Heater, fixing device, and image forming apparatus

Abstract

To prevent reduction in efficiency of heat transfer from a heater to a fixing film caused by a rugged shape of a protective layer that protects a resistance heating element provided on a substrate of the heater.SOLUTION: A heater (22) has a substrate (22a), at least one resistance heating element (22b) formed on the substrate (22a), and an electrode (22h) for supplying a current to the resistance heating element (22b). The heater has an auxiliary layer (22f) provided to overlap only a part of the area of the resistance heating element (22b) provided on the substrate (22a), and a protective layer (22d) laminated on the auxiliary layer (22f) and provided to cover the whole area of the resistance heating element (22b).SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a fixing device and an image forming apparatus including a heater.

Background Art

[0002] An electrophotographic image forming apparatus has a fixing device that fixes toner to a sheet in a fixing nip portion formed by a fixing film and a pressure roller. In such a fixing device, heat of a heater is transferred to the fixing film by rotating the fixing film in contact with the heater, and the toner is fixed to the sheet sandwiched in the fixing nip portion.

[0003] A heater disposed inside the fixing film has a substrate, a resistance heating element or a conductive pattern on the substrate, and a protective layer for protecting the resistance heating element or the conductive pattern. In such a heater, since the thickness of the resistance heating element or the conductive pattern is about 10 μm in the thickness direction of the substrate, unevenness of about 10 μm in height occurs on the surface of the protective layer between the region where the resistance heating element or the conductive pattern is provided and the region where it is not provided. As a result, the region where the fixing film contacts the heater (hereinafter referred to as the inner surface nip) is narrowed, and the heat transfer efficiency from the heater to the fixing film may decrease.

[0004] Patent Document 1 discloses a configuration in which convex portions are provided on a substrate with a gap from a conductive pattern for the purpose of smoothing the unevenness generated on the surface of the protective layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As in Patent Document 1, a configuration in which convex portions are provided on a substrate with a gap from a resistance heating element or a conductive pattern has a concave shape at a position corresponding to the gap on the surface of the protective layer, and there is room for improvement in smoothing.

[0007] The present invention has been made to solve the above problems, and an object thereof is to improve the heat transfer efficiency from a heater to a fixing film by obtaining a wide inner nip, and to heat-fix a toner image on a recording material to the recording material in a good state.

Means for Solving the Problems

[0008] In order to achieve the above object, a heater according to the present invention includes a substrate, at least one resistance heating element provided on the substrate and extending along the longitudinal direction of the substrate, and a power supply electrode provided on the substrate for supplying current to the resistance heating element. In the heater, an insulating auxiliary layer provided so as to overlap only a part of the region of the resistance heating element, and a protective layer laminated on the auxiliary layer and provided so as to cover all regions of the resistance heating element for protecting the resistance heating element.

Effects of the Invention

[0009] According to the present invention, the heat transfer efficiency from the heater to the fixing film can be improved by obtaining a wide inner nip, and the toner image on the recording material can be heat-fixed to the recording material in a good state.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0011] [Example 1] (1) Image forming apparatus First, with reference to FIG. 1, the configuration and operation of an image forming apparatus (laser printer) 100 using an electrophotographic method will be described. FIG. 1 is a cross-sectional view of the image forming apparatus 100. As will be described later, the image forming apparatus 100 is equipped with a heater in which a resistance heating element and a conductive pattern are formed on a substrate, and a fixing device 9 having the heater.

[0012] As shown in FIG. 1, a photosensitive drum 1, which is an example of an image carrier, is rotationally driven in the direction of the arrow, and its surface is uniformly charged by a charging roller 2. The surface of the charged photosensitive drum 1 is scanned by a laser beam L corresponding to image information by a laser scanner 3. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 1. The electrostatic latent image is developed by toner supplied from a developing device 4. The toner image formed on the photosensitive drum 1 is transferred to a recording material P fed from a paper feed cassette 6 along the conveyance direction of the arrow at a transfer nip portion between a transfer roller 5 and the photosensitive drum 1. In the present embodiment, the photosensitive drum 1, the charging roller 2, the laser scanner 3, the developing device 4, and the transfer roller 5 are an example of an image forming unit.

[0013] The recording material P onto which the toner image has been transferred is conveyed to the fixing device 9, and in the fixing device 9, the toner image is heat-fixed onto the recording material P. Thereafter, the recording material P is discharged onto the paper discharge tray 11. Note that the toner remaining on the photosensitive drum 1 after transfer is recovered by the cleaner 8. The fixing device 9 will be described in detail in the following item (2).

