JP2023167273A - Nip forming unit, fixing device, and image forming apparatus - Google Patents

Abstract

To restore a deformed part in a short time without damaging an endless belt.SOLUTION: A nip forming unit comprises: a rotatable, flexible endless belt 20; a nip forming member (heater 22) that is provided to be contactable with an inner peripheral surface of the endless belt; a heating member (heater 22) that heats the nip forming member; a pressure member that is in pressure contact with the nip forming member with the endless belt therebetween to form a nip for sandwiching and conveying a body to be conveyed; a separation member that separates the body to be conveyed passing through the nip from the endless belt; and driving means that rotates to drive the pressure member and the endless belt, wherein the driving means drives the pressure member and the endless belt in a normal direction, and thereby the body to be conveyed is conveyed through the nip. Before conveying the body to be conveyed, the driving means drives the pressure member and the endless belt in a reverse direction to sequentially move, to the nip, an exit adjacent part of the endless belt adjacent to an exit side of the nip and an entrance adjacent part adjacent to an entrance side, and heat the adjacent parts by heating means.SELECTED DRAWING: Figure 8

Description

The present invention relates to a nip forming unit that includes a separation member that separates a conveyed object that has passed through a nip from an endless belt, and to a fixing device and an image forming apparatus that include the nip forming unit.

In image forming apparatuses such as copying machines and printers, cylindrical thin low heat capacity heat resistant resin films are used as fixing devices for fixing images formed on recording media such as paper, as described in Patent Documents 1 to 3, for example. A tensionless fixing device using a tensionless fixing device is known. This tensionless fixing device has high heat transfer efficiency and starts up quickly, so it is suitable for on-demand systems.

The fixing devices disclosed in Patent Documents 1 and 2 separate the paper from the fixing belt using a separating member fixedly arranged close to the fixing belt. When such a separating member is used, if the distance between the fixing belt and the separating member is too small, the separating member comes into contact with the fixing belt and the belt is likely to be damaged, which causes abnormal images to occur.

Furthermore, if the gap between the fixing belt and the separation member is too large, paper passes through this large gap and gets wrapped around the fixing belt, making it easy for paper jams to occur. Therefore, it is necessary to move the separating member as close to the fixing belt as possible without coming into contact with the fixing belt.

However, in the tensionless fixing method, the fixing belt tends to swing in the radial direction (flapping) during rotation. In other words, since the fixing belt is made of a thin resin film, when the belt stops rotating, a flat plate is formed between the inner nip forming member (planar heater) and the outer pressure member (pressure roller). Easy to deform.

In addition, arc-shaped deformation quirks with a large radius of curvature are likely to be formed in the front and rear portions of the flat plate-shaped deformation quirks (the part adjacent to the entrance and the part adjacent to the exit of the nip). In other words, the cross-sectional shape of the fixing belt tends to be a so-called "rice ball" shape or a shape including a horseshoe arch.

When the fixing belt starts rotating (forward rotation) in such a curly state, the rotation trajectory of the fixing belt changes irregularly from vertical to horizontal (uneven rotation). Such rotational unevenness is particularly noticeable when the fixing device is not sufficiently warmed up, such as immediately after the machine main body is powered on, because the bending rigidity of the fixing film is high.

Therefore, the fixing belt comes into contact with the separation member on the downstream side, causing damage to the belt, which may cause abnormal images to occur. Therefore, the fixing devices of Patent Documents 1 and 2 reverse the fixing belt until the temperature of the pressure member reaches a predetermined temperature before passing the recording medium through the nip, so that the fixing belt is connected to the downstream separating member. This is to remove the deformation of the fixing belt while preventing contact.

However, if the fixing belt is rotated in the opposite direction until the temperature of the pressure member reaches a predetermined temperature, the fixing belt will be in sliding contact with the nip forming member for a longer period of time, causing premature deterioration of the sliding surface of the parts, and the damage to the fixing device. There is a problem that the lifespan is shortened. Furthermore, since it takes a considerable amount of time for the temperature of the pressure member to reach a predetermined temperature, the job cannot be started during that time, resulting in a delay in starting the job.

On the other hand, in the fixing device of Patent Document 3, in order to prevent uneven gloss and streaks in images due to deformation habits (bent marks) of the belt, the fixing belt is rotated between the nip entrance area and the nip exit area by rotating the belt in the normal and reverse directions. Heat in small increments. As a result, the deformation of the portion adjacent to the entrance and the portion adjacent to the exit can be quickly removed without causing the fixing belt to idle for a long period of time (nip ironing effect).

However, when the fixing belt is rotated in the forward direction, the deformed kinks may come into contact with the separation member on the downstream side, potentially damaging the belt, resulting in abnormal images.

Therefore, an object of the present invention is to remove deformation defects in a short time without damaging the endless belt.

In order to solve the above problem, a nip forming unit of the present invention includes a rotatable flexible endless belt, a nip forming member provided so as to be able to come into contact with the inner peripheral surface of the endless belt, and the nip forming member. a heating member that heats, a pressure member that presses against the nip forming member via the endless belt to form a nip that pinches and conveys the conveyed object, and a pressure member that presses the conveyed object that has passed through the nip with the nip forming member from the endless belt. A separating member for separating the object, and a driving means for rotationally driving the pressing member and the endless belt, and the pressing member and the endless belt are sequentially driven by the driving means, so that the conveyed object is In a nip forming unit that is conveyed through a nip, before conveying the object to be conveyed, the driving means reversely drives the pressure member and the endless belt to form the nip of the endless belt. A nip forming unit characterized in that an outlet adjacent portion adjacent to an exit side and an inlet adjacent portion adjacent to an inlet side are sequentially moved to the nip and heated by the heating means.
It is characterized by

