Fixing apparatus and image forming apparatus

Abstract

To improve the quality of an image to be fixed to a medium by using an annular belt.SOLUTION: An image forming apparatus 201 comprises a fixing belt 277 having an elastic layer 82 with a thickness of 300 [μm] or more, in which a height T1 that is the differential value between the maximum value and the minimum value appearing in a thickness distribution curve is adjusted to be less than 101 [μm]. The image forming apparatus 201 can thus prevent the occurrence of pressure release where pressure applied to a medium M is locally reduced and satisfactorily reduce the generation of white dots in a nip area N of a fixing unit 250.SELECTED DRAWING: Figure 18

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) using toner (also called a developer) is formed by a developing device, transferred to a sheet of paper (also called a medium), and the image is printed by applying heat and pressure to this sheet of paper by a fixing device. Among these, the fixing device is configured such that, for example, rollers, an annular belt, etc. are respectively arranged above and below the paper conveyance path, and the paper is sandwiched in a nip region formed between them, and heat and pressure are applied to the paper.

[0003] As this fixing device, there is one configured such that a fixing belt (also called an annular belt) circulates around the periphery of a roller, a pressure member, etc. in the upper or lower part of the conveyance path. In this fixing device, compared with the case where at least one of the upper and lower parts of the conveyance path is constituted by one roller, the length along the conveyance direction of the nip region (so-called nip width) can be configured to be relatively long, and the fixing property can be enhanced (for example, see 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 the above-described fixing device, in order to improve the quality of an image, although the elastic layer of the fixing belt may be configured to be relatively thick, due to problems such as manufacturing accuracy, the thickness may become non-uniform.

[0006] Consequently, in a fixing device, if the fixing belt thickness is uneven, when it is sandwiched between rollers or pressure members in the nip region, uneven pressure is applied to the media. As a result, in an image forming apparatus, there is a problem that areas of insufficient fixing may occur in the formed image, potentially degrading the quality of the image.

[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 using an annular belt. [Means for solving the problem]

[0008] In order to solve these problems, the fixing device of the present invention, A substrate and located outside the substrate Outer surface It has a surface layer that forms a substrate and an elastic layer with a thickness of 377 to 607 [μm] provided between the substrate and the surface layer. Driving at a predetermined speed do The device comprises an annular belt and an opposing member that faces the outer circumferential surface of the annular belt and forms a nip region between itself and the annular belt. The nip region has a first load region in which a load is applied between itself and the opposing member, and a second load region in which a stronger load is applied than in the first load region. The annular belt has a thickness in the circumferential direction of the annular belt at a first position in the width direction. Regarding this, when measured every 0.4 mm in the circumferential direction, all of the preceding occurrences during driving Local maximum and Appearing after this The difference from the minimum value is less than 101 [μm], and the length from the point where the thickness of the annular belt is maximum to the point where it is minimum in the circumferential direction is greater than the length of the first load region in the nip region. long I did that.

[0009] 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.

[0010] This invention relates to the thickness of an annular belt in the circumferential direction. Regarding all of the things that appear in advance when driving Local maximum and Appearing after thisAppropriately define an upper limit for the difference value from the local minimum, and set the length from the local maximum to the local minimum to be longer than the length of the first load region. long Therefore, in this invention, This avoids a sharp change in the thickness of the annular belt from a maximum to a minimum within a relatively narrow angular range, thereby As the media passes through the nip region together with the annular belt, variations in the pressure applied to the media can be kept to a minimum. As a result, the present invention can form high-quality images in which the developer adhering to the media is uniformly fixed. [Effects of the Invention]

[0011] 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 using an annular belt. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing the configuration of an image forming apparatus. [Figure 2] This is a schematic diagram showing the configuration of the process unit. [Figure 3] This is a schematic cross-sectional view showing the configuration of the fixing unit. [Figure 4] This is a schematic cross-sectional view showing the structure of the anchoring belt. [Figure 5] This is a schematic diagram showing the pressure distribution in the nip region. [Figure 6] This is a schematic perspective view showing the composition of the media. [Figure 7] This is a schematic diagram showing the deformation of the heating belt in response to the depressions in the medium. [Figure 8] This is a schematic diagram showing how the measured values ​​from a microhardness tester change over time. [Figure 9] This is a schematic diagram showing the values ​​and measurement results of each part of the fixing belt according to the first embodiment, as well as the gloss level. [Figure 10] This is a schematic diagram showing the relationship between the load hardness ratio and the gloss level in the fixing belt according to the first embodiment. [Figure 11]It is a schematic diagram showing the relationship between the thickness of the elastic layer and the load hardness ratio in the fixing belt according to the first embodiment. [Figure 12] It is a schematic diagram showing the values and measurement results of each part in the fixing belt according to the second embodiment, and the gloss bell. [Figure 13] It is a schematic diagram showing the relationship between the thickness of the elastic layer and the gloss level in the fixing belt according to the second embodiment. [Figure 14] It is a schematic diagram showing the relationship between the printed image when no white spots occur and the film thickness of the fixing belt. [Figure 15] It is a schematic diagram showing the relationship between the printed image when white spots occur and the film thickness of the fixing belt. [Figure 16] It is a schematic diagram showing the measurement locations of the film thickness in the fixing belt. [Figure 17] It is a schematic diagram showing the relationship between the pressure distribution in the nip region and the film thickness of the fixing belt. [Figure 18] It is a schematic diagram showing the distance between the maximum and minimum values and the film thickness difference in the film thickness profile. [Figure 19] It is a schematic diagram showing the relationship between the width direction interval and the film thickness difference value at a plurality of width measurement positions in the fixing belt. [Figure 20] It is a schematic diagram showing the presence or absence of white spots in each width direction film thickness difference. [Figure 21] It is a schematic diagram showing the relationship between the width direction film thickness difference and the presence or absence of white spots.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings. [[ID=三十九]]

[0014] [1. First Embodiment] [1-1. Configuration of Image Forming Apparatus] As shown in FIG. 1, the image forming apparatus 1 according to the first embodiment is an electrophotographic printer and can form, that is, print, a color image on a film-like medium M.

[0015] The image forming apparatus 1 has various components arranged inside a roughly box-shaped housing 2. For the purposes of this explanation, the rightmost part in Figure 1 will be considered the front of the image forming apparatus 1, and the vertical, horizontal, and front-to-back directions will be defined and explained based on the perspective of viewing this front. The image forming apparatus 1 is designed to accommodate a medium M with a horizontal length of 170 mm, and forms images while transporting it along a transport path, which will be described later. For this reason, each part inside the image forming apparatus 1 has a length corresponding to the medium M in the horizontal direction.

[0016] The image forming apparatus 1 is centrally controlled by a control unit 3. This control unit 3 is connected to a higher-level device such as a computer (not shown), and upon receiving print instructions or print data from this higher-level device, it executes an image forming process (also called a printing process) to form a print image on the surface of the medium M.

[0017] A media cassette 10 for housing the media M is provided in the front part of the housing 2. This media cassette 10 is constructed as a hollow rectangular parallelepiped, with its top open, and rotatably supports the media supply shaft 11 inside. The media supply shaft 11 forms a media supply roll MR1 when a long piece of media M is wound around it.

[0018] A pickup roller 12 is positioned on the rear upper side of the media supply shaft 11. The pickup roller 12 is cylindrical in shape with its central axis aligned in the left-right direction and is rotatably supported. When driving force is supplied from a driving force source (not shown), the pickup roller 12 rotates counterclockwise as shown in the figure, thereby pulling the media M from the media supply roll MR1 and feeding it to the rear. Inside the image forming apparatus 1, a transport path W for transporting the media M is formed behind the pickup roller 12, and is generally in a straight line along the front-rear direction.