[0014] (2) Fixing device 9 The fixing device 9 mounted on the image forming apparatus 100 will be described with reference to FIGS. 2 to 4. FIG. 2 is a schematic cross-sectional view of the fixing device 9. FIG. 3 is an exploded perspective view of the film assembly unit 20 used in the fixing device 9. FIG. 4 is a front view of the fixing device.

[0015] The fixing device 9 is of a tensionless type film heating method. The fixing device 9 of the tensionless type film heating method uses an endless belt-shaped or cylindrical heat-resistant film. And at least a part of the circumference of the film is always tension-free (a state where no tension is applied), and the film is rotationally driven by the rotational driving force of the pressure body. Hereinafter, the fixing device of the film heating method will be described in detail.

[0016] The configuration of the fixing device 9 will be described with reference to the cross-sectional view of FIG. 2. The fixing device 9 has a cylindrical film 23 which is an example of a first rotating body, and a heater 22 which is a heating body. The fixing device 9 also has a pressure roller 30 which is an example of a second rotating body and forms a fixing nip portion N with the heater 22 via the film 23. A sliding grease 60 for improving the slidability with the heater 22 is applied to the inner surface of the film 23.

[0017] The reinforcing member 24 is made of a metal such as iron, and presses the heater 22 toward the pressure roller 30 via the film guide 21. The reinforcing member 24 is a member that maintains its strength so as not to be greatly deformed even by the pressure that presses against the pressure roller 30 to form the fixing nip portion N. The film guide 21 also has a function of guiding the rotation of the film 23. The film guide 21 is, for example, a molded product of a heat-resistant resin such as PPS (polyphenylene sulfite) or liquid crystal polymer. PPS was used in this embodiment. The pressure roller 30 receives power from the motor M via a gear (not shown) and rotates in the direction of arrow b. When the pressure roller 30 rotates, the film 23 is driven to rotate in the direction of arrow a.

[0018] For the heater 22, a ceramic substrate 22a is used. The substrate 22a has an elongated plate shape, a resistance heating element 22b that generates heat when energized, an auxiliary glass layer 22f provided between the resistance heating elements 22b, and a glass coat layer 22d that protects the surfaces of the resistance heating element 22b and the auxiliary glass layer 22f. The configuration of the heater 22 will be described in detail in section (3).

[0019] A thermistor 25, which is a temperature sensing element, is in contact with the side of the heater substrate 22a that contacts the film guide 21. The energization of the resistance heating element 22b is controlled according to the temperature detected by the thermistor 25.

[0020] The thickness of the film 23 is preferably about 20 μm or more and 100 μm or less in order to ensure good thermal conductivity. As the film base layer 23a, a single-layer film made of a material such as PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether), or PPS is suitable for the film 23. Alternatively, a composite layer film in which a release layer 23b is coated on the surface of a material such as PI (polyimide), PAI (polyamideimide), PEEK (polyetheretherketone), or PES (polyethersulfone) is also suitable.

[0021] As the release layer 23b, PTFE, PFA, FEP (tetrafluoroethylene-perfluoroalkyl vinyl ether), etc. are suitable. Further, pure metals such as SUS, Al, Ni, Cu, Zn, etc. having high thermal conductivity, alloys, etc. are used for the base layer, and those obtained by performing the above-described coating treatment and coating of a fluororesin tube on the release layer are also suitable.

[0022] In this embodiment, PI with a thickness of 60 μm was used as the film base layer 23a, and a PFA with a thickness of 12 μm coated was used for the film release layer 23b in consideration of both wear of the release layer 23b due to paper passage and thermal conductivity. Further, the longitudinal length of the film 23 was 240 mm.

[0023] The pressure roller 30 is an example of a pressure rotating body, and has a core metal 30a made of a material such as iron or aluminum, an elastic layer 30b made of a material such as silicone rubber, and a release layer 30c made of a material such as PFA. The pressure roller 30 receives power from the motor M via gears (not shown) and rotates in the direction of arrow b. When the recording material P is nipped and conveyed at the nip portion N, the toner image T on the recording material P is heat-fixed to the recording material P. The recording material P that has passed through the nip portion N is conveyed to the paper discharge tray 11.

