JP7516797B2 - Fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a fixing device and an image forming apparatus equipped with the same.

Conventionally, in fixing devices that form a toner image on paper and fix the image to the paper using heat and pressure, a belt fixing method has been proposed in order to improve energy efficiency, in which a roller that forms a nip and a heating roller equipped with a heat source are placed inside an endless belt and the endless belt is tensioned.

To further improve energy efficiency, a fixing method has been proposed in which the roller that constitutes the nip is replaced with a fixed pad member (fixing member), as disclosed in JP 2019-40144 A (Patent Document 1), JP 2019-40013 A (Patent Document 2), and JP 2013-218225 A (Patent Document 3).

JP 2019-40144 A JP 2019-40013 A JP 2013-218225 A

However, in the fixing device disclosed in Patent Document 1, the upstream side of the pad member is formed flat in the transport direction of the recording medium, and the downstream side of the pad member is formed as a curved surface. As a result, in the rear half of the nip portion formed by the pad member and the pressure roller (specifically, near the exit portion of the nip portion), a portion of the pad is convex relative to the pressure roller. In the portion of the pad that is convex relative to the pressure roller, there is a concern that shear force due to sliding resistance will cause slight movement of the toner. In this case, the underlying paper may be exposed, resulting in a whitish image. In other words, the image density will decrease.

In the fixing device disclosed in Patent Document 2, the nip formation region of the pad member that forms a nip with the pressure roller is configured with an arc-shaped curved surface, and the region downstream from the nip formation region is configured with an inclined surface that slopes toward the pressure roller as it moves downstream in the conveying direction. The inclined surface is not in contact with the pressure roller. In such a case, it becomes difficult to provide a peak pressure in the latter half of the nip portion, which may result in poor toner melting properties.

In the fixing device described in Patent Document 3, the upstream and downstream sides of the pad member are each configured with a curved surface that is concave with respect to the pressure roller, and the curvature of the curved surface of the pad member on the upstream side is greater than the curvature of the curved surface of the pad member on the downstream side. In such a case, a peak pressure exists in the front half of the nip portion, which can cause the toner to melt poorly.

The present invention has been made in consideration of the above problems, and the object of the present invention is to provide a fixing device and an image forming apparatus that can improve the toner melting efficiency while suppressing a decrease in image density.

The fixing device according to the present invention includes an endless belt, a fixing member disposed inside the endless belt, a roller disposed outside the endless belt facing the fixing member and forming a nip portion together with the fixing member, and a heating member for heating the endless belt. The fixing member has a curved surface portion disposed upstream in the direction of rotation of the endless belt in a nip portion forming region forming the nip portion, and a flat surface portion disposed downstream in the direction of rotation and connected to the curved surface portion. The curved surface portion is curved in an arc shape so as to be concave with respect to the roller. The flat surface portion is located on a tangent to the curved surface portion that is in contact with a connecting position connected to the curved surface portion, or is provided so as to be inclined toward the roller from the tangent. In the distribution of pressure applied to the nip portion forming region, a peak position exists on the flat surface portion.

In the fixing device according to the present invention, it is preferable that the flat portion is located on the tangent line.

In the fixing device according to the present invention, it is preferable that the radius of curvature of the curved surface portion is greater than the radius of curvature of the roller.

In the fixing device according to the present invention, it is preferable that the peak position in the distribution of pressure applied to the nip forming region is located at the connection position.

In the fixing device according to the present invention, it is preferable that the connection position is located downstream in the rotation direction of the endless belt from an imaginary line extending from the center of the roller in the pressure contact direction in which the roller is pressed against the fixing member.

The image forming apparatus according to the present invention is equipped with the fixing device described above.

The present invention provides a fixing device and an image forming device that can improve the toner melting efficiency while suppressing a decrease in image density.

1 is a schematic diagram showing an image forming apparatus according to a first embodiment; 1 is a schematic cross-sectional view of a fixing device according to a first embodiment. 5A and 5B are diagrams illustrating a state in which a pressure roller presses a pad member in the fixing device according to the first embodiment. 5 is a diagram showing the distribution of pressure applied to a nip portion forming region in the fixing device according to the first embodiment; FIG. 10 is a diagram showing a first state in which a toner image moves through a nip portion in a fixing device according to a comparative example. FIG. 13 is a diagram showing a second state in which a toner image moves through a nip portion in a fixing device according to a comparative example. FIG. 13 is a diagram showing a third state in which a toner image moves through a nip portion in a fixing device according to a comparative example. FIG. 11 is a diagram showing a state in which a pressure roller presses a pad member in a fixing device according to a second embodiment. FIG. 10 is a diagram showing the distribution of pressure applied to a nip portion forming region in a fixing device according to a second embodiment; FIG. 6 is a diagram showing the distribution of pressure applied to a nip portion forming region in a fixing device according to Reference Example 1. FIG. 11 is a diagram showing the distribution of pressure applied to a nip portion forming region in a fixing device according to Reference Example 2. FIG. 13 is a diagram showing a state in which a pressure roller presses a pad member in a fixing device according to a third embodiment. FIG. 13 is a diagram showing the distribution of pressure applied to a nip portion forming region in a fixing device according to a third embodiment. FIG. FIG. 11 is a diagram showing the conditions and results of a first verification experiment conducted to verify the effects of the embodiment. FIG. 11 is a diagram showing the conditions and results of a second verification experiment conducted to verify the effects of the embodiment. 6 is a diagram showing a state in which a pressure roller presses a pad member in a fixing device according to Comparative Example 1. FIG. 13 is a diagram showing a state in which a pressure roller presses a pad member in a fixing device according to Comparative Example 2. FIG. 13 is a diagram showing a state in which a pressure roller presses a pad member in a fixing device according to Comparative Example 3. FIG. 13 is a diagram showing a state in which a pressure roller presses a pad member in a fixing device according to Comparative Example 4. FIG. 10 is a diagram showing a state in which a pressure roller presses a pad member in a fixing device according to a first modified example. FIG.

