JP2007127732A - Heater, fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heater achieving low power consumption by reducing the heat capacity of the entire heater while securing rigidity necessary for the heater, and to provide a fixing device achieving low power consumption and the shortening of warming-up time, and an image forming apparatus equipped with the fixing device. <P>SOLUTION: The heater 93 has a heating element 93A energized to generate heat and formed like a belt or a plate, and an insulating layer 93B formed on the heating element 93A. The plurality of heating elements 93A are laminated through the insulating layers 93B. It is desirable that the plurality of heating elements 93A are connected in series. It is desirable that the plurality of heating elements 93A are constituted of one belt-like member formed integrally, and are laminated by folding the belt-like member. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heater, a fixing device, and an image forming apparatus.

In an image forming apparatus such as a printer, a copying machine, or a facsimile that employs an electrophotographic system, a recording medium such as paper that carries a toner image formed with toner in an unfixed state is heated and pressurized to thereby form the toner image. Is fixed to the recording medium (see, for example, Patent Document 1).
For example, the fixing device according to Patent Document 1 includes a pair of rollers that are pressed against each other and a heater that heats one of the pair of rollers. The recording medium is heated and pressurized by passing the recording medium through the nip formed by the pressure contact between the pair of rollers, and the toner image formed on the recording medium is transferred to the recording medium. To settle.

Further, in Patent Document 1, a heater includes a heating element composed of a linear or spiral nickel wire or nichrome wire to ensure a resistance value and a calorific value necessary for heat generation, and thermal insulation that supports the heating element. Body and heat conductor. Such a heater has low rigidity of the heating element itself, but since the heating element is supported by a thermal insulator or a thermal conductor, the rigidity required for the entire heater can be ensured.
However, in the heater according to Patent Document 1 as described above, the heating element must be supported by a separate member, and the heat capacity of the entire heater is increased. For this reason, the efficiency of heat conduction from the heater to the roller decreases, resulting in an increase in power consumption and a longer warm-up time.

JP 2004-302461 A

  An object of the present invention is to reduce the heat capacity of the heater by reducing the heat capacity of the entire heater while ensuring the rigidity required for the heater, and to reduce the warm-up time with low power consumption. Another object of the present invention is to provide a fixing device that can perform the above-described processing, and an image forming apparatus including the fixing device.

Such an object is achieved by the present invention described below.
The heater of the present invention comprises a heating element that forms a belt or plate that generates heat when energized,
An insulating layer formed on the heating element,
A plurality of the heating elements are laminated via the insulating layer.
Thereby, the rigidity required for the whole heater can be obtained, without supporting a heat generating body with another member. Moreover, since it is not necessary to support a heat generating body with another member, the heat capacity of the whole heater can be reduced and power consumption can be reduced.

In the heater of the present invention, it is preferable that the plurality of heating elements are connected in series.
As a result, it is possible to increase the cross-sectional area of the heating element and obtain the necessary rigidity for the entire heater while ensuring the resistance value necessary for the heating element.
In the heater according to the present invention, it is preferable that the plurality of heating elements are constituted by one integrally formed belt-like member and are laminated so that the belt-like member is folded.
Thereby, a heater having a laminated structure can be obtained without using an expensive film forming apparatus. As a result, the cost of the heater can be reduced.

In the heater according to the present invention, it is preferable that the belt-shaped member is composed of an Fe—Cr—Al alloy as a main material.
Thereby, the heat capacity of the whole heater can be reduced and the power consumption can be reduced while ensuring the rigidity necessary for the heater more reliably.
In the heater of the present invention, it is preferable that the insulating layer is composed of Al ₂ O ₃ as a main material.
Thereby, an insulating layer can be formed comparatively easily only by heat-processing a base material.

In the heater of the present invention, it is preferable that the plurality of heating elements are arranged in the vicinity of the surface of the roller and heat the roller.
Thereby, a roller can be heated rapidly.
In the heater of the present invention, it is preferable that each of the heating elements is curved so as to follow the peripheral surface of the roller.
Thereby, the contact area of a heater and a roller can be increased, and the heat transfer efficiency from a heater to a roller can be improved more.

A fixing device of the present invention includes the heater of the present invention, and heats a recording medium carrying an unfixed image by heat from the heater, thereby fixing the unfixed image on the recording medium. To do.
Thereby, the warm-up time can be shortened with low power consumption.
The fixing device according to the present invention includes a pair of rollers that rotate while being pressed against each other, and the heater is arranged to heat at least one of the pair of rollers, and the pair of rollers. The fixing is preferably performed by passing the recording medium between rollers and heating and pressing.
As a result, it is possible to shorten the warm-up time with low power consumption while making the fixing device relatively simple and highly durable.

