JP2021156927A - Fixing device and image forming apparatus - Google Patents

Abstract

To provide a fixing device that can improve the melting efficiency of toner while preventing a reduction in the concentration of the toner.SOLUTION: A fixing device 50B comprises: an endless belt; a fixing member 52; a roller 51 that is arranged opposite to the fixing member on the outside of the endless belt and forms a nip part; and a heating member that heats the endless belt. The fixing member 52 has a curved surface part R1 that is provided on the upstream side in the direction of rotation of the endless belt in a nip part forming area R, and a flat surface part R2 that is provided on the downstream side in the rotation direction and connected with the curved surface part R1. The curved surface part R1 is curved in an arc shape to be concave with respect to the roller 51. The flat surface part R2 is provided to be located on the tangent TL1 of the curved surface part R1 that is in contact with a connection position P1 at which the flat surface part is connected with the curved surface part R1, or to be inclined toward the roller 51 with respect to the tangent TL1. A peak position is present in the flat surface part R2 in the distribution pf pressures applied to the nip part forming area R.SELECTED DRAWING: Figure 12

Description

The present invention relates to a fixing device and an image forming device including the fixing device.

Conventionally, in a fixing device that forms a toner image on paper and fixes the image on the paper by heat and pressure, in order to improve energy saving, a roller that constitutes a nip and a heating roller equipped with a heat source are installed inside the endless belt. A belt fixing method has been proposed in which the endless belt is placed and stretched.

In order to further improve energy saving, it is disclosed in Japanese Patent Application Laid-Open No. 2019-40144 (Patent Document 1), Japanese Patent Application Laid-Open No. 2019-40013 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2013-218225 (Patent Document 3). As described above, a fixing method has been proposed in which the rollers constituting the nip are changed to fixed pad members (fixing members).

JP-A-2019-40144 Japanese Unexamined Patent Publication No. 2019-4003 Japanese Unexamined Patent Publication No. 2013-218225

However, in the fixing device disclosed in Patent Document 1, the upstream side of the pad member is formed flat and the downstream side of the pad member is formed on a curved surface in the transport direction of the recording medium. Therefore, on the latter half side of the nip portion formed by the pad member and the pressure roller (specifically, in the vicinity of the outlet portion of the nip portion), a portion where the pad is convex with respect to the pressure roller is generated. In the portion of the pad that is convex with respect to the pressure roller, there is a concern that minute movement of toner may occur due to the action of shearing force due to sliding resistance. In this case, the underlying paper may be exposed, resulting in a whitish image. That is, the image density is reduced.

In the fixing device disclosed in Patent Document 2, in the pad member, the nip forming region forming the pressure roller and the nip portion is composed of an arcuate curved surface, and the region downstream from the nip forming region is It is composed of an inclined surface that inclines toward the pressure roller side toward the downstream side in the transport direction. The inclined surface is in a non-contact state with the pressure roller. In such a case, it becomes difficult to provide the peak pressure on the latter half side of the nip portion, and the meltability of the toner may deteriorate.

In the fixing device described in Patent Document 3, each of the upstream side and the downstream side of the pad member is formed of 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 on the downstream side. It is larger than the curvature of the curved surface of the pad member. In such a case, a peak pressure exists on the first half side of the nip portion, and the meltability of the toner may deteriorate.

The present invention has been made in view of the above problems, and an object of the present invention is a fixing device and an image forming device capable of improving the melting efficiency of toner while suppressing a decrease in image density. Is to provide.

The fixing device based on the present invention is arranged to face the fixing member on the outside of the endless belt, the fixing member arranged inside the endless belt, and the fixing member, and forms a nip portion together with the fixing member. A roller and a heating member for heating the endless belt are provided. The fixing member is provided on the curved surface portion provided on the upstream side in the rotation direction of the endless belt and on the downstream side in the rotation direction in the nip portion forming region forming the nip portion, and is connected to the curved surface portion. It has a flat 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 the tangent line of the curved surface portion in contact with the connection position connected to the curved surface portion, or is provided so as to be inclined toward the roller side with respect to the tangent line. In the distribution of pressure applied to the nip portion forming region, the peak position exists in the plane portion.

In the fixing device based on the present invention, it is preferable that the flat surface portion is provided so as to be located on the tangent line.

In the fixing device based on the present invention, the radius of curvature of the curved surface portion is preferably larger than the radius of curvature of the roller.

