JP5794140B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a so-called film heating type fixing device and an image forming apparatus including the fixing device.

A film heating type fixing device is, for example, a heater provided with a nip portion formed by a film-like fixing belt made of an endless belt and a pressure roller provided on the outer periphery of the fixing belt on the inner periphery of the fixing belt. The toner on the recording sheet that passes through the nip portion is melted and fixed by centralized heating.
When there is no recording sheet at the nip portion, the fixing belt rotates by following the rotation of the pressure roller by the friction force between the fixing roller and when the recording sheet exists, Due to the frictional force between the recording sheet and the recording sheet conveyed by the frictional force between them, the recording sheet rotates following the movement of the recording sheet.

As the heater, a heater in which a resistance heating element is formed on one main surface of an elongated rectangular plate-like substrate is used, and ceramic such as aluminum oxide or aluminum nitride is used for the substrate.
When aluminum oxide is used, a resistance heating element is generally formed on the surface of the substrate (main surface facing the fixing belt), and a temperature measuring element for controlling the temperature of the resistance heating element is provided on the back surface of the substrate. (Surface heating type). On the other hand, when aluminum nitride is used, the thermal conductivity is higher than that of aluminum oxide. Therefore, a resistance heating element is formed on the back surface of the substrate (the main surface far from the fixing belt), and an electric insulating layer is formed thereon. It is more common to provide a temperature measuring element because it has better thermal efficiency (backside heating type).

  Further, in both the surface heat generation type and the back surface heat generation type, a coating layer made of glass is usually provided on the front surface side of the substrate in order to ensure slidability with the fixing belt.

JP 2009-42417 A JP 2011-81160 A JP 2006-91139 A

Incidentally, in recent years, as image forming apparatuses such as copying machines and printers have been increased in speed (higher system speed), further slidability between the heater and the fixing belt is ensured, that is, the friction coefficient between the two is reduced. Is becoming a challenge. This is because the higher the system speed, the faster the fixing belt wears and the shorter the service life.
For this reason, there is a case where heat-resistant grease is applied to the inner peripheral surface of the fixing belt to reduce the coefficient of friction with the heater, but there is a problem that management of the application amount is troublesome. That is, if the coating amount is too small, the intended purpose cannot be achieved, and if it is too large, the inside of the image forming apparatus may be soiled with grease.

Note that the above-described problem is not limited to the above-described fixing device having a fixing belt that rotates and travels following a pressure roller. For example, a fixing device that has a fixing belt that rotates around a driving roller and a driven roller. It is common to both.
SUMMARY An advantage of some aspects of the invention is that it provides a fixing device that improves the slidability between a heater and a fixing belt without using grease, and an image forming apparatus including the fixing device. And

  In order to achieve the above object, a fixing device according to the present invention includes an endless fixing belt that is rotated, a heater provided on an inner peripheral side of the fixing belt, and the heater via the fixing belt. A pressure roller that presses from the outer peripheral side of the fixing belt and forms a fixing nip with the fixing belt, and fixes the toner image formed on the recording sheet passing through the fixing nip to the recording sheet; In the fixing device, the heater includes a substrate having a resistance heating element formed on one main surface thereof, and a coating layer formed on an opposing main surface of the substrate facing the inner peripheral surface of the fixing belt. The coating layer is made of a ceramic coating film having a three-dimensional crosslinked matrix structure having a siloxane bond formed by a sol-gel method.

Further, the substrate is made of ceramics, the resistance heating element is formed on the opposing main surface, and the coating layer covers the opposing main surface so as to include the resistance heating element. And
Furthermore, the area | region which is closely_contact | adhered with the said coating layer of the said opposing main surface is roughened in the range of surface roughness Ra = 1 [micrometer]-20 [micrometer], It is characterized by the above-mentioned.

Further, the surface of the coating layer that comes into sliding contact with the inner peripheral surface of the fixing belt is mirror-finished.
In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus that forms an image on a recording sheet by an electrophotographic method, and is a fixing device for a toner image formed on the recording sheet. The fixing device is provided.