[0024] Next, it will be described with reference to the exploded perspective view of FIG. 3. As shown in FIG. 3, after the film guide 21 and the reinforcing member 24 are fitted, the film 23 is externally fitted with a margin in the circumferential length to the outer circumferences of the film guide 21 and the reinforcing member 24. The axial direction of the cylindrical shape of the film 23 is hereinafter referred to as the longitudinal direction.

[0025] Both ends of the reinforcing member 24 protrude from both ends of the film 23, and flange members 26 are fitted to both ends respectively, and the whole is assembled as a film assembly unit 20.

[0026] The power supply terminal of the heater 22 also protrudes from one side end of the film 23, and the power supply connector 27 is fitted. The power supply connector 27 contacts the power supply electrode 22h of the heater 22 with a contact pressure to form a power supply path.

[0027] The heater clip 28 is formed from a metal plate bent in a U-shape and has spring properties.

[0028] Next, an explanation will be given with reference to the front view of FIG. 4. The flange member 26 restricts the longitudinal movement of the rotating film 23 and regulates the position of the film during the operation of the fixing device. The film assembly unit 20 is provided opposite to the pressure roller 30. The left-right movement in the figure is restricted by the frame side plate 42, and the up-down movement is supported by the top plate side housing 41 of the fixing device so as to be movable. A pressure spring 45 is attached to the top plate side housing 41 of the fixing device in a compressed state. The pressing force of the pressure spring 45 is received by both ends of the reinforcing member 24 via the flange member 26, the reinforcing member 24 is pressed toward the pressure roller 30 side, and the entire film assembly unit 20 is pressed toward the pressure roller 30 side.

[0029] A bearing member 31 is provided to pivotally support the shaft of the pressure roller 30. The bearing member 31 receives the pressing force from the film assembly unit 20 via the pressure roller 30. In order to rotatably support the shaft of the pressure roller, which becomes relatively hot, a bearing material having heat resistance and excellent slidability is used. The bearing member 31 is attached to the bottom side housing 43 of the fixing device.

[0030] (3) Heater 22 With reference to FIG. 5, the configuration and manufacturing method of the heater 22 in the fixing device 9 will be described. FIG. 5(a) is a longitudinal plan view of the heater 22, and FIG. 5(b) is a cross-sectional view in the short direction of the heater 22 along line a shown in FIG. 5(a).

[0031] (3-1) Substrate 22a The heater 22 has a substrate 22a made of ceramics. The type of ceramics is not particularly limited and can be appropriately selected in consideration of the required mechanical strength, the linear expansion coefficient suitable for forming the heating element, the ease of obtaining the plate material in the market, etc.

[0032] The thickness of the substrate 22a may be determined in consideration of strength, heat capacity, and heat dissipation performance. When the thickness of the substrate 22a is thin, the heat capacity is small, which is advantageous for quick start-up. However, if it is too thin, distortion problems are likely to occur during the heat molding of the heating element. Conversely, when the thickness of the substrate 22a is thick, it is advantageous in terms of distortion during the heat molding of the heating element. However, if it is too thick, the heat capacity is large, which is disadvantageous for quick start-up. The preferred thickness of the substrate 22a is 0.3 mm to 2.0 mm when considering the balance of mass productivity, cost, and performance.

[0033] In this embodiment, an alumina substrate with a width of 6 mm, a length of 300 mm, and a thickness of 1 mm was prepared as the substrate 22a.

[0034] (3-2) Resistance heating element 22b The resistance heating element 22b is obtained by printing a resistance heating element paste, which is a mixture of (A) a conductive component, (B) a glass component, and (C) an organic binder component, on the substrate 22a and then firing it.

[0035] When the resistance heating element paste is fired, the (C) organic binder component burns out and the (A) and (B) components remain, so that the heating element 22b containing the conductive component and the glass component is formed.

[0036] Here, as the (A) conductive component, silver-palladium (Ag·Pd), ruthenium oxide (RuO 2 ), semiconductorized barium titanate (BaTiO 3 ) etc. are used alone or in combination. The sheet resistance value is preferably 0.1 [Ω / □] to 100 [kΩ / □].

[0037] Also, as long as it is a trace amount that does not impair the characteristics of the present invention in addition to the above (A) to (C), it is not a problem that other materials are included.

[0038] In this embodiment, a resistive heating element paste containing silver and palladium (Ag·Pd) as the conductive component and other glass components and organic binder components was used. Further, after coating the ceramic substrate 22a by screen printing, it was dried at 180°C and fired at 850°C to form the resistive heating element 22b. The thickness of the resistive heating element 22b after firing was 10 μm, the length was 220 mm, and the width was 0.9 mm. As shown in Fig. 5(b), two resistive heating elements 22b were formed, and the distance between them was 2.8 mm.

