contact with the unfixed toner t in the fixing nip portion N is to heat and fix the toner image surface as uniformly as possible.

  By providing the elastic layer 801b on the fixing roller 801 side, when the toner image t passes through the fixing nip portion N, the elastic layer 801b is deformed along the toner layer, so that the toner that is unevenly placed on the image. However, it is encased in the elastic layer 801b and uniformly heated, whereby uniform fixing is achieved.

  The image fixed uniformly in this way has no gloss unevenness, and has a feature that the light transmittance of the image is excellent particularly when fixing an OHT (transparent sheet for an overhead projector).

  However, in a heat roller type fixing device having such an elastic layer, the heat capacity of the heat roller itself increases, and the time required to raise the temperature of the fixing roller 801 to a temperature suitable for toner image fixing. There was a problem that (warm-up time) was long. Further, the cost of the fixing member is also expensive.

  On the other hand, as a low-cost fixing device having a short warm-up time, a film fixing type fixing device used in a monochrome printer or the like is well known. An example of such a film fixing device is shown in FIG.

  In this fixing device, a thin fixing film 911 is sandwiched between a heater 912 fixedly supported by a support member 915 and an elastic pressure roller 914 to form a fixing nip portion N, and the fixing film 911 is attached to the heater 912. The recording material P carrying the toner image t is nipped and conveyed between the fixing film 911 and the pressure roller 914 in the fixing nip portion, and is moved by the heat from the heater 912 via the fixing film 911. The upper toner image is heated. The unfixed toner image t on the recording material P receives heat and pressure when passing through the fixing nip portion N, and is fixed on the recording material P as a completed fixed image (permanently fixed image).

  The fixing film 911 is, for example, an endless film made of a heat-resistant resin having a thickness of about 50 μm, and a release layer (such as a fluororesin coating layer) having a thickness of about 10 μm is formed on the surface. The heater 912 is a ceramic. A resistance heating element is formed on a substrate. The temperature detection means 913 is brought into contact with the heater 912, the temperature of the heater 912 is detected, and the temperature is controlled by a control means (not shown) so that the temperature of the heater 912 becomes a desired temperature.

  Further, in order to reduce the heat capacity of the fixing film 911, the fixing film 911 is not provided with an elastic layer.

  In the fixing device having such a configuration, since the heat capacity of the fixing film 911 is extremely small, the power is supplied to the heater 912, and then the temperature of the fixing nip portion N is raised to a temperature capable of fixing the toner image in a short time. It is possible.

  However, when a film fixing device using such a fixing film 911 not provided with an elastic layer is used as a fixing device of a color image forming apparatus, unevenness due to the presence or absence of the surface of the recording material P or the toner layer or unevenness of the toner itself. As a result, the surface of the fixing film 911 cannot follow, and the difference in heat applied from the fixing film between the convex portion and the concave portion is caused. The convex part that is in good contact with the fixing film conducts heat well from the fixing film, and the concave part is less likely to conduct heat from the fixing film than the convex part.

  In a color image, since a plurality of color toner layers are mixed and used, the unevenness of the toner layer is larger than that of a black and white image, and if the fixing film as a fixing member does not have an elastic layer, uneven glossiness of the fixed image may occur. When the recording material is OHT, the image quality deteriorates due to an increase in image quality, and the transparency is poor when a fixed image is projected, resulting in a decrease in image quality.

Therefore, a fixing device constituting a low-cost color-on-demand fixing device by using a fixing belt (fixing film) having an elastic layer as disclosed in Patent Document 1 for a film fixing device has been proposed. ing.
Japanese Patent Laid-Open No. 11-15303

  However, silicone rubber and other materials with high thermal conductivity used for the elastic layer of the fixing belt are easily deformed, and if left for a long time without rotating in a pressurized state, the warm-up time at the start of printing alone is not sufficient. There has been a problem that the image reflectance deteriorates because the reflectance of the image changes only in the portion that has been pressurized without returning from the deformed state.

  Also, since the life of the fixing sleeve is shortened, the fixing belt is separated from the pressure roller by the automatic pressure releasing means that automatically releases the pressure in the sleep mode where the operation is not performed for a long time or when the power is turned off. There was a need to avoid it. However, in the case where energization heat is generated with the fixing belt and the fixing pressure roller being released due to some abnormality, the heater is not properly transferred from the heater to the fixing belt and the fixing pressure roller. Since the heater is energized and heated, the heating rate of the heater is remarkably increased, the elastic layer of the fixing belt is damaged by heat, and the life is shortened.

