JP3276580B2 - Fixing device - Google Patents

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 in an electrophotographic apparatus utilizing an electrophotographic process such as a copying machine, a facsimile, a printer, etc., and more particularly, to a fixing device used in an electrophotographic apparatus capable of performing full-color printing. It is about.

[0002]

2. Description of the Related Art Conventionally, a fixing device used in an electrophotographic apparatus utilizing an electrophotographic process, such as a copying machine, a facsimile, a printer, etc., as shown in FIG.
The image forming apparatus includes a fixing roller 101 and a pressure roller 102 that presses the fixing roller 101. The fixing roller 10
A heater lamp 103 as a heating source is disposed inside the unit 1 so that the surface of the fixing roller 101 is heated from the inside.

In the fixing device having the above-described structure, an image formed of unfixed toner T is carried on a pressure contact portion (fixing portion) between the fixing roller 101 and the pressure roller 102 whose surfaces are heated to a predetermined temperature. By loading paper (recording material) P,
The toner T is melted by heat and the toner T is fixed on the paper P. In this way, a device in which a heating source such as a heater lamp 103 is provided inside the fixing roller 101 to heat the surface of the fixing roller 101 is referred to as an internal heating type fixing device.

If the toner carried on the paper P is a toner such as a color toner having poor releasability, the toner adheres to the surface of the fixing roller 101 during fixing, that is, a so-called offset phenomenon occurs. For this reason, the fixing device is provided with an oil application mechanism 105 for applying oil to the surface of the fixing roller 101 and a peeling claw 106 for peeling the sheet P after fixing from the fixing roller 101. The oil application mechanism 105 is provided with an oil 10 for preventing offset.
4 is applied to the surface of the fixing roller 101 via a pair of application rollers 107.

Some fixing devices do not require the offset oil. For example, JP
As disclosed in JP-A-3-313182, JP-A-4-358186, and JP-A-5-2349, unfixed toner is transferred via a thin endless film (endless belt) that moves in synchronization with paper. A method of fixing the toner by heating a sheet carrying an image (hereinafter, referred to as a method)
(Referred to as a film heating method).

In this film heating type fixing device, as shown in FIG. 13, for example, an unfixed portion is formed on a pressure contact portion between an endless film-shaped fixing belt 201 stretched in a recording material conveying direction and a pressing roller 203. By carrying in a sheet P carrying an image formed by the toner T, the image formed by the unfixed toner T is fixed on the sheet P.

The pressure roller 203 of the fixing belt 201
A heating element 202 is disposed on the inner side of the side, and heats a fixing unit formed between the fixing belt 201 and the pressure roller 203. Therefore, the sheet P passing through the fixing unit is heated by the heat energy from the heating element 202, and the toner carried on the sheet P is melted and fixed.

In the above-described fixing device, the sheet P on which toner has been fixed is cooled downstream of the fixing belt 201 (hereinafter, referred to as self-cooling) to separate the fixing belt 201 from the sheet P. I have. Therefore, in the fixing device of the film heating type, since the self-cooling is performed on the downstream side of the fixing belt 201, the toner does not adhere to the fixing belt 201. Thus, it is not necessary to apply oil for preventing offset.

In other words, according to the above-described film heating method, a fixing belt 201 having a small heat capacity can be used, and cooling by heat radiation is performed immediately after passing through the heating section. And the adhesive force with the fixing belt 201 is relatively weakened, so that it is possible in principle to prevent offset.

[0010]

However, the above-mentioned conventional fixing devices of the respective heating systems have the following problems.

(I) Problems of the fixing device of the internal heating type: Since there is a heat source inside and the heat transfer of the rubber layer is poor, the warm-up time is long, and the fixing roller core material 101a
The boundary temperature between the rubber layer 101b and the rubber layer 101b rises.
There is a problem that b is likely to be peeled off due to deterioration.

In particular, in the case of a fixing device utilizing a full-color electrophotographic process, the fixing temperature is increased, and a large amount of heat energy is supplied to the multi-layered color toner.
It is necessary to color the toner in a high melting state. As described above, when the toner is separated from the fixing roller 101 in a high molten state, the cohesive force inside the toner is lower than the adhesive force between the fixing roller 101 and the toner. I do.

