JP2008225148A - Heater unit, fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heater unit having excellent mechanical strength and achieving reduction in cost and shortening warm-up time, a fixing device and an image forming apparatus. <P>SOLUTION: The heater unit 1 has: a cylindrical casing 11 having heat conductivity; a heater 12 housed in the casing 11 and energized to generate heat; and filler 13 with which space between the casing 11 and the heater 12 is filled and which is principally composed of inorganic powder having insulating property and heat conductivity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

In image forming apparatuses such as printers, copiers, and facsimiles employing an electrophotographic system, a toner image is formed by heating and pressurizing a recording medium such as paper carrying a toner image formed with toner in an unfixed state. A fixing device for fixing to a recording medium is provided (for example, see Patent Document 1).
Such a fixing device generally includes a heater unit as a heat source. As such a heater unit, one using a ceramic heater as a heat source is known as disclosed in Patent Document 1. In such a heater unit, one surface of a plate-shaped ceramic heater is joined and supported by a holder.

  However, the heater unit according to Patent Document 1 increases the size of the holder and complicates the shape of the holder in order to ensure sufficient mechanical strength (suppress bending). When the size of the holder is increased, the heat capacity of the entire heater unit is increased, the time required for raising the temperature to a desired temperature is increased, and the cost of the holder is increased if the shape of the holder is complicated.

JP-A-5-313528

  An object of the present invention is to provide a heater unit, a fixing device, and an image forming apparatus that have excellent mechanical strength, can be reduced in cost, and can be shortened in warm-up time.

Such an object is achieved by the present invention described below.
The heater unit of the present invention has a thermal conductivity and a cylindrical casing,
A heater housed in the casing and generating heat when energized;
It is filled between the said casing and the said heater, It has a filler mainly comprised by the inorganic powder which has insulation and heat conductivity.

  Thereby, a heater can be firmly supported by a casing via a filler. Therefore, the mechanical strength of the heater unit can be improved. Further, even if the casing is relatively thin and small, excellent mechanical strength can be obtained, so that the heat capacity of the heater unit can be suppressed and the warm-up time can be shortened. Further, since the casing can have a relatively simple shape, the cost of the heater unit can be reduced. Further, since the inorganic powder has insulating properties, the insulation treatment on the surface of the heater can be omitted or simplified, and in this respect also, the cost of the heater unit can be reduced.

In the heater unit of the present invention, the inorganic powder is preferably composed of an oxide-based ceramic and / or a nitride-based ceramic.
Such an inorganic powder is excellent in insulation and thermal conductivity. Therefore, the insulation process on the heater surface can be omitted and the cost of the heater unit can be reduced. In addition, heat can be quickly transferred from the heater to the casing, so that the warm-up time can be shortened. Furthermore, since such inorganic powder is hard, the mechanical strength of the heater unit can be improved.

The fixing device of the present invention includes a heater unit that heats a recording medium carrying an unfixed image, and a pressure roller that pressurizes the recording medium. The heater unit heats the recording medium, and A pressure roller presses the recording medium to fix the unfixed image on the recording medium,
The heater unit is
A casing having thermal conductivity and a cylindrical shape;
A heater housed in the casing and generating heat when energized;
It is filled between the said casing and the said heater, It has a filler mainly comprised by the inorganic powder which has insulation and heat conductivity.

  Thereby, a heater can be firmly supported by a casing via a filler. Therefore, the mechanical strength of the heater unit can be improved. Further, even if the casing is relatively thin and small, excellent mechanical strength can be obtained, so that the heat capacity of the heater unit can be suppressed and the warm-up time can be shortened. Further, since the casing can have a relatively simple shape, the cost of the heater unit can be reduced. Further, since the inorganic powder has insulating properties, the insulation treatment on the surface of the heater can be omitted or simplified, and in this respect also, the cost of the heater unit can be reduced.

