JP2023064854A - Fixing device and image forming apparatus - Google Patents

Abstract

To efficiently transfer heat of a resistance heating element to a fixing belt without reducing the strength of the fixing belt to significantly reduce the fixing start-up time.SOLUTION: A fixing device 20 has a rotatable endless fixing belt 650, a rotatable pressure roller 70 that forms, with the fixing belt 650, a fixing nip part N where a recording material P can be sandwiched; and a heater 600 that is arranged inside the fixing belt 650 and heats the fixing belt 650. The heater 600 includes an overcoat layer 623 that is in contact with an inner surface of the fixing belt 650. The overcoat layer 623 has a film thickness of 0.1 μm or more and 10 μm or less, a thermal conductivity of 10 W/(m K) or more, and a withstand voltage of 1000 V or more.SELECTED DRAWING: Figure 3

Description

The present invention relates to a fixing device for heat-treating a recording medium carrying an unfixed image or a fixed image, and an image forming apparatus such as an electrophotographic device or an electrostatic recording device equipped with the fixing device.

2. Description of the Related Art Conventionally, a heat roller type fixing device is often used in an image forming apparatus. Further, in recent years, image forming apparatuses have come to use film heating type fixing devices from the viewpoint of quick start and energy saving.

A film heating type fixing device includes a heater having a resistance heating element on a ceramic substrate, a flexible member such as a fixing belt that moves while being in contact with the heater, a sliding pressure unit, and a pressure roller. and The sliding pressurizing section is arranged inside the fixing belt, and presses the fixing belt while sliding on the inner surface of the fixing belt. The pressure roller forms a nip portion with the sliding pressure portion via the fixing belt. A recording material bearing an unfixed toner image is heated by a heater while being nipped and conveyed in the nip portion of the fixing device. As a result, the unfixed toner image is heat-fixed on the recording material.

A film heating type fixing device has the advantage that it takes a short time to raise the temperature to a fixable temperature after the start of power supply to the heater. Therefore, a printer equipped with a film heating type fixing device can shorten the time from when a print command is input to when the first image is output. Such a printer also has the advantage of consuming less power while waiting for a print command.

In addition, in the film heating type fixing device, the heat capacity of the film, which is the heating member, is smaller than that of the heat roller type fixing device. Paper control. Such a low-heat-capacity film-heating type fixing device includes an overcoat layer for insulating and protecting the resistance heating element on the ceramic substrate from the inner peripheral surface of the fixing belt. The primary reason a resistive heating element requires a conformal material such as an overcoat layer is to prevent shorting of conductors in the fixing device.

Patent Literature 1 discloses a heating device having a resistance heating element provided on a sliding surface and a non-sliding surface with a fixing film, and an overcoat layer for ensuring dielectric strength of the resistance heating element. . In Patent Document 1, each of the overcoat layers provided on both the sliding surface and the non-sliding surface is heat-resistant glass with a thickness of about 50 μm. Further, in Patent Document 1, the dielectric strength of the heat-resistant glass of the overcoat layer is about 20 MV/m to 40 MV/m. ing.

JP 2003-337484 A

However, in Patent Document 1, the existence of the overcoat layer having a thickness of 50 μm hinders the heat transfer of the heat of the resistance heating element to the fixing belt, and the time required to raise the temperature to the fixable temperature is time. There is a problem that the fixing start-up time becomes long. On the other hand, in order to improve the thermal efficiency of the fixing belt, it is possible to increase the thermal conductivity by increasing the amount of thermally conductive filler added in the fixing film made of resin, for example. However, in this case, the addition of a large amount of heat-conducting filler leads to a decrease in the tear strength of the fixing film, resulting in problems such as tearing of the fixing film during running.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fixing device and an image forming apparatus capable of efficiently transferring heat from a resistance heating element to the fixing belt without lowering the strength of the fixing belt, thereby significantly shortening the start-up time of fixing. That is.

A fixing device according to the present invention includes a rotatable endless fixing belt, a rotatable pressure member forming a nip portion capable of nipping a recording material between the fixing belt and the fixing belt, and a a heating member arranged to heat the fixing belt, the heating member having a first surface layer in contact with the inner surface of the fixing belt, the first surface layer having a thickness of 0; .1 μm or more and 10 μm or less, a thermal conductivity of 10 W/(m·K) or more, and a withstand voltage of 1000 V or more.