Accordingly, in order to make the adhesive force between the fixing roller 101 and the toner lower than the internal cohesive force, as described above, the oil 104 for preventing offset is applied to the fixing roller 10.
1 needs to be applied to the surface.

However, when the offset preventing oil 104 is applied to the surface of the fixing roller 101, the following problems occur.

The oil 104 is uniformly spread on the fixing roller 10.
A complicated mechanism is required to apply the coating to a single coating, resulting in an increase in the cost of the apparatus.

The fixing roller 101 is fixed by the oil 104.
The rubber layer 101b deteriorates and swells, and the life of the fixing roller 101 is shortened.

The oil 104 spills, fouling the device and adversely affecting other equipment.

The oil 104 adheres to the paper P and stains the user's hands or gives discomfort.

When OHP is used for the paper P, the oil 104 adheres to the surface of the OHP, thereby reducing the transmittance of the OHP.

[0020] Periodic maintenance such as reinforcement of the oil 104 is required, which is not user-friendly.

(II) Film-heating type fixing device: The film-heating type fixing device has an advantage that it is not necessary to apply oil to prevent offset. Another advantage is that the warm-up time can be reduced because the heat capacity of the film used as the fixing means is smaller than that of the fixing roller.

However, as shown in FIG. 13, since the fixing belt 201 is in the form of an endless belt, the control of the tension applied to the fixing belt 201 and the fixing belt 2
Since a mechanism for preventing meandering of the fixing belt 201 and for preventing wrinkles due to thermal expansion of the fixing belt 201 is required, the driving mechanism of the fixing belt 201 becomes very complicated, which causes a problem of increasing the cost of the apparatus.

Further, since the fixing belt 201 is made thinner in order to reduce the heat capacity, its life is shorter than that of a roller-shaped fixing roller. In particular, since the fixing belt 201 slides on the heating element 202, it is worn and its life is shortened. In addition, when the rotation speed of the fixing belt 201 is increased in order to improve the printing speed, the life of the fixing belt 201 is further shortened. For this reason, there arises a problem that it cannot be adapted to an electrophotographic device having a high printing speed.

The above problems can be solved to some extent by increasing the thickness of the fixing belt 201. However, by increasing the thickness of the fixing belt 201, the heat capacity of the fixing belt 201 increases. As a result, the warm-up time is lengthened, and the advantage of shortening the warm-up time of the film heating type fixing device is reduced.

If the heat capacity of the fixing belt 201 is large, the toner on the sheet after fixing cannot be cooled sufficiently until it becomes a solid state, which may cause an offset phenomenon. For this reason, in order to prevent the offset phenomenon, a forced cooling unit such as a blowing unit is required on the downstream side in the moving direction of the fixing belt 201 in order to sufficiently cool the toner on the sheet after fixing to a solid state. Becomes in this case,
A problem arises in that thermal efficiency is deteriorated, and the device becomes complicated and large.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object a short warm-up time, excellent thermal efficiency and excellent temperature uniformity, and fixation of a color toner without applying oil. It is an object of the present invention to provide a fixing device which can perform high-speed printing, is excellent in durability and safety, has a simple structure, and is inexpensive to manufacture.

[0027]

According to a first aspect of the present invention, there is provided a fixing device comprising:
In order to solve the above-mentioned problem, a fixing roller having a surface heated from the outside and a plurality of pressure rollers arranged in parallel with the fixing roller are stretched and pressurized to press an outer peripheral surface of the fixing roller. A fixing device that includes a belt and conveys a recording material on which an unfixed toner image is formed to a pressure contact portion formed by the fixing roller and the pressure belt to thermally fuse the toner to the recording material and fix the toner. In the pressure contact portion, from the upstream side in the conveying direction of the recording material, a heat storage region set at a temperature equal to or higher than the softening point of the toner, and a heat radiation set at a temperature required for cooling and solidifying the melted toner. The regions are sequentially formed.

