Fixing apparatus and image forming apparatus

Abstract

To improve the quality of an image to be fixed to a medium having fine irregularities formed on its surface.SOLUTION: When printing an image on a coated paper medium M, an image forming apparatus 1 causes a heating belt 72 of a fixing unit 40 to have a value of a hardness ratio after 0.2 s fall within a range R1 of 0.738 or more and 0.837 or less, which is measured by using a microhardness tester. The image forming apparatus 1 can thus reliably deform the shape of the heating belt 72 according to dents D in the medium M within 0.2 [s] while the medium M passes through a nip area N of the fixing unit 40. Consequently, the image forming apparatus 1 can sufficiently fix toner to the medium M in both a flat part and the dents D, and can prevent the occurrence of glossiness unevenness in the image printed on the medium M and provide uniform glossiness to the image.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a fixing device and an image forming apparatus, and is suitable for application to, for example, an electrophotographic printer.

Background Art

[0002] In recent years, as an image forming apparatus, for example, a toner image (also called a developer image) formed using toner (also called a developer) by a developing device is transferred to a sheet (also called a medium), and heat and pressure are applied to this sheet by a fixing device to fix it, thereby printing an image. Among these, the fixing device is configured to, for example, arrange rollers, an annular belt, etc. above and below the conveyance path of the sheet, sandwich the sheet at a nip portion formed between them, and apply heat and pressure to the sheet.

[0003] Further, in an image forming apparatus, there are cases where an image is printed on a sheet having relatively large irregularities formed on the paper surface in advance, such as so-called embossed paper. However, in such a sheet, the fixing property of the toner becomes low, particularly in the recessed portions. Therefore, a proposal has been made to improve the fixing property by defining the pushing depth in the fixing belt (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in an image forming apparatus, there are cases where an image is printed on a sheet having enhanced surface smoothness, such as so-called glossy paper. Since this glossy paper has a configuration in which a resin layer is superimposed on the surface of the base paper, for example, it is possible to give a high gloss to the printed image.

[0006] However, in actual glossy paper, fine irregularities are formed on the surface of the paper base, and as a result, fine irregularities may also appear on the surface of the resin layer. In such cases, even if the image forming apparatus uses a fixing belt within the range of the specified indentation depth as described above, it may not be able to properly fix the toner to the glossy paper in the areas with these irregularities. As a result, the image forming apparatus had a problem in which the printed image may have localized areas that lack gloss, i.e., uneven gloss, which could lead to a decrease in image quality.

[0007] This invention was made in consideration of the above points, and aims to propose a fixing device and an image forming device that improve the quality of images fixed to a medium having fine irregularities formed on its surface. [Means for solving the problem]

[0008] To solve these problems, the fixing device of the present invention is provided with an annular belt having an outer surface and traveling at a predetermined speed, and an opposing member facing the outer surface of the annular belt and forming a nip region with the annular belt at a pressure equivalent to a load of 27 to 36 kg. The annular belt comprises a base, a surface layer located outside the base and forming the outer surface, and an elastic layer provided between the base and the surface layer. In the annular belt, when measuring the hardness of the outer surface using a hardness tester, the first hardness value (A) is defined as the measurement value obtained after a measurement time has elapsed equivalent to the time required for a predetermined position on the outer surface to pass through the nip region after the start of the hardness measurement, and the second hardness value (B) is defined as the measurement value obtained when the hardness tester's measurement value saturates. The ratio of the first hardness value (A) to the second hardness value (B) (A / B) is set to be between 0.738 and 0.837.

[0009] Furthermore, in the fixing device of the present invention, an annular belt having an outer surface and traveling at a predetermined speed, and facing the outer surface of the annular belt, At a pressure equivalent to a load of 27-36 kgAn opposing member is provided that forms a nip region with the annular belt, and the annular belt is configured such that, in hardness measurement of the outer surface using a hardness tester, the measured value at the point when a measurement time equivalent to the time required for a predetermined position on the outer surface to pass through the nip region after the start of hardness measurement is 56.4 to 65.5 [°].

[0010] Furthermore, the image forming apparatus of the present invention is provided with a developing unit that deposits a developer image onto the surface of a medium using a developer, and a fixing unit having the above-described configuration that fixes the developer image onto the medium.

[0011] The present invention The annular belt is composed of a base, a surface layer, and an elastic layer. In a configuration where the opposing member applies pressure equivalent to a load of 27-36 kg to the annular belt, by appropriately defining the ratio of the first hardness value to the second hardness value in the annular belt, the annular belt can deform to conform to the fine irregularities formed on the medium during the transit time as the medium passes through the nip region together with the annular belt. As a result, the present invention can uniformly fix the developer adhering to the flat portions and finely uneven portions of the medium, thereby forming an image with a uniform gloss. [Effects of the Invention]

[0012] According to the present invention, it is possible to realize a fixing device and an image forming device that improve the quality of images fixed to a medium having fine irregularities formed on its surface. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing the configuration of an image forming apparatus. [Figure 2] This is a schematic perspective view showing the configuration of the fixing section. [Figure 3] This is a schematic cross-sectional view showing the structure of the fixing section. [Figure 4] This is a schematic cross-sectional view showing the configuration of the heating belt. [Figure 5] This is a schematic cross-sectional view showing the configuration of the pressurizing section. [Figure 6]It is a schematic diagram showing the deformation of the heating belt according to the depression of the medium. [Figure 7] It is a schematic diagram showing the state of the time change of the measurement value by the microhardness meter. [Figure 8] It is a schematic diagram showing the values of each part in the heating belt, the measurement results, and the evaluation level. [Figure 9] It is a schematic diagram showing the relationship between the hardness ratio after 0.2 s and the evaluation level in the heating belt.

Embodiments for Carrying out the Invention

[0014] Hereinafter, embodiments for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0015] [1. Configuration of the Image Forming Apparatus] As shown in FIG. 1, the image forming apparatus 1 is an electrophotographic printer and can form, that is, print, a color image on a medium M such as plain paper or coated paper. Incidentally, the image forming apparatus 1 does not have an image scanner function for reading a document or a communication function using a telephone line, and is a single-function SFP (Single Function Printer) having only a printer function.

[0016] Various components are arranged inside a housing 2 formed in a substantially box shape in the image forming apparatus 1. Incidentally, hereinafter, the right end portion in FIG. 1 is defined as the front of the image forming apparatus 1, and the vertical direction, the horizontal direction, and the front-rear direction when viewed facing this front are defined and then described. Further, the image forming apparatus 1 can support a medium M of up to A3 size, and forms an image while conveying it along a conveyance path described later with the short side of the medium M along the horizontal direction. For this reason, each part in the image forming apparatus 1 has a length corresponding to the short side (297 [mm]) in the A3 size in the horizontal direction.

