JP2024168994A - Fixing device and image forming apparatus - Google Patents

Abstract

To provide a fixing device that can guarantee proper heat fixing in a passing area, while suppressing excessive heating in non-passing areas.SOLUTION: A fixing device comprises: a fixing belt that heats toner on a sheet while rotating about an axis; a pressure roller that applies a pressure to the toner on the sheet passing through a pressing area while rotating about an axis; and a heater 33 that is in contact with an inner face of the fixing belt and heats the fixing belt. The fixing belt is set with a passing area A1 in contact with a sheet, and non-passing areas A2 not in contact with the sheet. The heater 33 has a heat generation unit provided on one face of a substrate 36 and generating heat upon energization, and a soaking member 38 provided on the other face of the substrate 36 and absorbing heat generated from the heat generation unit and moving the heat in an axial direction. The soaking member 38 is formed to increase heat capacity in end areas corresponding to the non-passing areas A2 compared to a center area corresponding to the passing area A1.SELECTED DRAWING: Figure 5

Description

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

Electrophotographic image forming apparatuses are equipped with a fixing device that thermally fixes toner on a recording material (medium). For example, the fixing device has a cylindrical film, a heater that contacts the inner surface of the film, and a heat-conducting member that contacts the heater (Patent Document 1). The heat-conducting member is divided into multiple parts in the generatrix direction (axial direction) of the film to suppress warping and increase adhesion to the heater. In addition, one of the heat-conducting members is in continuous contact with the heater from the center (paper passing portion) to the end (non-paper passing portion) of the heater's heating area, suppressing excessive temperature rise in the non-paper passing portion of the film.

JP 2016-95433 A

However, the heat-conducting member of the fixing device described above absorbs heat from the paper-passing area to the non-paper-passing area, so there is a risk that the heat required for thermal fixing will be lost in the paper-passing area. As a result, the fixing device described above may not be able to properly thermally fix the toner on the recording material.

The present invention takes the above problems into consideration and provides a fixing device and an image forming device that can ensure proper thermal fixing in the passing area while suppressing excessive heating in the non-passing area.

The fixing device according to the present invention includes a fixing belt formed in a cylindrical shape and rotating around an axis to heat the toner on the medium, a pressure roller rotating around an axis to form a pressure area between the fixing belt and the pressure roller, which pressurizes the toner on the medium passing through the pressure area, and a heater that contacts the inner surface of the fixing belt facing the pressure area and heats the fixing belt. The fixing belt has a passing area in the center of the axial direction that contacts the medium, and a non-passing area on both sides or one side of the axial direction that does not contact the medium. The heater has a substrate that extends in the axial direction corresponding to the fixing belt, a heat generating part that is provided on one side of the substrate and generates heat when current is applied, and a heat equalizing member that is provided on the other side of the substrate and absorbs the heat generated by the heat generating part and moves it in the axial direction. The heat equalizing member is formed so that the heat capacity is increased in the end area corresponding to the non-passing area more than in the central area corresponding to the passing area.

In this case, the heat equalizing member may be formed so that it becomes wider in the direction in which the medium passes from the central region toward the end region.

In this case, the heat equalizing member may be formed so that its thickness increases from the central region toward the end region.

In this case, the heater may further include a temperature detector that is in contact with the heat equalizing member and detects the temperature of the heater, and the contact portion of the temperature detector with the heat equalizing member may be narrower in the direction in which the medium passes than the non-contact portion of the temperature detector.

In this case, the heater may further include a temperature detector that is in contact with the uniform heat member and detects the temperature of the heater, and the contact portion of the temperature detector with the uniform heat member may be thinner than the non-contact portion of the temperature detector.

The image forming apparatus according to the present invention is equipped with the fixing device described above.

The present invention makes it possible to suppress excessive heating in non-passing areas while ensuring proper thermal fixation in passing areas.

