JP2024124844A - Image heating device and image forming device - Google Patents

Abstract

To decrease a reduction in the temperature at the ends to prevent failure of image fixing, even if a recording material with the largest width is fed through heating means having a heating area divided in a width direction of the recording material.SOLUTION: An image heating device comprises: heating means that has a heating area generating heat upon energization divided in a width direction orthogonal to a conveyance direction of a recording material; and a pressure member that is arranged opposite to the heating means, and sandwiches the recording material between the heating means and the pressure member, and the image heating device heats an image formed on the recording material with heat of the heating means. Of the heating areas, the heating areas located at the outermost ends in the width direction of the recording material have a larger resistance value than that of the other heating area.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image heating device and an image forming apparatus that heat an image formed on a recording material.

In image forming devices such as electrophotographic devices and electrostatic recording devices, an unfixed toner image is formed on a sheet-like recording material, and the toner image is then fixed onto the recording material by applying heat and pressure using a fixing device.

One of the conventional fixing devices is one that uses a ceramic heater as a heating means. This fixing device has quick start (on-demand) properties, and employs an energy-saving fixing belt heating method that minimizes power supply to the fixing device and reduces power consumption when the image forming device is on standby. A fixing device using the fixing belt heating method forms a fixing nip section by interposing a fixing belt between a ceramic heater as a heating means and a pressure roller as a pressure member. In this fixing nip section, the fixing belt and the pressure roller sandwich and transport a recording material carrying an unfixed toner image, and the toner image is fixed to the recording material by heat and pressure.

However, in recent years, there has been a demand for the fixing devices of image forming apparatuses to be able to increase temperature even more rapidly in order to shorten the warm-up time and to be able to handle recording materials of various sizes. If the thermal capacity of the fixing heater is reduced to shorten the warm-up time, then a heating element with a length that matches the maximum width of the recording material alone will result in the temperature of the non-paper passing area, where the recording material does not pass, becoming too high compared to the paper passing area where the recording material does pass (hereinafter referred to as "edge temperature rise"). Furthermore, there is a limit to the temperature control possible with only a heating element with a length that matches the maximum width of the recording material used in the image forming apparatus (hereinafter referred to as "maximum recording material width") in order to handle recording materials of various sizes.

Therefore, Patent Document 1 discloses a technology for a split heater equipped with heat generating areas that can be independently controlled according to the recording material width. Patent Document 1 makes it possible to narrow the area that heats up in the non-paper passing area by heating the appropriate heat generating area according to the recording material, and further suppresses the rise in temperature at the edge. It can also accommodate recording materials of various sizes.

JP 2020-86078 A

However, with the split heaters disclosed in Patent Document 1, when a recording material close to the maximum recording material width is passed through, even if all split heaters are turned on, the temperature on the end side of the heating element of the split heater located at the very end (hereinafter referred to as the "endmost heating element") drops. This is because there are no split heaters on the end side of the endmost heating element, and the temperature on the end side is taken away by the recording material. Therefore, in this state, it is not possible to provide a sufficient amount of heat to the recording material, which may cause poor image fixing.

To prevent the temperature at the ends from dropping, the heater length can be increased and a ceramic heater larger than the maximum recording material width can be used to solve the problem, but extending the heater length would result in a bulkier fixing device and would raise concerns about the increased cost of the ceramic heater.

The object of the present invention is to provide an image heating device and an image forming device that can reduce poor image fixing without lowering the temperature at the ends, even when the maximum recording material width is passed through the split heater.

A representative configuration of the present invention for achieving the above object is an image heating device that includes a heating means in which a heat generating area that generates heat when current is applied is divided in a width direction perpendicular to the conveying direction of the recording material, and a pressure member that is disposed opposite the heating means and holds the recording material between the heating means and the pressure member, and heats an image formed on the recording material by the heat of the heating means, and is characterized in that the heat generating area located at the extreme end of the recording material in the width direction has a higher resistance value than the other heat generating areas.

According to the present invention, even if the widest recording material is passed through a heating means in which the heat generation area is divided in the width direction of the recording material, the temperature drop at the edge can be reduced and poor image fixing can be suppressed.