[0017] The image forming apparatus 1 is configured to be overall controlled by a control unit 3. This control unit 3 is connected to a host device such as a computer device (not shown), and when receiving a print instruction or print data from this host device, it executes an image forming process (also referred to as a printing process) for forming a print image on the surface of a medium M.

[0018] An operation panel 4 for displaying various information and receiving operation inputs is provided near the front of the upper surface of the housing 2. This operation panel 4 has, for example, a touch panel in which a display panel such as a liquid crystal panel and a touch sensor are combined, or LEDs (Light Emitting Diodes), etc. Based on the control of the control unit 3, it displays various information and also receives operation inputs from the user.

[0019] A tray 5 for accommodating the medium M is provided at the lowermost part inside the housing 2. This tray 5 is capable of accommodating a medium M of up to A3 size with its short side along the left - right direction. A paper feeding and conveying unit 10 is provided in the front - upper part of the tray 5. The paper feeding and conveying unit 10 forms a paper feeding and conveying path W1, which is the path for conveying the medium M, by conveying guides 11 that face each other at a predetermined interval.

[0020] Also, the paper feeding and conveying unit 10 has a pickup roller 12, a paper feeding roller 13, a separation roller 14, a registration roller 15, a pressure roller 16, and a pair of conveying rollers 17, etc. arranged along this paper feeding and conveying path W1. Each roller is formed in a columnar shape with its central axis along the left - right direction and is rotatably supported. Also, a driving force is transmitted from a paper feeding motor (not shown) to some of the rollers. The pairs of conveying rollers 17 and 18 have conveying rollers arranged at positions facing each other across the paper feeding and conveying path W1.

[0021] The paper feed and transport unit 10 picks up and transports the media M stored in the tray 5 one by one, separating them by rotating each roller appropriately based on the control of the control unit 3. Specifically, the pickup roller 12 pulls the media M out of the tray 5. The paper feed roller 13 moves the media M pulled out of the tray 5 by the pickup roller 12 along the paper feed transport path W1. When multiple media M are removed from the tray 5, the separation roller 14 separates the uppermost media M from the other media M. The registration roller 15 and pressure roller 16 correct the orientation (the orientation of each side relative to the direction of travel) of the media M if it is skewed relative to the paper feed transport path W1, so that it can move correctly. The transport roller pair 17 transports the media M along the paper feed transport path W1 and then sends it diagonally upward and backward.

[0022] In the paper feed transport section 10, a transfer section 20 is positioned below the transport roller pair 17 on the rear upper side, and four developing sections 30 are positioned above it. Between the transfer section 20 and each developing section 30, a straight transfer transport path W2 is formed, connected to the paper feed transport path W1 and extending diagonally upwards and rearward.

[0023] The transfer section 20 is composed of a drive roller 21, an idler roller 22, a transfer belt 23, and four transfer rollers 24, etc. The drive roller 21, the idler roller 22, and each of the transfer rollers 24 are all formed in a cylindrical shape with their central axis aligned in the left-right direction, and each is supported so as to be rotatable.

[0024] The drive roller 21 is positioned relatively far rear and can be rotated by a driving force supplied from a power source (not shown). The idler roller 22 is positioned slightly in front of and below the drive roller 21, near the transport roller pair 17. Each transfer roller 24 is discretely arranged between the drive roller 21 and the idler roller 22 at approximately equal intervals.

[0025] The transfer belt 23 is a flexible, endless belt that is stretched around the drive roller 21, idler roller 22, and each transfer roller 24. The upper portion of the transfer belt 23 is stretched linearly along the transfer transport path W2. Each transfer roller 24 has its upper end near the inner circumference of the upper portion of the transfer belt 23. Therefore, in the transfer unit 20, when the drive roller 21 rotates counterclockwise as shown in Figure 1, the transfer belt 23 is driven, and the idler roller 22 and each transfer roller 24 are rotated accordingly. At this time, the upper portion of the transfer belt 23 travels diagonally upward and backward along the transfer transport path W2.

[0026] The four developing units 30 (30K, 30Y, 30M, and 30C), also called image forming units, are arranged above the transfer unit 20, aligned along the transfer transport path W2, that is, in an oblique direction from the front lower side to the rear upper side. Each developing unit 30 corresponds to a respective color: black (K), yellow (Y), magenta (M), and cyan (C), but differs only in color; they are all configured similarly.

[0027] The developing unit 30 is composed of a developing unit 31 and an exposure unit 32. The developing unit 31 includes a toner storage unit for storing toner as a developer, multiple rollers, and a photoreceptor drum 34. Each of these rollers and the photoreceptor drum 34 is cylindrical or cylindrical with its central axis aligned in the left-right direction and is rotatable. The photoreceptor drum 34 is located at the very bottom of the developing unit 31 and is in contact with the transfer belt 23, with the transfer belt 23 sandwiched between it and the transfer roller 24.

[0028] The exposure processing unit 32 has multiple LEDs aligned along the left-right direction above the photoreceptor drum 34. Based on the control of the control unit 3, the exposure processing unit 32 appropriately emits light from each LED, thereby exposing the outer surface of the photoreceptor drum 34 and forming an electrostatic latent image. In response, the developing processing unit 31 deposits toner onto the outer surface of the photoreceptor drum 34, thereby forming a toner image (also called a developer image).

[0029] At this time, if the medium M is being transported along the transfer transport path W2, the transfer unit 20 transfers the toner image from the photoreceptor drum 34 to the medium M, and adheres the toner image to the surface of the medium M.

[0030] Behind the transfer unit 20, that is, behind the developing unit 30C which is located at the very rear, is the fixing unit 40. The fixing unit 40 transports the medium M along the fixing transport path W3, and applies heat and pressure to the medium M to fix the toner image to the surface of the medium M, and then feeds it out diagonally upward and backward (details will be described later).

[0031] A double-sided printing unit 50 is provided on the rear and underside of the fixing unit 40. The double-sided printing unit 50 forms a circulating transport path W4 and a temporary retraction transport path W5, etc., using a switch 51 provided on the rear side of the fixing unit 40, as well as multiple transport guides and multiple transport roller pairs. Of these, the circulating transport path W4 is formed to connect the switch 51 and the transport roller pair 17 of the paper feed transport unit 10.