FIG. 1 is a schematic diagram (front view) illustrating a printer according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device according to a first embodiment of the present invention. FIG. 2 is a bottom view illustrating a heater of the fixing device according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. FIG. 2 is a plan view illustrating a heater of the fixing device according to the first embodiment of the present invention. FIG. 4 is a plan view illustrating a heater of a fixing device according to a modified example of the first embodiment of the present invention. FIG. 11 is a side view illustrating a heater of a fixing device according to a second embodiment of the present invention. FIG. 11 is a side view illustrating a heater of a fixing device according to a modified example of the second embodiment of the present invention. FIG. 11 is a plan view illustrating a heater of a fixing device according to a third embodiment of the present invention. FIG. 11 is a cross-sectional view illustrating a heater of a fixing device according to a fourth embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. Note that Fr, Rr, L, R, U, and D shown in the drawings indicate front, rear, left, right, top, and bottom. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention.

[Printer overall configuration]
A printer 1 as an example of an image forming apparatus will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (front view) showing the printer 1.

The printer 1 has a device main body 2 that has a roughly rectangular parallelepiped exterior. A paper feed cassette 3 that stores paper P (medium) is provided at the bottom of the device main body 2. A paper output tray 4 is provided on the top surface of the device main body 2. Note that the paper P is not limited to being made of paper, and may be made of resin, etc.

Inside the device body 2, a transport path 8 is formed as a passage for the paper P. The transport path 8 is formed in a roughly S-shape between the paper feed cassette 3 and the paper discharge tray 4. At the upstream end of the transport path 8, a paper feed device 5 is provided that removes the paper P from the paper feed cassette 3. An image forming device 6 is provided in the middle of the transport path 8, and a fixing device 20 is provided downstream of the transport path 8.

The imaging device 6 has a toner container 10, a drum unit 11, and an optical scanning device 12. The toner container 10 contains, for example, black toner (developer). The drum unit 11 has a photoconductor drum 13, a charging device 14, a developing device 15, and a transfer roller 16. The charging device 14, the developing device 15, and the transfer roller 16 are arranged around the photoconductor drum 13 in the order of the image formation process. The transfer roller 16 contacts the photoconductor drum 13 from below to form a transfer nip. The toner may be a two-component developer made of a mixture of toner and carrier, or a one-component developer made of magnetic toner.

The control device (not shown) of the printer 1 appropriately controls each device and executes the image formation process as follows. The charging device 14 charges the surface of the photosensitive drum 13. The photosensitive drum 13 receives the scanning light emitted from the optical scanning device 12 and carries an electrostatic latent image. The developing device 15 develops the electrostatic latent image on the photosensitive drum 13 into a toner image using toner supplied from the toner container 10. The paper P is sent from the paper feed cassette 3 to the transport path 8 by the paper feed device 5, and the toner image on the photosensitive drum 13 is transferred to the paper P passing through the transfer nip. The fixing device 20 thermally fixes the toner image to the paper P. The paper P is then discharged to the paper output tray 4.

[First embodiment: fixing device]
Next, the fixing device 20 according to the first embodiment will be described with reference to Figures 2 to 4. Figure 2 is a cross-sectional view that typically shows the fixing device 20. Figure 3 is a bottom view that typically shows the heater 33. Figure 4 is a cross-sectional view taken along line IV-IV in Figure 3. Figure 5 is a plan view that typically shows the heater 33.

As shown in FIG. 2, the fixing device 20 includes a fixing belt 31, a pressure roller 32, and a heater 33. The fixing belt 31 and the pressure roller 32 are provided inside the housing 30 (see FIG. 1). The heater 33 is a heat source for heating the fixing belt 31.

<Fixing belt>
The fixing belt 31 is an endless belt, and is formed in a generally cylindrical shape that is long in the front-rear direction (axial direction). The surface layer of the fixing belt 31 is made of a synthetic resin material having heat resistance and elasticity, such as polyimide resin. The fixing belt 31 is disposed in the upper part of the inside of the housing 30. A pair of generally cylindrical caps (not shown) are attached to both ends of the fixing belt 31 in the axial direction. Note that a belt guide (not shown) for maintaining the generally cylindrical shape of the fixing belt 31 may be provided inside the fixing belt 31.