According to the above configuration, in the pressure contact portion formed by the fixing roller and the pressure belt, first, the toner on the recording material in the heat storage region is brought into a high-temperature and molten state sufficient to develop a color. Then, the toner melted in the heat radiation area is cooled and solidified. At this time, in the heat radiation area of the press contact portion,
Since the toner is cooled until it is cooled and solidified, the cohesive force at this time becomes larger than the adhesive force between the toner and the fixing roller, and the toner is completely fixed on the recording material.

Thus, it is not necessary to apply an oil for preventing offset to the fixing roller in order to prevent offset after fixing, so that various problems caused by the oil for preventing offset can be solved. In particular, since a mechanism for applying the oil for preventing offset is not required, the apparatus can be simplified, and an image forming apparatus such as a printer including the fixing device can be provided at low cost.

According to a second aspect of the present invention, in order to solve the above-mentioned problems, in addition to the configuration of the first aspect, the pressing belt further comprises:
It is formed of a material having thermal conductivity, and at least one of the plurality of pressure rollers is disposed in contact with the fixing roller via the pressure belt in the heat storage area. Features.

According to the above configuration, since the pressure belt is formed of a material having thermal conductivity, heat energy from the fixing roller is easily transmitted. Moreover, at least one of the plurality of pressure rollers is disposed in contact with the heat storage region via the pressure belt in the heat storage region, so that the pressure roller receives the heat from the fixing roller in the heat storage region of the pressure unit. Thermal energy is supplied to the pressure roller in contact with the fixing roller via the pressure belt.

As a result, thermal energy accumulates in the pressure roller that is in contact with the fixing roller via the pressure belt, so that the toner on the recording material conveyed into the heat storage area loses thermal energy from the fixing roller. Then, thermal energy from the pressure roller flows. For this reason, the heat storage region is in a high-temperature melting state, and can efficiently supply thermal energy to the toner on the recording material.

According to a third aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the second aspect, the pressure roller, which is disposed in contact with the fixing roller via a pressure belt, is a heat storage material. It is characterized by consisting of.

According to the above construction, in addition to the function of the second aspect, the heat energy flowing from the fixing roller is easily accumulated in the pressure roller which is arranged in contact with the fixing roller via the pressure belt. In the heat storage region of the fixing section, the high temperature state can be maintained with little heat energy. This reduces the energy required to heat the fixing roller, so that an economical fixing device can be provided.

According to a fourth aspect of the present invention, there is provided a fixing device which solves the above problems.
Fixing roller whose surface is heated from the outside ,
A plurality of pressure rollers arranged in parallel with the fixing roller
Pressurizing belt for pressing the outer peripheral surface of the fixing roller.
And a belt formed by the fixing roller and the pressure belt.
Transport the recording material on which the unfixed toner image is formed
The toner is thermally fused to the recording material by
In the fixing device, a recording material is conveyed to the pressing portion.
From the upstream side in the direction
Heat storage area and the temperature to cool and solidify the melted toner.
The set heat radiation area is formed in order, and
The belt is formed of a thermally conductive material,
At least one pressure roller among the plurality of pressure rollers
Roller in the heat storage area via the pressure belt.
Roller, and a pressure bell
The pressure roller that is in contact with the
The conveyance timing of the recording material to the press contact
The pressure roller made of the heat storage material generates heat from the fixing roller.
Characterized by being set after heat is stored by
I have.

According to the above configuration, the recording material is carried to the pressure contact portion.
Before being sent, it can be fully heated
Therefore, the unfixed toner on the recording material is
Can be reliably melted. As a result, the toner
If the color is color, there is no poor color development due to insufficient temperature
To provide high-quality color images.
Wear.

According to a fifth aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the second , third or fourth aspect , the pressure roller existing in the heat radiation area is made of a heat insulating material. It is characterized by.

According to the above arrangement, since the heat energy flowing from the pressure belt is not accumulated in the pressure roller in the heat radiation area, the molten toner on the recording material can be cooled and solidified effectively.

According to a sixth aspect of the present invention, in order to solve the above-mentioned problem, in addition to any one of the first to fifth aspects, the surface of the fixing roller is provided upstream of the pressure contact portion in the recording material conveying direction. A heating roller for heating from the outside is provided.