The following describes in detail the embodiments of the present invention with reference to the drawings. In the embodiments described below, the same or common parts are given the same reference numerals in the drawings, and their description will not be repeated.

(Embodiment 1)
Fig. 1 is a schematic diagram showing an image forming apparatus according to embodiment 1. With reference to Fig. 1, an image forming apparatus 100 according to embodiment 1 will be described.

In FIG. 1, an image forming device 100 is shown as a color printer. Below, the image forming device 100 is described as a color printer, but the image forming device 100 is not limited to a color printer. For example, the image forming device 100 may be a monochrome printer, a fax machine, or a multi-functional peripheral (MFP) that combines a monochrome printer, a color printer, and a fax machine.

The image forming apparatus 100 includes image forming units 1Y, 1M, 1C, and 1K, an intermediate transfer belt 30, a primary transfer roller 31, a secondary transfer roller 33, a cassette 37, a driven roller 38, a drive roller 39, a timing roller 40, a fixing device 50, a housing 80, and a control device 101.

The housing 80 defines the outer shell of the image forming device 100. Inside the housing 80, image forming units 1Y, 1M, 1C, and 1K, intermediate transfer belt 30, primary transfer roller 31, secondary transfer roller 33, cassette 37, driven roller 38, drive roller 39, timing roller 40, fixing device 50, and control device 101 are housed.

The image forming unit is made up of image forming units 1Y, 1M, 1C, and 1K, intermediate transfer belt 30, primary transfer roller 31, secondary transfer roller 33, cassette 37, driven roller 38, drive roller 39, and timing roller 40. This image forming unit forms a toner image on paper S, which serves as a recording medium, transported along a transport path 41, which will be described later.

Image forming units 1Y, 1M, 1C, and 1K are arranged in order along intermediate transfer belt 30. Image forming unit 1Y receives toner from toner bottle 15Y and forms a yellow (Y) toner image. Image forming unit 1M receives toner from toner bottle 15M and forms a magenta (M) toner image. Image forming unit 1C receives toner from toner bottle 15C and forms a cyan (C) toner image. Image forming unit 1K receives toner from toner bottle 15K and forms a black (BK) toner image.

Image forming units 1Y, 1M, 1C, and 1K are arranged along intermediate transfer belt 30 in the order of the rotation direction of intermediate transfer belt 30. Image forming units 1Y, 1M, 1C, and 1K each include a photoconductor 10, a charging device 11, an exposure device 12, a developing device 13, and a cleaning device 17.

The charging device 11 uniformly charges the surface of the photoreceptor 10. The exposure device 12 irradiates the photoreceptor 10 with laser light in response to a control signal from the control device 101, exposing the surface of the photoreceptor 10 according to the input image pattern. As a result, an electrostatic latent image corresponding to the input image is formed on the photoreceptor 10.

The developing device 13 applies a developing bias to the developing roller 14 while rotating the developing roller 14, causing toner to adhere to the surface of the developing roller 14. This causes the toner to be transferred from the developing roller 14 to the photoreceptor 10, and a toner image corresponding to the electrostatic latent image is developed on the surface of the photoreceptor 10.

The photoconductor 10 and the intermediate transfer belt 30 are in contact with each other at the portion where the primary transfer roller 31 is provided. The primary transfer roller 31 has a roller shape and is configured to be rotatable. A transfer voltage of the opposite polarity to that of the toner image is applied to the primary transfer roller 31, so that the toner image is transferred from the photoconductor 10 to the intermediate transfer belt 30. A yellow (Y) toner image, a magenta (M) toner image, a cyan (C) toner image, and a black (BK) toner image are transferred from the photoconductor 10 to the intermediate transfer belt 30 in succession in a superimposed manner. As a result, a color toner image is formed on the intermediate transfer belt 30.

The intermediate transfer belt 30 is stretched over a driven roller 38 and a drive roller 39. The drive roller 39 is driven to rotate by, for example, a motor (not shown). The intermediate transfer belt 30 and the driven roller 38 rotate in conjunction with the drive roller 39. This causes the toner image on the intermediate transfer belt 30 to be transported to the secondary transfer roller 33.

The cleaning device 17 is pressed against the photoreceptor 10. The cleaning device 17 collects the toner remaining on the surface of the photoreceptor 10 after the toner image is transferred.

Paper S is set in cassette 37. The paper S is sent one by one from cassette 37 along transport path 41 by timing roller 40 to secondary transfer roller 33. Secondary transfer roller 33 has a roller shape and is configured to be rotatable. Secondary transfer roller 33 applies a transfer voltage of the opposite polarity to the toner image to the paper S being transported. As a result, the toner image is attracted from intermediate transfer belt 30 to secondary transfer roller 33, and the toner image on intermediate transfer belt 30 is transferred to paper S. In this way, primary transfer roller 31, intermediate transfer belt 30, and secondary transfer roller 33 correspond to a transfer section that transfers the toner image from photoconductor 10 to paper S.