In the fixing device according to the aspect of the invention, it is preferable that the heater extends along the axial direction of the roller.
Thereby, a roller can be heated over the whole region of the axial direction (longitudinal direction).
In the fixing device according to the aspect of the invention, it is preferable that the heater is disposed so as to be in contact with the inner peripheral surface of the roller and is in sliding contact with the inner peripheral surface of the roller by the rotation of the roller.
Thereby, since the roller is directly heated by the heater, the temperature of the roller can be raised to a desired temperature very quickly. As a result, the warm-up time can be further shortened. In particular, since the heater of the present invention can directly contact the roller without covering the heating element with another member, the heat conduction efficiency from the heater to the roller is extremely high.

In the fixing device according to the aspect of the invention, it is preferable that the heater is provided with a coating layer for improving the slidability at least in a portion in sliding contact with the inner peripheral surface of the roller.
Thereby, even if it is the structure which makes a heater contact a roller, the improvement of durability of a heater can be aimed at. In particular, since the coating is performed not on the inner peripheral surface of the roller but on the contact portion of the heater, the durability of the heater can be improved relatively easily.

In the fixing device according to the aspect of the invention, it is preferable that the heater is curved along the inner peripheral surface of the roller.
Thereby, the contact area of a heater and a roller can be increased, and the heat transfer efficiency from a heater to a roller can be improved more.
The image forming apparatus of the present invention is an image forming apparatus that forms an image on a recording medium by a series of image forming processes including charging, exposure, development, transfer, and fixing.
The fixing device according to the present invention is provided.
Thereby, the warm-up time can be shortened with low power consumption.

Hereinafter, preferred embodiments of a heater, a fixing device, and an image forming apparatus of the present invention will be described with reference to the accompanying drawings.
<Image forming apparatus>
First, the image forming apparatus of the present invention, that is, the image forming apparatus provided with the fixing device of the present invention will be briefly described.

FIG. 1 is a schematic cross-sectional view of the overall configuration showing an embodiment of an image forming apparatus according to the present invention.
An image forming apparatus 10 according to this embodiment shown in FIG. 1 records an image on a recording medium mainly by a series of image forming processes including exposure, development, transfer, and fixing. As shown in FIG. 1, such an image forming apparatus 10 has a photosensitive member 20 that carries an electrostatic latent image and rotates in the direction of an arrow in the figure, and sequentially, along the rotation direction, a charging unit 30, An exposure unit 40, a developing unit 50, a primary transfer unit 60, and a cleaning unit 75 are provided. In addition, the image forming apparatus 10 is provided with a paper feed tray 82 that accommodates a recording medium P such as paper at the bottom in FIG. A next transfer unit 80 and a fixing device 90 are sequentially arranged along the conveyance direction of the recording medium P. Further, in the image forming apparatus 10, when an image is formed on both sides of a recording medium, the recording medium P fixed on one side by the fixing device 90 is reversed and returned to the secondary transfer unit 80. The conveyance part 88 is provided.

The photoconductor 20 has a cylindrical conductive substrate (not shown) and a photosensitive layer (not shown) formed on the outer peripheral surface thereof, and can rotate around the axis in the direction of the arrow in FIG. It has become.
The charging unit 30 is a device for uniformly charging the surface of the photoconductor 20 by corona charging or the like.
The exposure unit 40 receives image information from a host computer such as a personal computer (not shown) and irradiates a laser on the uniformly charged photoreceptor 20 to form an electrostatic latent image. It is a device to do.

  The developing unit 50 includes four developing devices, a black developing device 51, a magenta developing device 52, a cyan developing device 53, and a yellow developing device 54. These developing devices are converted into latent images on the photosensitive member 20. It is an apparatus that visualizes the latent image as a toner image, selectively used correspondingly. The black developing device 51 uses black (K) toner, the magenta developing device 52 uses magenta (M) toner, the cyan developing device 53 uses cyan (C) toner, and the yellow developing device 54 uses yellow (Y) toner.

