JP7122173B2 - Heater, fixing device and image forming device - Google Patents

Description

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

An electrophotographic image forming apparatus includes a fixing device that thermally fixes toner on a medium.

For example, the heater of the fixing device described in Japanese Patent Application Laid-Open No. 2002-200000 includes a substrate that is long in a direction orthogonal to the conveying direction of the recording material, a resistance heating element that is formed on the substrate in a pattern that is long in the longitudinal direction of the substrate, and a resistance heating element. It has a first conductor portion and a second conductor portion formed over the longitudinal direction at both ends in the short direction of the body. The resistance heating element generates heat when a current flows in the recording material conveying direction between the first conductor and the second conductor. The first conductor portion has a plurality of divided conductors divided in the longitudinal direction. In the fixing device, electric power is supplied independently to each resistance heating element corresponding to the divided conductor, thereby suppressing the temperature rise in the non-paper passing area through which the recording material does not pass.

Japanese Patent No. 5241144

In the heater described above, the plurality of divided conductors and the plurality of resistance heating elements corresponding thereto are formed to have different lengths and are elongated in the longitudinal direction. This resistance heating element (energization heating resistance layer) was a thin film formed by screen printing or the like. Such a thin film tends to have non-uniform density and the like, resulting in uneven electrical resistance. In the case of a resistance heating element that is elongated in the longitudinal direction and unevenness of electric resistance is distributed in the longitudinal direction, there is a problem that the resistance heating element cannot generate heat uniformly.

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a heater, a fixing device, and an image forming apparatus that can uniformly generate heat from a resistance heating element.

In order to achieve the above-described object, the heater of the present invention includes a substrate, a plurality of heat generating portions arranged on one surface of the substrate in a first direction, and formed on one surface of the substrate, each and a plurality of electrode portions electrically connected to both sides of the heat generating portion in a second direction orthogonal to the first direction, each of the heat generating portions including a plurality of resistors arranged in the first direction. Each of the resistive heating elements has a dimension ratio of 1 or more and 100 or less of the dimension in the second direction to the dimension in the first direction.

In this case, the plurality of resistance heating elements preferably have the same size in the second direction.

In this case, the plurality of electrode portions include a common electrode commonly connected to the plurality of heat generating portions and a plurality of individual electrodes connected to each of the heat generating portions, and the common electrode and each Each of the individual electrodes has a lead portion extending from a portion connected to the heat generating portion to a position outside the heat generating portion in the first direction, and the length of the lead portion of the common electrode is is shorter than the length of the lead portion of the individual electrode.

In this case, the common electrode and each of the individual electrodes each have an electrode terminal portion at the tip of the lead portion, and the length of the electrode terminal portion of the common electrode in the first direction is It is preferable that the electrode end portion of the individual electrode is longer than the length in the first direction.

In order to achieve the above object, a fixing device of the present invention provides a fixing member that heats toner on a medium while rotating around its axis, and a pressure area formed between the fixing member while rotating around its axis. a pressure member that presses the toner on the medium passing through the pressure region; and a heater that is provided in correspondence with the pressure region across the fixing member and heats the fixing member. The heater includes a substrate, a plurality of heat generating portions arranged on one surface of the substrate in the axial direction of the fixing member, and the heat generating portions formed on the one surface of the substrate. and a plurality of electrode portions electrically connected to both sides in a passage direction orthogonal to the axial direction, each of the heat generating portions being composed of a plurality of resistance heating elements arranged in the axial direction, and each The resistance heating element has a dimension ratio of the dimension in the passing direction to the dimension in the axial direction of 1 or more and 100 or less.

In this case, it is preferable that each of the plurality of resistance heating elements has the same dimension in the passing direction.

In this case, the plurality of electrode portions include a common electrode commonly connected to the plurality of heat generating portions and a plurality of individual electrodes connected to each of the heat generating portions, and the common electrode and each Each of the individual electrodes has a lead portion extending from a portion connected to the heat generating portion to a position outside the heat generating portion in the axial direction, and the length of the lead portion of the common electrode is It is preferably shorter than the length of the lead portion of the individual electrode.

In this case, the common electrode and each of the individual electrodes each have an electrode terminal portion at the tip of the lead portion, and the length of the electrode terminal portion of the common electrode in the axial direction is It is preferably longer than the axial length of the electrode end portion of the individual electrode.

In this case, each of the electrode portions has an electrode terminal portion at a distal end portion extending from a portion connected to the heat generating portion to a position outside the heat generating portion in the axial direction, and the plurality of resistance heating elements It is preferable that the dimensional ratio is set so as to increase gradually or stepwise as the distance from the electrode terminal portion increases.

In other cases, it is preferred that the resistive heating element corresponding to the axial end of the medium passing through the pressurized region has a larger dimensional ratio than the other resistive heating elements.