According to the present invention, the heat of the resistance heating element can be efficiently transferred to the fixing belt without reducing the strength of the fixing belt, and the fixing start-up time can be greatly shortened.

1 is a schematic diagram of an image forming apparatus according to Embodiment 1 of the present invention; FIG. 1 is a schematic cross-sectional view of a fixing device according to Embodiment 1 of the present invention; FIG. 2 is a schematic diagram showing the configuration of a heater of the fixing device according to Embodiment 1 of the present invention; FIG. 3 is a ternary phase diagram of diamond-like carbon in the fixing device according to Embodiment 1 of the present invention; FIG. FIG. 7 is a diagram showing the effect of shortening the fixing start-up time of the fixing device according to the first embodiment of the present invention; FIG. 7 is a schematic diagram showing the configuration of a heater of a fixing device according to Embodiment 2 of the present invention;

Hereinafter, embodiments will be described in detail with reference to the drawings.

(Embodiment 1)
<Configuration of Image Forming Apparatus>
A configuration of the image forming apparatus 50 according to Embodiment 1 of the present invention will be described in detail with reference to FIG.

The image forming apparatus 50 forms a full-color image on the recording material P according to image information input from an external host device (not shown) connected in a communicable manner, and outputs the image. Here, the external host device is a computer, an image reader, or the like. Also, the image forming apparatus 50 is an electrophotographic full-color printer here.

Specifically, the image forming apparatus 50 includes an image forming section 1Y, an image forming section 1M, an image forming section 1C, an image forming section 1Bk, a laser exposure device 7, an intermediate transfer belt 8, a secondary transfer It has a facing roller 9 and a tension roller 10 . Further, the image forming apparatus 50 includes a secondary transfer roller 11, a belt cleaning device 12, a cassette paper feed section 13A, a cassette paper feed section 13B, a cassette paper feed section 13C, a paper feed roller 14, and a registration roller. 16 and . Further, the image forming apparatus 50 has a manual feed tray 17 , a paper feed roller 18 , a vertical guide 19 , a fixing device 20 , a paper discharge roller 22 and a paper discharge tray 23 .

The image forming units 1Y, 1M, 1C, and 1Bk as image forming units are located below the intermediate transfer belt 8 in the moving direction of the intermediate transfer belt 8 in FIG. are arranged in a line with Each of the image forming section 1Y, the image forming section 1M, the image forming section 1C, and the image forming section 1Bk has a laser exposure type electrophotographic process mechanism. Image forming units 1Y, 1M, 1C, and 1Bk each apply yellow (Y), magenta (M), and cyan (Y) to the surface of the rotating photosensitive drum 2 at predetermined control timings. C) and black (Bk) toner images are formed.

In the case of the monochrome print mode, only the image forming section 1Bk that forms a black toner image is controlled in its image forming operation. Since the electrophotographic imaging principle and process for forming a toner image on the photosensitive drum 2 are well known, the description thereof will be omitted.

Each of the image forming section 1Y, the image forming section 1M, the image forming section 1C, and the image forming section 1Bk includes a photosensitive drum 2, a primary charger 3, a developing device 4, a transfer roller 5, a drum cleaner device 6, It has

The photosensitive drum 2 is a drum-type electrophotographic photosensitive member as an image bearing member which is rotated clockwise at a predetermined speed as indicated by an arrow in FIG. A primary charger 3 , a developing device 4 , a transfer roller 5 and a drum cleaning device 6 are arranged around the photosensitive drum 2 .

A primary charger 3 charges the photosensitive drum 2 .

The developing device 4 forms a toner image on the photosensitive drum 2 by supplying toner to the electrostatic latent image formed on the photosensitive drum 2 .

The transfer roller 5 is arranged inside the intermediate transfer belt 8 and is in pressure contact with the photosensitive drum 2 via the intermediate transfer belt 8 . The transfer roller 5 primarily transfers the toner image formed on the photosensitive drum 2 onto the intermediate transfer belt 8 .

The drum cleaner device 6 removes transfer residual toner remaining on the photosensitive drum 2 during primary transfer from the photosensitive drum 2 .