The timing of conveying the paper S to the secondary transfer roller 33 is adjusted by the timing roller 40 to match the position of the toner image on the intermediate transfer belt 30. The timing roller 40 transfers the toner image on the intermediate transfer belt 30 to the appropriate position on the paper S.

The fixing device 50 applies pressure and heat to the paper S passing by it. This fixes the toner image to the paper S. In this way, the fixing device 50 fixes the toner image on the paper S transported along the transport path 41. The paper S with the fixed toner image is discharged to the tray 48.

In the above, the image forming apparatus 100 employs a tandem printing method, but the printing method of the image forming apparatus 100 is not limited to the tandem method. The arrangement of each component in the image forming apparatus 100 may be changed as appropriate according to the printing method employed. The printing method of the image forming apparatus 100 may be a rotary method or a direct transfer method. In the case of the rotary method, the image forming apparatus 100 is composed of one photoconductor 10 and multiple developing devices 13 configured to be rotatable on the same axis. During printing, the image forming apparatus 100 guides each developing device 13 to the photoconductor 10 in sequence to develop a toner image of each color. In the case of the direct transfer method, the image forming apparatus 100 transfers the toner image formed on the photoconductor 10 directly to the paper S.

Figure 2 is a schematic cross-sectional view of a fixing device according to an embodiment. The fixing device 50 will be described with reference to Figure 2.

The fixing device 50 includes a pressure roller 51, a pad member 52 as a fixing member, a heating roller 53 as a heating member, a fixing belt 54, a fixed member 55, a lubricant application section 56, a holding member 57, and a sliding member 58.

The pressure roller 51 is disposed outside the fixing belt 54. The pressure roller 51 faces the pad member 52. The pressure roller 51 presses the pad member 52 by sandwiching the fixing belt 54 between the pressure roller 51 and the pad member 52. As a result, the pressure roller 51 and the pad member 52 form a nip portion N through which the recording medium is transported.

The pressure roller 51 rotates due to torque from a drive source. The fixing belt 54 rotates in conjunction with the rotation of the pressure roller 51. As the pressure roller 51 rotates, the fixing belt 54 rotates in the opposite direction to the rotation direction of the pressure roller 51.

The pressure roller 51 is composed of, for example, a core metal, an elastic layer, and a release layer. The outer shape of the pressure roller 51 is arbitrary, but is preferably 20 mm or more and 100 mm or less.

The core is made of a metal such as aluminum or iron. The core may have a pipe shape, in which case it is preferable that the thickness is 0.1 mm or more and 10 mm or less. The core may be solid or have an irregular cross-sectional shape such as a three-arrow shape. The elastic layer is made of a highly heat-resistant resin such as silicone rubber or fluororubber. It is preferable that the thickness of the elastic layer is 1 mm or more and 20 mm or less. The release layer is provided so as to cover the elastic layer. It is preferable that the release layer is made of a fluorine tube or a fluorine-based coating that provides release properties. It is preferable that the thickness of the release layer is 5 μm or more and 100 μm or less.

The pad member 52 is disposed inside the fixing belt 54. The pad member 52 is disposed so as to face the pressure roller 51 with the fixing belt 54 sandwiched therebetween. The pad member 52 is made of, for example, a heat-resistant resin such as polyphenylene sulfide, polyimide, or liquid crystal polymer, a metal material such as iron, or ceramic. The pad member 52 may be made of a fixing member made of silicone rubber, fluororubber, or the like, and two parts made of the above materials.

The sliding member 58 is sandwiched between the fixing belt 54 and the pad member 52. The sliding member 58 reduces the sliding resistance between the fixing belt 54 and the pad member 52. This allows the fixing belt 54 to rotate stably.

The sliding member 58 is made of glass cloth as a base material, with the sliding surface coated with a fluororesin. Specifically, the sliding member 58 is made of fluorofiber fabric, a fluororesin sheet, or a glass coat.

Note that the fixing belt 54 and the sliding member 58 will wear out as they continue to slide. In such a case, there is a concern that the sliding resistance will increase and the fixing belt 54 will not rotate properly. For this reason, a lubricant is supplied between the fixing belt 54 and the sliding member 58. This can suppress the wear of the fixing belt 54 and the sliding member 58 and improve durability. The lubricant is preferably a silicon-based or fluorine-based lubricant with high heat resistance, and more specifically, fluorine grease is preferable. By using grease that has a high viscosity and contains solid components, the lubricant is more likely to remain in the nip portion N. For this reason, when grease is used, wear of the fixing belt 54 and the sliding member 58 can be suppressed for a longer period of time compared to when oil is used. Furthermore, it is preferable that the surface of the sliding member 58 has unevenness in order to hold the lubricant in the nip portion N. The size of the unevenness is arbitrary. From the viewpoint of maintaining the lubricant and suppressing image unevenness caused by unevenness, it is preferable that the surface roughness Ra of the sliding member 58 is 1 μm or more and 50 μm or less.

