JP6908431B2 - Heater, fixing device - Google Patents

Description

The embodiments described in this specification relate to a technique for fixing a toner image formed on a sheet to the sheet.

Conventionally, there is known a fixing device in which a sheet is conveyed by an endless belt and a pressure roller, and the sheet is heated by a plate-shaped heater inside the endless belt. A pressing region of the sheet (endless belt) is formed by the heater and the pressurizing roller. The length of the pinching area in the sheet transport direction is referred to as the nip width. The fixing device fixes the toner image on the sheet to the sheet by heating the sheet conveyed to the nip width while narrowing the pressure.

The following techniques are disclosed.

Japanese Unexamined Patent Publication No. 2015-219418

When the nip width is increased, the heater can be sufficiently pressed against the sheet via the endless belt, and the sheet can be heated satisfactorily. In order to increase the nip width, it is conceivable to increase the load on the heat generating member by the pressure roller or increase the diameter of the pressure roller. However, when the load on the heat generating member by the pressure roller is increased, the heat generating member may be cracked or the endless belt may be deteriorated. When the diameter of the pressure roller is increased, the heat capacity of the pressure roller increases and the heat from the heat generating member is taken away by the pressure roller. Therefore, when the diameter of the pressure roller is increased, it is necessary to increase the amount of heat generated by the heat generating member.

It is an object of the embodiment to provide a technique that makes it possible to increase the nip width between the heater and the pressurizing body.

The heater of the embodiment has a heating element and a protective layer. The protective layer covers the heating element, and at least a part of the surface has a convex portion that is convex toward the heating element.

The fixing device of the embodiment includes an endless belt, a heater, and a pressurizing body. The pressurizing body is installed at a position facing the heater with the endless belt sandwiched between them, and together with the endless belt, forms a nip for sandwiching the sheet to be conveyed. The heater has a heating element and a protective layer that covers the heating element and contacts the endless belt. The surface of the protective layer on the side facing the pressurizing body has a concave surface portion that is concave with respect to the pressurizing body.

The image forming apparatus of the embodiment includes a transfer unit and a fixing apparatus having the above configuration. The transfer unit transfers the image to be formed onto the sheet. The fixing device fixes the image transferred on the sheet to the sheet.

It is a figure which shows the outline of the image forming apparatus of an embodiment. It is a figure which shows the structure of the fixing device of an embodiment. It is a figure which shows the structural example of the heat generation resistance member of embodiment. It is a figure which showed the heating member of embodiment and the conventional heating member. It is the figure which showed the heating member of an embodiment, and is the figure which paid attention to the end part of the protective layer. It is a figure which shows the structural example of another fixing device.

Hereinafter, the image forming apparatus and the fixing apparatus of the embodiment will be described with reference to the drawings.

FIG. 1 is a schematic view of the image forming apparatus of the embodiment. The image forming apparatus 1 includes a reading unit R, an image forming unit P, a paper cassette unit C, and a fixing device 30. The reading unit R reads the document sheet installed on the platen with a CCD (Charge-Coupled Device) image sensor or the like, and converts an optical signal into digital data. The image forming unit P is a unit that acquires the original image read by the reading unit R or the print data from an external personal computer, and forms and fixes the toner image on the sheet.

The image forming unit R includes a laser scanning unit 200 and photosensitive drums 201Y, 201M, 201C, and 201K. The laser scanning unit 200 has a polygon mirror 208 and an optical system 241 and is formed on a sheet based on image signals of each color of yellow (Y), magenta (M), cyan (C), and black (K). The image is applied to the photosensitive drums 201Y to 201K.

The photosensitive drums 201Y to 201K hold each color toner supplied from a developing device (not shown) according to the above irradiation position. The photosensitive drums 201Y to 201K sequentially transfer the retained toner image to the transfer belt 207. The transfer belt 207 is an endless belt, and the roller 213 is rotationally driven to convey the toner image to the transfer position T.

The transport path 101 transports the sheets stocked in the paper feed cassette unit C in the order of the transfer position T, the fixing device 30, and the discharge tray 211. The sheet stocked in the paper cassette unit C is conveyed to the transfer position T by the guidance of the transfer path 101, and the transfer belt 15 transfers the toner image to the sheet at the transfer position T.

The sheet on which the toner image is formed is conveyed to the fixing device 30 according to the guidance of the transfer path 101. The fixing device 30 heats and melts the toner image so that it penetrates into the sheet and fixes it. This prevents the toner image on the sheet from being disturbed by an external force. The transport path 101 transports the sheet on which the toner image is fixed to the discharge tray 211, and discharges the sheet to the outside of the image forming apparatus 1.

