JP6447158B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device.

  In an image forming apparatus such as a copying machine, a printer, or a facsimile, a toner image is formed based on image information on an image carrier, and the toner image is transferred onto a recording material such as paper or OHP. Then, the recording material carrying the toner image is passed through a fixing device to fix the toner image on the recording material by heat and pressure.

  In the fixing device, a belt method or a film method is often used in order to save energy.

  Patent Document 1 discloses a configuration in which a thermal energy is applied to a recording material by sandwiching the film and the recording material in close contact with a plate-like heating body that contacts a thin-walled cylindrical heat-resistant film and a pressure roller. Since the film is as thin as about 100 μm, the start-up time is substantially the time until the temperature of the plate-like heating body having a small heat capacity rises. Therefore, the rise time can be shortened and the preheating power can be reduced.

  In addition, energy is saved by changing the temperature and heating area of the heating element in accordance with the image formed on the recording material, and reducing the energy supply to the non-image area (the area where no image exists in the image forming area). Such a configuration is also disclosed.

  One of the problems with brittle materials such as ceramics that are often used in plate-shaped heating elements is prevention of breakage against large loads. In particular, ceramics and glass have a phenomenon that the fracture strength called static fatigue is lowered, and even a load that can withstand a short period of time may be broken if the load state is long. For this reason, when ceramic or glass is used as the heating member of the fixing device, it is necessary to reduce the stress acting on the substrate as much as possible.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device that can be used for a long period of time by reducing stress and moment acting on the heating member to prevent the heating member from being damaged due to static fatigue.

The problems include a fixing member that rotates in contact with an unfixed image, a pressure member that forms a fixing nip portion between the fixing member, a heating member that extends in a direction perpendicular to the recording material conveyance direction, and the fixing A heat transfer member that contacts the member and transfers heat of the heating member; and a support member that supports the heating member from the opposite side of the heat transfer member, and carries an unfixed image on the fixing nip portion. In the fixing device that performs fixing through a recording material, the heating member includes a base material and a resistance heating element formed inside the base material, and the support member includes the resistance heating element formed therein. The surface region of the heating member that is not in contact with the recording material in the conveyance direction has a predetermined support interval, and the length of the heat transfer member in the recording material conveyance direction is greater than the support interval of the support member. , the heat transfer member into contact with said heating member That area, and larger than the area of the heating region of the resistance heating element, the central portion of the recording material conveyance direction of the heat transfer member is thicker than the end portion of the recording material conveyance direction of the heat transfer member It is solved by a fixing device characterized by being thin .

  According to the fixing device of the present invention, since the area where the heat transfer member contacts the heating member is larger than the area of the heating region of the heating member, the pressure contact force of the pressure member is dispersed not only in the resistance heating element but also in the base material. Act. Therefore, the stress and moment acting on the heating member can be reduced to prevent the heating member from being damaged due to static fatigue, and can be used for a long time.

1 is a schematic diagram illustrating a configuration of a printer that is an image forming apparatus according to an embodiment of the present disclosure. FIG. 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. It is sectional drawing of the direction orthogonal to the recording material conveyance direction of a heating member. It is a top view of a heating member. It is a top view which shows the 2nd structural example of a heating member. It is sectional drawing of the direction orthogonal to a recording material conveyance direction which shows the relationship between a heating member, a heat-transfer member, and a supporting member. FIG. 6 is a cross-sectional view (No. 2) in a direction orthogonal to the recording material conveyance direction, showing a relationship among a heating member, a heat transfer member, and a support member. FIG. 6 is a sectional view (No. 3) in a direction orthogonal to the recording material conveyance direction, showing a relationship among a heating member, a heat transfer member, and a support member. FIG. 6 is a cross-sectional view (part 4) in a direction orthogonal to the recording material conveyance direction, showing a relationship among a heating member, a heat transfer member, and a support member. FIG. 10 is a sectional view (No. 5) in a direction orthogonal to the recording material conveyance direction, showing a relationship among a heating member, a heat transfer member, and a support member. (A) shows a state before pressure contact by the pressure roller, and (b) shows a pressure contact state by the pressure roller.