[0032] When performing double-sided printing, the double-sided printing unit 50 switches the switch 51 based on the control of the control unit 3 to move the medium M to the temporary retraction transport path W5. Subsequently, after the end of the medium M has passed the switch 51, the double-sided printing unit 50 reverses the direction of travel of the medium M and moves it along the circulating transport path W4, where it merges with the paper feed transport path W1 of the paper feed transport unit 10 near the transport roller pair 17. As a result, the double-sided printing unit 50 moves the medium M from the paper feed transport path W1 to the transfer transport path W2 again with its front and back sides reversed, and transfers the image to the back side of the medium M. Incidentally, when the double-sided printing unit 50 does not perform double-sided printing on the medium M, and when an image has been transferred to the back side of the medium M, it moves the medium M diagonally upward and backward.

[0033] A paper discharge and transport unit 60 is located behind or above the switch 51. The paper discharge and transport unit 60 has a configuration similar to a part of the paper feed and transport unit 10, and a paper discharge and transport path W6, which is the path for transporting the medium M, is formed by transport guides 61 that are facing each other at a predetermined distance apart, and an outlet 62 is formed at the end of the path. In addition, transport roller pairs 63 and 64, etc., are sequentially arranged in the paper discharge and transport unit 60 along this paper discharge and transport path W6.

[0034] The paper discharge and transport unit 60 rotates the transport roller pair 63 and 64 according to the control of the control unit 3, thereby transporting the medium M received from the fuser unit 40 via the switch 51 along the paper discharge and transport path W6 and discharging it from the discharge port 62, placing it on the discharge tray 6 formed on the upper surface of the housing 2.

[0035] In this way, the image forming apparatus 1 sequentially transports the medium M along each transport path W, transfers the toner image formed by the developing unit 30 to the medium M, and fixes it in the fixing unit 40, thereby forming an image, that is, printing.

[0036] [2. Configuration of the fixing unit] Next, the configuration of the fixing section 40 will be described. Figure 2 is a schematic perspective view of the fixing section 40. Figure 3 is a schematic cross-sectional view of the fixing section 40. As shown in Figure 2, the fixing section 40 is configured as a rectangular parallelepiped that is elongated in the left-right direction.

[0037] The fixing unit 40 has a configuration in which multiple components are incorporated inside a fixing housing 41 that is formed in the shape of a hollow rectangular parallelepiped. Elongated holes that are long in the left-right direction and penetrate in the front-back direction are formed on the front and rear sides of the fixing housing 41, respectively, so that the medium M can pass through.

[0038] Inside the fixing housing 41, a heating unit 42 is positioned at the top, and a pressurizing unit 43 is positioned below it. The heating unit 42 is formed in a cylindrical shape with its central axis aligned in the left-right direction. Incidentally, the heating unit 42 is supported by the fixing housing 41 so that it can be displaced roughly in the vertical direction.

[0039] As shown in Figure 3, the heating section 42 is broadly composed of a central heating section 71 located in the center and a heating belt 72 surrounding it. The central heating section 71 is constructed as a hollow rectangular parallelepiped that is long in the left-right direction and is composed of supports 73 and 74, a heat conduction plate 75, a heater 76, a separation plate 77, and a temperature sensor 78, etc.

[0040] Support 73 is a molded part made of, for example, a heat-resistant resin material, and is configured as a whole in the shape of a hollow rectangular prism aligned in the left-right direction with the top surface omitted. Support 74 is formed by bending, for example, a plate-shaped metal member, and is configured as a whole in the shape of a hollow rectangular prism aligned in the left-right direction with the bottom surface omitted. The front plate of support 74 abuts against the front side of the front plate of support 73. The rear plate of support 74 abuts against the rear side of the rear plate of support 73. Therefore, when supports 73 and 74 are combined, they form a single rectangular prism aligned in the left-right direction.

[0041] The heat conduction plate 75 is formed as a plate that is long in the left-right direction and thin in the vertical direction, and is located below the lower plate of the support 73. This heat conduction plate 75 is made of a metal material with relatively high thermal conductivity, such as stainless steel, and efficiently transfers the heat generated by the heater 76, which will be described later. The heater 76, which serves as a heating element, is formed as a plate that is long in the left-right direction and thin in the vertical direction, and is located below the support 73. This heater 76 generates heat based on power supplied from a predetermined power supply unit, according to the control of the control unit 3 (Figure 1).

[0042] The separation plate 77 is mainly composed of a long, horizontally oriented, and thin, plate-shaped lower plate, with portions bent upward from its front and rear edges forming the front and rear plates, respectively. The lower plate of this separation plate 77 is located below the heater 76, separating the heater 76 from the heating belt 72 and preventing them from directly contacting each other.

[0043] The temperature sensor 78 is located on the upper side of the lower plate inside the support 73. This temperature sensor 78 detects the temperature of the heater 76 via the heat conduction plate 75, generates an electrical signal corresponding to the detected temperature, and notifies the control unit 3 (Figure 1) of this signal. Based on the notified temperature, the control unit 3 controls the power supplied to the heater 76 to adjust it to the desired temperature.

[0044] The heating belt 72, which functions as an annular belt, is an endless belt with a hollow cylindrical shape and sufficient length in the left-right direction, and is arranged to circumfer the heating central section 71. As shown in the schematic cross-sectional view in Figure 4, the heating belt 72 has a layered structure in which three types of members, namely a base 81, an elastic layer 82, and a surface layer 83, are sequentially stacked.

[0045] The substrate 81 is located on the innermost side of the heating belt 72 and is made of, for example, polyimide. The thickness of the substrate 81 can be approximately 50 to 120 μm. In this embodiment, the thickness of the substrate 81 is approximately 70 to 90 μm. The substrate 81 can also be made of a metal material, in which case its thickness can be approximately 20 to 60 μm.

[0046] The elastic layer 82 is located between the substrate 81 and the surface layer 83 and is made of, for example, silicone rubber. The thickness of the elastic layer 82 can be approximately 100 to 350 [μm], and in this embodiment it is approximately 150 to 300 [μm]. The hardness of the silicone rubber constituting this elastic layer 82 is preferably approximately 7 to 50 [°] according to the measurement method of durometer type A (shear A) based on JIS K 6253. In this embodiment, a material with a hardness of approximately 12 to 40 [°] was used as the elastic layer 82.

[0047] The surface layer 83 is located on the outermost part of the heating belt 72 and is made of, for example, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer). The thickness of the surface layer 83 can be approximately 8 to 40 [μm]. In this embodiment, the thickness of the surface layer 83 was set to 13 to 30 [μm].

[0048] Incidentally, a liquid lubricant is applied to the inner surface of the heating belt 72. As a result, this lubricant is interposed between the separation plate 77 and the heating belt 72. This allows the heating belt 72 to slide smoothly against the separation plate 77.