According to the above arrangement, the fixing roller is heated by the heating roller provided on the upstream side of the pressure contact portion in the recording material conveyance direction, so that the fixing roller is heated from the recording material inlet side of the pressure contact portion. become. This makes it possible to minimize the loss of heat energy supplied from the heating roller to the fixing roller between the heating roller and the pressure contact portion. Therefore, the fixing roller can be heated to a temperature required for melting the toner with a small amount of energy, so that the energy required for the fixing device can be reduced.

According to a seventh aspect of the present invention, in order to solve the above-mentioned problem, in addition to any one of the first to sixth aspects, the pressure belt has a large number of ventilation holes. Features.

According to the above-described structure, by forming a large number of ventilation holes in the pressure belt, high-temperature air that has settled in the heat-dissipating region of the pressure-contact portion is positively discharged to the outside of the belt, thereby increasing the convective heat transfer coefficient. As a result, the heat radiation performance of the pressure belt can be improved and stabilized, and the cooling effect of the toner can be enhanced. Thus, the heat radiation effect in the heat radiation area of the press contact portion can be enhanced, so that the toner melted in the heat storage area can be reliably cooled and solidified in this heat radiation area. As a result, the toner can be completely fixed on the recording material, so that the offset can be surely eliminated.

Note that, in addition to any one of the above-described configurations, the pressure belt can be configured to be made of metal .

According to the above configuration, since the pressure belt is made of metal, a belt having excellent heat conductivity, a small heat capacity, and a high radiation cooling effect can be obtained. This allows
The heat energy from the fixing roller in the heat storage area can be efficiently transmitted to the pressing roller that is in contact with the fixing roller via the pressing belt. Further, heat energy from the fixing roller in the heat radiation area can be efficiently released to the outside of the pressure belt. Therefore, a stable temperature change can be given to the toner at the pressure contact portion between the fixing roller and the pressure belt, so that stable fixing without offset can be performed.

According to an eighth aspect of the present invention, in order to solve the above-mentioned problem, in addition to any one of the first to seventh aspects, the fixing roller is characterized in that a central portion has a hollow structure. .

According to the above configuration, since the central portion of the fixing roller is hollow, heat energy from the surface of the fixing roller is not accumulated inside the fixing roller. Can be eliminated.
Thereby, the cooling effect of the toner in the heat radiation area of the press contact portion can be enhanced.

According to a ninth aspect of the present invention, in order to solve the above-mentioned problems, in addition to any one of the first to eighth aspects, the vicinity of a recording material outlet of a pressure contact portion of the pressure belt with the fixing roller is provided. It is characterized in that cooling means for cooling is provided.

According to the above configuration, since the cooling means for cooling the vicinity of the recording material outlet at the pressure contact portion of the pressure belt is provided, the pressure belt can be forcibly cooled.
As a result, the convective heat transfer coefficient of the pressure belt can be increased, the heat radiation performance of the pressure belt can be improved and stabilized, and the cooling effect of the toner in the heat radiation area can be enhanced.

According to a tenth aspect of the present invention, there is provided a fixing device which solves the above problem.
Fixing roller whose surface is externally heated
And a plurality of pressure rollers arranged in parallel with the fixing roller
And presses the outer peripheral surface of the fixing roller.
And a pressure belt.
Recording material on which an unfixed toner image is formed
The toner is thermally fused to the recording material by transporting
Fixing device odor to wear Te, the above-mentioned press-contact portion, of the recording medium
Set the temperature above the softening point of the toner from the upstream side in the transport direction
Heat storage area and temperature for cooling and solidifying the melted toner.
The heat radiation area set at each time is formed in order,
Near the exit of the recording material at the pressure contact portion of the pressure belt with the fixing roller
Cooling means for cooling the side is provided, and
Temperature detection that detects the temperature of the pressure belt near the exit of the recording material
Means, based on the detection information of the temperature detecting means,
Cooling control means for controlling the cooling capacity of the cooling means is provided.
It is characterized by having been.

