JP7528626B2 - Heater member, heating device, fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a heater member, a heating device, a fixing device, and an image forming apparatus, and in particular to a heater member having a resistance pattern that generates heat when electricity is passed through it, and a heating device, a fixing device, and an image forming apparatus that use the heater member.

Various types of fixing devices are known for use in electrophotographic image forming devices. One type uses a heater member to directly heat a thin fixing belt with low heat capacity (see Patent Documents 1 to 3). The heater member is composed of a substrate and a resistance pattern (planar heater). A pressure roller is disposed on the outside of the fixing belt as a pressure member, and the fixing nip is formed by pressing the fixing belt against the heater member with the pressure roller sandwiching the fixing belt.

The fixing devices in Patent Documents 1 to 3 have multiple resistor patterns arranged in the longitudinal direction of the substrate. Then, a first resistor pattern in the longitudinal center is energized to heat small-sized paper. In addition, a second resistor pattern is arranged at both ends in the longitudinal direction, and large-sized paper is heated by simultaneously energizing the first and second resistor patterns.

These resistor patterns are generally formed by printing resistive material on a ceramic substrate or the like in one go using screen printing. The area and thickness of each resistor pattern are made constant so that the resistance value (heat distribution) is uniform in the longitudinal direction of the substrate. To achieve this uniformity, since the first resistor pattern in the center is wider and has a larger area than the second resistor patterns on both ends, at least the first resistor pattern is divided into multiple patterns in the longitudinal direction and these multiple patterns are connected in parallel.

However, as the number of parallel-connected resistor patterns increases, it becomes more difficult to control the temperature of the fixing belt and ensure safety in the event of a disconnection. In the fixing device of Patent Document 1 (Patent Publication No. 6336026), the first resistor pattern in the center is divided into 15 parallel sections, and the second resistor patterns on both ends are divided into three parallel sections. The temperature of the fixing belt is controlled by four thermistors, and if a malfunction causes the temperature of the first or second resistor pattern to reach the high-temperature threshold, a safety element disposed between the two resistor patterns cuts off the current to the heater member (see Figure 3).

As can be seen from this, increasing the number of parallel-connected resistor patterns leads to a complex structure, difficulty in miniaturization, and increased costs. Therefore, rather than dividing the resistor pattern into multiple patterns in the longitudinal direction, it is possible to create a resistor pattern in which multiple resistors extending in the longitudinal direction are connected in parallel, as shown in Figures 3A and 6A, which will be described later.

However, in this case, as shown in FIG. 3C (described later), the amount of heat generated by conductor 338a, which connects the ends of multiple resistors 332-1 to 332-3 in parallel in the short direction, is reduced in the areas where it overlaps with each of resistors 332-1 to 332-3 (hatched areas), which may result in poor fixing.

The object of the present invention is to suppress the reduction in heat generation caused by a conductor that connects the ends of multiple resistors in parallel in the short direction.

In order to solve the above problem, the heater member of the present invention is characterized by having a resistor pattern having multiple rows of resistors formed in the longitudinal direction of a substrate and generating heat when current is passed through them, the multiple rows of resistors being arranged spaced apart from each other in a lateral direction perpendicular to the longitudinal direction of the substrate, and a conductor having a resistivity smaller than that of the resistors and connecting the ends of the resistors adjacent to each other in parallel at both longitudinal ends of the resistor pattern, a part of the conductor extending in the lateral direction and partially overlapping the ends of the resistors.

The present invention makes it possible to suppress the reduction in heat generation caused by conductors connected in parallel.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating the principle of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a fixing device. FIG. FIG. 2 is a plan view of a heater member according to a basic embodiment of the present invention. FIG. 4 is an enlarged plan view of a conductor connecting the ends of resistors of the heater element in parallel. FIG. 13 is a comparative example of a parallel-connected conductor that reduces heat generation. 1A and 1B are cross-sectional views of a heater member showing two examples in which the position of the resistor pattern is changed. 1A is a plan view of a thermistor, FIG. 1B is a side view, and FIG. FIG. 2 is a plan view of a heater member according to an application embodiment of the present invention. FIG. 4 is an enlarged plan view of a parallel connection conductor at an end of a resistor pattern. FIG. 13 is an enlarged plan view of a conductor with a different parallel connection shape. FIG. 13 is an enlarged plan view of a conductor with a different parallel connection shape. FIG. 13 is a plan view of a heater element in which the ends of a resistor pattern are inclined. FIG. 4 is an enlarged plan view of a parallel connection conductor at an end of a resistor pattern. FIG. 13 is an enlarged plan view of a conductor with a different parallel connection shape. 1A to 1C are diagrams illustrating configurations of fixing devices of different models. 1A to 1C are diagrams illustrating configurations of fixing devices of different models. 1A to 1C are diagrams illustrating configurations of fixing devices of different models.

Below, a heater member, a fixing device, and an image forming apparatus (laser printer) according to an embodiment of the present invention will be described with reference to the drawings. A laser printer is one example of an image forming apparatus, and the image forming apparatus is of course not limited to a laser printer. In other words, the image forming apparatus can be configured as any one of a copier, a facsimile, a printer, a printing machine, and an inkjet recording apparatus, or as a multifunction machine that combines at least two or more of these.

The same or corresponding parts in each drawing are given the same reference numerals, and their repeated explanations are appropriately simplified or omitted. Furthermore, the dimensions, materials, shapes, relative positions, etc. in the explanations of each component are merely examples, and are not intended to limit the scope of this invention unless otherwise specified.

In the following embodiments, the "recording medium" which is a sheet material will be described as "paper", but the "recording medium" is not limited to paper. The "recording medium" includes not only paper but also overhead projector sheets, fabric, metal sheets, plastic films, and prepreg sheets made of carbon fibers pre-impregnated with resin.

"Recording media" includes all media onto which developer or ink can be attached, recording paper, and recording sheets. In addition to plain paper, "paper" also includes cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, etc.

In addition, "image formation" as used in the following explanation refers not only to imparting meaningful images such as characters or figures to a medium, but also to imparting meaningless images such as patterns to a medium.

(Laser printer configuration)
1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. Note that the image forming apparatus may be a printer, a copier, a facsimile, or a combination machine of these.

The image forming device 100 shown in FIG. 1 has four imaging units 1Y, 1M, 1C, and 1Bk that are image forming sections. Each imaging unit 1Y, 1M, 1C, and 1Bk is detachably attached to the image forming device main body 103, and has the same configuration except that it contains developers of different colors, yellow, magenta, cyan, and black, which correspond to the color separation components of a color image.

Specifically, each imaging unit 1Y, 1M, 1C, 1Bk includes a drum-shaped photoconductor 2 as an image carrier, a charging device 3 that charges the surface of the photoconductor 2, a developing device 4 that supplies toner as a developer to the surface of the photoconductor 2 to form a toner image, and a cleaning device 5 that cleans the surface of the photoconductor 2.