  The YMCK developing unit 50 in the present embodiment is rotatable so that the above-described four developing devices 51, 52, 53, 54 are selectively opposed to the photoconductor 20. Specifically, in this YMCK developing unit 50, four developing devices 51, 52, 53, and 54 are respectively held by four holding portions 55a, 55b, 55c, and 55d of a holding body 55 that can rotate around a shaft 50a. The four developing devices 51, 52, 53, and 54 are selectively opposed to the photoconductor 20 while maintaining the relative positional relationship by the rotation of the holding body 55.

The intermediate transfer member 61 has an endless belt-like intermediate transfer belt 70, and this intermediate transfer belt 70 is stretched by a primary transfer roller 60, a driven roller 72, and a drive roller 71, and is rotated by the rotation of the drive roller 71. 1 is driven to rotate in the direction of the arrow shown in FIG.
The primary transfer roller 60 is a device for transferring a single color toner image formed on the photoconductor 20 to the intermediate transfer belt 70.

  On the intermediate transfer belt 70, a toner image of at least one of black, magenta, cyan, and yellow is carried. For example, when a full-color image is formed, four color toner images of black, magenta, cyan, and yellow are sequentially formed. The toner images are transferred to form a full-color toner image. In the present embodiment, the drive roller 71 also functions as a backup roller for the secondary transfer roller 80 described later. Further, the primary transfer roller 60, the driving roller 71, and the driven roller 72 are supported by the base body 73.

The secondary transfer roller 80 is a device for transferring a single-color or full-color toner image formed on the intermediate transfer belt 70 to a recording medium P such as paper, film, or cloth.
The fixing device 90 is a device for fusing the toner image to the recording medium P and fixing it as a permanent image by heating and pressing the recording medium P that has received the transfer of the toner image. The fixing device 90 includes the roller unit of the present invention. The fixing device 90 will be described in detail later.

The cleaning unit 75 has a rubber cleaning blade 76 that contacts the surface of the photoconductor 20 between the primary transfer roller 60 and the charging unit 30, and the toner image is transferred onto the intermediate transfer belt 70 by the primary transfer roller 60. Then, the toner remaining on the photoreceptor 20 is scraped off and removed by the cleaning blade 76.
The conveyance unit 88 reverses the front and back of the conveyance roller pair 88A and 88B for nipping and conveying the recording medium P fixed on one surface by the fixing device 90 and the conveyance medium pair 88A and 88B. And a conveyance path 88 </ b> C for guiding the registration roller 86. As a result, when an image is formed on both sides of the recording medium, the recording medium P fixed on one side by the fixing device 90 is reversed and returned to the secondary transfer roller 80.

Next, the operation of the image forming apparatus 10 configured as described above will be described.
First, in response to a command from a host computer (not shown), the photosensitive member 20, the developing roller (not shown) provided in the developing unit 50, and the intermediate transfer belt 70 start to rotate. The photoreceptor 20 is sequentially charged by the charging unit 30 while rotating.
The charged area of the photoconductor 20 reaches the exposure position as the photoconductor 20 rotates, and the exposure unit 40 forms a latent image corresponding to the image information of the first color, for example, yellow Y, in the area. .

The latent image formed on the photoconductor 20 reaches the development position as the photoconductor 20 rotates, and is developed with yellow toner by the yellow developing device 54. As a result, a yellow toner image is formed on the photoreceptor 20. At this time, in the YMCK developing unit 50, the yellow developing device 54 faces the photoconductor 20 at the developing position.
The yellow toner image formed on the photoconductor 20 reaches the primary transfer position (that is, the portion where the photoconductor 20 and the primary transfer roller 60 face each other) as the photoconductor 20 rotates. Transfer (primary transfer) is performed on the transfer belt 70. At this time, a primary transfer voltage (primary transfer bias) having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roller 60. During this time, the secondary transfer roller 80 is separated from the intermediate transfer belt 70.

The same processing as described above is repeatedly executed for the second color, the third color, and the fourth color, so that the toner images of the respective colors corresponding to the respective image signals are transferred onto the intermediate transfer belt 70 in an overlapping manner. The As a result, a full-color toner image is formed on the intermediate transfer belt 70.
On the other hand, the recording medium P is conveyed from the paper feed tray 82 to the secondary transfer roller 80 by the paper feed roller 84 and the registration roller 86.

  The full-color toner image formed on the intermediate transfer belt 70 reaches the secondary transfer position (that is, the portion where the secondary transfer roller 80 and the driving roller 71 face each other) as the intermediate transfer belt 70 rotates, and the secondary transfer. The image is transferred (secondary transfer) to the recording medium P by the roller 80. At this time, the secondary transfer roller 80 is pressed against the intermediate transfer belt 70 and a secondary transfer voltage (secondary transfer bias) is applied.

