JP6459541B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a thermal fixing device in an electrophotographic image forming apparatus, and an image forming apparatus such as a copying machine, a printer, and a facsimile equipped with the fixing device.

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

  As a fixing device that realizes energy saving, a technique of heating a thin belt or film as a fixing member by a resistance heater in which a resistance heating element is formed on a ceramic or glass substrate is known. Hereinafter, a conventional film heat fixing device will be introduced as such an energy saving fixing device.

  Patent Document 1 discloses a film heat fixing device using a plate heater. This apparatus sandwiches a film and a recording material in close contact with a plate-like heating body that contacts a thin cylindrical heat-resistant film and a pressure roller, and gives thermal energy to the recording material. Since the film is as thin as about 100 μm, it is only necessary to raise the temperature of the plate-like heating body having a small heat capacity for rising, so that the rising time can be shortened and the preheating power can be reduced.

  Patent Document 2 discloses a configuration in which an insulating layer (ceramics, glass) and a resistance heating element are sequentially formed on a metal substrate, and a thin cylindrical heat-resistant film is heated via the metal substrate and the insulating layer. In the configuration in which a thin film is directly heated by a plate-like heating body, the film temperature of the non-sheet passing portion is likely to overheat, and the heat resistance and wear of the film are problems. However, by heating the film through the metal substrate, temperature uniformity occurs in the longitudinal direction in the metal substrate, so that it is possible to prevent an excessive increase in the film temperature of the non-sheet passing portion.

  In the film heating and fixing device using the plate heater of Patent Document 3, a holder for supporting the heater is required. The holder needs to be insulative in order to improve energy saving performance, and to have a complicated shape in order to also serve as a film guide. Therefore, as in Patent Document 3, a thermoplastic resin (LCP, liquid crystal polyester, etc.) is often used for the holder. In this fixing device, the heat of the heater is prevented from escaping to the holder side instead of the film side, and the heater is supported only at both ends in the short direction of the heater so that the holder itself is not melted by heat. The holder is provided with a countersink so that the part directly below is hollow.

  As described above, when the countersink portion is provided in the holder and the heater is supported only at both ends in the short side direction of the heater, the heater is bent in the short side direction due to the force applied to the fixing nip, and a large stress may be generated inside. There is. In particular, in the case of a resistance heater using a glass substrate, a sufficient safety factor can be obtained because the fracture stress varies greatly depending on the number of microscopic scratches and static fatigue (strength gradually decreases with long-term load) as a characteristic of glass. I need to take it. Therefore, there is no choice but to reduce the load applied to the fixing nip in order to reduce the stress applied to the heater. As a result, since the fixing nip width is reduced and the fixing nip pressure is reduced, it has not been possible to cope with an increase in the speed of an apparatus that requires a wide fixing nip width and a high fixing nip pressure.

Therefore, in the present invention, in a fixing device that heats a fixing member by a resistance heater in which a resistance heating element is formed on a plate-like substrate , a large fixing nip and a device of the apparatus are suppressed while suppressing heat escape from the heater to the heater support member. The task is to achieve high speed.

In order to solve this problem, a fixing member, a heating member that is provided in contact with the fixing member and heats the fixing member, and a pressure that presses against the heating member via the fixing member to form a fixing nip. And a heating device that heats an unfixed toner image on the recording material conveyed to the fixing nip to fix the recording material on the recording material. A resistance heating element is formed on the plate- like substrate. And a heater support member that supports the heater from a surface opposite to the surface of the heater that faces the fixing member, and the heater support member is within the fixing nip width and has the resistance heat generation. The fixing device is characterized in that the heater is supported by at least two contact portions sandwiching the body, and the contact portion is formed with a side surface and a gap of the heater support member .