In order to achieve the object described above, an image forming apparatus of the present invention includes any one of the fixing devices described above.

According to the present invention, the resistance heating element of the heater can be uniformly heated.

1 is a schematic diagram (front view) showing a printer according to an embodiment of the present invention; FIG. 1 is a cross-sectional view schematically showing a fixing device according to an embodiment of the invention; FIG. It is a bottom view which shows typically the heater which concerns on one Embodiment of this invention. FIG. 4 is a sectional view along IV-IV in FIG. 3; It is a bottom view showing typically a part of heater concerning one embodiment of the present invention. It is a bottom view showing typically the heater concerning the 1st modification of one embodiment of the present invention. It is a bottom view showing typically the heater concerning the 2nd modification of one embodiment of the present invention. It is a bottom view showing typically the heater concerning the 3rd modification of one embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each figure, "Fr" indicates "front", "Rr" indicates "rear", "L" indicates "left", "R" indicates "right", and "U" indicates "Upper" is indicated and "D" indicates "Lower".

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

The printer 1 includes a device main body 2 having a substantially rectangular parallelepiped appearance. A paper feed cassette 3 for storing sheets S (medium) such as plain paper is provided in the lower portion of the apparatus main body 2 . A discharge tray 4 is provided on the upper surface of the apparatus main body 2 . Note that the sheet S is not limited to being made of paper, and may be made of resin or the like.

The printer 1 also includes a paper feeder 5 , an image forming device 6 , and a fixing device 7 . The paper feeder 5 is provided at the upstream end of the transport path 8 extending from the paper feed cassette 3 to the paper discharge tray 4 . The image forming device 6 is provided in the middle portion of the transport path 8 , and the fixing device 7 is provided downstream of the transport path 8 .

The image forming device 6 includes 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 includes a photosensitive drum 13 , a charging device 14 , a developing device 15 and a transfer roller 16 . The transfer roller 16 contacts the photosensitive drum 13 from below to form a transfer nip. The toner may be a two-component developer in which toner and carrier are mixed, or may be a one-component developer composed of magnetic toner.

A control device (not shown) of the printer 1 appropriately controls each device and executes image forming processing as follows. The charging device 14 charges the surface of the photosensitive drum 13 . The photosensitive drum 13 receives scanning light emitted from the optical scanning device 12 and carries an electrostatic latent image. The developing device 15 uses the toner supplied from the toner container 10 to develop the electrostatic latent image on the photosensitive drum 13 into a toner image. The sheet S is fed from the sheet feeding cassette 3 to the conveying path 8 by the sheet feeding device 5, and the toner image on the photosensitive drum 13 is transferred onto the sheet S passing through the transfer nip. The fixing device 7 fixes the toner image on the sheet S. As shown in FIG. After that, the sheet S is ejected onto the paper ejection tray 4 .

[Fixing device]
Next, the fixing device 7 will be described with reference to FIGS. 2 to 5. FIG. FIG. 2 is a sectional view schematically showing the fixing device 7. As shown in FIG. FIG. 3 is a bottom view schematically showing the heater 23. FIG. FIG. 4 is a sectional view taken along line IV-IV of FIG. FIG. 5 is a bottom view schematically showing part of the heater 23. As shown in FIG.

As shown in FIG. 2, the fixing device 7 includes a fixing belt 21, a pressure roller 22, and a heater . The fixing belt 21 and the pressure roller 22 are provided inside the housing 20 (see FIG. 1). A heater 23 is a heat source for heating the fixing belt 21 .

<Fixing belt>
The fixing belt 21, which is an example of a fixing member, is an endless belt and is formed in a substantially cylindrical shape elongated in the front-rear direction (axial direction). The surface layer of the fixing belt 21 is made of, for example, a heat-resistant and elastic synthetic resin material such as polyimide resin. The fixing belt 21 is arranged inside and above the housing 20 . A pair of substantially cylindrical caps (not shown) are attached to both ends of the fixing belt 21 in the axial direction. A belt guide (not shown) may be provided inside the fixing belt 21 to hold the substantially cylindrical shape of the fixing belt 21 .

A pressing member 24 is provided inside the fixing belt 21 . The pressing member 24 is made of, for example, a metal material and is formed into a substantially square tubular shape elongated in the axial direction. The pressing member 24 axially passes through the fixing belt 21 (and the cap) and is supported by the housing 20 . The fixing belt 21 described above is rotatably supported with respect to the pressing member 24 .