  According to the fixing device having the above configuration, the surface of the coating layer made of the ceramic coating film having the three-dimensional cross-linked matrix structure having the siloxane bond formed on the inner peripheral surface of the rotating fixing belt is formed by the sol-gel method. Therefore, the slidability is improved as compared with the case where a coating layer made of glass is used without using grease.

1 is a diagram illustrating a schematic configuration of a tandem full-color printer. FIG. 2 is a perspective view illustrating a schematic configuration of a fixing device. It is the enlarged view which looked at the heater and its vicinity from the direction along the axial center of a pressure roller. (A) is a top view of a heater, (b) is the DD line sectional drawing in (a).

Hereinafter, an embodiment of a fixing device according to the present invention will be described based on an example used for a printer.
<Overall configuration of printer>
FIG. 1 is a diagram showing a schematic configuration of a tandem type full-color printer 2 (hereinafter simply referred to as “printer 2”).

  The printer 2 forms an image by a known electrophotographic method, and faces the transfer belt 4, the driving roller 6 that stretches the transfer belt 4, the driven roller 8, the backup rollers 10 and 12, and the transfer belt 4. Image forming units 14Y, 14M, 14C, and 14K for Y (yellow), M (magenta), C (cyan), and K (black) that are arranged at predetermined intervals along the running direction of the transfer belt 4; A sheet feeding device 16 for feeding a recording sheet and a fixing device 18 are configured to be housed in a housing 20.

Each of the image forming units 14Y,..., 14K includes, in addition to the photosensitive drums 22Y, 22M, 22C, and 22K that are image carriers and the LED arrays 24Y, 24M, 24C, and 24K for exposing and scanning the surface of the photosensitive drum. And a known charging charger, developing device, cleaner (none of which is not shown), and primary transfer rollers 26Y, 26M, 26C, and 26K.
The paper feeding device 16 includes a paper feeding cassette 28 for storing recording sheets, a pickup roller 30 for feeding out the recording sheets from the paper feeding cassette 28, and a registration roller 34 for timing to send the recording sheets to a secondary transfer roller 32 described later. Etc.

Each of the photosensitive drums 22Y,..., 22K is uniformly charged by the charging charger after the residual toner on the surface is removed by the cleaner before being exposed to the LED arrays 24Y,. When the exposure is performed in a uniformly charged state, an electrostatic latent image is formed on the surface of the photosensitive drums 22Y,.
Each electrostatic latent image is developed by a developing device of each color, whereby toner images of Y, M, C, and K are formed on the surface of the photosensitive drums 22Y,. The images are sequentially transferred onto the surface of the transfer belt 4 by the electrostatic action of the primary transfer rollers 26Y,.

At this time, the image forming operation for each color is executed with the timing shifted from the upstream side to the downstream side so that the toner image is transferred in a superimposed manner at the same position on the traveling transfer belt 4. .
On the other hand, in the paper feeding device 16, the recording sheet is fed from the paper feeding cassette 28 in accordance with the timing of image formation on the transfer belt 4 described above, and the position where the secondary transfer roller 32 and the driving roller 6 face each other (hereinafter referred to as the following). , Referred to as “secondary transfer position”).

At the secondary transfer position, the toner image on the transfer belt 4 is retransferred (secondary transfer) to the recording sheet by the electrostatic action of the secondary transfer roller 32.
The recording sheet to which the toner image has been transferred is further conveyed to the fixing device 18. The recording sheet is pressed under high heat in the fixing device 18, and toner particles on the surface thereof are fused and fixed on the sheet surface, and then discharged onto a discharge tray 38 by a discharge roller 36.
<Fixing device>
FIG. 2 is a perspective view illustrating a schematic configuration of the fixing device 18.

