Heater, fixing device

Abstract

If the longitudinal heating length of a heater using a PTC heating element, where the rate of resistance change changes at the Curie point, is greater than or equal to the longitudinal heating length of a heater using a resistance heating element that does not have a Curie point, then power consumption will be wasted when feeding narrow paper. [Solution] A fixing device for fixing an unfixed toner image formed on a recording material to the recording material, comprising a heating member for heating a belt and a pressurizing rotating body that forms a fixing nip between itself and the belt for clamping and transporting the recording material and for rotationally driving the belt, wherein the heating member comprises a substrate 610, a first heater 620 having a resistive element having a Curie point arranged along the longitudinal direction of the substrate, and a second heater 630 having a resistive heating element without a Curie point arranged on the substrate, wherein the longitudinal length of the first heater is shorter than the longitudinal length of the second heater.

Description

TECHNICAL FIELD

[0001] The present invention relates to a heater for heating an image on a sheet, and a fixing apparatus provided with the heater. BACKGROUND ART

[0002] An electrophotographic image forming apparatus includes a fixing apparatus that fixes a toner image transferred onto a recording medium such as paper. The fixing apparatus includes a belt-shaped fixing member heated by a heater, and a pressure member disposed to face the fixing member, and in a nip portion formed between the fixing member and the pressure member, the paper on which the toner image is placed is passed, and the toner image is fixed by heating and pressing (thermocompression bonding).

[0003] In general, such a heater has an elongated substrate, a heating element provided on one surface of the substrate and extending in the longitudinal direction of the substrate, and a protective portion covering the heating element. The width of paper to be passed varies, and the longitudinal size of the heater is designed to match the maximum paper width. However, when a narrow-width paper is passed, the nip portion that the paper does not contact may rapidly overheat (hereinafter referred to as temperature rise in non-paper-passing portion), which may damage the fixing member.

[0004] The heater disclosed in Patent Document 1 below is a hybrid heater having two types of heating methods each using a positive characteristic heating element material (PTC heating element) and a resistance heating element that generates heat by forming a resistance trace on a ceramic substrate. Further, Patent Document 1 describes an operation at the time of printing using the above hybrid heater. It is proposed that a heater using a resistance heating element (hereinafter referred to as resistance heating heater) is preferentially used during warm-up and when wide paper is passed, and a PTC heater is used when narrow paper is passed to suppress temperature rise in the non-paper-passing portion. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0005] PATENT DOCUMENT 1 U.S. Patent No. 9551962 SUMMARY OF THE INVENTION [Problems that the invention aims to solve]

[0006] While PTC heaters suppress power input to the non-paper-feed section when feeding narrow paper, they cannot reduce it to zero. The hybrid heater described in Patent Document 1 is designed so that the longitudinal length of the PTC heater is longer than the longitudinal length of the resistance heating heater, which leads to the following problems.

[0007] For example, consider the case of creating an image forming apparatus that can handle paper up to 320 mm wide (e.g., SRA3 size), with a commonly used paper width of 297 mm (e.g., A3 size), which is slightly smaller than the maximum paper width. In order to fix the toner image in the area within the maximum paper width, the longitudinal length of the resistance heating element used during warm-up and when feeding wide paper needs to be approximately 320 mm, which is the maximum paper width. If the longitudinal length of the PTC heater is designed to be 320 mm or longer, as in the hybrid heater described in Patent Document 1, the area outside the 297 mm paper width will be unnecessarily heated, potentially compromising energy efficiency.

[0008] This invention was developed and proposed in view of the above-mentioned problems. The object of this invention is to propose a hybrid heater having two heating methods, a PTC heater (first heater) and a resistance heating heater (second heater), that suppresses temperature rise in the non-paper-feeding section while providing an energy-saving heater and fixing device. [Means for solving the problem]

[0009] To achieve the above objective, the fixing device according to the present invention is a fixing device for fixing an unfixed toner image formed on a recording material to the recording material, and comprises an endless belt, a heating member for heating the belt, and a pressurizing rotating body that forms a fixing nip between itself and the belt for gripping and transporting the recording material and for rotationally driving the belt, wherein the heating member comprises a substrate, a first heater having a resistive element having a Curie point within the operating temperature range of the fixing device arranged along the longitudinal direction of the substrate, and a second heater having a resistive heating element not having a Curie point within the operating temperature range arranged on the substrate, wherein the longitudinal length of the first heater is shorter than the longitudinal length of the second heater. [Effects of the Invention]

[0010] According to the present invention, in a hybrid heater having two heating methods, a PTC heater and a resistance heating heater, it is possible to improve energy-saving performance while suppressing the temperature rise of the non-paper-feeding section. [Brief explanation of the drawing]