<Pressure roller>
The pressure roller 22, which is an example of a pressure member, is formed in a substantially cylindrical shape elongated in the front-rear direction (axial direction). The pressure roller 22 is arranged inside and below the housing 20 . The pressure roller 22 includes a metal core 22A and an elastic layer 22B such as silicone sponge laminated on the outer peripheral surface thereof. Both ends of the cored bar 22A in the axial direction are rotatably supported by the housing 20 . A drive motor (not shown) is connected to the core bar 22A via a gear train or the like, and the pressure roller 22 is rotationally driven by the drive motor. The fixing device 7 includes a pressure adjusting section (not shown) that moves the pressure roller 22 up and down to adjust the contact pressure of the pressure roller 22 against the fixing belt 21 . A pressure area N is formed between the fixing belt 21 and the pressure roller 22 by pressing the pressure roller 22 against the fixing belt 21 . The pressurized region N is a range from a position on the upstream side of the sheet S where the pressure is 0 Pa to a position on the downstream side of the sheet S where the pressure is 0 Pa again via a position where the maximum pressure is applied. pointing to the area.

<Heater>
A heater 23 as an example of a heater is formed in a substantially rectangular plate shape elongated in the front-rear direction (axial direction). (See FIG. 3) The heater 23 is fixed to the lower surface of the pressing member 24 via the holding member 25 . The holding member 25 is made of, for example, a heat-resistant resin material and has a substantially semi-cylindrical shape elongated in the axial direction. The holding member 25 is curved along the lower inner surface of the fixing belt 21 .

As shown in FIGS. 3 and 4, the heater 23 includes a substrate 30, a heat insulating layer 31, and a heat generating contact portion 32. As shown in FIGS. The base material 30 is fixed to the lower surface of the holding member 25 . The heat insulating layer 31 is formed on the lower surface of the base material 30 and forms a substrate together with the base material 30 . The heat generating contact portion 32 is formed on the lower surface of the heat insulating layer 31 . In this specification, the “passing direction (second direction)” is a direction orthogonal to the axial direction (first direction), and is the direction in which the sheet S passes through the pressure area N of the fixing device 7 ( direction). Also, in the following description, the terms "upstream" and "downstream" and like terms refer to the concept of "upstream" and "downstream" and like terms in the direction of passage.

As shown in FIG. 4 , the heater 23 is held on the lower surface of the holding member 25 with the heat-generating contact portion 32 facing the pressure roller 22 , and the heat-generating contact portion 32 contacts the inner surface of the fixing belt 21 . The heater 23 receives the fixing belt 21 pressed against the pressure roller 22 , so that the pressure area N is formed in the contact portion between the fixing belt 21 and the pressure roller 22 . The heater 23 is provided corresponding to the pressurized area N across the fixing belt 21 (see also FIG. 2), and has a function of heating the fixing belt 21 . The housing 20 is provided with a temperature sensor (not shown) for detecting the surface temperature of the fixing belt 21 or the temperature of the heater 23 .

As shown in FIGS. 3 and 4, the base material 30 is made of an electrically insulating material such as ceramic and is formed into a substantially rectangular plate shape elongated in the axial direction. Both upper and lower surfaces of the base material 30 are formed substantially smooth.

The heat insulating layer 31 is laminated (film-formed) on one surface (entire lower surface) of the base material 30 . The heat insulating layer 31 is formed on the base material 30 with a material having electrical insulation and low thermal conductivity, such as ceramic (glass). The heat insulating layer 31 has a function of regulating the transfer of heat generated in the heat generating contact portion 32 to the base material 30 side.

The heat generating contact portion 32 is laminated on one surface (lower surface) of the heat insulating layer 31 . The heat generating contact portion 32 includes a plurality (eg, five) of heat generating portions 41 to 45, a plurality (eg, six) of electrode portions 51 to 56, and a coating layer 60. As shown in FIG.

The plurality of heat generating portions 41 to 45 are formed on the lower surface of the heat insulating layer 31 with a conductive material such as metal having a higher resistance value than the electrode portions 51 to 56, for example. As shown in FIG. 3, the plurality of heat generating portions 41 to 45 are arranged in a line in the axial direction. Also, each of the heating portions 41 to 45 is composed of a plurality of resistance heating elements 40 arranged in a row in the axial direction. Although the details will be described later, each of the plurality of resistance heating elements 40 is formed in a substantially rectangular shape elongated in the passage direction. All resistance heating elements 40 are formed to have approximately the same size.

The heat generating portion 41 arranged in the center in the axial direction is composed of a plurality of resistance heating elements 40 arranged in a range corresponding to the front-to-rear width of a small size (for example, A5 size) sheet S passing through the pressure area N. there is The two heat generating portions 42 and 43 arranged on both sides in the axial direction of the heat generating portion 41 are arranged in a range corresponding to the front-to-rear width of a medium-sized (for example, B5 size) sheet S passing through the pressure area N. It is composed of a resistance heating element 40 . The two heat generating portions 44 and 45 arranged on both sides in the axial direction of the heat generating portions 42 and 43 are arranged in a range corresponding to the front-to-rear width of a normal size (for example, A4 size) sheet S passing through the pressure area N. It is composed of a plurality of resistance heating elements 40 .