The fixing device 18 is a so-called film heating type fixing device, and includes a fixing belt 40 having a thin seamless belt shape and a pressure roller 42 provided in parallel to the fixing belt 40.
The fixing belt 40 has a two-layer structure including a base layer on the inner peripheral side and a surface layer on the outer peripheral side (the two-layer structure is not shown).

The base layer is made of a polyimide film, and its thickness is set to about 100 [μm] in order to reduce the heat capacity. The surface layer is provided to ensure the releasability of the toner, and is composed of a PTFE (tetrafluorinated resin) coating layer.
The base layer is not limited to polyimide, but formed of polyamideimide, PEEK (polyether ether ketone resin), PES (polyether sulfone), etc., and the surface layer is not limited to PTFE, but PFA (perfluoroalkoxy fluororesin), It may be formed of FEP (tetrafluoroethylene / hexafluoropropylene copolymer) or the like. Alternatively, the base layer may be formed of a metal such as stainless steel.

Further, in order to realize higher image quality, a fixing belt constituted by a composite layer in which an elastic rubber layer (intermediate layer) made of silicone or the like is provided between a base layer and a surface layer may be used.
The pressure roller 42 has a heat resistant elastic layer 46 made of silicone rubber or the like formed on the outer periphery of the core metal 44.
Inside the fixing belt 40, a holding member 48 having the same length as the fixing belt 40 is provided, and the holding member 48 holds a heater 50 that is a heating member. The overall length of the heater 50 is substantially the same as that of the fixing belt 40.

The heater 50 held by the holding member 48 is opposed to the pressure roller 42 via the fixing belt 40, and the pressure roller 42 presses the heater 50 via the fixing belt 40, whereby the pressure roller 42. And a fixing belt 40 are formed with a nip portion.
FIG. 3 shows an enlarged view of the nip portion and the vicinity thereof viewed from the direction along the axis of the pressure roller 42. In addition, in FIG. 3, the heater 50 and the holding member 48 are represented with sectional drawing.

The holding member 48 includes a first holding member 47 that directly holds the heater 50 and a second holding member 49 that holds the first holding member 47 in the housing 20.
The first holding member 47 is made of polyimide. The first holding member 47 has an arc-shaped cross section, and also functions as a guide member for guiding the inner peripheral surface of the fixing belt 40 to realize smooth rotational travel. The holding member 47 is not limited to polyimide, and may be formed of other heat resistant resins such as polyamide imide, PEEK, PPS (polyphenylene sulfide), liquid crystal polymer, and the like.

The second holding member 49 is made of ceramic, metal, glass or the like. Note that the holding member 48 may directly attach the first holding member 47 to the housing 20 without providing the second holding member 49.
As described above, the pressure roller 42 presses the heater 50 held by the holding member 48 via the fixing belt 40. As a result, a part of the cylindrical outer peripheral surface of the elastic layer 46 of the pressure roller 42 is elastically deformed into a flat shape along the flat surface of the heater 50 and is sandwiched between the flat surface and the pressure roller 42. The fixed fixing belt 40 is also elastically deformed into a flat shape. A nip portion is formed between the elastic layer 46 elastically deformed in a plane and the fixing belt 40.

  The pressure roller 42 is rotationally driven in the direction of arrow A by rotational power transmitted from a motor (not shown) via a power transmission mechanism (not shown). As a result, when the recording sheet S is not in the nip portion, the fixing belt 40 rotates in the direction of the arrow B by the frictional force generated between the fixing belt 40 and the pressure roller 42. On the other hand, when the recording sheet S is in the nip portion, the recording sheet S is conveyed in the direction of the arrow C by the frictional force generated between the pressure roller 42 and the fixing belt by the frictional force generated between the recording sheet S. 40 will run in the direction of arrow B.

While the recording sheet S passes through the nip portion, heat from the heater 50 is transmitted to the toner on the recording sheet S through the fixing belt 40. As a result, the toner is melted and fixed on the recording sheet S.
4A shows a plan view of the heater 50, and FIG. 4B shows a cross-sectional view taken along the line D / D in FIG. 4A. In FIG. 4A, a coating layer 64 to be described later is indicated by a one-dot chain line, and the inside covered by the coating layer 64 is indicated by a solid line.