The fixing device of the present invention includes an endless belt-like belt-like member provided along the outer peripheral surface of the casing, and a pressure roller pressed against the belt-like member. The recording medium is sandwiched and conveyed between the belt-shaped member and the pressure roller while the pressure rollers are pressed against each other, thereby pressing the recording medium while heating it to thereby form the unfixed image on the recording medium. It is preferable to be configured so as to be fixed to.
Accordingly, heat from the heater can be efficiently transmitted to the recording medium as compared with a fixing method such as a roller method. In addition, since heat from the heater can be released over the entire circumference of the casing, the belt-shaped member can be efficiently heated to achieve excellent fixability.

In the fixing device of the present invention, it is preferable that the casing is slidably provided on the inner peripheral surface of the belt-shaped member.
Thereby, a belt-shaped member can be heated efficiently.
In the fixing device of the present invention, it is preferable that the casing is pressed against the pressure roller via the belt-shaped member.
Thereby, the heat from the heater can be efficiently transmitted to the recording medium.

In the fixing device according to the aspect of the invention, it is preferable that the contour on the belt-like member side in the cross section of the casing is convexly curved.
Thereby, sliding with a casing and a belt-shaped member can be made smoother.
In the fixing device according to the aspect of the invention, it is preferable that a contour of the casing in a cross section is circular.
Thereby, a casing can be formed using an inexpensive material, and as a result, the heater unit can be made at a lower cost.

In the fixing device according to the aspect of the invention, it is preferable that a contour of the casing in a cross section is a quadrangle.
Thereby, the bending rigidity of a casing can be improved. Therefore, when adopting a configuration in which the casing is pressed against the pressure roller via a belt-like member, the casing is prevented from bending due to the pressing of the pressure roller, thereby preventing the nip shape from changing and exhibiting excellent fixing characteristics. Can be made. Further, the casing can be formed using an inexpensive material, and as a result, the heater unit can be made at a lower cost.

In the fixing device of the present invention, it is preferable that the inorganic powder is composed of an oxide ceramic and / or a nitride ceramic.
Such an inorganic powder is excellent in insulation and thermal conductivity. Therefore, it is possible to reduce the cost of the fixing device by omitting the insulation treatment on the heater surface. In addition, heat can be quickly transferred from the heater to the casing, so that the warm-up time can be shortened. Furthermore, since such inorganic powder is hard, the mechanical strength of the heater unit can be improved.

In the fixing device of the present invention, it is preferable that the filler is press-fitted between the casing and the heater.
Thereby, the mechanical strength of the heater unit can be further improved.
In the fixing device of the present invention, it is preferable that the casing is made of metal.
Thereby, the mechanical strength and thermal conductivity of the casing can be made excellent while making the casing inexpensive.

In the fixing device of the present invention, it is preferable that the heater includes a heating element having PTC characteristics and a pair of electrodes for applying a voltage to the heating element.
Thus, since the heating element has PTC characteristics (self-temperature controllability), the heater can be maintained at a predetermined temperature without providing a temperature sensor such as a thermistor. Therefore, the cost of the heater unit (fixing device) can be further reduced.

The image forming apparatus of the present invention has a fixing device for fixing the unfixed image to the recording medium by heating and pressurizing the recording medium carrying the unfixed image,
The fixing device includes a heater unit that heats a recording medium that carries an unfixed image, and a pressure roller that pressurizes the recording medium. The heater unit heats the recording medium, and the pressure roller Presses the recording medium to fix the unfixed image on the recording medium,
The heater unit is
A casing having thermal conductivity and a cylindrical shape;
A heater housed in the casing and generating heat when energized;
It is filled between the said casing and the said heater, It has a filler mainly comprised by the inorganic powder which has insulation and heat conductivity.
Thereby, since the heater unit has excellent mechanical strength, the reliability of the image forming apparatus can be improved. In addition, it is possible to provide an image forming apparatus capable of reducing the cost and shortening the warm-up time.

Hereinafter, preferred embodiments of a heater unit, a fixing device, and an image forming apparatus of the present invention will be described with reference to the accompanying drawings.
(First embodiment)
First, a first embodiment of the present invention will be described.
<Image forming apparatus>
FIG. 1 is a schematic cross-sectional view of the overall configuration of the image forming apparatus according to the first embodiment of the present invention.