The plurality of resistance heating elements 40 are formed to have the same size in the axial direction and the same size in the passing direction. In this specification, the term "same size" does not require that the size be exactly the same, but means that a slight manufacturing error is allowed.

As shown in FIG. 5, in this heater 23, for example, the dimension (W) in the axial direction (front-rear direction) of the resistance heating element 40 (hereinafter also referred to as "width (W)") is set to about 5 mm. The dimension (L) (hereinafter also referred to as “length (L)”) in the passing direction (horizontal direction) is set to about 20 mm. Thus, the length (L) of the resistance heating element 40 is set to be equal to or greater than the width (W) of the resistance heating element 40 . Also, in this resistance heating element 40, the dimension ratio (L/W) of the length (L) to the width (W) is set to "4".

As shown in FIG. 3, the plurality of electrode portions 51 to 56 are formed on the lower surface of the heat insulating layer 31 with a conductive material (having a lower resistance value than the resistance heating element 40) such as metal. . A plurality of electrode portions 51 to 56 are electrically connected to both sides of each heat generating portion 41 to 45 in the passing direction. Specifically, the plurality of electrode portions 51 to 56 includes a common electrode 56 commonly connected to the plurality of heat generating portions 41 to 45, and a plurality (eg, five) of electrodes connected to each of the heat generating portions 41 to 45. and individual electrodes 51-55. The individual electrode 51 is connected to the downstream end portion (right end portion) of each resistance heating element 40 that constitutes the heating portion 41 in the center in the axial direction. Similarly, the other individual electrodes 52-55 are connected to the downstream ends of the respective resistance heating elements 40 constituting the heating portions 42-45, respectively. On the other hand, the common electrode 56 is connected to the upstream ends (left ends) of all the resistance heating elements 40 . Incidentally, in this specification, in the description common to the individual electrodes 51 to 55 and the common electrode 56, they are simply referred to as "electrode portions 51 to 56".

Each of the electrode portions 51 to 56 has a leading end portion of a lead portion 51B to 56B extending from a portion (connection portion 51C to 56C) connected to the heat generating portions 41 to 45 to a position axially outside the heat generating portions 41 to 45. It has electrode terminal portions 51A to 56A connected to . The lead portions 51B to 56B are portions drawn from the portions connected to the heat generating portions 41 to 45, and are formed between the axial outer ends of the heat generating portions 41 to 45 and the electrode terminal portion 56A. Since the electrode terminal portions 51A to 56A are connection terminals for electrically connecting to an external device such as a power supply, they are drawn out axially outside the heat generating portions 41 to 45 by the lead portions 51B to 56B. Specifically, the lead portion 51B of the individual electrode 51 extends axially on both sides from the connection portion 51C with the heat generating portion 41 . The pair of electrode terminal portions 51A are connected to both ends of the pair of lead portions 51B and are bent upstream (to the left). The lead portions 52B and 54B of the individual electrodes 52 and 54 and the lead portions 53B and 55B of the individual electrodes 53 and 55 extend axially outward away from the connection portions 52C to 55C with the heat generating portions 42 to 45. . The electrode terminal portions 52A to 55A are connected to the tip portions of the lead portions 52B to 55B and bent upstream. The electrode terminal portions 52A and 53A are arranged axially inside the pair of electrode terminal portions 51A, and the electrode terminal portions 54A and 55A are arranged axially inside the electrode terminal portions 52A and 53A. On the other hand, the lead portion 56B of the common electrode 56 extends axially on both sides from the connection portion 56C with the heat generating portions 41-45. The pair of electrode terminal portions 56A are connected to both ends of the lead portion 56B and bent downstream (to the right). The pair of electrode terminal portions 56A are arranged axially inside the electrode terminal portions 54A and 55A.

The length of the lead portion 56B of the common electrode 56 is set shorter than the length of the lead portions 51B-55B of the individual electrodes 51-55. Here, the length of the lead portions 51B to 56B is the distance H from the boundary with the portions (connecting portions 51C to 56C) connected to the heat generating portions 41 to 45 to the electrode terminal portions 51A to 56A (see FIG. 3). ). That is, the lead portions 51B to 56B connect the connection portions 51C to 56C with the heat generating portions 41 to 45 and the electrode terminal portions 51A to 56A. The length means the length in the axial direction of the lead portions 51B to 56B. The axial length (width) of the electrode terminal portion 56A of the common electrode 56 is set longer than the axial length (width) of the electrode terminal portions 51A to 55A of the individual electrodes 51 to 55. there is

As shown in FIG. 4, the coat layer 60 covers the heat generating portions 41 to 45 and the electrode portions 51 to 56 (excluding the electrode terminal portions 51A to 56A). The coat layer 60 is made of a material such as ceramic that has electrical insulation and a small sliding frictional force with respect to the fixing belt 21 . The coat layer 60 forms a surface that contacts the inner surface of the fixing belt 21 . A material having electrical insulation such as the heat insulation layer 31 and the coat layer 60 is laminated on portions where the heat generating portions 41 to 45 and the electrode portions 51 to 56 are not laminated.