Schematic diagram of an image forming apparatus Schematic cross-sectional view of a fixing device Structural diagram of the fixing heater in the fixing device 1A and 1B are enlarged views of a main portion showing the shape of a fixing heater, and a table showing the relationship between the recording material and the heater temperature. FIG. 13 is a diagram showing the relationship between the amount of current supplied to each heating element when a recording material is passed through the fixing heater. Circuit diagram around the fixing heater

The following describes in detail the preferred embodiments of the present invention by way of example, with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments should be appropriately changed depending on the configuration and various conditions of the device to which the present invention is applied, and are not intended to limit the scope of the present invention to these alone.

(Image forming apparatus)
The image forming apparatus according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of the image forming apparatus according to this embodiment.

As shown in FIG. 1, the image forming apparatus 100 has four image forming stations as an image forming section that forms an image on a recording material. The first image forming station (y) forms an image of yellow, the second image forming station (m) forms an image of magenta, the third image forming station (c) forms an image of cyan, and the fourth image forming station (k) forms an image of black.

The configurations of these image forming stations are the same except for the color of the toner used as the developer. Therefore, in the following explanation, the configuration of the yellow image forming station will be explained as a representative example, and explanations of the image forming stations of the other colors will be omitted.

In the image forming station (y), 101y indicates a photosensitive drum which is a first image carrier, 102y indicates a charging roller, 103y indicates an exposure device, 104y indicates a developer, 105y indicates a primary transfer roller, and 106y indicates a photosensitive cleaner. 107 indicates an intermediate transfer belt which is a second image carrier, 108 indicates a secondary transfer roller, and 110 indicates an intermediate transfer belt cleaner. 111 indicates a paper feed cassette, 112 indicates a pickup roller, 113 indicates a paper feed roller, 114 indicates a registration roller, and 115, 116, 117, and 118 indicate conveying rollers. Ey indicates the laser light for exposure, and P indicates a recording material such as paper.

When a CPU (not shown), which controls the entire image forming apparatus, receives an image formation command on a recording material P, the photosensitive drum 101y, the developer 104y, and the secondary transfer roller 108 are each driven to rotate at a predetermined speed in the direction of the arrow shown in FIG. 1 by a drive device (not shown).

During this rotation process, the photosensitive drum 101y is uniformly charged to a predetermined polarity and potential by the charging roller 102y. Next, an electrostatic latent image is formed on the charged photosensitive drum 101y by laser irradiation from the exposure device 103y in response to an image signal. After that, a toner image is developed using toner by the developer 104y at the development position on the photosensitive drum 101y on which the electrostatic latent image has been formed. The toner image formed on the photosensitive drum 101y is transferred to the intermediate transfer belt 107 by the primary transfer roller 105y at the primary transfer section.

Similarly, the toner images of each color developed on the photosensitive drums 101 at the other image forming stations are transferred in layers onto the intermediate transfer belt 107 by the primary transfer rollers 105. The four-color toner images on the intermediate transfer belt 107 are sent to the secondary transfer section.

In the above process, the toner remaining on the photosensitive drum 101 and the intermediate transfer belt 107 is scraped off and collected by the photosensitive drum cleaner 106 and the intermediate transfer belt cleaner 110, respectively.

Meanwhile, recording material P stored in a paper feed cassette 111 is fed by a pickup roller 112 and fed one sheet at a time by a paper feed roller 113. The fed recording material P has its skew corrected by a registration roller 114. The recording material P whose skew has been corrected is sent to a secondary transfer section at a predetermined timing by the registration roller 114. The paper feed roller 113 is provided to prevent double feeding of recording material P, and the registration roller 114 is provided to prevent skew of recording material P.

The four color toner images transferred onto the intermediate transfer belt 107 are transferred to the surface of the recording material P by the secondary transfer roller 108 at the secondary transfer section. At this time, the recording material P is sent to the secondary transfer section by the registration roller 114 in time with the toner image on the intermediate transfer belt 107 passing through the secondary transfer roller 108. The four color toner images on the intermediate transfer belt 107 are transferred all at once to the surface of the recording material P by the voltage applied to the secondary transfer roller 108 by a high-voltage board (not shown).

The recording material P onto which the toner image has been transferred by the secondary transfer roller 108 is sent to the fixing device 1. The fixing device 1 fixes the image (toner image) formed on the recording material P onto the recording material P.

The recording material P with the fixed image is then discharged outside the image forming apparatus 100 via conveying rollers 115, 116, 117, and 118. In this way, the recording material P with the color image formed is obtained.

The image forming operation by the image forming apparatus 100 described above is performed by instructions from a user via the operation unit 119 on the top surface of the image forming apparatus 100 or via a network. This series of image forming operations is controlled by a CPU (not shown) as a control unit in accordance with each input signal via the operation unit 119 or the network.