  An image forming apparatus 10 of the present 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, an intermediate transfer member 61, 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. The transfer body 61 and the fixing device 90 are sequentially arranged along the conveyance direction of the recording medium P. Further, when forming an image on both sides of the recording medium, the image forming apparatus 10 reverses the recording medium P fixed on one side by the fixing device 90 and returns it to the secondary transfer position described later. The conveyance part 88 for making it do 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 has 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, 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 driving roller 71, and the rotation of the driving roller 71 is performed. As a result, it is rotationally driven 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 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 according to the present invention will be described in detail with reference to FIGS.
FIG. 2 is a schematic cross-sectional view showing the fixing device provided in the image forming apparatus shown in FIG. 1, and FIG. 3 is a view for explaining the heater unit provided in the fixing device shown in FIG.
The fixing device 90 employs a so-called belt fixing system. As shown in FIG. 2, the heater unit 1 according to the present invention and an endless belt-like belt provided so as to surround the outer periphery of the heater unit 1 are used. The member 91, rollers 92 and 93 that stretch the belt-like member 91 in cooperation with the heater unit 1 inside the belt-like member 91, and the pressure that is pressed against the heater unit 1 via the belt-like member 91 And a roller 94.

The fixing device 90 has a recording medium P that carries a toner image T in an unfixed state (that is, carries an unfixed image) at a nip portion N formed by the belt-shaped member 91 and the pressure roller 94 being pressed against each other. By sandwiching and conveying the recording medium P), the recording medium P is heated and pressurized to fix the toner image T to the recording medium P.
In such a fixing device 90, the belt-shaped member 91 has a small heat capacity, so that the heat of the heater unit 1 can be efficiently transmitted to the recording medium P. Therefore, power saving and warm-up time can be reduced.

Hereinafter, each part which comprises the fixing device 90 is demonstrated sequentially.
As shown in FIGS. 2 and 3, the heater unit 1 includes a cylindrical casing 11, a heater 12 housed in the casing 11, and a filler 13 filled between the casing 11 and the heater 12. have.
The casing 11 has thermal conductivity, has a cylindrical shape, and is installed non-rotatingly.
In such a casing 11, the contour on the belt-like member 91 side in the cross section is convexly curved, so that the sliding between the casing 11 and the belt-like member 91 can be made smoother. In particular, since the outline in the cross section of the casing 11 is circular, the casing 11 can be manufactured using an inexpensive material, and as a result, the heater unit 1 can be made at a lower cost.

In the present embodiment, the shape of the nip portion N corresponds to the shape of the outer peripheral surface of the casing 11.
The constituent material of the casing 11 is not particularly limited, and resin, metal, ceramics, glass, or a composite material thereof can be used, but aluminum, iron, stainless steel, aluminum alloy, copper alloy, and the like can be used. A metal can be preferably used, and stainless steel, an aluminum alloy, or a copper alloy is particularly preferable. When the casing 11 is made of such a metal, the mechanical strength and thermal conductivity of the casing 11 can be made excellent while making the casing 11 inexpensive.

Moreover, it is preferable that the sliding surface with the belt-shaped member 91 of the casing 11 is subjected to a treatment for improving the slidability. Such treatment is not particularly limited, but a method of forming a thin film made of a hard and slidable material such as DLC (Diamond Like Carbon) is preferably used.
Moreover, although the thickness of the casing 11 is not specifically limited, It is preferable that it is about 0.2-0.3 mm. The casing 11 formed with a thickness in such a range can have excellent mechanical strength and thermal conductivity. In the present embodiment, since the casing 11 is pressed by the pressure roller 94, the casing 11 is configured to have a mechanical strength that can withstand the pressing.

Further, the length of the casing 11 is not particularly limited, but is set to be slightly longer than the size (width) of the recording medium P to be used in the present embodiment.
In the present embodiment, a pair of seal members 14 are provided so as to close the openings on both end faces of the casing 11. The seal member 14 has a function of protecting the inside of the casing 11.

