JP2001228731A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain a high-quality image by preventing increase of driving torque of a endless belt with time, and thus securing a stable traveling performance. SOLUTION: The fixing device is equipped with a fixing member 1 disposed rotatably, an endless belt 2 rotatably disposed by pressure to the fixing member 1 which belt clamps a recording medium K carrying an unfixed toner image T at the nip part N formed between the fixing members 1 and endless belts 2, a pressurizing member 3 which is disposed fixedly within the endless belt 2 and pressurizes the endless belt 2 toward the fixing member 1, and a heating source H for heating the nip part N. A porous resin member 4 is provided at a portion of the pressurizing member 3 opposed to the endless belt 2, and a lubricant is held in the porous resin member 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used for fixing an unfixed image by heating and pressing in an image forming apparatus such as a copying machine, a printer, a facsimile, and the like.
In particular, the present invention relates to an improvement of a so-called belt nip type fixing device that allows a recording medium to pass through a nip formed between a fixing member and an endless belt.

[0002]

2. Description of the Related Art Conventionally, as a belt nip type fixing device of this type, for example, a rotatable heating fixing roll having a heating source, an endless belt pressed against the heating fixing roll and rolling together, and an endless belt And a pressure pad that presses the endless belt toward the heat-fixing roll to form a nip between the endless belt and the heat-fixing roll, and passes the sheet through the nip. In this case, an unfixed toner image on the sheet is fixed by heating and pressing (see JP-A-8-262903).

[0003]

However, in such a belt nip type fixing device, if the coefficient of friction between the endless belt and the pressure pad is large, the torque for driving the endless belt increases, and the endless belt is driven. Since the stress acting on the heat-fixing roll for driving the belt, that is, the driving torque, also increases, the stress acting on the gear receiving portion of the thin heat-fixing roll core increases, causing a technical problem that the gear and the core may be damaged. Was seen. In addition, in such an embodiment, the load on the drive motor also increases as a matter of course, and more power is required. Further, if the frictional force between the endless belt and the pressure pad becomes not negligible compared to the driving force of the endless belt by the heat fixing roll, slip occurs between the heat fixing roll and the endless belt. When the sheet holding the unfixed toner image is passed through the nip under the conditions, there is also a technical problem that the slip causes an image shift in the unfixed toner image on the sheet.

Therefore, in order to solve such a problem,
JP-A-10-213984 discloses a glass fiber sheet in which modified silicone oil is interposed as a lubricant between a pressure pad and an endless belt, and the surface of the pressure pad is impregnated with polytetrafluoroethylene. There is proposed a technique for improving the slip of the endless belt by covering the endless belt. Also, JP-A-11-219
No. 052 discloses a lubricant supply member for supplying a lubricant to an inner peripheral surface of an endless belt, and a lubricant is supplied to a nip portion through the endless belt to improve the slip of the endless belt. Technology has also been proposed.

[0005] However, when these techniques are employed, although the torque for driving the endless belt can be initially reduced, the torque for driving the endless belt increases with the passage of time. There was a technical problem that a serious problem would occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and is intended to prevent a drive torque of an endless belt from increasing with time and secure a stable running performance to achieve high quality. To provide a fixing device capable of stably obtaining the above image.

[0007]

That is, according to the present invention, as shown in FIG. 1, a fixing member 1 rotatably disposed,
An unfixed toner image T is placed in a nip N formed rotatably in contact with the fixing member 1 and formed between the fixing member 1 and the fixing member 1.
Endless belt 2 on which a recording medium K carrying a sheet is sandwiched
A pressure member 3 fixedly disposed inside the endless belt 2 and pressing the endless belt 2 toward the fixing member 1 side; and a heating source H for heating the nip portion N.
And a porous resin member 4 is provided at a portion of the pressure member 3 facing the endless belt 2, and a lubricant is held in the porous resin member 4.

In such technical means, if the fixing member 1 is rotatably provided, the fixing member 1 has a roll shape.
A belt or the like may be selected as appropriate. Further, the endless belt 2 may be supported in a non-stretched state as shown in FIG. 1, or may be supported in a stretched state by, for example, hanging over a plurality of rolls. .