For manufacturing the heater 23 described above, for example, a film forming technique such as sputtering, a printed circuit board manufacturing technique, a screen printing technique, or a combination of these techniques can be used. For example, the heat-insulating layer 31 and the heat-generating contact portion 32 (heat-generating portions 41-45, electrode portions 51-56, coating layer 60) may be formed on the substrate 30 by sputtering. Further, for example, the heat insulating layer 31 and the heat-generating contact portion 32 are formed on the base material 30 by repeating processes such as exposure, development, etching, peeling, lamination, etc. using a photomask, which is a manufacturing technology for printed circuit boards. good too. Further, for example, the heat insulating layer 31 and the heat generating contact portion 32 may be formed by applying (screen printing) an electrically insulating paint or a conductive paint onto the base material 30 . With these manufacturing methods, the heat insulating layer 31, the heat generating portions 41 to 45, and the electrode portions 51 to 56 can be formed with high accuracy.

The electrodes 51 to 56 of the heater 23, the drive motor, etc. are electrically connected to a power source (not shown) through various drive circuits (not shown). Also, the heater 23 (electrode portions 51 to 56), drive motor, temperature sensor, etc. are electrically connected to the controller of the printer 1 through various circuits. The control device controls connected devices and the like.

[Function of Fixing Device]
Here, mainly referring to FIG. 2, the operation (fixing process) of the fixing device 7 will be described.

First, the control device drives and controls the drive motor and the heater 23 . The pressure roller 22 is rotated by receiving the driving force of the drive motor, and the fixing belt 21 is rotated following the pressure roller 22 (see solid line thin arrow in FIG. 2). Each resistance heating element 40 generates heat by causing current to flow in the passing direction between the plurality of electrode portions 51 to 56 sandwiching the heat generating portions 41 to 45 . Thereby, the pressure area N of the fixing belt 21 is heated.

At this time, the control device changes the heating units 41 to 45 (see FIG. 3) that generate heat according to the size of the sheet S. FIG. For example, when a normal size sheet S passes through the pressure area N, the control device supplies power to all the heat generating portions 41 to 45 to cause all the heat generating portions 41 to 45 to generate heat. Further, for example, the control device heats the heat generating portions 41 to 43 when a medium-sized sheet S passes through the pressure area N, and heats when a small-sized sheet S passes through the pressure area N. The part 41 is heated. Accordingly, it is possible to match the size of the sheet S and heat only the necessary portion of the fixing belt 21 (pressing area N). As a result, it is possible to suppress excessive temperature rise at both ends of the fixing belt 21 in the axial direction.

The temperature sensor detects the surface temperature of the fixing belt 21 and sends a detection signal to the control device through the input circuit. When the control device receives a detection signal from the temperature sensor indicating that the set temperature (for example, 150 to 200° C.) has been reached, the control device controls the heater 23 so as to maintain the set temperature while performing the image forming process already described. Start execution. The sheet S to which the toner image has been transferred enters the housing 20, and the fixing belt 21 heats the toner (toner image) on the sheet S passing through the pressure area N while rotating forward about its axis. The pressure roller 22 presses the toner on the sheet S passing through the pressure area N while rotating around its axis. Then, the toner image is fixed on the sheet S. Then, the sheet S on which the toner image has been fixed is delivered to the outside of the housing 20 and ejected onto the paper ejection tray 4 .

By the way, since the resistance heating element 40, which is a thin film, tends to have non-uniform density and the like, the electric resistance tends to be uneven. If the resistance heating element 40 is long in the axial direction, the unevenness of the electric resistance will be distributed in the axial direction, and the current will flow in the direction in which it is easy to flow. For this reason, the resistance heating element 40 may not be able to generate heat uniformly. Therefore, in the fixing device 7 (heater 23) according to the present embodiment, the length (L) of the resistance heating element 40 is made equal to or greater than the width (W) of the resistance heating element 40, and the heating efficiency (η) of the resistance heating element 40 is set to are improving.

Here, the heat generation efficiency (η) can be obtained by Equation 1 below.

[Number 1]
η = ((C x T) + G) / (P x t) x 100
C: Heat capacity of resistance heating element [J/K]
T: Temperature rising in 1 second [K]
G: Heat dissipation amount [J]
P: Power supply [W]
t: power supply time [s]

For example, the width (W) of the resistance heating element 40 is fixed at 3 mm, and the length (L) of the resistance heating element 40 is changed to 3 mm, 4 mm, and 5 mm (dimension ratio (L/W)=1.67). When the heat generation efficiency (η) was measured, it was as follows.
(1) Length (L) of resistance heating element 40 = 3 mm
Dimension ratio (L/W) = 1.00, heat generation efficiency (η) = 94%
(2) Length (L) of resistance heating element 40 = 4 mm
Dimension ratio (L/W) = 1.33, heat generation efficiency (η) = 97%
(3) Length (L) of resistance heating element 40 = 5 mm
Dimension ratio (L/W) = 1.67, heat generation efficiency (η) = 99%

As described above, it was confirmed that the heating efficiency (η) tends to increase as the dimensional ratio (L/W) of the resistance heating element 40 increases.