(Fixing device)
Next, the fixing device 1 will be described with reference to Fig. 2. Fig. 2 is a schematic cross-sectional view of the fixing device 1 taken along the conveying direction of the recording material P.

The image forming apparatus 100 is equipped with the fixing device (fixing section) 1 as an image heating device that heats the image formed on the recording material P.

As shown in FIG. 2, the fixing device 1 includes a fixing heater unit 2 and a pressure roller 3. When the toner image is fixed, the recording material P is sandwiched and transported between the fixing heater unit 2 and the pressure roller 3.

As shown in FIG. 2, the fixing heater unit 2 includes a ceramic heater (hereinafter referred to as the "fixing heater") 20, a heater holder 2b with a semicircular barrel-shaped cross section, a reinforcing metal plate 2c, and a fixing film 2a which is a cylindrical endless belt. The heater holder 2b is a support that supports the fixing heater 20. The reinforcing metal plate 2c is in an inverted U-shape and is provided so that the fixing heater unit 2 does not deform when pressed by the pressure roller 3.

The fixing heater 20, which serves as a heating means, includes a plurality of heating elements 21-23 and a substrate 25 on which the plurality of heating elements 21-23 are arranged in the transport direction of the recording material P. The substrate 25 is an insulating, heat-resistant, low-heat-capacity substrate whose longitudinal direction is the width direction perpendicular to the transport direction of the recording material P.

The fixing heater 20 has multiple heating elements 21-23 on one side of a substrate 25. The heating elements 21-23 are covered with a protective glass 26 to ensure insulation. The fixing heater 20 is fixed to and supported by a heater holder 2b.

Furthermore, the fixing heater 20 may be provided with a polyimide layer having a thickness of about 10 μm as a sliding layer on the contact surface side with the fixing film 2a of the substrate 25. This sliding layer (polyimide layer) reduces the friction resistance between the fixing film 2a and the fixing heater 20, thereby reducing the driving torque and preventing wear on the inner surface of the fixing film 2a.

The fixing film 2a is made by forming a silicone rubber layer (elastic layer) of about 300 μm thick on a cylindrical substrate of 30 μm thick stainless steel by ring coating. The elastic layer is further covered with a PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer) resin tube of 20 μm thick as the outermost layer of the fixing film 2a.

The inner surface of the fixing film 2a is coated with grease to improve sliding between the heater holder 2b and the inner surface of the fixing film 2a.

In addition to stainless steel, the fixing film 2a may be made of a cylindrical substrate made of nickel-based metal material or heat-resistant resin such as polyimide. In addition, when a heat-resistant resin such as polyimide is used as the substrate, a polyimide layer as a sliding layer is not necessary.

The pressure roller 3 is disposed facing the fixing heater 20 via the fixing film 2a. Here, the pressure roller 3 is provided below the fixing heater unit 2. The pressure roller 3 is a multi-layer pressure member in which a silicone rubber layer (elastic layer) 3b having a thickness of about 3 mm and a PFA resin tube (surface layer) 3c having a thickness of about 40 μm are laminated on a stainless steel core (shaft) 3a. Both ends of the core 3a of the pressure roller 3 are rotatably supported by bearings between the side plates (not shown) of the device frame.

The heater holder 2b is made of a highly heat-resistant liquid crystal polymer resin, and holds the fixing heater 20 while guiding the fixing film 2a. Both ends of the heater holder 2b are urged toward the pressure roller 3 with a total pressure of 90 to 320 [N] by a pressure mechanism (not shown). As a result, the lower surface of the fixing heater 20 (the surface opposite to the heating surface) is pressed against the elastic layer of the pressure roller 3 with a predetermined pressure through the fixing film 2a, forming a fixing nip portion N of a predetermined width required for fixing. In other words, the pressure roller 3 is disposed opposite the fixing heater 20 through the fixing film 2a, and the fixing film 2a is brought into contact with the fixing heater 20 to form a clamping portion (fixing nip portion N) that clamps the recording material P between the fixing film 2a and the pressure roller 3.

In the fixing device 1 configured as described above, the pressure roller 3 is driven to rotate in the conveying direction of the recording material P (counterclockwise in FIG. 2) by a drive system (not shown). When the pressure roller 3 is driven to rotate, the fixing film 2a slides closely against the substrate surface of the fixing heater 20 and rotates around the heater holder 2b.