The full-color toner image transferred to the recording medium P is heated and pressurized by the fixing device 90 and fused to the recording medium P. Thereafter, the recording medium P is discharged to the outside of the image forming apparatus 10 by the discharge roller pair 87.
On the other hand, after the primary transfer position has elapsed, the toner adhering to the surface of the photoconductor 20 is scraped off by the cleaning blade 76 of the cleaning unit 75 to prepare for charging for forming the next latent image. The toner that has been scraped off is collected by a residual toner collecting section in the cleaning unit 75.

  In the case of forming an image on both sides of the recording medium, the recording medium P fixed on one side by the fixing device 90 is once sandwiched between the discharge roller pair 87, and then the discharge roller pair 87 is driven in reverse. By driving the conveyance roller pair 88A, 88B, the recording medium P is turned upside down through the conveyance path 88C and returned to the secondary transfer roller 80, and an image is printed on the other surface of the recording medium P by the same operation as described above. Form.

<Fixing device>
Here, the fixing device 90 including the roller unit of the present invention will be described in detail with reference to FIGS.
2 is a schematic cross-sectional view showing a preferred embodiment of the fixing device 90, FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2, and FIG. 4 is provided in the fixing device shown in FIGS. FIG. 5 is an enlarged vertical sectional view of the heater provided in the fixing device shown in FIGS. 2 and 3.

As shown in FIG. 2, the fixing device 90 detects a temperature of the fixing roller 91 and a fixing roller 91 and a pressure roller 92 that are a pair of rollers that rotate in contact with each other, a heater 93 that heats the fixing roller 91, and the fixing roller 91. And a temperature detector 94 for the purpose.
In the fixing device 90, a recording medium carrying an unfixed image is conveyed from below in FIG. 2 to the nip portion N formed by the pressure contact between the fixing roller 91 and the pressure roller 92. The unfixed image is fixed on the recording medium by heating and pressurizing the recording medium. In the present embodiment, the recording medium conveyed to the nip portion N carries an unfixed image on the fixing roller 91 side.

The fixing roller 91 has a cylindrical shape and is a rotating body provided to be rotatable around an axis thereof.
2 and 3, the fixing roller 91 includes a cylindrical metal base (core metal) 91A, an elastic layer 91B covering the outer peripheral surface of the base 91A, and an outer peripheral surface of the elastic layer 91B. And a release layer (not shown).

The base 91A has a cylindrical shape and is made of a metal such as iron or an aluminum alloy.
The thickness of the base 91A is not particularly limited, but it is preferable to make the heat capacity as small as possible while ensuring the strength necessary for the base 91A. Specifically, the thickness of the base portion 91A varies depending on the constituent material of the base portion 91A and the like, but is preferably 0.1 to 3 mm, and more preferably 0.2 to 1 mm. Thereby, the warm-up time can be more reliably shortened while the durability of the fixing roller 91 is excellent.
Cylindrical flanges 96 are fitted into both ends of the base 91A. Thereby, even if the base 91A is thin, the base 91A can be rotatably supported via the bearing 97 while ensuring the rigidity required for the base 91A.
On the other hand, an elastic layer 91B is formed on the outer peripheral surface of the base portion 91A so as to cover it.

  The constituent material of the elastic layer 91B is not particularly limited. For example, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, nitrile rubber, chloroprene rubber, butyl rubber, acrylic rubber, ethylene-propylene rubber, hydrin rubber, urethane rubber , Various rubber materials such as silicone rubber and fluoro rubber (especially those vulcanized), styrene, polyolefin, polyvinyl chloride, polyurethane, polyester, polyamide, polybutadiene, trans polyisoprene, Various thermoplastic elastomers such as fluororubber-based and chlorinated polyethylene are listed, and one or more of these can be used in combination. Among these, as a constituent material of the elastic layer 91B, for example, Si rubber, EPDM, fluorine rubber, or the like can be suitably used.