[0049] The pressing section 43 (Figures 2 and 3), which serves as the opposing member, is formed in a cylindrical shape with its central axis aligned in the left-right direction, and has a diameter of approximately 30 mm. This pressing section 43 is also called a pressure roller. As shown in the schematic cross-sectional view in Figure 5, the pressing section 43 has a structure in which an elastic layer 92, a primer layer 93, and a surface layer 94 are sequentially laminated on a central material 91.

[0050] The core material 91 is made of, for example, free-cutting steel (also called SUM) and is formed in a cylindrical shape with its central axis aligned in the left-right direction. The diameter of the core material 91 is approximately 24 mm. The elastic layer 92 is, for example, silicone rubber and is laminated to the circumferential surface of the core material 91 to a thickness of approximately 3 mm. The primer layer 93 is, for example, non-conductive RTV (Room Temperature Vulcanizing) silicone rubber and is formed to a thickness of approximately 5 μm or less on the outer surface of the elastic layer 92. The surface layer 94 is, for example, non-conductive PFA and has a thickness of 15 to 25 μm.

[0051] Furthermore, compression springs 44 are incorporated on the left and right sides of the fixing housing 41 of the fixing unit 40 (Figures 2 and 3). These compression springs 44 are coil springs and bias the heating unit 42 to the pressurizing unit 43 via parts not shown.

[0052] In this fixing unit 40, it is desirable that a pressure equivalent to a load of 27 to 36 kg acts between the heating unit 42 and the pressurizing unit 43 due to the compression spring 44, the weight of the heating unit 42, etc. In this embodiment, the fixing unit 40 is operated with a pressure equivalent to a load of 30 kg acting between the heating unit 42 and the pressurizing unit 43.

[0053] As a result, in the fixing unit 40, the heating unit 42 is pressed against the pressurizing unit 43, and the pressurizing unit 43 elastically deforms, forming a nip region N between the heating belt 72 and the pressurizing unit 43. Incidentally, inside the image forming apparatus 1 (Figure 1), a fixing transport path W3 is formed along this nip region N. In the fixing unit 40, the nip width WN (Figure 3), which is the length of this nip region N along the transport direction (i.e., roughly the front-to-back direction), is set to 8 to 11 [mm].

[0054] When printing is performed in the image forming apparatus 1, the fixing unit 40 generates heat by heating the heater 76 of the heating unit 42 and rotates the pressurizing unit 43 to make the heating belt 72 circulate. In the fixing unit 40, when the medium M is transported along the fixing transport path W3, the medium M is clamped in the nip region N by the heating belt 72 and the pressurizing unit 43. At this time, the fixing unit 40 fixes the toner by applying heat and pressure while the heating belt 72 is in contact with the medium M and the heating belt 72 is traveling at the same speed as the medium M.

[0055] Furthermore, the image forming apparatus 1 may use high-resistance paper as the medium M, such as coated paper or water-resistant paper, that is, paper that generates relatively large resistance during feeding. Specifically, coated papers such as "Kareka®" manufactured by Kokusai Paper & Pulp Trading Co., Ltd., "Lamifree®" manufactured by Nakagawa Manufacturing Co., Ltd., or "Ecocrystal®" manufactured by Tomoegawa Manufacturing Co., Ltd. can be used. In this case, the image forming apparatus 1 is designed to improve the toner fixing efficiency and fixing performance on the medium M by reducing the transport speed (i.e., paper feeding speed) of the medium M compared to when using plain paper.

[0056] In the image forming apparatus 1, the transport speed when using coated paper or the like can be set to approximately 50 to 80 mm / s, and the nip width WN can be set to 8 to 11 mm. In this embodiment, the transport speed was set to 55 mm / s and the nip width WN was set to 11 mm. As a result, in the image forming apparatus 1, the transit time required for a predetermined location on the medium M to pass through the nip region N in the fixing unit 40 is approximately 0.2 seconds.

[0057] In this embodiment, for example, if the transport speed of the medium M is 80 [mm / s] and the nip width WN is 8 [mm], the passage time required for a predetermined point of the medium M to pass through the nip region N is 0.1 [s]. Also, for example, if the transport speed of the medium M is 50 [mm / s] and the nip width WN is 11 [mm], the passage time required for a predetermined point of the medium M to pass through the nip region N is 0.22 [s].

[0058] [3. Evaluation of the heating belt] Incidentally, the coated paper mentioned above has a structure in which a relatively thin surface layer of resin or the like is superimposed on the surface of a base material made of paper (i.e., cellulose, etc.). This coated paper fills in the relatively small irregularities formed on the surface of the base material with the surface layer, resulting in a smoother surface compared to ordinary paper. For this reason, when an image is printed on coated paper using an image forming apparatus 1, etc., it is expected to be finished in a high-quality state with a uniform gloss.

[0059] However, in actual coated paper, due to irregularities formed on the substrate, fine depressions D may be formed on its surface, such as circular or elliptical depressions with a diameter or major axis of approximately 1 to 5 mm and a depth of approximately 10 μm.

[0060] When fixing a toner image to a medium M made of coated paper or the like, it is desirable for the fixing unit 40 to deform a part of the heating belt 72 so that it fits into the recess D as the recess D passes through the nip region N, and to bring the surface of the heating belt 72 into contact with the inner surface of the recess D, thereby pressing the toner onto the surface of the medium M.

[0061] On the other hand, in the image forming apparatus 1, as described above, when coated paper or the like is used as the medium M, the transport speed of the medium M is set to 55 [mm / s], and consequently, the time it takes for the medium M to pass through the nip region N of the fixing unit 40 is approximately 0.2 [s]. This means that in the fixing unit 40, if the heating belt 72 can deform to a shape corresponding to the depression D within 0.2 [s] after contacting the medium M and beginning to deform, then heat and pressure can be appropriately applied to the medium M. In other words, in the image forming apparatus 1, if the deformation speed and hardness of the heating belt 72 of the fixing unit 40 are within an appropriate range, then toner can be appropriately fixed even in the depression D, and gloss can be produced in the image.

[0062] Here, the relationship between the deformation speed and hardness of the heating belt 72 and its ability to conform to the medium M will be explained with reference to Figures 6(A) to (C). Figures 6(A) to (C) are schematic cross-sectional views showing the heating belt 72 in contact with the surface of the medium M in which a depression D has been formed in the nip region N.