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

In the fixing device based on the present invention, the connection position is on the downstream side in the rotation direction of the endless belt with respect to the virtual line extending from the center of the roller in the pressure contact direction in which the roller is pressed against the fixing member. It is preferably located at.

The image forming apparatus based on the present invention includes the fixing apparatus.

According to the present invention, it is possible to provide a fixing device and an image forming device capable of improving the melting efficiency of toner while suppressing a decrease in image density.

It is the schematic which shows the image forming apparatus which concerns on Embodiment 1. FIG. It is the schematic sectional drawing of the fixing device which concerns on Embodiment 1. FIG. It is a figure which shows the state which a pressure roller presses a pad member in the fixing device which concerns on Embodiment 1. FIG. It is a figure which shows the distribution of the pressure applied to the nip part formation region in the fixing device which concerns on Embodiment 1. FIG. It is a figure which shows the 1st state in which a toner image moves a nip part in the fixing device which concerns on a comparative form. It is a figure which shows the 2nd state in which a toner image moves a nip part in the fixing device which concerns on a comparative form. It is a figure which shows the 3rd state in which a toner image moves a nip part in the fixing device which concerns on a comparative form. It is a figure which shows the state which a pressure roller presses a pad member in the fixing device which concerns on Embodiment 2. FIG. It is a figure which shows the distribution of the pressure applied to the nip part formation region in the fixing device which concerns on Embodiment 2. It is a figure which shows the distribution of the pressure applied to the nip part formation region in the fixing device which concerns on Reference Example 1. FIG. It is a figure which shows the distribution of the pressure applied to the nip part formation region in the fixing device which concerns on Reference Example 2. FIG. It is a figure which shows the state which a pressure roller presses a pad member in the fixing device which concerns on Embodiment 3. FIG. It is a figure which shows the distribution of the pressure applied to the nip part formation region in the fixing device which concerns on Embodiment 3. It is a figure which shows the condition and result of the 1st verification experiment performed in order to verify the effect of embodiment. It is a figure which shows the condition and result of the 2nd verification experiment performed in order to verify the effect of embodiment. It is a figure which shows the state which a pressure roller presses a pad member in the fixing device which concerns on Comparative Example 1. FIG. It is a figure which shows the state which a pressure roller presses a pad member in the fixing device which concerns on a comparative example 2. FIG. It is a figure which shows the state which a pressure roller presses a pad member in the fixing device which concerns on a comparative example 3. FIG. It is a figure which shows the state which a pressure roller presses a pad member in the fixing device which concerns on a comparative example 4. FIG. It is a figure which shows the state which a pressure roller presses a pad member in the fixing device which concerns on modification 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments shown below, the same or common parts are designated by the same reference numerals in the drawings, and the description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a schematic view showing an image forming apparatus according to the first embodiment. The image forming apparatus 100 according to the first embodiment will be described with reference to FIG.

FIG. 1 shows an image forming apparatus 100 as a color printer. Hereinafter, the image forming apparatus 100 as a color printer will be described, but the image forming apparatus 100 is not limited to the color printer. For example, the image forming apparatus 100 may be a monochrome printer, a fax machine, or a monochrome printer, a color printer, and a multi-function peripheral (MFP).

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

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

By the image forming unit 1Y, 1M, 1C, 1K, the intermediate transfer belt 30, the primary transfer roller 31, the secondary transfer roller 33, the cassette 37, the driven roller 38, the drive roller 39, and the timing roller 40. An image forming unit is configured. This image forming unit forms a toner image on the paper S as a recording medium which is conveyed along the conveying path 41 described later.

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

The image forming units 1Y, 1M, 1C, and 1K are arranged along the intermediate transfer belt 30 in the order of rotation of the intermediate transfer belt 30, respectively. The 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, respectively.

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

The developing device 13 applies a developing bias to the developing roller 14 while rotating the developing roller 14 to adhere toner to the surface of the developing roller 14. As a result, the toner is transferred from the developing roller 14 to the photoconductor 10, and the toner image corresponding to the electrostatic latent image is developed on the surface of the photoconductor 10.

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

The intermediate transfer belt 30 is stretched on the driven roller 38 and the driving roller 39. The drive roller 39 is rotationally driven 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. As a result, the toner image on the intermediate transfer belt 30 is transferred to the secondary transfer roller 33.

The cleaning device 17 is pressure-contacted with the photoconductor 10. The cleaning device 17 collects the toner remaining on the surface of the photoconductor 10 after the transfer of the toner image.