According to the above configuration, the cooling capacity of the cooling means
Is the nearest pressure bell where the pressure belt separates from the fixing roller
Control based on the temperature of the
The temperature in the region can be kept constant. This
To stabilize the cooling effect of the toner in the heat radiation area.
be able to.

According to an eleventh aspect of the present invention, in order to solve the above problem, in addition to the configuration of the ninth or tenth aspect, the cooling means is provided in a region surrounded by the pressure belt and the pressure roller. It is characterized by being.

[0052] According to the arrangement, according to claim 9 or 10
In addition to the above-mentioned operation, the cooling means can forcibly discharge high-temperature air that has settled in the area surrounded by the pressure belt and the pressure roller, so that the cooling effect of the pressure belt can be further enhanced.

[0053]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] The following will describe an embodiment of the present invention with reference to FIGS. 1 to 5 and FIG. In this embodiment, a case where the fixing device is applied to a monochrome laser printer as an electrophotographic device will be described.

As shown in FIG. 2, the laser printer according to the present embodiment has a paper feed unit 10, an image forming device 20, a laser scanning unit 30, and a fixing device 50.

The laser printer having the above-described configuration is provided with
To transport the paper P to the image forming apparatus 20. The image forming apparatus 20 forms a toner image based on the laser beam 34 from the laser scanning unit 30, and transfers the toner image to a sheet P as a conveyed recording material.
Then, the sheet P on which the toner image has been transferred is fixed to the fixing device 50.
To fix the toner image on the paper P. Finally, the sheet P on which the toner image has been fixed is discharged to the outside of the apparatus by sheet discharge rollers 41 and 42 provided downstream of the fixing device 50 in the sheet conveyance. That is, the sheet P is fed along the path indicated by the arrow E in FIG.
0, and are conveyed in the order of the fixing device 50, and are discharged outside the device.

The paper supply section 10 includes a paper supply tray 11, a paper supply roller 12, a paper separation friction plate 13, a pressure spring 14, a paper detection actuator 15, a paper detection sensor 16, and a control circuit 17.

The paper feed tray 11 can hold a plurality of papers P thereon. The paper feed roller 12 rotates in the direction of the arrow to rotate the paper P mounted on the paper feed tray 11.
Is supplied to the image forming apparatus 20 side. At this time, the paper separating friction plate 13 is pressed against the paper feed roller 12 by a pressure spring 14 so as to separate a plurality of papers P mounted on the paper feed tray 11 one by one.

The paper detection sensor 16 is, for example, an optical sensor, and the paper detection actuator 15
Is made of a member that can be tilted in the sheet conveying direction by the sheet P fed by the sheet feeding roller 12. That is, when the sheet detection actuator 15 is not tilted, the optical path is interrupted and indicates the OFF state, and when the sheet detection actuator 15 is tilted, the optical path passes and indicates the ON state.

Accordingly, the sheet detection sensor 16 detects that the sheet P is fed to the image forming apparatus 20 by turning the sensor on when the sheet detection actuator 15 is tilted, and controls the detection signal. The signal is output to the circuit 17.

The control circuit 17 includes a paper detection sensor 16
The image signal based on the detection signal from the laser scanning unit 3
The light emitting diode 31 is sent to the laser diode light emitting unit 31 to control lighting / non-lighting of the light emitting diode 31a. The control circuit 17 includes a fixing device 50 described later.
Of heating control means.

The laser scanning section 30 includes the laser diode light emitting unit 31, a scanning mirror 32, a scanning mirror motor 33, and reflection mirrors 35, 36 and 37.

The scanning mirror motor 33 is provided below the scanning mirror 32, and rotates the scanning mirror 32 at a high speed and a constant speed. The laser diode light emitting unit 31 is provided on a scanning mirror 32, and rotates together with the scanning mirror 32. That is, the laser diode light emitting unit 31
Is configured to irradiate the reflecting mirror 36 with the laser beam 34 from the light emitting diode 31a while rotating at high speed and constant speed. The irradiated laser light 34 is reflected in the order of the reflection mirrors 36, 35, and 37, and
To the exposure point X.

The laser diode light emitting unit 31
Is configured to selectively expose the photosensitive member 21 of the image forming apparatus 20 based on the lighting / non-lighting information from the control circuit 17 described above.