The image forming apparatus 100 also includes an exposure device 6 that exposes the surface of each photoconductor 2 to light to form an electrostatic latent image, a paper feeder 7 that supplies paper P as a recording medium, a transfer device 8 that transfers the toner image formed on each photoconductor 2 to the paper P, a fixing device 300 that fixes the toner image transferred to the paper P, and a paper discharge device 10 that discharges the paper P outside the apparatus.

The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body stretched by multiple rollers, four primary transfer rollers 12 as primary transfer members that transfer the toner image on each photoconductor 2 to the intermediate transfer belt 11, and a secondary transfer roller 13 as a secondary transfer member that transfers the toner image transferred onto the intermediate transfer belt 11 to paper P. Each of the multiple primary transfer rollers 12 is in contact with the photoconductor 2 via the intermediate transfer belt 11.

As a result, the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other, forming a primary transfer nip between them. Meanwhile, the secondary transfer roller 13 comes into contact with one of the rollers that stretch the intermediate transfer belt 11 via the intermediate transfer belt 11. As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

In addition, a paper transport path 14 is formed within the image forming apparatus 100 along which the paper P sent from the paper feeder 7 is transported. A pair of timing rollers 15 is provided on the paper transport path 14 midway between the paper feeder 7 and the secondary transfer nip (secondary transfer roller 13).

Next, the printing operation of the image forming device will be described with reference to FIG.

When an instruction to start a printing operation is given, in each of the imaging units 1Y, 1M, 1C, 1Bk, the photoconductor 2 is rotated clockwise in FIG. 1, and the surface of the photoconductor 2 is charged to a uniform high potential by the charging device 3. Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original document read by the original reading device or the print information instructed to be printed from the terminal, thereby lowering the potential of the exposed portion and forming an electrostatic latent image. Toner is then supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

When the toner images formed on each photoconductor 2 reach the primary transfer nip (position of the primary transfer roller 12) as each photoconductor 2 rotates, they are transferred to the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1, so that they overlap one another. Then, as the intermediate transfer belt 11 rotates, the toner images transferred onto the intermediate transfer belt 11 are transported to the secondary transfer nip (position of the secondary transfer roller 13) and transferred to the paper P that has been transported through the secondary transfer nip.

This paper P is supplied from the paper feed device 7. The paper P supplied from the paper feed device 7 is temporarily stopped by the timing roller 15, and then transported to the secondary transfer nip in time with the toner image on the intermediate transfer belt 11 reaching the secondary transfer nip. In this way, a full-color toner image is carried on the paper P. In addition, after the toner image is transferred, the toner remaining on each photoconductor 2 is removed by each cleaning device 5.

The paper P with the transferred toner image is transported to the fixing device 300, which fixes the toner image onto the paper P. The paper P is then discharged outside the device by the paper discharge device 10, completing the printing process.

(Laser printer principle)
2A is a principle diagram of a laser printer as one embodiment of an image forming apparatus 100 equipped with a fixing device 300 of the present invention. The image forming apparatus 100 has an image carrier 2 (e.g., a photosensitive drum) and a drum cleaning device 5. It also has a charging device 3 as a charging means for uniformly charging the surface of the image carrier, a developing device 4 as a developing means for performing visible image processing of an electrostatic latent image formed on the image carrier, a transfer means T disposed below the image carrier 2, a charge removing device, etc.

The exposure device 6 is disposed above the image carrier 2. This exposure device 6 performs writing scanning according to image information, i.e., it reflects laser light Lb from a laser diode on a mirror 6a and irradiates the image carrier 2 based on image data.

A paper feeder 50 having a tray for stacking paper P is installed below the image forming device 100. This paper feeder 50 can store a large number of sheets of paper P as recording media in a bundle, and is unitized with a paper feed roller 60 as a means for transporting paper P.

A pair of registration rollers 250 is disposed downstream of the paper feed roller 60 as a separation and transport means. The paper P fed from the paper feed device 50 is temporarily stopped by the pair of registration rollers 250. This temporary stop creates slack in the leading edge of the paper P, correcting the skew of the paper P.

The paper P, which has been struck by the pair of registration rollers 250 and has a slackened leading edge, is sent to the transfer nip N of the transfer means T in time for the toner image on the image carrier 2 to be suitably transferred. The toner image on the image carrier 2 is then electrostatically transferred to the desired transfer position by the bias applied to the transfer nip N.

The fixing device 300 is disposed downstream of the transfer nip N. The fixing device 300 includes a fixing belt 310 as a fixing member that is heated by a resistance pattern 332 (described later), and a pressure roller 320 as a pressure member that rotates while contacting the fixing belt 310 with a predetermined pressure.

(Laser printer operation)
Next, a basic operation of the laser printer according to this embodiment will be described. The paper feed roller 60 rotates in response to a paper feed signal from the control unit of the image forming apparatus 100. This rotation of the paper feed roller 60 separates the topmost sheet of the stack of papers P loaded in the paper feed device 50 and sends it out to the paper feed path.

When the leading edge of the sent-out paper P reaches the nip of the registration roller pair 250, it forms a slack and waits in that state. Then, the toner image on the image carrier 2 is transferred to the paper P at the optimal timing (synchronization), and the leading edge skew of the paper P is corrected.

The charging device 3 uniformly charges the surface of the image carrier 2 to a high potential. The exposure device 6 then reflects laser light Lb based on image data on a mirror 6a and irradiates the surface of the image carrier 2.

When the surface of the image carrier 2 is irradiated with the laser light Lb, the potential of the irradiated area decreases, forming an electrostatic latent image. The developing device 4 has a developer carrier 4a that carries a developer containing toner, and transfers unused black toner supplied from a toner bottle via the developer carrier 4a to the surface portion of the image carrier 2 on which the electrostatic latent image is formed.

The image carrier 2 to which the toner has been transferred forms (develops) a toner image on its surface. Then, the toner image formed on the image carrier 2 is transferred to paper P by transfer means T.

The drum cleaning device 5 uses a cleaning blade 5a to remove residual toner adhering to the surface of the image carrier 2 after the transfer process. The removed residual toner is collected in a waste toner storage unit.

The paper P with the transferred toner image is transported to the fixing device 300. The paper P transported to the fixing device 300 is sandwiched between the fixing belt 310 and the pressure roller 320, and the unfixed toner image is fixed to the paper P by applying heat and pressure. The paper P with the fixed toner image is sent out from the fixing device 300.

(Fixing device)
Next, the configuration of the fixing device 300 will be described. As shown in Fig. 2B, the fixing device 300 according to this embodiment has a fixing belt 310 made of an endless belt member as a fixing member, a pressure roller 320 as an opposing member that contacts the outer circumferential surface of the fixing belt 310 to form a nip N, and a heater member 330 that heats the fixing belt 310. The heater member 330 is held by a heater holder 344, and the heater holder 344 is reinforced in the longitudinal direction by a stay 350 as a reinforcing member.

As shown in FIG. 2C, the heater holder 344 has a recess 344a for fitting and arranging the heater member 330, and multiple rib portions 344b located upstream of the recess 344a in the paper feed direction. The rib portions 344b are intended to reduce friction with the inner peripheral surface of the fixing belt 310 and to maintain stable running of the fixing belt 310. The short-side length (length in the paper feed direction) of the rib portions 344b is, for example, about 1 mm, and the protrusion amount is, for example, about 0.5 mm.