According to the present invention, deformation defects can be removed in a short time without damaging the endless belt.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a fixing device. It is a perspective view of a heater, a heater holder, and a guide part. FIG. 3 is a plan view of the heater. FIG. 2 is a diagram showing the atomic crystal structure of graphene. FIG. 2 is a diagram showing the atomic crystal structure of graphite. FIG. 3 is a diagram showing a power supply circuit to a heater. 5 is a flowchart showing a heater control operation. 7 is a flowchart showing a pre-sheet feeding control operation of a fixing belt and a heater. FIG. 3 is a diagram showing deformation habits of the fixing belt. FIG. 7 is a diagram illustrating a control operation of the fixing belt before paper passing. It is a figure explaining the difference in the curl removal effect depending on belt temperature. It is a figure which shows the other example of an electroconductive member. It is a figure which shows the other example of an electroconductive member. FIG. 2 is a perspective view of a conductive member having a bent portion and its surroundings. It is a figure which shows an example of the arrangement|positioning of a conductive member in the longitudinal direction. FIG. 14 is a diagram showing an example in which the arrangement of conductive members in the longitudinal direction is different from FIG. 13; FIG. 2 is a side sectional view of a fixing device according to an embodiment in which a conductive member is provided in an insertion hole of a guide rib. FIG. 3 is a side cross-sectional view of a fixing device according to an embodiment in which conductive members extend in different directions. FIG. 3 is a plan view of the heater. FIG. 3 is a diagram showing power supply to a heater. 18 is a plan view of a heater having a resistance heating element different in shape from FIG. 17. FIG. FIG. 20 is a plan view of a heater in which the shape of the resistance heating element is different from FIGS. 17 and 19. FIG.

Hereinafter, the present invention will be explained based on the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are given the same reference numerals as much as possible so that they can be easily distinguished. Omitted.

(Image forming device)
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 shown in FIG. 1 includes four image forming units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming apparatus main body.

Each of the image forming units 1Y, 1M, 1C, and 1Bk has the same configuration except that it accommodates developers of different colors of yellow, magenta, cyan, and black corresponding to the color separation components of a color image. Specifically, each of the image forming units 1Y, 1M, 1C, and 1Bk includes a drum-shaped photoreceptor 2 as an image carrier, a charging device 3 that charges the surface of the photoreceptor 2, and a charging device 3 that charges the surface of the photoreceptor 2. It includes a developing device 4 that supplies toner as a developer to form a toner image, and a cleaning device 5 that cleans the surface of the photoreceptor 2.

The image forming apparatus 100 also includes an exposure device 6 that exposes the surface of each photoconductor 2 to form an electrostatic latent image, a paper feed device 7 that supplies paper P as a conveyed object or recording medium, and each photoconductor 2. A transfer device 8 that transfers the toner image formed on the body 2 to the paper P, a fixing device 9 as a nip forming unit that fixes the toner image transferred to the paper P, and a paper discharge device that discharges the paper P out of the device. A device 10 is provided. In addition to paper P (plain paper), recording media include cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, plastic films, prepregs, copper foil, etc. included.

The transfer device 8 includes an endless intermediate transfer belt 11 as an intermediate transfer body stretched by a plurality of rollers, and four primary transfer members that transfer the toner images on each photoreceptor 2 to the intermediate transfer belt 11. It has a primary transfer roller 12 and a secondary transfer roller 13 as a secondary transfer member that transfers the toner image transferred onto the intermediate transfer belt 11 to the paper P. Each of the plurality of primary transfer rollers 12 is in contact with the photoreceptor 2 via the intermediate transfer belt 11.

As a result, the intermediate transfer belt 11 and each photoreceptor 2 come into contact with each other, and a primary transfer nip is formed between them. On the other hand, the secondary transfer roller 13 is in contact with one of the rollers that stretches the intermediate transfer belt 11 via the intermediate transfer belt 11 . As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

Further, within the image forming apparatus 100, a paper transport path 14 is formed through which the paper P sent out from the paper feeder 7 is transported. A pair of timing rollers 15 are provided on the paper transport path 14 from the paper feed device 7 to the secondary transfer nip (secondary transfer roller 13).

Next, the printing operation of the image forming apparatus will be explained with reference to FIG. When an instruction to start printing is given, the photoreceptor 2 in each image forming unit 1Y, 1M, 1C, and 1Bk is driven to rotate clockwise in FIG. charged to a potential.

Next, the exposure device 6 exposes the surface of each photoreceptor 2 based on the image information of the document read by the document reading device or the print information instructed to print from the terminal, thereby increasing the potential of the exposed portion. and an electrostatic latent image is formed. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoreceptor 2.

When the toner image formed on each photoreceptor 2 reaches the primary transfer nip (the position of the primary transfer roller 12) as each photoreceptor 2 rotates, the intermediate transfer belt that is rotated counterclockwise in FIG. 11 so as to be sequentially overlapped. The toner image transferred onto the intermediate transfer belt 11 is conveyed to the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and is conveyed at the secondary transfer nip. The image is transferred to paper P.

This paper P is supplied from the paper feeder 7. The paper P supplied from the paper feeding device 7 is once stopped by a timing roller 15, and then conveyed to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 11 reaches the secondary transfer nip. In this way, a full-color toner image is carried on the paper P. Further, after the toner image is transferred, the toner remaining on each photoreceptor 2 is removed by each cleaning device 5.

The paper P onto which the toner image has been transferred is conveyed to the fixing device 9, and the toner image is fixed onto the paper P by the fixing device 9. Thereafter, the paper P is discharged from the apparatus by the paper discharge device 10, and a series of printing operations is completed.

(Fixing device)
Next, an embodiment of the fixing device 9 as a nip forming unit will be described. As shown in FIG. 2, the fixing device 9 according to the present embodiment includes a fixing belt 20 made of an endless belt, and a pressurizing member that contacts the outer peripheral surface of the fixing belt 20 to form a fixing nip N. The roller 21 , the heater 22 as a heating member that heats the fixing belt 20 , the heater holder 23 as a holding member that holds the heater 22 , the stay 24 as a support member that supports the heater holder 23 , and the temperature of the fixing belt 20 are controlled. A thermistor 25 or the like is provided as a temperature detecting means.

The fixing belt 20 has a cylindrical base made of polyimide (PI), for example, with an outer diameter of 25 mm and a thickness of 40 to 120 μm. On the outermost layer of the fixing belt 20, a release layer with a thickness of 5 to 50 μm made of a fluororesin such as PFA or PTFE is formed in order to increase durability and ensure release properties.

An elastic layer made of rubber or the like and having a thickness of 50 to 500 μm may be provided between the base and the release layer. Further, the base of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK, or a metal base such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 20 may be coated with polyimide, PTFE, or the like as a sliding layer.