A heater 12 is arranged in such a casing 11.
The heater 12 includes a plurality of heating elements 121, a pair of electrodes 122, 123 that sandwich the plurality of heating elements 121, and a pair of extraction electrodes 124, 125 for energizing the pair of electrodes 122, 123. Each heating element 121 is caused to generate heat by applying a voltage between the pair of electrodes 122 and 123.

Each heating element 121 has a long plate shape and generates heat when energized. The plurality of heating elements 121 are juxtaposed along the longitudinal direction (axial direction) of the casing 11.
The constituent material of the heating element 121 is not particularly limited. For example, indium tin oxide (ITO), carbon-based material, titanium oxide-based ceramic (BaTiO ₃ , PbTiO ₃ ), Fe—Cr—Al alloy, Ni-Cr alloy etc. are mentioned.

Among the materials described above, as the constituent material of the heating element 121, a material having positive resistance temperature characteristics (PTC (Positive Temperature Coefficient) characteristics) such as ITO, a carbon-based material, BaTiO ₃ + PbTiO ₃ is preferable. By using a material having PTC characteristics, the temperature can be adjusted without using a temperature control device such as a thermostat or a temperature sensor such as a thermistor (having self-temperature controllability). Further, by omitting the temperature control device and the temperature sensor, the fixing device 90 can be reduced in cost, size, and power saving.

In addition, when a voltage is applied to a material having PTC characteristics, the temperature of the material itself rises due to Joule heat, but once it reaches a predetermined temperature, the electrical resistance increases rapidly, the current is suppressed, and the predetermined temperature is reduced. 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 pair of electrodes 122 and 123 sandwiching the heating element 121 is for energizing each heating element 121.

In the present embodiment, each of the electrodes 122 and 123 is formed to have a slightly longer dimension than a long body in which a plurality of heating elements 121 are arranged in parallel. An extraction electrode 124 is bonded to the surface of the electrode 122 opposite to the heating element 121, and an extraction electrode 125 is bonded to the surface of the electrode 123 opposite to the heating element 121.
Each extraction electrode 124, 125 has a rod shape extending in the axial direction (that is, the longitudinal direction) of the casing 11, and one end portion thereof protrudes from an opening at one end of the casing 11 (more specifically, 1 described above). One seal member 14 of the pair of seal members 14 is penetrated). A wiring 15 is connected to the extraction electrode 124, and a wiring 16 is connected to the extraction electrode 125. These wirings 15 and 16 are connected to a power supply circuit (not shown), and the heating element 121 can be energized from the outside of the casing 11 through the pair of electrodes 122 and 123 through the pair of extraction electrodes 124 and 125. It is possible.

  The constituent materials of the electrodes 122 and 123 and the extraction electrodes 124 and 125 are not particularly limited, and various electrode materials can be used. In particular, the constituent materials of the electrodes 122 and 123 are silver. A paste can be suitably used. When silver paste is used as the constituent material of each electrode 122, 123, each electrode 122, 123 can be joined to the heating element 121 and each extraction electrode 124, 15 without using a conductive adhesive or the like. . As a result, also in this respect, cost reduction and warm-up time can be shortened. Further, as will be described later, each electrode 122, 123 and each extraction electrode 124, 15 are pressed against the heating element 121 by the filler 13 filled between the casing 11 and the heater 12. It is possible to prevent a bonding failure between the heater 123 and the heating element 121 and the extraction electrodes 124 and 15.

The filler 13 filled between the casing 11 and the heater 12 is mainly composed of an inorganic powder having insulating properties and thermal conductivity.
Thus, by filling the filler between the casing 11 and the heater 12, the heater 12 can be firmly supported on the casing 11 via the filler 13. Therefore, the mechanical strength of the heater unit 1 can be improved. Further, even if the casing 11 is relatively thin and small, excellent mechanical strength can be obtained, so that the heat capacity of the heater unit 1 can be suppressed and the warm-up time can be shortened. Further, since the casing 11 can have a relatively simple shape, the cost of the heater unit 1 can be reduced. Further, since the inorganic powder has insulating properties, the insulation treatment on the surface of the heater 12 can be omitted or simplified, and in this respect also, the cost of the heater unit 1 can be reduced.