[0039] (3-3) Power supply electrode 22h and conductive pattern 22g The power supply electrode 22h and the conductive pattern 22g shown in Fig. 5 are mainly composed of silver (Ag), platinum (Pt), gold (Au), silver and platinum (Ag·Pt) alloy, silver and palladium (Ag·Pd) alloy, etc. And, similar to the resistive heating element paste, a paste in which (A) a conductive component, (B) a glass component, and (C) an organic binder component are mixed is printed on the ceramic substrate 22a and then fired.

[0040] The power supply electrode 22h and the conductive pattern 22g are provided for the purpose of supplying current and voltage to the resistive heating element 22b, and the resistance is made sufficiently low with respect to the resistive heating element 22b.

[0041] Here, for the aforementioned resistive heating element paste, power supply electrode, and conductive pattern paste, it is necessary to select a material that softens and melts at a temperature lower than the melting point of the substrate 22a and a heat-resistant material in view of the actual use temperature.

[0042] In this embodiment, a paste for the power supply electrode and the conductive pattern containing silver as the conductive component and other glass components and organic binder components was prepared. Then, after coating the ceramic substrate 22a by screen printing, it was dried at 180°C and fired at 850°C to form the power supply electrode 22h and the conductive pattern 22g.

[0043] (3-4) Protective layer 22d The protective layer 22d shown in Fig. 5 is provided to cover the resistive heating element 22b and the conductive pattern 22g for the purpose of protecting them. Different from the auxiliary glass layer 22f described later, the protective layer 22d covers all regions of the resistive heating element 22b. As the material, glass or PI (polyimide) is preferable from the viewpoint of heat resistance, and a thermally conductive filler having insulating properties may be mixed as necessary. In this embodiment, glass is used as the protective layer 22d. The protective layer 22d was formed by applying a glass paste by screen printing and then drying at 180°C and firing at 850°C. Also, defects such as through-holes and foreign matters may occur during printing, drying, and firing of the protective layer 22d. Therefore, in order to prevent a decrease in the withstand voltage of the protective layer 22d, it is desirable to provide a plurality of layers laminated. In this embodiment, as shown in Fig. 5(b), three layers of the protective layer 22d are laminated and provided.

[0044] Here, in this embodiment, for the purpose of improving the uneven shape of the surface of the protective layer 22d, an auxiliary glass layer 22f is provided so as to fill the space between the two resistive heating elements 22b before forming the protective layer 22d. The auxiliary glass layer 22f intersects the vertical line b with respect to the ceramic substrate 22a described at the end of the resistive heating element 22b, and is provided so that a part of the region overlaps on the resistive heating element 22b. The overlapping length x in this embodiment was set to 100 μm. Also, the film thickness of the auxiliary glass layer 22f indicated by the arrow U was set to 10 μm, which is substantially the same as the film thickness of the resistive heating element 22b. Incidentally, in the vicinity of the region where the auxiliary glass layer 22f and the resistive heating element 22b partially overlap, the auxiliary glass layer 22f is laminated to a position slightly thicker than the thickness indicated by the arrow U because it is laminated on the resistive heating element 22b. Also, at the central portion in the short side direction (the left-right direction in Fig. 5(b)) of the substrate 22a, the auxiliary glass layer 22f tends to be slightly thinner than the thickness indicated by the arrow U due to the adhesion to the substrate 22a.

[0045] As shown in Fig. 5(a), the length of the auxiliary glass layer 22f was set to 220 mm, which is the same as that of the resistive heating element 22b.

[0046] The auxiliary glass layer 22f is formed by using the same type of glass paste as the protective layer 22d, screen-printing the protective layer glass paste so as to partially overlap the region of the resistance heating element 22b as described above, and then performing drying at 180°C and firing at 850°C. Thereafter, the protective layer 22d-1, the protective layer 22d-2, and the protective layer 22d-3 are sequentially formed by the same printing, drying, and firing processes.

[0047] The auxiliary glass layer 22f is an example of the auxiliary layer in this embodiment, and materials other than glass may be adopted as in the case of the protective layer 22d. In that case, PI (polyimide) is preferable from the viewpoint of heat resistance. However, a heat conduction filler having insulating properties may be mixed as necessary.