  The present invention has been made under such circumstances. In a fixing device using a fixing member having an elastic layer, which is suitable for a color image forming apparatus, an excessive rise in an abnormal state in a pressure release state is provided. The task is to prevent the temperature and ensure safety.

  In order to solve the above-described problems, in the present invention, the image forming apparatus is configured as the following (1) to (4), and the fixing device is configured as the following (5) and (6).

(1) a fixing unit that heats and fixes a recording material carrying an image at a nip formed by a first fixing member having an elastic layer and a second fixing member disposed opposite to the first fixing member;
A pressure mechanism that pressurizes the first fixing member and the second fixing member;
A pressure release mechanism for releasing the pressure of the first fixing member and the second fixing member and separating them from each other;
A fixing power supply for supplying power to the heat generating part of the first fixing member;
A blocking means for detecting the operation of the pressure release mechanism and blocking power supply to the fixing power supply device;
An image forming apparatus.

(2) In the image forming apparatus according to (1),
The blocking means includes a mechanical switch that detects the separation between the first fixing member and the second fixing member by the pressure release mechanism, and performs an blocking operation based on on / off of the mechanical switch. .

(3) In the image forming apparatus of (1),
The blocking means detects a separation between the first fixing member and the second fixing member by the pressure release mechanism;
An image forming apparatus comprising: a relay that cuts off power supply to the fixing power supply device based on an output signal of the detection means.

(4) In the image forming apparatus according to any one of (1) to (3),
An image forming apparatus comprising a temperature protection element that cuts off power supply to the heat generating portion when the temperature of the first fixing member becomes higher than a predetermined temperature.

(5) a fixing unit that heats and fixes a recording material carrying an image at a nip formed by a first fixing member having an elastic layer and a second fixing member disposed opposite to the first fixing member;
A pressure mechanism that pressurizes the first fixing member and the second fixing member;
A pressure release mechanism for releasing the pressure of the first fixing member and the second fixing member and separating them from each other;
Detecting means for detecting a separation between the first fixing member and the second fixing member by the pressure release mechanism for shutting off the power supply to the heat generating portion of the first fixing member;
A fixing device provided with

(6) In the fixing device according to (5),
A fixing device including a temperature protection element that cuts off power supply to the heat generating portion when the temperature of the first fixing member becomes higher than a predetermined temperature.

  According to the present invention, in a fixing device using a fixing member having an elastic layer, it is possible to prevent overheating when the device is abnormal in a pressure release state and to ensure safety.

  Hereinafter, the best mode for carrying out the present invention will be described in detail by way of examples.

  FIG. 1 is a cross-sectional view illustrating a configuration of a fixing device in an “image forming apparatus” according to a first exemplary embodiment. The fixing device used in this embodiment is a fixing belt heating method and a pressure rotating body driving method (tensionless type). Note that the overall configuration and operation of the image forming apparatus according to the present exemplary embodiment are the same as those in the related art, and thus description thereof is omitted.

a The overall configuration 101 of the fixing device is a fixing belt as a first fixing member, which is a cylindrical (endless belt-like) member in which an elastic layer is provided on the belt-like member. The fixing belt 101 will be described in detail later in section c.

  Reference numeral 102 denotes a pressure roller as a second fixing member, which includes a cored bar portion 102a and a rubber portion 102b. Reference numeral 103 denotes a heat-resistant / rigid heater holder having a substantially semicircular arc-shaped cross section, and 104 is a fixing heater as a heat source. The fixing belt 101 is loosely fitted on the heater holder 103. In this embodiment, the fixing heater 101 is a ceramic heater which will be described in detail in section b below. A thermistor 40 detects the temperature of the fixing heater 101 for temperature control.

  The heater holder 103 is formed of a liquid crystal polymer resin having high heat resistance, plays a role of holding the fixing heater 16 and guiding the fixing belt 101. In this example, DuPont Zenite 7755 (trade name) was used as the liquid crystal polymer. The maximum usable temperature of Zenite 7755 is about 270 ° C.