Further, the pressing member 3 may be appropriately selected as long as it is fixedly disposed and presses the endless belt 2 toward the fixing member 1, but it is possible to prevent deterioration due to heat during fixing. From the viewpoint of performing the heat treatment, it is preferable that the heat treatment device be constructed of a material having heat resistance.

Further, if the heating source H is for heating the nip portion N, for example, as shown in FIG.
Heating the nip portion N via the fixing member 1, as well as heating the endless belt 2 and the pressing member 3, as in the type in which the fixing member 1 is heated externally, such as the type in which the fixing member 1 is heated externally. For example, a material for heating the nip N may be appropriately selected.

The porous resin member 4 is made of a resin having a large number of pores. For example, the porous resin member 4 is formed by foaming a resin to make it porous, or by stretching the resin uniaxially or biaxially. Porous materials and the like can be mentioned. here,
In an embodiment employing a porous resin member which is made porous by stretching the resin uniaxially or biaxially, for example, a fiber woven with the porous resin (a porous resin fiber woven fabric)
Alternatively, it is preferable to laminate the porous resin fiber woven fabric and the porous resin film (porous resin film). The material may be appropriately selected from polyethylene resin, fluororesin, etc., but in consideration of heat resistance, release property, durability, sliding resistance, etc., a porous tetrafluoroethylene resin is used. It is preferable to use (tetrafluoroethylene porous resin).

Further, in the present invention, it is necessary to hold the lubricant in the porous resin member 4. However, in this method, the porous resin member 4 may be impregnated with the lubricant in advance. Further, a lubricant may be supplied to the porous resin member 4 from the outside. Here, in the latter aspect, from the viewpoint of simply and stably supplying the lubricant, it is preferable to provide a lubricant supply means 5 for supplying the lubricant to the inner peripheral surface of the endless belt 2. .

The lubricant may be appropriately selected from oil, grease and the like, but it is preferable to use oil from the viewpoint of improving lubricity. When oil is used as the lubricant, the type thereof may be appropriately selected from silicone oil, fluorine oil and the like, but it is preferable to use silicone oil in consideration of safety. Further, in an embodiment in which silicone oil is used as a lubricant, the viscosity is preferably 50 to 3000 cs at room temperature. Here, the lower limit is determined from the viewpoint of preventing unnecessary evaporation of the silicone oil, while the upper limit is set to prevent the silicone oil from increasing the sliding resistance. It is determined based on the viewpoint of prevention.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a schematic configuration of a fixing device according to a first embodiment of the present invention. In FIG. 1, the fixing device according to the present embodiment includes a heat fixing roll 10 as a fixing member, an endless belt 20 having a thin film shape, and a pressing pad 30 as a pressing member. Here, the endless belt 20 is pressed against the heating / fixing roll 10 by a pressing pad 30 arranged inside the belt, and the unfixed toner image T is carried between the heating / fixing roll 10 and the endless belt 20. A nip portion N through which a recording sheet S as a recording medium can pass is formed.

In the present embodiment, the heat fixing roll 1
Numeral 0 has a cylindrical core 11, an elastic layer 12 and a release layer 13 formed on the surface thereof, and a heating source 14 is provided inside the core 11.

The material of the core 11 is not particularly limited as long as it is a material having excellent mechanical strength and good thermal conductivity. Examples of the material include metals such as aluminum, SUS, iron, copper, and brass. Alloys and the like.

The material of the elastic layer 12 can be appropriately selected from known materials for the elastic layer 12, and for example, silicone rubber, fluorine rubber or the like can be used. The method for forming the elastic layer 12 on the surface of the core 11 is not particularly limited. For example, an injection molding method or a coating method known per se can be adopted.

Further, the release layer 13 is provided to suitably prevent the offset of the unfixed toner image T and to operate the fixing device in a stable state. There is no particular limitation as long as it has an appropriate release property with respect to the toner, for example,
Fluorine rubber, silicone rubber, fluorine resin and the like are used.