[0011] [Figure 1] Cross-sectional view of an image forming apparatus according to an embodiment of the present invention. [Figure 2] Cross-sectional view of a fixing device according to an embodiment of the present invention. [Figure 3] Front view of a fixing device according to an embodiment of the present invention. [Figure 4] Longitudinal side view of a heater according to an embodiment of the present invention [Figure 5] Short cross-sectional view of a heater according to an embodiment of the present invention [Figure 6] Surface transmission diagram of a heater according to an embodiment of the present invention [Figure 7] Rear view hierarchical diagram of a heater according to an embodiment of the present invention [Figure 8] Diagram illustrating the longitudinal heating length of the PTC heating element and resistance heating element according to an embodiment of the present invention. [Figure 9] Explanatory diagram of the heater surface and connector according to an embodiment of the present invention [Figure 10] Diagram illustrating the back surface and connector of a heater according to an embodiment of the present invention. [Figure 11] Explanatory diagram of a heater cross section and contact terminals according to an embodiment of the present invention [Figure 12] Graph of resistance-temperature characteristics of a PTC heating element according to an embodiment of the present invention [Figure 13] Explanatory diagram of effects of the embodiment of the present invention [Description of Embodiments]

[0012] Hereinafter, embodiments of the heater and the fixing device according to the present invention will be described with reference to the drawings.

[0013] [Present Embodiment] [Image Forming Apparatus] Figure 1 is a cross-sectional view of a printer 1 which is the image forming apparatus of the present embodiment. The printer 1 is an image forming apparatus that transfers a toner image formed on a photosensitive drum 11 in an image forming unit 10 onto a sheet P as a recording material, fixes the image on the sheet P by a fixing device 40, and forms the toner image (image) on the sheet P. Hereinafter, the configuration will be described in detail with reference to Figure 1.

[0014] As shown in Figure 1, the printer 1 is provided with an image forming unit (image forming station) 10 that forms toner images of respective colors Y (yellow), M (magenta), C (cyan), and Bk (black). The image forming unit 10 includes four photosensitive drums 11 (11Y, 11M, 11C, 11K) corresponding to the respective colors Y, M, C, and K (Bk) in order from the left side of Figure 1. Further, the following components having the same configuration are arranged around each photosensitive drum 11: a charger 12 (12Y, 12M, 12C, 12K), an exposure device 13 (13Y, 13M, 13C, 13K), a developing device 14 (14Y, 14M, 14C, 14K), a primary transfer blade 17 (17Y, 17M, 17C, 17K), and a cleaner 15 (15Y, 15M, 15C, 15K). Hereinafter, the configuration for forming the Bk color toner image will be representatively described, and the configurations corresponding to other colors will be denoted by the same reference numerals with descriptions thereof omitted. Therefore, unless otherwise distinguished, the above-described configurations are expressed as follows: that is, they are simply referred to as the photosensitive drum 11, the charger 12, the exposure device 13, the developing device 14, the primary transfer blade 17, and the cleaner 15.

[0015] The photosensitive drum 11 serving as an electrophotographic photosensitive member is rotationally driven in the arrow direction (the counterclockwise direction in Figure 1) by a driving source (not shown). Around the photosensitive drum 11, the charger 12, the exposure device 13, the developing device 14, the primary transfer blade 17, and the cleaner 15 are sequentially arranged along the rotational direction thereof.

[0016] The surface of the photosensitive drum 11 is pre-charged by the charger 12. Thereafter, the photosensitive drum 11 is exposed by the exposure device 13 that irradiates laser light in accordance with image information, so that an electrostatic latent image is formed thereon. This electrostatic latent image is developed into a Bk color toner image by the developing device 14. At this time, the same process is performed for other colors as well. Then, the toner images on each photosensitive drum 11 are sequentially primarily transferred onto an intermediate transfer belt 31 by the primary transfer blade 17. After the primary transfer, toner remaining on the photosensitive drum 11 without being transferred is removed by the cleaner 15. In this manner, the surface of the photosensitive drum 11 is cleaned, and a state enabling the next image formation is achieved.

[0017] Meanwhile, the sheets P placed in the feed cassette 20 or multi-feed tray 25 are fed one by one by a feed mechanism (not shown) and sent to the register roller pair 23. A sheet P is a material on which an image is formed on its surface. Specific examples of sheets P include plain paper, cardboard, resin sheet-like material, and film for overhead projectors. The register roller pair 23 stops the sheet P and straightens its orientation if it is skewed relative to the transport direction. Then, the register roller pair 23 synchronizes with the toner image on the intermediate transfer belt 31 and feeds the sheet P between the intermediate transfer belt 31 and the secondary transfer roller 35. The intermediate transfer roller 35 transfers the color toner image on the intermediate transfer belt 31 to the sheet P. After that, the sheet P is fed toward the fixing device (image heating device) 40. The fixing device 40 then heats and pressurizes the unfixed toner image T formed on the sheet P to fix it to the sheet P.

[0018] [Fusing device] Next, we will describe the fuser unit 40, which is an image heating device used in printer 1. Figure 2 is a cross-sectional view of the fuser unit 40. Figure 3 is a front view of the fuser unit 40.