Furthermore, the fixing belt 20 may be configured of a base material, a surface layer, and an adhesive layer without an elastic layer. Without the elastic layer, the rigidity of the belt as a whole would be low, and the belt would easily become deformed when stopped, as will be described later.

The pressure roller 21 has an outer diameter of 25 mm, for example, and includes a solid iron core 21a, an elastic layer 21b formed on the surface of the core 21a, and a release layer formed on the outside of the elastic layer 21b. 21c. The elastic layer 21b is made of silicone rubber and has a thickness of, for example, 3.5 mm. In order to improve mold releasability, it is desirable to form a mold release layer 21c made of a fluororesin layer having a thickness of, for example, about 40 μm on the surface of the elastic layer 21b.

Note that by making the belt diameter of the fixing belt 20 larger than the diameter of the pressure roller 21, the width of the heater 22 can be increased, so that it can be applied to high-production machines. Further, when the belt diameter is large, the deformation of the entire fixing belt 20 with respect to the nip width becomes small, so it is possible to suppress the deformation habit and stabilize the paper separation property. However, if the width of the heater 22 is made too wide, the deformation tendency will also increase. Therefore, the width of the heater 22 is preferably set to an appropriate size.

The pressure roller 21 is urged toward the fixing belt 20 by the urging means, so that the pressure roller 21 is pressed against the heater 22 via the fixing belt 20. As a result, a fixing nip N is formed between the fixing belt 20 and the pressure roller 21.

Therefore, the heater 22 also functions as a nip forming member. Further, the pressure roller 21 is configured to be rotationally driven by a driving means, and when the pressure roller 21 rotates in the direction of the arrow in FIG. 2, the fixing belt 20 is driven to rotate accordingly. Since the fixing belt 20 is driven to rotate, the diameter of the fixing belt 20 (belt diameter) needs to be configured to be larger than inner members such as the heater 22 and the heater holder 23. Note that the drive means for the pressure roller 21 and the heater 22 can be controlled by a control section 220 in FIG. 5, which will be described later, a controller of the machine body, or the like.

The heater 22 is a planar heating member provided longitudinally across the width direction of the fixing belt 20, and includes a plate-shaped base material 30, a resistance heating element 31 provided on the base material 30, and a resistor. It is composed of an insulating layer 32 that covers a heating element 31, and the like. Further, the heater 22 is in contact with the inner peripheral surface of the fixing belt 20 on the insulating layer 32 side, and the heat generated from the resistance heating element 31 is transmitted to the fixing belt 20 via the insulating layer 32. Ru.

The insulating layer 32 is made of heat-resistant glass with a thickness of 75 μm, for example. The resistive heating element 31 and the power supply line 33 are covered with the insulating layer 32 to insulate and protect them, and maintain slidability with the fixing belt 20.

In this embodiment, the resistance heating element 31 and the insulating layer 32 are provided on the fixing belt 20 side (fixing nip N side) of the base material 30; It may be provided on the heater holder 23 side. In that case, since the heat of the resistance heating element 31 is transferred to the fixing belt 20 via the base material 30, it is desirable that the base material 30 is made of a material with high thermal conductivity such as aluminum nitride. Furthermore, by configuring the base material 30 from a material with good thermal conductivity, the fixing belt 20 can be sufficiently heated even if the resistance heating element 31 is placed on the opposite side of the base material 30 from the fixing belt 20 side. is possible.

The heater holder 23 and the stay 24 are arranged on the inner peripheral side of the fixing belt 20. The stay 24 is made of a metal channel material, and both ends of the stay 24 are supported by both side plates of the fixing device 9. Since the heater holder 23 and the heater 22 held therein are supported by the stay 24, the heater 22 can reliably apply the pressing force of the pressure roller 21 when the pressure roller 21 is pressed against the fixing belt 20. The fixing nip N is stably formed by receiving the fixing nip.

Since the heater holder 23 tends to reach a high temperature due to the heat of the heater 22, it is desirable that the heater holder 23 be formed of a heat-resistant material. For example, if the heater holder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP, heat transfer from the heater 22 to the heater holder 23 is suppressed, and the fixing belt 20 can be efficiently heated.

(●Paper separation mechanism)
A paper separation mechanism 300 is provided on the downstream side (right side) of the fixing nip N. The paper separation mechanism 300 has a separation plate 310 as a separation member, and the separation plate 310 separates the paper from the fixing belt 20.

The separation plate 310 can be made of heat-resistant metal or resin. For example, stainless steel can be used as the heat-resistant metal. As the heat-resistant resin, for example, polyimide or PEEK can be used.

The separation plate 310 may be made of a heat-resistant material other than metal or resin. The separation plate 310 extends parallel to the axial direction of the fixing belt 20 with a width larger than the paper size, and both ends of the separation plate 310 in the longitudinal direction are supported by a pair of left and right side plates.

(●Heater configuration)
FIG. 4 is a plan view of the heater 22 according to this embodiment. As shown in FIG. 4A, the heater 22 according to this embodiment has a plurality of resistance heating elements 31 arranged at intervals in the longitudinal direction (belt width direction).

In other words, the plurality of resistance heating elements 31 constitute the heating section 35 that is divided into a plurality of parts in the belt width direction. The heat generating section 35 can be divided into at least three or four or more parts: an end heater (end heating member) that heats both ends and a central heater (center heating member) that heats the center. Thereby, by selecting the heater to be energized in accordance with the paper width, it is possible to suppress overheating of the non-sheet passing portion of the fixing belt 20.

Each resistance heating element 31 is electrically connected in parallel via a power supply line 33 to a pair of electrode sections 34 provided at both longitudinal ends of the base material 30 . The power supply line 33 is made of a conductor having a resistance value smaller than that of the resistance heating element 31.

From the viewpoint of ensuring insulation between the resistance heating elements 31, the gap between the adjacent resistance heating elements 31 is preferably 0.2 mm or more, and more preferably 0.4 mm or more. In addition, if the gap between adjacent resistance heating elements 31 is too large, the temperature will tend to drop in the gap, so from the viewpoint of suppressing temperature unevenness in the longitudinal direction, it is preferably 5 mm or less, and 1 mm or less. is even more preferable.