The control unit 801 is a unit that collectively controls the devices and mechanisms in the image forming device 1, and includes, for example, a central processing unit such as a CPU (Central Processing Unit) and a volatile / non-volatile storage device. As one embodiment, the central processing unit controls the device and the mechanism in the image forming device 1 by calculating and executing the program stored in the storage device. Further, a part of the function may be implemented as a circuit.

The transfer unit 40 is configured to include each unit until the image (toner image) to be formed is conveyed to the transfer position T and transferred onto the sheet.

FIG. 2 is a diagram showing a configuration example of the fixing device 30. The fixing device 30 has a plate-shaped heater 32 and an endless belt 34 suspended from a plurality of rollers. Further, the fixing device 30 has a drive roller 33 that suspends the endless belt 34 and drives it to rotate in a certain direction. The fixing device 30 has a tension roller 35 that suspends the endless belt 34 and applies tension. Further, the fixing device 30 has a pressure roller 31 having an elastic layer formed on the surface thereof. In the heater 32, the heat generating portion side is in contact with the inner side surface of the endless belt 34, and presses the heater 32 in the direction of the pressurizing roller 31. As a result, the sheet 105 on which the toner image is placed is sandwiched between the contact portion (nip portion) formed by the pressurizing roller 31 and heated and pressurized.

The pressurizing roller 31 (heating body) is installed at a position facing the heater 32 with the endless belt 34 interposed therebetween. The pressure roller 31 and the endless belt 34 form a nip for sandwiching the sheet to be conveyed. In other words, the nip refers to a pressure region of the sheet (endless belt 34) formed by the heater 32 and the pressure roller 31. The length of the nip in the sheet transport direction is called the nip width.

The endless belt 34 has a base layer (Ni / SUS / PI: thickness 60 to 100 μm), an elastic layer (Si rubber: thickness 100 to 300 μm), and a release layer (PFA: thickness) in order from the side in contact with the heater 32. It consists of each layer (15 to 50 μm). The numerical values and materials of each thickness are examples.

The endless belt 34 may use the rotation of the pressure roller 31 as a belt power source.

FIG. 3 is a diagram showing a heat generation resistance member included in the heater 32. The heat generation resistance member 60 (heating element) is a plate-shaped member arranged so as to face the surface of the sheet 105 to be conveyed, and is composed of a plurality of resistance members 61. The resistance member 61 is a cell region in which a plurality of heat generation resistance members 60 are subdivided in a direction perpendicular to the sheet transport direction (Y-axis direction). Both ends of each of the resistance members 61 are connected to the electrodes 62, and heat is generated when the resistance member 61 is energized. The electrode 62 is formed of an aluminum layer.

In the present embodiment, the heat generation resistance member 60 subdivided into a plurality of cells shown in FIG. 3 is used, but a plate-shaped heat generation resistance member that is integrated without being subdivided may be used.

FIG. 4A illustrates the configuration of the heater 32 of the embodiment, and FIG. 4B illustrates the configuration of the conventional heating member for comparison. In FIG. 4, the endless belt 34 is omitted.

In the heater 32 shown in FIG. 4A, the heat generation resistance member 60 described above is laminated on the ceramic substrate 70. Further, a protective layer 90 of the heat-resistant member is laminated to cover the heat-generating resistance member 60. The protective layer 90 is provided to prevent the ceramic substrate 70 and the heat generation resistance member 60 from coming into contact with the endless belt 34 (not shown). By providing the protective layer 90, wear of the endless belt 34 is suppressed. In this example, the ceramic substrate 70 has a thickness of 1 to 2 mm, the material of the protective layer 90 is Sio2, and the thickness thereof is 60 to 80 μm.

The surface 90A of the pressure roller 31 of the protective layer 90 facing the roller surface 31A has a recessed shape (concave shape) with respect to the facing pressure roller 31. In other words, the surface 90A of the protective layer 90 on the side facing the pressure roller 31 has a concave surface portion that is concave with respect to the pressure roller 31. The surface 90A of the protective layer 90 has a curved surface that is convex toward the heat generation resistance member 60. As described above, the protective layer 90 covers the heat generation resistance member 60, and at least a part of the surface 90A has a convex surface portion that is convex toward the heat generation resistance member 60. The surface 90A of the protective layer 90 has a shape that engages with the roller surface 31A of the pressure roller 31 and is scraped off in an arc shape that wraps the roller surface. As shown in FIG. 4A, the protective layer 90 has a shape in which the outer portions near the ends 91 and 92 are thick (high in the X-axis direction) and the central portion is thin (low in the X-axis direction). is doing.