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

The transfer timing of the paper S to the secondary transfer roller 33 is adjusted by the timing roller 40 according to 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 an appropriate position on the paper S.

The fixing device 50 pressurizes and heats the paper S passing through itself. As a result, the toner image is fixed on 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 on which the toner image is fixed is discharged to the tray 48.

Although the image forming apparatus 100 that employs the tandem method as the printing method has been described above, the printing method of the image forming apparatus 100 is not limited to the tandem method. The arrangement of each configuration in the image forming apparatus 100 can be appropriately changed according to the printing method adopted. As the printing method of the image forming apparatus 100, a rotary method or a direct transfer method may be adopted. In the case of the rotary system, the image forming apparatus 100 is composed of one photoconductor 10 and a plurality of developing apparatus 13 rotatably configured on the same axis. At the time of printing, the image forming apparatus 100 guides each developing apparatus 13 to the photoconductor 10 in order to develop a toner image of each color. In the case of the direct transfer method, the image forming apparatus 100 directly transfers the toner image formed on the photoconductor 10 to the paper S.

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

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 fixing member 55, a lubricant application portion 56, and a holding member 57. , And a sliding member 58.

The pressure roller 51 is arranged outside the fixing belt 54. The pressure roller 51 faces the pad member 52. The pressurizing roller 51 sandwiches the fixing belt 54 with the pad member 52 to pressurize 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 conveyed.

The pressure roller 51 is rotated by the torque from the drive source. The fixing belt 54 rotates as the pressure roller 51 rotates. As the pressure roller 51 rotates, the fixing belt 54 rotates in the direction opposite 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 metal is made of a metal such as aluminum or iron. The core metal may have a pipe shape, and in this case, the thickness is preferably 0.1 mm or more and 10 mm or less. The core metal may be a solid one or a deformed one having a cross-sectional shape such as a three-pointed arrow shape. The elastic layer is made of a highly heat-resistant resin such as silicone rubber or fluororubber. The thickness of the elastic layer is preferably 1 mm or more and 20 mm or less. The release layer is provided so as to cover the elastic layer. The release layer preferably has a structure in which a release property such as a fluorine tube or a fluorine-based coating is imparted. The thickness of the release layer is preferably 5 μm or more and 100 μm or less.

The pad member 52 is arranged inside the fixing belt 54. The pad member 52 is arranged so as to face the pressure roller 51 with the fixing belt 54 in between. The pad member 52 is made of, for example, a heat-resistant resin such as polyphenylene sulfide, polyimide, or a liquid crystal polymer, a metal material such as iron, or ceramic. The pad member 52 may be composed 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. As a result, the fixing belt 54 rotates stably.

As the sliding member 58, a glass cloth is used as a base material and the sliding surface is coated with a fluororesin. Specifically, as the sliding member 58, a fluorofiber woven fabric, a fluororesin sheet, a glass coat, or the like is used.

The fixing belt 54 and the sliding member 58 continue to slide, causing wear. In such a case, there is a concern that the sliding resistance will increase and the fixing belt 54 will not rotate properly. Therefore, a lubricant is supplied between the fixing belt 54 and the sliding member 58. As a result, wear of the fixing belt 54 and the sliding member 58 can be suppressed, and durability can be improved. As the lubricant, a silicon-based or fluorine-based lubricant having high heat resistance is preferable, and more specifically, fluorine grease is preferable. By using grease having a high viscosity and containing a solid component, the lubricant tends to remain in the nip portion N. Therefore, when grease is used, wear of the fixing belt 54 and the sliding member 58 can be suppressed for a longer period of time as compared with the case where oil is used. Further, it is preferable that the surface of the sliding member 58 has irregularities 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, the surface roughness Ra of the sliding member 58 is preferably 1 μm or more and 50 μm or less.

The heating roller 53 is arranged 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. As the heating source 53a, in addition to the halogen lamp, one that heats the fixing belt 54 by induction heating (IH) or one that uses the fixing belt 54 as a resistance heating element to generate heat may be used.

The heating roller 53 has a cylindrical shape and is made of a metal such as aluminum and 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. 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 heating source 53a, it is preferable that the inner peripheral surface of the heating roller 53 is black. In order to prevent scratches on the outer surface due to foreign matter or the like, the outer peripheral surface of the heating roller 53 may be coated with polytetrafluoroethylene (PTFE) or the like.