The thickness of the elastic layer 91B is preferably smaller than the thickness of the elastic layer 92B of the pressure roller 91 described later. More specifically, the thickness of the elastic layer 91B is not particularly limited, but is preferably 0.1 to 3 mm, and more preferably 0.5 to 1.5 mm. As a result, as shown in FIG. 2, the adhesion between the outer surface of the fixing roller 91 and the toner image on the recording medium is ensured while the nip portion N having a concave curved surface on the pressure roller 92 side is reliably formed. It can be improved to achieve good fixability.
A release layer (not shown) is formed so as to cover the outer peripheral surface of the elastic layer 91B.
The thickness of the release layer is preferably 10 to 80 μm, and more preferably 20 to 50 μm. Thereby, the elasticity of the elastic layer 91 </ b> B can be sufficiently exhibited while maintaining the strength required for the release layer.

Moreover, as a constituent material of the release layer, for example, PTFE, PFA, and the like can be suitably used.
In the inner space of the fixing roller 91 as described above, the heater 93 is fixedly disposed so as to be slidable on the inner peripheral surface of the fixing roller 91 (that is, the inner peripheral surface of the base portion 91A). The heater 93 will be described in detail later.

On the other hand, a temperature detector 94 such as a thermistor for detecting the temperature of the fixing roller 91 is provided on or in close proximity to the outer peripheral surface of the fixing roller 91. Based on the temperature detected by the temperature detector 94, the driving of the heater 93 described above is controlled by the energization circuit 95 so that the outer surface of the fixing roller 91 becomes the target temperature.
The pressure roller 92 has a cylindrical shape or a columnar shape, is rotatable around its axis, and is in pressure contact with the fixing roller 91 as described above.

2 and 3, the pressure roller 92 includes a columnar metal base (core metal) 92A, an elastic layer 92B covering the outer peripheral surface of the base 92A, and an outer periphery of the elastic layer 92B. And a release layer 92C covering the surface.
As a constituent material of the elastic layer 92B, for example, Si rubber, EPDM, fluorine rubber, or the like can be suitably used.

Further, the thickness of the elastic layer 92B is preferably 0.3 to 10 mm, and more preferably 0.6 to 8 mm. Thereby, it is possible to make the width of the nip portion N sufficient while improving the durability of the elastic layer 92B.
In addition, the thickness of the release layer 92C is preferably 10 to 80 μm, and more preferably 20 to 50 μm. Thereby, the elasticity of the elastic layer 92B can be sufficiently exhibited while maintaining the strength required for the release layer 92C.
Moreover, as a constituent material of the release layer 92C, for example, PTFE, PFA, or the like can be suitably used.

<Heater>
Here, the heater 93 will be described in detail.
As shown in FIGS. 4 and 5, the heater 93 includes a plurality of heating elements 93A having a strip shape or a plate shape, and an insulating layer 93B formed on the heating elements 93A. The heating element 93A is the insulating layer 93B. A plurality of layers are stacked via Thereby, the rigidity required for the whole heater 93 can be obtained, without supporting the heat generating body 93A with another member. In addition, since it is not necessary to support the heating element 93A with a separate member, the heat capacity of the entire heater 93 can be reduced and the power consumption can be reduced.

  In such a heater 93, a heating element 93A constituting one layer and two insulating layers 93B formed on both sides thereof are integrally formed (joined), and each set is bonded. It is joined via the layer 93C. In addition, a coating layer (coating) 93D for reducing frictional resistance is formed on the surface of the heater 93 that is in contact with the inner peripheral surface 91A1 of the base 91A of the fixing roller 91.

Hereinafter, each part which comprises the heater 93 is demonstrated in detail sequentially.
As shown in FIG. 5, the plurality of heating elements 93 </ b> A are configured by one integrally formed belt-like member, and are stacked so that the belt-like members are folded. Thereby, the heater 93 having a laminated structure can be obtained without using an expensive film forming apparatus. As a result, the cost of the heater 93 can be reduced.

The constituent material of the heating element 93A (strip member) is not particularly limited. For example, indium tin oxide (ITO), carbon-based material, barium titanate-based ceramic (BaTiO ₃ ), Fe—Cr—Al (Fe—Cr). -Al alloy), Ni-Cr (Ni-Cr alloy) and the like.
Among these, Fe—Cr—Al is preferable as a constituent material of the heating element 93A. That is, the heating element 93A is preferably composed of Fe—Cr—Al as a main material. Thereby, the heat capacity of the entire heater 93 can be reduced and the power consumption can be reduced while ensuring the rigidity required for the heater 93 more reliably.
In this case, the insulating layer 93B is preferably composed of Al ₂ O ₃ as a main material. As a result, the insulating layer 93B can be formed relatively easily only by heat-treating the belt-shaped member constituting the heating element 93A.