(Embodiment)
FIG. 1 is a schematic diagram illustrating a configuration of a printer that is an image forming apparatus according to an embodiment of the present disclosure. As shown in FIG. 1, the printer includes a paper feeding unit 4, a registration roller pair 6, a photosensitive drum 8 that is an image carrier, a transfer unit 10, a fixing device 12, and the like.

  The paper feed means 4 includes a paper feed tray 14 in which paper P as recording material is stored in a stacked state, and a paper feed roller 16 that separates and feeds the paper P in the paper feed tray 14 one by one in order from the top. Have. The paper P sent out by the paper feeding roller 16 is temporarily stopped by the registration roller pair 6 to correct the posture deviation. Then, at the timing synchronized with the rotation of the photosensitive drum 8, that is, the timing at which the leading edge of the toner image formed on the photosensitive drum 8 coincides with the predetermined position of the leading edge of the sheet P in the transport direction, the registration roller pair 6 It is sent to the transcription site N.

  Outside the photosensitive drum 8, a charging roller 18 that is a charging unit and a mirror 20 that constitutes a part of the exposure unit are arranged in the rotation direction indicated by the arrows. Further, a developing unit 22 including a developing roller 22a, a transfer unit 10, and a cleaning unit 24 including a cleaning blade 24a are disposed.

  Between the charging roller 18 and the developing unit 22, exposure light Lb is irradiated on the exposure unit 26 on the photosensitive drum 8 through the mirror 20 and scanned.

  When the photosensitive drum 8 starts to rotate, the surface of the photosensitive drum 8 is uniformly charged by the charging roller 18. Based on the image information, the exposure light Lb is irradiated and scanned on the exposure unit 26 to form an electrostatic latent image corresponding to the image to be created. The formed electrostatic latent image is moved to the developing means 22 by the rotation of the photosensitive drum 8, where toner is supplied and visualized to form a toner image.

  The toner image formed on the photosensitive drum 8 is transferred to the sheet P that has entered the transfer portion N at a predetermined timing in the transfer unit 10 by applying a transfer bias.

  The paper P carrying the toner image (unfixed image) is conveyed toward the fixing device 12, fixed on the fixing device 12, and then discharged and stacked on the paper discharge tray.

  Residual toner remaining on the photosensitive drum 8 without being transferred at the transfer portion N reaches the cleaning unit 24 as the photosensitive drum 8 rotates, and is scraped off by the cleaning blade 24 a while passing through the cleaning unit 24. Removed.

  Thereafter, the residual potential on the photosensitive drum 8 is removed by the charge eliminating means, and is prepared for the next image forming step.

  FIG. 2 is a cross-sectional view showing a fixing device according to an embodiment of the present invention. As shown in FIG. 2, the fixing device 12 is a fixing belt 28 that is a fixing member that rotates in contact with an unfixed image, and a pressure member that presses against the outer peripheral surface of the fixing belt 28 to form a fixing nip portion SN. A pressure roller 30 and a heating unit 60 for heating the fixing belt 28 are provided.

  The fixing belt 28 includes a belt base, an elastic layer coated on the surface of the base, and a release layer formed on the surface of the elastic layer. The belt base is made of nickel, for example, and has an outer diameter of 30 mm and a thickness of 10 to 70 μm. The belt base is not limited to nickel, and may be formed of a heat resistant resin material such as SUS or PI (polyimide). The elastic layer is made of, for example, silicone rubber and has a thickness of 50 to 150 μm. The release layer only needs to increase the durability and ensure the release property. For example, the release layer is formed of a fluorine-based resin such as PFA or PTFE and has a thickness of 5 to 50 μm.