The fixing device 1 is equipped with a thermistor 2d as a temperature detection means for detecting the fixing temperature. The thermistor 2d is installed on the upper surface (non-heated surface) of the fixing heater 20, which is a heat source, in contrast to the lower surface (heated surface). Thermistor 2d has the function of detecting the central temperature of the fixing heater 20.

The fixing device 1 is equipped with a thermostat 2e. The thermostat 2e is a temperature-sensitive switch in which the bimetal is reversed and the contacts are opened when the temperature of the fixing heater 20 reaches a predetermined temperature (target temperature). When the temperature of the fixing heater 20 exceeds the predetermined temperature, the contacts of the thermostat 2e are opened, and the power supply to the fixing heater 20 is cut off. The power supplied to the fixing heater 20 is AC power.

When the pressure roller 3 is rotated and the cylindrical fixing film 2a is driven to rotate, electricity is passed to the fixing heater 20 (AC power is supplied). Then, when the temperature of the fixing heater 20 reaches the target temperature and is in a temperature-adjusted state, the recording material P carrying the unfixed toner image is introduced into the fixing nip N.

In the fixing nip N, the surface of the recording material P that carries the toner image is in close contact with the outer surface of the fixing film 2a. The recording material P moves together with the fixing film 2a in the fixing nip N. As the recording material P is sandwiched and transported in the fixing nip N, heat from the fixing heater 20 is applied to the recording material P via the fixing film 2a. The unfixed toner image is melted and fixed onto the recording material P by the heat from the fixing heater 20. After passing through the fixing nip N, the recording material P is separated from the fixing film 2a and transported.

(fixing heater)
Next, the fixing heater 20 will be described in detail with reference to Fig. 3. Fig. 3 is a structural diagram of the fixing heater 20 in this embodiment.

The fixing heater 20 has multiple heating elements 21 to 23 arranged in the transport direction of the recording material P. Note that, although the fixing heater 20 is illustrated here as having three heating elements 21 to 23, the present invention is not limited to this and can be applied to multiple heating elements.

The heating elements 21-23 are provided on one side of the substrate 25, which is made of a ceramic material such as alumina or aluminum nitride, that comes into contact with the fixing film 2a. The heating elements 21-23 are made of silver-palladium (Ag/Pd) or the like, and are printed and fired on the one side of the substrate 25.

The fixing heater 20 is configured so that each of the heating elements 21 to 23 can be powered independently. Specifically, one longitudinal end of each of the heating elements 21 to 23 of the fixing heater 20 is connected to an independent electrode 31 to 33, and the other end is connected to a common electrode 35. Furthermore, the heating elements 21 to 23 are covered with a protective glass 26.

The multiple heating elements 21-23 each have a heating area 21a-23a, and when electricity is applied through each electrode 31-33, the heating area of the energized heating element lights up and generates heat. Each heating element 21-23 also has a non-heating area 21b-23b that does not generate heat when electricity is applied. In the fixing heater 20, the heating areas 21a-23a of each heating element 21-23 are divided in the width direction perpendicular to the transport direction as follows, and are provided in positions that do not overlap in the transport direction.

The width direction perpendicular to the recording material transport direction is also the same direction as the longitudinal direction of the substrate 25 described above, so in the following explanation, the direction perpendicular to the recording material transport direction is referred to as the width direction or longitudinal direction of the recording material. The direction perpendicular to the longitudinal direction of the substrate 25 is also referred to as the short direction, because it is the same direction as the recording material transport direction and is shorter than the longitudinal length of the substrate 25.

In the fixing heater 20, the first heating element 21 has one heating area 21a sandwiched between non-heating areas 21b, 21b on both sides in the longitudinal direction. The other heating elements, the second heating element 22 and the third heating element 23, have heating areas 22a, 23a on both sides in the longitudinal direction, sandwiched between non-heating areas 22b, 23b, respectively.

Of the three heating elements 21-23, the heating area 21a of the first heating element 21 is located in the center in the longitudinal direction. In the fixing heater 20, the center in the longitudinal direction through which the recording material P passes is the center point O, which is indicated by a dashed line in the figure. The heating areas 22a, 23a of the other heating elements 22, 23 are arranged from the center point O toward the outside in the longitudinal direction of the fixing heater 20 in the order of the first heating area 21a, the second heating area 22a, and the third heating area 23a. In addition, the heating elements 21-23 (their heating areas) are shaped symmetrically in the longitudinal direction of the fixing heater 20 with respect to the center point O.