The laser exposure device 7 has a polygon mirror, a reflecting mirror, or the like, and exposes the charged photosensitive drum 2 by emitting light corresponding to time-series electric digital pixel signals of image information supplied from an external host device. As a result, an electrostatic latent image is formed on the photosensitive drum 2 .

The intermediate transfer belt 8 is a flexible endless belt. The intermediate transfer belt 8 is stretched between a secondary transfer opposing roller 9 and a tension roller 10, and is rotated counterclockwise at a predetermined speed as indicated by an arrow in FIG. The intermediate transfer belt 8 is rotationally driven in the direction of rotation of the photosensitive drums 2 and in the forward direction at a speed corresponding to the rotational speed of the photosensitive drums 2 . The intermediate transfer belt 8 contacts the photosensitive drum 2 to form a primary transfer portion. On the outer surface of the intermediate transfer belt 8, the toner images formed on the respective photosensitive drums 2 are successively superimposed and transferred in the primary transfer portion to form four unfixed full-color toner images synthesized. .

The secondary transfer opposing roller 9 is driven to rotate the intermediate transfer belt 8 .

The tension roller 10 stretches the intermediate transfer belt 8 together with the secondary transfer opposing roller 9 .

The secondary transfer roller 11 is in pressure contact with the secondary transfer facing roller 9 via the intermediate transfer belt 8 . The secondary transfer roller 11 contacts the intermediate transfer belt 8 to form a secondary transfer portion. The secondary transfer roller 11 collectively secondary-transfers the full-color toner images on the intermediate transfer belt 8 onto the surface of the recording material P at the secondary transfer portion to form an unfixed toner image. The secondary transfer roller 11 conveys the recording material P on which the unfixed toner image is formed toward the longitudinal guide 19 .

The belt cleaning device 12 cleans the intermediate transfer belt 8 by removing residual adhering matter such as secondary transfer residual toner on the intermediate transfer belt 8 after the recording material P has been separated, so that the intermediate transfer belt 8 can be repeatedly operated. Serve the statue.

Each of the cassette sheet feeding section 13A, the cassette sheet feeding section 13B, and the cassette sheet feeding section 13C stacks and accommodates recording materials P of different sizes.

The paper feed roller 14 is driven at a predetermined paper feed timing. By being driven, the paper feed roller 14 separates and feeds one recording material P stacked and housed in the selected cassette paper feed section 13A, cassette paper feed section 13B, or cassette paper feed section 13C. The sheet is conveyed to registration rollers 16 via a vertical conveying path 15 .

The registration rollers 16 move the recording material P conveyed through the vertical conveying path 15 or the re-conveying path 24 in the conveying direction at the timing when the leading edge of the toner image transferred onto the intermediate transfer belt 8 reaches the secondary transfer portion. The recording material P is conveyed so that the leading edge of the recording material P reaches the secondary transfer portion.

The manual feed tray 17 is a multi-purpose tray on which recording materials P are stacked.

The paper feed roller 18 is driven when manual paper feed is selected, and separates and feeds the recording materials P stacked and set on the manual feed tray 17 one by one and feeds them through the vertical conveying path 15 . Then, it is conveyed to the registration rollers 16 .

The longitudinal guide 19 guides the conveyance of the recording material P separated from the intermediate transfer belt 8 and conveyed from the secondary transfer portion to the fixing device 20 .

The fixing device 20 applies heat and pressure to the recording material P guided by the longitudinal guide 19 and conveyed, onto which the unfixed toner images of a plurality of colors or monochrome have been transferred. By applying heat and pressure to the recording material P, the fixing device 20 fuses and mixes the unfixed toner images of a plurality of colors to fix them on the surface of the recording material P as a permanently fixed image, or forms a monochromatic unfixed toner image. is melted and fixed on the surface of the recording material P as a permanent image. The fixing device 20 conveys the recording material P on which the unfixed toner image has been fixed to the discharge roller 22 via the conveyance path 21 . Details of the configuration of the fixing device 20 will be described later.

The paper discharge roller 22 discharges the recording material P conveyed from the conveying path 21 onto the paper discharge tray 23 when the single-sided print mode is selected. When the double-sided print mode is selected, the discharge roller 22 reversely rotates just before the trailing edge of the printed recording material P in the conveying direction passes through the surface, thereby switching the recording material P. The sheet is back-conveyed and introduced into the re-conveyance path 24 .