Further, the heating source 14 is not particularly limited as long as it has a shape and a structure that can be accommodated inside the core 11, and can be appropriately selected according to the purpose. Can be used. Heat fixing roll 1 heated by the heating source 14
The surface temperature of 0 can be measured, for example, by a temperature-sensitive element 15 arranged in contact with the surface of the heat-fixing roll 10, and the temperature can be controlled to be constant by a control unit. The temperature sensing element 15 is not particularly limited, and for example, a thermistor, a temperature sensor, or the like is used. The control means is not particularly limited, and for example, a temperature controller, a computer, or the like is used. Note that reference numeral 1
Reference numeral 6 denotes a motor that drives the heat fixing roll 10 to rotate.

The shape and size of the endless belt 20 are not particularly limited, and can be appropriately selected from those known per se according to the purpose. The structure of the endless belt 20 may be a single-layer structure, but in this embodiment, as shown in FIG. 2, a resin film 22 as a release layer is formed on the surface of a substrate 21. Is used. Here, as a material of the base material 21 of the endless belt 20,
For example, polymers such as thermosetting polyimide, thermoplastic polyimide, polyamide, and polyamideimide, and metals such as stainless steel, nickel, and copper are used. The resin film 22 preferably has good releasability of toner adhering to the surface. Examples of the material include PTFE (polytetrafluoroethylene) and PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer). And a fluororesin such as FEP (tetrafluoroethylene-hexafluoropropylene copolymer).

Further, the pressing pad 30 includes a support 31 having a substantially concave cross section and an elastic body 32 disposed on the support 31.
And a low friction sheet 33 fixedly disposed to cover the support 31 and the elastic body 32 facing the endless belt 20.
And a belt travel guide 34 provided so that the endless belt 20 rotates smoothly.

At both ends of the belt running guide 34, flange-shaped members (not shown) for restricting the endless belt 20 from shifting are provided. The support 31 has a function of fixing the elastic body 32. The support 31 is fixed to the endless belt 2 by a compression coil spring (not shown).
The fixing roller 10 is pressed through the heat fixing roll 10.

The shape, structure, size, and the like of the pressing pad 30 are not particularly limited and can be appropriately selected depending on the purpose. It may be a structure composed of a plurality of members having different functions as in the embodiment.

As a material of the elastic body 32, for example,
Silicone rubber, fluorine rubber, or the like can be used. Here, when silicone rubber is used, if silicone oil is used as a lubricant, the silicone rubber swells. In order to prevent the swelling, it is preferable to provide a fluororesin or fluorine rubber coating layer on the surface.

In this embodiment, the low friction sheet 33 is made of a porous resin obtained by extending a PTFE (polytetrafluoroethylene) resin in a biaxial direction to make it porous. As its shape, film shape,
The shape of the woven fabric, the shape of the film / woven fabric lamination, etc. may be appropriately selected. In the present embodiment, as shown in FIG. 3, a film layer 33a and a woven fabric layer 33b are used. The film layer 33a is disposed so as to face the endless belt 20. This is because this configuration is most excellent in durability and sliding resistance.

The belt travel guide 34 is provided with an oil supply section 40 as a lubricant supply means for supplying silicone oil as a lubricant to the inner surface of the endless belt 20. The oil supply unit 40 is provided with a felt 41 that is disposed in contact with the inner surface of the endless belt 20.
And a case 42 for holding the felt 41. The felt 41 is impregnated with silicone oil having a viscosity of 50 to 3000 cs. Further, the felt 41 abuts on almost the entire area of the endless belt 20 in the axial direction, and supplies the silicone oil to the entire inner peripheral surface of the endless belt 20 as the endless belt 20 rotates. The supply amount of the silicone oil does not need to be large, and therefore, the contact pressure of the felt 41 against the endless belt 20 is small, and it is sufficient that the contact pressure is small.
The felt 41 to be impregnated with the silicone oil may be a sponge or the like as long as it has a large number of continuous pores, has heat resistance at a fixing temperature and an appropriate elastic modulus.

Next, the operation of the fixing device according to the present embodiment will be described. In FIG. 2, when the motor 16 is driven to rotate, the heat fixing roll 10 rotates, and the endless belt 20 also rotates following the rotation of the heat fixing roll 10. At this time, if there is a recording sheet S holding the unfixed toner image T at the entrance of the nip portion N formed between the heat fixing roll 10 and the endless belt 20, the recording sheet S is moved to the nip portion N. It is taken in and passes through the nip N. In the nip portion N, the recording sheet S is pressed by the heat fixing roll 10 and the endless belt 20 pressed toward the heat fixing roll 10 by the pressing pad 30, and the recording sheet S is pressed by the heat fixing roll 10. Heated. As a result, the unfixed toner image T on the recording sheet S is heated and pressed and fixed on the recording sheet S.