The heating roller 53 is disposed inside the fixing belt 54. The heating roller 53 has a heating source 53a inside. The heating source 53a heats the fixing belt 54. The heating source 53a is, for example, a halogen lamp. In addition to the halogen lamp, the heating source 53a may be one that inductively heats the fixing belt 54 (IH) or one that uses the fixing belt 54 as a resistance heating element to generate heat.

The heating roller 53 has a cylindrical shape and is made of metal such as aluminum or stainless steel (SUS). The outer shape of the heating roller 53 is arbitrary, but is preferably 10 mm or more and 100 mm or less. In addition, the thickness of the heating roller 53 is preferably 0.1 mm or more and 5.0 mm or less.

When a halogen lamp is used as the heat source 53a, it is preferable to paint the inner surface of the heating roller 53 black. To prevent damage to the outer surface caused by foreign matter, the outer surface of the heating roller 53 may be coated with polytetrafluoroethylene (PTFE) or the like.

The fixing belt 54 is endless. The fixing belt 54 is rotatably stretched around the pad member 52 and the heating roller 53. The fixing belt 54 includes a base layer, an elastic layer, and a release layer.

The outer diameter of the fixing belt is arbitrary, but is preferably 10 mm or more and 100 mm or less. The base layer is preferably made of polyimide, SUS, nickel electrocasting, etc. The thickness of the base layer is preferably 5 μm or more and 100 μm or less. The elastic layer is preferably made of a highly heat-resistant material such as silicone rubber or fluororubber. The thickness of the elastic layer is preferably 10 μm or more and 300 μm or less. The release layer is preferably made of a material that has releasability, such as fluororesin or fluorine-based coating. The thickness of the release layer is preferably 5 μm or more and 100 μm or less.

The pad member 52 and the holding member 57 are fixed to the fixed member 55. When viewed along the width direction of the fixing belt 54 (perpendicular to the paper surface), the fixed member 55 has an angular U-shape. The fixed member 55 is arranged so that the tip of the U-shape faces the heating roller 53. The pad member 52 is fixed to the bottom 55a of the U-shape of the fixed member 55 (the part of the fixed member 55 that faces the pressure roller 51). The holding member 57 is fixed to the part 55b of the fixed member 55 on the downstream side in the transport direction of the paper S (the direction of the arrow B in FIG. 2).

The lubricant application unit 56 is disposed so as to contact the inner peripheral surface of the fixing belt 54. The lubricant application unit 56 is disposed downstream of the pad member 52 and upstream of the heating roller 53 in the rotation direction of the fixing belt (the direction of the arrow C in FIG. 2).

The lubricant supplied to the fixing belt 54 may be pushed out from the longitudinal ends by the pressure of the nip portion N, resulting in a decrease in the amount. The lubricant application section 56 collects the pushed out lubricant and reapplies the lubricant. The lubricant may be the same as that described above.

The lubricant application section 56 can be made of fibrous materials with high heat resistance, such as aramid fibers and fluorine fibers, porous materials with high heat resistance, such as silicone sponge, and felt members.

The lubricant application portion 56 is not limited to the above-mentioned materials, but may be a hard chrome plating layer or a plating layer formed by dispersing fluororesin in nickel plating solution and depositing it at the same time.

The fixing belt 54, which passes through the nip portion N and heads toward the heating roller 53, is wound around the holding member 57. The holding member 57 guides the rotation of the fixing belt 54 and holds the lubricant application section 56. The holding member 57 has an accommodating recess 57a that accommodates the lubricant application section 56. The accommodating recess 57a is provided at approximately the center of the holding member 57 in the rotation direction of the fixing belt 54. By holding the lubricant application section 56 within the accommodating recess 57a, the lubricant application section 56 can be stably brought into contact with the fixing belt 54.

Figure 3 is a diagram showing the state in which the pressure roller presses the pad member in the fixing device according to the first embodiment. For convenience, the sliding member 58 is omitted from Figure 3. The specific shape of the pad member 52 will be described with reference to Figure 3.

As shown in FIG. 3, the pad member 52 has a curved surface portion R1 provided on the upstream side of the rotation direction of the endless belt and a flat surface portion R2 provided on the downstream side of the rotation direction in the nip portion forming region R that forms the nip portion N. The nip portion forming region R is composed of the curved surface portion R1 and the flat surface portion R2.

When viewed from the axial direction of the pressure roller 51, the curved surface portion R1 is curved in a concave arc shape toward the pressure roller 51. The radius of curvature of the curved surface portion R1 is larger than the radius of curvature of the outer circumferential surface of the pressure roller 51 when the pad member 52 is not being pressed.

Generally, if the radius of curvature of the curved surface R1 is smaller than the radius of curvature of the outer peripheral surface of the pressure roller 51 described above, the nip width can be increased, but the wrap angle of the fixing belt 54 around the pressure roller 51 becomes larger. In such a case, the recording medium will be significantly curved at the entrance of the nip portion N when passing through it. If the radius of curvature of the curved surface R1 is made larger than the radius of curvature of the outer peripheral surface of the pressure roller 51, as in this embodiment, it is possible to prevent the recording medium from being significantly curved.

The flat portion R2 is connected to the curved portion R1 at the connection position P1. That is, the flat portion R2 has an upstream end portion that is connected to the curved portion R1 on the upstream side in the rotation direction. When viewed from the axial direction of the pressure roller 51, the flat portion R2 is arranged so as to be located on the tangent line TL1 of the curved portion R1 that is in contact with the connection position P1.