In the fixing device 7 (heater 23) according to this embodiment, the length (L) of the resistance heating element 40 is set to 20 mm, and the width (W) of the resistance heating element 40 is set to 5 mm. is not limited to The length (L) of the resistance heating element 40 can be set in the range of 3 mm or more and 20 mm or less in consideration of the ease of manufacture, the maximum length of the pressurized area N, and the like. The width (W) of the resistance heating element 40 can be set in the range of 0.2 mm or more and 5 mm or less in consideration of manufacturing easiness, dimension ratio (L/W), and the like. Each resistance heating element 40 may be formed so that the dimension ratio (L/W) of the dimension (L) in the passage direction to the dimension (W) in the axial direction is 1 or more and 100 or less.

In the fixing device 7 (heater 23) according to the present embodiment described above, the dimension (L) in the passing direction of the resistance heating element 40 is set to be equal to or larger than the dimension (W) in the axial direction. With this configuration, the extension of the width (W) of the resistance heating element 40 can be suppressed, so that the risk of uneven distribution of electric resistance in the axial direction of the resistance heating element 40 can be reduced. As a result, the electric current can be uniformly applied to the entire resistance heating element 40, so that the resistance heating element 40 can be uniformly heated. That is, heat generation efficiency (η) can be improved. In this specification, the term “uniform” does not require complete uniformity (equal), but means that an error of several degrees is allowed in the case of heat generation temperature, for example.

Further, according to the fixing device 7 of the present embodiment, all the resistance heating elements 40 are formed to have the same length (L) and the same width (W). The resistance value can be made constant. Thereby, the heating efficiency (η) of each resistance heating element 40 can be made constant. In the present specification, the term "constant" does not mean that there is no change, but means that an error of several percent is allowed in the heat generation efficiency (η), for example.

Further, according to the fixing device 7 (heater 23) according to the present embodiment, since the lead portion 56B of the common electrode 56 is shorter than the lengths of the other lead portions 51B to 55B, the electric resistance of the common electrode 56 can be reduced. It can be made small, and power loss can be suppressed.

By the way, the electrode terminal portions 51A to 56A are arranged on both sides in the axial direction of the heat generating portions 41 to 45, but due to the demand for miniaturization of the heater 23, etc., they are arranged in a limited range on the substrate 30. It has to be narrowed down. However, since a large current flows through the common electrode 56, there is a demand to suppress power loss due to electrical resistance. In this regard, according to the fixing device 7 (heater 23) according to the present embodiment, the width of the electrode terminal portion 56A of the common electrode 56 is wider than the widths of the other electrode terminal portions 51A to 55A. can be further reduced, and power loss can be effectively suppressed. Depending on the magnitude of the current flowing through the common electrode 56, the width of the electrode terminal portion 56A of the common electrode 56 may be the same as the widths of the other electrode terminal portions 51A to 55A.

[First modification]
In the circuits (the resistance heating element 40, the electrode portions 51 to 56, etc.) that constitute the heater 23 as described above, the effect of the voltage drop increases as the distance from the electrode terminal portions 51A to 56A increases. Therefore, it is necessary to adjust the resistance value of the resistance heating element 40 located away from the electrode terminal portions 51A to 56A. Therefore, as shown in FIG. 6, in the fixing device 7 (heater 23) according to the first modified example of the present embodiment, the dimensional ratio (L/W) of the plurality of resistance heating elements 40 is It is set to increase stepwise as the distance from . That is, all of the resistance heating elements 40 are formed to have the same length (L), and a plurality of resistance heating elements 40 (hereinafter referred to as a reference numeral to distinguish from the other resistance heating elements 40) constituting a part of the heating portion 41 40A and 40B) are shorter (narrower) in the axial direction than the other resistance heating elements 40 . In addition, the plurality of resistance heating elements 40A arranged near the center in the axial direction of the heating portion 41 are axially shorter (narrower) than the plurality of resistance heating elements 40B arranged on both axial sides of the resistance heating element 40A. formed. That is, the resistance heating elements 40, 40A, and 40B are formed to have the same length (L) and different widths (W). According to this configuration, the resistance values of the resistance heating elements 40A and 40B can be adjusted by relatively narrowing the axial dimension (W) of the resistance heating elements 40A and 40B apart from the electrode terminal portions 51A to 56A. can be easily done. In the above example, the dimensional ratio (L/W) of the plurality of resistance heating elements 40 is changed stepwise, but the dimensional ratio (L/W) of the plurality of resistance heating elements 40 is not limited to this. may be set so as to gradually increase with increasing distance from the electrode end portions 51A to 56A (not shown).