The paper discharge tray 23 stacks the recording materials P discharged by the paper discharge rollers 22 .

<Structure of Fixing Device>
A configuration of the fixing device 20 according to Embodiment 1 of the present invention will be described in detail with reference to FIGS. 1 and 2. FIG.

The fixing device 20 has a power source 30 , a control section 51 , a heater unit 60 , a pressure roller 70 , a CPU 100 and an entrance guide 223 .

The power supply 30 supplies power to a power supply unit of a resistance heating element (not shown) under the control of the control unit 51 .

The control unit 51 controls energization of the heater 600 by the power supply 30 under the control of the CPU 100 .

The heater unit 60 is installed above the pressure roller 70 and includes a heater 600 , a fixing belt 650 , a film guide 660 and a reinforcing sheet metal 670 . The heater unit 60 is arranged parallel to the pressure roller 70 with the heater 600 facing downward.

A heater 600 as a heating member is fixed and supported on the lower surface of the film guide 660, is arranged inside the fixing belt 650, and serves as both a pressure member and a heat source. Heater 600 has a contact surface with the inner surface of fixing belt 650 , and heats fixing belt 650 while slidably pressing fixing belt 650 toward pressure roller 70 . The details of the configuration of heater 600 will be described later.

The fixing belt 650 is composed of a heat-resistant cylindrical endless film. The fixing belt 650 is loosely fitted around the film guide 660 and is rotated at a predetermined speed following the rotation of the pressure roller 70 by being pressed against the pressure roller 70 . The fixing belt 650 slides with its inner surface in close contact with the heater 600 and rotates around the film guide 660 clockwise in FIG. Fixing belt 650 is heated by heater 600 .

The fixing belt 650 is configured by forming a silicone rubber layer (elastic layer) with a thickness of about 250 μm on a stainless cylindrical base material with a thickness of 30 μm by a ring coating method. The fixing belt 650 has a structure in which a silicone rubber layer is covered with a PFA resin tube having a thickness of 20 μm, and the PFA resin tube is used as the outermost surface layer.

A polyimide film having a thickness of, for example, 4 μm is formed on the inner surface of the fixing belt 650 in order to improve slidability with respect to the heater 600 . The thickness of the polyimide film is preferably 1 μm or more from the viewpoint of durability, and preferably 20 μm or less from the viewpoint of suppressing deterioration in heat transfer efficiency. In order to ensure slidability between the fixing belt 650 and the film guide 660, the inner surface of the fixing belt 650 is coated with a grease-like heat-resistant fluorine-based lubricant containing fluorine-based fine particles and fluorine-based oil as a heat-resistant lubricant. agent is applied.

The film guide 660 is a support (heater holder) that supports the heater 600 and has a semi-arcuate cross section. The film guide 660 is made of highly heat-resistant liquid crystal polymer resin, and serves to hold the heater 600 and guide the rotation of the fixing belt 650 . The liquid crystal polymer resin forming the film guide 660 is exemplified here by DuPont's Zenite 7755 (trade name).

The film guide 660 is urged in the axial direction of the pressure roller 70 by a pressure mechanism (not shown) with a force of 156.8 N (16 kgf) at one end and a total pressure of 313.6 N (32 kgf). The above total pressure is not limited to 313.6N, and may be any value between 90N and 320N.

The film guide 660 is urged by a pressure mechanism (not shown) to bring the lower surface, which is the heating surface of the heater 600 , into pressure contact with the pressure roller 70 via the fixing belt 650 to form the fixing nip portion N. The film guide 660 presses the lower surface of the heater 600 against the elastic force of the elastic layer 72 against the pressure roller 70 via the fixing belt 650 with a predetermined pressing force.

The reinforcing sheet metal 670 has an inverted U shape and is provided to prevent deformation when the heater unit 60 is pressed by the pressure roller 70 .

A pressure roller 70 as a pressure member can be rotated counterclockwise in FIG. 2 by a drive system (not shown). The pressure roller 70 and the fixing belt 650 form a fixing nip portion N having a predetermined width in which the recording material P can be nipped.

Specifically, the pressure roller 70 has a multi-layer structure in which a metal core 71, an elastic layer 72, and a surface layer 73 are laminated in order.