(Pressing member, holding member)
A pressing member 34 and a holding member 35 are provided inside the fixing belt 31. The pressing member 34 is formed in an axially long, approximately rectangular tube shape made of a metal material such as an aluminum alloy or stainless steel. The pressing member 34 penetrates the fixing belt 31 (and the cap) in the axial direction (front-rear direction), and both front and rear ends of the pressing member 34 protruding from the fixing belt 31 are supported by the housing 30. The fixing belt 31 described above is supported rotatably relative to the pressing member 34. The holding member 35 is formed in an axially long, approximately semi-cylindrical shape made of a heat-resistant resin material, for example. The holding member 35 is formed slightly shorter in the axial direction than the fixing belt 31 and is disposed inside the fixing belt 31. The holding member 35 is fixed to the lower surface of the pressing member 34 and has a curved surface that follows the lower inner surface of the fixing belt 31. A fitting portion 35A into which the heater 33 is fitted is recessed in the lower portion of the holding member 35.

<Pressure roller>
The pressure roller 32 is formed in a generally cylindrical shape that is long in the front-rear direction (axial direction). The pressure roller 32 is disposed at the lower inside of the housing 30. The pressure roller 32 has a core 32A made of aluminum alloy, stainless steel, or the like, and an elastic layer 32B made of silicone sponge or the like laminated on the outer circumferential surface of the core 32A. Both ends of the core 32A in the axial direction are rotatably supported by the housing 30. A drive motor (not shown) is connected to the core 32A via a gear train or the like, and the pressure roller 32 is rotated by the drive motor.

The fixing device 20 also has a pressure adjustment unit (not shown) that adjusts the contact pressure of the pressure roller 32 against the fixing belt 31 by raising and lowering the pressure roller 32. The pressure roller 32 is pressed against the fixing belt 31 to form a pressure area N between the fixing belt 31 and the pressure roller 32. The fixing belt 31 heats the toner on the paper P passing through the pressure area N while rotating around its axis, and the pressure roller 32 pressurizes the toner on the paper P passing through the pressure area N while rotating around its axis. The toner image is fixed on the paper P by the paper P passing through the pressure area N. The pressure area N refers to the area from the upstream position in the conveying direction of the paper P where the pressure is 0 Pa, through the position where the pressure is maximum, to the downstream position in the conveying direction of the paper P where the pressure is 0 Pa again. In this specification, the direction in which the paper P passes through the pressure area N is called the "passing direction". The passing direction is the same direction as the conveying direction of the paper P and is perpendicular to the axial direction (front-back direction). In this specification, "upstream" and "downstream" and similar terms refer to "upstream" and "downstream" and similar concepts in the passing or conveying direction.

The paper P passes through the vicinity of the center in the axial direction of the pressure area N. More specifically, the paper P is transported with the center of its own front-to-rear width roughly aligned with the center in the front-to-rear direction (axial direction) of the pressure area N. For this reason, the fixing belt 31 (or the pressure area N) has a passing area A1 in the axial center that contacts the paper P, and a non-passing area A2 on both sides in the axial direction that does not contact the paper P (see FIG. 3). The paper P being transported always contacts the vicinity of the axial center of the passing area A1, regardless of the size of the paper P (dimension in the front-to-rear direction). In contrast, normal size (e.g. A4 size) paper P contacts both sides of the passing area A1 in the axial direction, but small and medium size (e.g. A5, B5, etc.) paper P does not contact them.

<Heater>
2, the heater 33 is provided inside the fixing belt 31. Specifically, the heater 33 is fitted into the fitting portion 35A of the holding member 35, and is in contact with the inner surface of the fixing belt 31 facing the pressure region N. The heater 33 heats the fixing belt 31 from the inside.

As shown in Figures 3 and 4, the heater 33 has a substrate 36, a heat generating portion 37, and a heat equalizing member 38.

(substrate)
The substrate 36 is made of an electrically insulating material such as ceramic. The substrate 36 is formed in a generally rectangular plate shape that is elongated in the axial direction to correspond to the fixing belt 31. The substrate 36 is formed to be slightly shorter than the fixing belt 31 in the axial direction, and is disposed inside the fixing belt 31.

(heat generating part)
The heating section 37 is provided on the lower surface (one surface) of the substrate 36 (see FIG. 4). As shown in FIG. 3, the heating section 37 is composed of five divided heating sections 41 to 45 arranged in a row in the axial direction. Each divided heating section 41 to 45 is composed of a plurality of resistance heating elements 40 arranged in a row with gaps in the axial direction. Each resistance heating element 40 is formed in a substantially rectangular shape elongated in the passing direction by a metal material with a high electric resistance value. All the resistance heating elements 40 are formed to be substantially the same size. The heating section 37 is formed to be shorter than the entire axial length of the fixing belt 31 and longer in the axial direction than the passing area A1 of the fixing belt 31. In other words, some of the resistance heating elements 40 of the divided heating sections 44 and 45 located on both outer sides in the axial direction face the non-passing area A2 of the fixing belt 31.