The fixing device that heats the fixing member by a resistance heater to the resistance heating elements are formed on the plate-like substrate, while maintaining the fixing nip width has wide, can be secured even energy saving by reducing the heat escaping from the heater to the heater support member . A high-speed and energy-saving fixing device can be realized.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment. 1 is a schematic diagram illustrating an embodiment of a fixing device. It is detail drawing of a resistance heating element. FIG. 3 is an enlarged view in the vicinity of a fixing nip. It is a perspective view inside a heater holder. It is a schematic diagram which shows how the heater bends. It is a schematic diagram which shows another embodiment of a heating member. FIG. 6 is a diagram illustrating an example in which the peak value of the fixing nip pressure is on the downstream side in the transport direction from the center of the fixing nip. It is a schematic diagram of the fixing device provided with the heater which concerns on another embodiment.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment.
As shown in FIG. 1, a printer as an example of an image forming apparatus includes a paper feeding unit 4, a registration roller pair 6, a photosensitive drum 8 as an image carrier, a transfer unit 10, a fixing device 12, and the like. .

  The paper feeding means 4 feeds the paper P as a recording material stored in a stacked state and the paper P stored in the paper feeding tray 14 one by one in order from the top. It has a roller 16 and the like. The paper P delivered by the paper supply roller 16 is temporarily stopped by the registration roller pair 6 to correct the posture deviation. Thereafter, the sheet P is synchronized with the rotation of the photosensitive drum 8, that is, at the timing when the leading end of the toner image formed on the photosensitive drum 8 and the predetermined position of the leading end of the sheet P in the transport direction coincide. It is sent to the transfer site N by the registration roller pair 6.

  Around the photosensitive drum 8, in the order of rotation indicated by arrows, a charging roller 18 as a charging unit, a mirror 20 constituting a part of the exposure unit, a developing unit 22 including a developing roller 22a, a transfer unit 10, and a cleaning device. A cleaning means 24 provided with a blade 24a is disposed.

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

  The image forming operation in the printer is performed in the same manner as in the past. That is, when the photosensitive drum 8 starts to rotate, the surface of the photosensitive drum 8 is uniformly charged by the charging roller 18, and the exposure light Lb is irradiated and scanned on the exposure unit 26 based on the image information to create an image to be created. An electrostatic latent image corresponding to is formed.

The electrostatic latent image is moved to the developing means 22 by the rotation of the photosensitive drum 8, where toner is supplied to be visualized to form a toner image.
The toner image formed on the photosensitive drum 8 is transferred onto the paper P that has entered the transfer portion N at a predetermined timing by applying a transfer bias by the transfer means 10.

The paper P carrying the toner image is conveyed toward the fixing device 12, fixed by the fixing device 12, and then discharged and stacked on a paper discharge tray (not shown).
Residual toner remaining on the photosensitive drum 8 without being transferred at the transfer portion N reaches the cleaning means 24 as the photosensitive drum 8 rotates, and is scraped off by the cleaning blade 24 a while passing through the cleaning means 24. To be cleaned.
Thereafter, the residual potential on the photosensitive drum 8 is removed by a neutralizing unit (not shown), and is prepared for the next image forming process.

FIG. 2 is a schematic diagram illustrating an embodiment of a fixing device. 2 and 3, the directions of the fixing belt 38 and the pressure roller 30 are different from those shown in FIG. 1 for convenience.
<Belt configuration>
The fixing belt 38 as a fixing member has a nickel (Ni) base having an outer diameter of 30 mm and a thickness of 10 to 70 μm, and an elastic layer coated on the surface of the base. The elastic layer is made of silicon rubber and has a thickness of 50 to 150 μm.

In the outermost layer of the fixing belt 38, a release layer made of a fluorine-based resin such as PFA or PTFE is formed in order to increase durability and secure release properties, and the thickness thereof is 5 to 50 μm.
The fixing belt substrate is not limited to nickel, and may be a metal substrate such as SUS or a heat resistant resin such as polyimide (PI).

<Pressure roller>
The pressure roller 30 as a pressure member has an outer diameter of 30 mm, and is formed of a hollow iron core 30a, an elastic layer 30b formed on the surface of the iron core 30a, and a release layer 30c. Yes.

The elastic layer 30b is made of silicon rubber and has a thickness of 5 mm. It is desirable to form a release layer 30c made of a fluororesin layer having a thickness of about 40 μm on the surface of the elastic layer 30b in order to improve the release property.
The pressure roller 30 is pressed against the fixing belt 38 by an urging means (not shown). The pressure roller 30 is pressed against the heater 50 via the fixing belt 38 to form the fixing nip SN.