When viewed from the axial direction of the pressure roller 51, the connection position P1 is located upstream of the rotation direction of the fixing belt 54 with respect to an imaginary line VL1 extending from the center O1 of the pressure roller 51 in the pressure contact direction (DR1 direction in the figure) in which the pressure roller 51 presses against the pad member 52.

When viewed from the axial direction of the pressure roller 51, a normal line VL2 perpendicular to the flat portion R2 from the connection position P1 is parallel to the virtual line VL1 and is located on the entrance side of the nip portion N with respect to the virtual line VL1.

Figure 4 is a diagram showing the distribution of pressure applied to the nip formation region R in the fixing device according to embodiment 1. With reference to Figure 4, the distribution of pressure applied to the nip formation region R in the pressure contact state in which the pressure roller 51 is in pressure contact with the pad member 52 will be described.

The pressure distribution can be measured, for example, by conveying a sensor sheet (manufactured by Nitta Corporation) between the pad member 52 and the pressure roller 51 and using a surface pressure distribution measurement system (manufactured by Nitta Corporation).

As shown in FIG. 4, the pressure distribution in the nip formation region R increases from the upstream side (entrance portion) of the nip portion toward the downstream side (exit portion), reaches a peak, and then decreases. In this pressure distribution, the pressure peak is located in the flat portion R2. Furthermore, the rate of increase in pressure in the curved portion R1 is smaller than the rate of increase in pressure in the flat portion R2.

As described above, in the fixing device according to the first embodiment, the nip forming region R is formed by the curved portion R1 and the flat portion R2 that are concave with respect to the pressure roller 51, so that a sudden increase in pressure can be suppressed on the entrance side of the nip N. This makes it possible to suppress the occurrence of wrinkles on the recording medium on the entrance side of the nip N.

Figures 5 to 7 are diagrams showing the first to third states in which a toner image moves through the nip portion in a fixing device according to a comparative embodiment. With reference to Figures 5 to 7, the fixing of a toner image when a convex portion is formed in the nip portion forming region R relative to the pressure roller 51 will be described.

As shown in Figures 5 to 7, in the fixing device according to the comparative embodiment, a convex portion 52a that is convex with respect to the pressure roller 51 is formed downstream of the nip portion forming region R in order to improve the melting property of the toner. This allows the nip pressure to be maximized downstream of the nip portion.

Figure 5 shows the first state in which the toner image T passes through the nip portion N, specifically, the state immediately before the toner image T passes through the convex portion 52a. The paper S on which the toner image T is formed is a textured paper. The paper S has a concave portion Sa.

Here, the convex portion 52a is considerably larger than the concave portion Sa of the textured paper. For this reason, it is difficult for it to follow the uneven shape of the textured paper. For this reason, in the second state shown in FIG. 6, that is, in the state where the concave portion Sa faces the convex portion 52a, a portion of the toner image T present between the concave portion Sa and the convex portion 52a is insufficiently melted. In addition, because the fixing belt 54 is rotating, a shear force acts on the insufficiently melted toner image T due to the sliding resistance between the fixing belt 54 and the pad member 52. The shear force acts largely on the convex portion 52a.

As shown in FIG. 7, in the third state, i.e., when the concave portion Sa of the paper S passes over the convex portion 52a, the shear force causes the insufficiently melted toner image to move slightly upstream in the transport direction. As a result, the underlying recording medium is locally exposed, resulting in a decrease in image density.

Referring again to FIG. 3, in the fixing device 50 according to the first embodiment, as described above, the nip forming region R is constituted by the curved portion R1 and the flat portion R2 that are concave with respect to the pressure roller 51, so that no portion that is convex with respect to the pressure roller 51 is formed in the nip forming region R. Therefore, when the toner image T passes through the nip N, the shear force acting on the toner image T due to the sliding resistance between the fixing belt 54 and the pad member 52 can be suppressed. As a result, the toner image T can be suppressed from moving upstream in the transport direction, and a decrease in image density can be suppressed.

Furthermore, as shown in FIG. 4, in the pressure distribution in the nip formation region R, the presence of a peak pressure on the flat surface portion R2 side, i.e., downstream of the nip portion N, can improve the melting property of the toner.

As described above, the fixing device 50 according to embodiment 1 and the image forming device 100 equipped with the fixing device 50 can improve the toner melting efficiency while suppressing a decrease in image density.

(Embodiment 2)
8 is a diagram showing a state in which the pressure roller presses the pad member in the fixing device according to the second embodiment. A fixing device 50A according to the second embodiment will be described with reference to FIG.

As shown in FIG. 8, the fixing device 50A according to the second embodiment differs from the fixing device 50 according to the first embodiment in the connection position P1 where the flat surface portion R2 is connected to the curved surface portion R1. The other configurations are almost the same.

In the second embodiment, when viewed from the axial direction of the pressure roller 51, the connection position P1 is located on an imaginary line VL1 extending from the center O1 of the pressure roller 51 in the pressure contact direction (DR1 direction in the figure) in which the pressure roller 51 presses against the pad member 52. Also, when viewed from the axial direction of the pressure roller 51, a normal line VL2 perpendicular to the flat portion R2 from the connection position P1 overlaps with the imaginary line VL1.