The split heating section 41, located in the center of the axial direction, corresponds to the front-to-rear width of a small-sized (e.g., A5 size) sheet of paper P passing through the pressure application area N. The split heating section 41 and the two adjacent split heating sections 42, 43 correspond to the front-to-rear width of a medium-sized (e.g., B5 size) sheet of paper P passing through the pressure application area N. All of the split heating sections 41 to 45 correspond to the front-to-rear width of a normal-sized (e.g., A4 size) sheet of paper P passing through the pressure application area N.

Five individual electrodes 51-55 and a common electrode 56 are formed on the underside of the substrate 36 (see Figures 3 and 4). The five individual electrodes 51-55 and the common electrode 56 are formed, for example, from a metal material with a lower electrical resistance value than the resistive heating element 40. Note that in this specification, when describing the five individual electrodes 51-55 and the common electrode 56 in common, they will simply be referred to as "electrode portions 51-56."

As shown in FIG. 3, the individual electrode 51 is connected to the downstream end (right end) of the divided heating section 41 (resistance heating element 40) located in the center in the axial direction. The other individual electrodes 52-55 are connected to the downstream ends of the divided heating sections 42-45, respectively. The common electrode 56 is connected to the upstream ends (left ends) of all the resistance heating elements 40. Each of the multiple electrode sections 51-56 extends from the portion connected to the heating section 37 to both outside sides of the heating section 37 in the axial direction. The multiple electrode sections 51-56 are electrically connected to external devices (not shown), such as a power source, on both sides of the substrate 36 in the axial direction.

The heat generating portion 37 and the electrode portions 51 to 56 are covered with a coating layer 57 (see FIG. 4). The coating layer 57 is made of a material that is electrically insulating, such as ceramic, and has a small sliding friction force against the fixing belt 31. The coating layer 57, the heat generating portion 37, and the electrode portions 51 to 56 can be formed with high precision on the substrate 36 by, for example, a film formation technique such as sputtering, a printed circuit board manufacturing technique, a screen printing technique, or a combination of these techniques.

The heater 33 is fitted into the fitting portion 35A of the holding member 35 with the heat generating portion 37 (coat layer 57) facing the pressure roller 32, and the coat layer 57 is in contact with the inner surface of the fixing belt 31 (see Figures 2 and 4). The heater 33 receives the fixing belt 31 pressed against the pressure roller 32, forming a pressure area N at the contact portion between the fixing belt 31 and the pressure roller 32.

[Function of Fixing Device]
Here, we will briefly explain the operation (fixing process) of the fixing device 20. The electrodes 51 to 56 of the heater 33, the drive motor, etc. are electrically connected to a power source (not shown) and a control device via various drive circuits (not shown).

The control device drives and controls the drive motor and heater 33. The pressure roller 32 rotates by receiving the driving force of the drive motor, and the fixing belt 31 rotates following the pressure roller 32 (see the solid thin arrow in Figure 2). The heat generating section 37 (each resistance heating element 40) generates heat when electricity is applied via the electrode sections 51 to 56, and the fixing belt 31 (pressure region N) heats up.

At this time, the control device changes the divided heating sections 41 to 45 that generate heat (energize) depending on the size of the paper P. For example, when a normal-sized paper P passes through the pressure area N, the control device supplies power to all divided heating sections 41 to 45, causing all divided heating sections 41 to 45 to generate heat. Also, for example, when a medium-sized paper P passes through the pressure area N, the control device causes the divided heating sections 41 to 43 to generate heat, and when a small-sized paper P passes through the pressure area N, the control device causes the divided heating section 41 to generate heat. This makes it possible to heat only the necessary parts of the fixing belt 31 (pressure area N) according to the size of the paper P. As a result, the power used can be kept to a minimum. It is also possible to prevent excessive temperature rise at both ends of the axial direction of the fixing belt 31.