  The pressure roller 102 is formed by forming a silicone rubber layer 102b having a thickness of about 3 mm on a stainless steel core metal 102a by injection molding and coating a PFA resin tube having a thickness of about 40 μm thereon. The pressure roller 102 is arranged such that both end portions of the core metal are rotatably supported by bearings between a side plate (not shown) and a front side plate of the apparatus frame 105. A heating assembly including the heater 104, the heater holder 103, the fixing belt 101 and the like is disposed above the pressure roller 102 in parallel with the pressure roller 102 with the heater 104 facing downward, and is provided inside the heater holder 103. A pressure mechanism comprising a pressure stay 106 and pressure springs 107 provided at both ends of the pressure stay 106 is attached along the axial direction of the pressure roller 102 with a force of 98 N (10 kgf) on one side and a total pressure of 196 N (20 kgf). As a result, the downward surface of the fixing heater 104 is brought into pressure contact with the elastic layer of the pressure roller 102 via the fixing belt 101 with a predetermined pressing force against the elasticity of the elastic layer, and a predetermined width required for heat fixing. The fixing nip portion N is formed. It also has a pressure release mechanism consisting of a pressure release stay 108, a pressure release cam 109, and a motor M2. During jamming, etc., the motor M2 is rotated and the pressure release cam 109 is rotated to release the pressure. The transfer material P can be easily removed.

  A switch 110 detects whether the fixing belt 101 and the pressure roller 102 are released from pressure or are pressed.

  Reference numeral 413 (see FIG. 4) is disposed inside the pressure stay 106 and the sleeve guide 103 so as to come into contact with the fixing heater 104, and temperature protection for stopping power supply to the fixing heater 104 when the temperature becomes abnormally high. It is an element.

  The pressure roller 102 is rotationally driven by the driving means M in the counterclockwise direction indicated by the arrow at a predetermined peripheral speed. A rotational force acts on the cylindrical fixing belt 101 by the pressure frictional force at the fixing nip portion N between the outer surface of the pressure roller 102 and the fixing belt 101 by the rotational driving of the pressure roller 102, so that the fixing belt 101 is While the inner surface of the heater holder 103 slides in close contact with the downward surface of the fixing heater 104, the outer periphery of the heater holder 103 is rotated in the clockwise direction indicated by the arrow. Grease is applied to the inner surface of the fixing belt 101 to ensure slidability between the heater holder 103 and the inner surface of the fixing belt 101.

  The pressure roller 102 is rotationally driven, and accordingly, the cylindrical fixing belt 101 is driven and rotated, and the fixing heater 104 is energized. The fixing heater 104 rises in temperature and rises to a predetermined temperature. In this state, the transfer material P carrying an unfixed toner image is introduced between the fixing belt 101 and the pressure roller 102 in the fixing nip portion N, and the toner image carrying surface side of the transfer material P is fixed to the fixing nip portion N. The fixing belt 101 is in close contact with the outer surface of the fixing belt 101, and is nipped and conveyed through the fixing nip N together with the fixing belt 101. In this nipping and conveying process, heat of the fixing heater 104 is applied to the transfer material P via the fixing belt 101, and an unfixed toner image on the transfer material P is heated and pressed on the transfer material P to be melted and fixed. . The recording material P that has passed through the fixing nip N is discharged from the fixing belt 101.

b Fixing heater 104
In this embodiment, the fixing heater 104 serving as a heat source is formed by applying a conductive paste containing silver / palladium alloy in a film having a uniform thickness on a substrate made of aluminum oxide (alumina) or aluminum nitride by screen printing. In this way, a ceramic heater is used in which a resistance heating element is formed and a glass coat made of pressure-resistant glass is applied.

The fixing heater 104
1. A horizontally long alumina substrate whose longitudinal direction is the direction orthogonal to the paper passing direction,
2. A conductive paste containing silver palladium (Ag / Pd) alloy, which is applied to the surface side of the alumina substrate along the length by screen printing in a linear or belt shape and generates heat when current flows, has a thickness of about 10 μm, A resistance heating element layer having a width of about 1 to 5 mm,
3. As the power supply pattern for the resistance heating element layer, the first and second electrode portions and the extended electric circuit portion, which are similarly patterned by screen printing of silver paste on the surface side of the alumina substrate,
4). A thin glass coat or polyimide having a thickness of about 10 μm, which can withstand the rubbing against the fixing belt 101 and is formed on the resistance heating element layer and the extension circuit portion to ensure protection and insulation. coat,
Etc.

c Fixing belt 101
The fixing belt 101 is formed by coating a polyimide rubber with an endless film formed in a cylindrical shape with a thickness of 50 μm, a silicone rubber layer as an elastic layer by a ring coating method, and covering a PFA resin tube with a thickness of 30 μm. .