  The pressure roller 30 includes a solid iron cored bar 30a and an elastic layer 30b formed on the surface of the cored bar 30a. The core metal 30a is made of, for example, iron, and has an outer shape of about 40 mm and a thickness of about 2 mm. The elastic layer 30b is made of, for example, silicone rubber and has a thickness of about 5 mm. It is desirable to form a fluororesin (PFA or PTFE) layer having a thickness of about 40 μm on the surface of the elastic layer 30b in order to improve the releasability. The pressure roller 30 is pressed against the fixing belt 28 by an urging unit. The pressure roller 30 is rotated by a driving force transmitted from a driving source such as a motor provided in the image forming apparatus via a gear. The fixing belt 28 is rotated by the pressure roller 30.

  The heating unit 60 includes a heating member 56 that extends in a direction orthogonal to the conveyance direction of the paper P, a heat transfer member 50 that contacts the one surface in the longitudinal direction of the heating member 56 and equalizes the temperature, and transfers heat to the fixing belt 28. Have The heating means 60 is on the opposite side of the heat transfer member 50 and has a support member 57 that supports the heating member 56.

  The heating unit 60 functions as a nip forming member that forms the fixing nip SN with the pressure roller 30. Further, since the heating unit 60 is supported by the stay 61 connected to the side plate of the fixing device 12, the bending due to the pressing force of the pressure roller 30 is prevented, and a uniform nip width is obtained in the longitudinal direction. A low friction sheet may be interposed between the heat transfer member 50 and the inner peripheral surface of the fixing belt 28.

  A first thermistor 34 that detects the surface temperature of the fixing belt 28 is provided on the downstream side of the fixing nip SN, and a second thermistor 36 that detects the temperature of the heating member 56 is provided on the support member 57. Further, a power supply 40 for supplying power to the heating member 56 and a heating control means 42 for controlling the power supply 40 based on the detected temperatures of the first and second thermistors are provided. The heating control means 42 means a microcomputer including a CPU, ROM, RAM, I / O interface and the like.

  FIG. 3 is a cross-sectional view of the heating member in a direction orthogonal to the recording material conveyance direction. As shown in FIG. 3, the heating member 56 has a ruthenium oxide-based resistance heating element 56a printed and fired on a low thermal conductivity base material 56b such as plate glass, and an OC (overcoat) layer 56c thereon. Is formed. Although the OC layer 56c located on the fixing belt 28 side is also formed of glass or the like, it is thinner than the base material 56b and easily transfers heat to the OC layer side rather than heat transfer to the base material side. Will improve.

  FIG. 4 is a plan view of the heating member. As shown in FIG. 4, the heating member 56 includes a plurality of resistance heating elements 56a arranged in a direction (longitudinal direction) orthogonal to the recording material conveyance direction. The resistance heating element 56a includes a common wiring Wcom and individual wirings W1 to W1. W5 is connected. The common wiring Wcom and the individual wirings W1 to W5 form a comb-like conductive portion with respect to the resistance heating element 56a, and the resistance heating element 56a has a plurality of heating regions (H1 to H5).

  The first thermistor 34 that detects the surface temperature of the fixing belt 28 and the second thermistor 36 that detects the temperature of the heating member 56 are arranged corresponding to each heating region. Therefore, each heating region can be individually and independently heated by turning ON / OFF the individual wirings W1 to W5. Note that the heating regions H1 and H5 at the ends are arranged so as to cover both ends of the maximum sheet passing size.

  The heating control means 42 controls the temperature of each heating region in consideration of the detected temperature of each thermistor and the paper passing size information, and changes the heating rate of the heating member 56. In this way, by controlling the heating according to the paper passing size information, it is possible to avoid a situation where the temperature of the non-paper passing area becomes too high, and the member is damaged or the image quality is deteriorated due to the excessive temperature rise in the non-paper passing area. Can be suppressed.

  Actually, the power supply to the heating area corresponding to the non-sheet passing area may be completely stopped (off). However, if the temperature is excessively lowered, the temperature may be raised to the fixing temperature of the next image area. It may not be in time. In order to avoid this, temperature control is performed such that the temperature is kept at a second target temperature that is lower than the first target temperature corresponding to the fixing temperature of the image area but is equal to or higher than a predetermined temperature with respect to room temperature. . Therefore, power is also supplied to the heating area corresponding to the non-sheet passing area.