[0019] A cutter unit 13 is positioned behind the pickup roller 12. The cutter unit 13 cuts the medium M based on the control of the control unit 3.

[0020] On the rear side of the cutter unit 13, multiple transport roller pairs 14 and a medium sensor 15 are appropriately arranged along the transport path W. Each transport roller pair 14 is configured with a transport roller positioned above and below the transport path W. Each transport roller is formed in a cylindrical shape with its central axis aligned in the left-right direction, and is rotatably supported, with one end pressed against the other. The transport roller pair 14 moves the medium M backward along the transport path W by gripping it with the upper and lower transport rollers. The medium sensor 15 detects the medium M passing through the transport path W, generates a predetermined detection signal, and supplies it to the control unit 3. The control unit 3 controls the operation of each part based on this detection signal.

[0021] An intermediate transfer unit 20 is positioned above the transport roller pair 14 and the medium sensor 15. This intermediate transfer unit 20 consists of intermediate rollers 21 and 22, five primary transfer rollers 23, a secondary transfer roller 24, a secondary transfer backup roller 25, and an intermediate transfer belt 26, etc. Of these, the intermediate rollers 21 and 22, the five primary transfer rollers 23, the secondary transfer rollers 24, and the secondary transfer backup roller 25 are all formed in a cylindrical shape with their central axis aligned in the left-right direction and are rotatably supported.

[0022] The intermediate roller 21 is positioned above the conveyor roller pair 14, etc. The intermediate roller 22 is positioned slightly behind the intermediate roller 21 and receives driving force from a driving force source (not shown). Five primary transfer rollers 23 are arranged sequentially in a straight line between the intermediate rollers 21 and 22, at approximately equal intervals from each other. A predetermined high voltage is applied to the primary transfer rollers 23.

[0023] The secondary transfer roller 24 is positioned between the intermediate rollers 21 and 22 in the front-rear direction and adjacent to the upper side of the transport path W. The secondary transfer backup roller 25 is positioned directly below the secondary transfer roller 24 and in contact with it. In other words, the secondary transfer roller 24 and the secondary transfer backup roller 25 grip the medium M located on the transport path W. Hereinafter, the secondary transfer roller 24 and the secondary transfer backup roller 25 will be collectively referred to as the secondary transfer section 27, and the section gripped by both rollers will be referred to as the secondary transfer nip section 28.

[0024] The intermediate transfer belt 26 is a flexible, endless belt that is stretched around the intermediate rollers 21 and 22, the five primary transfer rollers 23, and the secondary transfer roller 24. Based on the control of the control unit 3, the intermediate transfer unit 20 rotates the intermediate roller 22 and the primary transfer rollers 23 clockwise in the figure, thereby causing the intermediate transfer belt 26 to move clockwise in the figure.

[0025] Above each primary transfer roller 23, five process units 30 (30K, 30Y, 30M, 30C, and 30S) are arranged sequentially in the front-to-back direction. Each process unit 30 is also called an image forming unit or developing unit, and while they correspond to the respective colors of black (K), yellow (Y), magenta (M), cyan (C), and spot color (S), they are all similarly configured, differing only in color. The spot colors are special colors not typically used in general color printing, such as white or clear (transparent).

[0026] As shown in the schematic side view in Figure 2, the process unit 30 is positioned adjacent to the exposure unit 31. This process unit 30 includes a toner storage unit 32, a supply roller 33, a charging roller 34, a photoreceptor drum 35, and a developing blade 36, among other things. Each of these rollers and the photoreceptor drum 35 is configured to be cylindrical or cylindrical with its central axis aligned in the left-right direction, and is rotatable.

[0027] The exposure unit 31 is located above the photoreceptor drum 35 and has multiple LEDs (Light Emitting Diodes) aligned in the left-right direction. The toner storage unit 32 stores toner as a developer. The photoreceptor drum 35 is in contact with the intermediate transfer belt 26 near its lower end and sandwiches the intermediate transfer belt 26 between itself and the primary transfer roller 23.

[0028] In this process unit 30, the photoreceptor drum 35 rotates clockwise in the figure, and each roller rotates counterclockwise in the figure, due to the driving force supplied from a predetermined driving force source. The charging roller 34 uniformly charges the outer surface of the photoreceptor drum 35. The exposure unit 31 illuminates each LED as appropriate based on the control of the control unit 3, thereby exposing the outer surface of the photoreceptor drum 35 to light and forming an electrostatic latent image.

[0029] The supply roller 33 has a thin film of toner from the toner storage section 32 attached to its circumferential surface. The photoreceptor drum 35 forms a toner image (also called a developer image) by transferring toner from the supply roller 33 according to the formed electrostatic latent image. This toner image is transferred to the intermediate transfer belt 26 by a high voltage applied to the primary transfer roller 23. Any toner remaining on the outer surface of the photoreceptor drum 35 is scraped off by the developing blade 36.

[0030] The intermediate transfer unit 20 (Figure 1) moves along the intermediate transfer belt 26, sequentially transferring toner images of each color from each process unit 30. These toner images reach the secondary transfer section 27, where they are transferred to the medium M in the secondary transfer nip section 28.

[0031] A fixing unit 50 is located behind the secondary transfer unit 27. The fixing unit 50 transports the medium M along the transport path W 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 to the rear (details will be described later).

[0032] A transport roller pair 17 and a medium sensor 18 are located at the rear of the fixing unit 50. The transport roller pair 17 is configured similarly to the transport roller pair 14 and feeds the medium M in the rearward direction. The medium sensor 18 is configured similarly to the medium sensor 15 and detects the medium M, generates a predetermined detection signal, and supplies it to the control unit 3. The control unit 3 controls the operation of each part based on this detection signal.

[0033] A media winding unit 60 is provided at the rear of the image forming apparatus 1. In this media winding unit 60, a media winding shaft 62 is rotatably supported inside a media cassette 61. A pair of transport rollers 63 is provided on the front upper side of the media winding shaft 62. The media winding unit 60 transports the media M, i.e., the media M on which the image has been formed, discharged from the image forming apparatus 1 to the rear by the pair of transport rollers 63, and then winds it onto the media winding shaft 62, thereby forming a media winding roller MR2.

[0034] In this way, the image forming apparatus 1 can form an image, that is, print, by transporting the medium M along the transport path W, transferring the toner image formed by the process unit 30 onto the medium M, and fixing it in the fixing unit 50.

[0035] [1-2. Configuration of the Fixing Unit] Next, the configuration of the fixing unit 50 will be described. Figure 3 is a schematic cross-sectional view of the fixing unit 50. The fixing unit 50 is broadly composed of an upper fixing unit 51 located above the transport path W and a lower fixing unit 52 located below the transport path W. Like other parts provided in the image forming apparatus 1, this fixing unit 50 has sufficient length in the left-right direction.

[0036] The upper fixing unit 51 includes a pressure pad 71, a drive roller 72, heaters 73 and 74, guide rollers 75 and 76, and a fixing belt 77, etc.

[0037] The pressure pad 71 has a shape similar to a trapezoid when viewed from the left or right, and its lower surface is flat. The drive roller 72 is formed in a cylindrical shape with its central axis aligned along the left-right direction and is rotatably supported. When driving force is supplied from a driving force source (not shown), it rotates clockwise as shown in the figure. The heaters 73 and 74 generate heat when power is supplied from a power supply unit (not shown) based on the control of the control unit 3 (Figure 1).