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 101. In this example, a material having a thermal conductivity of about 4.19 × 10 ⁻³ J / sec · cm · K and a silicone rubber having a high thermal conductivity were used.

  On the other hand, it is desirable to make the rubber layer of the fixing belt 101 as thick as possible from the viewpoint of image quality such as OHT permeability and minute gloss unevenness on the image. According to the study by the present inventors, it has been found that a rubber thickness of 200 μm or more is necessary to obtain a satisfactory level of image quality. The silicone rubber layer in this example was 250 μm thick.

  Further, by providing a fluororesin layer on the surface of the fixing belt 101, the surface releasability is improved, and an offset phenomenon that occurs when the toner once adheres to the surface of the fixing belt 101 and moves to the transfer material P again. Can be prevented.

  Further, when the fluororesin layer on the surface of the fixing belt 101 is a PFA tube, a uniform fluororesin layer can be formed more easily.

  FIG. 2 shows a side view of the fixing device during pressurization. FIG. 3 shows a side view of the fixing device when pressure is released. In this embodiment, the switch 110 is not turned on when pressure is released (OFF), and the switch 110 is turned on when pressure is applied (ON). However, the position of the switch 110 may be changed so that the switch is not turned on when pressure is applied.

  FIG. 4 is a block diagram of an electric circuit for energizing the fixing device in this embodiment. In the figure, 400 is a commercial AC power supply, 401 is a triac that supplies power to the heater, 402 is a main body control device including a CPU, 403 is a triac drive circuit, 404 is a line filter, 405 is a relay, and 406 is a DC power supply voltage. Yes, it is a line that supplies the same 24V voltage as the motor of the apparatus main body and the power source of the high voltage power source. 410 is a fixing device, 104 is a heater, 40 is a thermistor, 413 is a temperature protection element, and a temperature fuse or a thermo switch is used. Reference numeral 110 denotes a pressure detection switch.

  When the fixing belt 101 and the pressure roller 102 are pressurized, the pressure detection switch 414 is turned on (see 110 in FIG. 2), so that the relay 405 that has cut off the AC power is supplied with current from the DC power voltage 406. Since the relay contact is turned on and current can be supplied from the AC power source, power can be supplied to the heater 104 by the control of the triac 401. Further, when the pressure release is performed, the pressure detection switch 110 is turned off, so that the relay 405 is stopped from supplying power and cannot supply current from the AC power source.

  Therefore, even if the energization to the fixing heater 104 is maintained in a state where the pressurization of the fixing belt 101 and the fixing pressure roller 102 is released due to some abnormality, the current supply from the AC power source to the fixing heater 104 is supplied by the relay 405. Since it is forcibly cut off, it is possible to prevent overheating when the device is abnormal in the pressure release state and to ensure safety, and the elastic layer of the fixing belt is heated by energization in the pressure release state. It will not be damaged and will not reduce the lifespan.

  Further, even if the pressure release is performed for some reason, the pressure detection switch 110 is not turned OFF, or the contact of the relay 405 is not turned OFF, the energization to the fixing heater 104 is not cut off, and the fixing belt 101 is excessive. When the temperature rises, the temperature fuse or thermo switch 413, which is a temperature protection element, is turned off to cut off the power supply to the fixing heater 104, thereby ensuring the safety of the fixing device.

  FIG. 5 shows a modification in which the AC power supply line is directly turned off and on by the pressure detection switch 110.

  In this embodiment, an example in which a resistance heating element (ceramic heater) is used has been shown. However, as long as the fixing film or belt is driven by a pressure roller, the heat source may of course be induction heating or a halogen heater.

  FIG. 6 is a cross-sectional view illustrating the configuration of the fixing device in the “image forming apparatus” according to the second embodiment. The same functional parts as those in the first embodiment are denoted by the same reference numerals, and redundant description thereof is omitted here. Note that the overall configuration and operation of the image forming apparatus according to the present exemplary embodiment are the same as those in the related art, and thus description thereof is omitted.