The resistance heating element 31 is made of a material having PTC (positive temperature resistance coefficient) characteristics, and has a characteristic that the resistance value increases (heater output decreases) as the temperature increases. Due to this feature, for example, when a sheet of paper whose width is smaller than the entire width of the heating section 35 is passed through, the heat of the fixing belt 20 is not taken away by the sheet in the area outside the paper width, so the resistance heating element corresponding to that area is 31 temperature rises.

Since the voltage applied to the resistance heating element 31 is constant, when the temperature of the resistance heating element 31 outside the width of the paper rises and its resistance value increases, the output (heat amount) decreases relatively and the end temperature rises. is suppressed. Further, by electrically connecting the plurality of resistance heating elements 31 in parallel, it is possible to suppress the temperature rise in the non-sheet passing portion while maintaining the printing speed.

Note that the heating element constituting the heating section 35 may be other than a resistance heating element having PTC characteristics. Further, the heating elements may be arranged in multiple rows in the lateral direction of the heater 22.

The resistance heating element 31 can be formed, for example, by applying a paste prepared by mixing silver palladium (AgPd), glass powder, etc. onto the base material 30 by screen printing or the like, and then firing the base material 30. . In this embodiment, the resistance value of the resistance heating element 31 is set to 80Ω at room temperature.

As the material of the resistance heating element 31, in addition to the above-mentioned materials, a resistance material such as silver alloy (AgPt) or ruthenium oxide (RuO2) may be used. The feeder line 33 and the electrode portion 34 can be made of silver (Ag) or silver palladium (AgPd) by screen printing or the like.

(●Base material)
Preferable materials for the base material 30 include ceramics such as alumina and aluminum nitride, which have excellent heat resistance and insulation properties, and nonmetallic materials such as glass and mica. In this embodiment, an alumina base material having a width of 8 mm in the cross-array direction, a width of 270 mm in the array direction, and a thickness of 1.0 mm is used.

Alternatively, the base material 30 may be formed by laminating an insulating material on a conductive material such as metal. As the metal material for the base material 30, aluminum, stainless steel, etc. are preferable because of their low cost. By forming the base material 30 from a stainless steel plate, cracking due to thermal stress can be suppressed. Furthermore, in order to improve the thermal uniformity of the heater 22 and improve the image quality, the base material 30 may be made of a material with high thermal conductivity such as copper, graphite, graphene, etc.

The insulating layer 32 is made of heat-resistant glass with a thickness of 75 μm, for example. The resistive heating element 31 and the power supply line 33 are covered with the insulating layer 32 to insulate and protect them, and maintain slidability with the fixing belt 20.

Graphene is a flaky powder. Graphene consists of a planar hexagonal lattice structure of carbon atoms, as shown in FIG. 4B. A graphene sheet is a sheet of graphene, and is usually a single layer. A single layer of carbon may contain impurities.

Further, graphene may have a fullerene structure. The fullerene structure is generally recognized as a compound formed by forming a polycyclic ring in which the same number of carbon atoms are condensed in a cage shape with a 5-membered ring and a 6-membered ring, such as C60, C70 and C80 fullerenes. or other closed cage-like structures with three-coordinated carbon atoms.

Graphene sheets are man-made and can be produced, for example, by chemical vapor deposition (CVD). A commercially available graphene sheet can be used. The size and thickness of the graphene sheet, the number of layers of the graphite sheet described below, etc. are measured using, for example, a transmission electron microscope (TEM).

Additionally, graphite, which is made by layering graphene, has large thermal conduction anisotropy. As shown in FIG. 4C, graphite has a layer in which the plane of the condensed six-membered ring of carbon atoms spreads out in a planar manner, and has a crystal structure in which these layers are stacked in many layers.

In this crystal structure, adjacent carbon atoms within a layer form covalent bonds, and carbon atoms between layers form van der Waals bonds. Covalent bonds have a stronger bonding force than van der Waals bonds, and have a large anisotropy between bonds within layers and bonds between layers.

By configuring the base material 30 from graphite, the heat transfer efficiency in the arrangement direction is greater than that in the thickness direction (that is, the stacking direction of the members), and heat transfer to the heater holder 23 can be suppressed. Therefore, temperature unevenness in the arrangement direction of the heaters 22 can be efficiently suppressed, and the heat flowing to the heater holder 23 side can be suppressed to a minimum. Further, by forming the base material 30 from graphite, the base material 30 can have excellent heat resistance that does not oxidize up to about 700 degrees.

The physical properties and dimensions of the graphite sheet can be changed as appropriate depending on the functions required of the base material 30. For example, by using high-purity graphite or single crystal graphite, or by increasing the thickness of the graphite sheet, the anisotropy of heat conduction can be enhanced.

Furthermore, in order to increase the speed of the fixing device 9, the heat capacity of the fixing device 9 may be reduced by using a thin graphite sheet. Further, when the width of the fixing nip N or the heater 22 is large, the width of the base material 30 in the arrangement direction may be increased accordingly.

From the viewpoint of increasing mechanical strength, the number of layers of the graphite sheet is preferably 11 or more. Further, the graphite sheet may partially include a single layer and a multilayer portion.

(Power supply circuit)
FIG. 5 is a diagram showing a power supply circuit to the heater according to this embodiment. As shown in FIG. 5, in this embodiment, the power supply circuit for supplying power to each resistance heating element 31 is configured by electrically connecting the AC power source 200 and the electrode section 34 of the heater 22. There is. Further, the power supply circuit is provided with a triac 210 that controls the amount of power supplied.

The amount of power supplied to each resistance heating element 31 is controlled by the control unit 220 via the triac 210 based on the temperature detected by the thermistor 25 as a temperature detection means. The control unit 220 is composed of a microcomputer including a CPU, ROM, RAM, I/O interface, and the like.

In this embodiment, the thermistors 25 as temperature detection means are arranged in the central region in the longitudinal direction of the heater 22, which is within the minimum paper passing width, and at one end in the longitudinal direction of the heater 22, respectively. Further, a thermostat 27 is disposed at one longitudinal end of the heater 22 as a power cutoff means for cutting off power supply to the resistance heating element 31 when the temperature of the resistance heating element 31 exceeds a predetermined temperature. ing. The thermistor 25 and thermostat 27 detect the temperature of the resistance heating element 31 by contacting the back surface of the base material 30 (the side opposite to the side on which the resistance heating element 31 is arranged).