  FIG. 5 is a plan view showing a second configuration example of the heating member. As shown in FIG. 5, the heating regions (H1 and H5, H2 and H4) that are symmetrically located from the center in the longitudinal direction may be simultaneously turned on / off. As a result, the number of switching elements such as triacs and FETs for turning on / off can be reduced.

  4 and 5, the number of heating regions is five, but the number of heating regions may be increased by 9 divisions or may be reduced by 3 divisions. Further, the present invention is effective even with a heating member in which the heating region is not divided into a plurality.

  Hereinafter, characteristic portions of the present invention will be described.

  FIG. 6 is a cross-sectional view in a direction orthogonal to the recording material conveyance direction, showing the relationship between the heating member, the heat transfer member, and the support member. As shown in FIG. 6, the support member 57 is in contact with the surface region of the heating member 56 in which the resistance heating element 56a is not formed with a predetermined support interval. The support member 57 is in contact with the heating member 56 only on a part of the surface, and a heat-resistant resin such as LCP and a material having low thermal conductivity is used, so that most of the heat of the heating member 56 (resistance heating element 56a) is conducted. Not. The heat transfer member 50 on the opposite side of the support member 57 has one surface in surface contact with the heating member 56 and the other surface in surface contact with the fixing belt 28. The heat transfer member 50 is made of a material having high thermal conductivity such as copper or aluminum. Therefore, the heat of the heating member 56 (resistance heating element 56 a) is uniformly conducted to the fixing belt 28 via the heat transfer member 50.

  As described above, since the heating unit 60 functions as a nip forming member that forms the fixing nip portion SN with the pressure roller 30, stress and moment act on the heating unit 60 by the pressure contact force of the pressure roller 30. To do. Here, since the heating member 56 is formed of a brittle material such as glass, there is a problem that fatigue failure is likely to occur. In order to prevent fatigue failure, it is necessary to reduce the stress and moment acting on the heating member 56 as much as possible.

  Therefore, in the present embodiment, the area where the heat transfer member 50 is in contact with the heating member 56 is made larger than the area of the heating region of the resistance heating element 56a. In this way, the pressure contact force of the pressure roller 30 acts in a distributed manner not only on the resistance heating element 56a but also on the base material 56b, and as a result, the stress and moment acting on the heating member 56 are reduced. . Therefore, fatigue failure of the heating member 56 can be prevented and the fixing device 12 can be used for a long time.

  Next, an advantageous configuration other than reducing the stress and moment acting on the heating member 56 will be described.

  The heating member 56 and the heat transfer member 50 may be improved in adhesion with a heat conductive grease, a heat conductive sheet, or the like, and heat transfer to the heat transfer member 50 may be improved. As a result, it is possible to ensure heat uniformity in the longitudinal direction of the heat transfer member 50 and to improve the heating characteristics of the fixing belt 28.

  A nip region is formed when the pressure roller 30 and the heat transfer member 50 come into contact with each other via the fixing belt 28. If both ends of the support member 57 are wider than the contact surface and protrude toward the fixing belt 28, the fixing nip SN can be lengthened. Further, the separation of the recording material can be improved by the protrusion on the downstream side of the fixing nip SN.

(Modification)
The present invention has various modifications other than the above-described embodiment. Hereinafter, modified examples will be described with reference to the drawings.

  FIG. 7 is a sectional view (No. 2) in a direction orthogonal to the recording material conveyance direction, showing the relationship among the heating member, the heat transfer member, and the support member. As shown in FIG. 7, in order to further reduce the stress and moment acting on the heating member 56, it is desirable to make the width L2 of the heat transfer member 50 larger than the support interval L1 of the support member 57. When the width L2 is wider than the support interval L1, the pressure contact force of the pressure roller 30 is received by the support member 57, so that the stress and moment acting on the heating member 56 can be significantly reduced compared to the previous embodiment. .