The non-heating region 22b of the second heating element 22 has the same longitudinal length as the first heating region 21a. Therefore, the second heating region 22a of the second heating element 22, which is symmetrical in the longitudinal direction with respect to the center point O, does not overlap with the first heating region 21a in the conveying direction.

The non-heating region 23b of the third heating element 23 has a longitudinal length equal to the combined length of the first heating region 21a and the second heating regions 22a on either side of it. Therefore, the third heating region 23a of the third heating element 23, which is symmetrical in the longitudinal direction with respect to the center point O, does not overlap with the first heating region 21a and the second heating regions 22a on either side of it in the transport direction.

Note that the length of the heat generating region of the heat generating element and the location of the heat generating region in the fixing heater shown in FIG. 3 are examples and are not limited to these. The length of the heat generating region of the heat generating element and the location of the heat generating region are appropriately determined depending on the widths of the multiple recording materials that the image forming device can handle, etc.

As an example, the width of the first heat generating region 21a of the first heat generating element 21 is 168 mm, and it is arranged so as to be linearly symmetrical at the center (center point O) of the maximum recording material width, which is the maximum width of the recording material. The width of the second heat generating region 22a of the second heat generating element 22 is 62 mm, and it is arranged in the direction of both electrodes from the boundary between the first heat generating region 21a and the first non-heat generating region 21b of the first heat generating element 21. Furthermore, the width of the third heat generating region 23a of the third heat generating element 23 is 22 mm, and it is arranged in the direction of both electrodes from the boundary between the second heat generating region 22a and the non-heat generating region 22b of the second heat generating element 22.

Of the heat generating areas 21a-23a of the multiple heat generating elements 21-23, the heat generating area 23a located at the extreme end in the width direction of the recording material P has a shape different from the shapes of the other heat generating areas 21a, 22a. For example, in this embodiment, as shown in FIG. 3, the heat generating area 23a located at the extreme end is formed in a tapered shape in which the outermost part in the width direction of the recording material P is narrower in length in the conveying direction of the recording material than the inner part.

In other words, of the heat generating areas 21a-23a of the multiple heat generating elements 21-23, the heat generating area 23a located at the extreme end in the width direction of the recording material P is made to have a higher resistance value than the other heat generating areas 21a, 22a. In other words, the shape of the heat generating area 23a located at the extreme end (the heat generating area 23a closest to the electrode) is made tapered so that it becomes narrower toward the outside, so that the resistance value is made higher than the other heat generating areas 21a, 22a.

More specifically, the heat generating region 23a located at the end is formed in a tapered shape such that the outermost portion 23a1 in the width direction of the recording material P is narrower in the conveying direction of the recording material P than the inner portion 23a2.

Next, the shape of the fixing heater 20 in this embodiment will be described in comparison with the shape of the fixing heater in the comparative example with reference to Figures 4(a) and 4(b). Figures 4(a) and 4(b) are enlarged views of the main part of the heating region 23a located at the extreme end of the fixing heater 20 shown in Figure 3 (circular frame area).

Figure 4(a) shows a schematic diagram of the shape of the fixing heater 20 of the comparative example and the heater temperature of the fixing heater 20 when the maximum recording material width is passed through. In the fixing heater 20 of the comparative example, the heat generating area 23a located at the extreme end is formed in a shape that has the same length in the conveying direction of the recording material from the inner side to the outermost side in the width direction of the recording material P.

Figure 4(b) shows a schematic diagram of the shape of the fixing heater 20 in this embodiment and the heater temperature of the fixing heater 20 when the maximum recording material width is passed. In this embodiment, the heating area 23a located at the extreme end is formed in a tapered shape in which the outermost part 23a1 in the width direction of the recording material P is narrower in the conveying direction of the recording material P than the inner part 23a2.

Here, we will explain the threshold value α at a predetermined position from the end of the heat generating areas 21a-23a of each heat generating element 21-23. This is the criterion for determining whether or not to light up and generate heat in the end of the heat generating area adjacent to that heat generating area when a recording material that exceeds the threshold value α of each heat generating area is passed through, centered on the maximum recording material width. In other words, if the width (length in the width direction) of the recording material P exceeds the threshold value α of the heat generating area 21a, the heat generating area 22a on the end side adjacent to that heat generating area 21a will also be generated to generate heat. Also, if the threshold value α of the second heat generating area 22a is exceeded, the heat generating area 23a on the end side adjacent to that heat generating area 22a will also be generated to generate heat.