[0048] Thereafter, the configurations of other embodiments and comparative examples will be described, and finally the effects will be collectively described. Note that since the same configurations as those in the first embodiment are adopted for the image forming apparatus and the fixing apparatus other than the heater 22 in other embodiments and comparative examples, the description thereof will be omitted.

[0049] [Comparative Example 1] FIG. 6(a) is a plan view of the heater 22 in the longitudinal direction of this comparative example, and FIG. 6(b) is a cross-sectional view of the heater 22 in the short transverse direction taken along line a shown in FIG. 6(a). Different from the heater 22 of the first embodiment, the auxiliary glass layer 22f is provided with a gap y from the resistance heating element 22b. The gap y in this comparative example was set to 100 μm. Other parameters are the same as those in the first embodiment.

[0050] [Comparative Example 2] FIG. 7(a) is a plan view of the heater 22 in the longitudinal direction of this comparative example, and FIG. 7(b) is a cross-sectional view of the heater 22 in the short transverse direction taken along line a shown in FIG. 7(a). In this comparative example, different from the heaters 22 of the first embodiment and the comparative example 1, the feature is that the auxiliary glass layer 22f is not provided. Other parameters are the same as those in the first embodiment.

[0051] [Second Embodiment] FIG. 8(a) is a plan view of the heater 22 in the longitudinal direction in this embodiment, and FIG. 8(b) is a cross-sectional view of the heater 22 in the short-side direction along line a shown in FIG. 8(a).

[0052] As shown in FIG. 8, the heater 22 in this embodiment uses a substrate 22a that is wider than that in Embodiment 1. The size of the substrate 22a is 8 mm in width, 300 mm in length, and 1 mm in thickness, and the material is alumina, the same as in Embodiment 1. The resistive heating element 22 has the same thickness and size as in Embodiment 1, and the distance between the two resistive heating elements 22 is also set to 2.8 mm, the same as in Embodiment 1.

[0053] In the embodiment, an auxiliary glass layer 22f is provided so as to fill the space between the two resistive heating elements 22b, the same as in Embodiment 1, and additional auxiliary glass layers 22f are provided in both end directions in the short-side direction of the heater 22. In this embodiment, for all the auxiliary glass layers 22f, the overlapping length with the resistive heating element 22b is set to 100 μm. This overlapping length x does not necessarily have to be the same for all, and may be appropriately set to an optimal value according to the shape of the protective layer 22d. Also, as shown in FIG. 8(b), the auxiliary glass layer 22f and the protective layer 22d provided at the outermost ends in the short-side direction of the heater 22 are provided with a distance z = 0.6 mm therebetween.

[0054] [Comparative Example 3] FIG. 9(a) is a plan view of the heater 22 in the longitudinal direction in this embodiment, and FIG. 9(b) is a cross-sectional view of the heater 22 in the short-side direction along line a shown in FIG. 9(a).

[0055] As shown in FIG. 9(b), in this comparative example, the auxiliary glass layer 22f and the protective layer 22d provided at the outermost ends in the short-side direction of the heater 22 are characterized by being provided without a gap therebetween. Other parameters are the same as in Embodiment 2.

[0056] [Comparative Example 4] FIG. 10(a) is a plan view of the heater 22 in the longitudinal direction in this embodiment, and FIG. 10(b) is a cross-sectional view of the heater 22 in the short-side direction along line a shown in FIG. 10(a).

[0057] As shown in FIG. 10(b), in this comparative example, the thickness of the auxiliary glass layer 22f was set to 15 μm, which is thicker than the thickness of 10 μm in Examples 1 and 2. Other parameters are the same as those in Example 2.

[0058] [Comparative Example 5] FIG. 11(a) is a plan view of the heater 22 in the longitudinal direction in this example, and FIG. 11(b) is a cross-sectional view of the heater 22 in the short transverse direction along line a shown in FIG. 11(a).

[0059] As shown in FIG. 11(b), in this comparative example, for all the auxiliary glass layers 22f, the overlapping length x with the resistance heating element 22b was set to 300 μm. Other parameters are the same as those in Example 2.

[0060] (4) Operational Effects 〈Surface Shape of the Protective Layer 22d〉 Regarding the heaters 22 of the above Examples 1 to 2 and Comparative Examples 1 to 5, the uneven shape of the protective layer 22d-3, which is the outermost surface of the protective layer 22d, was observed.