(●Heater control operation)
Next, the heater control operation according to this embodiment will be described with reference to the flowchart in FIG. 6A. First, when a printing operation is started in the image forming apparatus (S1 in FIG. 6A), the control unit 220 starts supplying power from the AC power supply 200 to each resistance heating element 31 of the heater 22 (S2 in FIG. 6A). .

As a result, each resistance heating element 31 starts generating heat, and the fixing belt 20 is heated. At this time, the temperature T4 of the resistance heating element 31 located in the central region of the heater 22 is detected by the thermistor (center thermistor) 25 located in the central region in the longitudinal direction of the heater 22 (S3 in FIG. 6A). Then, the control unit 220 controls the amount of power supplied to each resistance heating element 31 by the triac 210 so that each resistance heating element 31 reaches a predetermined temperature based on the temperature T4 obtained from the central thermistor 25 ( S4 in Figure 6A).

At the same time, the temperature T8 of the resistance heating element 31 is also detected by the thermistor (end thermistor) 25 disposed on the longitudinal end side of the heater 22 (S5 in FIG. 6A). Then, it is determined whether the temperature T8 detected by the end thermistor 25 is equal to or higher than a predetermined temperature TN (T8≧TN) (S6 in FIG. 6A), and if it is less than the predetermined temperature TN, an abnormal low temperature occurs (a wire breakage occurs). As a result, the power supply to the heater 22 is cut off (S7 in FIG. 6A), and an error display is displayed on the operation panel of the image forming apparatus (S8 in FIG. 6A). On the other hand, if the detected temperature T8 is equal to or higher than the predetermined temperature TN, it is determined that no abnormal low temperature has occurred and the printing operation is started (S9 in FIG. 6A).

In addition, in the event that the temperature control based on the detection by the central thermistor 25 becomes impossible due to damage or disconnection of the resistance heating element 31, the other resistance heating elements 31 including the resistance heating element 31 at the longitudinal end There is a risk of abnormally high temperatures. In that case, when the resistance heating element 31 reaches a predetermined temperature or higher, the thermostat 27 is activated to cut off the power supply to the resistance heating element 31, thereby preventing the resistance heating element 31 from becoming abnormally high temperature. . Note that before the start of energization (S2) in FIG. 6A, the control in FIG. 6B can be added as described later. By the control shown in FIG. 6B, the deformation habits A, B, and C shown in FIG. 7 of the fixing belt 20 can be removed.

In the fixing device 9 according to the present embodiment, when a printing operation is started, the pressure roller 21 is driven to rotate, and the fixing belt 20 starts to rotate in a driven manner. Furthermore, the fixing belt 20 is heated by supplying electric power to the resistance heating element 31 of the heater 22 . Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in FIG. By being conveyed to the fixing nip N, the unfixed toner image is heated and pressurized and fixed to the paper P.

(●Fusing belt deformation and its removal)
The fixing belt 20 can be made of polyimide, which is a heat-resistant resin, as described above, but because of its thin thickness, it is likely to develop deformation defects A, B, and C as shown in FIG. 7 while the fixing belt 20 is not rotating. When the fixing belt 20 is rotated with these deformation quirks A, B, and C attached, the trajectory of the fixing belt 20 changes.

That is, in the fixing nip N when rotation is stopped, the fixing belt 20 is sandwiched between the planar heater 22 and the pressure roller 21, and a flat plate-like deformation habit A occurs. In addition, arcuate deformation quirks B and C with a large radius of curvature occur at the entrance adjacent portion and the exit adjacent portion of the fixing nip N. These deformation habits B and C become stronger (the radius of curvature becomes larger) when the sliding surface of the heater 22 is formed into a concave shape to improve paper separation.

Since there is a large difference in cooling time between the fixing belt 20 and the heater 22, deformation defects A, B, and C are more likely to occur. When the fixing belt starts to rotate (sequentially) with these deformation habits A, B, and C attached, since there is no member inside the fixing belt 20 that restricts belt deformation, the rotational trajectory of the fixing belt 20 is vertically ⇔ The belt 20 fluctuates irregularly in a horizontally long manner (occurrence of flapping), and the belt 20 comes into contact with the separation plate 310 on the downstream side.

Conventionally (Patent Documents 1 and 2), the fixing belt 20 is rotated in reverse until the pressure roller 21 reaches a predetermined temperature to remove the deformation defects A, B, and C, but the life of the fixing device 9 is limited. There were issues with the length of time being shortened and the start of the job being delayed. Therefore, in this embodiment, the rotation of the fixing belt 20 is controlled as shown in FIG. The rotation control in FIG. 8 is performed based on the flowchart in FIG. 6B, and reference symbols (S1a to S1f) in the flowchart are used as necessary.
(Rotation control of fixing belt)

In FIG. 8, the fixing belt 20 with the deformed quirks A, B, and C is reversed, and the deformed quirks C and B are sequentially removed. First, from the stopped state, the fixing belt 20 is reversed (rotated clockwise) by a predetermined angle from the left end to the center in FIG. 8 (S1a in FIG. 6B). As a result, the deformed habit C on the exit side reaches the fixing nip N shown in FIG.

Here, the fixing belt 20 is temporarily stopped (S1b in FIG. 6B), and the heater 22 is temporarily energized (S1c in FIG. 6B). Note that when the fixing belt 20 is reversed, the deformation quirks C and B do not move downstream, so even when the deformation quirks C and B are large, the possibility of contacting the separating plate 310 can be reduced.

Thereafter, the fixing belt 20 is reversed (rotated clockwise) by a predetermined angle again (S1d in FIG. 6B). As a result, the deformed habit B on the entrance side now reaches the fixing nip N in FIG. Here, the fixing belt 20 is temporarily stopped (S1e in FIG. 6B), and the heater 22 is temporarily energized (S1f in FIG. 6B).