In the comparative fixing heater 20 shown in FIG. 4(a), the maximum recording material width exceeds the threshold value α of the heat generating area 23a located at the very end, so unless the heat generating area on the adjacent end side is turned on, the power required for this recording material cannot be provided. However, since the heat generating area 23a is located at the very end in the width direction, there is no heat generating area adjacent to it on the end side. Therefore, with the shape of the fixing heater 20 of the comparative example, when paper close to the maximum recording material width is passed through, it is unable to provide sufficient power, so heat is absorbed by the recording material, and the heater temperature on the end side drops.

In contrast, in the fixing heater 20 of this embodiment shown in FIG. 4(b), the resistance value of the outermost portion 23a1 of the heat generating area 23a located at the outermost end is made larger than that of the inner portion 23a2, and the amount of power is increased. In other words, the outermost portion 23a1 of the heat generating area 23a located at the outermost end is formed in a tapered shape that becomes narrower toward the outside.

Here, the heat generating region 23a located at the extreme end is formed in such a way that the portion 23a1, which is on the outer side of the end of the maximum recording material width of the recording material P in the width direction of the recording material P, is narrower in length in the recording material transport direction than the portion 23a2, which is on the inner side.

Here, the start position of the tapered shape of the heat generating area 23a located at the very edge is outside the maximum recording material width, but this is not limited to this. The start position of the tapered shape of the heat generating area 23a located at the very edge may be outside the area where an image is formed on the recording material, instead of the maximum recording material width described above (the broken line position shown in FIG. 4B). In other words, in the heat generating area 23a, the outermost part 23a1 in the width direction of the recording material P is not limited to the part outside the edge of the recording material P, but may be the part outside the area where an image is formed on the recording material P.

In other words, the heat generating area 23a located at the extreme end may be formed such that the portion 23a1, which is on the outer side of the area of the image to be formed on the recording material P in the width direction of the recording material P, is narrower in length in the conveying direction of the recording material than the portion 23a2, which is on the inner side.

In this way, by making the heating area 23a located at the very end into a tapered shape as shown in FIG. 4B, the length of the heating area in the transport direction is narrowed and the resistance value is increased, so the amount of power in the tapered portion of the heating area is increased. As a result, the amount of power on the end side of the heating area 23a at the very end is greater than that of other heating areas, so the amount of heat increases. Because the amount of heat on the end side of the heating area 23a at the very end is greater, the threshold α of the heating area 23a can also be made shorter in the width direction compared to the comparative example. Because the amount of power is proportional to the resistance value, by making the threshold α of the heating area 23a at the very end an appropriate tapered shape so that it does not cross the maximum recording material width, sufficient heat can be supplied even when a recording material of the maximum recording material width is passed through.

Next, using FIG. 5, the amount of current flowing through each heating element (heating area) in the fixing heater 20 in this embodiment when various recording materials are passed through will be described. Below, we will explain separately the cases when three types of recording materials P1 to P3 with different width lengths are passed through.

First, we will explain what happens when recording material P1 is passed through. The width of recording material P1 falls within the first heat generation area 21a of the first heat generation element 21, and does not cross the threshold value α of the first heat generation area 21a. Therefore, the heater control means 50 determines that sufficient heat can be secured for this recording material P1 by simply supplying power to the first heat generation element 21. In other words, only the first heat generation element 21 generates heat. Electricity is supplied to the first heat generation element 21 so that the amount of power required for recording material P1 is obtained, and temperature adjustment control is performed. The amount of power supplied at this time is, for example, 60%.

Next, a case where recording material P2 is passed will be described. The width of recording material P2 straddles the threshold value α of the first heat generating region 21a of the first heat generating element 21. Therefore, the heater control means 50 judges that a sufficient amount of heat can be secured for this recording material P2 by supplying power to the first heat generating element 21 and the second heat generating element 22. That is, the first heat generating element 21 and the second heat generating element 22 generate heat. In order to obtain the amount of power required for recording material P2, the first heat generating element 21 is energized at maximum power, and the second heat generating element 22 is energized to compensate for the remaining amount of power required, thereby performing temperature adjustment control. In this case, the amount of power supplied is, for example, 100% to the first heat generating element 21 and 15% to the second heat generating element 22.