[0063] For example, as shown in Figure 6(A), if the hardness of the heating belt 72 is relatively low and the deformation rate is relatively slow, the heating belt 72 cannot fully enter the depression D, and heat and pressure cannot be sufficiently transferred to the toner on the inner surface of the depression D. In other words, in this case, the heating belt 72 is slow to follow the shape of the medium M, including the depression D, or has poor responsiveness, and therefore cannot sufficiently follow the medium M within the passage time. In this case, the medium M will have a state where gloss is not locally displayed in the area where the depression D is formed, resulting in so-called gloss unevenness, and thus the image quality will be evaluated as low.

[0064] On the other hand, as shown in Figure 6(B), when the hardness of the heating belt 72 is within an appropriate range and the deformation rate is appropriate, the heating belt 72 can fully penetrate the depression D, and heat and pressure can be sufficiently transmitted to the toner on the inner surface of the depression D. In other words, in this case, the heating belt 72 has high conformability to the shape of the medium M, including the depression D, and has good responsiveness. In this case, the medium M will have sufficient gloss even in the area where the depression D is formed, and will have a uniform gloss, resulting in a high image quality.

[0065] Furthermore, as shown in Figure 6(C), if the hardness of the heating belt 72 is relatively high, the heating belt 72 cannot fully penetrate the recess D, and heat and pressure cannot be sufficiently transferred to the toner on the inner surface of the recess D. In other words, in this case, the heating belt 72 has poor conformability to the shape of the medium M, including the recess D, and its responsiveness is poor. In this case, as in the case of Figure 6(A), the medium M will have a state where gloss is not locally displayed in the area where the recess D is formed, resulting in so-called gloss unevenness, and thus the image quality will be evaluated as low.

[0066] Thus, in the fixing unit 40, as long as the hardness and deformation speed of the heating belt 72 are within an appropriate range, it can properly follow the shape of the media M, so that the toner is properly fixed in each part and the possibility of uneven gloss is reduced.

[0067] Incidentally, when measuring the hardness of a relatively thin component such as the heating belt 72, hardness measurement is generally performed using a so-called microhardness tester. With this microhardness tester, a probe (also called a measuring terminal), for example, formed in a cylindrical shape, is brought into contact with the target component, and a predetermined load or speed is applied to push it in. The hardness can then be measured based on the displacement of the probe.

[0068] In this embodiment, the "Micro Rubber Hardness Tester MD-1capa" manufactured by Polymer Instruments Co., Ltd. was used as the micro hardness tester. In this embodiment, a cylindrical probe with a diameter of 0.16 [mm] was used for measurement, the descent speed (i.e., indentation speed) of the probe was set to 3.2 [mm / s], and the load was set to 22 to 332 [Nm].

[0069] Figure 7 is a graph showing an example of the temporal change in measured values ​​obtained by a microhardness tester for several heating belts 72 with different configurations. The vertical axis represents the hardness value, converted to a relative value [%] with respect to the hardness value at the time of final saturation (hereinafter referred to as the saturation hardness value). The horizontal axis represents the elapsed time from the start of measurement, with values ​​plotted every 0.1 [s]. Hereafter, the characteristic curve formed by connecting each plot shown in Figure 7 will also be called a profile.

[0070] Figure 7 shows how the measured value by the microhardness tester increases over time after the start of measurement, and how the profile shape differs depending on the configuration of the heating belt 72. Thus, the difference in profile shape of the heating belt 72 indicates that the deformation rate of the heating belt 72 is different.

[0071] Therefore, in this embodiment, the hardness of the heating belt 72 is measured using this microhardness tester. In this embodiment, the measured value at 0.2 seconds after the start of measurement (hereinafter referred to as the 0.2-second hardness value) is considered to be a value corresponding to the rate at which the heating belt 72 deforms. Hereafter, this 0.2 seconds will also be referred to as the measurement time.

[0072] Furthermore, in this embodiment, the relationship between the hardness value after 0.2s in the heating belt 72 and the quality of the image printed on the medium M using the heating belt 72 was investigated. In this embodiment, the hardness value after 0.2s was normalized and comparisons were made easier by expressing the hardness value after 0.2s as a relative ratio to the saturation hardness value, which is the hardness value that was finally converged (hereinafter referred to as the 0.2s hardness ratio). For the sake of explanation, the hardness value after 0.2s and the saturation hardness value will also be referred to as the first hardness value and the second hardness value, respectively.

[0073] Specifically, in this embodiment, as an evaluation test, twelve types of heating belts 72 (72A to 72L) with various configurations of the elastic layer 82 and surface layer 83 were prepared, and the hardness of each heating belt 72 was measured using a microhardness tester. Table T1 shown in Figure 8 summarizes the specifications and measurement results of each heating belt 72 in tabular format.

[0074] Table T1 lists the specifications for each heating belt 72, including the thickness [μm] of the elastic layer 82, the hardness [°] of the elastic layer 82, and the thickness [μm] of the surface layer 83. Table T1 also lists the measured values ​​of the saturation hardness [°] and hardness [°] after 0.2s for each heating belt 72, as well as the hardness ratio after 0.2s calculated based on these values. The hardness ratio after 0.2s was rounded to the fourth decimal place.

[0075] Next, in this embodiment, printing tests were performed using each heating belt 72 (72A to 72L) in the fixing unit 40 of the image forming apparatus 1, and coated paper as the medium M, to print the test images described later. The obtained printing results were then evaluated. In these printing tests, the image forming apparatus 1 used was the "C844" manufactured by Oki Electric Industry Co., Ltd.

[0076] In this printing test, an image with a uniform black color across the entire surface (a so-called solid color image) was used as the test image. Furthermore, when gloss unevenness occurs on the printed medium M, it is thought that minute irregularities are formed on its surface, making it non-flat. In other words, it is thought that the degree of gloss unevenness increases on medium M as the area of ​​the flat parts decreases and the area of ​​the non-flat parts increases.

[0077] Therefore, in this embodiment, as an evaluation of the printing result of medium M, an evaluation was performed that divided the medium M into multiple "levels" based on the ratio of the area of ​​the flat portion on the surface of medium M. Each of these divided levels has a high correlation with the degree to which gloss unevenness occurs. In other words, in this embodiment, by using the ratio of the flat portion on the surface of medium M after printing, the degree to which gloss unevenness occurs in medium M is expressed by an objective index.

[0078] Specifically, in this embodiment, the test image was printed onto the medium M by an image forming apparatus 1 in which each heating belt 72 was incorporated into the fixing unit 40. In this embodiment, "Lamifree®" manufactured by Nakagawa Manufacturing Co., Ltd. was used as the medium M.