Assuming that the diameter of the pressure roller 31 is Rp and the arcuate diameter of the protective layer 90 is R1, the relationship between these curvatures is 1 / Rp> 1 / R1.
Will be. That is, the arcuate diameter R1 of the protective layer 90 is longer than the diameter Rp of the pressure roller 31, and therefore has a gentler diameter. In other words, the curvature of the concave portion of the protective layer 90 is smaller than the curvature of the surface of the pressure roller 31.

On the other hand, the surface of the protective layer 80 of the conventional heating member shown in FIG. 4B has a flat shape. By forming the surface into an arc shape like the protective layer 90 of the present embodiment, the nip with the pressure roller 31 is larger than that of the conventional flat surface protective layer 80 shown in FIG. 4 (B). The width can be increased. By forming the surface in an arc shape in this way, it is possible to secure a predetermined nip width without increasing the load of the pressure roller 31 and without increasing the diameter of the pressure roller 31. Can be done.

Here, consider a case where the surface 90A of the protective layer 80 has a convex surface portion that is convex with respect to the pressure roller 31. In this case, the convex surface portion hits the heater 32 and a strong load is applied to the heater 32, so that the heater 32 is easily damaged. In the present embodiment, since the surface 90A of the protective layer 80 has a concave portion that is concave with respect to the pressure roller 31, the pressure roller 31 can be used while ensuring the nip width between the protective layer 80 and the pressure roller 31. The load on the protective layer 80 can be kept within an appropriate range.

Further, the protective layer 90 shown in FIG. 4A has the thinnest central portion, but the thickness T1 of the thinnest portion is 60 μm or more. This is to ensure the strength of the protective layer, and in the present embodiment, at least 60 μm or more is secured.

As shown in FIG. 4A, the protective layer 90 is symmetrical, which is based on the pressure roller 31 coming into contact with the central portion of the protective layer 90. It may be asymmetrical depending on the contact position with the pressure roller 31.

FIG. 5 is a diagram showing the protective layer 90, and is a diagram paying particular attention to the shapes of the ends 91 and 92 (the shape of the edge). In FIG. 5, the endless belt 34 is omitted. The end portion 91 is located on the upstream side in the sheet transport direction, and is a joint portion formed by the surface 90A and the upstream side side surface 90B of the protective layer 90. The end portion 92 is located on the downstream side in the sheet transport direction, and is a joint portion formed by the surface 90A and the downstream side surface 90C of the protective layer 90. Hereinafter, the end portion 91 (edge) is referred to as an upstream end portion, and the end portion 92 (edge) is referred to as a downstream end portion. As shown in FIG. 5, the tip shapes of the upstream side end portion 91 and the downstream side end portion 92 are both provided with a curvature and have an arc shape. The diameter and size of the tip arc shape of the upstream end 91 and the tip arc shape of the downstream end 92 are different.

Assuming that the diameter of the tip arc shape (diameter of the edge) of the upstream end 91 is r1 and the diameter of the tip arc shape of the downstream end 92 (diameter of the edge) is r2, these curvatures are ,
1 / r2> 1 / r1
The magnitude relationship is established. That is, the diameter r1 of the upstream end portion 91 is larger and gentler than the diameter r2 of the downstream end portion 92. In this embodiment, the ratio of r1 and r2 r1: r2 = 2: shall be the order of 1. By increasing the diameter of the upstream end portion 91 and making it gentle, the seat can easily enter the nip portion. Further, by increasing the diameter on the inlet side, it is possible to reduce the load of carrying in the sheet, and it is possible to correspond to various sheets such as thick paper. Further, with respect to the surface 90A of the protective layer 90, the portion on the upstream side has a larger curvature than the portion (pinching region) forming the nip width in FIG. 4 (A) so as to be closer to the pressurizing roller 31. It has a curved surface shape. As described above, in the present embodiment, since the curvature of the portion on the upstream side of the surface 90A of the protective layer 90 is increased, the sheet 105 can be brought into contact with the protective layer 90 at the portion at an earlier stage. Therefore, in the present embodiment, the amount of heat that the sheet 105 receives from the heat generation resistance member 60 can be increased.