When the fixing belt 31 reaches the set temperature, the image forming process described above begins. As the paper P onto which the toner image has been transferred passes through the pressure area N, the toner image is heated and pressurized, and fixed to the paper P.

<Heat uniformity member>
Incidentally, the fixing belt 31 has a smaller heat capacity than a roller or the like, so the fixing device 20 using the fixing belt 31 has the advantage of requiring less time to warm up. However, for example, when small-sized paper P is continuously fixed, the paper P (toner image) takes heat in the passing area A1 of the fixing belt 31, so that excessive temperature rise is suppressed, but the non-passing area A2 where the paper P does not pass may become excessively heated. In this fixing device 20, a heat equalizing member 38 is provided on the heater 33 to suppress excessive temperature rise in the non-passing area A2 of the fixing belt 31. To be precise, when small-sized paper P is continuously fixed, both sides of the passing area A1 in the axial direction also become excessively heated, but the heat equalizing member 38 also suppresses excessive temperature rise on both sides of the passing area A1 in the axial direction.

4 and 5, the heat equalizing member 38 is provided on (in contact with) the upper surface (the other surface) of the substrate 36. A lubricant (not shown), such as silicone grease, is applied between the heat equalizing member 38 and the substrate 36. The lubricant brings the heat equalizing member 38 and the substrate 36 into close contact with each other, and also facilitates the transfer of heat from the heater 33 to the heat equalizing member 38. The heat equalizing member 38 is formed in the shape of a plate that is long in the axial direction, for example, from a metal material such as an aluminum alloy. The heat equalizing member 38 is formed to be shorter in the axial direction than the substrate 36, and longer in the axial direction than the heat generating portion 37 (the range in which all the resistance heating elements 40 are formed). Both sides of the heat equalizing member 38 in the axial direction face the non-passing area A2 of the fixing belt 31 (see FIG. 5). The heat equalizing member 38 absorbs the heat generated by the heater 33 and transfers it in the axial direction. In other words, the heat equalizing member 38 equalizes the temperature of the heater 33 in the axial direction. As a result, the temperature of the fixing belt 31 is uniformed in the axial direction, and excessive temperature rise in the non-passage area A2 is suppressed. Note that in this specification, the term "uniform" does not mean only a completely constant state, but also means that some degree of error is allowed.

The fixing device 20 is provided with a temperature detector 46 that detects the temperature of the heater 33 and cuts off power supply to the heater 33 if the temperature is abnormal. The temperature detector 46 is, for example, a thermo-cut or other heat-sensitive element, and is provided in contact with the heat equalizing member 38. In detail, the temperature detector 46 is attached to the top surface of the fitting portion 35A of the holding member 35, and the lower part of the temperature detector 46 is in contact with the upper surface of the heat equalizing member 38 (see also FIG. 2). The temperature detector 46 is in contact with the heat equalizing member 38 slightly rearward of the axial center (see FIG. 5).

Here, if the heat equalizing member 38 is formed to the same width in the axial direction (width that suppresses excessive temperature rise in the non-passing area A2), when the fixing process is performed continuously, heat is taken by the continuously passing paper P (toner image), and there is a risk that the temperature of the central area in the axial direction of the heater 33 will drop too much. As a result, the temperature of the passing area A1 of the fixing belt 31 will also drop, and there is a risk that the toner on the paper P cannot be properly thermally fixed. In addition, there is a problem that a lot of power is required and it takes time to heat the heat equalizing member 38 formed to the same width uniformly in the axial direction. Therefore, in the fixing device 20 according to the first embodiment, the heat equalizing member 38 is formed to have a higher heat capacity in the end area corresponding to the non-passing area A2 than in the central area corresponding to the passing area A1.

Specifically, as shown in FIG. 5, the heat equalizing member 38 is formed so as to become wider in the direction in which the paper P passes (left-right direction) from the central region in the axial direction toward the end regions on both sides in the axial direction. The heat equalizing member 38 gradually becomes wider in the passing direction from the center in the axial direction toward both sides, and is shaped so as to be constricted at the center in the axial direction when viewed from above. The contours of the left and right edges of the heat equalizing member 38 are formed in arcs that are recessed toward the center in the left-right direction. The width (left-right dimension) of the narrowest part in the center of the axial direction of the heat equalizing member 38 is set in the range of about 2 mm to 7 mm, and the width (left-right dimension) of the widest part at both ends of the axial direction of the heat equalizing member 38 is set in the range of about 3 mm to 8 mm. The difference between the narrowest part and the widest part is set to about 1 mm. The heat equalizing member 38 has the same thickness along the axial direction. The thickness of the heat equalizing member 38 is about 0.25 mm. Note that the width and thickness of the heat equalizing member 38 described above are merely examples and may be changed as appropriate.