The fixing belt 310 is made of a flexible sleeve-shaped rotating member, and has a cylindrical body made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 μm, for example. A release layer made of fluorine-based resin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost layer of the fixing belt 310 to enhance durability and ensure releasability.

An elastic layer made of rubber or the like having a thickness of 50 to 500 μm may be provided between the base and the release layer. The base of the fixing belt 310 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal base such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 310 may be coated with polyimide, PTFE, or the like as a sliding layer.

The pressure roller 320 has an outer diameter of, for example, 25 mm and is composed of a solid iron core 321, an elastic layer 322 formed on the surface of the core 321, and a release layer 323 formed on the outside of the elastic layer 322. The elastic layer 322 is made of silicone rubber and has a thickness of, for example, 3.5 mm. To improve the release properties of the surface of the elastic layer 322, it is desirable to form a release layer 323 made of a fluororesin layer having a thickness of, for example, about 40 μm.

The heater member 330 is provided longitudinally across the width of the fixing belt 310 and is arranged so as to contact the inner peripheral surface of the fixing belt 310. The heater member 330 may be in non-contact with the fixing belt 310 or indirect contact via a low-friction sheet or the like, but having the heater member 330 in direct contact with the fixing belt 310 improves the efficiency of heat transfer to the fixing belt 310.

The heater member 330 can also be in contact with the outer peripheral surface of the fixing belt 310, but since there is a risk that the fixing quality will decrease if the outer peripheral surface of the fixing belt 310 is damaged by contact with the heater member 330, it is better for the heater member 330 to be in contact with the inner peripheral surface of the fixing belt 310.

The heater member 330 is composed of a substrate 331, a resistor pattern 332 laminated on the nip N side of the substrate 331, and an insulating layer 333.

The substrate 331 can be made of a ceramic, such as alumina or aluminum nitride. Since the linear expansion coefficient of ceramic is close to that of glass, when glass is used for the insulating layer 333, there is an advantage in that shear force is less likely to be applied to the resistor pattern 332 due to misalignment between the substrate 331 and the insulating layer 333 during thermal expansion.

In addition, ceramics have a higher thermal conductivity than metals such as stainless steel, making it advantageous for conducting heat to the fixing belt 310 via the substrate 331. In addition to ceramics, other materials such as glass and mica are also preferred for the substrate 331, as they have excellent heat resistance and insulation properties. In this embodiment, an alumina substrate with a short side width of 8 mm, a long side width of 270 mm, and a thickness of 1.0 mm is used.

The heater holder 344 and the stay 350 are disposed on the inner periphery of the fixing belt 310. The stay 350 is made of a metal channel material, and both ends of the stay 350 are supported by the side walls of the fixing device 300.

The stay 350 supports the surface of the heater holder 344 opposite the heater member 330. This allows the heater member 330 and heater holder 344 to be supported without bending significantly due to the pressure from the pressure roller 320. A nip N is then stably formed between the fixing belt 310 and the pressure roller 320.

The heater holder 344 is desirably made of a heat-resistant material because it is prone to becoming hot due to the heat of the heater member 330. For example, if the heater holder 344 is made of a heat-resistant resin with low thermal conductivity such as LCP or PEEK, heat transfer from the heater member 330 to the heater holder 344 is suppressed, making it possible to heat the fixing belt 310 efficiently.

The pressure roller 320 and the fixing belt 310 are pressed against each other by a spring that serves as a biasing member. This forms a nip N between the fixing belt 310 and the pressure roller 320. The pressure roller 320 also functions as a drive roller that is rotated by a driving force transmitted from a drive means provided in the image forming apparatus main body 103.

Meanwhile, the fixing belt 310 is configured to rotate in accordance with the rotation of the pressure roller 320. When rotating, the fixing belt 310 slides against the heater member 330. To improve the sliding properties of the fixing belt 310, a lubricant such as oil or grease may be interposed between the heater member 330 and the fixing belt 310.

When the printing operation is started, the pressure roller 320 is rotated and the fixing belt 310 starts to rotate. In addition, the fixing belt 310 is heated by supplying power to the heater member 330. Then, when the temperature of the fixing belt 310 reaches a predetermined target temperature (fixing temperature), as shown in FIG. 2B, the paper P carrying the unfixed toner image is transported between the fixing belt 310 and the pressure roller 320 (nip N), and the unfixed toner image is heated and pressurized to be fixed to the paper P.

(Basic embodiment of heater member)
Fig. 3A shows a basic embodiment of heater member 330. As shown in Fig. 3A, the main body of heater member 330 is composed of substrate 331. In the longitudinal direction of substrate 331, three rows of resistor patterns 332 that constitute the main body of the resistor pattern and generate heat when electricity is applied are formed linearly, parallel to each other, and at equal intervals.

The three rows of resistor pattern 332 are spaced apart from each other in the short direction perpendicular to the long direction of substrate 331, and are connected in parallel to electrodes 337a and 337b as described below. A thermistor TM1 serving as a first temperature detection element is disposed in the center of resistor pattern 332 in the long direction (minimum paper width).

In FIG. 3A, this thermistor TM1 is disposed across the first resistor 332-1 and the second resistor 332-2 from the upstream side in the paper feed direction of the three-row resistor pattern 332. Here, "across" means that the thermistor TM1 overlaps both of the resistors 332-1 and 332-2 in the two rows of resistor pattern 332 in a plan view of the three-row resistor pattern 332 from its thickness direction.

By positioning the thermistor TM1 upstream in the paper feed direction, the temperature on the upstream side of the nip where the fixing belt 310 enters, which is the coldest, can be accurately detected and controlled, thereby maintaining good fixing performance. In addition, by positioning the thermistor TM1 in the longitudinal center of the resistor pattern 332 (minimum paper width), it is possible to make it less susceptible to the effect of temperature rise in non-paper passing areas when paper is passing, and good fixing performance can be maintained.

Thermostat TH is disposed adjacent to thermistor TM1 in the longitudinal center (minimum paper width) of resistor pattern 332. This thermostat TH is disposed across all three rows of resistor pattern 332. Here, "across" means that in a plan view of the three rows of resistor pattern 332 seen from the thickness direction, thermostat TH overlaps all three rows of resistor pattern 332 (332-1 to 332-3).

Thermostat TH is connected between one of electrodes 337a, 337b (described later) and power source W, and is configured so that when any of resistors 332-1 to 332-3 reaches a high temperature threshold (e.g., greater than 180°C and less than 200°C), thermostat TH cuts off the power supply to resistor pattern 332 for safety reasons. For simplicity, the wiring of thermostat TH is omitted in FIG. 3A.

Thermostat TH generally consists of a dish-shaped bimetal housed within a housing, and is preferably arranged so that the bimetal of thermostat TH overlaps all three rows (332-1 to 332-3) of resistor pattern 332 in the plan view.

In addition, a different thermistor TM2 is disposed as a second temperature detection member at one end of the resistor pattern 332 in the longitudinal direction outside the minimum paper width (the right end in FIG. 3A). The position of this thermistor TM2 is the paper passing end region of the maximum paper width.