The core metal 71 is made of stainless steel, and both ends thereof are rotatably supported by bearings between a rear side plate and a front side plate of the apparatus frame of the image forming apparatus 50 (both of which are not shown in FIG. 1).

The elastic layer 72 is made of silicone rubber and has a thickness of about 2.5 mm.

The surface layer 73 is a fluorine-based resin tube such as PFA resin having a thickness of about 50 μm.

The CPU 100 executes image formation sequence control by exchanging signals such as color separation image signals with an external host device (not shown). The CPU 100 acquires temperature information by sampling a signal corresponding to a detected temperature value input from a thermistor 630 (described later) of the heater 600 at predetermined intervals. The CPU 100 determines the details of temperature control of the heater 600 based on the acquired temperature information, and controls energization of the heater 600 by the controller 51 according to the determined details of the temperature control of the heater 600 .

The entrance guide 223 guides and introduces the recording material P bearing the unfixed toner image conveyed from the secondary transfer portion into the fixing nip portion N. As shown in FIG.

In the fixing device 20 having the above configuration, the fixing belt 650 is driven to rotate as the pressure roller 70 is driven to rotate, and the heater 600 is energized. Then, when the temperature of the heater 600 rises to the set temperature and is in a temperature-controlled state, the recording material P bearing the unfixed toner image is guided along the entrance guide 223 to the fixing nip portion N and introduced. be done.

At the fixing nip portion N, the recording material P moves together with the fixing belt 650 while the toner image bearing surface of the recording material P is in close contact with the outer surface of the fixing belt 650 . At this time, heat from the heater 600 is applied to the recording material P via the fixing belt 650, and the unfixed toner image is fused and fixed on the recording material P. FIG.

The recording material P that has passed through the fixing nip portion N is separated from the fixing belt 650 and discharged.

<Structure of heater>
A configuration of the heater 600 of the fixing device 20 according to Embodiment 1 of the present invention will be described in detail with reference to FIGS. 2 and 3. FIG.

The heater 600 includes a substrate 610 , a resistive heating element 620 , an overcoat layer 623 and a thermistor 630 . Note that the thermistor 630 is omitted in FIG.

The substrate 610 is elongated with its longitudinal direction extending in the width direction orthogonal to the conveying direction of the recording material P (the direction orthogonal to the paper surface in FIG. 3), and is made of a material having insulating properties, heat resistance, and low heat capacity. It is The substrate 610 has a plate strip shape and is made of ceramics with a thickness of 1.0 mm.

The resistance heating element 620 is provided on the surface of the substrate 610 so that its longitudinal direction is parallel to the longitudinal direction of the substrate 610 . The resistance heating element 620 is composed of a main resistance heating element 621 and a sub resistance heating element 622 .

The main resistance heating element 621 is configured to have a heat generation distribution in which the temperature is highest at the center in the longitudinal direction, corresponding to small size paper.

The sub-resistance heating element 622 is configured to have a heat generation distribution in which both ends in the longitudinal direction have the highest temperature.

A DLC (diamond-like carbon) film is used for the overcoat layer 623 as the first surface layer. The overcoat layer 623 is formed on the surface of the substrate 610 and serves as a sliding surface and a contact surface of the substrate 610 with the inner surface of the fixing belt 650 and is a surface layer of the heater 600 . The overcoat layer 623 rubs against the fixing belt 650 while being in close contact with the inner surface of the fixing belt 650 with the fluorine-based lubricant applied to the inner surface of the fixing belt 650 interposed therebetween. The details of the configuration of the overcoat layer 623 will be described later.

The thermistor 630 is installed on the back surface of the substrate 610 opposite to the surface on which the heater 600 is provided (the surface opposite to the heating surface), detects the temperature of the heater 600, and responds to the detected temperature value. This signal is output to the CPU 100 via an A/D converter (not shown).

<Structure of overcoat layer>
The configuration of the overcoat layer 623 of the heater 600 of the fixing device 20 according to Embodiment 1 of the present invention will be described in detail with reference to FIGS. 3 and 4. FIG.

FIG. 4 is a ternary phase diagram consisting of sp ² bonds, sp ³ bonds and hydrogen for DLC. There are two types of bonding states between carbon atoms: sp ² bonding and sp ³ bonding. The ratio of sp ³ binding to the sum of sp ² binding and sp ³ binding (sp ³ /(sp ² +sp ³ )) is called the sp ³ ratio.