[0079] Next, in this embodiment, the surface shape of the medium M was observed using a laser microscope and a microscopic image was captured. In this embodiment, a confocal microscope "OPTELICS® HYBRID" manufactured by Lasertec Corporation was used as the laser microscope.

[0080] Next, in this embodiment, the laser microscope was used to perform a binarization process based on the brightness of each pixel in the obtained microscope image, thereby separating the planar portion from the non-planar portion. Furthermore, in this embodiment, the ratio of the area of ​​the planar portion to the area of ​​the entire microscope image was calculated and defined as the toner planar area ratio [%]. The following settings were adopted for the laser microscope.

[0081] Light intensity: 50% Brightness: 500 Objective lens: 10x (magnification 185x) Number of patchwork pieces: 8 vertical x 8 horizontal (image area of ​​11 mm x 11 mm) Binarization method: Brightness values Planar area extraction threshold: 85~190 (luminance value)

[0082] Furthermore, in this embodiment, the calculated toner planar area ratio [%] value was divided into five evaluation levels, from "Level 1" with relatively many gloss unevennesses to "Level 5" with almost no gloss unevennesses, by setting the following thresholds. The thresholds for each evaluation level were set appropriately by visually observing the state of gloss unevenness in multiple media M with various toner planar area ratios [%], so that significant differences could be observed between each level.

[0083] Level 1: Less than 31.2% Level 2: 31.2% or higher, less than 35.9% Level 3: 35.9% or higher, less than 40.6% Level 4: 40.6% or higher, less than 45.3% Level 5: 45.3% or higher

[0084] As a result of conducting such evaluation tests on each heating belt 72, the evaluation levels shown in Table T1 (Figure 8) were obtained. Figure 9 is a graph with the hardness ratio after 0.2s and the evaluation level on the horizontal and vertical axes, respectively, and plots were placed based on the values ​​for each heating belt 72. In Figure 9, plots where the evaluation level is level 4 or higher are represented by the symbol "○", and plots where the evaluation level is level 3 or lower are represented by the symbol "×". Below, the correlation between the hardness ratio after 0.2s and the evaluation level in this evaluation test will be explained based on Figures 8 and 9.

[0085] In this evaluation test, the evaluation level was level 4 or higher when the hardness ratio value after 0.2s was within the range R1 of 0.738 (73.8%) to 0.837 (83.7%). In this case, as shown in Figure 6(B), the fixing unit 40 showed a relatively fast response to indentation in the heating belt 72 and high conformability to the depressions D formed in the medium M. Therefore, the image forming apparatus 1 can apply heat and pressure evenly to each part of the medium M in the nip region N of the fixing unit 40, and can effectively reduce gloss unevenness in the image printed on the medium M. In this case, the hardness of the elastic layer 82 was in the range of 12 to 20 [°], and the hardness value after 0.2s was in the range of 56.4 to 65.5 [°].

[0086] Furthermore, in this evaluation test, the evaluation level was set to level 5 when the hardness ratio [%] value after 0.2s was within the range R2 of 0.793 (79.3%) to 0.837 (83.7%). At this time, the fixing unit 40 is considered to have an even faster response to indentation and even higher conformability to the depressions D formed in the medium M. As a result, the image forming apparatus 1 can significantly reduce gloss unevenness in the image printed on the medium M, and can obtain extremely high-quality printing results.

[0087] On the other hand, in this evaluation test, if the hardness ratio value after 0.2s was less than 0.738, the evaluation level was level 3 or lower. In this case, as shown in Figure 6(A), the fixing unit 40 shows a relatively slow response to indentation in the heating belt 72, and it is considered that it has poor ability to follow the depressions D formed in the medium M. As a result, the image forming apparatus 1 generates a relatively large amount of gloss unevenness in the image printed on the medium M.

[0088] Furthermore, in this evaluation test, the evaluation level was also level 3 or lower when the hardness ratio [%] value after 0.2s was greater than 0.837. In this case, as shown in Figure 6(C), the heating belt 72 becomes relatively hard in the fixing unit 40, so its elasticity is relatively small, and it is thought that its ability to follow the depressions D formed in the medium M is also low. As a result, the image forming apparatus 1 generates a relatively large amount of gloss unevenness in the image printed on the medium M.

[0089] Thus, this evaluation test revealed a relationship in which the degree of gloss unevenness in the image printed on medium M changes depending on the value of the 0.2s hardness ratio. Furthermore, this evaluation test revealed the range of 0.2s hardness ratios and 0.2s hardness values ​​that can effectively reduce the degree of gloss unevenness.

[0090] Based on the above, in the fixing section 40 of the image forming apparatus 1 according to this embodiment, a heating belt 72 is used such that the hardness ratio value after 0.2 s is at least within the range R1 of 0.738 to 0.837, and preferably within the range R2 of 0.793 to 0.837.

[0091] [4. Effects, etc.] In the above configuration, the image forming apparatus 1 according to this embodiment has the property that when printing an image on a coated paper medium M, the heating belt 72 of the fixing unit 40 is sufficiently deformed in the time it takes for the medium M to pass through the nip region N. Specifically, in the image forming apparatus 1, the heating belt 72 is one in which the value of the hardness ratio after 0.2s, measured using a microhardness tester, falls within the range R1 of at least 0.738 to 0.837.

[0092] Therefore, the image forming apparatus 1 can reliably deform the shape of the heating belt 72 to match the depressions D in the medium M and bring it into contact with its surface during the approximately 0.2 seconds it takes for the medium M to pass through the nip region N of the fixing unit 40 (Figure 6(B)). As a result, the image forming apparatus 1 can apply heat and pressure with the heating belt 72 to sufficiently fix the toner in both the flat areas and depressions D of the medium M, and can give the image printed on the medium M a uniform gloss without unevenness.

[0093] Furthermore, with respect to the heating belt 72 of the fixing unit 40, the image forming apparatus 1 can effectively suppress the occurrence of gloss unevenness even when the hardness value after 0.2 s is between 56.4° and 65.5° (Figure 8), thus achieving an evaluation level of level 4 or higher.

[0094] Furthermore, the image forming apparatus 1 may also employ a heating belt 72 in the fixing unit 40 such that the hardness ratio after 0.2 s falls within the range R2 of 0.793 to 0.837. In this case, the image forming apparatus 1 can further fix the toner to both the flat areas and depressions D of the medium M using the heating belt 72, significantly suppressing the occurrence of gloss unevenness in the image printed on the medium M and providing even better gloss.