Thermistor TM2 is disposed across the second resistor 332-2 and the third resistor 332-3 from the upstream side in the paper feed direction of the three-row resistor pattern 332. Here, "across" means that thermistor TM2 overlaps both of the two rows (332-2 and 332-3) of resistor pattern 332 in a plan view of the three-row resistor pattern 332 from its thickness direction.

By locating the thermistor TM2 downstream in the paper feed direction, it is possible to accurately detect and control the temperature of the fixing belt 310, which has been receiving heat from the resistance pattern 332 for a long time and has accumulated heat, thereby effectively functioning as a sensor to prevent excessive temperature rise. Note that although the thermistor TM2 is located at the right end of the resistance pattern 332 in FIG. 3A, it may also be located at the opposite left end.

In the embodiment of FIG. 3A, either one (or both) of the thermistors TM1 and TM2 overlaps the entire three-row resistor pattern 332. Therefore, the temperature of all of the three-row resistor pattern 332 can be reliably detected by thermistors TM1 and TM2.

As a result, when the temperature of any of resistors 332-1 to 332-3 exceeds the set temperature, thermistor TM1 or TM2 detects the temperature rise, and the temperature of resistor pattern 332 can be maintained and controlled at the desired temperature (e.g., 170°C) by current control using a triac based on the detection result. Then, regardless of the paper size, the toner image carried on the paper is fixed to the paper at the desired fixing temperature (e.g., 170°C).

By locating thermostat TH and thermistors TM1 and TM2 within the paper passing area for all paper sizes, it is possible to prevent the influence of temperature rises at the ends of non-paper passing areas. This allows thermostat TH to cut off current early in the event of abnormal heat generation due to a malfunction. If thermostat TH is located in a non-paper passing area, the operating temperature of thermostat TH must be set high to prevent false detection, which puts safety at a disadvantage.

Thermistor TM1 (TM2) is disposed on the surface (upper surface in FIG. 4) opposite the nip forming surface (lower surface in FIG. 4) of heater member 330, as shown in FIG. 4(a) and FIG. 4(b) described below.

In this embodiment, the dimensions and resistance values of the three-row resistor pattern 332 are as follows:
Width of resistors in one row of resistor pattern 332 in the short side direction: 2.0 mm
- Short-side spacing between three rows of resistors: 0.7 mm
Short side width of resistor pattern 332: 7.4 mm = (2.0 x 3) + (0.7 x 2)
Resistance value of resistor pattern 332: 16Ω
-Longitudinal width of resistor pattern 332: 216 to 220 mm

The three-row resistor pattern 332 can be formed by applying a resistor material paste, for example, made of silver palladium (AgPd) and glass powder, to the substrate 331 by screen printing or the like, and then firing the substrate 331. In addition to the above, a resistor material such as a silver alloy (AgPt) or ruthenium oxide (RuO ₂ ) may be used as the resistor material. When using a resistor material having a positive temperature coefficient of resistance (PTC), a material with a temperature coefficient of resistance of, for example, 300 ppm can be used.

The three-row resistor pattern 332 does not necessarily have to be linear as in FIG. 3A. Instead of being linear, it may be a continuous wave shape. This allows the resistor pattern 332 to be longer, and the resistivity of the resistor material paste to be reduced.

Two electrodes 337a, 337b to which an AC power source is connected are disposed at both longitudinal ends of the substrate 331. One electrode 337a is connected to one end of the three-row resistor pattern 332 by a conductor 338a having a lower (electrical) resistivity than the resistor pattern 332. The other electrode 337b is connected to the other end of the three-row resistor pattern 332 by a conductor 338b having a lower resistivity than the resistor pattern 332.

When the fixing device 300 is operating, the temperature of the fixing belt 310 is maintained and controlled at the desired fixing temperature (e.g., 170°C) by these thermistors TM1 and TM2. In other words, based on the temperature detection result of the resistor pattern 332 by thermistor TM1 or TM2, the temperature of the resistor pattern 332 is maintained and controlled at the desired temperature (e.g., 170°C) by current control using a triac.

Thermostat TH and thermistors TM1 and TM2 are biased toward the substrate 331 by an elastic member, such as a spring. This bias by the spring reduces the contact gap between the thermostat TH and thermistor TM relative to the substrate 331. Therefore, the accurate temperature of the resistance pattern 332 is transmitted to the thermostat TH and thermistors TM1 and TM2, and the accurate temperature of the resistance pattern 332 (332-2, 332-3 and 332-1, 332-2) can be detected by the thermistors TM1 and TM2.

The ends of the three rows of resistors 332-1 to 332-3 are connected in parallel by conductor 338a as shown in FIG. 3B. More specifically, conductor 338a overlaps with a portion of the end of each of resistors 332-1 to 332-3 in the short direction of resistors 332-1 to 332-3 in the area indicated by diagonal lines. Here, "partially overlapping" means that conductor 338a partially overlaps with the end of each of resistors 332-1 to 332-3 in a plan view of the three rows of resistors 332-1 to 332-3 seen in their thickness direction.

Conductor 338a does not overlap continuously in the short-side direction with the ends of resistors 332-1 to 332-3. Therefore, if the short-side width of the portion of the ends of resistors 332-1 to 332-3 where conductor 338a does not overlap is a, then this short-side width a is smaller than the width b of the portion excluding the ends of resistors 332-1 to 332-3 (a<b). In the portion of short-side width a, conductor 338a does not overlap, so a heat generating effect is obtained. Therefore, it is possible to suppress a drop in temperature at the ends of resistors 332-1 to 332-3.

In contrast, in Figure 3C, conductor 338a overlaps the ends of resistors 332-1 to 332-3 continuously in the short direction. Therefore, in the shaded areas of length c at the ends of resistors 332-1 to 332-3, current flows through conductor 338a and no heat is generated. This causes a drop in temperature in the shaded areas of length c.

(Example of resistor pattern and thermistor layout)
4A and 4B show examples of the arrangement of a resistor pattern 332 with respect to the thermistor TM1, as viewed from a longitudinal cross section of the heater member 330. In Fig. 4A, the resistor pattern 332 is formed on the fixing belt 310 side of the substrate 331. The resistor pattern 332 is fixed to the surface of the substrate 331 in a state where it is sandwiched between two layers of insulating glass 334.

The insulating glass 334 can be made of heat-resistant glass having a thickness of, for example, 75 μm. This insulating glass 334 ensures the insulation of the resistor pattern 332 and the like, and ensures sliding properties with the inner surface of the fixing belt 310.

Meanwhile, the thermistor TM1 is disposed on the back surface of the substrate 331, opposite the fixing belt 310 side. As shown in FIG. 5, which will be described later, thermistor TM1 is biased by spring 560 and abuts against the back surface of the substrate 331 of the heater member 330. Heat from the resistor pattern 332 on the front side of the substrate 331 is transferred in the thickness direction of the substrate 331 to the thermistor TM1 on the back side, so that the temperature of the resistor pattern 332 is detected by thermistor TM1.