[Second modification]
Further, as shown in FIG. 7, in the fixing device 7 (heater 23) according to the second modification of the present embodiment, the resistance heating element 40 ( ) has a larger dimensional ratio (L/W) than the other resistance heating elements 40 . That is, the pair of resistance heating elements 40C forming both ends in the axial direction of each of the heat generating portions 41 to 45 is formed axially shorter (narrower) than the other resistance heating elements 40. As shown in FIG. According to this configuration, a plurality of resistance heating elements 40 (40C) can be arranged according to the width of the sheet S by making the resistance heating element 40C narrow in the axial direction correspond to the width direction end of the standard size sheet S. becomes easier. As a result, the axial dimensions of the heat-generating portions 41 to 45 can be accurately matched to the width of the sheet S, and excessive temperature rise or insufficient heating of the widthwise end portions of the sheet S can be suppressed.

Note that in the fixing device 7 according to the first and second modifications of the present embodiment, the length (L) of the resistance heating element 40 is fixed and the width (W) is changed so that the dimensional ratio of the resistance heating element 40 is Although (L/W) was changed, the present invention is not limited to this. For example, if the length (L) of the resistance heating element 40 is changed while the width (W) of the resistance heating element 40 is fixed, the dimensions of the resistance heating element 40 can be changed as long as the length of the pressure area N in the passage direction does not change significantly. The ratio (L/W) may vary.

According to the heater 23 according to the present embodiment (including the first and second modifications; the same applies hereinafter), the electrode portions 51 to 56 are connected to the heat generating portions 41 to 45 (connection portions 51C to 45). 56C) on both sides in the axial direction, the electrode portions 51 to 56 can be formed short, and the electrical resistance of the electrode portions 51 to 56 can be reduced.

[Third Modification]
If it is desired to reduce the size of the heater 23, as shown in FIG. It may be pulled out in one direction. That is, the electrode terminal portions 51A, 52A, 54A and 56A of the electrode portions 51, 52, 54 and 56 may be provided on one side. With this configuration, the connection between the electrode terminal portions 51A, 52A, 54A, and 56A and the external device such as the power supply can be consolidated at one point, so that the size of the heater 23 can be reduced. In this case, the heat-generating portions 41, 42, and 44 correspond to three sizes of sheets S. As shown in FIG. That is, when the normal size sheet S passes through the pressure area N (see FIG. 2), the control device supplies electric power to all the heat generating portions 41, 42, and 44, and all the heat generating portions 41, 42, and 44 generate heat. Further, for example, the control device causes the heat generating portions 41 and 42 to generate heat when a medium-sized sheet S passes through the pressure area N, and generates heat when a small-sized sheet S passes through the pressure area N. The part 41 is heated. Moreover, in this case, it is preferable that the electrode terminal portion 56A of the common electrode 56 is arranged near the heating resistor 40 in consideration of an increase in electrical resistance.

In addition, in the fixing device 7 according to the present embodiment, the heat generating portions 41 to 45 correspond to three types of sheet S sizes, but the present invention is not limited to this. The heating portion (resistance heating element 40) may be formed so as to correspond to two or more sizes of sheets S. As shown in FIG. Further, in the fixing device 7 according to the present embodiment, the sheet S is configured to pass through the center of the pressure region N in the axial direction. It may be configured such that the sheet S passes through the position. Further, in the fixing device 7 according to the present embodiment, an example in which the drawer portions 51B to 56B extend long in the axial direction has been shown, but the present invention is not limited to this. For example, the drawer portions 51B to 56B may have portions extending upstream (left side) or downstream (right side). The length of the lead portions 51B to 56B in this case means the length of the electrode portions 51 to 56 of the portions connecting the connection portions 51C to 56C and the electrode terminal portions 51A to 56A.

Further, in the fixing device 7 according to the present embodiment, the pressure roller 22 is rotationally driven and the fixing belt 21 is driven to rotate. It may be driven to rotate.

Further, in the fixing device 7 according to the present embodiment, the pressure roller 22 is raised and lowered (moved in a direction toward or away from the fixing belt 21), but the present invention is not limited to this. For example, the fixing belt 21 may be moved toward or away from the pressure roller 22 .

Further, in the description of the present embodiment, as an example, the case where the present invention is applied to the monochrome printer 1 has been shown, but the present invention is not limited to this, and can be applied to, for example, color printers, copiers, facsimile machines, multifunction machines, and the like. may apply.

It should be noted that the description of the above embodiment shows one aspect of the heater, the fixing device, and the image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above embodiment.