<Heater area>
The heater 50 constituting the heating member 60 is a heating element in which a resistance heating element 50a is formed on a plate substrate 50b made of ceramics such as glass or alumina, and contacts the fixing belt 38 to heat it from the inside. The resistance heating element 50a is formed on the substrate by screen printing, an overcoat (OC) layer is further formed on the resistance heating element 50a and the plate-like substrate 50b, and the resistance heating element 50a is insulated from the outside.

  The heater 50 is supported by a heater holder 53 that is a heater support member. The detailed configuration of the heater holder 53 will be described later.

  The heater 50 is in contact with the heat transfer member 52 via the heat transfer auxiliary member 51. The heat transfer member 52 is made of a highly heat conductive material such as copper or aluminum, and is installed between the heater 50 and the fixing belt 38 to efficiently transfer the heat of the heater 50 to the fixing belt 38. The heat transfer member 52 improves the heat transfer performance in the heater longitudinal direction, and can reduce the temperature deviation in the longitudinal direction of the fixing belt 38.

  Since both the heater 50 and the heat transfer member 52 have high rigidity, it is difficult to uniformly contact each other in the entire longitudinal direction due to the effects of surface roughness, warpage, and undulation. It is provided between the members 52. As the heat transfer auxiliary member 51, heat conductive grease, a heat conductive sheet (TIM), or the like can be used.

  The heater 50 heats the fixing belt 38 via the heat transfer member 52 and the heat transfer auxiliary member 51, raises the temperature of the fixing belt 38 by heat transfer, and the unfixed image on the recording material conveyed to the fixing nip SN. Can be fixed by heating.

  The heater holder 53 is supported by the stay 61. The stay 61 is supported by both side plates (not shown), receives the pressing force of the pressure roller 30, and forms a fixing nip SN.

  Since the heat transfer member 52 is in sliding contact with the fixing belt 38, a low friction coating layer is formed on the surface of the heat transfer member in contact with the fixing belt 38 in order to reduce torque or belt wear. . As a material for the coating layer, DLC (diamond-like carbon), PTFE or the like having a low friction coefficient is suitable. Considering the heat transfer performance of the heat transfer member 52 and the fixing belt 38, it is desirable that the coating layer is thin, and is preferably about 2 to 50 μm.

<Sensor and heating control>
A thermistor 34 as a temperature detecting means for detecting the temperature of the fixing belt 38 is provided downstream of the fixing nip SN and inside the fixing belt. The thermistor 34 is electrically connected to the heating control means 55. In accordance with the detected temperature detected by the thermistor 34, the heating control means 55 controls the power supply 57 to control the power supplied to the heater 50, thereby controlling the temperature of the fixing belt 38 to a desired temperature. Here, the heating control means means a microcomputer including a CPU, ROM, RAM, I / O interface and the like.

  As shown in FIG. 3, the resistance heating element 50a has a plurality of heating regions (regions 1 to 5) in the longitudinal direction. Individual heating (1-5 ch) and common wiring are connected to each heating region, and heating control is possible individually. Each heating region is composed of a plurality of heating elements. For example, in the region 3, a resistance heating element is formed on a comb-like electrode, and the heating element is heated by ten heating elements. By making each region a common ground in a comb shape, the width of the heating region can be narrowed even if a plurality of heating regions are provided. In the conventional multiple heater configuration, the heating area increases as the number of heaters increases. As a result, the heating region in the longitudinal direction can be narrowed to suppress temperature unevenness during heating in the vicinity of the heater, or a fixing device with a narrow width of the fixing nip SN can be formed.

  In FIG. 3, the heating region is divided into five parts, but it may be more than nine parts or less, or less than three parts. Further, in FIG. 3, each region is individually controlled for heating, but it may be configured such that heating regions at symmetrical positions from the longitudinal center can be turned ON / OFF simultaneously. Thereby, the number of switch elements required for heating control can be reduced. Each heating region of the resistance heating element 50a can be heated independently, and the heating rate of the resistance heating element 50a is changed based on the size information of the paper P. Since heating is controlled in accordance with the size information so that the temperature of the non-sheet passing portion does not become too high, damage to the member and deterioration in image quality due to excessive temperature rise in the non-sheet passing portion are suppressed.