Here, the ^sp2 bond is mainly the bonding state of graphite and the ^sp3 bond is mainly the bonding state of diamond. In DLC, these two kinds of bonding states exist in an amorphous state. As a method for forming a DLC film (diamond-like carbon film), it is possible to adopt an arc ion plating method, a sputtering method, or a laser ablation method using graphite as a raw material.

The ^sp3 ratio of the DLC film in the overcoat layer 623 should be 40% or more and 90% or less, preferably 60% or more and 80% or less. If the ^sp3 ratio is less than 40%, the ^sp3 bond, which is a high-energy bond, is insufficient, resulting in insufficient wear resistance. On the other hand, if the ^sp3 ratio exceeds 90%, the hardness is too high and the material becomes brittle, resulting in poor durability.

As the DLC, it is also possible to use DLC with a low hydrogen atom content (hereinafter referred to as “hydrogen-free DLC”). For example, ta-C, which is a type of hydrogen-free DLC, can be used as DLC. However, although hydrogen-free DLC has high hardness and is excellent in abrasion resistance, it is brittle and weak against elastic deformation such as bending or elongation. Therefore, depending on the rigidity of the substrate on which the hydrogen-free DLC film is formed, the hydrogen-free DLC film may easily peel off.

Therefore, as a hydrogen-free DLC film, the ratio of the number of hydrogen atoms to the sum of the number of hydrogen atoms (H) and the number of carbon atoms (C) (the number of H atoms/(the number of H atoms + the number of C The number of atoms)) is preferably greater than 0% and 30% or less. In particular, for a hydrogen-free DLC film, (the number of H atoms/(the number of H atoms + the number of C atoms)) is greater than 0% and 10% or less, from the viewpoint of suppression of peeling and durability. preferable.

The film thickness, which is the thickness of the DLC film, is preferably 0.1 μm or more and 10 μm or less. The film thickness of the DLC film is preferably 0.1 μm or more because if it is too thin, the insulating property is lost due to the tunnel effect. Further, by setting the film thickness of the DLC film to 10 μm or less, it is possible to suppress an increase in cost due to the use of the DLC film.

The substrate 610 on which the DLC film is formed is a plate strip-shaped substrate having high heat resistance, high electrical insulation, high rigidity and high thermal conductivity. The substrate 610 is made of ceramics such as alumina (Al ₂ O ₃ ) or aluminum nitride (AlN).

A DLC film having an sp ³ ratio of 40% or more and 90% or less has excellent adhesion to the substrate 610 made of the above ceramics. In particular, the overcoat layer 623 using a hydrogen-free DLC in which (the number of H atoms/(the number of H atoms + the number of C atoms)) is greater than 0% and is 5% or less, the inner surface of the fixing belt 650 can be maintained for a long time. Even if it is slid across the substrate 610, it is difficult to separate from the substrate 610. As shown in FIG.

The reason why the overcoat layer 623 needs to be insulated is to prevent fire or smoke that may occur due to a short circuit between the resistance heating element 620, which is a conductor of the heater 600, and other conductors such as the base material of the fixing belt 650. It is for Therefore, the resistance heating element 620 requires an overcoat layer 623 having a high withstand voltage for insulation protection.

The dielectric strength required for the overcoat layer 623 is 1000 V or higher. Also, the dielectric strength can be obtained by dividing the dielectric strength by the film thickness of the overcoat layer.

From this, for example, when the overcoat layer is made of general heater glass, the dielectric strength is 20 MV / m. cannot be guaranteed.

On the other hand, the dielectric strength of the overcoat layer 623 of the present embodiment is 100 MV/100 MV/100 MV/100 MV/100 MV/100 MV/1000 MV/1000 MV/1000 MV/1000 MV/1000 MV/100 MV/1000 MV/100 MV/1000 MV/100 MV/100 MV/100 MV. m or more is required. Further, when the dielectric strength of the overcoat layer 623 is set to 1000 V or more, the dielectric strength of the overcoat layer 623 is set to 100 MV/m or more by setting the film thickness of the overcoat layer 623 to 0.1 μm or more and 10 μm or less. Become.