  FIG. 8 is a sectional view (No. 3) in the direction orthogonal to the recording material conveyance direction, showing the relationship among the heating member, the heat transfer member, and the support member. As shown in FIG. 8, the central portion of the heat transfer member 50 in the recording material conveyance direction is formed thinner than the end portion. In this case, the support member 57 mainly receives the pressure contact force of the pressure roller 30. For this reason, since the load which acts on the center part of the width direction of the heat-transfer member 50 reduces, the stress and moment which act on the heating member 56 can be reduced markedly compared with previous embodiment.

  FIG. 9 is a sectional view (No. 4) in a direction orthogonal to the recording material conveyance direction, showing the relationship among the heating member, the heat transfer member, and the support member. As shown in FIG. 9, either one of the end portions of the heat transfer member 50 is formed thin. That is, the surface where the heat transfer member 50 receives the pressure contact force of the pressure roller 30 and the surface where the support member 57 supports the heating member 56 overlap each other. Also in this case, since the pressing force of the pressure roller 30 can be received mainly by the support member 57, the stress and moment acting on the heating member 56 can be reduced.

  FIG. 10 is a cross-sectional view (No. 5) showing the relationship between the heating member, the heat transfer member, and the support member in a direction orthogonal to the recording material conveyance direction. As shown in FIG. 10A, when the heat transfer member 50 does not receive the pressure contact force from the pressure roller 30, the heat transfer member 50 and the heating member 56 are separated from each other. On the other hand, as shown in FIG. 10B, when the heat transfer member 50 receives a pressure contact force from the pressure roller 30, the heat transfer member 50 is deformed and contacts the heating member 56. In this case, since a part of the pressure contact force of the pressure roller 30 is used for the deformation of the heat transfer member 50, the pressure contact force acting on the central portion of the heating member 56 is reduced. Therefore, the stress and moment acting on the heating member 56 can be reduced.

  As described above, since the fixing device according to the embodiment and the modification can reduce the stress and moment acting on the heating member 56, the heating member can be prevented from being damaged due to static fatigue and used for a long time.

DESCRIPTION OF SYMBOLS 4 Paper feed means 6 Registration roller pair 8 Photosensitive drum 10 Transfer means 12 Fixing device 14 Paper feed tray 16 Paper feed roller 18 Charging roller 20 Mirror 22 Developing means 22a Developing roller 24 Cleaning means 24a Cleaning blade 26 Exposure part 28 Fixing belt 30 Pressure roller 30a Metal core 30b Elastic layer 34 First thermistor 36 Second thermistor 40 Power supply 42 Heating control means 50 Heat transfer member 56 Heating member 56a Resistance heating element 56b Base material 56c OC layer 57 Support member 60 Heating means 61 Stay

Japanese Patent Laid-Open No. 06-95540

Claims (4)

A fixing member that rotates in contact with an unfixed image;
A pressure member that forms a fixing nip with the fixing member;
A heating member extending in a direction perpendicular to the recording material conveyance direction;
A heat transfer member that contacts the fixing member and transfers heat of the heating member;
A support member that supports the heating member from the opposite side of the heat transfer member,
In a fixing device for fixing through a recording material carrying an unfixed image in the fixing nip portion,
The heating member is composed of a base material and a resistance heating element formed inside the base material,
The support member is in contact with a surface region of the heating member, in which the resistance heating element is not formed, with a predetermined support interval in the recording material conveyance direction,
The length of the heat transfer member in the recording material conveyance direction is larger than the support interval of the support member,
The area where the heat transfer member is in contact with the heating member is larger than the area of the heating region of the resistance heating element ;
The fixing device according to claim 1, wherein a central portion of the heat transfer member in the recording material conveyance direction is thinner than an end portion of the heat transfer member in the recording material conveyance direction . The fixing device according to claim 1 , wherein a surface on which the heat transfer member receives a pressure contact force of the pressure member and a surface on which the support member supports the heating member overlap. 3. The fixing device according to claim 1 , wherein the heat transfer member is deformed and comes into contact with the heating member when being brought into pressure contact with the pressure member. An image forming apparatus comprising the fixing device according to claim 1 .

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