[0038] The guide roller 75 is located above the pressure pad 71 and the heaters 73 and 74. The guide roller 76 is located in front of the pressure pad 71. Both the guide rollers 75 and 76 are formed in a cylindrical shape with their central axis aligned in the left-right direction and are rotatably supported.

[0039] The anchoring belt 77, as an annular belt, is an endless belt with a hollow cylindrical shape and sufficient length in the left-right direction, possessing flexibility and heat resistance. As shown in the schematic cross-sectional view in Figure 4, the anchoring belt 77 has a layered structure in which three types of members, a base 81, an elastic layer 82, and a surface layer 83, are sequentially laminated. The inner diameter of the anchoring belt 77 can be approximately 15 to 60 mm. In this embodiment, the inner diameter of the anchoring belt 77 is set to 42 to 48 mm.

[0040] The substrate 81 is located on the innermost side of the fixing belt 77 and is made of a metal material such as stainless steel. The thickness of the substrate 81 can be approximately 20 to 60 μm. In this embodiment, the thickness of the substrate 81 is approximately 40 to 60 μm. The substrate 81 can also be made of a resin material such as polyimide, in which case its thickness can be approximately 50 to 120 μm.

[0041] 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 1000 [μm], and in this embodiment it is approximately 300 to 800 [μm]. The hardness of the silicone rubber constituting this elastic layer 82 is preferably approximately 10 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 30 to 40 [°] was used as the elastic layer 82.

[0042] The surface layer 83 is located on the outermost part of the fixing belt 77 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 15 to 30 [μm].

[0043] The fixing belt 77 (Figure 3) is arranged to circle around the pressure pad 71, the drive roller 72, and the guide rollers 75 and 76. Therefore, when the drive roller 72 rotates clockwise, the fixing belt 77 travels in a clockwise direction. In addition, the fixing belt 77 becomes relatively hot, for example, 140-160°C, because heat is supplied to it from the heaters 73 and 74.

[0044] The lower fixing unit 52 is configured to be roughly symmetrical with the upper fixing unit 51, and includes a pressure pad 91, a pressure roller 92, a heater 93, guide rollers 95 and 96, and a pressure belt 97 as an opposing member.

[0045] Of these, the pressure pad 91, heater 93, guide rollers 95 and 96, and pressure belt 97 are configured in the same way as the pressure pad 71, heater 73, guide rollers 75 and 76, and fixing belt 77, respectively. The pressure roller 92, like the drive roller 72, is formed in a cylindrical shape with its central axis aligned in the left-right direction and is rotatably supported, but no driving force is supplied to it.

[0046] In this fixing unit 50, the pressure pads 71 ​​and 91 are biased toward each other, and the drive roller 72 and pressure roller 92 are also biased toward each other. As a result, in the fixing unit 50, the portion of the fixing belt 77 near the pressure pads 71 ​​and drive roller 72 and the portion of the pressure belt 97 near the pressure pads 91 and pressure roller 92 are in contact with each other on the conveyor path W. Hereinafter, this portion will be called the nip region N, and the length in the front-rear direction along the conveyor path W in this nip region N will be called the nip width WN. In this embodiment, the nip width WN is set to 20 to 23 [mm].

[0047] Furthermore, in the nip region N, the pressure from the drive roller 72 is higher than the pressure from the pressure pad 71, resulting in the pressure distribution shown in Figure 5. In Figure 5, the horizontal axis represents the position in the front-to-back direction, and the vertical axis represents the magnitude of the pressure. Hereafter, the region where pressure is applied by the pressure pad 71 will be referred to as the first load region AR1, and the region where pressure is applied by the drive roller 72 will be referred to as the second load region AR2.

[0048] In the fixing unit 50, a relatively weak pressure is applied mainly in the first load region AR1 to melt the toner on the medium M, and a stronger pressure than in the first load region AR2 is applied mainly in the second load region AR2 to fix the toner to the surface of the medium M. In this fixing unit 50, the fixing belt 77 and the pressure belt 97 can be configured with a relatively longer nip width WN compared to a case where at least one of the upper and lower parts of the conveyor path is configured with a single roller, thereby improving fixing performance.

[0049] In this anchoring unit 50, it is desirable that a pressure equivalent to a load of 25 to 35 kg acts between the upper anchoring unit 51 and the lower anchoring unit 52 due to the action of biasing members (not shown) or gravity. In this embodiment, the anchoring unit 50 is operated with a load of 30 kg acting between the upper anchoring unit 51 and the lower anchoring unit 52 in a range of 170 mm in the left-right direction.

[0050] Furthermore, in the image forming apparatus 1, the medium M may be a film, or a medium that generates relatively high resistance during feeding, such as coated paper or water-resistant paper. In this case, the image forming apparatus 1 is designed to improve the toner fixing efficiency and fixation performance of the medium M by reducing the transport speed (i.e., paper feeding speed) of the medium M compared to when using plain paper.

[0051] In the image forming apparatus 1, the transport speed when using a film medium M can be set to approximately 2 to 6 [ips (inches per second)], or 50.8 to 152.4 [mm / s], and in this embodiment, it was set to 4 [ips], or approximately 101.6 [mm / s]. In this case, since the nip width WN in the image forming apparatus 1 is 20 [mm], the passage time required for a predetermined point on the medium M to pass through the nip region N in the fixing unit 50 is approximately 0.2 [s].

[0052] With this configuration, when the fixing unit 50 rotates the drive roller 72 and moves the fixing belt 77, the pressure belt 97 can be moved in a counterclockwise direction as shown in the figure, following the rotation of the drive roller 72. At the same time, when the medium M is being transported along the transport path W, the fixing unit 50 applies heat and pressure to the portion of the medium M located within the nip region N. As a result, if a toner image has been transferred to the medium M in the secondary transfer section 27 (Figure 1), the fixing unit 50 can melt the toner and fix this toner image to the medium M.

[0053] [1-3. Details of the fixing belt] Incidentally, the medium M used in this embodiment is configured as the film described above. As shown in the schematic perspective view and cross-section in Figure 6, this medium M has a configuration in which coating layers ML2 and ML3 are superimposed on both sides of the substrate layer ML1, for example.

[0054] Furthermore, medium M has multiple fine pores H1, H2, and H3 formed in the base layer ML1 and coating layers ML2 and ML3, respectively, which diffusely reflect light to increase the degree of whiteness, improve ease of writing, and reduce weight.

[0055] This medium M is expected to produce a uniformly glossy, high-quality finish when an image containing a certain area (also called a solid area) filled with a single color is printed by an image forming apparatus 1, for example. However, since each layer of the medium M has voids, when a load (i.e., pressure) is applied to the nip area N of the fixing unit 50, the area of ​​the surface near where the voids are formed may deform locally and significantly, potentially forming fine depressions D.

[0056] When fixing a toner image to a medium M having such a configuration, it is desirable that the fixing unit 50 deforms a portion of the fixing belt 77 by the applied load as the recess D passes through the nip region N, causing it to enter the recess D and come into contact with the inner surface of the recess D, thereby pressing the toner onto the surface of the medium M.

[0057] On the other hand, in the image forming apparatus 1, as described above, when using a film-like medium M, the transport speed of the medium M is set to 4 [ips], or approximately 101.6 [mm / s], and consequently, the passage time of the medium M through the nip region N of the fixing unit 50 is approximately 0.2 [s]. This means that in the fixing unit 50, if the fixing belt 77 can deform to a shape corresponding to the depression D within 0.2 [s] after a load is applied and deformation begins while the fixing belt 77 is in contact with the medium M, 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 fixing belt 77 of the fixing unit 50 are within an appropriate range, it is possible to properly fix the toner even in the depression D and produce gloss in the image.