[0019] The fixing device 40 is an image heating device that heats the image on the sheet using a heater unit 60 (hereinafter referred to as unit 60). Unit 60 has a low heat capacity configuration in which an endless, flexible, thin fixing belt 603 (hereinafter referred to as belt 603) is heated by a heater 600 that contacts the inner surface of belt 603. Therefore, belt 603 can be heated efficiently, and it has excellent start-up performance when fixing begins. As shown in Figure 2, when belt 603 is clamped between heater 600 and pressure roller 70 (hereinafter referred to as roller 70), a fixing nip section N is formed. In other words, a fixing nip section is formed between belt 603 and roller 70, which acts as a pressure rotating body, to clamp and transport the recording material. The pressure roller 70 also clamps and transports belt 603. Then, belt 603 rotates in the direction of the arrow (clockwise, Figure 2), and roller 70 rotates in the direction of the arrow (counterclockwise, Figure 2), clamping and transporting the sheet P supplied to the nip section N. At this time, the heat from the heater 600 is applied to the sheet P via the belt 603, so that the toner image T on the sheet P is heated and pressurized at the nip section N and fixed to the sheet P. The sheet P that has passed through the fixing nip section N is separated from the belt 603 and discharged. In this embodiment, the fixing process is performed as described above.

[0020] Unit 60 is a unit for heating and pressurizing the image on sheet P. Unit 60 is installed so that its longitudinal direction is parallel to the longitudinal direction of roller 70. Unit 60 includes a heater 600, a heater holder 601, a support stay 602, and a belt 603.

[0021] The heater 600 is a heating element that slidably contacts the inner surface of the belt 603 to heat the belt 603. The heater 600 also presses the belt 603 from its inner surface toward the roller 70 so that the width of the nip portion N becomes the desired width. The shape of the heater 600 will be described in detail later, but it is a plate-shaped member with a width (length in the left-right direction in Figure 2) of approximately 15 mm and a longitudinal length (length in the back-front direction in Figure 2) of approximately 400 mm. The heater 600 comprises a substrate 610 whose longitudinal side is perpendicular to the direction of conveying the sheet P (the width direction of the sheet P), a resistance heating element 620 (a resistance heating element without a Curie point), and a plurality of PTC heating elements 630 (resistive elements with a Curie point) arranged along the longitudinal direction.

[0022] The heater 600 is fixed to the lower surface of the heater holder 601 along the longitudinal direction of the heater holder 601. In this embodiment, the PTC heating element 630 is provided on the back side of the substrate 610 (the side that does not slide against the belt 603), but it may also be provided on the front side of the substrate 610 (the side that slides against the belt 603). In other words, in a cross section perpendicular to the transport direction, the resistance heating element 620 as the second heater is positioned closer to the pressurized rotating body than the PTC heater as the first heater, but the opposite arrangement may also be used. However, since multiple PTC heating elements 630 are arranged, it is desirable to provide a component that provides a uniform heating effect so that the heat supplied to the belt 603 does not become uneven due to non-heating parts between the elements. Details of the heater 600 will be described later.

[0023] The belt 603 is a cylindrical (endless) belt (film) that heats the image on the sheet at the nip portion N. For example, the belt 603 may consist of a base material 603a with an elastic layer 603b, and a release layer 603c on the elastic layer 603b. The base material 603a can be a metal material such as stainless steel or nickel, or a heat-resistant resin such as polyimide. The elastic layer 603b can be a material with elasticity and heat resistance, such as silicone rubber or fluororubber. The release layer 603c can be a fluororesin or a silicone resin.

[0024] In this embodiment, the belt 603 uses a cylindrical nickel member as the base material 603a, with an outer diameter of approximately φ30 mm, a longitudinal length (width direction, front-back direction in Figure 2) of approximately 330 mm, and a thickness of approximately 30 μm. An elastic layer 603b of silicone rubber with a thickness of approximately 400 μm is formed on this base material 603a, and a fluororesin tube (release layer 603c) with a thickness of approximately 20 μm is further coated on the elastic layer 603b. A polyimide layer with a thickness of approximately 10 μm may be provided as a sliding layer 603d on the substrate 610 on the contact surface side with the belt 603. When a polyimide layer is provided, the frictional resistance between the fixing belt 603 and the heater 600 can be reduced, thereby suppressing wear on the inner surface of the belt 603. To further improve sliding properties, a lubricant such as grease may be applied to the inner surface of the belt.

[0025] The heater holder 601 (hereinafter referred to as holder 601) is a component that holds the heater 600 in a state where it is pressed toward the inner surface of the belt 603. Furthermore, the holder 601 has a semi-circular cross-section (the surface shown in Figure 2) and functions to restrict the rotational trajectory of the belt 603. A heat-resistant resin or the like is used for the holder 601. In this example, DuPont's Zenite 7755 (trade name) was used.

[0026] The support stay 602 supports the heater 600 via the holder 601. The support stay 602 is preferably made of a material that is resistant to bending even when subjected to high pressure, and in this embodiment, SUS304 (stainless steel) was used.

[0027] As shown in Figure 3, the support stay 602 is supported at both ends in its longitudinal direction by the left and right flanges 411a and 411b. The flanges 411a and 411b are collectively referred to as flange 411. Flange 411 restricts the longitudinal movement and circumferential shape of the belt 603. Heat-resistant resin or the like is used for flange 411. In this embodiment, PPS (polyphenylene sulfide) was used.