  In FIG. 6, reference numeral 511 denotes a sensor flag, which is configured to shield the photosensor 512 at the time of pressurization by an opaque resin attached to a pressurization separation shaft. The sensor flag may be disk-shaped, and a configuration may be adopted in which a notch is provided and light is guided during pressurization.

  FIG. 7 shows a block diagram of an electric circuit for energizing the fixing device in this embodiment. At the time of pressurization, the photosensor 512 is shielded by the sensor flag 511, the photosensor 512 is turned off, and the relay 605 is turned on via the protection circuit 617 and the FET 608, so that the fixing heater 104 can be energized. When the pressure release is performed, the photosensor 512 is not shielded by the sensor flag 511, the photosensor 512 is turned on, and the relay 605 is turned off via the protection circuit 617 and the FET 608. No current can be supplied to 104.

  Therefore, even if energization to the fixing heater 104 is maintained in a state where the pressure of the fixing belt 101 and the fixing pressure roller 102 is released due to some abnormality, the current supply from the AC power source to the fixing heater 104 is supplied by the relay 605. Since it is forcibly cut off, it is possible to prevent overheating when the device is abnormal in the pressure release state and to ensure safety, and the elastic layer of the fixing belt is heated by energization in the pressure release state. It will not be damaged and will not reduce the lifespan.

  Also, in this embodiment, even if the pressure release is performed for some reason, if the photosensor 512 is not turned on or the contact of the relay 605 is not turned off and the fixing heater 104 is excessively heated, the temperature protection is performed. The temperature fuse or thermo switch 413 as an element is turned off to stop the power supply to the fixing heater 104, the elastic layer of the fixing belt 101 is prevented from being damaged by heat and the life is shortened, and the safety of the fixing device is prevented. Is secured.

Sectional drawing which shows the structure of the fixing device used in Example 1. FIG. Side view of the fixing device under pressure Side view of the fixing device in the pressure release state Electrical circuit block diagram Electrical circuit block diagram Sectional drawing which shows the structure of the fixing device used in Example 2. Electrical circuit block diagram Sectional drawing which shows the structure of a prior art example Sectional drawing which shows the structure of a prior art example

Explanation of symbols

101 Fixing Belt 102 Pressure Roller 104 Fixing Heater 107 Pressure Spring 108 Pressure Release Stay 110 Switch

Claims (6)

A fixing unit that sandwiches and conveys and heats and fixes a recording material carrying an image at a nip formed by a first fixing member having an elastic layer and a second fixing member disposed opposite to the first fixing member;
A pressure mechanism that pressurizes the first fixing member and the second fixing member;
A pressure release mechanism for releasing the pressure of the first fixing member and the second fixing member and separating them from each other;
A fixing power supply for supplying power to the heat generating part of the first fixing member;
A blocking means for detecting the operation of the pressure release mechanism and blocking power supply to the fixing power supply device;
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The blocking means includes a mechanical switch that detects the separation between the first fixing member and the second fixing member by the pressure release mechanism, and performs a blocking operation based on on / off of the mechanical switch. An image forming apparatus. The image forming apparatus according to claim 1.
The blocking means detects a separation between the first fixing member and the second fixing member by the pressure release mechanism;
An image forming apparatus comprising: a relay that cuts off power supply to the fixing power supply device based on an output signal of the detection means. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus comprising: a temperature protection element that cuts off power supply to the heat generating portion when the temperature of the first fixing member becomes higher than a predetermined temperature. A fixing unit that heats and fixes a recording material carrying an image at a nip formed by a first fixing member having an elastic layer and a second fixing member disposed opposite to the first fixing member;
A pressure mechanism that pressurizes the first fixing member and the second fixing member;
A pressure release mechanism for releasing the pressure of the first fixing member and the second fixing member and separating them from each other;
Detecting means for detecting a separation between the first fixing member and the second fixing member by the pressure release mechanism for shutting off the power supply to the heat generating portion of the first fixing member;
A fixing device comprising: The fixing device according to claim 5.
A fixing device comprising: a temperature protection element that cuts off power supply to the heat generating portion when the temperature of the first fixing member becomes higher than a predetermined temperature.

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