Next, a case where the recording material P3 is passed will be described. The width of the recording material P3 straddles the threshold value α of the second heating element 22. Therefore, the heater control means 50 judges that a sufficient amount of heat can be secured for this recording material P3 by supplying power to the first heating element 21, the second heating element 22, and the third heating element 23. That is, the first heating element 21, the second heating element 22, and the third heating element 23 generate heat. In order to obtain the amount of power required for the recording material P3, the first heating element 21 and the second heating element 22 are energized to the maximum power, and the third heating element 23 is energized to compensate for the remaining amount of power required, thereby performing temperature adjustment control. The amount of power supplied at this time is, for example, 100% for the first heating element 21 and the second heating element 22, and 40% for the third heating element 23.

As described above, the heating elements 21 to 23 to be energized are determined according to the width of the recording material P, and the power required for each recording material is spread from the heating element 21 located at the center of the fixing heater 20 to the heating elements 22 and 23 on the adjacent end sides, increasing the amount of power.

Next, using FIG. 6, we will explain how power is supplied to the heating element in the fixing heater 20 in this embodiment and how the temperature of the fixing heater 20 is controlled. FIG. 6 is a circuit diagram around the fixing heater.

An AC voltage source 51 supplied to the image forming apparatus 100 supplies power to the heating elements 21, 22 and 23 in the fixing heater 20 through switch means 52, 53 and heater power control means 61, 62, 63 for each heating element. The temperature of the fixing heater 20 is detected by a thermistor 2d as a temperature detection means. The heater control means 50 controls the power to the heating elements 21, 22 and 23 so that the detected temperature becomes the target temperature previously stored in the heater control means 50. The control performed by the heater control means 50 will now be described.

When the image forming apparatus 100 is in a print mode during operation or a standby mode during standby, the heater control means 50 turns on the switch means 52 to prepare for supplying power to the heating elements 21, 22, and 23. Next, the heater control means 50 controls the heater power control means 61, 62, and 63 according to the size of the recording material P fed through the image forming apparatus 100 and the pre-stored lighting pattern in order to light up each heating element. By lighting up the heating elements 21, 22, and 23, the fixing heater 20 is heated. The heater control means 50 monitors the temperature information detected by the thermistor 2d located near the fixing heater 20, and varies the timing of turning on or off the heating elements 21, 22, and 23 based on the temperature information.

As described above, in the fixing heater 20 in which the heat generation area is divided in the width direction of the recording material, the heat generation element 23 located at the extreme end is made to have a higher resistance value than the other heat generation elements 21 and 22. This reduces the temperature drop at the ends and suppresses poor image fixing even when the widest recording material is passed through.

In the above-mentioned embodiment, the heating element located at the end is tapered to have a higher resistance than the other heating elements, but the present invention is not limited to this, and other methods may be used to change the resistance. For example, the heating element 23 (heating area 23a) located at the end may be made of a different material (resistance material) from the other heating elements 21 and 22 (heating areas 21a and 22a) to increase the resistance. Alternatively, the heating element 23 (heating area 23a) located at the end may be made to have a different thickness from the other heating elements 21 and 22 (heating areas 21a and 22a) to increase the resistance. Even with this configuration, the same effect as the above-mentioned embodiment can be obtained.

In the above embodiment, the fixing heater 20 has three heating elements 21 to 23, but the present invention is not limited to this and can be applied to multiple heating elements. Also, the electrode positions for supplying power to each heating element are located at the ends of the fixing heater 20, but the present invention is not limited to this.

In the above-mentioned embodiment, an example was described in which the invention was applied to an electrophotographic full-color image forming apparatus having multiple photosensitive drums, but the invention is not limited to this and can also be applied to various types of image forming apparatuses, monochrome image forming apparatuses, etc.

In the above embodiment, a printer is used as an example of an image forming apparatus, but the present invention is not limited to this. For example, other image forming apparatuses such as a copier or facsimile machine, or other image forming apparatuses such as a multifunction machine that combines the functions of these, may be used. In addition, an image forming apparatus that uses an intermediate transfer body, transfers toner images of each color to the intermediate transfer body in a sequentially overlapping manner, and transfers the toner images carried on the intermediate transfer body to a recording material all at once is exemplified, but the present invention is not limited to this. An image forming apparatus that uses a recording material carrier, transfers toner images of each color to the recording material carried on the recording material carrier in a sequentially overlapping manner may be used. Similar effects can be obtained by applying the present invention to an image heating device used in these image forming apparatuses.