[0058] Here, the relationship between the deformation speed and hardness of the fixing belt 77 and its ability to follow the medium M will be explained with reference to Figures 7(A) to (C). Figures 7(A) to (C) are schematic cross-sectional views showing the fixing belt 77 in contact with the surface of the medium M in which a depression D has been formed in the nip region N.

[0059] For example, as shown in Figure 7(A), if the fixing belt 77 has relatively low hardness and therefore deforms relatively slowly, the fixing belt 77 cannot fully penetrate 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 fixing belt 77 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.

[0060] On the other hand, as shown in Figure 7(B), when the hardness of the fixing belt 77 is within an appropriate range and the deformation speed is appropriate, the fixing belt 77 can fully penetrate the recess D, and heat and pressure can be sufficiently transmitted to the toner on the inner surface of the recess D. In other words, in this case, the fixing belt 77 has high conformability to the shape of the medium M, including the recess D, and has good responsiveness. In this case, the medium M will have sufficient gloss even in the area where the recess D is formed, and will have a uniform gloss, resulting in a high image quality.

[0061] Furthermore, as shown in Figure 7(C), if the hardness of the fixing belt 77 is relatively high, the fixing belt 77 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 fixing belt 77 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 7(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.

[0062] Thus, in the fixing unit 50, as long as the hardness and deformation speed of the fixing belt 77 are within an appropriate range, it can properly follow the shape of the media M, thus ensuring good toner fixation in each part and reducing the possibility of uneven gloss.

[0063] Incidentally, when measuring the hardness of a relatively thin component such as the fixing belt 77, hardness measurement is generally performed using a so-called microhardness tester. In this microhardness tester, a probe (also called a measuring terminal), which is formed in the shape of a cylinder or the like, is brought into contact with the target component, and a predetermined load or speed is applied to push it in, and the hardness can be measured based on the amount of displacement of the probe.

[0064] 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].

[0065] Figure 8 is a graph illustrating an example of the temporal change in measured values ​​obtained by a microhardness tester for several anchoring belts 77 with different configurations. The vertical axis represents the hardness value, converted to a relative value [%] with respect to the hardness value at the point of 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]. In the following, the characteristic curve formed by connecting each plot shown in Figure 8 will also be referred to as a profile.

[0066] Figure 8 shows how the measured value from the microhardness tester increases over time after the start of measurement, and how the profile shape differs depending on the configuration of the anchoring belt 77. Thus, the difference in profile shape of the anchoring belt 77 indicates that the deformation rate of the anchoring belt 77 is different.

[0067] Therefore, in this embodiment, the hardness of the anchoring belt 77 is measured using this micro-hardness tester. In this embodiment, the measured value at 0.2 [s] after the start of measurement (hereinafter referred to as the load hardness value) is considered to be a value corresponding to the rate at which the anchoring belt 77 deforms. Hereafter, this 0.2 [s] will also be referred to as the measurement time.

[0068] Furthermore, in this embodiment, the relationship between the load hardness value of the fixing belt 77 and the quality of the image printed on the medium M using the fixing belt 77 was investigated. In this embodiment, the load hardness value was normalized and made easier to compare by expressing it as a relative ratio (hereinafter referred to as the load hardness ratio) to the saturation hardness value, which is the hardness value that was finally converged. For the sake of explanation, the load hardness value and the saturation hardness value will also be referred to as the first hardness value and the second hardness value, respectively, below.

[0069] Specifically, in this embodiment, as an evaluation test, five types of fixing belts 77 (77A to 77E) with various configurations of the elastic layer 82 and surface layer 83 were prepared, and the hardness of each fixing belt 77 was measured using a microhardness tester.

[0070] In this evaluation test, for each anchoring belt 77, the thickness [μm] of the elastic layer 82, the hardness [°] of the elastic layer 82, and the thickness [μm] of the surface layer 83 were measured. Of these, the thickness of the elastic layer 82 was measured at multiple locations separated in the left-right direction (also called the width direction), and the maximum and minimum values ​​were identified for each anchoring belt 77, and the average value was calculated.

[0071] Table TBL1, shown in Figure 9, summarizes the specifications and measurement results of each fixing belt 77 in tabular format. Table TBL1 lists the maximum, minimum, and average values ​​of the thickness [μm] of the elastic layer 82, as well as the hardness [°] of the elastic layer 82 and the thickness [μm] of the surface layer 83 as specifications for each fixing belt 77.

[0072] Table TBL1 also lists the measured saturation hardness value [°] and load hardness value [°] for each anchoring belt 77, as well as the load hardness ratio calculated based on both. For the load hardness ratio, the maximum, minimum, and average values ​​measured at multiple points separated in the left-right direction of each anchoring belt 77 were rounded to the fourth decimal place. For the saturation hardness value and load hardness value, only the average values ​​of the measurements taken at multiple points separated in the left-right direction of each anchoring belt 77 are listed.

[0073] Next, in this embodiment, printing tests were performed using each fixing belt 77 (77A to 77E) in the fixing unit 50 of the image forming apparatus 1, and using the film-like medium M described above, to print the test images described later. The obtained printing results were then evaluated. In this printing test, the image forming apparatus 1 used was the "Pro1050" manufactured by OKI Electric Industry Co., Ltd. The transport speed of the medium M was set to 4 [ips], or approximately 101.6 [mm / s].

[0074] In this printing test, the test image was an image uniformly filled with a mixture of cyan and magenta (a so-called solid color 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, on medium M, it is thought that the degree of gloss unevenness increases as the area of ​​the flat parts decreases and the area of ​​the non-flat parts increases.

[0075] 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.

[0076] Specifically, in this embodiment, the test image was printed onto the medium M by an image forming apparatus 1 in which each fixing belt 77 was incorporated into the fixing unit 50. In this embodiment, "Yupo Tack (registered trademark) base paper [high-performance product]" manufactured by Yupo Corporation was used as the medium M.

[0077] 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.

[0078] 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.

[0079] 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)

[0080] Furthermore, in this embodiment, the calculated toner planar area ratio [%] value was divided into 10 gloss levels, from "Level 1" with relatively many gloss unevennesses to "Level 10" 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 on multiple media M with varying toner planar area ratios [%], so that significant differences could be observed between each level.

[0081] Incidentally, in this evaluation test, although multiple load hardness ratios were calculated for each anchoring belt 77 based on saturation hardness values ​​at multiple locations separated in the left-right direction, each anchoring belt 77 was classified into one gloss level, and its value is shown in Table TBL1 (Figure 9).

[0082] Furthermore, with respect to the fixing belt 77, because the elastic layer 82 is relatively thick, the surface layer 83 may not be able to withstand the pressure in the nip region N, causing it to crack (hereinafter referred to as surface cracking), which can significantly degrade the image quality of the formed image. Therefore, in this evaluation test, the presence or absence of this surface cracking was also evaluated, and the results are shown in Table TBL1 (Figure 9).

[0083] Furthermore, in this evaluation test, a comprehensive evaluation was conducted for each fixing belt 77 based on knowledge regarding gloss level, surface cracking, and the hardness of the elastic layer 82. The results were divided into three stages represented by the symbols "○", "△", and "×", and are shown in Table TBL1 (Figure 9).

[0084] The symbol "○" indicates a high evaluation, where the gloss level is level 5 or higher and no problems such as surface cracking occur. The symbol "△" indicates a moderate evaluation, where the gloss level is level 5 or higher, but some problems such as surface cracking occur. One example of this problem is when the load hardness ratio exceeds a relatively high value of 0.700, the elastic layer 82 becomes too hard, causing a decrease in adhesion, especially when multiple colors are mixed. The symbol "×" indicates a low evaluation, where the gloss level is level 4 or lower.