The fixing belt 54 is provided in an endless shape. The fixing belt 54 is rotatably stretched on 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 composed of polyimide, SUS, nickel electroformed or the like. The thickness of the base layer is preferably 5 μm or more and 100 μm or less. The elastic layer is preferably a material having high heat resistance such as silicone rubber and fluororubber. The thickness of the elastic layer is preferably 10 μm or more and 300 μm or less. The release layer is preferably configured to have releasability such as a fluororesin and a 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 fixing member 55. The fixing member 55 has an angular U-shape when viewed along the width direction (vertical direction of the paper surface) of the fixing belt 54. The fixing member 55 is arranged so that the tip side of the U-shape faces the heating roller 53. The pad member 52 is fixed to the U-shaped bottom portion 55a of the fixing member 55 (the portion of the fixing member 55 facing the pressure roller 51). The holding member 57 is fixed to the portion 55b on the downstream side of the fixing member 55 in the transport direction of the paper S (direction of arrow B in FIG. 2).

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

The amount of the lubricant supplied to the fixing belt 54 may be reduced by being pushed out from the end portion in the longitudinal direction by the pressure of the nip portion N. The lubricant application unit 56 collects the extruded lubricant and reapplies the lubricant. As the lubricant, the same one as described above can be adopted.

As the lubricant coating portion 56, a fibrous material having high heat resistance such as aramid fiber and fluorine fiber, a porous material having high heat resistance such as silicon sponge, a felt member and the like can be adopted.

The lubricant coating portion 56 is not limited to the above-mentioned members, and may be a hard chrome plating layer or a plating layer in which a fluororesin is dispersed in a nickel plating solution and precipitated at the same time.

A fixing belt 54 that passes through the nip portion N and faces 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 portion 56. The holding member 57 has an accommodating recess 57a for accommodating the lubricant application portion 56. The accommodating recess 57a is provided substantially in the center of the holding member 57 in the rotation direction of the fixing belt 54. By holding the lubricant coating portion 56 in the accommodating recess 57a, the lubricant coating portion 56 can be stably brought into contact with the fixing belt 54.

FIG. 3 is a diagram showing a state in which the pressure roller pressurizes the pad member in the fixing device according to the first embodiment. In FIG. 3, the sliding member 58 is omitted for convenience. A specific shape of the pad member 52 will be described with reference to FIG.

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

The curved surface portion R1 is curved in an arc shape that is concave with respect to the pressure roller 51 when viewed from the axial direction of the pressure roller 51. The radius of curvature of the curved surface portion R1 is larger than the radius of curvature of the outer peripheral surface of the pressure roller 51 when the pad member 52 is not pressed.

Generally, when the radius of curvature of the curved surface portion 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 fixing belt 54 to the pressure roller 51 The winding angle of is increased. In such a case, when passing through the nip portion N, the recording medium is greatly curved at the inlet portion of the nip portion. When the radius of curvature of the curved surface portion R1 is made larger than the radius of curvature of the outer peripheral surface of the pressure roller 51 as in the present embodiment, it is possible to prevent the recording medium from being greatly curved.

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

The connection position P1 is a virtual extension from the center O1 of the pressure roller 51 in the pressure contact direction (DR1 direction in the drawing) in which the pressure roller 51 presses against the pad member 52 when viewed from the axial direction of the pressure roller 51. It is located on the upstream side of the fixing belt 54 in the rotation direction with respect to the line VL1.

The normal VL2 perpendicular to the flat surface portion R2 from the connection position P1 when viewed from the axial direction of the pressurizing roller 51 is parallel to the virtual line VL1 and nips with respect to the virtual line VL1. It is located on the entrance side of part N.

FIG. 4 is a diagram showing the distribution of pressure applied to the nip portion forming region in the fixing device according to the first embodiment. With reference to FIG. 4, the distribution of the pressure applied to the nip portion forming 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 is measured, for example, by transporting a sensor sheet (Nitta Corporation system) between the pad member 52 and the pressure roller 51 and using a surface pressure distribution measurement system (Nitta Corporation system). be able to.

As shown in FIG. 4, in the pressure distribution of the nip forming region R, the pressure once increased from the upstream side (inlet portion) to the downstream side (outlet portion) of the nip portion, and the pressure reached its peak. After that, the pressure decreases. In such a pressure distribution, the pressure peak position exists in the flat surface portion R2. Further, the rate of increase in pressure at the curved surface portion R1 is smaller than the rate of increase in pressure at the flat surface portion R2.