Figure 9 is a diagram showing the distribution of pressure applied to the nip portion forming region in the fixing device according to embodiment 2. With reference to Figure 9, the distribution of pressure applied to the nip portion forming region R2 in the above-mentioned pressure contact state will be described.

As shown in FIG. 9, the pressure distribution applied to the nip formation region increases from the upstream side (entrance) to the downstream side (exit) of the nip, reaches a peak, and then decreases. In this pressure distribution, the pressure peak is located at the upstream end of the flat portion R2, i.e., at the connection position P1.

Even when configured in this manner, the upstream side of the nip forming region R is configured with an arc-shaped curved surface portion R1 that is concave with respect to the pressure roller 51, and the downstream side of the nip forming region R is configured with a flat surface portion R2. Furthermore, the flat surface portion R2 is located on a tangent line TL1 of the curved surface portion R1 that is in contact with the connection position P1, and the peak position in the distribution of pressure applied to the nip forming region R is located on the flat surface portion R2. Therefore, with the fixing device 50A according to the second embodiment, substantially the same effect as in the first embodiment can be obtained.

Figure 10 is a diagram showing the distribution of pressure applied to the nip portion forming region in the fixing device of Reference Example 1. The fixing device of Reference Example 1 will be described with reference to Figure 10.

The fixing device of Reference Example 1 differs from the fixing device 50 of Embodiment 1 in that the position of the connection position P1 is different. The other configurations are almost the same. In the fixing device of Reference Example 1, the connection position P1 is shifted upstream of the nip portion N compared to the fixing device 50 of Embodiment 1.

As shown in FIG. 10, by shifting the connection position P1 upstream of the nip portion, the position of the transition point where the pressure changes from the curved portion R1 to the flat portion R2 also shifts upstream of the nip portion.

Figure 11 is a diagram showing the distribution of pressure applied to the nip portion forming region in the fixing device of Reference Example 2. The fixing device of Reference Example 2 will be described with reference to Figure 11.

The fixing device of Reference Example 2 differs from the fixing device 50 of Embodiment 1 in that the position of the connection position P1 is different. The other configurations are almost the same. In the fixing device of Reference Example 2, the connection position P1 is shifted downstream of the nip portion N compared to the fixing device 50 of Embodiment 1.

As shown in FIG. 11, by shifting the connection position P1 downstream of the nip, the position of the transition point where the pressure changes from the curved portion R1 to the flat portion R2 also shifts downstream of the nip.

For this reason, in the fixing device 50 according to embodiment 1, when the connection position P1 is misaligned due to an installation error, as in reference examples 1 and 2, the pressure distribution applied to the nip portion forming region R can vary significantly.

On the other hand, in the pressure distribution of the nip portion according to the second embodiment, as described above, the pressure increases substantially constantly until the pressure peaks. Therefore, in the fixing device 50A according to the second embodiment, the pressure fluctuations in the pressure distribution of the nip portion can be suppressed. In addition, the fluctuations in the nip width due to the fluctuations in the installation error of the connection position P1 can also be suppressed.

(Embodiment 3)
12 is a diagram showing a state in which the pressure roller presses the pad member in the fixing device according to the third embodiment. A fixing device 50B according to the third embodiment will be described with reference to FIG.

As shown in FIG. 12, the fixing device 50B according to the third embodiment differs from the fixing device 50 according to the first embodiment in the connection position P1 where the flat surface portion R2 is connected to the curved surface portion R1. The other configurations are almost the same.

In the third embodiment, when viewed from the axial direction of the pressure roller 51, the connection position P1 is located downstream (downstream of the nip portion N) in the rotation direction of the fixing belt 54 from an imaginary line VL1 extending from the center O1 of the pressure roller 51 in the pressure contact direction (DR1 direction in the figure) in which the pressure roller 51 presses against the pad member 52. Also, when viewed from the axial direction of the pressure roller 51, a normal line VL2 perpendicular to the flat portion R2 from the connection position P1 passes through the center O1 of the pressure roller 51.

Figure 13 is a diagram showing the distribution of pressure applied to the nip portion forming region R in the fixing device according to embodiment 3. With reference to Figure 13, the distribution of pressure applied to the nip portion forming region R in the above-mentioned pressure contact state will be described.

As shown in FIG. 13, the pressure distribution in the nip forming region R increases from the upstream side (entrance portion) of the nip toward the downstream side (exit portion), reaches a peak, and then decreases. In this pressure distribution, the pressure peak is located at the upstream end of the flat portion R2, i.e., the connection position P1.

Even when configured in this manner, the upstream side of the nip forming region R is configured with an arc-shaped curved surface portion R1 that is concave with respect to the pressure roller 51, and the downstream side of the nip forming region R is configured with a flat surface portion R2. Furthermore, the flat surface portion R2 is located on a tangent line TL1 of the curved surface portion R1 that contacts the connection position P1, and the peak position in the distribution of pressure applied to the nip forming region R exists in the flat surface portion R2. Therefore, with the fixing device 50B according to the third embodiment, substantially the same effect as in the first embodiment can be obtained.

Furthermore, in the above pressure distribution according to embodiment 3, the pressure increases at a substantially constant rate until the pressure peaks. Therefore, in the fixing device 50B according to embodiment 3, pressure fluctuations in the pressure distribution at the nip portion can be suppressed. In addition, fluctuations in the nip width due to fluctuations in the installation error of the connection position P1 can also be suppressed.