According to the fixing device 20 according to the first embodiment described above, the wider the heat equalizing member 38, the larger the heat capacity, so that the heat of the end region of the heater 33 can be actively absorbed by the heat equalizing member 38. This makes it possible to suppress excessive temperature rise in the non-passing region A2 of the fixing belt 31, and to heat the fixing belt 31 uniformly along the axial direction. In addition, the narrower the heat equalizing member 38, the smaller the heat capacity, so that the heat equalizing member 38 is prevented from absorbing too much heat in the central region of the heater 33. This makes it possible to suppress the temperature of the passing region A1 of the fixing belt 31 from dropping too much. As a result, it is possible to ensure proper thermal fixing in the passing region A1 while suppressing excessive heating in the non-passing region A2. Furthermore, since the heat equalizing member 38 has a shape that is narrowed in the center in the axial direction, the heat equalizing member 38 can be heated uniformly in the axial direction with less energy (power) and in a short time, compared to a member formed with the same width (wide width) in the axial direction.

In the fixing device 20 according to the first embodiment, the heat equalizing member 38 is formed so as to gradually widen in the passing direction from the center in the axial direction to both sides, but the present invention is not limited to this. For example, as shown in FIG. 6, the central region of the heat equalizing member 38 may be formed with a first width in the axial direction, and the end regions of the heat equalizing member 38 may be formed with a second width wider than the first width in the axial direction, so that a step is formed between the central region and the end regions when viewed from above.

[Second embodiment: fixing device]
Next, the fixing device 21 (heat equalizing member 39) according to the second embodiment will be described with reference to Fig. 7. Fig. 7 is a side view showing a schematic diagram of the heater 33 of the fixing device 21 according to the second embodiment. In the following description, the same or corresponding components as those of the fixing device 20 according to the first embodiment are denoted by the same reference numerals, and description of the same or corresponding components will be omitted.

In the fixing device 21 according to the second embodiment, the heat equalizing member 39 is formed so that the thickness increases from the central region in the axial direction toward the end regions on both sides in the axial direction. The heat equalizing member 39 gradually becomes thicker from the center in the axial direction toward both sides, and is recessed in the central part in the axial direction when viewed from the side. The upper surface of the heat equalizing member 39 is formed in a curved shape with the central part in the axial direction recessed. The thickness (thinnest part) of the heat equalizing member 39 at the center in the axial direction is about 0.1 mm, and the thickness (thickest part) of both ends in the axial direction of the heat equalizing member 38 is about 0.5 mm (the difference between the thinnest part and the thickest part is about 0.4 mm). The heat equalizing member 39 has the same width (horizontal dimension) along the axial direction. The horizontal width of the heat equalizing member 39 is about 5 mm. The width and thickness of the heat equalizing member 39 described above are merely examples and may be changed as appropriate.

According to the fixing device 21 of the second embodiment described above, the thicker the heat-equalizing member 39, the greater the thermal capacity, so that the heat in the end regions of the heater 33 can be actively absorbed by the heat-equalizing member 38. Also, the thinner the heat-equalizing member 39, the smaller the thermal capacity, so that the heat-equalizing member 39 is prevented from absorbing too much heat in the central region of the heater 33. In this way, the fixing device 21 can obtain the same effects as the fixing device 20 of the first embodiment, such as preventing excessive heating in the non-passage region A2 while ensuring proper thermal fixing in the pass-through region A1.

In the fixing device 21 according to the second embodiment, the heat equalizing member 39 is formed so that it gradually becomes thicker from the center toward both sides in the axial direction, but the present invention is not limited to this. For example, as shown in FIG. 8, the central region of the heat equalizing member 38 may be formed with a first thickness along the axial direction, and the end regions of the heat equalizing member 38 may be formed with a second thickness along the axial direction that is thicker than the first thickness, and a step may be formed between the central region and the end regions when viewed from the side.