In contrast, in FIG. 4B, the resistor pattern 332 is formed on the substrate 331 of the heater member 330 on the side opposite the fixing belt 310. The resistor pattern 332 is fixed to the rear surface of the substrate 331 while being sandwiched between two layers of insulating glass 335.

The resistor pattern 332 in FIG. 4(b) is located close to thermistor TM1 with insulating glass 335 in between, so it can detect temperature more accurately than in FIG. 4(a). In addition, in FIG. 4(b), the heat of the resistor pattern 332 is uniformly distributed in the longitudinal and lateral directions by the substrate 331, so improvement in fixing quality can be expected.

Furthermore, by forming the heater member 330 on the opposite side to the fixing belt 310, the freedom of selection of materials to be provided on the surface of the base material 331 that slides against the fixing belt 310 and the freedom of surface processing are increased. In order to improve the sliding property with the fixing belt 310, for example, a coating 336 having lubricity such as polyimide or PTFE can be provided on the surface of the base material 331. When the heater member 330 is formed on the opposite side to the fixing belt 310 as shown in FIG. 4(b), ceramics such as alumina and aluminum nitride (AlN) that have high thermal conductivity can be suitably used as the material for the base material 331.

(Thermistor Structure)
5 shows the structure of thermistor TM1 (TM2) and the state of attachment to heater member 330. Thermistor TM1 (TM2) has a temperature detection element 520 on the lower part of a main body 510, and the lower part of main body 510 including the temperature detection element 520 is covered with heat-resistant protective tape 530.

Thermistor TM1 (TM2) is disposed on the back surface of heater member 330, the back surface of which is held by heater holder 344. Temperature detection element 520 is disposed in the center of main body 510 in the longitudinal direction of heater member 330.

A pair of springs 560 are arranged on the left and right sides of the upper surface of the main body 510, sandwiching the temperature detection element 520 in the longitudinal direction of the heater member 330. The biasing force of the springs 560 presses the temperature detection element 520 of thermistor TM1 (TM2) against the back surface of the heater member 330.

The pair of lead portions 520a of the temperature detection element 520 are connected to two lead wires 550 via the welded portion 520b and the conductive member 520c. The lead wires 550 are drawn out from the longitudinal ends of the heater member 330 and connected to a heating control means (controller). The heating control means refers to a microcomputer including a CPU, ROM, RAM, I/O interface, etc.

(Application of heater member)
6A shows an application embodiment of a heater member 330, which has three resistor patterns 332a, 332b, and 332c in the longitudinal direction of a substrate 331. That is, the three resistor patterns 332a, 332b, and 332c are a first resistor pattern 332a formed in the center in the longitudinal direction and second resistor patterns 332b and 332c formed at both ends in the longitudinal direction. Note that the boundary between the first resistor pattern 332a and the second resistor patterns 332b and 332c is formed so as not to overlap the above-mentioned rib portion 344b when viewed in the lateral direction.

The three resistance patterns 332a, 332b, and 332c can be formed by applying a resistance material paste having the same resistivity, which is made by mixing, for example, silver palladium (AgPd) and glass powder, to the base material 331 by screen printing or the like, and then firing the base material 331. In addition to these, resistance materials such as silver alloy (AgPt) and ruthenium oxide (RuO ₂ ) may also be used as the resistance material. When using a resistance material having a positive temperature coefficient of resistance (PTC), a material with a temperature resistance coefficient of, for example, 300 ppm can be used.

By selectively energizing and heating these three resistance patterns 332a, 332b, and 332c, each paper size (A3 to A6) is efficiently heated. That is, when large-sized paper such as A3 and B4 paper is passed through and heated, all resistance patterns 332a, 332b, and 332c are energized and heated. In contrast, when small-sized paper such as A4, B5, A5, B6, and A6 is passed through and heated, only the central resistance pattern 332a is energized and heated.

(First Resistor Pattern)
The first resistor pattern 332a in the center of the longitudinal direction of the substrate 331 has five rows of resistors 332a1 to 332a5 as first resistors that extend linearly in the longitudinal direction of the substrate 331. A thermostat TH1 as a current interrupting member is disposed so as to completely encompass these five rows of resistors 332a1 to 332a5 in a plan view. This thermostat TH1 is disposed on the surface of the heater member 330 opposite the nip forming surface, similar to the thermistor TM1 in FIG.

A thermistor TM1 serving as a first temperature detection member is disposed near the thermostat TH1. This thermistor TM1 is disposed across two rows of resistors 332a1 and 332a2 on the upstream side in the paper feed direction, which is the short side direction.

Thermostat TH1 and thermistor TM1 are also positioned approximately in the center of the substrate 331 in the longitudinal direction, where they are less susceptible to temperature rises in non-paper passing areas when paper is passing through, and are arranged within the range of the minimum paper width (e.g., A6 paper width). This allows good fixation to be maintained.

Here, "straddling" means that in a plan view of the five rows of resistors 332a1 to 332a5 seen in the thickness direction, the thermistor TM1 overlaps both of the two rows of resistors 332a1 and 332a2. By positioning the thermistor TM1 upstream in the paper feed direction, it is possible to accurately detect and control the temperature upstream of the nip where the coldest fixing belt 310 enters, thereby maintaining good fixing performance.

At the longitudinal end of the first resistor pattern 332a, another thermistor TM2 is disposed as a second temperature detection member. This thermistor TM2 is disposed across the three rows of resistors 332a3-332a5 on the downstream side in the paper feed direction. Here, "across" means that the thermistor TM2 overlaps the three rows of resistors 332a3-332a5 in a plan view of the three rows of resistors 332a3-332a5 viewed in the thickness direction.

By locating thermistor TM2 downstream of thermistor TM1 in the paper feed direction, it is possible to accurately detect and control the temperature of the fixing belt 310, which has been exposed to heat from the first resistance pattern 332a for a long time and has accumulated heat, thereby effectively functioning as a sensor to prevent excessive temperature rise. Note that although thermistor TM2 is located at the right end of the first resistance pattern 332a in FIG. 6A, it may also be located at the opposite left end.

Five rows of resistors 332a1 to 332a5 have the same length, width, and thickness and are arranged parallel to each other at equal intervals. By arranging them in five rows, the amount of heat generated per row can be reduced.

The first resistor pattern 332a in the longitudinal center of the substrate 331 has a larger heat generating area than the second resistor patterns 332b and 332c at both ends in the longitudinal direction. Therefore, the first resistor pattern 332a in the center requires a large amount of power, and conversely, the resistance value needs to be small.

By making the five rows of resistors 332a1 to 332a5 linear (shortest length), the resistance value can be reduced. As a result, as described below, the first resistor pattern 332a in the center of the longitudinal direction and the second resistor patterns 332b and 332c at both ends of the longitudinal direction can be formed from a material paste with the same resistivity.

Both longitudinal ends of the five rows of resistors 332a1 to 332a5 are connected in parallel to electrodes 337c and 337f via low resistivity conductors 338c, 338f2 and 338f3. The second resistor patterns 332b and 332c are connected in parallel to electrodes 337d, 337e and 337f via low resistivity conductors 338d, 338e, 338f1 and 338f2. The right electrode 337f is connected to one pole of a 100V AC power supply PW, and the other electrodes 337c, 337d and 337e are connected to the other pole of the 100V AC power supply PW via switches SW1 and SW2.