As described above, when viewed from the axial direction of the pressure roller 51, the connection position P1 is located downstream of the virtual line VL1 in the rotation direction of the fixing belt 54 (downstream of the nip portion N). That is, in the third embodiment, the virtual line VL1 passes near the center of gravity of the pad member 52. Therefore, the force acting to rotate the pad member 52 can be suppressed compared to when the connection position P1 is located upstream of the virtual line VL1 or on the virtual line VL1. As a result, even if slack is provided between the parts in consideration of ease of assembly, the pad member 52 can be suppressed from rotating. As a result, the pressure distribution as described above can be easily obtained.

(Verification experiment)
Fig. 14 is a diagram showing the conditions and results of a first verification experiment conducted to verify the effects of the embodiment. Fig. 15 is a diagram showing the conditions and results of a second verification experiment conducted to verify the effects of the embodiment. Figs. 16 to 19 are diagrams showing the state in which the pressure roller presses the pad member in each fixing device according to Comparative Example 1 to Comparative Example 4. The verification experiments will be described with reference to Figs. 14 to 19.

As shown in FIG. 14, in the first verification experiment, the fixing devices of Comparative Example 1, Comparative Example 2, and Example 1 were used to evaluate paper wrinkles, measure the nip width, and confirm the position of the pressure peak.

To evaluate paper wrinkles, a recording medium, paper, was passed through the nip to check whether paper wrinkles that would cause quality defects occurred on the paper. To measure the nip width, the transport of a measurement film (e.g., an overhead projector (OHP)) was stopped when the film passed through the nip, and a part of the film was thermally deformed. The film was then passed through the nip, and the length of the deformed part was measured. To check the position of the pressure peak, a sensor sheet (manufactured by Nitta Corporation) was transported between the pad member 52 and the pressure roller 51, and the pressure distribution was measured using a surface pressure distribution measurement system (manufactured by Nitta Corporation). The position of the pressure peak in the pressure distribution was confirmed. Note that the greater the nip width and the greater the position of the pressure peak downstream of the nip N, the higher the toner melting efficiency.

The fixing device according to Example 1 has the same configuration as the fixing device 50 according to the first embodiment. The fixing devices 50X1 and 50X2 according to Comparative Examples 1 and 2 differ from the fixing device 50 according to the first embodiment in the shape of the nip portion forming region R in the pad member 52.

As shown in Figures 14 and 16, in the pad member 52 of Comparative Example 1, the upstream side of the nip forming region R is configured as a convex portion that is convex with respect to the pressure roller 51, and the downstream side of the nip forming region R is configured as a flat portion.

As shown in Figures 14 and 17, in the pad member 52 of Comparative Example 2, the upstream side of the nip portion forming region R is configured as a flat portion, and the downstream side of the nip portion forming region R is also configured as a flat portion.

As shown in FIG. 14 again, in Comparative Example 1, the upstream side of the nip formation region R is configured with a convex portion, so that the pressure increases suddenly near the convex portion upstream of the nip. This makes it difficult for the paper to smoothly enter the nip portion, and paper wrinkles that result in poor quality are generated. As a result, the paper wrinkles cannot be evaluated. In addition, the nip width is 9.8 mm, and the peak position in the above pressure distribution is located upstream of the nip formation region R. Therefore, in Comparative Example 1, the toner melting efficiency in the nip portion N was poor.

In Comparative Example 2, although the upstream side of the nip formation region R is composed of a flat portion, the pressure on the upstream side of the nip is still high. This makes it difficult for the paper to smoothly enter the nip, and paper wrinkles that result in poor quality are generated. As a result, the paper wrinkles cannot be evaluated. In addition, the nip width is 11.1 mm, and the peak position in the above pressure distribution is located on the central side of the nip formation region R. For this reason, the toner melting efficiency in the nip N is insufficient.

In Example 1, the upstream side of the nip formation region R is formed with a curved surface that is concave with respect to the pressure roller 51, thereby suppressing the increase in pressure upstream of the nip N. This allows the paper to smoothly enter the nip N, and no paper wrinkles that would cause poor quality results. Furthermore, the nip width is 16.7 mm, and the peak position in the pressure distribution is located downstream of the nip formation region. This improves the toner melting efficiency in the nip N.

As shown in FIG. 15, in the second verification experiment, the fixing devices of Comparative Example 3, Example 1, and Comparative Example 4 were used to evaluate the image density and confirm the position of the pressure peak.

To evaluate image density, the recording medium after the image was fixed was observed to confirm whether there were any areas where the underlying recording medium was locally exposed. When there are any areas where the recording medium is exposed in this way, the image density decreases. Note that exposure of the recording medium occurs when the toner image moves slightly upstream in the transport direction due to insufficient melting while the toner image is being fixed by the fixing device.

The fixing device according to Example 1 has the same configuration as the fixing device 50 according to the first embodiment. The fixing devices 50X3 and 50X4 according to Comparative Examples 3 and 4 differ from the fixing device 50 according to the first embodiment in the shape of the nip portion forming region R in the pad member 52.

As shown in Figures 15 and 18, in the pad member 52 of Comparative Example 3, the upstream side of the nip portion forming region R is configured as a concave portion that is concave relative to the pressure roller 51, and the downstream side of the nip portion forming region R is configured as a convex portion that is convex relative to the pressure roller 51.