The image forming apparatus 20 includes a photosensitive member 21, a transfer roller 22, a charging member 23, a developing roller 24, a developing unit 25, and a cleaning unit 26.

The photoreceptor 21 is selectively discharged by the laser beam 34 from the laser scanning unit 30 on the surface of the photoreceptor 21, and an electrostatic latent image is formed on the surface.

The developing unit 25 has a developing roller 24 for supplying toner to the photosensitive member 21, and charges the toner by stirring the toner accumulated therein.
The toner is made to adhere to the surface of the developing roller 24. The toner image corresponding to the electrostatic latent image formed on the surface of the photoconductor 21 is formed on the photoconductor 21 by the action of an electric field formed by the developing bias voltage applied to the developing roller 24 and the potential of the surface of the photoconductor 21. To be formed.

In the image forming apparatus 20, the transfer roller 22 transfers the toner image formed on the surface of the photoconductor 21 by the action of the electric field given by the applied transfer voltage between the photoconductor 21 and the transfer roller 22. The paper is sucked and transferred to the fed paper P. At this time, the toner on the photoconductor 21 is transferred to the sheet P by the transfer roller 22, and the untransferred toner is collected by the cleaning unit 26.

The paper P on which the toner image has been transferred by the image forming apparatus 20 is conveyed to a fixing device 50, where the toner image is fixed. That is, in the fixing device 50, the surface temperature is 180 ° C.
A suitable temperature and pressure are applied to the paper P by the fixing roller 51 kept at a constant pressure and a pressing mechanism 52 as a pressing means stored at about 140 ° C. Then, the toner is melted by heat and fixed to the paper P, and a robust image is formed. The fixing device 50 will be described later in detail.

The paper P on which the toner image has been fixed by the fixing device 50 is transported outside the device by paper transport rollers 41 and 42 provided on the paper side of the fixing device 50.

The fixing device 50 is of an external heating type in which the fixing roller 51 is heated by a heating roller 53 arranged in contact with the fixing roller 51.

Here, the fixing device 50 will be described below with reference to FIG.

The fixing device 50 is, as shown in FIG.
A fixing roller 51, a pressing mechanism 52, and a heating roller 53 as a heating unit are provided.

First, the pressing mechanism 52 will be described.

The pressing mechanism 52 is connected to the fixing roller 51.
And a first pressure roller 52b provided immediately below the first pressure roller 52b along the fixing roller 51.
Pressure roller 52c disposed on the downstream side in the transport direction of
And the first pressure roller 52b and the second pressure roller 52c
And a pressure belt 52a stretched with a predetermined tension by the rollers 52b, 52c, and 52d.

The first to third pressure rollers 51b to 51d
Are arranged in parallel with the fixing roller 51.

The pressure belt 52a is fixed to the fixing roller 51 by the first to third pressure rollers 51b to 51d.
To form a press-contact portion (fixing nip portion).
The fixing nip is for fixing the toner T on the sheet P.

The first pressing roller 52b and the third pressing roller 52d press the pressing belt 52a against the fixing roller 51 at the fixing nip. A nip entrance area Wa is formed. The fixing nip entrance area Wa is defined between a pressing start point Q between the fixing roller 51 and the first pressing roller 52b and a pressing end point R between the fixing roller 51 and the third pressing roller 52d. This is a pressure contact area between the pressure belt 51 and the pressure belt 52a.

Further, the fixing nip portion presses the pressure belt 52a against the fixing roller 51 by the second pressure roller 52c and the third pressure roller 52d, and the fixing nip exit area which is an exit area of the fixing nip portion. The region Wb is formed.
The fixing nip exit area Wb is located between the fixing roller 51 and the third
The end point R of the pressure contact with the pressure roller 52d and the fixing roller 51
The pressure contact area between the fixing roller 51 and the pressure belt 52a, which is indicated between the pressure contact end point S of the fixing belt 51 and the pressure belt 52a.