As described above, in the fixing device according to the first embodiment, the nip portion N is formed by forming the nip portion forming region R by the curved surface portion R1 and the flat surface portion R2 which are concave with respect to the pressure roller 51. It is possible to suppress a sudden increase in pressure on the inlet side. As a result, it is possible to suppress the occurrence of wrinkles on the recording medium on the inlet side of the nip portion N.

5 to 7 are views showing the first to third states in which the toner image moves the nip portion in the fixing device according to the comparative mode. With reference to FIGS. 5 to 7, fixing of the toner image when a portion convex with respect to the pressure roller 51 is formed in the nip portion forming region R will be described.

As shown in FIGS. 5 to 7, in the fixing device according to the comparative form, in the downstream side of the nip portion forming region R for the purpose of improving the meltability of the toner, it is convex with respect to the pressure roller 51. The convex portion 52a is formed. As a result, the nip pressure can be maximized on the downstream side of the nip portion.

FIG. 5 shows a first state in which the toner image T passes through the nip portion N, specifically, a 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 uneven paper. The paper S has a recess Sa.

Here, the convex portion 52a is considerably larger than the concave portion Sa of the concavo-convex paper. Therefore, it is difficult to follow the uneven shape of the uneven paper. Therefore, in the second state shown in FIG. 6, that is, in the state where the concave portion Sa faces the convex portion 52a, a part of the toner image T existing between the concave portion Sa and the convex portion 52a becomes insufficiently melted. Further, since the fixing belt 54 is rotating, a shearing force acts on the toner image T which is insufficiently melted due to the sliding resistance between the fixing belt 54 and the pad member 52. The shearing force acts largely on the convex portion 52a.

As shown in FIG. 7, in the third state, that is, in the state where the concave portion Sa of the paper S passes through the convex portion 52a, the insufficiently melted toner image moves minutely to the upstream side in the transport direction due to the shearing force. .. As a result, the underlying recording medium is locally exposed, resulting in a decrease in image density.

With reference to FIG. 3 again, in the fixing device 50 according to the first embodiment, as described above, the nip portion forming region R is formed by the curved surface portion R1 and the flat surface portion R2 which are concave with respect to the pressure roller 51. By configuring the structure, a portion that is convex with respect to the pressure roller 51 is not formed in the nip portion forming region R. Therefore, when the toner image T passes through the nip portion N, the shearing force acting on the toner image T can be suppressed by the sliding resistance between the fixing belt 54 and the pad member 52. As a result, it is possible to suppress the movement of the toner image T to the upstream side in the transport direction, and it is possible to suppress a decrease in image density.

Further, as shown in FIG. 4, in the pressure distribution in the nip forming region R, the meltability of the toner can be improved by the presence of the peak pressure on the flat surface portion R2 side, that is, on the downstream side of the nip portion N. ..

As described above, in the fixing device 50 according to the first embodiment and the image forming apparatus 100 provided with the fixing device 50, it is possible to improve the melting efficiency of the toner while suppressing the decrease in the image density.

(Embodiment 2)
FIG. 8 is a diagram showing a state in which the pressure roller pressurizes the pad member in the fixing device according to the second embodiment. The 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 has a different connection position P1 in which the flat surface portion R2 is connected to the curved surface portion R1 when compared with the fixing device 50 according to the first embodiment. .. Other configurations are almost the same.

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

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

As shown in FIG. 9, the pressure distribution applied to the nip portion forming region increases once from the upstream side (inlet portion) to the downstream side (outlet portion) of the nip portion, and the pressure peaks. After reaching, the pressure decreases. In such a pressure distribution, the pressure peak position exists at the upstream end portion of the flat surface portion R2, that is, at the connection position P1.

Even in this case, the upstream side of the nip portion forming region R is formed by the arcuate curved surface portion R1 which is concave with respect to the pressure roller 51, and the downstream side of the nip portion forming region R is the flat surface portion R2. It is composed of. Further, the flat surface portion R2 is located on the tangent line TL1 of the curved surface portion R1 in contact with the connection position P1, and the peak position exists in the flat surface portion R2 in the distribution of the pressure applied to the nip portion forming region R. Therefore, in the fixing device 50A according to the second embodiment, substantially the same effect as that of the first embodiment can be obtained.

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

The fixing device according to Reference Example 1 is different from the fixing device 50 according to the first embodiment in that the position of the connection position P1 is different. Other configurations are almost the same. In the fixing device according to Reference Example 1, the connection position P1 is shifted to the upstream side of the nip portion N as compared with the fixing device 50 according to the first embodiment.