As shown in Figures 15 and 19, in the pad member 52 of Comparative Example 4, the upstream side of the nip portion forming region R is configured as a concave portion that is concave relative to the pressure roller 51, and the downstream side of the nip portion forming region R is configured as a convex portion that is convex relative to the pressure roller 51.

As shown again in FIG. 15, in Comparative Example 3, the upstream side of the nip forming region R was composed of concave portions and the downstream side was composed of convex portions, so that the peak position in the above pressure distribution was located downstream of the nip forming region R. On the other hand, because the downstream side of the nip forming region R was composed of convex portions, exposed areas of the recording medium were confirmed and the image density was reduced. For this reason, the image density was evaluated as poor.

In Comparative Example 3, the convex portion formed downstream of the nip portion forming region R has difficulty following the unevenness of the recording medium, so the toner image is partially insufficiently melted. In addition, the shear force generated by the sliding resistance between the fixing belt 54 and the pad member 52 acts strongly on the convex portion. As a result, the part of the toner image that was insufficiently melted was moved by the shear force, and the above-mentioned exposed part of the recording medium was confirmed.

In Comparative Example 4, both the upstream and downstream sides of the nip forming region R are configured with recesses, and no protrusions are formed in the nip forming region R. Therefore, in Comparative Example 4, no exposed areas of the recording medium were observed as in Comparative Example 3, and no reduction in image density occurred. As a result, the image density was evaluated as good.

However, because both the upstream and downstream sides of the nip forming region R are made up of recesses, the peak position in the pressure distribution was confirmed to be approximately in the center of the nip forming region R. For this reason, the toner melting efficiency was reduced compared to Example 1, in which the peak pressure was present downstream of the nip forming region R.

In Example 1, the upstream side of the nip forming region R is configured with a recess, and the downstream side of the nip forming region R is formed with a flat portion, and no protrusions are formed in the nip forming region R. Therefore, even in Example 1, no exposed portion of the recording medium was observed as in Comparative Example 3, and no decrease in image density occurred. As a result, the image density was evaluated as good.

Furthermore, the peak position in the above pressure distribution was confirmed downstream of the nip forming region R, and as explained in the first verification experiment above, the toner melting efficiency in the nip N was improved.

As described above, it has been experimentally confirmed that the fixing device according to the embodiment can improve the toner melting efficiency while suppressing the decrease in image density.

(Variation 1)
20 is a diagram showing a state in which the pressure roller presses the pad member in the fixing device according to Modification 1. In the above-described first to third embodiments, the flat surface portion R2 formed on the downstream side of the nip portion forming region R is located on the tangent line TL1 of the curved surface portion R1 that is in contact with the connection position P1, but this is not limiting. As in the fixing device 50C according to Modification 1, the flat surface portion R2 may be inclined toward the pressure roller 51 side with respect to the tangent line TL1.

Even in this case, the peak position in the distribution of pressure applied to the nip forming region is present on the flat surface, and the same effect as that of the fixing device 50 according to the first embodiment is obtained.

The above-mentioned embodiments of the present invention are illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims.

1C, 1K, 1M, 1Y Image forming unit, 10 Photoconductor, 11 Charging device, 12 Exposure device, 13 Developing device, 14 Developing roller, 15C, 15K, 15M, 15Y Toner bottle, 17 Cleaning device, 30 Intermediate transfer belt, 31 Primary transfer roller, 33 Secondary transfer roller, 37 Cassette, 38 Driven roller, 39 Drive roller, 40 Timing roller, 41 Transport path, 48 Tray, 50, 50A, 50B, 50C, 50X1, 50X2, 50X3, 50X4 Fixing device, 51 Pressure roller, 52 Pad member, 52a Convex portion, 53 Heating roller, 53a Heat source, 54 Fixing belt, 55 Fixed member, 55a Bottom, 56 Lubricant application portion, 57 Holding member, 57a Storage recess, 58 Sliding member, 80 housing, 100 image forming device, 101 control device.

Claims (6)

An endless belt,
a fixing member disposed inside the endless belt;
a roller disposed outside the endless belt and facing the fixing member, the roller forming a nip portion together with the fixing member;
a heating member for heating the endless belt,
the fixing member has a curved surface portion provided on an upstream side in a rotation direction of the endless belt in a nip portion forming region that forms the nip portion, and a flat surface portion provided on a downstream side in the rotation direction and connected to the curved surface portion,
The curved surface portion is curved in an arc shape so as to be concave with respect to the roller,
the flat portion is located on a tangent line of the curved portion that contacts a connection position where the flat portion is connected to the curved portion, or is inclined toward the roller from the tangent line,
In the distribution of pressure applied to the nip portion forming region, a peak position exists on the flat portion ,
The curved surface portion and the flat surface portion are provided continuously . The fixing device according to claim 1, wherein the flat surface is disposed on the tangent line. The fixing device according to claim 1 or 2, wherein the radius of curvature of the curved surface is greater than the radius of curvature of the roller. The fixing device according to any one of claims 1 to 3, wherein the peak position in the distribution of pressure applied to the nip forming region is at the connection position. The fixing device according to claim 4, wherein the connection position is located downstream in the rotation direction of the endless belt from an imaginary line extending from the center of the roller in a pressure contact direction in which the roller is pressed against the fixing member. An image forming apparatus equipped with the fixing device according to any one of claims 1 to 5.

Images