In this way, by rotating the fixing belt 20 in the reverse direction⇒stopping (heating)⇒reversing⇒stopping (heating), the deformation quirks C and B can be removed in order. Further, by only rotating the fixing belt 20 in the reverse direction without rotating it forward at all, it is possible to reduce the possibility that the belt will come into contact with the separation plate 310 and be damaged. Further, since the rotation angle of the fixing belt 20 in the reverse direction is only about 300 degrees until the deformation quirks C and B are sequentially removed, the life of the fixing device 9 is only slightly shortened.

Moreover, since the heat of the heater 22 can be applied intensively to the deformed quirks B and C, the deformed quirks B and C can be removed in a short time. Therefore, the delay in starting a job can be reduced to a minimum.

The rotational speed when the fixing belt 20 is rotated by a predetermined angle is preferably slower than the rotational speed during the printing operation. The rotation control shown in FIG. 8 is performed before the heater 22 is fully energized for printing operation, but at this time, the viscosity of the grease in the sliding parts such as the fixing nip N is high. Therefore, since the sliding load on the fixing belt 20 is large, the load on the drive system can be reduced by driving the fixing belt 20 at a low speed.

Next, a suitable temperature for heating the deformation patterns B and C of the fixing belt 20 with the heater 22 will be discussed. In FIG. 8, the heat of the heater 22 is concentratedly applied to the deformation patterns B and C, but it is desirable to minimize the heating by the heater 22 to minimize the delay in starting a job.

(Belt temperature and curl removal effect)
FIG. 9 shows an investigation of the correlation between the temperature of the fixing belt 20 and the curl removal effect. As shown in the figure, it can be seen that the curl removal effect cannot be obtained when the belt temperature is lower than 50° C. (X mark: 0% reduction in deformed curl).

On the other hand, when the belt temperature reaches 75° C., the effect of removing curls begins to appear (△ mark: reduction in deformation curls exceeding 0%). It can be seen that the effect of removing curls when the belt temperature is 100° C. or higher is reliably obtained (marked with ◯: 100% reduction in deformed curls). From this, it can be seen that the current application time when the fixing belt 20 is temporarily stopped and temporarily energized is the time when the belt temperature becomes 75° C. or higher, preferably 100° C. or higher.

When the temperature of the fixing belt 20 reaches 100° C., the process immediately moves to the next step. However, the optimum temperature is preferably changed depending on the type of fixing belt, since the effect of removing curls changes depending on the type of base material and elastic layer of the fixing belt 20 used, and the type and thickness of the surface release layer.

Further, when the heater 22 has an end heater and a center heater, the temperature of the end heater can be made higher than the temperature of the center heater when heating the deformation quirks B and C of the fixing belt 20. The end heaters tend to drop in temperature due to heat radiation, so set them to a slightly higher temperature than the central heater.

Further, even when the fixing belt 20 is not rotating, the fixing belt 20 and the pressure roller 21 may be at high temperatures, and the fixing device 9 may not be in a cold state (60° C. or lower). In such a case, there is little possibility that the fixing belt 20 has deformation quirks A, B, and C.

Therefore, the rotation control shown in FIG. 8 may be performed only when the fixing device 9 is in a cold state (60° C. or lower). Thereby, unnecessary rotational control of the fixing belt 20 can be avoided, shortening of the life of the fixing device 9 can be suppressed, and job start delays can be minimized.

(Modified example of thermistor arrangement)
The thermistor 25 can be provided upstream of the center position NA of the fixing nip N in the rotational direction of the fixing belt 20, in other words, on the entrance side of the fixing nip N, as shown in FIG. 10, for example. Since the inlet side of the fixing nip N is an area where heat is easily absorbed by the paper P, the thermistor 25 detects the temperature of this area to ensure the fixing performance of the fixing device 9 and effectively eliminate the fixing offset. can be suppressed to

(Modified example of fixing device and image forming device)
The fixing device of the present invention can also be configured as modified examples shown in FIGS. 11 to 13. The configuration of each fixing device shown in FIGS. 11 to 13 will be briefly described below.

First, in the fixing device 9 shown in FIG. 11, a pressure roller 44 is arranged on the opposite side of the fixing belt 20 from the pressure roller 21 side. The pressure roller 44 is a counter rotating member that rotates opposite the fixing belt 20 as a rotating member. This pressing roller 44 and the heater 22 are configured to sandwich the fixing belt 20 and heat it.

On the other hand, on the pressure roller 21 side, a nip forming member 45 is arranged on the inner periphery of the fixing belt 20 . The nip forming member 45 is supported by the stay 24. The nip forming member 45 and the pressure roller 21 form a fixing nip N with the fixing belt 20 sandwiched therebetween.

Next, in the fixing device 9 shown in FIG. 12, the above-described pressure roller 44 is omitted, and in order to ensure the circumferential contact length between the fixing belt 20 and the heater 22, the heater 22 It is formed into an arc shape. The rest of the configuration is the same as the fixing device 9 shown in FIG. 11.

Finally, the fixing device 9 shown in FIG. 13 will be explained. The fixing device 9 includes a heating assembly 92, a fixing roller 93 as a fixing member, and a pressure assembly 94 as an opposing member.

The heating assembly 92 includes the heater 22, the heater holder 23, the stay 24, the heating belt 120 as a rotating member, and the like described in the previous embodiment. The fixing roller 93 is a counter rotating member that rotates opposite the heating belt 120 as a rotating member.

Further, the fixing roller 93 includes a solid iron core 93a, an elastic layer 93b formed on the surface of the core 93a, and a release layer 93c formed on the outside of the elastic layer 93b. . Further, a pressure assembly 94 is provided on the side opposite to the heating assembly 92 with respect to the fixing roller 93 .

The pressure assembly 94 includes a nip forming member 95 and a stay 96, and a pressure belt 97 is rotatably arranged to enclose the nip forming member 95 and stay 96. Then, the paper P is passed through the fixing nip N2 between the pressure belt 97 and the fixing roller 93, and the image is fixed by heating and applying pressure.

The fixing devices shown in FIGS. 11 to 13 described above are similar in that the amount of heat generated by the heater 22 is reduced in the divided region B between the resistance heating elements 31 of the heater 22. Therefore, similarly to the embodiment described above, by providing the temperature sensing element of the temperature sensing member at a position corresponding to the divided area B of the heater 22, the portion of the rotating member corresponding to the divided area can be sufficiently heated. . This ensures sufficient image fixability and prevents problems such as fixation offset.