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

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

The fixing device according to Reference Example 2 is different from the fixing device 50 according to the first embodiment in that the position of the connection position P1 is different. Other configurations are almost the same. In the fixing device according to Reference Example 2, the connection position P1 is shifted to the downstream side of the nip portion N as compared with the fixing device 50 according to the first embodiment.

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

Therefore, in the fixing device 50 according to the first embodiment, when the connection position P1 is displaced due to an installation error as in Reference Example 1 and Reference Example 2, the fixing device 50 is applied to the nip portion forming region R. The pressure distribution can fluctuate 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 peak is reached. Therefore, in the fixing device 50A according to the second embodiment, it is possible to suppress the fluctuation of the pressure in the pressure distribution of the nip portion. Further, the fluctuation of the nip width due to the fluctuation of the installation error of the connection position P1 can be suppressed.

(Embodiment 3)
FIG. 12 is a diagram showing a state in which the pressure roller pressurizes the pad member in the fixing device according to the third embodiment. The 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 has a different connection position P1 in which the flat surface portion R2 is connected to the curved surface portion R1 when compared with the fixing device 50 according to the first embodiment. .. Other configurations are almost the same.

In the third embodiment, the connection position P1 is the pressure roller 51 in the pressure contact direction (DR1 direction in the drawing) in which the pressure roller 51 presses against the pad member 52 when viewed from the axial direction of the pressure roller 51. It is located on the downstream side (downstream side of the nip portion N) in the rotation direction of the fixing belt 54 with respect to the virtual line VL1 extending from the center O1. Further, the normal VL2 perpendicular to the flat surface portion R2 from the connection position P1 when viewed from the axial direction of the pressure roller 51 passes through the center O1 of the pressure roller 51.

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

As shown in FIG. 13, the pressure distribution of the nip portion forming region R increases once from the upstream side (inlet portion) to the downstream side (outlet portion) of the nip portion, and the pressure reaches its peak. After that, the pressure decreases. In such a pressure distribution, the pressure peak position exists at the upstream end portion of the flat surface portion R2, that is, at the connection position P1.

Even in this case, the upstream side of the nip portion forming region R is formed by the arcuate curved surface portion R1 which is concave with respect to the pressure roller 51, and the downstream side of the nip portion forming region R is the flat surface portion R2. It is composed of. Further, the flat surface portion R2 is located on the tangent line TL1 of the curved surface portion R1 in contact with the connection position P1, and the peak position exists in the flat surface portion R2 in the distribution of the pressure applied to the nip portion forming region R. Therefore, in the fixing device 50B according to the third embodiment, substantially the same effect as that of the first embodiment can be obtained.

Further, in the pressure distribution according to the third embodiment, the pressure increases substantially constant until the pressure peak is reached. Therefore, in the fixing device 50B according to the third embodiment, it is possible to suppress the fluctuation of the pressure in the pressure distribution of the nip portion. Further, the fluctuation of the nip width due to the fluctuation of the installation error of the connection position P1 can be suppressed.

Further, as described above, the connection position P1 is on the downstream side (downstream side of the nip portion N) in the rotation direction of the fixing belt 54 with respect to the virtual line VL1 when viewed from the axial direction of the pressure roller 51. To position. That is, in the third embodiment, the virtual line VL1 passes near the center of gravity of the pad member 52. Therefore, as compared with the case where the connection position P1 is located on the upstream side of the virtual line VL1 or on the virtual line VL1, the force acting to rotate the pad member 52 can be suppressed. As a result, in consideration of assembling property, it is possible to suppress the rotation of the pad member 52 even when looseness is provided between the parts. As a result, it becomes easy to obtain the above pressure distribution.

(Verification experiment)
FIG. 14 is a diagram showing the conditions and results of the first verification experiment performed to verify the effect of the embodiment. FIG. 15 is a diagram showing the conditions and results of the second verification experiment performed to verify the effect of the embodiment. 16 to 19 are views showing a state in which the pressure roller pressurizes the pad member in each of the fixing devices according to Comparative Examples 1 to 4. The verification experiment will be described with reference to FIGS. 14 to 19.

As shown in FIG. 14, in the first verification experiment, the fixing device according to Comparative Example 1, Comparative Example 2, and Example 1 was used to evaluate paper wrinkles, measure the nip width, and position the pressure peak. Confirmed.