  The inorganic powder of the filler 13 is not particularly limited as long as it has insulating properties and thermal conductivity. However, nitride ceramics such as SiN (silicon nitride) and AlN (aluminum nitride), MgO (magnesia) ), Or ceramics such as composite ceramics thereof, in particular, oxide ceramics (especially MgO) and / or nitride ceramics (especially AlN). Is preferred. Such an inorganic powder is excellent in insulation and thermal conductivity. Therefore, the insulation process on the surface of the heater 12 can be omitted, and the cost of the heater unit 1 can be reduced. In addition, heat can be transferred quickly from the heater 12 to the casing 11 to shorten the warm-up time. Furthermore, since such inorganic powder is hard, the mechanical strength of the heater unit 1 can be improved.

The filler 13 may contain other components in addition to the inorganic filler as described above. For example, the filler 13 may contain a small amount of an adhesive made of a thermosetting resin.
Such a filler is preferably press-fitted between the casing 11 and the heater 12. Thereby, the mechanical strength of the heater unit 1 can be further improved.

A belt-like member 91 is provided so as to surround the outer periphery of the casing 11 of the heater unit 1 as described above.
The belt-shaped member 91 has an endless belt shape (endless belt shape), and is rotatably disposed while forming a nip portion N by pressure contact with the pressure roller 94.
The constituent material of the belt-like member 91 is not particularly limited, but a material having heat resistance to the heat of the heater unit 1 is preferably used. For example, a metal such as stainless steel or nickel alloy, polyimide Resins such as silicone resins are preferably used.

Further, the thickness of the belt-like member 91 is determined according to the constituent material of the belt-like member 91 and is not particularly limited, but is preferably 0.03 to 1 mm, for example, 0.03 to 0.5 mm. More preferably.
In addition to the heater unit 1, a pair of rollers 92 and 93 are disposed inside the belt-shaped member 91 having such an endless belt shape. The belt-shaped member 91 includes the heater unit 1 and the pair of rollers 92. , 93. That is, tension is applied to the belt-like member 91 by the cooperation of the heater unit 1 and the pair of rollers 92 and 93 while allowing the belt-like member 91 to rotate.

Each of the rollers 92 and 93 is provided so as to be rotatable around its own axis. In the present embodiment, each of the rollers 92 and 93 is provided so as to be rotatable around its axis, and is driven to rotate as the belt-shaped member 91 rotates. Note that one of the pair of rollers 92 and 93 may be rotationally driven to rotationally drive the belt-shaped member 91.
A pressure roller 94 is pressed against the belt-like member 91 stretched by the pair of rollers 92 and 93 and the heater unit 1.

The pressure roller 94 has a cylindrical shape or a columnar shape, and is rotatable about its axis. In the present embodiment, the pressure roller 94 is rotated by a driving force of a driving unit such as a motor (not shown).
As shown in FIG. 2, the pressure roller 94 covers a cylindrical metal base (core metal) 941, an elastic layer 942 that covers the outer peripheral surface of the base 941, and an outer peripheral surface of the elastic layer 942. A release layer 943.

  As a constituent material of the elastic layer 942, for example, Si rubber, EPDM, fluorine rubber, or the like can be suitably used.

The thickness of the elastic layer 942 is not particularly limited, but 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 making the durability of the elastic layer 942 excellent.
The thickness of the release layer 943 is not particularly limited, but is preferably 10 to 80 μm, and more preferably 20 to 50 μm. Thereby, the elasticity of the elastic layer 942 can be sufficiently exhibited while maintaining the strength required for the release layer 943.
Further, the constituent material of the release layer 943 is not particularly limited, but for example, PTFE, PFA, and the like can be suitably used.