[0028] A compressed pressure spring 415a is provided between flange 411a and pressure arm 414a. A compressed pressure spring 415b is also provided between flange 411b and pressure arm 414b. Hereafter, pressure springs 415a and 415b will be collectively referred to as pressure spring 415. With this configuration, the elastic force of the pressure springs 415 is transmitted to the heater 600 via flange 411 and support stay 602. The belt 603 is then pressed against the upper surface of roller 70 with a predetermined pressing force, forming a nip portion N of a predetermined width. In this embodiment, the pressing force is approximately 156.8 N at one end and the total pressing force is approximately 313.6 N (32 kgf).

[0029] As shown in Figure 3, the connector 700 is a power supply member that electrically connects to the heater 600 to supply power to the heater 600. The connector 700 is detachably attached to one end of the heater 600 in the longitudinal direction. Because the connector 700 is provided to the heater 600 in a way that allows for easy attachment and detachment, the assembly of the fixing device 40 and the replacement of the belt 603 or heater 600 in the event of damage can be easily performed, resulting in excellent maintainability.

[0030] As shown in Figure 2, the roller 70 is a nip-forming member that forms a nip portion N by cooperating with the belt 603 by contacting the outer surface of the belt 603. The roller 70 has a multilayer structure in which an elastic layer 72 is sequentially laminated on a metal core 71, and a release layer 73 is sequentially laminated on the elastic layer 72. Examples of materials for the core 71 include SUS (stainless steel), SUM (sulfur and sulfur composite free-cutting steel), and Al (aluminum). Examples of materials for the elastic layer 72 include an elastic solid rubber layer, an elastic sponge rubber layer, or an elastic cellular rubber layer. Examples of materials for the release layer 73 include fluororesin materials.

[0031] The roller 70 in this embodiment has a configuration comprising an iron core 71, an elastic layer 72 of foamed silicone rubber on the core 71, and a release layer 73 of a fluororesin tube on the elastic layer 72. The dimensions of the portion of the roller 70 having the elastic layer 72 and the release layer 73 are an outer diameter of approximately φ25 mm and a length of approximately 330 mm.

[0032] Figure 4 is a longitudinal side view of the heater 600 in Embodiment 1. The thermistor 660, installed on the back side (opposite the sliding surface) of the heater 600, is responsible for detecting the temperature of the heater 600. The thermistor is connected to the control circuit via an A / D converter and transmits an output corresponding to the detected temperature to the control circuit.

[0033] The control circuit is a circuit equipped with a CPU that performs calculations associated with various controls and a non-volatile medium such as ROM that stores various programs. The ROM stores programs, and the CPU reads and executes them to perform various controls. Note that the control circuit may also be an integrated circuit such as an ASIC, as long as it performs the same function. The control circuit is electrically connected to the power supply to control the power supply's energization. The control circuit is also electrically connected to the thermistor to acquire its output. The control circuit reflects the temperature information acquired from the thermistor in the power supply's energization control. In other words, the control circuit controls the power supplied to the heater 600 via the power supply based on the thermistor's output. In this embodiment, the control circuit adjusts the amount of heat generated by the heater 600 by controlling the wavenumber of the power supply's output. By performing this control, the heater 600 is kept constant at a predetermined temperature for fixing (for example, approximately 180°C).

[0034] As shown in Figure 3, the core metal 71 of the roller 70 is rotatably held via bearings 42a and 42b on the rear and front sides of the side plate 41. A gear G is provided at one end of the core metal 71 in the axial direction, and transmits the driving force of the motor M to the core metal 71 of the roller 70. As shown in Figure 2, the roller 70, to which the driving force from the motor M has been transmitted, rotates in the direction of the arrow (clockwise). Then, at the nip section N, the driving force is transmitted to the belt 603 via the roller 70, causing the belt 603 to rotate in the direction of the arrow (counterclockwise).

[0035] Motor M is a drive mechanism that drives the roller 70 via gear G. The control circuit is electrically connected to motor M to control the power supply to motor M. When power is supplied by the control circuit, motor M starts rotating (driving) gear G.

[0036] The control circuit controls the rotation of motor M. The control circuit rotates roller 70 and belt 603 at a predetermined speed via motor M. Then, as the fixing process is performed, the speed of sheet P, which is held and conveyed by the nip section N, is adjusted to a predetermined process speed (for example, approximately 200 mm / sec).

[0037] [heater] Next, the heater 600 used in the fixing device 40 will be described in detail using the longitudinal side view in Figure 4 and the short cross-sectional view in Figure 5 (position A in Figure 4).

[0038] As shown in Figure 4, electrical contacts 621, 623, and 633 are provided as part of a conductor pattern on one longitudinal end 610a of the substrate 610. On the other longitudinal end 610c of the substrate 610, a resistive heating element 620 and a PTC heating element 630 are provided, as will be described in more detail later, as shown in Figure 5. An intermediate region 610b is provided between the one end 610a and the other end 610c of the substrate.