[0095] In particular, in this embodiment, instead of using the simple hardness of the heating belt 72, i.e., the saturation hardness value, the 0.2s hardness value, which is the value measured by a microhardness tester 0.2 [s] after the start of measurement, is used. In this embodiment, this 0.2 [s] time is defined as the time required for the medium M to pass through the nip region N, and is specifically calculated based on the transport speed of the medium M and the nip width WN, which is the length of the nip region N. As a result, the image forming apparatus 1 can employ an appropriate heating belt 72 that deforms to match the depression D while the medium M passes through the nip region N.

[0096] Furthermore, in this embodiment, it was confirmed that as long as the hardness ratio value after 0.2 s falls within the range R1 of at least 0.738 to 0.837, the occurrence of gloss unevenness can be well suppressed even if the transit time required to pass through the nip region N is changed to 0.1 to 0.2 [s] by changing the transport speed and nip width WN.

[0097] Therefore, if the hardness ratio of the heating belt 72 reaches 0.738 or more and 0.837 or less by the time the nip passage is completed when it passes through the nip region N, the occurrence of uneven gloss can be suppressed in both the flat parts and depressions D in the medium M. In other words, the conditions required for the heating belt 72 do not necessarily need to match the elapsed time after the start of measurement by the microhardness tester with the time it takes to pass through the nip region N. For example, the conditions required for the heating belt 72 may be that the hardness ratio is within the range R1 of 0.738 or more and 0.837 or less when 0.16 ± 0.06 [s] has elapsed after the start of measurement by the microhardness tester.

[0098] From another perspective, in this embodiment, the microhardness tester is used in a manner that differs somewhat from the usual method. Normally, when using a microhardness tester, the probe is pressed against the object to be measured, and after a certain amount of time has passed and the value has stabilized, the value at this point (i.e., the saturated hardness value) is taken as the measured value.

[0099] In contrast, in this embodiment, the change in the heating belt 72 over time caused by pressing the probe of the microhardness tester against the medium M is considered to be very close to the change in the heating belt 72 over time when it is in contact with the depression D of the medium M. As a result, in this embodiment, the change in the shape of the heating belt 72 over time can be captured by sequentially reading the change in the measured value of the microhardness tester over time.

[0100] From another perspective, the image forming apparatus 1 is configured to ensure that the nip width WN of the nip region N is as large as possible in order to properly fix the toner to the medium M. Specifically, in the fixing section 40 (Figure 3), the heating section 42 is not a roller like the pressurizing section 43, but rather a heating belt 72 is made to circumfer the heating central section 71, and the heater 76 and separation plate 77 provided in the heating central section 71 have sufficient length in the front-to-back direction. In a fixing section 40 with this configuration, it is necessary to make the heating belt 72 that circumfers the heating central section 71 relatively thin, making it difficult to give the heating belt 72 sufficient thickness, and as a result, it was difficult to select the hardness of the heating belt 72.

[0101] In this regard, this embodiment focuses on the followability and responsiveness of the heating belt 72 during the passage time (i.e., 0.2 s) through the nip region N, and identifies good ranges R1 and R2 (Figure 9) by using the hardness ratio after 0.2 s as an indicator. As a result, the image forming apparatus 1 can appropriately improve the followability and responsiveness of the relatively thin heating belt 72 while ensuring a relatively large nip width WN in the fixing section 40 (Figure 3), and obtain good glossiness in the formed image.

[0102] Furthermore, in this embodiment, the toner planar area ratio based on the brightness of each pixel in the microscope image is used as an indicator, and the evaluation level is divided according to this value. Therefore, in this embodiment, regarding the presence and degree of gloss unevenness, instead of relying on ambiguous divisions based on visual inspection, the objective evaluation level of each heating belt 72 can be appropriately determined by clear divisions according to a uniform standard. As a result, the image forming apparatus 1 can print an image with sufficient glossiness, in which gloss unevenness is hardly visible, on the medium M by using an appropriate heating belt 72 selected based on an appropriately evaluated level.

[0103] With the above configuration, when printing an image on coated paper medium M, the image forming apparatus 1 ensures that the heating belt 72 of the fixing unit 40 is positioned such that the hardness ratio value after 0.2 s, measured using a microhardness tester, falls within the range R1 of at least 0.738 to 0.837. Therefore, the image forming apparatus 1 can reliably deform the shape of the heating belt 72 to match the depressions D in the medium M during the approximately 0.2 s it takes for the medium M to pass through the nip region N of the fixing unit 40. This allows the image forming apparatus 1 to sufficiently fix toner to both the flat areas and depressions D in the medium M, suppressing uneven gloss in the printed image and providing a uniform gloss.

[0104] [5. Other Embodiments] In the above-described embodiment, the nip width WN in the fixing section 40 is set to 8-11 [mm], the transport speed of the medium M is set to 55 [mm / s], and the passage time required for a predetermined point on the medium M to pass through the nip region N is set to approximately 0.2 [s]. Accordingly, the case in which the hardness value after 0.2 s or the hardness ratio after 0.2 s is used in the evaluation of the heating belt 72 is also described. However, the present invention is not limited to this, and by setting the nip width WN in the fixing section 40 and the transport speed of the medium M to various values, the passage time may be set to various times, such as 0.1 [s] or 0.4 [s]. In this case, the hardness or hardness ratio at the point when the passage time has elapsed after the start of measurement may be used in accordance with the passage time. Alternatively, the hardness or hardness ratio at a point when a shorter time has elapsed than the passage time may be used.

[0105] In the above-described embodiment, the evaluation test of the heating belt 72 involved calculating the toner planar area ratio based on the brightness values ​​of the microscope image obtained using a laser microscope, and using this to classify the belt into five evaluation levels (levels 1 to 5). However, the present invention is not limited to this, and the belt may be classified into each evaluation level by various methods, such as classifying it based on the subjective visual inspection of the evaluator. Furthermore, the number of evaluation levels to be classified into is not limited to five levels, but may be four levels or less, or six levels or more.

[0106] Furthermore, in the embodiments described above, the case in which the thickness of the base 81 in the heating belt 72 is approximately 70 to 90 [μm], the thickness of the elastic layer 82 is approximately 150 to 300 [μm], and the thickness of the surface layer 83 is approximately 13 to 30 [μm] was described (Figure 8). However, the present invention is not limited to this, and the thicknesses of the base 81, elastic layer 82, and surface layer 83 may be other values.

[0107] Furthermore, in the embodiments described above, the case where the hardness of the elastic layer 82 in the heating belt 72 is 12 to 20° was described. However, the present invention is not limited to this, and the hardness of the elastic layer 82 may be set to various other values.