In the fixing device 90 having the configuration described above, a power supply circuit (not shown) applies a voltage to the pair of extraction electrodes 124 and 125 and the pair of electrodes 122 and 123 through the pair of wirings 15 and 16. To do. As a result, the heating element 121 is energized, and the heating element 121 generates heat.
The heat of the heater 12 that has generated heat in this way is radiated radially through the filler 13 and the casing 11. As a result, the nip portion N is heated.

On the other hand, the pressure roller 94 is rotationally driven by a driving force of a driving means (not shown). As a result, the belt-shaped member 91 is driven to rotate while the belt-shaped member 91 and the outer peripheral surface of the casing 11 of the heater unit 1 slide. At this time, the rollers 92 and 93 are driven to rotate as the belt-shaped member 91 rotates.
When the recording medium P carrying the unfixed toner image T is introduced into the nip portion N, the recording medium P is pressed and heated while being nipped and conveyed by the belt-like member 91 and the pressure roller 94. As a result, the toner image T is fused and fixed to the recording medium P.

  According to the image forming apparatus 10 described above, the heater 12 can be firmly supported on the casing 11 via the filler 13. Therefore, the mechanical strength of the heater unit 1 can be improved, and as a result, the reliability of the fixing device 90 and the image forming apparatus 10 can be improved. Further, even if the casing 11 is relatively thin and small, excellent mechanical strength can be obtained, so that the heat capacity of the heater unit 1 can be suppressed and the warm-up time can be shortened. Further, since the casing 11 can have a relatively simple shape, the cost of the heater unit 1 can be reduced. In addition, since the inorganic powder of the filler 13 has insulating properties, the insulation treatment on the surface of the heater 12 can be omitted or simplified, and in this respect also, the cost of the heater unit 1 can be reduced. Can do.

In particular, since the fixing device 90 employs a belt fixing method, heat from the heater 12 can be efficiently transferred to the recording medium P as compared with a fixing method such as a roller method. Further, since the heater unit 1 radiates heat radially in the radial direction, that is, heat can be released from the heater 12 over the entire circumference of the casing 11, the belt-shaped member 91 is efficiently heated. Thus, excellent fixability can be realized.
Further, since the casing 11 is slidably provided on the inner peripheral surface of the belt-like member 91, the belt-like member 91 can be efficiently heated.
Furthermore, since the casing 11 is pressed against the pressure roller 94 via the belt-like member 91, the heat from the heater 12 can be efficiently transmitted to the recording medium P.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIG. Hereinafter, the second embodiment will be described with a focus on differences from the first embodiment described above, and description of similar matters will be omitted.
FIG. 4 is a schematic cross-sectional view showing a schematic configuration of a fixing device according to the second embodiment of the present invention.
The fixing device of the present embodiment is the same as the fixing device of the first embodiment except that the cross-sectional shape of the casing of the heater unit is different.

The fixing device 90 </ b> A of the present embodiment includes a heater unit 1 </ b> A that is pressed against the pressure roller 94 via the belt-like member 91.
The heater unit 1 </ b> A has a casing 11 </ b> A that houses the heater 12, and a filler 13 is filled between the casing 11 </ b> A and the heater 12.
In the present embodiment, as shown in FIG. 4, the casing 11 </ b> A has a rectangular tube shape. Therefore, the outline in the cross section of the casing 11A is a quadrangle. Thereby, the bending rigidity of the casing 11A can be improved. Therefore, when the configuration in which the casing 11A is pressed against the pressure roller 94 via the belt-like member 91 as in the present embodiment is adopted, the bending of the casing 11A is suppressed and the variation of the shape of the nip portion N is prevented. Therefore, good fixing characteristics can be exhibited. Further, the casing 11A can be formed using an inexpensive material that is not complicated in shape, and as a result, the heater unit 1A can be made at a lower cost.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIG. Hereinafter, the third embodiment will be described with a focus on differences from the first embodiment described above, and description of similar matters will be omitted.
FIG. 5 is a schematic cross-sectional view showing a schematic configuration of a fixing device according to a third embodiment of the present invention.
The fixing device of the present embodiment is the same as the fixing device of the first embodiment, except that the belt-like member 91 is stretched differently.