Therefore, by operating the switches SW1 and SW2, the central resistor pattern 332a and the resistor patterns 332b and 332c at both ends can be energized/cut off independently. This allows the fixing device 300 to be adapted to various paper sizes, and by turning off the power to unnecessary parts, the energy saving performance of the fixing device 300 can be improved. In addition, by operating the switch SW2 to intermittently energize and heat only the second resistor patterns 332b and 332c at both ends, the tendency for temperature sagging at both ends of the paper passing portion of the fixing belt 310 can be suppressed.

The arrangement of switches SW1 and SW2 can also be changed so that switches SW1 and SW2 are connected in series, as shown in the dashed rectangular frame in FIG. 6A. That is, in the lower dashed rectangular frame in FIG. 6A, switch SW2 branches off between switch SW1 and electrode 337c. By changing the position of switch SW1, it is possible to switch between ON-OFF control of central resistor pattern 332a and ON-OFF control of full-width resistor patterns 332a to 332c.

The five rows of resistors 332a1-332a5 mentioned above do not necessarily have to be linear as in FIG. 6A. Instead of being linear, they may be shaped like a continuous wave. This allows the length of the resistors 332a1-332a4 to be increased, and the resistivity of the resistor material paste to be reduced.

(conductor connecting resistors in parallel)
The ends of the five rows of resistors 332a1 to 332a5 are connected in parallel by five conductors 338c1 to 338c5 as shown in FIG. 6B. More specifically, the conductors 338c1 to 338c5 overlap a portion of the end of each of the resistors 332a1 to 332a5 in the short-side direction (paper feed direction) of the resistors 332a1 to 332a5. Here, "partially overlapping" means that the conductors 338c1 to 338c5 partially overlap the end of each of the resistors 332a1 to 332a5 in a plan view of the five rows of resistors 332a1 to 332a5 seen in their thickness direction.

The conductors 338c1 to 338c5 do not overlap continuously with the ends of the resistors 332a1 to 332a5 in the short-side direction. Therefore, if the short-side width of the portions of the ends of the resistors 332a1 to 332a5 where the conductors 338c1 to 338c5 do not overlap is a, then the short-side width a is smaller than the short-side width b of the portions excluding the ends of the resistors 332a1 to 332a5 (a<b).

In the area of width a in the short direction, the conductors 338c1 to 338c5 do not overlap, so heat generation is achieved. This makes it possible to suppress temperature drops at the ends of the resistors 332a1 to 332a5.

Figure 6C shows a modified parallel connection of conductors 338c1 to 338c5. That is, the short-side width d1 of the ends of resistors 332a1 to 332a5 is made larger than the short-side width d2 of the other ends (d2<d1).

The conductors 338c1 to 338c5 partially overlap the ends of the resistors 332a1 to 332a5 in the short-side direction, which is the width d1 of the short sides. This allows the amount of heat generated at the ends to be increased by the increased width d1 of the short sides, and suppresses the drop in temperature at the ends of the resistors 332a1 to 332a5.

Figure 6D also shows a modified parallel connection of conductors 338c1 to 338c5. That is, the short-side width d1 of the ends of resistors 332a1 to 332a5 is made larger than the short-side width d2 of the other ends (d2<d1). And, conductors 338c1 to 338c5 partially overlap the ends of resistors 332a1 to 332a5 with a width of d1-d2 in the short side direction.

Therefore, the short-side width d3 of the ends of resistors 332a1-332a5 where conductors 338c1-338c5 do not overlap is equal to d2 (d3=d2), and uniform heat generation is achieved over the entire longitudinal length of resistors 332a1-332a5. In this way, it is possible to suppress temperature drops at the ends of resistors 332a1-332a5.

(Second Resistor Pattern)
The second resistor patterns 332b, 332c at both ends in the longitudinal direction are composed of second resistors that are continuous in a zigzag pattern in the lateral direction of the substrate 331. The lateral width of the second resistor patterns 332b, 332c at both ends is the same as the lateral width of the first resistor pattern 332a at the center. The longitudinal width of the second resistor patterns 332b, 332c is a fraction of the longitudinal width of the first resistor pattern 332a at the center.

The second resistor patterns 332b and 332c are zigzag and arranged in five rows in the short direction of the substrate 331. The line width and thickness of the resistor patterns 332b and 332c are set so that the resistance value (heat distribution) is uniform in the long direction of the substrate 331, including the first resistor pattern 332a.

By increasing the length of the second resistor patterns 332b, 332c by zigzag folding, the resistivity of the resistor material paste can be reduced and uneven temperature distribution in the short direction can be suppressed. If the second resistor patterns 332b, 332c are not zigzag folded but are instead made into a single pattern in the short direction, localized high temperature areas can be formed, resulting in poor fixing, which is not preferable.

Thermistor TM3 is disposed as a third temperature detection member across the first and second rows from the upstream side of one (left) resistor pattern 332b in the paper feed direction. The thermistor TM3 is disposed in the paper feed end area of the maximum paper width.

The term "straddling" means that the thermistor TM3 overlaps both the first and second rows of the resistor pattern 332b in a plan view of the resistor pattern 332b in its thickness direction. By positioning the thermistor TM3 upstream in the paper feed direction, it is possible to accurately detect and control the temperature upstream of the nip where the coldest fixing belt 310 enters, thereby maintaining good fixing performance.

The longitudinal position of thermistor TM3 is approximately at the longitudinal center of resistor pattern 332b. In this way, by arranging thermistor TM3 at the central position of resistor pattern 332b, the accurate temperature of second resistor pattern 332b can be detected. Since second resistor pattern 332b is continuous in a zigzag pattern, current to second resistor pattern 332b is cut off even if a break occurs at any stage in the paper feed direction. For this reason, it is not necessary to arrange thermistor TM3 so that it includes the entire width in the paper feed direction (short direction).

In the other (right) resistor pattern 332c, a thermostat TH2 is disposed as a second current interrupting member across all five rows in the paper feed direction. The longitudinal position of the thermostat TH2 does not necessarily have to be in the longitudinal center of the resistor pattern 332c. "Across all five rows in the paper feed direction" means that the thermostat TH2 overlaps all five rows in the paper feed direction when viewed in a plan view of the resistor pattern 332c from its thickness direction.

As described above, a thermistor TM3 is provided on one of the second resistor patterns 332b, 332c, and a thermostat TH2 is provided on the other. This is because the second resistor patterns 332b, 332c are connected in parallel, and this configuration is sufficient for controlling the temperature of the second resistor patterns 332b, 332c and cutting off the current when overheating occurs.

The temperature of the fixing belt 310 is controlled to the desired temperature by controlling the power supplied to the heater member 330 by the heating control means (controller) according to the detected temperature detected by the aforementioned thermistors TM1 and TM3. However, when paper is being passed through, the temperature of the fixing belt 310 is controlled to the desired temperature by appropriately supplying additional power in addition to the detected temperature, taking into account the amount of heat dissipated by the paper passing through. Note that, as mentioned above, the heating control means refers to a microcomputer including a CPU, ROM, RAM, I/O interface, etc.