[0108] Furthermore, in the embodiments described above, the case in which the pressurizing section 43 of the fixing section 40 (Figures 2 and 3) is configured as a pressurizing roller with an elastic layer 92 or the like formed on the circumferential surface of the central material 91 was described. However, the present invention is not limited to this, and various configurations are possible, such as configuring the pressurizing section 43 to combine a heating central section and a heating belt, similar to the heating section 42.

[0109] Furthermore, the embodiments described above described the case in which a medium M is used in which a surface layer such as resin is provided on the surface of the paper that is the base material, and fine depressions D are formed on that surface, such as coated paper. However, the present invention is not limited to this, and various media in which fine depressions or irregularities are formed on the surface, similar to coated paper, may be used.

[0110] Furthermore, the above-described embodiment describes a case in which a cylindrical probe is pressed into the heating belt 72, which is the object to be measured, using a microhardness tester, and the hardness of the heating belt 72 is measured based on the displacement of the probe. However, the present invention is not limited to this, and probes of various shapes may be used, for example, probes with hemispherical tips or elliptical cylindrical probes. Alternatively, a hardness tester that measures the hardness of the object to be measured by various other methods may be used. In this case, it is sufficient that the time change of a physical quantity corresponding to the displacement of the probe can be obtained. Also, regarding the various values ​​in the microhardness tester, the diameter of the probe may be other than 0.16 [mm], the descent speed of the probe may be other than 3.2 [mm / s], and the load may be other than 22 to 332 [Nm].

[0111] Furthermore, the above-described embodiment described a case in which the image forming apparatus 1 (Figure 1) is provided with four developing units 30. However, the present invention is not limited to this, and for example, the image forming apparatus 1 may be provided with one to three or five or more developing units 30.

[0112] Furthermore, the above-described embodiment described the case in which the present invention is applied to an image forming apparatus 1 which is a single-function SFP. However, the present invention is not limited to this, and may also be applied to image forming apparatuses with various other functions, such as an MFP (Multi-Function Peripheral) that has the functions of a copier or a facsimile machine.

[0113] Furthermore, the present invention is not limited to the embodiments described above and other embodiments. That is, the scope of application of the present invention extends to embodiments that arbitrarily combine some or all of the embodiments described above and other embodiments, as well as embodiments that extract some of them.

[0114] Furthermore, in the above-described embodiment, the case in which the fixing unit 40 as a fixing device is composed of a heating belt 72 as an annular belt and a pressurizing unit 43 as an opposing member was described. However, the present invention is not limited to this, and the fixing device may be composed of an annular belt and an opposing member of various other configurations. [Industrial applicability]

[0115] The present invention can be used, for example, when fixing a toner image formed on a medium by an electrophotographic method to the medium using a fixing unit. [Explanation of symbols]

[0116] 1...Image forming apparatus, 20...Transfer section, 30...Developing section, 40...Fixing section, 42...Heating section, 43...Pressurizing section, 71...Heating center section, 72...Heating belt, 73...Support, 74...Support, 75...Heat conductive plate, 76...Heater, 77...Separation plate, 78...Temperature sensor, 81...Substrate, 82...Elastic layer, 83...Surface layer, 91...Core material, 92...Elastic layer, 93...Primer layer, 94...Surface layer, M...Media, D...Indentation, N...Nip area, WN...Nip width, R1...Range, R2...Range.

Claims

1. An annular belt having an outer surface and traveling at a predetermined speed, A counter member facing the outer circumferential surface of the annular belt, forming a nip region with the annular belt at a pressure equivalent to a load of 27 to 36 kg, Equipped with, The aforementioned annular belt is Substrate and, A surface layer located on the outside of the substrate and forming the outer surface, An elastic layer provided between the substrate and the surface layer It has, In the annular belt, when the hardness of the outer surface is measured using a hardness tester, the first hardness value (A) is defined as the measurement value obtained after a measurement time has elapsed corresponding to the time required for a predetermined position on the outer surface to pass through the nip region, and the second hardness value (B) is defined as the measurement value obtained when the hardness tester's measurement value saturates. In this case, the ratio (A / B) of the first hardness value (A) to the second hardness value (B) is 0.738 or more and 0.837 or less. A fixing device characterized by the following features.

2. The hardness tester applies a predetermined load to the measuring terminal, presses the measuring terminal against the outer surface to be measured at a predetermined pressing speed, and obtains the first hardness value and the second hardness value based on the displacement of the measuring terminal. The fixing device according to feature 1.

3. The annular belt has a ratio (A / B) of 0.793 or more and 0.837 or less. The fixing device according to claim 1 or 2.

4. The thickness of the substrate is 70 to 90 [μm], The thickness of the elastic layer is 150 to 300 [μm]. The thickness of the surface layer is 13 to 30 [μm]. The fixing device according to feature 1.

5. The hardness of the elastic layer is 12 to 20 degrees. The fixing device according to feature 4.

6. The opposing member is a roller in which an elastic layer is formed on the circumferential surface of a rotatably supported central axis. A fixing device according to any one of claims 1 to 5, characterized by the features described above.

7. An annular belt having an outer surface and traveling at a predetermined speed, A counter member facing the outer circumferential surface of the annular belt, forming a nip region with the annular belt at a pressure equivalent to a load of 27 to 36 kg, Equipped with, The aforementioned annular belt is Substrate and, A surface layer located on the outside of the substrate and forming the outer surface, An elastic layer provided between the substrate and the surface layer It has, The annular belt, in hardness measurement of the outer surface using a hardness tester, has a measured value of 56.4° or more and 65.5° or less at the time when a measurement time equivalent to the time required for a predetermined position on the outer surface to pass through the nip region has elapsed since the start of the hardness measurement. A fixing device characterized by the following features.

8. The aforementioned annular belt is Substrate and, An elastic layer formed on the surface of the substrate, with a thickness of 250 to 300 [μm], A surface layer formed on the surface of the elastic layer, with a thickness of 15.0 to 29.6 [μm] and The fixing device according to claim 7, characterized by having the following features.

9. The hardness of the elastic layer is 12 to 20 degrees. The fixing device according to feature 8.

10. A heating member disposed on the inner circumference side of the annular belt, in a position facing the opposing member. A fixing device according to any one of claims 1 to 9, characterized by comprising the above.

11. The time required for the medium sandwiched between the annular belt and the opposing member to pass through the nip region is 0.16 ± 0.06 [s]. The fixing device according to feature 1.

12. A developing unit that uses a developer to deposit a developer image onto the surface of the medium, A fixing apparatus according to any one of claims 1 to 11, for fixing the developer image onto the medium, An image forming apparatus equipped with the following.

Images