The fixing device 90B of the present embodiment includes a backup member 95 that is pressed against the pressure roller 94 via the belt-like member 91, and a heater unit 1B that stretches the belt-like member 91 in cooperation with the backup member 95. have.
The backup member 95 has a function of forming the nip portion N by being pressed by the pressure roller 94 via the belt-like member 91. Such a backup member 95 is formed so as to make the shape, range, pressure distribution, and the like of the nip portion N suitable for the fixing process. In the present embodiment, the contour of the backup member 95 in the cross section is curved so as to be convex toward the pressure roller 94. Further, the outline of the backup member 95 on the side opposite to the pressure roller 94 in the cross section is linear.
On the other hand, the heater unit 1 </ b> B has a casing 11 </ b> B that houses the heater 12, and a filler 13 is filled between the casing 11 </ b> B and the heater 12.

In the present embodiment, as shown in FIG. 5, the casing 11 </ b> B has a semi-oval shape in which the outline in the cross section is a long oval cut along half the short axis.
In such a casing 11B, the contour on the belt-like member 91 side in the cross section thereof is convexly curved, so that sliding between the casing 11B and the belt-like member 91 can be made smoother.
The contour on the backup member 95 side in the cross section of the casing 11 </ b> B is linear, and is formed so as to be parallel to the contour on the side opposite to the pressure roller 94 in the cross section of the backup member 95. Thereby, the heater unit 1B can heat the backup member 95 efficiently.

In the fixing device 90B configured as described above, the heater unit 1B heats the belt-shaped member 91 and the backup member 95. As a result, the nip portion N is heated. When the recording medium P carrying the unfixed toner image T is introduced into the nip portion N, the recording medium P is pressed and heated while being nipped and conveyed by the belt-like member 91 and the pressure roller 94. As a result, the toner image T is fused and fixed to the recording medium P.
Also by the fixing device 90B (heater unit 1B) of the present embodiment as described above, the same effect as that of the fixing device 90 (heater unit 1) of the first embodiment described above can be obtained.

(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to FIG. Hereinafter, the fourth embodiment will be described with a focus on differences from the first embodiment described above, and description of similar matters will be omitted.
FIG. 6 is a schematic cross-sectional view showing a schematic configuration of a fixing device according to a fourth embodiment of the present invention.
The fixing device of this embodiment is the same as the fixing device of the first embodiment except that the shape of the casing is different and a holder for supporting the casing is provided.

The fixing device 90 </ b> C of the present embodiment includes a heater unit 1 </ b> C that is pressed against the pressure roller 94 via the belt-like member 91.
The heater unit 1C includes a casing 11C that houses the heater 12 and supports the heater 12 via a filler 13, and a holder 17 that supports the casing 11C.

The casing 11C has an elliptical (oval) outline in cross section.
On the other hand, the holder 17 has a U-shaped cross section so as to cover the casing 11C from the side opposite to the nip portion N. The surface of the casing 11 </ b> C opposite to the nip portion N is joined to the holder 17 via the joining material 18.
By supporting the casing 11C on the holder 17 in this manner, the rigidity of the heater unit 1C in the normal direction of the nip portion N can be increased. Therefore, even when the rigidity of the casing 11C in the normal direction of the nip portion N is low as in the present embodiment, the deformation of the casing 11C can be prevented and the belt-shaped member 91 can be stably driven. In particular, in this embodiment, a part of the holder 17 is provided so as to be slidable with the belt-like member 91, and also serves as a guide for guiding the belt-like member 91. Therefore, the running stability of the belt-like member 91 is extremely good.

The constituent material of the holder 17 is not particularly limited, but can be the same constituent material as that of the casing 11 described above.
Further, the bonding material 18 is not particularly limited, but is preferably mainly composed of a heat insulating material. Thereby, the heat of the heater 12 can be efficiently used for heating the nip portion N.
Also by the fixing device 90C (heater unit 1C) of the present embodiment as described above, the same effect as that of the fixing device 90 (heater unit 1) of the first embodiment described above can be obtained.