Furthermore, the features of the heat equalizing member 39 of the fixing device 21 according to the second embodiment may be combined with the heat equalizing member 38 of the fixing device 21 according to the first embodiment. That is, the heat equalizing member may be formed so as to be wider and thicker in the direction in which the paper P passes (left-right direction) from the central region in the axial direction toward the end regions on both sides in the axial direction (not shown).

[Third embodiment: fixing device]
Next, the fixing device 22 (heat equalizing member 38) according to the third embodiment will be described with reference to Fig. 9. Fig. 9 is a plan view showing a schematic diagram of the heater 33 of the fixing device 22 according to the third embodiment.

Some temperature detection units 46 have a heat capacity per unit volume that is approximately equal to that of the heat equalizing member 38. In this case, the temperature detection unit 46 in contact with the heat equalizing member 38 may take heat from the heat equalizing member 38. As a result, the part with which the temperature detection unit 46 is in contact (contact part) becomes lower in temperature than the part with which the temperature detection unit 46 is not in contact (non-contact part), and the temperature of the heat equalizing member 38 becomes non-uniform along the axial direction. This can lead to the temperature of the fixing belt 31 (pressure region N) also becoming non-uniform, which can cause a problem in that proper thermal fixing cannot be performed.

To address this problem, in the fixing device 22 according to the third embodiment, the contact portion of the temperature detection unit 46 on the heat equalizing member 38 is narrower in the direction in which the paper P passes than the non-contact portion of the temperature detection unit 46. In other words, the heat capacity of the portion of the heat equalizing member 38 that the temperature detection unit 46 contacts is reduced by the heat capacity of the temperature detection unit 46. Specifically, at the contact position of the temperature detection unit 46, the heat equalizing member 38 has a pair of recesses 47 recessed toward the center from both left and right sides. Each recess 47 is a cutout that is approximately rectangular (or may be U-shaped) when viewed from above, and the lower surface of the temperature detection unit 46 contacts the portion remaining between the pair of recesses 47.

According to the fixing device 22 of the third embodiment described above, it is possible to suppress a decrease in temperature of the contact portion (between the pair of recesses 47) of the heat equalizing member 38 with the temperature detection unit 46, and to make the temperature of the heat equalizing member 38 (fixing belt 31) uniform along the axial direction. This allows the toner image on the paper P to be properly thermally fixed.

[Fourth embodiment: fixing device]
Next, the fixing device 23 (heat equalizing member 38) according to the fourth embodiment will be described with reference to Fig. 10. Fig. 10 is a cross-sectional view that typically illustrates the heater 33 of the fixing device 23 according to the fourth embodiment.

In the fixing device 23 according to the fourth embodiment, in order to obtain the same effect as the fixing device 22 according to the third embodiment, the contact portion of the temperature detection unit 46 on the heat equalizing member 38 is formed thinner than the non-contact portion of the temperature detection unit 46. Specifically, at the contact position of the temperature detection unit 46, the heat equalizing member 38 has a bottomed hole 48 recessed downward from the top surface. The bottomed hole 48 is a depression that is approximately rectangular (or may be circular) when viewed from above, and the temperature detection unit 46 contacts the bottom surface of the bottomed hole 48.

According to the fixing device 23 of the fourth embodiment described above, it is possible to suppress a temperature drop in the contact portion of the heat equalizing member 38 with the temperature detection unit 46, and to make the temperature of the heat equalizing member 38 (fixing belt 31) uniform along the axial direction. This allows the toner image on the paper P to be properly thermally fixed.

In the fixing devices 22 and 23 according to the third and fourth embodiments, the pair of recesses 47 and the bottomed hole 48 are formed in the heat equalizing member 38 of the fixing device 20 according to the first embodiment, but the present invention is not limited to this. The pair of recesses 47 and the bottomed hole 48 may be formed in the heat equalizing member 39 of the fixing device 21 according to the second embodiment (not shown).

The features (recess 47 and bottomed hole 48) of the heat equalizing member 38 (39) of the fixing device 22, 23 according to the third and fourth embodiments may be combined. That is, the contact portion of the heat equalizing member 38 with the temperature detection unit 46 may be narrower and thinner in the direction in which the paper P passes than the non-contact portion of the temperature detection unit 46 (not shown).