[0085] Figure 10, shown below, is a graph with the load hardness ratio and evaluation level on the horizontal and vertical axes, respectively, with plots placed based on the values ​​for each anchoring belt 77. Figure 11 is a graph with the thickness of the elastic layer 82 and the load hardness ratio on the horizontal and vertical axes, respectively, with plots placed based on the values ​​for each anchoring belt 77. In addition, symbols representing the overall evaluation are plotted in each graph.

[0086] In Figures 10 and 11, the load hardness ratios obtained from multiple locations separated in the left-right direction are plotted for each anchoring belt 77. Therefore, in Figure 10, the multiple plots for a single anchoring belt 77 are distributed across a range from the minimum to the maximum value of the load hardness ratio.

[0087] Below, we will explain the correlation between the load hardness ratio and the evaluation level in this evaluation test, based on Figures 9, 10, and 11.

[0088] In this evaluation test, as shown in Figure 10, the evaluation level was level 5 or higher when the load hardness ratio value was at least 0.566 (56.6%) or higher. At this time, as shown in Figure 7(B), the fixing unit 50 is considered to have a relatively fast response to indentation in the fixing belt 77 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 50, and can effectively reduce gloss unevenness in the image printed on the medium M.

[0089] Furthermore, in this evaluation test, as shown in Figure 10, if the load hardness ratio value is set to 0.898 (89.8%) or less, considering an upper limit, i.e., within range R1, then the evaluation level can be considered to be level 5 or higher. In this case as well, as shown in Figure 7(B), the fixing unit 50 shows a relatively fast response to indentation in the fixing belt 77 and is considered to have high conformability to the depressions D formed in the medium M. In this case, the thickness of the elastic layer 82 is in the range of 377 to 834 [μm].

[0090] Furthermore, in this evaluation test, as shown in Figure 11, when the load-hardness ratio value was within the range R2 of 0.566 (56.6%) to 0.698 (69.8%) and the thickness of the elastic layer 82 was within the range R3 of 377 [μm] to 607 [μm], the evaluation level was level 5 or higher, and no other problems occurred. In this case, the fixing unit 50 is considered to have a relatively fast response to indentation, and the thickness and hardness of the elastic layer 82 are not excessively large, but within an appropriate range. 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 without causing image cracking or a decrease in fixing rate.

[0091] On the other hand, in this evaluation test, if the load hardness ratio value was less than 0.566, the evaluation level was level 4 or lower. In this case, as shown in Figure 7(A), the fixing unit 50 showed a relatively slow response to indentation in the fixing belt 77, and it is considered that it had poor ability to follow the indentations D formed in the medium M. As a result, the image forming apparatus 1 produced a relatively large amount of gloss unevenness in the image printed on the medium M.

[0092] 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 load hardness ratio. Furthermore, this evaluation test also revealed the range of load hardness ratios and load hardness values ​​that can effectively reduce the degree of gloss unevenness.

[0093] Based on the above, in the fixing unit 50 of the image forming apparatus 1 according to this embodiment, the load hardness ratio value of the fixing belt 77 was selected to be at least 0.566, preferably 0.898 or less, and even more preferably 0.698 or less. In addition, in the fixing unit 50 of the image forming apparatus 1, the thickness of the elastic layer 82 of the fixing belt 77 was set to be between 377 [μm] and 607 [μm].

[0094] In the fixing unit 50, if the hardness ratio of the fixing belt 77 reaches at least 0.566 by the time the nip passage is completed when it passes through the nip region N, the occurrence of gloss unevenness can be suppressed in both the flat parts and depressions D in the medium M. For this reason, the measurement time of the hardness value using a hardness tester when obtaining the hardness ratio of the fixing belt 77 may be other than 0.2 [s].

[0095] Specifically, in this embodiment, since the nip width WN is 20 [mm], for example, if the conveying speed is 50.8 [mm / s], the time to complete passing through the nip is 0.39 [s]. In this case, the time to measure the hardness value using the hardness tester is 0.39 [s]. Also, for example, if the conveying speed is 152.4 [mm / s], the time to complete passing through the nip is 0.13 [s]. In this case, the time to measure the hardness value using the hardness tester is 0.13 [s]. Therefore, in this embodiment, it is sufficient that the hardness ratio value reaches at least 0.566 or higher after the time required to pass through the nip region, specifically 0.26 ± 0.13 [s], has elapsed.

[0096] [1-4. Effects, etc.] In the above configuration, the image forming apparatus 1 according to the first embodiment has the property that when printing an image on a film-like medium M, the fixing belt 77 of the fixing unit 50 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 fixing belt 77 is one in which the load hardness ratio value measured using a microhardness tester is at least 0.566 or higher.

[0097] Therefore, the image forming apparatus 1 can reliably deform the shape of the fixing belt 77 to match the depressions D of 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 50 (Figure 7(B)). As a result, the image forming apparatus 1 can sufficiently fix the toner by applying heat and pressure with the fixing belt 77 to both the flat parts and depressions D of the medium M, and can give the printed image on the medium M a uniform gloss without unevenness. In particular, the image forming apparatus 1 can give the printed image a uniform gloss even on a film-like medium M in which multiple fine pores are formed for purposes such as increasing flexibility.

[0098] Furthermore, the image forming apparatus 1 can also set the load-hardness ratio of the fixing belt 77 of the fixing unit 50 to be between 0.566 and 0.898, that is, within the range R1 shown in Figure 10. In this case, the image forming apparatus 1 can effectively avoid the occurrence of uneven gloss in the printed image due to excessively high hardness in the elastic layer 82, which reduces its ability to follow the medium M.

[0099] Furthermore, the image forming apparatus 1 can also configure the fixing belt 77 of the fixing unit 50 so that the load-hardness ratio value is between 0.566 and 0.698, and the thickness of the elastic layer 82 is between 377 [μm] and 607 [μm], that is, so that it falls within the ranges R2 and R3 in Figure 11. In this case, the image forming apparatus 1 can avoid a situation that can occur when the thickness of the elastic layer 82 in the fixing belt 77 is large, where the surface layer 83 cannot withstand the pressure in the nip region N, resulting in a significant decrease in image quality.

[0100] In this embodiment, in particular, instead of using the simple hardness of the fixing belt 77, i.e., the saturation hardness value, the load 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 fixing belt 77 that deforms to match the depression D while the medium M passes through the nip region N.

[0101] 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.

[0102] In contrast, in this embodiment, the change in the fixing belt 77 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 fixing belt 77 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 fixing belt 77 over time can be captured by sequentially reading the change in the measured value of the microhardness tester.

[0103] From another perspective, in the image forming apparatus 1, in order to properly fix the toner to the film-like medium M, the fixing unit 50 was designed to have a relatively long nip width WN in the nip region N. Specifically, in the fixing unit 50, the upper fixing unit 51 was not simply composed of rollers, but rather had a fixing belt 77 circulating around the pressure pad 71 and the drive roller 72, and the lower fixing unit 52 had a similar configuration. In a fixing unit 50 with such a configuration, it is necessary to form the fixing belt 77 relatively thin, making it difficult to give the fixing belt 77 sufficient thickness, and as a result, it was difficult to select the hardness of the fixing belt 77.

[0104] In this regard, in this embodiment, we focused on the followability and responsiveness of the fixing belt 77 during the passage time (i.e., 0.2 [s]) through the nip region N, and used the load-hardness ratio as an indicator to identify a good range R1 (Figure 10), etc. As a result, in the image forming apparatus 1, while securing a relatively large nip width WN in the fixing unit 50 (Figure 3), the followability and responsiveness of the relatively thin fixing belt 77 can be appropriately improved, and good glossiness can be obtained in the formed image.