The heater 50 includes a substrate 52 having an elongated rectangular plate shape. The substrate 52 is a heat-resistant material and is made of ceramic (in this example, aluminum oxide) that is an electrically insulating material.
On one main surface 52A of the substrate 52 (the main surface on the side facing the inner peripheral surface of the fixing belt 40), a pair of resistance heating elements 54 and 56 in the form of strips are formed in parallel to the longitudinal direction. . The resistance heating elements 54 and 56 are formed by baking a resistor paste containing a silver-based material including an alloy of silver (Ag) / palladium (Pd) at a high temperature to form a thick film having a predetermined resistance value. is there. In addition, the resistor paste may be ruthenium-based, carbon-based, or the like.

One end portions of the resistance heating elements 54 and 56 are electrically connected by a connection body 58. The connection body 58 is formed by firing a silver-based conductor paste.
Power supply terminals 60 and 62 are connected to the other ends of the resistance heating elements 54 and 56, respectively. The power supply terminals 60 and 62 are also formed by firing a silver-based conductor paste.
The heater 50 also has a coating layer 64 that covers all of the resistance heating elements 54 and 56. The coating layer 64 is made of a ceramic coating (hereinafter simply referred to as “ceramic coating”) having a three-dimensional crosslinked matrix structure having a siloxane bond, formed by a sol-gel method. Thermolon coating (trade name) manufactured by Thermolon Japan Co., Ltd. can be used as the ceramic film having the above structure. The thermolon coating is formed using THERMOLON (registered trademark of Thermolon Limited) which is a coating agent. The thickness of the covering layer 64 on the resistance heating elements 54 and 56 is set in the range of 20 [μm] to 100 [μm].

  The ceramic film exhibits the same slidability as that of the fluororesin between the fixing belt 40 and the ceramic film. It has been confirmed that by using the ceramic film for the coating layer 64, the frictional force with the fixing belt 40 is reduced as compared with the case where heat-resistant grease is applied to the glass film. Thereby, even when the system speed is improved and the traveling speed of the fixing belt 40 is increased, smooth rotation of the fixing belt 40 can be secured as compared with the case where the glass film is used, and the fixing belt 40 is not worn. Progress can be suppressed. In addition, since the torque required to rotationally drive the pressure roller can be reduced, for example, the load on the motor serving as the drive source is reduced.

Moreover, the thermal conductivity of the ceramic film is 2 [W / (m · K)] to 3 [W / (m · K)], compared with 2 [W / (m · K)] of the glass film. It has the same or better thermal conductivity.
Furthermore, the ceramic film has a hard pencil hardness of 9H and is excellent in wear resistance.
Still further, the friction coefficient is reduced, and good thermal conductivity, and to increase the hardness, the coating layer 64, may be obtained by addition of _{SiO 2, Al 2 O 3,} TiO 2 in the ceramic coating Absent.

As described above, the coating layer 64 functions as a protective layer that protects the resistance heating elements 54 and 56 and reduces the sliding resistance (dynamic friction coefficient) of the fixing belt 40, thereby protecting the fixing belt 40 from abrasion. To do.
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described form, and for example, the following form may be adopted.
(1) In the above embodiment, the heater 50 is a front surface heating type in which a resistance heating element is formed on the main surface of the substrate facing the fixing belt, which is a member to be heated, and thus the recording sheet. The heater in the fixing device according to the invention is not limited to the front surface heat generation type, but can be applied to the back surface heat generation type. That is, the substrate main surface (hereinafter referred to as the “back surface”) opposite to the fixing belt, which is a heated member, and thus the substrate main surface on the side facing the recording sheet (hereinafter referred to as “front (front) surface”). The heater may be formed by forming a resistance heating element on the surface and forming a ceramic film having a three-dimensional crosslinked matrix structure having a siloxane bond formed by a sol-gel method on the surface. In this case, the substrate is preferably formed of aluminum nitride in consideration of thermal conductivity.
(2) Before forming a ceramic film having a three-dimensional crosslinked matrix structure having a siloxane bond on the substrate surface by a sol-gel method, the surface of the substrate is made to have a surface roughness Ra (center line average roughness) = 1 [μm ] To 20 [μm] may be roughened. By roughening the area of the main surface of the substrate that is in close contact with the ceramic film, the ceramic film is less likely to be peeled off from the substrate due to the so-called anchor effect.