In the fixing devices 20-23 according to the first to fourth embodiments, the heat generating section 37 is divided into five divided heat generating sections 41-45 to correspond to three different sizes of paper P, but the present invention is not limited to this. The heat generating section 37 may be divided into three divided heat generating sections to correspond to two or more different sizes of paper P, or it may not be divided (neither is shown).

In addition, in the fixing devices 20 to 23 according to the first to fourth embodiments, the heat generating section 37 (each of the divided heat generating sections 41 to 45) is composed of a plurality of resistive heat generating elements 40, but the present invention is not limited to this. For example, the heat generating section 37 may be a single resistive heat generating element extending from one side to the other in the axial direction, or may be a U-shaped resistive heat generating element that extends from one side to the other in the axial direction and then folds back to extend from the other side to one side in the axial direction (neither is shown).

In addition, in the fixing devices 20-23 according to the first to fourth embodiments, the paper P passes through the center of the pressure area N in the axial direction, but this is not limited, and the paper P may pass through a position closer to one side of the pressure area N in the axial direction. In this case, the non-passing area A2 is set only on one side of the axial direction of the fixing belt 31 (or the pressure area N). The heat equalizing members 38, 39 are formed so that they become wider (thicker) in the passing direction from the central area toward one side in the axial direction (one end area) (not shown).

In addition, in the fixing devices 20 to 23 according to the first to fourth embodiments, the pressure roller 32 is driven to rotate and the fixing belt 31 is rotated accordingly, but this is not limited to the above, and the fixing belt 31 may be driven to rotate and the pressure roller 32 may be rotated accordingly. In addition, the pressure roller 32 is raised and lowered (moved in a direction approaching or moving away from) the fixing belt 31, but this is not limited to the above, and the fixing belt 31 may be moved in a direction approaching or moving away from the pressure roller 32 (not shown).

In addition, in the description of this embodiment, the present invention has been applied to a monochrome printer 1 as an example, but the present invention is not limited to this and may be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device.

The above embodiment is merely an example of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above embodiment. The present invention may be modified, substituted, or altered in various ways without departing from the spirit of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept.

1. Printer (image forming device)
20, 21, 22, 23 Fixing device 31 Fixing belt 32 Pressure roller 33 Heater 36 Substrate 37 Heat generating section 38, 39 Heat equalizing member 46 Temperature detection section A1 Passing area A2 Non-passing area N Pressure area P Paper (medium)

Claims (6)

a fixing belt formed in a cylindrical shape and rotating about an axis to heat the toner on the medium;
a pressure roller that rotates around an axis to form a pressure area between the pressure roller and the fixing belt and pressurizes the toner on the medium passing through the pressure area;
a heater that contacts an inner surface of the fixing belt facing the pressure region and heats the fixing belt,
The fixing belt has a passing region in the center in the axial direction, which contacts the medium, and a non-passing region on either or both sides in the axial direction, which does not contact the medium;
The heater is
a substrate extending in an axial direction corresponding to the fixing belt;
a heat generating portion provided on one surface of the substrate and generating heat when energized;
a heat equalizing member provided on the other surface of the substrate, absorbing heat generated from the heat generating portion and transferring the heat in the axial direction;
2. The fixing device according to claim 1, wherein the heat equalizing member is formed so as to have a larger heat capacity in an end region corresponding to the non-passage region than in a central region corresponding to the passage region. The fixing device according to claim 1, characterized in that the heat equalizing member is formed so as to become wider in the direction in which the medium passes from the central region toward the end region. The fixing device according to claim 1 or 2, characterized in that the heat equalizing member is formed so that its thickness increases from the central region toward the end regions. The heater further includes a temperature detector that is provided in contact with the uniform temperature member and detects a temperature of the heater.
The fixing device according to claim 1 , wherein the contact portion of the temperature equalizing member is formed to be narrower in a passing direction of the medium than the non-contact portion of the temperature equalizing member. The heater further includes a temperature detector that is provided in contact with the uniform temperature member and detects a temperature of the heater.
5. The fixing device according to claim 1, wherein the contact portion of the temperature equalizing member with the temperature detection portion is thinner than the non-contact portion of the temperature detection portion. An image forming apparatus comprising the fixing device according to claim 1.

Images