FIG. 4 is an enlarged view around the fixing nip.
<Heat transfer member 52>
The cross-sectional shape of the heat transfer member 52 constituting the heating member 60 is substantially U-shaped, and the heat transfer member 52 is inserted into the gap in the short direction between the heater 50 and the heater holder 53 so as to cover the heater 50. It is. As a result, the heater 50 is confined to the heater holder 53 and the heat transfer member 52, and it is possible to prevent the fragments from scattering when the heater is broken.

  The heat transfer member 52 can be made cheaper than extrusion molding by bending a thin copper plate. Further, when heat transfer grease is used as the heat transfer auxiliary member 51, the viscosity decreases during heating and the heat transfer grease may flow out between the heater 50 and the heat transfer member 52. Since the heater 50 is covered with this, the outflow can be prevented.

  As shown in FIG. 4, the heat transfer member 52 has a shape protruding toward the pressure roller 30 on the downstream side in the transport direction of the paper P. As a result, the paper P is discharged to the pressure roller side, and the peelability between the fixing belt 38 and the paper P is improved.

  In addition, as shown in FIG. 4, the heat transfer member 52 and the heater 50 are not in contact with each other on the downstream side in the transport direction of the paper P, and a gap is provided. This prevents heat from flowing back from the heat transfer member 52 to the plate-like substrate 50b on the downstream side in the transport direction while transferring the heat generated by the resistance heating element 50a to the heat transfer member 52 via the heat transfer auxiliary member 51. In addition, the heat of the resistance heating element 50a can be efficiently applied to the fixing belt 38.

  As described above, since the heat transfer member 52 is formed separately from the heater 50, if it is necessary to replace the heat transfer member 52, the heat transfer member 52 can be replaced individually, thereby reducing the running cost. I can do it.

  In particular, the heat transfer member 52 and the fixing belt 38 are always in sliding contact with each other, and the heat transfer member 52 is rubbed at the same position at all times, so that wear is severe. The entire circumference of the rotating fixing belt is worn. Therefore, although it is necessary to replace the heat transfer member 52, the expensive heater 50 can be used as it is.

<Heater holder 53>
The heater holder 53 that constitutes the heating member 60 is likely to become high temperature due to the heat of the heater 50, and is thus formed of a resin such as LCP having high heat resistance. Moreover, heat insulation can be improved by forming the heater holder 53 with resin. Furthermore, as shown in FIG. 4, the heater holder 53 has contact portions 53a and 53b extending in the longitudinal direction, and the contact portions 53a and 53b do not contact the heater 50 directly above the resistance heating element 50a that is at the highest temperature. Then, contact is made at two locations across the resistance heating element 50a. Thereby, the amount of heat flowing from the heater 50 to the heater holder 53 is further reduced, so that the heat is efficiently transmitted to the fixing belt 38. The heater holder 53 supports the heater 50 from a surface opposite to the surface of the heater facing the fixing belt 38.

  The heating member 60 includes a heater 50 having a resistance heating element 50a formed on a plate-like substrate 50b, and a heater holder 53 as a heater support member that supports the heater from a surface opposite to the surface of the heater facing the fixing belt 38. It consists of. The heating member 60 may further include a heat transfer member 52 that is inserted into a gap between the heater and the heater holder 53 so as to cover the heater 50.

FIG. 5 shows a perspective view of the inside of the heater holder 53.
In the example of FIG. 5A, the contact portions 53a and 53b of the heater holder 53 continuously extend linearly in the longitudinal direction of the heater. On the other hand, in the example of FIG. 5B, the contact portions 53a and 53b of the heater holder 53 extend linearly intermittently in the longitudinal direction of the heater and are divided into a plurality. The heater holder 53 shown in FIG. 5 (b) has a smaller contact area with the heater and can reduce the amount of heat escaping to the heater holder 53, so that it is more energy efficient. However, since the heater holder 53 shown in FIG. 5 (b) is superior in terms of stable support of the heater, it is desirable to use these properly depending on the durable years.