The fixing nip entrance area Wa is a heat storage area for accumulating thermal energy from the fixing roller 51 to melt the toner T on the sheet P. On the other hand, the fixing nip exit area Wb is a heat radiating area for releasing the thermal energy given in the fixing nip entrance area Wa in order to cool and solidify the melted toner T on the paper P.

Therefore, the fixing roller 51 and the pressing mechanism 5
2 is formed with the toner T on the sheet P.
And a heat dissipation area for cooling and solidifying the melted toner T. The temperature setting in each area of the fixing nip will be described later.

When the fixing roller 51 rotates in the direction indicated by the arrow A, the pressing belt 52a and the first to third members constituting the pressing mechanism 52 are driven by the fixing roller 51.
The rollers 52b to 52d rotate in the direction of arrow B.

At this time, the first pressure roller 52b and the third pressure roller 52d are arranged so as to contact the fixing roller 51 via the pressure belt 52a, while the second pressure roller 52c is The pressing belt 52 a is pressed toward the fixing roller 51, but is arranged so as not to contact the fixing roller 51.

Thus, while heat energy from the fixing roller 51 flows into the first pressure roller 52b and the third pressure roller 52d,
Thermal energy from the fixing roller 51 is prevented from flowing into the second pressure roller 52c. The flow of the thermal energy from the fixing roller 51 will be described later.

In the present embodiment, the first to third pressure rollers 52b to 52d adjust the width of the fixing nip entrance area Wa to about 10 mm and the width of the fixing nip exit area Wb to about 15 mm. The tension on the pressure belt 52a is adjusted.

The pressing belt 52a has a circumference of 60 mm,
It is formed of a metal material having a thickness of 0.05 mm, such as aluminum or nickel, which has excellent thermal conductivity, a small heat capacity, and a high radiation cooling effect. This pressure belt 52a is
Although the contact surface with the fixing roller 51 may be a metal surface as it is, a synthetic resin material having excellent heat resistance and releasability, for example, a polymer material such as silicon rubber or fluorine rubber,
Alternatively, it may be coated with a fluororesin such as PFA (tetrafluoroethylene = perfluoroalkylvinylether copolymer resin) or PTFE (tetrafluoroethylene resin), or a mixture of a fluororesin and a fluororubber.

As described above, since the pressure belt 52a is made of a metal material having an excellent thermal conductivity, a small heat capacity, and a high heat radiation cooling effect, the pressure belt 52a from the fixing roller 51 in the fixing nip entrance area Wa as a heat storage area. The first and third pressure rollers 52b, 52 that are disposed in contact with the fixing roller 51 via a pressure belt 52a efficiently with heat energy.
d, the heat energy from the fixing roller 51 in the fixing nip exit area Wb, which is a heat radiation area, can be efficiently discharged to the outside of the pressure belt 52a.

Therefore, in the fixing nip portion between the fixing roller 51 and the pressure belt 52a, a stable temperature change can be given to the toner, so that stable fixing without offset can be performed.

The first pressure roller 52b and the third pressure roller 52d use a solid metal roller having a high heat storage effect such as aluminum or stainless steel having a diameter of 20 mm / 10 mm.

Since the first pressure roller 52b and the third pressure roller 52d are made of a metal material which is a heat storage material, the first and second pressure rollers 52b and 52d are in contact with the fixing roller 51 via the pressure belt 52a. Since the thermal energy flowing from the fixing roller 51 is likely to be accumulated in the third pressure rollers 52b and 52d, the high temperature state can be maintained with a small amount of thermal energy in the fixing nip entrance area Wa. Accordingly, the energy required for heating the fixing roller 51 can be reduced, and an economical fixing device can be provided.

As the second pressure roller 52c, which is a tension roller, an elastic roller made of an elastic resin such as rubber having a diameter of 20 mm and having heat insulating properties is used. As described above, the fixing nip exit area W which is the heat radiation area
Since the second pressure roller 52c present in b is made of a heat insulating material, heat energy flowing from the pressure belt 52a is not accumulated in the second pressure roller 52c in the fixing nip exit area Wb. Thereby, in the fixing nip exit area Wb, the toner T melted on the sheet P can be effectively cooled and solidified.

Next, the heating roller 53 will be described.