On the other hand, by reducing the diameter of the downstream end portion 92 and making it sharp, the downstream end portion 92 strongly hits the sheet via the endless belt 34, and the sheet can be easily peeled off from the fixing device 30. Further, since the protective layer 90 is a portion in contact with the endless belt 34, if the upstream end portion 91 and the downstream end portion 92 remain sharp, the endless belt 34 will deteriorate immediately. Therefore, in the present embodiment, the wear of the endless belt 34 can be suppressed by rounding both the upstream end 91 and the downstream end 92 in a circular shape.

The same can be said about the upstream end 91 and the downstream end 92 as follows. In the protective layer 90, the upstream end portion 91 in the sheet transport direction (one end portion 91 in the lateral direction of the heat generation resistance member 60) bulges in the stacking direction of the heat generation resistance member 60 and the protective layer 90, and The top surface is a curved surface. In the protective layer 90, the downstream end portion 92 (the other end portion of the heat generation resistance member 60 in the lateral direction) in the transport direction of the sheet bulges and tops in the stacking direction of the heat generation resistance member 60 and the protective layer 90. The surface is a curved surface. The curvature of the curved surface of the upstream end 91 (one end 91) is different from the curvature of the curved surface of the downstream end 92 (the other end). The curvature of the curved surface of the upstream end 91 is smaller than the curvature of the curved surface of the downstream end 92.

(Second Embodiment)
In the second embodiment, an example in which the configuration of the fixing device is changed from the first embodiment will be described. FIG. 6 is a diagram showing a configuration example of the fixing device 30A.

The film guide 36 has a semi-cylindrical shape and accommodates the heater 32 in the recess 361 on the outer peripheral surface.

The fixing film 34A (belt) is an endless rotating belt. The fixing film 34A is fitted on the outer peripheral surface of the film guide 36. The fixing film 34A is sandwiched between the film guide 36 and the pressure roller 31, and is driven by the rotation of the pressure roller 31.

The heater 32 comes into contact with the fixing film 34A and heats the fixing film 34A.

The sheet 105 on which the toner image is formed is conveyed between the fixing film 34A and the pressure roller 31. The fixing film 34A heats the sheet and fixes the toner image on the sheet to the sheet.

Aspects such as the heater 32 shown in FIGS. 3 to 5 can also be applied to the fixing device 30A of the second embodiment.

As described in detail above, in the embodiment, the nip width between the heater 32 and the pressure roller 31 can be increased.

The present invention can be practiced in various other forms without departing from its spirit or key features. Therefore, the above embodiments are merely exemplary in all respects and should not be construed in a limited way. The scope of the present invention is shown by the scope of claims, and is not bound by the text of the specification. Moreover, all modifications, modifications, substitutions and modifications that fall within the equivalent scope of the claims are all within the scope of the present invention.

1 Image forming device, 30, 30A fixing device, 32 heater, 31 pressure roller (heating element), 34, 34A endless belt, 33 drive roller, 35 tension roller, 40 transfer part, 60 heating resistance member (heating element) ,
61 resistance member, 62 electrodes, 70 ceramic substrate,
90 protective layer, 91 upstream tip, 92 downstream tip, 801 control,
C paper cassette unit, R reading unit, P image forming unit.

Claims (2)

A heater that heats the endless belt by facing the pressurizing body that sandwiches the sheet together with the endless belt and conveys the endless belt.
With a heating element
Said covering the heating body, at least a portion of the surface, have a, a protective layer having a convex portion that protrudes toward the heating element,
The curvature of the convex surface portion is smaller than the curvature of the surface of the pressurizing body.
In the protective layer, the upstream and downstream ends of the sheet in the transport direction bulge in the stacking direction of the heating element and the protective layer, and the top surface is a curved surface.
A heater in which the curvature of the curved surface of the upstream end is smaller than the curvature of the curved surface of the downstream end. It is a fixing device
With an endless belt,
A heater that heats the endless belt and
Wherein across the endless belt facing the heater includes a pressing body for conveying the sheet by sandwiching both said endless belt, and
The heater is
With a heating element
It has a protective layer that covers the heating element and comes into contact with the endless belt.
Wherein the surface of the pressure body facing the side of the protective layer, concave and Do Ri of curvature relative to the pressure body has a small concave portion than the curvature of the surface of the pressure body,
In the protective layer, the upstream and downstream ends of the sheet in the transport direction bulge in the stacking direction of the heating element and the protective layer, and the top surface is a curved surface.
A fixing device in which the curvature of the curved surface of the upstream end is smaller than the curvature of the curved surface of the downstream end.

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