[0039] The resistive heating element 620 and the PTC heating element 630 are resistors that generate Joule heat when an electric current is passed through them. The resistive heating element 620 is formed as a single heating element along its longitudinal direction on the substrate 610 and is located in region 610c near the approximate center of the substrate 610. The resistive heating element 620 is adjusted to have a width (shorter side length of the substrate 610) of 1 to 4 mm and a thickness of 5 to 20 μm so that its resistance value is a desired value. In this embodiment, the resistive heating element 620 has a width of approximately 2 mm and a thickness of approximately 10 μm. The total longitudinal length of the resistive heating element 620 is 322 mm. The PTC heating element 630 is a rectangular parallelepiped element, and multiple PTC heating elements are arranged longitudinally in region 610c near the approximate center of the substrate 610. In this embodiment, each element had a width (shorter side of the substrate 610) of approximately 12.4 mm, a length (longer side of the substrate 610) of approximately 23 mm, and a thickness of approximately 1.3 mm. Thirteen of these elements were arranged along the longitudinal direction. The total longitudinal length from end to end of the 13 PTC heating elements is 299 mm.

[0040] As shown in Figure 5, the configuration in the thickness direction of the short cross-section of the heater 600 includes a substrate 610, a resistive heating element 620 and a conductor pattern (wiring) on ​​the surface side (sliding surface side) of the substrate 610, and an insulating coating layer 640 covering the resistive heating element 620 and the conductor pattern. On the back side (opposite the sliding surface) of the substrate 610 is a conductor pattern (wiring), and in the 610c region, the substrate electrode 632, PTC heating element 630, and electrode 631 are stacked in order from the substrate 610. A thermistor 660 for detecting the temperature of the heater 600 is provided on electrode 631. In the 610b region on the back side (opposite the sliding surface) of the substrate 610, there is a spacer 634 with a thickness approximately equal to the thickness when the substrate electrode 632 and PTC heating element 630 are stacked.

[0041] The substrate 610 is a component that determines the dimensions and shape of the heater 600 and is a component that can contact the belt 603 along its longitudinal direction. The material used for the substrate 610 is a ceramic material such as alumina or aluminum nitride, which has excellent heat resistance, thermal conductivity, and electrical insulation properties. In this embodiment, an aluminum nitride plate member with a longitudinal length (left-right direction in Figure 4), a short-side length (left-right direction in Figure 5), and a thickness of approximately 0.7 mm is used.

[0042] Figure 6 is a surface (sliding surface side) transmission view of the heater 600. On the surface (sliding surface side) of the aluminum nitride substrate 610, a resistive heating element 620 and a conductor pattern (including electrical contacts 621, 623 and conductive pattern 622) are formed using a conductive thick-film paste and a thick-film printing method (screen printing method). In this embodiment, silver paste is used for the conductor pattern to reduce resistivity, and silver-palladium alloy paste is used for the resistive heating element 620 to increase resistivity. As shown in Figure 5, the resistive heating element 620 and the conductor pattern are covered with an insulating coating layer 640 made of heat-resistant glass with a thickness of approximately 50 μm, providing electrical protection to prevent leakage and short circuits. In this embodiment, heat-resistant glass is used for the insulating coating layer 640, but a heat-resistant resin such as polyimide may also be used. Electrical contacts 621 and 623 are not covered with the insulating coating layer 640 because they are electrically connected to the connector 700. The other end 610c in the longitudinal direction of the substrate 610 has a resistive heating element 620 and a conductive pattern 622, and the resistive heating element 620 is folded back by the conductive pattern 622.

[0043] Figure 7 is a hierarchical diagram of the back surface (opposite the sliding surface) of the heater 600. Figure 7(a) is a diagram illustrating the first layer. On the back side of the substrate 610, substrate electrodes 632 and a conductive pattern (including electrical contacts 633) are formed using a conductive thick-film paste and a thick-film printing method (screen printing method). The substrate electrodes 632, conductive pattern, and electrical contacts 633 were printed using silver paste to reduce resistivity. Figure 7(b) is a diagram illustrating the second layer. The 610b region is provided with a spacer 634 made of heat-resistant resin. In the 610c region, multiple PTC heating elements 630 are arranged longitudinally on a sheet-like member 650f. The PTC heating element 630 is a heating element using a Positive Temperature Coefficient Thermal-Resistor. In this embodiment, a heating element that exhibits its properties by adding a small amount of rare earth elements to barium titanate (BaTiO3), a ferroelectric material, is used. PTC heating elements have a point (minimum point, Curie point) where resistance decreases with temperature, and the rate of resistance change changes at the Curie point. Since PTC heating elements have the property that their resistance increases significantly above the Curie point temperature, heaters using PTC heating elements (hereinafter referred to as PTC heaters) can be used as self-regulating heaters that operate to maintain a constant temperature. When narrow paper is fed through, even if the nip area where the paper does not make contact overheats, the current flowing to the heater decreases due to self-regulation, reducing the amount of heat generated and effectively suppressing the temperature rise of the non-paper-feeding area. On the other hand, PTC heating elements have the disadvantage of having a high resistance value near room temperature and a long warm-up time (the time it takes for the fixing device to reach the target temperature). However, by creating a hybrid heater that has two types of heating methods, using a positive-resistance heating element material (PTC heating element) and a resistance heating element that generates heat by forming a resistance trace on a ceramic substrate, it is possible to compensate for the shortcomings of PTC heaters. In other words, during warm-up, power is preferentially supplied to the resistance heating element, which has a low resistance value near room temperature, thereby compensating for the shortcomings of the PTC heater.