[0105] 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 fixing belt 77 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 fixing belt 77 selected based on an appropriately evaluated level.

[0106] With the above configuration, when printing an image on a film-like medium M, the image forming apparatus 1 according to the first embodiment is configured such that the fixing belt 77 of the fixing unit 50 has a load hardness ratio value of at least 0.566, as measured using a microhardness tester. As a result, the image forming apparatus 1 can reliably deform the shape of the fixing belt 77 to match the minute depressions D of the medium M during the approximately 0.2 seconds it takes for the medium M to pass through the nip region N of the fixing unit 50. This allows the image forming apparatus 1 to sufficiently fix toner to both the flat areas and depressions D of the medium M, thereby suppressing the occurrence of gloss unevenness in the image printed on the medium M and providing a uniform gloss.

[0107] [2. Second Embodiment] The image forming apparatus 201 (Figure 1) according to the second embodiment differs from the image forming apparatus 1 according to the first embodiment in that it has a fixing unit 250 instead of a fixing unit 50, but is otherwise configured similarly. The fixing unit 250 (Figure 3) differs from the fixing unit 50 according to the first embodiment in that it has a fixing belt 277 instead of a fixing belt 77. This fixing belt 277 is configured similarly to the fixing belt 77 (Figure 4) in the first embodiment, with a base body 81, an elastic layer 82, and a surface layer 83 being sequentially laminated.

[0108] [2-1. Details of the fixing belt] In the second embodiment, as an evaluation test regarding the thickness of the elastic layer 82 in the fixing belt 277, first, similar to the first embodiment, measurements of load hardness values ​​and other parameters using a microhardness tester were performed on multiple types of fixing belts 277, and the evaluation level regarding gloss unevenness was classified.

[0109] Specifically, in the evaluation test in the second embodiment, seven types of anchoring belts 277 (277A to 277G) were used. Table TBL2 shown in Figure 12 summarizes some of the specifications, evaluation levels, and overall evaluations of the anchoring belts 277 used in this evaluation test.

[0110] In this evaluation test, when the thickness of the elastic layer 82 was less than 377 [μm], the degree of gloss unevenness was relatively large, resulting in an evaluation level of 4 or lower. On the other hand, in this evaluation test, when the thickness of the elastic layer 82 was 377 [μm] or more, the degree of gloss unevenness was relatively small in the image printed on medium M, good gloss was obtained, and an evaluation level of 5 or higher was achieved.

[0111] Furthermore, in this evaluation test, when the thickness of the elastic layer 82 was 607 [μm] or less, no surface cracking occurred in the surface layer 83, and good image quality was obtained in the image printed on the medium M. On the other hand, in this evaluation test, when the thickness of the elastic layer 82 was greater than 607 [μm], surface cracking occurred in the surface layer 83, and a decrease in image quality was observed in the image printed on the medium M.

[0112] Based on these factors, in this evaluation test, a high overall evaluation was given when the thickness of the elastic layer 82 was between 377 [μm] and 607 [μm], and this was indicated by the symbol "○" in Table TBL2. On the other hand, in this evaluation test, a low overall evaluation was given when the thickness of the elastic layer 82 was less than 377 [μm] or greater than 607 [μm], and this was indicated by the symbol "×" in Table TBL2.

[0113] Figure 13 is a graph in which the thickness of the elastic layer 82 and the gloss level in this evaluation test are plotted on the horizontal and vertical axes, respectively, with plots placed based on the values ​​of each fixing belt 277. In the graph of Figure 13, the symbol for the overall evaluation is plotted. From Figure 13, it can be seen that in the range R21 where the thickness of the elastic layer 82 is between 377 [μm] and 607 [μm], the gloss level value is in the range R22 where it is 5 or higher.

[0114] Incidentally, in the image forming apparatus 201, even though the fixing belt 277, which had a high overall evaluation, was used, problems were sometimes observed with the image quality of the images printed on the medium M.

[0115] For example, Figure 14(A) shows the result of printing a test image (i.e., a solid color image) similar to the evaluation test in the first embodiment, using a certain fixing belt 277 (hereinafter referred to as fixing belt 277J) in the image forming apparatus 201. Figure 14(A) shows the range of the medium M on which the image is printed, corresponding to the length of one rotation of the fixing belt 277. No problems with image quality occurred in Figure 14(A).

[0116] On the other hand, Figure 15(A), which corresponds to Figure 14(A), shows the result of printing the same test image using a different fixing belt 277 (hereinafter referred to as fixing belt 277K) in the image forming apparatus 201. In Figure 15(A), there are parts of the image where the toner has not been sufficiently fixed to the medium M, and which exhibit a color close to the white background color of the medium M (hereinafter referred to as white spots).

[0117] In this embodiment, we focused on the thickness of the fixing belt 277 (hereinafter referred to as film thickness), set up multiple measurement points on the fixing belt 277, and measured the film thickness at each measurement point using a film thickness measuring instrument (not shown).

[0118] Of the measurement points on the anchoring belt 277, the positions in the left-right direction (hereinafter also referred to as the width direction) were set at intervals of LA1 (e.g., 26 [mm]) in the width direction, starting from the left end at a position corresponding to the width direction end spacing LA0 (e.g., 6 [mm]). Hereafter, these positions will be referred to as width measurement positions PA1, PA2, ... from left to right. Furthermore, of the measurement points on the anchoring belt 277, the positions in the circumferential direction were set at intervals of LC1 (e.g., 0.4 [mm]) in the circumferential direction, as shown in the schematic diagram in Figure 14(B).

[0119] First, the film thickness was measured at each measurement point along the circumferential direction at width measurement positions PA3 and PA4 of the fixing belt 277J, and the film thickness distribution curves PF3J and PF4J shown in Figure 14(B) were obtained. Hereafter, such film thickness distribution curves will also be referred to as film thickness profiles. In Figure 14(B), the horizontal axis represents the position in the circumferential direction in terms of angle [°], and the vertical axis represents the film thickness [μm].

[0120] In Figure 14(B), both the film thickness distribution curves PF3J and PF4J show some degree of increase or decrease in film thickness depending on the circumferential position. However, the absolute values ​​of film thickness at each circumferential position, the circumferential position (hereinafter also referred to as phase) of the areas where increase or decrease occurs, and the degree of increase or decrease are roughly the same for both the film thickness distribution curves PF3J and PF4J. In other words, the degree of similarity between the waveforms of the film thickness distribution curves PF3J and PF4J is relatively high, and there is almost no difference in circumferential position (hereinafter also referred to as phase difference).

[0121] Next, for the fixing belt 277K, the film thickness was measured at each measurement point along the circumferential direction at width measurement positions PA3 and PA4, respectively. As a result, film thickness distribution curves PF3K (dashed line) and PF4K (solid line) were obtained, as shown in Figure 15(B), which corresponds to Figure 14(B).

[0122] In Figure 15(B), both the film thickness distribution curves PF3K and PF4K show some degree of increase or decrease in film thickness depending on the circumferential position. Furthermore, there are some differences between the film thickness distribution curves PF3K and PF4K in terms of the absolute value of the film thickness at each circumferential position and the circumferential position (i.e., phase) of the parts where the increase or decrease occurs. In other words, the degree of similarity between the waveforms of the film thickness distribution curves PF3K and PF4K is somewhat low, and there is a shift in circumferential position (i.e., a phase difference).