When the endless belt 20 is rotating, the inner peripheral surface of the endless belt 20 is coated with silicone oil by a felt 41. Then, with the rotation of the endless belt 20, the applied silicone oil reaches the nip portion N, that is, the portion of the pressing pad 30 that contacts the inner peripheral surface of the endless belt 20 facing the low friction sheet 33. Here, in the present embodiment, since the low-friction sheet 33 is made of a porous resin, the silicone oil is retained inside the porous resin and oozes out from the surface, and as a result, it is always The coefficient of friction between the endless belt 20 and the pressing pad 30 (the low friction sheet 33) is stably held low. Therefore, it is possible to effectively avoid a situation where the driving torque of the endless belt 20 increases with time. In addition, since there is no problem such as slippage between the rotation of the heat fixing roll 10 and the rotation of the endless belt 20, smooth rotation driving is maintained.
Heat and pressure fixing of a smooth image can be repeatedly performed over a long period of time.

Embodiment 2 This embodiment is substantially the same as Embodiment 1, but instead of removing the oil supply section 40, a low friction sheet 33 pre-impregnated with silicone oil is used. Things. Note that among the components of the fixing device according to the present embodiment, the same components as those of the fixing device according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof will be given here. Omitted.

Also in this embodiment, the low friction sheet 3
3 is made of a porous resin, a predetermined amount of silicone oil can be held in the low friction sheet 33. As a result, the gap between the endless belt 20 and the pressing pad 30 (low friction sheet 33) is always maintained. Is stably held low. Therefore, Embodiment 1
The same effect as described above can be obtained.

[0031]

Example ◎ Example 1 In the fixing device described in Embodiment 1 (see FIG. 2), the heat fixing roll 10 has an outer diameter of 24 mm and a thickness of 0.5 m.
m, silicone rubber (rubber hardness 33) as an elastic layer 12 on the outer surface of a cylindrical iron core 11 having a length of 310 mm.
Degree: JIS-A) is coated to a thickness of 500 μm, and PFA having a thickness of 30 μm is formed as a release layer 13 on the surface of the elastic layer 12.
The tube is covered. Inside the core 11, a 960 W (normally 600 W) halogen lamp is provided as a heating source 14, and the surface temperature of the heat fixing roll 10 is adjusted so that the surface of the heat fixing roll 10 is in contact with the surface of the heat fixing roll 10. The temperature is controlled to about 175 ° C. by a temperature sensor of the temperature element 15 and a temperature controller (not shown).

The endless belt 20 has a circumference of 94 mm,
A thermosetting polyimide having a thickness of 75 μm and a length of 330 mm was used as a substrate 21, and a perfluoroalkoxy fluororesin (PFA) was coated on the outer peripheral surface of the substrate 21 to a thickness of 30 μm to form a resin film 22. The elastic body 32 is a silicone rubber having a width of 10 mm, a thickness of 5 mm, and a length of 320 mm, and the low friction sheet 33 disposed on the surface thereof is
It is obtained by laminating a PTFE (polytetrafluoroethylene) porous resin fiber woven fabric and a PTFE porous resin film. Further, the heat fixing roll 10 is pressed with a load of 30 kg by a compression coil spring (not shown) via a thin-film endless belt 20.

The winding angle of the endless belt 20 around the heat fixing roll 10 was about 40 °, and the width of the nip N at this time was about 10 mm. The driving force from the motor 16 is transmitted to the heat fixing roll 10, and the heat fixing roll 10 and the endless belt 20
Rotated at ec speed.

The felt 41 of the oil supply unit 40
Is a felt having a width of 10 mm, a thickness of 5 mm, and a length of 300 mm impregnated with about 5 cm ³ of dimethyl silicone oil (viscosity at room temperature: 100 cs) as a lubricant.
Further, the surface of the pressing pad 30, that is, the low friction sheet 33
Also holds dimethyl silicone oil.