[0061] In the heater 22 of Example 1, as shown in FIG. 5(b), by providing the auxiliary glass layer 22f, the uneven shape generated in the protective layer 22d-3 could be smoothed. The height difference h of the uneven shape on the surface of the protective layer 22d-3 was 1 μm or less. That is, by adopting the configuration of the heater 22 of Example 1, the height difference on the surface of the protective layer 22d-3 can be made 1 μm or less.

[0062] In the heater 22 of Comparative Example 1, as shown in FIG. 6(b), due to the existence of the gap y region, concave shapes Y-1, Y-2, and Y-3 were generated in the protective layers 22d-1, 22d-2, and 22d-3, respectively. Each time the protective layer 22d was overlaid, the surface uneven shape tended to be gradually leveled, and the uneven shape of the concave shape Y-3 was more relaxed than that of the concave shape Y-1. However, due to the two concave shapes Y-3 generated on the surface of the protective layer 22d-3, the height difference h of the uneven shape of the protective layer 22d-3 became about 10 μm.

[0063] In the heater 22 of Comparative Example 2, as shown in FIG. 7(b), the concavo-convex shape of the protective layer 22d-3 was such that both ends in the short direction of the heater 22 were convex and the central portion was concave. There are two possible reasons for this. One is due to the resistance heating elements 22b provided at both ends in the short direction of the heater 22, and the protective layer 22d on the resistance heating element 22b may have swelled. The other is that when the glass paste is applied by screen printing, surface tension acts on both ends in the short direction of the heater 22 within the glass paste film, causing a phenomenon in which the glass paste film in the direction of both ends in the short direction of the heater 22 becomes thicker than the center. This phenomenon is called the saddle phenomenon. Due to these two reasons, the height difference h of the concavo-convex shape of the protective layer 22d-3 in this comparative example became as large as about 15 μm.

[0064] In the heater 22 of Example 2, as shown in FIG. 8(b), even for the heater 22 using the wide substrate 22a, by providing the auxiliary glass layer 22f as in this example, the concavo-convex shape generated in the protective layer 22d-3 could be smoothed. The height difference h of the concavo-convex shape of the protective layer 22d-3 was about 1 μm. The reason for providing the auxiliary glass layer 22f and the protective layer 22d with a distance z = 0.6 mm at the outermost ends in the short direction of the heater 22 is that the saddle phenomenon occurs when the protective layer 22d is printed. That is, it is to avoid the saddle phenomenon and the convex shape due to the auxiliary glass layer 22f being superimposed to form a large convex shape.

[0065] In the heater 22 of Comparative Example 3, as shown in FIG. 9(b), since the auxiliary glass layer 22f provided at the outermost ends in the short direction of the heater 22 and the protective layer 22d were provided without a distance therebetween, the saddle phenomenon and the convex shape due to the auxiliary glass layer 22f were superimposed. As a result, the height difference h of the concavo-convex shape of the protective layer 22d-3 became as large as about 12 μm.

[0066] In the heater 22 of Comparative Example 4, as shown in FIG. 10(b), since the thickness of the auxiliary glass layer 22f was set to 15 μm, which is thicker than the thickness (10 μm) of the resistive heating element 22b, a convex shape was imparted to the protective layer 22d. As a result, due to the two concave shapes Y-3 formed on the surface of the protective layer 22d-3, the height difference h of the uneven shape of the protective layer 22d-3 became about 5 μm.

[0067] In the heater 22 of Comparative Example 5, as shown in FIG. 11(b), since the overlapping length x of the auxiliary glass layer 22f and the resistive heating element 22b was set to 300 μm, the auxiliary glass layer 22f became a narrow convex shape in the overlapping region. Therefore, convex shapes X-1, X-2, and X-3 were formed on the protective layers 22d-1, 22d-2, and 22d-3, respectively. As a result, the height difference h of the uneven shape of the protective layer 22d-3 became about 5 μm.

[0068] <Inner nip measurement> Each of the heaters 22 of the above Examples 1 to 2 and Comparative Examples 1 to 5 was incorporated into the fixing device 9, and the inner nip was examined.

[0069] In the heater 22 of Example 1, as shown in FIG. 5(b), since the uneven shape on the surface of the protective layer 22d-3 was smooth, the width of the inner nip (hereinafter referred to as the inner nip width) could be obtained over most of the surface of the protective layer 22d-3. As a result, the inner nip width was 4.5 mm.

[0070] In the heater 22 of Comparative Example 1, as shown in FIG. 6(b), the inner nip was divided into three regions O, P, and Q due to the two concave shapes Y-3 formed on the surface of the protective layer 22d-3. The sum of the widths of these three inner nips was 3.4 mm.