  As shown in FIG. 4, the contact portions 53a and 53b of the heater holder 53 are arranged within the range of the fixing nip SN. This is due to the following reason.

FIG. 6 is a schematic diagram illustrating how the heater 50 bends.
FIG. 6A shows the pressure distribution within the width of the fixing nip SN. The pressure at the center of the fixing nip is the highest and the pressure at the end is low.
When the support interval between the contact portions 53a and 53b is wider than the width of the fixing nip SN (FIG. 6A), the heater 50 is greatly bent downward by the pressure from the pressure roller 30 received at the fixing nip SN. However, when the support interval between the contact portions 53a and 53b is narrower than the width of the fixing nip SN (FIG. 6B), in the reverse bending force region inside the fixing nip and outside the contact portions 53a and 53b, The pressure acts in a direction that prevents the heater 50 from bending downward. This is a structure called “simple beam on both sides” and is generally well known. That is, it is effective to reduce the amount of deflection of the heater 50 by making the width of the fixing nip SN wider than the support interval between the contact portions 53a and 53b and forming the reverse bending force region.

FIG. 7 is a schematic view showing another embodiment of the heating member 60.
In the example shown in FIG. 2, the contact portions 53 a and 53 b of the heater holder extend linearly and are in contact with the heater 50. However, in this example, as shown in FIG. 7, a countersink 59 is formed in a range narrower than the fixing nip SN on the surface of the heater holder 53 facing the resistance heating element 50 a, and the heater 50 is connected to the outside of the countersink 59. Contact portions 53c and 53d are formed in contact with each other. Accordingly, the support interval between the contact portions 53c and 53d is narrower than the width of the fixing nip SN, and the pressure of the heater 50 is deflected downward in the reverse bending force region inside the fixing nip and outside the countersink portion 59. Acts in the direction of preventing In this example, since the contact area between the heater holder 53 and the heater 50 increases, the heater 50 can be stably supported. However, the example of FIG. 2 in which these contact linearly is more desirable in terms of energy saving.

FIG. 8 is a diagram illustrating an example in which the peak value of the fixing nip pressure is on the downstream side in the transport direction from the center of the fixing nip.
In the embodiment, as shown in FIG. 6B, the pressure distribution in the sheet conveyance direction in the fixing nip is symmetric with respect to the center of the fixing nip SN. However, as shown in FIG. It can arrange | position in the downstream and can make the pressure of the conveyance direction downstream side higher than an upstream. It is known that by increasing the pressure on the downstream side in the transport direction, it is possible to apply pressure to sufficiently melted toner and to increase the fixing strength. For example, as shown in FIG. 4, by causing the heat transfer member 52 on the downstream side in the conveying direction to protrude toward the pressure roller 30, the fixing nip surface pressure on the downstream side in the conveying direction can be made higher than that on the upstream side. In this case, as shown in FIG. 8, the contact portion 53a on the downstream side in the transport direction is closer to the center of the fixing nip SN than the contact portion 53b, so that the deflection amount of the heater 50 can be further reduced even at the same support interval. This is because the fulcrum and the action point are close by bringing the pressure peak of the fixing nip SN close to the contact portion 53a, and a large reverse bending force region is formed on the downstream side in the conveying direction where the pressure is high. It depends on the effect that can be countered.

FIG. 9 is a schematic diagram of a fixing device including a heater according to another embodiment.
In the heater 50 of FIG. 9, unlike the heater shown in FIG. 2, the heat transfer member 52 is disposed in contact with the surface opposite to the surface in contact with the fixing belt 38 (the back surface of the heater 50). 51 is not provided. Therefore, the heater holder 53 as a support member supports the heat transfer member 52. The heater holder 53 supports the heat transfer member 52 at two contact portions 53a and 53b that are within the fixing nip width and sandwich the resistance heating element 50a. The heating member 60 includes a heater 50 in which a resistance heating element 50 a is formed on a plate-like substrate 50 b, the heat transfer member 52, and the heater holder 53. In the heating member 60, since the fixing belt 38 and the heater 50 are in direct contact with each other, the fixing belt 38 can be heated more quickly than in the case of FIG. 2, and the warm-up time can be shortened.