[0044] PTC heaters use a Curie temperature that is within the operating temperature range of the fixing device. In other words, the Curie temperature is within the operating temperature range of the fixing device, between room temperature (25°C) and the temperature at which the thermoswitch operates (e.g., 250°C). Similarly, heaters using heat-generating resistors will also have a temperature of around 1000°C at which the transfer resistance value increases sharply if the temperature continues to rise indefinitely, and the temperature will not rise any further. That is, the Curie temperature of a resistance heat-generating heater is outside the operating temperature range of the fixing device.

[0045] Figure 7(c) is a diagram illustrating the third layer. Electrodes 631 are provided to cover the spacer 634 and the PTC heating element 630. Since electrodes 631 conduct electricity from the substrate electrode 632 to the PTC heating element 630, it is preferable that they be made of a material with good conductivity; in this embodiment, SUS (stainless steel) is used. Since the spacer 634 is not energized, it is not necessary to cover it. Furthermore, if electrical contacts for energizing the substrate electrode 632 can be provided without using the spacer 634, then the spacer 634 becomes unnecessary. In addition, a thermistor 660 is provided to detect the temperature of the heater 600. Multiple thermistors 660 may be provided, and their placement does not necessarily have to be on the electrode 631; any location that can detect the temperature of the heater 600 is acceptable.

[0046] Figure 8 is an explanatory diagram illustrating the relationship and positional relationship between the total longitudinal length of the resistance heating element 620 and the total longitudinal length from end to end of the PTC heating element. In this embodiment, the transport center position in the width direction of the paper during paper feeding is set to be consistent regardless of the paper size. Therefore, the longitudinal center position of the resistance heating element 620, the longitudinal center position from end to end of the PTC heating element, and the width direction center position during paper transport are all positioned at the same location. As a result, the temperature distribution is symmetrical with respect to the center of the paper's width direction, regardless of the paper size.

[0047] The total longitudinal length Wa of the resistive heating element 620 is 322 mm, and the total longitudinal length Wb from end to end of the PTC heating element, which is located on the back surface of the heater 600, is 299 mm. The total longitudinal length Wb from end to end of the PTC heating element is shorter than the total longitudinal length Wa of the resistive heating element 620.

[0048] The reason the total length Wa of the resistive heating element 620 in the longitudinal direction was set to 322 mm is to ensure that it can heat the entire width of a sheet P of wide paper SRA3 size (width 320 mm), which is often requested for A3 size multifunction printers. This is because power is supplied to the resistive heating element 620 during startup and when feeding wide paper (details of the power supply method will be described later), hence the total length Wa of the resistive heating element 620 in the longitudinal direction was set to 322 mm.

[0049] The total length Wb of the PTC heating element in the longitudinal direction, from end to end, was set to 299 mm to ensure that the entire width of a sheet P of A3 size (width 297 mm), which is frequently used among paper sizes narrower than SRA3 size, can be heated. Furthermore, since power is supplied to the PTC heating element when narrow paper is fed through, the length was set to ensure that the entire width of frequently used paper types can be heated. From a power consumption perspective, it is most efficient to set the length of the PTC heater to approximately the maximum size of commonly used narrow paper. Alternatively, the length of the PTC heater in the longitudinal direction could be set to approximately the maximum printable width of the most frequently used paper type (A3 size) among paper types smaller than the maximum size that can be fed through.

[0050] In this embodiment, by shortening the total longitudinal length Wb from end to end of the PTC heating element to the total longitudinal length Wa of the resistance heating element 620, the energy-saving performance when feeding narrow paper is improved, but the effects will be described later.

[0051] The heater 600 in this embodiment is a hybrid heater. It consists of a resistive heating element 620 (second heater) with a resistive trace formed on the surface (sliding surface side) of the substrate 610, and a PTC heating element (first heater) with multiple PTC heating elements 630 arranged longitudinally on the back surface (opposite the sliding surface) of the substrate 610.