[0123] Furthermore, in the film thickness distribution curves PF3K and PF4K, peak shapes due to increases and decreases in film thickness repeatedly appear with relatively short periods of approximately 90°. Comparing Figure 15(B) with Figure 15(A), a white gap occurs in the circumferential direction, between the peak in the film thickness distribution curve PF3K and the peak in the film thickness distribution curve PF4K. Looking at this in detail, in Figure 15(B), a white gap occurs in the circumferential direction, where the film thickness changes from increasing to decreasing in the film thickness distribution curve PF3K, which has a preceding phase, and the film thickness increases in the film thickness distribution curve PF4K, which has a trailing phase. Hereafter, this range will be referred to as the film thickness increase / decrease range AT.

[0124] Next, the pressure distribution in the nip region N was investigated when fixing belts 277J and 277K were used in the fixing unit 250, respectively. As a result, it was found that in the fixing unit 250, when fixing belt 277K was used, a wider area of ​​reduced pressure was formed compared to the surrounding area. Hereafter, this formation of a reduced pressure area in the nip region N will also be referred to as pressure release.

[0125] From the above, it can be seen that in the image forming apparatus 201, when the film thickness changes abruptly from a relatively large to a relatively small thickness within a relatively narrow angle range, such as the film thickness increase / decrease range AT, with respect to the circumferential direction of the fixing belt 277, white spots (Figure 15(A)) are likely to occur in the printed image. Furthermore, in the image forming apparatus 201, when the phases of the film thickness profiles are shifted in relatively close locations in the width direction of the fixing belt 277, partial pressure leaks occur, and as a result, white spots are likely to occur in the printed image.

[0126] Here, we examine the relationship between the length and pressure of each part in the nip region N of the fixing unit 250 and the film thickness profile of the fixing belt 277K where white spots occur. Figure 17 shows the pressure distribution characteristics in the nip region N (Figure 5) and the film thickness distribution curve PF4K of the fixing belt 277K (Figure 15(B)) side by side.

[0127] Here, W1 [μm] is defined as the distance corresponding to the weak load region AR1 caused by the pressure pad 71, etc., in the pressure distribution characteristics in the nip region N. Also, W2 [°] is defined as the angle in the circumferential direction from the maximum value to the minimum value in the film thickness distribution curve PF4K, and T1 is defined as the peak height, which is the difference in film thickness at this point, i.e., the height difference.

[0128] In the image forming apparatus 201, white areas occurred in the circumferential direction of the fixing belt 277. do This occurs when the distance W2 of the film thickness distribution curve PF4K is smaller than the distance W1 corresponding to the weak load region AR1, and the peak height T1 is 101 [μm]. That's all. This is the case.

[0129] Therefore, the conditions for preventing white spots in the circumferential direction of the fixing belt 277 in the image forming apparatus 201 can be expressed as shown in equations (1) and (2) below. However, the constant r is the radius of the fixing belt 277 and is 21 to 24 [mm].

[0130]

number

[0131]

number

[0132] Next, we will consider the case where white areas occur in the width direction of the fixing belt 277 in the image forming apparatus 201. Here, we assume that a phase difference occurs in the film thickness distribution curves PF3K and PF4K (i.e., film thickness profile) at width measurement positions PA3 and PA4, as shown in fixing belt 277K (Figure 15(B)). In the following, width measurement positions PA3 and PA4 will also be referred to as the first position and the second position, respectively.

[0133] Figure 19 is a schematic diagram showing the anchoring belt 277 as viewed from the front. In Figure 19, line XA is a hypothetical line along the left-right direction (i.e., the width direction). Line XB is a hypothetical line connecting the outer surface at width measurement position PA3 and the outer surface at width measurement position PA4 with respect to a predetermined circumferential direction (e.g., downward direction) of the anchoring belt 277. Furthermore, angle α represents the angle between lines XA and XB.

[0134] In Figure 19, if the widthwise film thickness difference T2, which is the difference between the film thickness at width measurement position PA3 and the film thickness at width measurement position PA4, is relatively large, the fixing belt 277 may not be able to follow the medium M sufficiently in the nip region N, which may cause white spots to occur.

[0135] Therefore, we investigated the relationship between the magnitude of the widthwise film thickness difference T2 and the presence or absence of white spots, as shown in the table in Figure 20. TBL3 The survey results shown in this table are as follows. TBL3In this diagram, the symbol "○" indicates that no white spots occurred, and the symbol "×" indicates that white spots occurred. Figure 21 is a graph showing the relationship between the widthwise film thickness difference T2 and the presence or absence of white spots. In this graph, the presence or absence of white spots is associated with the value "0," and the absence of white spots is associated with the value "1."

[0136] From Figures 20 and 21, it can be seen that for the fixing belt 277, if the widthwise spacing LA1 is 26 [mm] and the widthwise film thickness difference T2 is 47 [μm] or less, the occurrence of white spots can be avoided. Also, in Figure 19, if the widthwise spacing LA1 is 26 [mm] and the widthwise film thickness difference T2 is 47 [μm], the angle α is 0.1 [°].

[0137] Therefore, the conditions for preventing white spots from occurring in the circumferential direction of the fixing belt 277 in the image forming apparatus 201 can be expressed as shown in equations (3) and (4) below.

[0138]

number

[0139]

number

[0140] [2-2. Effects, etc.] In the above configuration, the image forming apparatus 201 according to the second embodiment satisfies at least equation (1) above with respect to the height T1, which is the difference between the maximum and minimum values ​​appearing in the film thickness distribution curve of the fixing belt 277, where the thickness of the elastic layer 82 is 300 [μm] or more. As a result, the image forming apparatus 201 can effectively suppress the occurrence of white spots in the circumferential direction of the fixing belt 277.

[0141] Furthermore, the image forming apparatus 201 is configured to satisfy equation (2) above with respect to the distance W2 related to the film thickness distribution curve of the fixing belt 277 and the distance W1 corresponding to the weak load region AR1 in the nip region N. As a result, the image forming apparatus 201 can reliably suppress the occurrence of white spots in the circumferential direction of the fixing belt 277.

[0142] Furthermore, the image forming apparatus 201 is configured to satisfy equation (3) above with respect to the film thickness difference T2 in the width direction of the fixing belt 277. As a result, the image forming apparatus 201 can effectively suppress the occurrence of white spots in the width direction of the fixing belt 277.

[0143] In addition, the image forming apparatus 201 is configured to satisfy equation (4) with respect to the widthwise film thickness difference T2 and widthwise spacing LA1 of the fixing belt 277. As a result, the image forming apparatus 201 can reliably suppress the occurrence of white spots in the widthwise direction of the fixing belt 277, regardless of the widthwise spacing LA1.

[0144] As a result, the image forming apparatus 201 can prevent pressure leakage in the nip region N due to uneven film thickness of the fixing belt 277, and reliably avoid the occurrence of white spots (Figure 15(A)) in the image printed on the medium M.

[0145] In addition, the image forming apparatus 201 is configured such that the load-hardness ratio of the fixing belt 277 is at least 0.566, similar to the first embodiment. As a result, the image forming apparatus 201 is able to sufficiently fix the toner to both the flat areas and depressions D of the medium M, similar to the first embodiment, and the image printed on the medium M can have a uniform gloss without unevenness.

[0146] In other respects as well, the image forming apparatus 201 according to the second embodiment can obtain the same effects and advantages as the first embodiment.

[0147] With the above configuration, the image forming apparatus 201 according to the second embodiment is configured such that, in the fixing belt 277 where the thickness of the elastic layer 82 is 300 [μm] or more, the height T1, which is the difference between the maximum and minimum values ​​appearing in the film thickness distribution curve, is less than 101 [μm]. As a result, the image forming apparatus 201 can suppress the occurrence of pressure drops, in which the pressure applied to the medium M decreases locally in the nip region N of the fixing unit 250, and can effectively reduce the occurrence of white spots.