Further, the present invention is not limited to the fixing device as described in the above embodiments, but also includes a drying device that dries ink applied to paper, and furthermore, a drying device that dries ink applied to paper, and furthermore, a drying device that dries ink applied to paper. The present invention is also applicable to heating devices such as laminators for pressure bonding and thermocompression bonding devices such as heat sealers for thermocompression bonding the sealed portions of packaging materials. By applying the present invention to such a device, the portions of the rotating member corresponding to the divided regions can be sufficiently heated.

The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may be a monochrome image forming apparatus, a copying machine, a printer, a facsimile machine, or a multifunctional device thereof. For example, as shown in FIG. 14, an image forming apparatus 100 according to the present embodiment includes an image forming means 50 including a photoconductor drum, a paper transport section including a pair of timing rollers 15, a paper feeding device 7, and a fixing device 7. It includes a device 9, a paper ejection device 10, and a reading section 51. The paper feed device 7 includes a plurality of paper feed trays, each of which accommodates sheets of different sizes.

The reading unit 51 reads the image of the document Q. The reading unit 51 generates image data from the read image. The paper feed device 7 accommodates a plurality of sheets P and sends out the sheets P to a conveyance path. The timing roller 15 transports the paper P on the transport path to the image forming means 50.

Image forming means 50 forms a toner image on paper P. Specifically, the image forming means 50 includes a photosensitive drum, a charging roller, an exposure device, a developing device, a replenishing device, a transfer roller, a cleaning device, and a static eliminator.

The toner image shows, for example, an image of a document Q. The fixing device 9 heats and presses the toner image to fix the toner image on the paper P. The paper P with the toner image fixed thereon is transported to the paper ejecting device 10 by a transport roller or the like. Paper discharge device 10 discharges paper P to the outside of image forming apparatus 100 .

Next, the fixing device 9 used in the image forming apparatus 100 shown in FIG. 14 will be described. Descriptions of configurations common to those of the fixing device of the above-described embodiments will be omitted as appropriate.

As shown in FIG. 15, the fixing device 9 includes a fixing belt 20, a pressure roller 21, a heater 22, a heater holder 23, a stay 24, a thermistor 25, and the like. A fixing nip N is formed between the fixing belt 20 and the pressure roller 21. The nip width of the fixing nip N is 10 mm, and the linear speed of the fixing device 9 is 240 mm/s.

The fixing belt 20 includes a polyimide base and a release layer, and does not have an elastic layer. The release layer is made of a heat-resistant film material made of, for example, fluororesin. The outer diameter of the fixing belt 20 is approximately 24 mm.

The pressure roller 21 includes a core metal 21a, an elastic layer 21b, and a release layer 21c. The pressure roller 21 has an outer diameter of 24 to 30 mm, and the elastic layer 21b has a thickness of 3 to 4 mm.

The heater 22 includes a base material, a heat insulating layer, a conductor layer including a resistance heating element, and an insulating layer, and has a total thickness of 1 mm. Further, the width Y of the heater 22 in the cross direction is 13 mm.

As shown in FIG. 16, the conductor layer of the heater 22 includes a plurality of resistance heating elements 31, a power supply line 33, and electrode portions 34A to 34C. Also in this embodiment, as shown in the enlarged view of FIG. 16, divided regions B are formed in which a plurality of resistance heating elements 31 are divided in the arrangement direction. However, in FIG. 16, the divided area B is illustrated only in the range of the enlarged view, but in reality, the divided areas are provided between all the resistance heating elements 31.

The resistance heating element 31 constitutes three heating parts 35A to 35C. By energizing the electrode parts 34A, 34B, the heat generating parts 35A, 35C generate heat.

By energizing the electrode parts 34A and 34C, the heat generating part 35B generates heat. For example, when performing a fixing operation on a small size paper, the heat generating section 35B can be caused to generate heat, and when performing a fixing operation on a large size paper, all the heat generating sections can be caused to generate heat.

As shown in FIG. 17, the heater holder 23 holds the heater 22 in its recess 23b. The recess 23b is provided on the heater 22 side of the heater holder 23. The recesses 23b are provided inside the heater holder 23 on a surface 23b1 that is recessed toward the stay 24 side than the other surfaces of the heater 22 and is substantially parallel to the base material 30, and on both sides (or one side) in the arrangement direction of the heater holders 23. The heater holder 23 is configured by a wall portion 23b2 provided with a wall portion 23b2 arranged in the heater holder 23, and a wall portion 23b3 provided inside the heater holder 23 on both sides in the cross-arrangement direction.

The heater holder 23 has a guide portion 26 . The heater holder 23 is made of LCP (liquid crystal polymer).

As shown in FIG. 18, the connector 60 includes a housing made of resin (for example, LCP), and a plurality of contact terminals provided within the housing. The connector 60 is attached so as to sandwich the heater 22 and the heater holder 23 together from the front side and the back side. In this state, each contact terminal contacts (press-contacts) each electrode portion of the heater 22, thereby electrically connecting the heat generating portion 35 and a power source provided in the image forming apparatus via the connector 60.

This allows power to be supplied from the power source to the heat generating section 35. Note that, in order to ensure connection with the connector 60, at least a portion of each electrode portion 34 is not covered with an insulating layer and is exposed.

The flanges 53 are provided on both sides of the fixing belt 20 in the arrangement direction, and hold both ends of the fixing belt 20 from inside the belt. The flange 53 is fixed to the housing of the fixing device 9. The flange 53 is inserted into both ends of the stay 24 (see the arrow direction from the flange 53 in FIG. 18).

The direction in which the connector 60 is attached to the heater 22 and the heater holder 23 is the direction that crosses the arrangement of the heaters (see the direction of the arrow from the connector 60 in FIG. 18). When the connector 60 is attached to the heater holder 23, a convex portion provided on one of the connector 60 and the heater holder 23 may be engaged with a concave portion provided on the other, and the convex portion may move relatively within the concave portion. Further, the connector 60 is attached to the heater 22 and the heater holder 23 on one side in the arrangement direction and on the opposite side to the side where the drive motor of the pressure roller 21 is provided.