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.

1 is a schematic cross-sectional view of an overall configuration showing an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a fixing device provided in the image forming apparatus illustrated in FIG. 1. FIG. 3 is a diagram for explaining a heater unit provided in the fixing device shown in FIG. 2. FIG. 6 is a schematic cross-sectional view illustrating a schematic configuration of a fixing device according to a second embodiment of the present invention. FIG. 6 is a schematic cross-sectional view illustrating a schematic configuration of a fixing device according to a third embodiment of the present invention. FIG. 6 is a schematic cross-sectional view illustrating a schematic configuration of a fixing device according to a fourth embodiment of the present invention.

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, 90A 90B, 90C ... Fixing device 91 ... Belt-shaped member 92, 93 ... Roller 94 ... Pressure roller 941 ... Base 942 ... Elastic layer 943 ... Release layer 1, 1A 1B, 1C ... Heater unit 11, 11A, 11B, 11C ... Casing 12 ... Heater 121 ... Heating element 122, 123 ... Electrode 124, 125 ... Extraction electrode 14 ... Seal member 15, 16 ... Wiring 13 ... Filler 18 ... Bonding material 95 ... Backup member N ... Nip part P ... Recording medium T ... Toner image (unfixed image)

Claims (14)

A casing having thermal conductivity and a cylindrical shape;
A heater housed in the casing and generating heat when energized;
A heater unit comprising: a filler filled between the casing and the heater and mainly composed of an inorganic powder having insulating properties and thermal conductivity.   The heater unit according to claim 1, wherein the inorganic powder is composed of an oxide-based ceramic and / or a nitride-based ceramic. A heater unit that heats the recording medium carrying an unfixed image; and a pressure roller that pressurizes the recording medium. The heater unit heats the recording medium, and the pressure roller presses the recording medium. The unfixed image is fixed to the recording medium by applying pressure,
The heater unit is
A casing having thermal conductivity and a cylindrical shape;
A heater housed in the casing and generating heat when energized;
A fixing device comprising: a filler filled between the casing and the heater and mainly composed of an inorganic powder having insulating properties and thermal conductivity.   An endless belt-like belt-like member provided along the outer peripheral surface of the casing, and a pressure roller pressed against the belt-like member, and the belt-like member and the pressure roller are pressed against each other. The recording medium is sandwiched and conveyed between the belt-shaped member and the pressure roller, and the recording medium is pressed while heating to fix the unfixed image on the recording medium. The fixing device according to claim 3.   The fixing device according to claim 4, wherein the casing is slidably provided on an inner peripheral surface of the belt-shaped member.   The fixing device according to claim 5, wherein the casing is pressed against the pressure roller via the belt-shaped member.   The fixing device according to claim 5, wherein a contour of the belt-shaped member side in a cross section of the casing is convexly curved.   The fixing device according to claim 7, wherein a contour of the casing in a cross section is circular.   The fixing device according to claim 5, wherein a contour of the casing in a cross section is a quadrangle.   The fixing device according to claim 3, wherein the inorganic powder is made of an oxide ceramic and / or a nitride ceramic.   The fixing device according to claim 3, wherein the filler is press-fitted between the casing and the heater.   The fixing device according to claim 3, wherein the casing is made of metal.   The fixing device according to claim 3, wherein the heater includes a heating element having PTC characteristics and a pair of electrodes for applying a voltage to the heating element. A fixing device for fixing the unfixed image to the recording medium by heating and pressurizing the recording medium carrying the unfixed image;
The fixing device includes a heater unit that heats a recording medium that carries an unfixed image, and a pressure roller that pressurizes the recording medium. The heater unit heats the recording medium, and the pressure roller Presses the recording medium to fix the unfixed image on the recording medium,
The heater unit is
A casing having thermal conductivity and a cylindrical shape;
A heater housed in the casing and generating heat when energized;
An image forming apparatus comprising: a filler filled between the casing and the heater and mainly composed of an inorganic powder having insulating properties and thermal conductivity.

Images