[0071] In the heater 22 of Comparative Example 2, as shown in FIG. 7(b), the inner nip width was restricted by the large convex shapes at both ends in the short direction of the protective layer 22d-3. As a result, the inner nip width became as narrow as 3.0 mm.

[0072] In the heater 22 of Example 2, as shown in FIG. 8(b), an inner nip width could be obtained on most of the surface of the protective layer 22d-3. As a result, the inner nip width became 6.5 mm, which was the largest inner nip width compared with Example 1 and Comparative Examples 1 to 5.

[0073] In the heater 22 of Comparative Example 3, as shown in FIG. 9(b), the inner nip width was restricted by the large convex shapes at both ends in the short direction of the protective layer 22d-3. As a result, the inner nip width became 5.0 mm, which was narrower compared with Example 2.

[0074] In the heater 22 of Comparative Example 4, as shown in FIG. 10(b), due to the two concave shapes Y-3 formed on the surface of the protective layer 22d-3, the inner nip was divided into three regions O, P, and Q. The sum of the inner nip widths of these three regions was 3.8 mm.

[0075] In the heater 22 of Comparative Example 5, as shown in FIG. 11(b), due to the four convex shapes X-3 formed on the surface of the protective layer 22d-3, the inner nip was divided into five regions O, P, Q, V, and W. The inner nip widths of these five regions were 4.0 mm.

[0076] (Fixing property evaluation) Each of the heaters 22 of Examples 1 to 2 and Comparative Examples 1 to 5 was incorporated into the fixing device 9, and the image forming apparatus 100 was operated with the peripheral speed of the pressure roller 30 being 250 mm / s to evaluate the fixing property of the toner image on the recording material. At that time, the detection temperature (temperature control temperature) of the thermistor 25 was set in several steps to examine the temperature control temperature at which good fixing property could be obtained.

[0077] The above-mentioned inner nip widths and the temperature control temperatures at which good fixing property could be obtained are listed in Table 1.

[0078]

Table 1

[0079] As shown in Table 1, there is a correlation between the inner nip width and the temperature control temperature at which good fixing property can be obtained. It can be seen that the wider the inner nip width, the lower the temperature control temperature at which good fixing property can be obtained. The reason for this is that as the inner nip width becomes wider, the heat transfer efficiency from the heater 22 to the fixing film 23 improves, so there is no need to heat the heater 22 excessively.

[0080] On the other hand, when the temperature control temperature of the heater 22 increases, attention needs to be paid to the heat resistance temperature of the film guide 21 holding the heater 22 and the deformation due to heat. The deformation of the film guide 21 is also described in Table 1. As a result of continuously using the image forming apparatus 100 at the temperature control temperature at which good fixing property can be obtained, it was found that when the temperature control temperature becomes as high as exceeding 233°C, the surface of the heater 22 in contact with the film guide 21 deforms. The reason for the deformation is considered to be that in addition to the condition of high temperature, a strong pressing force is applied to the surface of the heater 22 in contact with the film guide 21. When the film guide 21 is deformed, it may lead to uneven pressing force, uneven fixing nip portion N and inner nip width, resulting in poor fixing property and poor conveyance of the recording material.

[0081] As shown in Table 1, for the configurations of Example 1, Example 2 and Comparative Example 3, good results were obtained in that the temperature control temperature at which good fixing property can be obtained is low and the film guide 21 does not deform. However, since it is conceivable to further increase the fixing temperature in the image forming apparatus 100 with a higher peripheral speed of the pressure roller 30, a configuration with a very wide inner nip width as in Example 2 is considered desirable.

[0082] As described above, in Example 2, the distance z = 0.6 mm between the auxiliary glass layer 22f provided at the outermost end in the short side direction of the heater 22 and the protective layer 22d was set. However, it may be appropriately changed according to the position of the resistance heating element 22 arranged on the substrate 22a, the thickness of the protective layer 22d, etc. In this example, it is desirable to set z≥0.5 mm.

[0083] Further, the ratio of (the thickness of the auxiliary glass layer 22f) / (the thickness of the resistive heating element 22b) is preferably in the range of 120% or less and 80% or more, and more preferably 100% as in Example 1 or Example 2.

[0084] Furthermore, regarding the overlapping length x of the auxiliary glass layer 22f and the resistive heating element 22b, it was found that Example 2 with x = 100 μm obtained better evaluation results. The optimum value of the overlapping length x is affected by the cross-sectional shapes of the auxiliary glass layer 22f and the resistive heating element 22b respectively, but it is desirable to set it to 200 μm or less.