In the above-described embodiment, a fixing device mounted on an image forming apparatus such as a printer or copier was exemplified as an image heating device. However, the present invention is not limited to such fixing devices, and can also be applied to image heating devices such as gloss imparting devices that improve the gloss of an image formed on a recording material. It can also be applied to image heating devices that are not mounted on an image forming apparatus.

In the above-described embodiment, the fixing heater 20 is configured to have a plurality of heating elements 21-23 arranged in the transport direction of the recording material P. The plurality of heating elements 21-23 are then divided in a width direction perpendicular to the transport direction, and the heating areas 21a-23a are provided at positions that do not overlap in the transport direction. However, the present invention is not limited to this. For example, the fixing heater 20 may be configured to have a single heating element. The single heating element is then divided in a width direction perpendicular to the transport direction, and the heating areas are provided at positions that do not overlap in the transport direction. Even with such a configuration, it is possible to obtain the same effects as those described above.

N: Fixing nip portion (clamping portion)
P... recording material 1... fixing device 2... fixing heater unit 2a... fixing film 2b... heater holder 2c... reinforcing plate 2d... thermistor 2e... thermostat 3... pressure roller (pressure member)
3a ... Core metal (shaft part)
3b ... Silicone rubber layer (elastic layer)
3c ... Resin tube (surface layer)
20: Fixing heater (heating means)
21 to 23 ... Heating elements 21a to 23a ... Heating regions 21b to 23b ... Non-heating regions 25 ... Substrate 26 ... Protective glasses 31 to 35 ... Electrode 100 ... Image forming apparatus

Claims (12)

a heating means having a heat generating region which generates heat when energized, the heat generating region being divided in a width direction perpendicular to a conveying direction of the recording material;
a pressure member disposed opposite the heating means and sandwiching a recording material between the heating means and the pressure member,
An image heating device that heats an image formed on a recording material by heat from the heating means,
13. An image heating device according to claim 12, wherein a heat generating region located at an end portion in a width direction of a recording material among said heat generating regions has a resistance value larger than that of other heat generating regions. The image heating device according to claim 1, characterized in that the heat generating region located at the extreme end is formed in a shape in which the outermost part in the width direction of the recording material is narrower in length in the conveying direction of the recording material than the inner part. The image heating device according to claim 2, characterized in that the heat generating region located at the extreme end is formed in such a shape that the outermost part in the width direction of the recording material is narrower in length in the conveying direction of the recording material than the inner part. The image heating device according to claim 2, characterized in that the heat generating region located at the extreme end is formed in a shape in which the portion outside the region of the image to be formed on the recording material in the width direction of the recording material is narrower in length in the conveying direction of the recording material than the portion inside the portion outside the region. The image heating device according to claim 2, characterized in that the heat generating region located at the extreme end is formed in a shape in which the length in the conveying direction of the recording material is narrower in the width direction of the recording material at the portion outside the end of the recording material than at the portion inside the end. The image heating device according to claim 1, characterized in that the heat generating region located at the extreme end is made of a material different from the other heat generating regions. The image heating device according to claim 1, characterized in that the heat generating region located at the extreme end is formed with a thickness different from that of the other heat generating regions. the heating means has a plurality of heating elements arranged in a conveying direction of the recording material,
2. The image heating apparatus according to claim 1, wherein the plurality of heat generating elements are divided in a width direction perpendicular to the transport direction, and the heat generating regions are provided at positions that do not overlap in the transport direction. The image heating device according to claim 1, characterized in that the heating means is divided in a width direction perpendicular to the transport direction, and the heat generating regions are provided at positions that do not overlap in the transport direction. The image heating device according to claim 8, characterized in that the heating means is configured such that one end of each heating element in the width direction is connected to an independent electrode and the other end is connected to a common electrode, and each heating element can be supplied with power independently. A cylindrical belt;
The heating means for heating the belt;
2. The image heating apparatus according to claim 1, further comprising: a pressure member disposed opposite the heating means via the belt, bringing the belt into contact with the heating means and sandwiching the recording material between the belt and the pressure member. An image forming apparatus having an image forming section that forms an image on a recording material, and a fixing section that fixes the image formed on the recording material to the recording material,
12. An image forming apparatus, comprising: the fixing unit comprising the image heating apparatus according to claim 1.

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