(Uniform heat density)
Here, the uniformity of the heat generation density of the first resistance pattern 332a and the second resistance patterns 332b and 332c will be described. If the required heat generation amount of the entire first resistance pattern 332a is 900 W, the heat generation amount per row is 180 W when divided into five equal parts. If the longitudinal length of the first resistance pattern 332a is 216 mm, the heat generation density [W/mm] is 0.83 [W/mm].

On the other hand, the second resistance patterns 332b and 332c at both ends in the longitudinal direction, which will be described later, are zigzag-folded in the short direction of the base material 331, thereby increasing their total length (increasing their resistance value). If the longitudinal length of the second resistance patterns 332b and 332c is 43 mm, then in order for the resistance patterns 332b and 332c to produce the same heat density [W/mm] in the longitudinal direction as the first resistance pattern 332a, a heat generation amount of 179 W each is required. The heat generation amount of 179 W is calculated using the following formula.
Central first resistor pattern 332a: 900 W/216 mm=4.17 W/mm
Second resistor patterns 332b, c at both ends: 179 W/43 mm=4.16 W/mm

When the longitudinal length of the second resistor patterns 332b, 332c is 43 mm and the second resistor patterns 332b, 332c are folded four times (five rows), the total length of the resistor patterns 332b, 332c is 215 mm. The heat density [W/mm] is 179 W/215 mm = 0.83 [W/mm], which is the same as the heat density of the first resistor pattern 332a described above. This means that the three resistor patterns 332a to 332c can be formed from a resistor material with the same resistivity. This allows the three resistor patterns 332a to 332c to be screen printed simultaneously, which contributes to lower costs.

(Resistor pattern with tapered ends)
7A is a plan view of the heater member 330 in which the ends of the resistor patterns 332a to 332c are inclined. More specifically, the ends of the three resistor patterns 332a to 332c at the center and both ends in the longitudinal direction are inclined at a predetermined angle with respect to the short side direction (paper passing direction). The layout of thermistors TM1 to TM3 and thermostats TH1 and TH2 is the same as in FIG. 6A.

In this embodiment, both ends of the longitudinal direction of each of the resistance patterns 332a to 332c are inclined at approximately 30° with respect to the short direction (paper feed direction). By inclining both ends of the longitudinal direction in this manner, it is possible to suppress a partial drop in temperature of the fixing belt 310.

In other words, the gap between the first resistance pattern 332a in the center and the second resistance patterns 332b, 332c on the left and right is not linearly visible in the short direction of FIG. 7A. This makes it possible to prevent the fixing belt 310 moving in the paper feed direction from being partially insufficiently heated when the resistance patterns 332a to 332c are generating heat, resulting in a drop in temperature.

Both longitudinal ends of the five rows of resistors 332a1 to 332a5 of the first resistor pattern 332a are connected in parallel to electrodes 337g and 337i via conductors 338j-338k and 338g-338l with lower resistivity than the resistors 332a1 to 332a5. The second resistor patterns 332b and 332c at both ends are connected in parallel to electrodes 337h and 337i via conductors 338h, 338i and 338j with lower resistivity. The right electrode 337i is connected to one pole of a 100V AC power supply PW, and the opposite electrodes 337g and 337h are connected to the other pole of the 100V AC power supply PW via switches SW1 and SW2.

Therefore, by operating the switches SW1 and SW2, the central resistor pattern 332a and the resistor patterns 332b and 332c at both ends can be energized/cut off independently. This allows the fixing device 300 to be adapted to various paper sizes, and by turning off the power to unnecessary parts, the energy saving performance of the fixing device 300 can be improved. In addition, by operating the switch SW2 to intermittently energize and heat only the second resistor patterns 332b and 332c at both ends, the tendency for temperature sagging at both ends of the paper passing portion of the fixing belt 310 can be suppressed.

The arrangement of switches SW1 and SW2 can also be changed so that switches SW1 and SW2 are connected in series, as shown in the dashed rectangular frame in FIG. 7A. That is, in the lower dashed rectangular frame in FIG. 7A, switch SW2 branches off between switch SW1 and electrode 337g. By changing the position of switch SW1, it is possible to switch between ON-OFF control of central resistor pattern 332a and ON-OFF control of full-width resistor patterns 332a to 332c.

(Parallel connection by conductors)
The left ends (areas surrounded by dashed lines) of the five rows of resistors 332a1 to 332a5 constituting the above-mentioned central first resistor pattern 332a can be connected in parallel with five conductors 338j1 to 338j5 as shown in Fig. 7B, instead of the conductor 338k in Fig. 7A. Similarly, on the opposite side of the resistors 332a1 to 332a5, they can be connected in parallel with five conductors connected to conductor 338g, instead of the conductor 338l in Fig. 7A.

More specifically, in Figure 7B, parts of the conductors 338j1 to 338j5 overlap the ends of the resistors 332a1 to 332a5 in the short-side direction (paper feed direction) of the resistors 332a1 to 332a5 in the shaded areas. The conductors 338c1 to 338c5 do not overlap continuously with the ends of the resistors 332a1 to 332a5 in the short-side direction.

Assuming that each resistor 332a1 to 332a5 has a width b in the short side direction, the conductors 338j1 to 338j5 overlap the ends of each resistor 332a1 to 332a5 with a short side width of b-c as indicated by diagonal lines. Therefore, at the end of the first row of resistor 332a1, a short side width c remains that does not overlap with conductor 338j1. The second to fifth rows of resistors 332a2 to 332a5 also have a short side width of 2c-b that does not overlap with conductors 338j2 to 338j5.

As a result, at the ends of resistors 332a1-332a5, heat is generated at the short-side widths c and 2c-b where conductors 338c1-338c5 do not overlap. This makes it possible to suppress temperature drops at the ends of resistors 332a1-332a5. The shaded areas do not generate heat, but because the shaded areas are distributed in the longitudinal direction, it is possible to suppress partial temperature drops in fixing belt 310 moving in the paper feed direction.

In the above description, the five conductors 338c1 to 338c5 are arranged linearly in the short side direction as shown in Figures 6B to 6D, or the five conductors 338j1 to 338j5 are arranged at an angle to the short side direction as shown in Figure 7B. However, the arrangement of the conductors is not limited to these.

In other words, the present invention also includes an arrangement in which the number of conductors at the same position in the longitudinal direction of the first resistor pattern 332a is reduced. In FIG. 8, of the five conductors 338c1 to 338c5, three conductors 338c1, 338c4, and 338c5 are at the same position in the longitudinal direction, but the remaining two conductors 338c2 and 338c3 are at different positions from the three conductors 338c1, 338c4, and 338c5. In this way, by dispersing the five conductors 338c1 to 338c5 in the longitudinal direction, it is possible to suppress a drop in temperature.