Moreover, the thermal conductivity of the overcoat layer 623 is preferably 10 W/(m·K) or more. Thereby, the heat from the resistance heating element 620 can be efficiently supplied to the fixing belt 650 .

<Comparative test of materials used for overcoat layer>
A comparison test of materials used for the overcoat layer 623 of the heater 600 of the fixing device 20 according to Embodiment 1 of the present invention will be described in detail with reference to FIG.

FIG. 5 compares the fixing start-up time required for the surface of the fixing belt 650 to reach the fixable temperature when three materials A, B, and C are used for the overcoat layer 623 . In FIG. 5, FIG. 5(a) shows the fixation start-up time when three materials A, B and C are used for the overcoat layer 623. FIG. FIG. 5(b) shows fixing start-up time, dielectric strength, film thickness and thermal conductivity when three materials A, B and C are used for the overcoat layer 623 .

Material A is a common heater glass blend of 85% glass and 15% alumina. When material A is used, the dielectric strength is about 20 MV/m, and the film thickness of the overcoat layer is required to be 50 μm or more in order to insulate and protect the resistance heating element as described above. The thickness was set to 60 μm. Also, the thermal conductivity of material A is 1.5 W/(m·K).

Material B is a hydrogen-free DLC with an ^sp3 ratio of about 40%. When material B is used, the dielectric strength is 100 MV/m, and the thickness of the overcoat layer is required to be 10 μm or more in order to provide insulation protection for the resistance heating element. bottom. Also, the thermal conductivity of material B is 10 W/(m·K).

Material C is a hydrogen-free DLC with an sp ³ ratio of about 90%, which is extremely close to diamond. When material C is used, the dielectric strength is 2000 MV/m, and the film thickness of the overcoat layer is required to be 0.5 μm or more in order to insulate and protect the resistance heating element. 0.6 μm. Also, the thermal conductivity of material C is 2000 W/(m·K).

For the verification, the comparison of fixing start-up time was performed only by the material difference of the overcoat layer 623 . At this time, the maximum input power was 1200 W, and the rotation speed of the fixing belt 650 was 320 mm/s.

As shown in FIG. 5, the fusing ramp-up time for material A was 7.8 seconds and the fusing ramp-up time for material B was 6.9 seconds. Also, the fixation start-up time of material C was slightly shorter than that of material B and was 6.35 seconds. Here, a hydrogen-free DLC film with a high ^sp3 ratio is brittle and fragile, and a hydrogen-free DLC film with a low ^sp3 ratio has insufficient abrasion resistance. Therefore, the overcoat layer 623 is desirably a hydrogen-free DLC film with an ^sp3 ratio between material B and material C of 60% or more and 80% or less.

In this embodiment, heater 600 includes an overcoat layer 623 that contacts the inner surface of fuser belt 650 . The overcoat layer 623 has a film thickness of 0.1 μm or more and 10 μm or less, a thermal conductivity of 10 W/(m·K) or more, and a withstand voltage of 1000 V or more. As a result, the heat of the resistance heating element 620 can be efficiently transferred to the fixing belt 650 without reducing the strength of the fixing belt 650, and the fixing start-up time can be greatly shortened.

(Embodiment 2)
The configuration of the image forming apparatus according to Embodiment 2 of the present invention is the same as that of FIG. 1, so the description thereof will be omitted. Also, since the configuration of the fixing device according to the present embodiment is the same except that the heater 1600 is used instead of the heater 600, the description thereof will be omitted.

<Structure of heater>
The configuration of heater 1600 of the fixing device according to Embodiment 2 of the present invention will be described in detail with reference to FIG.

In FIG. 6, parts having the same configuration as those in FIG.

The heater 1600 has a configuration in which a resistance heating element 620 and a resistance heating element 1620 are provided on both the front and back surfaces of a substrate 610 . The heater 1600 includes, for example, a resistance heating element 620 and a resistance heating element 1620 having different lengths in the longitudinal direction, so that the resistance heating element 620 and the resistance heating element 620 can be used for various sizes of paper such as small size paper or large size paper. The heating element 1620 is selectively heated. This makes it possible to maintain good fixability.

Specifically, the heater 1600 includes a substrate 610 , a resistive heating element 620 , an overcoat layer 623 , a thermistor 630 , a resistive heating element 1620 and an overcoat layer 1623 .