For example, when forming the insulating layer 93B composed of Al ₂ O ₃ as a main material, a band-shaped member composed of Fe—Cr—Al as a main material is heat-treated at 1000 ° C. for 2 hours in the atmosphere. Al ₂ O ₃ is deposited on the surface of the strip member to form an insulating layer 93B. At this time, an Al ₂ O ₃ layer is formed over the entire outer surface of the belt-like member by the heat treatment described above, and a portion of this layer necessary for energization to the heating element 93A is removed. Thereafter, the heater 93 can be obtained by folding the belt-shaped member.

In addition, when a material having a self-temperature adjusting function (PTC) such as ITO, carbon-based material, BaTiO ₃ or the like is used as a constituent material of the heating element 93A, the temperature can be adjusted without using a temperature control device such as a thermostat. It is. Further, the temperature control device can be omitted, and thus the fixing device 90 can be reduced in size and power can be saved.
In addition, when a voltage is applied to a material having a self-temperature adjusting function, the temperature of the material itself rises due to Joule heat, but once the temperature reaches a predetermined temperature, the electrical resistance increases rapidly, that is, the current is suppressed. The predetermined temperature can be maintained. Thus, the material having the self-temperature adjusting function is prevented from generating heat above a predetermined temperature, and is excellent in safety.

The thickness of the heating element 93A is appropriately selected depending on the constituent material of the heating element 93A, the amount of heat generated by the heating element 93A, and the like, and is not particularly limited, but is preferably 0.01 to 500 μm, for example. More preferably, the thickness is ˜100 μm, and further preferably 20 to 70 μm.
The width of the heating element 93A is appropriately selected depending on the constituent material of the heating element 93A, the amount of heat generated by the heating element 93A, and the like, and is not particularly limited, but is preferably 1 to 100 mm, for example, 5 to 50 mm. More preferably, it is 5-30 mm.

An insulating layer 93B is formed on the outer surface of the belt-shaped member constituting such a heating element 93A.
The constituent material of the insulating layer 93B is not particularly limited as long as it can withstand the heat generation of the heating element 93A and has insulation properties in addition to Al ₂ O ₃ as described above, and various inorganic materials and various organic materials. Can be used.

Further, as a method for forming the insulating layer 93B, for example, a spray pyrolysis method, a sputtering method, a dipping method, or the like can be used.
The insulating layer 93B does not cover the entire heating element 93A as long as it can prevent a short circuit between the heating elements 93A of two adjacent layers and contact between the heating element 93A and the base 91A of the fixing roller 91. May be.

The constituent material of the adhesive layer 93C is not particularly limited as long as it can withstand the heat generation of the heating element 93A and can hold the laminated structure as described above, but a ceramic adhesive or a glass adhesive is preferable. Can be used. When such an adhesive is used, the laminated structure as described above can be easily manufactured while suppressing an increase in the heat capacity of the heater 93.
Note that the adhesive layer 93C may be omitted if the above-described laminated structure can be maintained without the adhesive layer 93C. The insulating layer 93B may also serve as an adhesive layer.

  In the heater 93 as described above, as shown in FIG. 5, the belt-shaped members constituting the plurality of heating elements 93A are connected to the energization circuit 95 at both ends, and voltage is applied thereto. That is, the plurality of heating elements 93A are connected in series. As a result, it is possible to increase the cross-sectional area of the heating element 93A and obtain the necessary rigidity for the entire heater 93 while securing the necessary resistance value for the heating element 93A.

  The covering layer 93 </ b> D is formed on the surface of the insulating layer 93 </ b> B that is the layer closest to the inner surface of the fixing roller 91 (the lowermost layer in FIGS. 4 and 5). That is, the heater 93 is provided with a coating layer 93 </ b> D (coating) for improving the slidability at least in a portion in sliding contact with the inner peripheral surface of the fixing roller 91. Thereby, even when the heater 93 is brought into contact with the fixing roller 91, the durability of the heater 93 can be improved. In particular, since the coating is performed not on the inner peripheral surface of the fixing roller 91 but on the contact portion of the heater 93, the durability of the heater 93 can be improved relatively easily.