[0052] [connector] Next, the configuration of the connector 700 used in the fixing device 40 will be described in detail. Figure 9 is an explanatory diagram illustrating the front side (sliding surface side) of the connector 700 and the heater 600. Figure 10 is an explanatory diagram illustrating the back side (opposite side from the sliding surface) of the connector 700 and the heater 600. In this embodiment, the connector 700 is electrically connected to the heater 600 by being attached to the heater 600. In detail, the connector 700 has a contact terminal 720 that can be electrically connected by contacting the electrical contact 621, a contact terminal 710 that can be electrically connected by contacting the electrical contacts 623 and 633, and a contact terminal 730 that can be electrically connected by contacting the electrode 631. The connector 700 sandwiches the front and back of the area of ​​the belt 603 of the heater 600 that protrudes from the longitudinal direction, so that the connector 700 and the belt 603 do not come into contact, and each contact terminal is connected to each electrical contact. In the fixing device 40 of this embodiment, which has this configuration, soldering or the like is not used to connect the connector and the electrical contacts. Therefore, the connection between the heater 600, whose temperature rises during the fixing process, and the connector 700 can be maintained with high reliability. In addition, in the fixing device 40 of this embodiment, since the connector 700 is detachable from the heater 600, the belt 603 and the heater 600 can be easily replaced. The configuration of the connector 700 will be described in detail below with reference to the drawings.

[0053] As shown in Figures 9 and 10, the connector 700, equipped with metal contact terminals 710, 720, and 730, is attached to the heater 600 from the short side of the substrate 610 at one end 610a of the substrate. Figure 11 is an explanatory diagram of how each contact terminal 710, 720, and 730 is electrically connected to the electrodes on the heater substrate 610. Each contact terminal 710, 720, and 730 will be explained using contact terminal 720 as an example. As shown in Figure 11(a), contact terminal 720 is a component that electrically connects the electrical contact 621 and the control circuit. Contact terminal 710 is equipped with an electrical contact 721 for contacting the electrical contact 621 and a cable for connecting to the control circuit. Contact terminal 720 is U-shaped, and the heater 600 can be inserted into the U-shaped gap by moving it in the direction of the arrow in Figure 11(a). An electrical contact 721 is provided at the point where it contacts the electrical contact 621 of the contact terminal 720, and when this electrical contact 721 contacts the electrical contact 621, the electrical contact 621 and the contact terminal 720 are electrically connected. Because this electrical contact 721 has a leaf spring property, it makes contact with the electrical contact 621 while being pressed. Therefore, the contact terminal 720 can be fixed in place by sandwiching the front and back of the heater 600. Similarly, at the contact terminal 710, the electrical contact 623 and electrical contact 711 are in contact, as are the electrical contacts 633 and 712. At the contact terminal 730, the electrode 631 and electrical contact 732 are in contact. In the above description, an example was given in which the connector 700 is attached from the short end of the circuit board 610, but this is not the only way to attach the connector 700 to the circuit board 610. For example, the connector 700 may be attached from the long end of the circuit board.

[0054] [Method of supplying power to a hybrid heater] Next, the method of supplying power to the heater 600 will be explained. The heater 600 is a hybrid heater consisting of a second heater using a resistance heating element 620 on the surface side (sliding surface side) and a first heater with multiple PTC heating elements 630 arranged on the back side (opposite side from the sliding surface).

[0055] Figure 12 is a graph showing the resistance-temperature characteristics of the PTC heating element 630 in this embodiment. The resistivity at low temperature (room temperature) is approximately 150 Ω·cm, and the resistivity at approximately 200°C is approximately 110 Ω·cm. In this embodiment, 13 PTC heating elements 630 are arranged in parallel, so the combined resistance at low temperature is approximately 11.5 Ω, and the combined resistance at approximately 200°C is 8.5 Ω. When a voltage of 100 V is applied, the power consumption at low temperature is approximately 870 W, and the power consumption at approximately 200°C is approximately 1180 W. Therefore, the amount of heat generated by the first heater using the PTC heating element 630 is lower at low temperatures.

[0056] In this embodiment, the resistance of the second heater of the resistive heating element 620 is approximately 8.3Ω at room temperature, so when a voltage of 100V is applied, the power output is approximately 1200W. Given the limitations on the power available to the fixing device, in order to quickly raise the heater 600 to the target temperature, it is more efficient to supply the available power to the second heater of the resistive heating element 620 at or near room temperature. In this embodiment, the power supplied during startup is supplied only to the second heater of the resistive heating element 620.

[0057] Furthermore, when the fixing temperature rises to the target temperature and printing begins, the heaters to which power is supplied are switched according to the paper width. The second heater is located on the surface side (sliding surface side) of heater 600, so it is more efficient at supplying heat to sheet P than the first heater located on the back side, but when narrow paper is fed through, the non-feeding area heats up. Therefore, when feeding wide paper where heating of the non-feeding area is not an issue, power is supplied to the second heater during printing, and when feeding narrow paper, power is supplied to the first heater during printing.

[0058] [Verification of the improvement effect according to the present invention] A comparative simulation was performed between the conventional example (Pattern 1) and this embodiment (Pattern 2). In the conventional example, the "longitudinal heating length of the first heater," which has multiple PTC heating elements 630 arranged, and the "longitudinal heating length of the second heater," which uses a resistance heating element 620, were the same. In this embodiment, the "longitudinal heating length of the first heater" was shorter than the "longitudinal heating length of the second heater." The longitudinal heating length of the second heater using the resistance heating element 620 was 322 mm, and the longitudinal heating length of the first heater, which has multiple PTC heating elements 630 arranged, was 322 mm in Pattern 1 and 299 mm in Pattern 2.