In the evaluation of paper wrinkles, the paper, which is a recording medium, was passed through the nip portion, and it was confirmed whether or not paper wrinkles of poor quality were generated on the paper. In the measurement of the nip width, the transfer of the film was stopped at the timing when the measuring film (for example, OHP (Over Head Projector)) passed through the nip portion, and a part of the film was thermally deformed. Subsequently, the film was passed through the nip portion, and the length of the deformed portion was measured. In confirming the position of the pressure peak, a sensor sheet (Nitta Corporation system) is conveyed between the pad member 52 and the pressure roller 51, and the pressure distribution is distributed using the surface pressure distribution measurement system (Nitta Corporation system). Was measured. In the pressure distribution, the position where the pressure peaked was confirmed. The toner melting efficiency is improved when the nip width is large and the pressure peak is located on the downstream side of the nip portion N.

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

As shown in FIGS. 14 and 16, in the pad member 52 according to Comparative Example 1, the upstream side of the nip portion forming region R is composed of a convex portion that is convex with respect to the pressure roller 51, and the nip portion. The downstream side of the formation region R is composed of a flat surface portion.

As shown in FIGS. 14 and 17, in the pad member 52 according to Comparative Example 2, the upstream side of the nip portion forming region R is composed of a flat surface portion, and the downstream side of the nip portion forming region R is also a flat surface portion. It is configured.

As shown in FIG. 14 again, in Comparative Example 1, since the upstream side of the nip portion forming region R is composed of the convex portion, the pressure sharply increases in the vicinity of the convex portion on the upstream side of the nip portion. For this reason, it becomes difficult for the paper to smoothly enter the nip portion, and paper wrinkles resulting in poor quality occur. As a result, the evaluation of paper wrinkles was made impossible. The nip width was 9.8 mm, and the peak position in the pressure distribution was on the upstream side of the nip portion forming region R. Therefore, in Comparative Example 1, the melting efficiency of the toner at the nip portion N was poor.

In Comparative Example 2, although the upstream side of the nip portion forming region R is composed of a flat surface portion, the pressure is still high on the upstream side of the nip portion. For this reason, it becomes difficult for the paper to smoothly enter the nip portion, and paper wrinkles resulting in poor quality occur. As a result, the evaluation of paper wrinkles was made impossible. The nip width was 11.1 mm, and the peak position in the pressure distribution was on the center side of the nip portion forming region R. Therefore, the toner melting efficiency at the nip portion N was insufficient.

In the first embodiment, the upstream side of the nip portion forming region R is formed of a curved surface portion that is concave with respect to the pressure roller 51, so that the increase in pressure can be suppressed on the upstream side of the nip portion N. can. Therefore, the paper could smoothly enter the nip portion N, and no paper wrinkles resulting in poor quality occurred. Further, the nip width was 16.7 mm, and the peak position in the pressure distribution was on the downstream side of the nip portion forming region. Therefore, the toner melting efficiency at the nip portion N is improved.

As shown in FIG. 15, in the second verification experiment, the image density was evaluated and the position of the pressure peak was confirmed by using the fixing devices according to Comparative Example 3, Example 1, and Comparative Example 4.

As an evaluation of the image density, the recording medium after the image was fixed was observed, and it was confirmed whether or not there was a portion where the underlying recording medium was locally exposed. When there is a portion where the recording medium is exposed in this way, the image density decreases. The exposure of the recording medium occurs when the toner image due to insufficient melting moves minutely to the upstream side in the transport direction during the fixing of the toner image by the fixing device.

The fixing device according to the first embodiment has the same configuration as the fixing device 50 according to the first embodiment. The fixing devices 50X3 and 50X4 according to Comparative Example 3 and Comparative Example 4 are different in the shape of the nip portion forming region R in the pad member 52 when compared with the fixing device 50 according to the first embodiment.

As shown in FIGS. 15 and 18, in the pad member 52 according to Comparative Example 3, the upstream side of the nip portion forming region R is formed of a concave portion that is concave with respect to the pressure roller 51, and the nip portion is formed. The downstream side of the region R is composed of a convex portion that is convex with respect to the pressure roller 51.

As shown in FIGS. 15 and 19, in the pad member 52 according to Comparative Example 4, the upstream side of the nip portion forming region R is formed of a concave portion that is concave with respect to the pressure roller 51, and the nip portion is formed. The downstream side of the region R is composed of a convex portion that is convex with respect to the pressure roller 51.