  In this case as well, if the heat transfer member 52 is made too thick, a large amount of heat from the heater 50 escapes to the heat transfer member 52 and the energy saving performance is impaired. Therefore, the thickness of the heat transfer member 52 is preferably about 0.5 to 1.0 mm, and the heater 50 still bends in the short direction. Therefore, the contact portions 53a and 53b are provided in the fixing nip SN as described above. Is desirable.

According to the present invention, the heater holder that supports the heater in which the resistance heating element is formed on the glass substrate has at least two contact portions located across the position immediately below the resistance heating element having the highest temperature. The heat that escapes to can be reduced and energy saving can be secured.
Further, by arranging the contact portion in the fixing nip, the force applied to the heater or the fixing nip pressure can be directly received by the contact portion, and the amount of bending of the glass substrate can be reduced. As a result, a wide fixing nip width and a large pressure can be secured while ensuring the durability of the glass substrate, and the speed of the apparatus can be increased.

12 Fixing Device 30 Pressure Roller (Pressure Member)
38 Fixing belt (fixing member)
50 heater 50a resistance heating element 50b plate substrate 53 heater holder (heater support member)
53a, 53b Contact portion 60 Heating member P Recording material SN Fixing nip

Japanese Patent Laid-Open No. 06-95540 Japanese Patent Laid-Open No. 08-272240 Japanese Patent Laid-Open No. 10-213982

Claims (8)

A fixing member;
A heating member provided in contact with the fixing member and heating the fixing member;
A pressure member that presses against the heating member through the fixing member to form a fixing nip, and
In the fixing device for heating and fixing the unfixed toner image on the recording material conveyed to the fixing nip to the recording material,
The heating member is
A heater in which a resistance heating element is formed on a plate substrate;
A heater support member that supports the heater from a surface opposite to the surface of the heater facing the fixing member;
The heater support member supports the heater at at least two contact portions that are within the fixing nip width and sandwich the resistance heating element, and the contact portion is formed with a side surface of the heater support member and a gap. A fixing device.   The fixing device according to claim 1, wherein the contact portion of the heater support member is divided into a plurality of portions in a longitudinal direction of the heater. The peak value in the pressure distribution in the fixing nip is on the downstream side in the recording material conveyance direction from the center of the fixing nip,
2. The contact portion is located at two positions sandwiching the resistance heating element, and the contact portion on the downstream side in the recording material conveyance direction is closer to the fixing nip center than the contact portion on the upstream side. Or the fixing device according to 2; The heating member has a heat transfer member inserted into a gap between the heater and the heater support member so as to cover the heater,
The fixing device according to claim 3, wherein the heat transfer member protrudes toward the pressure member on the downstream side in the recording material conveyance direction. A fixing member;
A heating member provided in contact with the fixing member and heating the fixing member;
A pressure member that presses against the heating member through the fixing member to form a fixing nip, and
In the fixing device for heating and fixing the unfixed toner image on the recording material conveyed to the fixing nip to the recording material,
The heating member is
A heater in which a resistance heating element is formed on a plate substrate;
A heat transfer member in contact with a surface opposite to the surface of the heater facing the fixing member;
A support member for supporting the heat transfer member,
The fixing device supports the heat transfer member at at least two contact portions within a fixing nip width and sandwiching the resistance heating element. The fixing device according to claim 5 , wherein the contact portion of the support member is divided into a plurality of portions in a longitudinal direction of the heater. The peak value in the pressure distribution in the fixing nip is on the downstream side in the recording material conveyance direction from the center of the fixing nip,
The contact portion is located at two positions sandwiching the resistance heating element according to claim wherein the contact portion of the recording material conveying direction downstream side, characterized in that close to the fixing nip center than the contact portion of the upstream 5 Or the fixing device according to 6 ; An image forming apparatus having a fixing device according to any one of claims 1-7.

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