[0059] Figure 13 is a graph comparing the heater temperatures in the non-paper-feed areas of Pattern 1 and Pattern 2 when the heater temperature rise in the non-paper-feed area saturates after continuous feeding of A3-sized paper (297 mm wide). In this embodiment, the longitudinal center position of the resistance heating element 620, the longitudinal center position from end to end of the PTC heating element, and the widthwise center position during paper transport are all positioned at approximately the same location. As the temperature distribution is symmetrical with respect to the widthwise center of the paper, the graph shows the temperature distribution of one side of the non-paper-feed area. In the region from the transport center to 148 mm, which is the paper-feed area for A3-sized paper, both Pattern 1 and Pattern 2 maintain a temperature of 180°C. On the other hand, it can be seen that there is a difference in temperature distribution in the non-paper-feed area outside of 148 mm. In Pattern 1, since the PTC heating element 630 is positioned in the region from 148 mm to 161 mm from the transport center, which is outside the paper-feed area for A3-sized paper, the temperature is maintained below the Curie point of 230°C during printing. In Pattern 2, since the PTC heating element 630 is not placed in the area outside the paper feeding area for A3 size paper, there is no temperature rise in the non-paper feeding area outside 148 mm, and the temperature decreases smoothly towards the outside. Thus, there is a significant difference in the heater temperature of the non-paper feeding area when A3 size paper is continuously fed between Pattern 1 and Pattern 2, and Pattern 2 can suppress unnecessary heating more effectively than Pattern 1.

[0060] [Example 1] In the above embodiment, the "longitudinal heating length of the second heater" using a resistance heating element 620 was set to 322 mm, which is sufficient to heat the entire area of ​​the paper size with the maximum paper feedable width (SRA3 size, width 320 mm). The "longitudinal heating length of the first heater" using multiple PTC heating elements 630 was set to 299 mm, which is sufficient to heat the entire area of ​​a frequently used paper size (A3 size, width 297 mm) that is narrower than the paper size with the maximum paper feedable width. However, the approach to heating length changes slightly when the printable width of the main unit is narrower than the maximum paper feedable width. For example, if the product specifications are such that the maximum paper size with the maximum paper feedable is SRA3 size (width 320 mm) and the maximum printable width is 305 mm (with a margin of 7.5 mm on each side for SRA3 size), the heating length of the heater should be set as follows.

[0061] To heat the area with a maximum printable width of 305 mm, the "longitudinal heating length of the second heater" using the resistance heating element 620 is set to 307 mm. When paper is fed with the paper transport position centered, the area heated by the resistance heating element 620 in the non-feeding area outside the width of A3 paper is 5 mm on each side, which is sufficiently small. Therefore, even if heating is done using the resistance heating element 620 when feeding A3 paper, the temperature rise in the non-feeding area does not become a problem that would damage the fixing member. Since the most frequently used paper width narrower than A3 paper (297 mm) is the width of LDR paper (279 mm), the "longitudinal heating length of the first heater" with multiple PTC heating elements 630 is set to 281 mm. This makes it possible to suppress the temperature rise in the non-feeding area and minimize unnecessary heating of the non-feeding area. [Explanation of Symbols]

[0062] 1. Printer 10 Image forming unit 40 Fixing device 600 Heater 610 circuit board 620 Resistive heating element (first heater) 630 PTC heating element (second heater)

Claims

1. A fixing device for fixing an unfixed toner image formed on a recording material to the recording material, An endless belt, A heating member for heating the belt, A pressing rotating body that forms a fixing nip between itself and the belt for gripping and transporting the recording material, and rotates the belt, In a fixing device having, The heating element is circuit board and A first heater is provided, which has a resistive element having a Curie point within the operating temperature range of the fixing device, arranged along the longitudinal direction of the substrate. A second heater is provided on the substrate, which has a resistance heating element that does not have a Curie point within the operating temperature range. It has, The longitudinal length of the first heater is shorter than the longitudinal length of the second heater. A fixing device characterized by the following features.

2. The center position of the longitudinal length of the first heater and the center position of the longitudinal length of the second heater are at approximately the same position. The fixing device according to feature 1.

3. The longitudinal length of the second heater is longer than the maximum printable width. The fixing device according to feature 1.

4. The longitudinal length of the first heater is longer than the maximum printable width of the most frequently used paper type among paper types smaller than the maximum size that can be fed through. The fixing device according to feature 1.

5. Among paper sizes smaller than the maximum size that can be fed through a paper machine, A3 size is the most frequently used. The fixing device according to feature 4.

6. The resistive element having the Curie point is a PTC heating element. The fixing device according to feature 1.

7. The first heater is a heater in which a plurality of the PTC heating elements are arranged. The fixing device according to feature 6.

8. In a cross-section perpendicular to the transport direction of the recording material, The second heater is positioned closer to the pressurizing rotating body than the first heater. The fixing device according to feature 1.

Images