The constituent material of the covering layer 93D is not particularly limited as long as it can exhibit the above-described functions. However, a material having excellent characteristics such as heat resistance, slidability, and thermal conductivity is preferably used. Can do. For example, boron nitride, ummo, alumina, or the like can be used as a constituent material of the covering layer 93D, and boron nitride is particularly preferable from the above-described characteristics.
The covering layer 93D may be omitted. Further, the inner peripheral surface of the fixing roller 91 may be subjected to processing for improving slidability.
The heater 93 as described above extends along the axial direction of the fixing roller 91. As a result, the fixing roller 91 can be heated over the entire region in the axial direction (longitudinal direction).

  The heater 93 is disposed so as to be in contact with the inner peripheral surface of the fixing roller 91, and is in sliding contact with the inner peripheral surface of the fixing roller 91 by the rotation of the fixing roller 91, so that the fixing roller 91 is directly heated by the heater 93. Therefore, the fixing roller 91 can be raised to a desired temperature very quickly. As a result, the warm-up time can be further shortened. In particular, since the heater 93 of the present invention can directly contact the fixing roller 91 without covering the heating element 93A with another member, the heat conduction efficiency from the heater 93 to the fixing roller 91 is extremely high.

Further, as shown in FIG. 4, the heater 93 is curved so that the nip portion N side is convex in the width direction. That is, the heater 93 is curved along the inner peripheral surface of the fixing roller 91. Thereby, the contact area between the heater 93 and the fixing roller 91 can be increased, and the heat conduction efficiency from the heater 93 to the fixing roller 91 can be further improved.
In this case, the radius of curvature of the curved surface of the heater 93 is preferably substantially the same as the radius of curvature of the inner peripheral surface of the fixing roller 91 or slightly smaller than the radius of curvature of the inner peripheral surface of the fixing roller 91. More specifically, when the radius of curvature of the curved surface of the heater 93 is A and the radius of curvature of the inner peripheral surface of the fixing roller 91 is B, A / B is 0.9 to 1.1. Is preferable, and it is more preferable that it is 0.9-1.0. Accordingly, the contact area between the heater 93 and the fixing roller 91 can be increased, and damage due to contact between the corner portion of the heater 93 and the fixing roller 91 can be prevented without processing the heater 93 separately.

In the fixing device 90 and the image forming apparatus 10 including the heater 93 as described above, the warm-up time can be shortened with low power consumption.
As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to this.
For example, each unit constituting the image forming apparatus of the present invention can be replaced with any one that exhibits the same function, or other configurations can be added.

  For example, in the above-described embodiment, the description has been given of the case where the plurality of heating elements 93A are configured by one band-shaped member, but the heating elements 93A of each layer may be configured by separate members. In this case, the heating elements 93A are electrically connected to each other at the end of the heater 93 in the longitudinal direction. Further, depending on the constituent material, the number of layers, the resistance value, and the like of the heating element 93A, a plurality of heating elements 93A may be connected in parallel.

In the above-described embodiment, the example in which the seven heating elements 93A are stacked has been described, but the present invention is not limited to this. That is, the number of stacked heating elements is arbitrary as long as the strength required for the heater 93 can be obtained, and may be 6 or less or 8 or more.
In the above-described embodiment, the heating elements 93A of each layer have been described as having the same length. However, the heating elements 93A of each layer may have different lengths. In this case, for example, in the longitudinal direction of the fixing roller, a heat generating element formed in the entire region and a heat generating element formed only in the central part are combined to set the heat distribution in the central part higher than the end part. Can do.

In the above-described embodiment, the one heater 93 is configured to overheat the entire longitudinal direction of the fixing roller 91. However, the heater of the present invention is a part of the fixing roller 91 in the longitudinal direction. What is necessary is just to heat. In this case, a plurality of heaters 93 of the present invention may be used in combination, or a heater of the present invention and a heater other than the present invention may be used in combination.
In the above-described embodiment, the heater 93 is in contact with the fixing roller 91 only in the vicinity of the nip portion N and heats the fixing roller 91. However, the heater 93 is provided at other portions in the circumferential direction of the fixing roller 91. The fixing roller 91 may be heated by contact. Further, heating may be performed so that the heater contacts the entire circumferential direction of the fixing roller 91.

In the embodiment described above, the heater 93 is in contact with the inner peripheral surface of the fixing roller 91. However, the heater 93 is in contact with the outer peripheral surface of the fixing roller 91, and the fixing roller 91 is moved by the heater 93. You may make it heat. Alternatively, the heater 93 and the fixing roller 91 may not be in contact with each other, and the fixing roller 91 may be heated from the inside of the fixing roller 91.
Further, an endless belt-like or film-like member may be used in place of the fixing roller of the fixing device in the above-described embodiment.