(Other types of fixing devices)

In addition to the fixing device 300 described above, the present invention can also be applied to fixing devices 300 as shown in Figures 9 to 11. The fixing device 300 shown in Figure 9 has a pressure roller 370 disposed on the side of the fixing belt 310 opposite the pressure roller 320, and is configured to sandwich and heat the fixing belt 310 between this pressure roller 370 and a heater member 330.

On the other hand, on the pressure roller 320 side, a nip forming member 380 is disposed on the inner circumference of the fixing belt 310. The nip forming member 380 is supported by a stay 350, and the fixing belt 310 is sandwiched between the nip forming member 380 and the pressure roller 320 to form a nip N.

In the fixing device 300 shown in FIG. 10, a heat-generating member is disposed inside the fixing belt 310. Instead of omitting the pressure roller 370 described above, this heat-generating member has a base material 341 and an insulating layer 385 with an arc-shaped cross section to match the curvature of the fixing belt 310 in order to increase the circumferential contact length with the fixing belt 310. The resistance member 370 is disposed in the center of the arc-shaped base material 341. The rest is the same as the fixing device in FIG. 9.

The fixing device 300 shown in FIG. 11 is provided with a pressure belt 390 in addition to the fixing belt 310, and is configured with a heating nip (first nip) N1 and a fixing nip (second nip) N2 separated from each other. That is, a nip forming member 380 and a stay 381 are arranged on the opposite side of the pressure roller 320 from the fixing belt 310 side, and the pressure belt 390 is arranged rotatably so as to enclose the nip forming member 380 and the stay 381.

Then, the paper P is passed through the fixing nip N2 between the pressure belt 390 and the pressure roller 320, and the paper P is heated and pressurized to fix the image. The rest of the configuration is the same as the fixing device 300 shown in FIG. 2B.

The above describes various heater members 330 and fixing devices 300, but the present invention is not limited to the above-described embodiments and can be modified in various ways. For example, the temperature detection member of the above-described embodiment may be a semiconductor such as a thermistor whose resistance value changes with temperature, or a diode, transistor, or other device whose characteristic value changes with temperature characteristics.

The current interrupting member is not limited to a thermostat, and a temperature fuse or thermal protector can be used instead. The number of first resistors 332a1 to 332a5 in the first resistor pattern 332a in the above embodiment can be increased or decreased as necessary. In addition, the first resistor pattern 332a can be arranged in multiple patterns in the longitudinal direction, in addition to being arranged in a single pattern in the longitudinal center of the substrate 331, and can be arranged with, for example, fewer resistor patterns than in the past.

The heater member according to the present invention can be applied to fixing devices that directly heat a thin fixing belt, as well as to heat roller type fixing devices with a heater member disposed on the inner circumference. The heater member according to the present invention is not only applicable to fixing devices. For example, the heater member according to the present invention can also be applied to a drying device installed in an inkjet type image forming device to dry ink applied to paper, or to a heater in an inkjet print head.

Furthermore, the heater member according to the present invention can also be applied to a coating device (laminator) that heat-presses a film as a coating member onto the surface of a sheet material such as paper while the sheet material is transported by a belt member. The heater member according to the present invention is not limited to belt heating devices that heat a belt member, but can also be applied to heating devices that do not have a belt member.

1Y, 1M, 1C, 1Bk: Imaging unit 2: Photoconductor (image carrier)
3: Charging device 4: Developing device 4a: Developer carrier 5: Drum cleaning device 5a: Cleaning blade 6: Exposure device 6a: Mirror 7: Paper feed device 8: Transfer device 10: Paper discharge device 11: Intermediate transfer belt 12: Primary transfer roller 13: Secondary transfer roller 14: Paper transport path 15: Timing roller 50: Paper feed device 60: Paper feed roller 100: Image forming device 103: Image forming device main body 250: Pair of registration rollers 300: Fixing device 310: Fixing belt 320: Pressure roller 321: Iron core 321: Core 322: Elastic layer 323: Release layer 330, 330': Heater member 331: Base material 332: Resistor pattern 332a: First resistor pattern 332a1 to 332a5: First resistor 332b, 332c: Second resistor pattern 333: Insulating layer 334, 335: Insulating glass 336: Coating 337a to 337f: Electrodes 338a to 338l: Conductors 344: Heater holder 344a: Recess 344b: Rib portion 350: Stay 360: Heater substrate 370: Pressing roller 380: Nip forming member 381: Stay 390: Pressure belt Lb: Laser light N: Nip P: Paper PW: Power source SW1, SW2: Switches
TM1 to TM3: Thermistors (temperature detection components) TH1, TH2: Thermostats (current interruption components)
T: Transfer means

Patent No. 6336026 JP 2016-6499 A Patent No. 6228458

Claims (9)

a resistor pattern having a plurality of rows of resistors formed in a longitudinal direction of a base material and generating heat when energized, the plurality of rows of resistors being arranged spaced apart from each other in a lateral direction perpendicular to the longitudinal direction of the base material;
a conductor having a resistivity smaller than that of the resistor, connecting ends of the resistors adjacent to each other in parallel at both ends of the resistor pattern in the longitudinal direction, a part of the conductor extending in the lateral direction and partially overlapping the ends of the resistors;
having
When the width of the end of the resistor in the short-side direction is d1 and the width of the resistor other than the end is d2 in the short-side direction, d2<d1, and the width of the part of the conductor that partially overlaps the end of the resistor with width d1 is d1-d2 in the short-side direction.
A heater member characterized by: The heater member of claim 1, characterized in that the number of resistors in the resistor pattern is three or more, and the multiple conductors that connect the ends of the resistors in parallel are arranged at multiple different positions in the longitudinal direction. 3. The heater element of claim 2 , wherein a plurality of said conductors are arranged on a line inclined relative to said longitudinal direction. 4. The heater member according to claim 1, wherein a temperature detection member for detecting a temperature of the resistance pattern is arranged overlapping the resistor at a position spaced apart from the conductor in the longitudinal direction. a sleeve-shaped rotating member having flexibility;
The heater member according to any one of claims 1 to 4 , which is in sliding contact with an inner periphery of the rotating member;
a pressure member that sandwiches the rotary member and is in pressure contact with the heater member to form a nip between the rotary member and the pressure member,
A heating device comprising: a heater member that transfers heat from the heater member to the sheet material via the rotating member when the sheet material is nipped and conveyed by the nip. 6. A fixing device comprising the heating device of claim 5 , wherein a toner image carried on said sheet material is heated and fixed by passing said sheet material through said nip. a heater holder for holding a heater member, the heater holder having a plurality of ribs formed in the longitudinal direction and adapted to be in sliding contact with an inner periphery of the rotating member;
7. The fixing device according to claim 6, wherein the heater member has the resistor pattern as a first resistor pattern and has a second resistor pattern formed on both sides of the first resistor pattern in the longitudinal direction, and the boundary between the first resistor pattern and the second resistor pattern is shifted in position in the lateral direction so as not to overlap with the rib portion. 8. The fixing device according to claim 7 , wherein the second resistor pattern has second resistors arranged in a zigzag pattern in the lateral direction of the base material, the second resistors being connected in parallel to one another. 9. An image forming apparatus comprising: a paper feeder; an image forming section; a transfer device; and the fixing device according to claim 6 .

Images