The resistance heating element 1620 is provided on the back surface of the substrate 610 opposite to the surface on which the resistance heating element 620 is provided so that the longitudinal direction is parallel to the longitudinal direction of the substrate 610 . The resistance heating element 1620 is composed of a main resistance heating element 1621 and a sub resistance heating element 1622 .

The main resistance heating element 1621 is configured to have a heat generation distribution in which the temperature is highest at the center in the longitudinal direction, corresponding to small size paper.

The sub-resistance heating element 1622 is configured to have a heat generation distribution in which both ends in the longitudinal direction have the highest temperature.

A DLC film is used for the overcoat layer 1623 as the second surface layer. The overcoat layer 1623 does not slide or come into contact with the inner surface of the fuser belt 650 of the substrate 610 and is the surface layer of the heater 1600 . The overcoat layer 1623 has a film thickness of 0.1 μm or more and 10 μm or less, a thermal conductivity of 10 W/(m·K) or more, and a withstand voltage of 1000 V or more. Since the configuration of the overcoat layer 1623 is the same as that of the overcoat layer 623, detailed description thereof will be omitted.

In the heater 1600, the reason why the overcoat layer 1623 covers the resistance heating element 1620 on the side of the substrate 610 that does not slide against the fixing belt 650 is to prevent resistance fluctuation due to oxidation of the conductive portion of the resistance heating element 1620 and to provide insulation. This is for ensuring withstand voltage.

Also in the present embodiment, it was confirmed that when the DLC film was used for the overcoat layer 623 and the overcoat layer 1623, the fixation start-up time was shortened compared to the case where the glass coating material was used.

It goes without saying that the present invention is not limited to the above-described embodiments, and can be modified in various ways without departing from the gist of the present invention.

1Bk image forming section 1C image forming section 1M image forming section 1Y image forming section 2 photosensitive drum 3 primary charger 4 developing device 5 transfer roller 7 laser exposure device 8 intermediate transfer belt 9 secondary transfer counter roller 10 tension roller 11 secondary transfer Roller 14 Paper feed roller 16 Registration roller 20 Fixing device 30 Power source 50 Image forming apparatus 51 Control unit 60 Heater unit 70 Pressure roller 600 Heater 610 Substrate 620 Resistance heating element 621 Main resistance heating element 622 Sub resistance heating element 623 Overcoat layer 630 Thermistor 650 Fixing belt 660 Film guide 670 Reinforcing sheet metal 1600 Heater 1620 Resistance heating element 1621 Main resistance heating element 1622 Sub resistance heating element 1623 Overcoat layer

Claims (7)

a rotatable endless fixing belt;
a rotatable pressure member forming a nip portion capable of nipping a recording material between itself and the fixing belt;
a heating member disposed inside the fixing belt to heat the fixing belt;
has
The heating member is
a first surface layer in contact with the inner surface of the fixing belt;
The first surface layer is
The film thickness is 0.1 μm or more and 10 μm or less, the thermal conductivity is 10 W / (m K) or more, and the dielectric strength voltage is 1000 V or more.
A fixing device characterized by: The first surface layer is
Consists of a diamond-like carbon film having a ratio of sp ³ bonds of 40% or more and 90% or less;
The fixing device according to claim 1, characterized by: The first surface layer is
The ratio of the number of hydrogen atoms to the sum of the number of hydrogen atoms and the number of carbon atoms is greater than 0% and 30% or less.
3. The fixing device according to claim 2, wherein: The heating member is
Having a substrate made of ceramics,
The first surface layer is
formed on the surface of the substrate,
The fixing device according to any one of claims 1 to 3, characterized in that The substrate is
is aluminum nitride or alumina,
5. The fixing device according to claim 4, wherein: The heating member is
comprising a second surface layer that does not contact the inner surface of the fixing belt;
The second surface layer is
The film thickness is 0.1 μm or more and 10 μm or less, the thermal conductivity is 10 W / (m K) or more, and the dielectric strength voltage is 1000 V or more.
The fixing device according to any one of claims 1 to 5, characterized in that: a fixing device according to any one of claims 1 to 6;
an image forming means for forming a toner image on a recording material;
An image forming apparatus comprising:

Images