1 Printer (image forming device)
7 fixing device 21 fixing belt (fixing member)
22 pressure roller (pressure member)
23 heater (heater)
30 base material (substrate)
31 Thermal insulation layer (substrate)
40, 40A, 40B, 40C Resistance heating elements 41 to 45 Heat generating parts 51 to 55 Individual electrodes (electrode parts)
56 Common electrode (electrode part)
51A to 56A electrode end portion 51B to 56B lead portion 51C to 56C connection portion N pressure area S sheet (medium)

Claims (8)

a substrate;
a plurality of heat-generating parts arranged in a first direction on one surface of the substrate;
a plurality of electrode portions formed on one surface of the substrate and electrically connected to both sides of each of the heat generating portions in a second direction orthogonal to the first direction;
each of the heat generating units is composed of a plurality of resistance heating elements arranged in the first direction,
Each of the resistance heating elements has a dimension ratio of the dimension in the second direction to the dimension in the first direction of 1 or more and 100 or less ,
The plurality of electrode parts are
a common electrode connected in common to the plurality of heat generating parts;
and a plurality of individual electrodes connected to each of the heat generating portions,
each of the common electrode and each of the individual electrodes has a lead portion extending from a portion connected to the heat generating portion to a position outside the heat generating portion in the first direction;
the length of the lead portion of the common electrode is shorter than the length of the lead portion of each of the individual electrodes;
each of the common electrode and each of the individual electrodes has an electrode terminal portion at a tip portion of the lead portion;
A heater, wherein the length of the electrode end portion of the common electrode in the first direction is longer than the length of the electrode end portion of each of the individual electrodes in the first direction . 2. The heater according to claim 1, wherein each of said plurality of resistance heating elements has the same dimension in said second direction. a fixing member that heats the toner on the medium while rotating about its axis;
a pressure member that forms a pressure region between itself and the fixing member while rotating about an axis and presses the toner on the medium passing through the pressure region;
a heater provided corresponding to the pressurized area across the fixing member and heating the fixing member;
The heater is
a substrate;
a plurality of heat-generating portions arranged on one surface of the substrate in the axial direction of the fixing member;
a plurality of electrode portions formed on one surface of the substrate and electrically connected to both sides of each heat generating portion in a passing direction orthogonal to the axial direction;
each of the heat generating portions is composed of a plurality of resistance heating elements arranged in the axial direction;
Each of the resistance heating elements has a dimension ratio of the dimension in the passing direction to the dimension in the axial direction of 1 or more and 100 or less ,
The plurality of electrode parts are
a common electrode connected in common to the plurality of heat generating parts;
and a plurality of individual electrodes connected to each of the heat generating portions,
each of the common electrode and each of the individual electrodes has a lead portion extending from a portion connected to the heat generating portion to a position outside the heat generating portion in the axial direction;
the length of the lead portion of the common electrode is shorter than the length of the lead portion of each of the individual electrodes;
each of the common electrode and each of the individual electrodes has an electrode terminal portion at a tip portion of the lead portion;
The fixing device , wherein the axial length of the electrode terminal portion of the common electrode is longer than the axial length of the electrode terminal portion of each of the individual electrodes . 4. The resistive heating element according to claim 3 , wherein said resistive heating element corresponding to said axial end of said medium passing through said pressurized region has a larger dimension ratio than other said resistive heating elements. fuser. a fixing member that heats the toner on the medium while rotating about its axis;
a pressure member that forms a pressure region between itself and the fixing member while rotating about an axis and presses the toner on the medium passing through the pressure region;
a heater provided corresponding to the pressurized area across the fixing member and heating the fixing member;
The heater is
a substrate;
a plurality of heat-generating portions arranged on one surface of the substrate in the axial direction of the fixing member;
a plurality of electrode portions formed on one surface of the substrate and electrically connected to both sides of each heat generating portion in a passing direction orthogonal to the axial direction;
each of the heat generating portions is composed of a plurality of resistance heating elements arranged in the axial direction;
Each of the resistance heating elements has a dimension ratio of the dimension in the passing direction to the dimension in the axial direction of 1 or more and 100 or less,
The fixing device, wherein the resistance heating element corresponding to the axial end of the medium passing through the pressure area has a dimension ratio larger than that of the other resistance heating elements. 6. The fixing device according to claim 3 , wherein each of said plurality of resistance heating elements has the same dimension in said passing direction. each of the electrode portions has an electrode terminal portion at a distal end portion extending from a portion connected to the heat generating portion to a position outside the heat generating portion in the axial direction;
7. The dimensional ratio of the plurality of resistance heating elements according to any one of claims 3 to 6 , wherein the size ratio is set so as to increase gradually or stepwise as the distance from the electrode terminal portion increases. Fixing device. An image forming apparatus comprising the fixing device according to any one of claims 3 to 7 .

Images