[0085] As described above, as an example, the configuration in which the auxiliary glass layer 22f overlaps the resistive heating element 22b has been described. However, the same effect can be obtained even if the auxiliary glass layer 22f overlaps the conductive pattern as in the prior art.

[0086] In addition, in this embodiment, the expansion of the inner nip width due to the smooth surface of the protective layer 22d has been described. However, other good effects can also be obtained. For example, although the film 23 is driven to rotate passively by the rotational driving force of the pressure roller 30, the uneven shape of the protective layer 22d sliding on the inner surface of the film 23 is reduced, so that the rotation of the film 23 can be made smooth. As a result, when the recording material P passes through the fixing nip portion N, the speed difference between the film 23, the pressure roller 30, and the recording material P is reduced, and it is possible to suppress the end portion of the recording material P from polishing the surface of the film 23.

[0087] As described above, according to the present embodiment, the following effects can be obtained. That is, by providing the auxiliary glass layer 22f, the unevenness on the surface of the protective layer 22d can be smoothed. In addition, since a wide inner nip can be obtained, the heat transfer efficiency from the heater to the fixing film can be improved. And the toner image of the recording material can be heat-fixed to the recording material in a good state.

Description of Reference Numerals

[0088] 1 Photosensitive drum 2 Charging Roller 3 Laser Scanner 4 Developing Device 5 Transfer Roller 6 Paper Feed Cassette 9 Fixing Device 20 Film Assembly 21 Film Guide 22 Heater 22a Substrate 22b Resistance Heating Element 22d Protective Layer 22f Auxiliary Glass Layer 22g Conductive Pattern 22h Power Supply Electrode 23 Fixing Film 24 Reinforcing Member 25 Thermistor 26 Flange 27 Power Supply Connector 28 Heater Clip 30 Pressing Roller 31 Bearing Member 41 Top Plate Side Housing 42 Frame Side Plate 43 Bottom Side Housing 45 Pressing Spring 60 Sliding Grease

Claims

1. A substrate, at least one resistive heating element provided on the substrate and extending along the longitudinal direction of the substrate, a power supply electrode provided on the substrate for supplying current to the resistive heating element, In a heater having, an insulating auxiliary layer provided so as to overlap only a partial region of the resistive heating element, a protective layer laminated on the auxiliary layer and provided so as to cover all regions of the resistive heating element for protecting the resistive heating element, A heater characterized by having.

2. The heater according to claim 1, wherein the protective layer is provided in a region of the substrate excluding the electrode.

3. The at least one resistive heating element is two resistive heating elements, The heater according to claim 1, wherein the auxiliary layer is provided so as to fill between the two resistive heating elements.

4. The resistive heating element and the auxiliary layer overlap in the short-side direction of the heater, and the length in the short-side direction in the overlapping region is 200 μm or less. The heater according to claim 1, characterized in that.

5. The heater according to claim 1, wherein the height difference on the surface of the protective layer is 1 μm or less.

6. The heater according to claim 1, wherein an end portion of the auxiliary layer and an end portion of the protective layer in the short-side direction of the heater are provided at a distance from each other.

7. The heater according to claim 1, wherein the auxiliary layer is glass.

8. The heater according to claim 1, wherein the protective layer is composed of a plurality of layers.

9. The heater according to claim 1, wherein the ratio of the thickness of the auxiliary layer to the thickness of the resistive heating element is 120% or less.

10. The resistive heating element extends in the longitudinal direction of the heater, The heater according to claim 1, wherein the length in the short-side direction of the heater in a region where the resistive heating element and the auxiliary layer overlap is 200 μm or less.

11. The heater according to claim 1, characterized by having a conductive pattern for supplying current from the power supply electrode to the resistive heating element.

12. The heater according to claim 1, a first rotating body heated by the heater, a second rotating body forming a nip portion together with the fixing film, It has, and is characterized in that a toner image formed on a recording material in the nip portion is heat-fixed.

13. The fixing device according to claim 9, wherein the first rotating body is a fixing film.

14. The fixing device according to claim 13, wherein the heater is provided so as to be in contact with the inner surface of the fixing film, and the nip portion is formed by the heater and the second rotating body via the fixing film.

15. An image forming unit that forms a toner image on a recording material, The fixing device according to claim 14 that fixes the toner image formed by the image forming unit, An image forming apparatus characterized by comprising.

Images