  In the above-described embodiment, the example in which the heater of the present invention is applied to the heater for heating the fixing roller of the fixing device has been described. However, the present invention is not limited to this. For example, the pressure roller 92 may be heated using the heater of the present invention, or the heater of the present invention may be used if heating is required among various rollers provided in the image forming apparatus. It can be used and heated to reduce power consumption.

  The heater of the present invention is not limited to the application of heating a roller provided in an image forming apparatus that employs an electrophotographic system. For example, a roller provided in a thermal transfer recording apparatus such as data printing on a rewritable card. It may be used for heating the paper, or it may be used not only for heating the roller, but also for heating the paper after printing by an inkjet printer equipped with a line head mounted on an inkjet recording system. Is possible.

1 is a schematic cross-sectional view of an overall configuration showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic cross-sectional view illustrating a preferred embodiment of a fixing device provided in the image forming apparatus illustrated in FIG. 1. It is the sectional view on the AA line in FIG. FIG. 4 is an enlarged cross-sectional view of a heater provided in the fixing device shown in FIGS. 2 and 3. FIG. 4 is an enlarged longitudinal sectional view of a heater provided in the fixing device shown in FIGS. 2 and 3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Image forming device 20 ... Photoconductor 30 ... Charge unit 40 ... Exposure unit 50 ... Development unit 50a ... Shaft 51 ... Black development device 52 ... Magenta development device 53 ... Cyan developing device 54 ... Yellow developing device 55 ... Holding body 55a to 55d ... Holding section 60 ... Primary transfer roller 61 ... Intermediate transfer body 70 ... Intermediate transfer belt 71 Drive roller 72 Drive roller 73 Substrate 75 Cleaning unit 76 Cleaning blade 80 Secondary transfer roller 82 Paper feed tray 84 Paper feed roller 86 ... Registration roller 87 ... Discharge roller pair 88 ... Conveyance section 88A, 88B ... Conveyance roller pair 88C ... Conveyance path 90 ... Equipment 91 ... Fixing roller 91A ... Base 91B ... Elastic layer 92 ... Pressure roller 92A ... Base 92B ... Elastic layer 92C ... Release layer 93 ... Heater 93A ... · · · Heating element 93B · · · Insulating layer 93C · · · Adhesive layer 93D · · · Cover layer 94 · · · Temperature detector 95 · · · Current circuit 96 · · · Flange 97 · · · Bearing P · · · Recording Medium

Claims (14)

A belt-like or plate-like heating element that generates heat when energized;
An insulating layer formed on the heating element,
A heater, wherein a plurality of the heating elements are laminated via the insulating layer.   The heater according to claim 1, wherein the plurality of heating elements are connected in series.   The heater according to claim 2, wherein the plurality of heating elements are configured by a single band-shaped member formed integrally, and are stacked so that the band-shaped members are folded.   The heater according to claim 3, wherein the belt-shaped member is composed of a Fe—Cr—Al-based alloy as a main material. The heater according to claim 4, wherein the insulating layer is made of Al ₂ O ₃ as a main material.   The heater according to any one of claims 1 to 5, wherein the plurality of heating elements are arranged in the vicinity of a surface of the roller and heat the roller.   The heater according to claim 6, wherein each of the heating elements is curved along the peripheral surface of the roller.   A heater according to any one of claims 1 to 7, wherein the recording medium carrying an unfixed image is heated by the heat from the heater to fix the unfixed image on the recording medium. A fixing device.   A pair of rollers that rotate while being pressed against each other are provided, and the heater is disposed to heat at least one of the pair of rollers, and the recording medium is disposed between the pair of rollers. The fixing device according to claim 8, wherein the fixing is performed by passing and heating and pressurizing.   The fixing device according to claim 9, wherein the heater extends along an axial direction of the roller.   The fixing device according to claim 9, wherein the heater is disposed so as to contact an inner peripheral surface of the roller, and is in sliding contact with the inner peripheral surface of the roller by rotation of the roller.   The fixing device according to claim 11, wherein a coating layer for improving slidability is applied to at least a portion of the heater that is in sliding contact with the inner peripheral surface of the roller.   The fixing device according to claim 11, wherein the heater is curved so as to follow an inner peripheral surface of the roller. An image forming apparatus that forms an image on a recording medium by a series of image forming processes including charging, exposure, development, transfer, and fixing,
An image forming apparatus comprising the fixing device according to claim 8.

Images