[0148] [3. Other Embodiments] In the first embodiment described above, the nip width WN in the fixing unit 50 was set to 17 [mm], the transport speed of the medium M was set to 4 [ips], or approximately 101.6 [mm / s], and the passage time required for a predetermined point on the medium M to pass through the nip region N was set to approximately 0.2 [s]. Accordingly, the case in which the load hardness value and load hardness ratio after 0.2 [s] from the start of measurement are used in the evaluation of the fixing belt 77 was also described. However, the present invention is not limited to this, and by setting the nip width WN in the fixing unit 50 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 load hardness value and load hardness ratio at the time elapsed after the start of measurement may be used in accordance with the passage time. Alternatively, the load hardness value and load hardness ratio at a time shorter than the passage time may be used. The same applies to the second embodiment.

[0149] Furthermore, in the first embodiment described above, the evaluation test of the fixing belt 77 was described in which the toner planar area ratio was calculated based on the brightness value of the microscope image obtained using a laser microscope, and this was used to classify the material into 10 gloss levels. However, the present invention is not limited to this, and the material may be classified into gloss levels by various methods, such as classifying it into gloss levels based on the subjective visual inspection of the evaluator. Also, the number of gloss levels to be classified into is not limited to 10 levels, but may be 9 levels or less, or 11 levels or more. The same applies to the second embodiment.

[0150] Furthermore, in the first embodiment described above, the case where the inner diameter of the fixing belt 77 is 42 to 48 mm was described. However, the present invention is not limited to this, and the inner diameter of the fixing belt 77 may be smaller than 44 mm or larger than 48 mm, within the range of approximately 15 to 60 mm. The same applies to the second embodiment.

[0151] Furthermore, in the first embodiment described above, the case where the thickness of the elastic layer 82 constituting the fixing belt 77 (Figure 4) is approximately 300 to 800 [μm] was described. However, the present invention is not limited to this, and the thickness of the elastic layer 82 may be, for example, approximately 100 to 300 [μm] or approximately 800 to 1000 [μm]. The same applies to the second embodiment.

[0152] Furthermore, in the second embodiment described above, the case was described in which the height T1, which is the difference between the maximum and minimum values ​​appearing in the film thickness distribution curve of the fixing belt 277, is less than 101 [μm]. However, the present invention is not limited to this, and the upper limit of the height T1 may be determined according to these values. In this case, it is desirable that the relationship in equation (2) is satisfied.

[0153] Furthermore, in the second embodiment described above, regarding the width direction of the fixing belt 277, the case was described in which the width direction spacing LA1 is 26 [mm] and the width direction film thickness difference T2, which is the difference in film thickness at two width measurement positions PA separated by the width direction spacing LA1, is 47 [μm] or less. However, the present invention is not limited to this, and the width direction spacing LA1 may be set to various other values, and the upper limit of the width direction film thickness difference T2 may be set to a different value accordingly. In this case, it is sufficient that the relationship in equation (4) is satisfied.

[0154] Furthermore, in the first embodiment described above, the case where the load hardness ratio of the fixing belt 77 of the upper fixing unit 51 in the fixing unit 50 is set to at least 0.566 was described. However, the present invention is not limited to this, and for example, the load hardness ratio of the pressure belt 97 of the lower fixing unit 52 may also be set to at least 0.566. In this case, the load hardness ratios of the fixing belt 77 and the pressure belt 97 may be the same or different. The same applies to the second embodiment.

[0155] Furthermore, in the first embodiment described above, the case was described in which the medium M (Figure 6) was configured by laminating a substrate layer ML1, coating layers ML2 and ML3, and in which multiple fine pores H1, H2 and H3 were formed in each layer. However, the present invention is not limited to this, and for example, the medium M may be configured as a single layer, two layers, or four or more layers, and multiple fine pores may be formed in at least one of the layers. Also, the medium M is not limited to a film, and for example, a medium M formed by laminating a film onto a predetermined backing may be used. The same applies to the second embodiment.

[0156] Furthermore, in the first embodiment described above, a media cassette 10 is provided within the image forming apparatus 1, and a long media M is drawn out and supplied from the media supply roll MR1 (Figure 1). However, the present invention is not limited to this, and for example, media M consisting of cut paper of A3 size or A4 size may be stored in a predetermined media cassette, and the media may be supplied one sheet at a time from the media cassette. The same applies to the second embodiment.

[0157] Furthermore, the first embodiment described above described a case in which five process units 30 are provided in the image forming apparatus 1 (Figure 1). However, the present invention is not limited to this, and for example, one to four or five or more process units 30 may be provided in the image forming apparatus 1. The same applies to the second embodiment.

[0158] Furthermore, the present invention is not limited to the embodiments described above or any 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 any other embodiments described above, as well as embodiments that extract some of them.

[0159] Furthermore, in the second embodiment described above, the case in which the fixing unit 250 as a fixing device is configured with a fixing belt 277 as an annular belt and a pressure belt 97 as an opposing member was described. However, the present invention is not limited to this, and the fixing device may be configured with an annular belt and opposing member of various other configurations. [Industrial applicability]

[0160] 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]

[0161] 1, 201...Image forming apparatus, 30...Process unit, 50, 250...Fixing unit, 51...Upper fixing unit, 52...Lower fixing unit, 71...Pressure pad, 72...Drive roller, 77, 277, 277J, 277K...Fixing belt, 81...Substrate, 82...Elastic layer, 83...Surface layer, 91...Pressure pad, 92...Pressure roller, 97...Pressure belt, AR1...First load area, AR2...Second load area, D...Indentation, LA1...Width direction spacing, LC1...Circumferential spacing, M...Media, N...Nip area, PA...Width measurement position, T1...Height, T2...Width direction film thickness difference, W...Conveyor path, WN...Nip width, α...Angle.

Claims

1. An annular belt having a base body, a surface layer located on the outside of the base body and forming an outer peripheral surface, and an elastic layer provided between the base body and the surface layer and having a thickness of 377 to 607 [μm], which travels at a predetermined speed, An opposing member that faces the outer circumferential surface of the annular belt and forms a nip region with the annular belt, Equipped with, The nip region has a first load region that applies a load between it and the opposing member, and a second load region that applies a load stronger than that in the first load region. The annular belt, at a first position in the width direction, has a thickness in the circumferential direction of the annular belt such that, when measured every 0.4 mm in the circumferential direction, the difference between all the maximum values ​​that appear first during the run and the minimum values ​​that appear afterward is less than 101 μm, and the length of the annular belt from the portion where the thickness is the maximum value to the portion where the thickness is the minimum value in the circumferential direction is longer than the length of the first load region in the nip region. A fixing device characterized by the following features.

2. The annular belt is such that, in a predetermined circumferential direction, when the distance between the outer surface of the first position and the outer surface of the second position in the width direction is 26 mm, the angle between the straight line connecting the first position and the second position and the straight line along the width direction is 0.1° or less. The fixing device according to feature 1.

3. The annular belt is such that, when the distance between the second position and the first position in the width direction is 26 mm, the difference in height between the outer surface of the second position and the first position in a predetermined circumferential direction is 47 μm or less. The fixing device according to feature 1.

4. The annular belt has an inner diameter of 42 mm or more and 48 mm or less. A fixing device according to any one of claims 1 to 3, characterized by the features described above.

5. 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 4, for fixing the developer image onto the medium, An image forming apparatus equipped with the following.

Images