Note that a known treatment method such as a shot blast method or a chemical etching method can be used for the roughening treatment.
(3) Further, after forming a ceramic film having a three-dimensional cross-linked matrix structure having a siloxane bond, formed by a sol-gel method, on the main surface of the substrate, the surface of the ceramic film is subjected to a mirror surface treatment. Alternatively, the surface roughness may be reduced. Thus, by making the surface (sliding contact surface) in sliding contact with the inner peripheral surface of the fixing belt 40 of the coating layer 64 a mirror surface, the adhesion between the sliding contact surface and the inner periphery of the fixing belt can be improved. (Because air existing between the ceramic coating surface and the inner peripheral surface of the fixing belt can be eliminated as much as possible), heat transfer from the heater to the fixing belt is improved.

For example, a “wrapping method” or a “polishing method” can be used for the mirroring process.
(4) In the above embodiment, the fixing belt 40 is configured to rotate and follow the rotation of the pressure roller 42. However, the fixing belt is driven by a power source different from the pressure roller. It does not matter even if it is the composition which carries out rotation run independently. In other words, the fixing belt may be stretched between a driving roller and at least one driven roller, and the driving roller may be rotated by a rotational power source such as a motor to rotate the fixing belt. In this case, the traveling speed of the fixing belt is controlled to coincide with the peripheral speed of the pressure roller.
(5) In the above embodiment, the printer has been described as an example. However, the image forming apparatus according to the present invention is not limited to the printer, and other image forming apparatuses such as a copying machine, a facsimile, or a multifunction machine having these functions. It is applicable to. That is, the present invention can be applied to an image forming apparatus that forms an image on a recording sheet by an electrophotographic method, and that includes the fixing device described so far as a fixing device for a toner image formed on the recording sheet. It is.

  The fixing device according to the present invention can be suitably used as, for example, a fixing device for a toner image formed on the recording sheet of an image forming apparatus that forms an image on a recording sheet by electrophotography.

18 Fixing Device 40 Fixing Belt 42 Pressure Roller 50 Heater 52 Substrate 64 Coating Layer

Claims (5)

An endless fixing belt that rotates, and
A heater provided on the inner peripheral side of the fixing belt;
A pressure roller that presses the heater from the outer peripheral side of the fixing belt through the fixing belt and forms a fixing nip with the fixing belt;
A fixing device for fixing a toner image formed on a recording sheet passing through the fixing nip to the recording sheet,
The heater includes a substrate having a resistance heating element formed on one main surface thereof, and a coating layer formed on an opposing main surface of the substrate facing the inner peripheral surface of the fixing belt. A fixing device comprising a ceramic coating film having a three-dimensional crosslinked matrix structure having a siloxane bond formed by a sol-gel method.   The substrate is made of ceramics, the resistance heating element is formed on the opposing main surface, and the coating layer covers the opposing main surface so as to include the resistance heating element. The fixing device according to claim 1.   The region of the opposing main surface that is in close contact with the coating layer is roughened in a range of surface roughness Ra = 1 [μm] to 20 [μm]. The fixing device described.   The fixing device according to claim 1, wherein a surface of the coating layer that is in sliding contact with the inner peripheral surface of the fixing belt is mirror-finished. An image forming apparatus for forming an image on a recording sheet by an electrophotographic method,
An image forming apparatus comprising the fixing device according to claim 1 as a fixing device for a toner image formed on the recording sheet.

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