As shown in FIG. 19, thermistors 25 are provided on the center and end sides of the fixing belt 20 in the arrangement direction, facing the inner circumferential surface of the fixing belt 20, respectively. The heater 22 is controlled based on the temperatures detected by the thermistor 25 at the center and end portions of the fixing belt 20 in the arrangement direction. Note that one of these thermistors 25 is provided at a position corresponding to the divided area between the resistance heating elements of the heater 22, as in the above-described embodiment.

Thermostats 27 are provided on the center and end sides of the fixing belt 20 in the arrangement direction, facing the inner circumferential surface of the fixing belt 20, respectively. When the temperature of the fixing belt 20 detected by the thermostat 27 exceeds a predetermined threshold, the power supply to the heater 22 is stopped.

Flanges 53 that hold each end of the fixing belt 20 are provided at both ends of the fixing belt 20 in the arrangement direction. The flange 53 is made of LCP (liquid crystal polymer).

As shown in FIG. 20, the flange 53 is provided with a slide groove 53a. The slide groove 53a extends in the direction in which the fixing belt 20 approaches and separates from the pressure roller 21.

An engaging portion of the housing of the fixing device 9 engages with the slide groove 53a. By relatively moving this engaging portion within the slide groove 53a, the fixing belt 20 can move toward and away from the pressure roller 21.

Also in the fixing device 9 described above, by providing the temperature detection element of the thermistor 25 at a position corresponding to the divided area B of the heater 22, the portion of the fixing belt 20 corresponding to the divided area can be sufficiently heated. This ensures sufficient image fixability and prevents problems such as fixation offset.

In particular, in the case of an image forming apparatus that performs an image forming operation using a single color toner, hot offset is relatively less likely to occur compared to an image forming apparatus that performs an image forming operation using multiple color toners. Therefore, even if the heating member is controlled based on the detection result of the temperature detection element arranged at the position corresponding to the divided area as in the present invention, the hot offset is relatively high in the image forming apparatus using monochromatic toner. This has the advantage of being less likely to occur.

(Summary)
Although the embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the embodiments described above and can be modified in various ways. For example, only either the entrance adjacent portion or the exit adjacent portion of the fixing belt 20 may be moved to the fixing nip N and heated by the heater 22.

Furthermore, in the embodiment described above, the fixing belt 20 of the fixing device 9 has been described as an example of the endless belt, but the endless belt may be a photoreceptor belt. That is, in an image forming apparatus that transfers a toner image carried by a photoreceptor belt serving as an image carrier onto a recording medium serving as a conveyed member, the recording medium is separated from the photoreceptor belt by the aforementioned separation plate.

Further, the endless belt may be the intermediate transfer belt 11 shown in FIG. 1 as an image carrier. That is, the recording medium conveyed through the nip between the intermediate transfer belt 11 and the secondary transfer roller 13 is separated from the intermediate transfer belt 11 by the aforementioned separation plate.

Similarly, the endless belt may be an intermediate transfer belt used in an inkjet image forming apparatus. In addition, in other inkjet image forming apparatuses, when a pressure member is in pressure contact with a nip forming member via an endless belt to form a nip, and the object is conveyed by passing through the nip. Also, the conveyed object after passing through the nip can be separated from the endless belt by the above-mentioned separating plate.

Further, the separation plate 310 can be disposed so as to be movable in the direction toward and away from the fixing belt 20, and the separation plate 310 can be rotated and kept parallel to the heater holder 23. The fixing belt 20 may be configured to be movable in parallel in the direction toward and away from the fixing belt 20.

1Y, 1M, 1C, 1Bk: Image forming unit 2: Photoreceptor 3: Charging device 4: Developing device 5: Cleaning device 6: Exposure device 7: Paper feeding device 8: Transfer device 9: Fixing device 10: Paper ejection device 11 : Intermediate transfer belt 12: Primary transfer roller 13: Secondary transfer roller 14: Paper conveyance path 15: Timing roller 20: Fixing belt 21: Pressure roller 21a: Core bar 21b: Elastic layer 21c: Release layer 22: Heater 23 : Heater holder 24: Stay 25: Thermistor 27: Thermostat 30: Base material 31: Resistance heating element 32: Insulating layer 33: Power supply line 34: Electrode section 34A to 34C: Electrode section 35: Heat generating section 200: AC power supply 210: Triac 220 : Control unit 300: Paper separation mechanism 310: Separation plate (separation member) P: Paper (transferred object)

Patent No. 5305742 JP2009-288587A Japanese Patent Application Publication No. 2006-163295

Claims (5)

A rotatable flexible endless belt,
a nip forming member provided so as to be able to come into contact with the inner circumferential surface of the endless belt;
a heating member that heats the nip forming member;
a pressure member that comes into pressure contact with the nip forming member via the endless belt to form a nip that pinches and conveys the conveyed object;
a separation member that separates the conveyed object that has passed through the nip from the endless belt;
A driving means for rotationally driving the pressure member and the endless belt,
A nip forming unit in which the conveyed object is conveyed through the nip by sequentially driving the pressure member and the endless belt by the driving means,
Before conveying the conveyed object, the driving means reversely drives the pressure member and the endless belt so that the endless belt has a portion adjacent to the outlet adjacent to the outlet side of the nip and an adjacent portion adjacent to the inlet side of the nip. A nip forming unit characterized in that a portion adjacent to an inlet is sequentially moved to the nip and is heated by the heating means. 2. The nip forming unit according to claim 1, wherein the pressure member and the endless belt are driven at a rotational speed lower than a rotational speed when the pressure member and the endless belt are sequentially driven by the driving means. When the heating member has a central heating member that heats a central portion in the longitudinal direction of the nip forming member and an end heating member that heats both ends in the longitudinal direction, and heats the portion adjacent to the inlet and the portion adjacent to the outlet. 3. The nip forming unit according to claim 1, wherein the temperature of the end heating member is higher than the temperature of the central heating member. The conveyed object is a recording medium carrying a developer, and the developer is fixed on the recording medium by passing the recording medium through the nip of the nip forming unit according to claim 3. A fixing device characterized by: An image forming apparatus comprising the fixing device according to claim 4.

Images