Using the above-described fixing device, the heat fixing roll 10 and the endless belt 20 were continuously driven by the motor 16 and the motor load torque was measured. Then, a motor load torque required to separate the endless belt 20 from the heat fixing roll 10 and drive only the heat fixing roll 10 was subtracted from the motor load torque at this time to calculate a motor load torque difference. FIG. 4 (see ●) shows the relationship between the drive time and the motor load torque difference. According to this, 0.0
Since the difference of about 13 N · m is still 0.011 N · m even after operating for 55 hours, it is understood that the motor load torque is substantially constant regardless of the lapse of time. You.

Embodiment 2 Instead of removing the felt 41 which has been brought into contact with the inner surface of the endless belt 20 in FIG. 2, instead of removing the fixing device described in Embodiment 2, dimethyl silicone oil (viscosity at room temperature: 100 cs) is used in advance. Impregnated low friction sheet 33 (PTFE porous resin fiber woven fabric and PTFE
An evaluation experiment similar to that in Example 1 was performed using a fixing device using (for a sheet bonded to a porous resin film). The relationship between the drive time and the motor load torque difference is shown in FIG. According to this, initially 0.00
The difference, which was about 8 N · m, became 0.0 after 50 hours.
It is understood that the motor load torque gradually increases with time, that is, 12 N · m. However, this can be said to be a significant improvement over the comparative example described below.

Comparative Example In the fixing device described in Example 1, the low friction sheet 33 was changed to a conventionally used glass fiber sheet impregnated with PTFE, and the same evaluation as in Examples 1 and 2 was performed. An experiment was performed. The relationship between the drive time and the motor load torque difference is shown in FIG. According to this, it was found that the difference, which was about 0.011 Nm at the initial stage, increased to 0.023 Nm after only 24 hours. This can be attributed to the fact that the drive torque increased with the depletion of the silicone oil.

As described above, the advantage of using a porous resin as the low friction sheet 33 is understood.

[0039]

As described above, according to the present invention,
A porous resin member is provided at the portion of the pressure member facing the endless belt, and the lubricant is retained inside the porous resin member, so that the lubricant can ooze out of the porous resin member for a long period of time. As a result, it is possible to prevent the drive torque of the endless belt from increasing with time, secure stable running performance, and stably obtain high-quality images.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of a fixing device according to the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of a fixing device according to the first embodiment.

FIG. 3 is a sectional view of a low friction sheet.

FIG. 4 is a graph illustrating a relationship between a driving time of a fixing roll and a motor load torque difference.

[Explanation of symbols]

1 ... fixing member, 2 ... endless belt, 3 ... pressing member,
4 porous resin member, 5 lubricant supply means, H heating source, K recording medium, T unfixed toner image, 10 heating fixing roll, 14 heating source, 20 endless belt, 3
0: press pad, 33: low friction sheet, 33a: film layer, 33b: woven cloth layer, 40: oil supply unit, S: recording sheet

Claims (7)

[Claims] A fixing member rotatably disposed; and a recording medium rotatably pressed against the fixing member and carrying an unfixed toner image in a nip formed between the fixing member and the fixing member. An endless belt to be clamped, a pressure member fixedly disposed inside the endless belt and pressing the endless belt toward the fixing member side; and a heating source for heating the nip portion. A fixing device, wherein a porous resin member is provided at a portion of the pressure member facing the endless belt, and a lubricant is held in the porous resin member. 2. The fixing device according to claim 1, wherein the porous resin member is made of a porous resin fiber woven fabric. 3. The fixing device according to claim 1, wherein the porous resin member is formed by laminating a porous resin fiber woven fabric and a porous resin film. 4. The fixing device according to claim 1, wherein said porous resin member is made of a tetrafluoroethylene porous resin. 5. The fixing device according to claim 1, further comprising a lubricant supply unit that supplies a lubricant to an inner peripheral surface of the endless belt. 6. The fixing device according to claim 1, wherein the lubricant is silicone oil. 7. The fixing device according to claim 6, wherein the viscosity of the silicone oil is 50 to 3000 c at room temperature.
s, a fixing device.