As shown in FIG. 15 again, in Comparative Example 3, the upstream side of the nip portion forming region R is formed of a concave portion and the downstream side is formed of a convex portion, so that the peak position in the pressure distribution is formed of the nip portion. It was on the downstream side of region R. On the other hand, since the downstream side of the nip portion forming region R is composed of the convex portion, the exposed portion of the recording medium is confirmed, and the image density is lowered. Therefore, the image density was evaluated as poor.

In Comparative Example 3, the convex portion formed on the downstream side of the nip portion forming region R does not easily follow the unevenness of the recording medium, so that the toner image is partially melted insufficiently. Further, the shearing force generated by the sliding resistance between the fixing belt 54 and the pad member 52 acts greatly on the convex portion. Therefore, a part of the toner image that was insufficiently melted was moved by the shearing force, so that the exposed portion of the recording medium was confirmed.

In Comparative Example 4, both the upstream side and the downstream side of the nip portion forming region R are formed of concave portions, and no convex portion is formed in the nip portion forming region R. Therefore, in Comparative Example 4, the exposed portion of the recording medium as in Comparative Example 3 was not confirmed, and the image density did not decrease. As a result, the image density was evaluated as good.

On the other hand, since both the upstream side and the downstream side of the nip portion forming region R are composed of recesses, the peak position in the pressure distribution was confirmed substantially in the center of the nip portion forming region R. Therefore, the melting efficiency of the toner is lower than that of Example 1 in which the peak pressure exists on the downstream side of the nip portion forming region R.

In the first embodiment, the upstream side of the nip portion forming region R is formed by a concave portion, the downstream side of the nip portion forming region R is formed by a flat portion, and the convex portion is not formed in the nip portion forming region R. .. Therefore, also in Example 1, the exposed portion of the recording medium as in Comparative Example 3 was not confirmed, and the image density did not decrease. As a result, the image density was evaluated as good.

Further, the peak position in the pressure distribution was confirmed on the downstream side of the nip portion forming region R, and as described in the first verification experiment described above, the toner melting efficiency in the nip portion N was improved.

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

(Modification example 1)
FIG. 20 is a diagram showing a state in which a pressure roller pressurizes a pad member in the fixing device according to the first modification. In the above-described first to third embodiments, the case where 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 in contact with the connection position P1 has been described as an example. However, it is not limited to this. Like the fixing device 50C according to the first modification, the flat surface portion R2 may be inclined toward the pressure roller 51 side with respect to the tangent line TL1.

Also in this case, in the distribution of the pressure applied to the nip portion forming region, the peak position exists in the flat portion, and almost the same effect as that of the fixing device 50 according to the first embodiment can be obtained.

As described above, the embodiment invented this time is an example in all respects and is not limiting. The scope of the present invention is indicated by the claims and includes all modifications within the meaning and scope equivalent to 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 Conveyance path, 48 trays, 50, 50A, 50B, 50C, 50X1, 50X2, 50X3, 50X4 Fixing device , 51 Pressurizing roller, 52 Pad member, 52a Convex part, 53 Heating roller, 53a Heating source, 54 Fixing belt, 55 Fixing member, 55a Bottom, 56 Lubricant coating part, 57 Holding member, 57a Accommodating recess, 58 Sliding Members, 80 housings, 100 image forming devices, 101 control devices.

Claims (6)

With an endless belt,
With the fixing member arranged inside the endless belt,
A roller arranged on the outside of the endless belt so as to face the fixing member and forming a nip portion together with the fixing member.
A heating member for heating the endless belt is provided.
The fixing member is provided on the curved surface portion provided on the upstream side in the rotation direction of the endless belt and on the downstream side in the rotation direction in the nip portion forming region forming the nip portion, and is connected to the curved surface portion. Has a flat surface
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 the tangent line of the curved surface portion in contact with the connection position connected to the curved surface portion, or is provided so as to be inclined toward the roller side with respect to the tangent line.
A fixing device in which a peak position exists in the flat surface portion in the distribution of pressure applied to the nip portion forming region. The fixing device according to claim 1, wherein the flat surface portion is provided so as to be located on the tangent line. The fixing device according to claim 1 or 2, wherein the radius of curvature of the curved surface portion is larger than the radius of curvature of the roller. The fixing device according to any one of claims 1 to 3, wherein the peak position exists at the connection position in the distribution of the pressure applied to the nip portion forming region. The fixing device according to claim 4, wherein the connection position is located on the downstream side in the rotation direction of the endless belt with respect to a virtual line extending from the center of the roller in the pressure contact direction in which the roller is pressed against the fixing member. .. An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 5.

Images