The heating roller 53 has a heater lamp 54 as a heating source inside, and is provided upstream of the fixing nip with respect to the rotation direction of the fixing roller 51. At this time, the center of the heating roller 53 is
And is pressed against the fixing roller 51 with a predetermined pressing force.

FIG. 1 shows a state in which the heating roller 53 is in contact with the fixing roller 51, and a pressure contact portion formed between the fixing roller 51 and the heating roller 53 is a heating nip portion Wc. In the present embodiment, the width of the heating nip Wc is 5 mm. Further, when the heating roller 53 is pressed against the fixing roller 51, the heating roller 53 rotates in the direction of arrow C following the rotation of the fixing roller 51, similarly to the pressing belt 52a.

As the heating roller 53, a hollow cylindrical member made of aluminum, stainless steel or the like is used. Aluminum or stainless steel may be used as it is, but a synthetic resin material having excellent heat resistance and release properties, for example, a polymer material such as silicon rubber or fluorine rubber, or PFA, P
It may be coated with a fluororesin such as TFE or a mixture of a fluororesin and a fluororubber.

In this embodiment, an aluminum cylindrical roller having a diameter of 15 mm and a thickness of 0.5 mm is used. The rated output of the heater lamp 54 disposed inside the heating roller 53 is 400 W.

A thermistor (not shown) as a temperature detecting means is provided on the peripheral surface of the heating roller 53 so as to detect the surface temperature of the heating roller 53. Further, a thermistor 55 as a temperature detecting unit for detecting the surface temperature of the fixing roller 51 is disposed near the downstream side of the heating nip portion Wc with respect to the rotation direction of the fixing roller 51.

The heating roller 53 is provided upstream of the fixing nip in the recording material conveyance direction. As a result, the fixing roller 51 is heated by the heating roller 53 provided on the upstream side of the fixing nip in the recording material conveyance direction, so that the fixing roller 51 is heated from the recording material inlet side of the fixing nip. Therefore, loss of heat energy supplied from the heating roller 53 to the fixing roller 51 between the heating roller 53 and the fixing nip portion can be minimized. As a result, the fixing roller 51 can be heated to a temperature necessary for melting the toner with little energy.
Can be heated, so that energy required for the fixing device can be reduced.

Next, the fixing roller 51 will be described.

The fixing roller 51 is a roller having a diameter of 30 mm. As shown in FIG. 1, a heat insulating layer 51b made of a heat resistant elastic material is formed on a core material 51a, and the heat insulating layer 51b is formed on the heat insulating layer 51b. It has a configuration in which a coating layer 51c made of a heat-resistant release material is coated.

The core member 51a for obtaining the strength of the fixing roller 51 is obtained by processing aluminum, stainless steel or the like into a solid or hollow cylindrical shape. In this embodiment, the core 51a has a diameter of 15 mm and a thickness of 2 mm.
Using a stainless steel solid cylindrical shaft. The hollow cylindrical core member 51a will be described in a second embodiment.

The heat insulating layer 51b serves to prevent the heat of the coating layer 51c heated by the heating roller 53 from escaping into the fixing roller 51, and to form the first pressure roller 52b and the second pressure roller via the pressure belt 52a. 52c is provided for the purpose of appropriately elastically deforming and obtaining a predetermined nip width.

As the heat-resistant elastic material constituting the heat-insulating layer 51b, there is a rubber material having excellent heat resistance, such as fluorine rubber and silicon rubber. In the present embodiment, a silicone rubber foam is formed to have a thickness of 7.5 mm as the heat insulating layer 51b.
This silicone rubber foam has low thermal conductivity and excellent heat insulation properties, and has low hardness and is suitable for obtaining a predetermined nip width at low pressure.

The coating layer 51c receives the heat from the heating roller 53 at the heating nip Wc and applies the heat to the toner T on the paper P at the fixing nip to fix the toner T. 51 is provided for the purpose of preventing contamination due to the attachment of toner or the like to the surface of the surface 51.

As the heat-resistant release material constituting the coating layer 51c, a fluororesin such as PFA or PTFE is used. In the present embodiment, a 50 μm thick PF is used as the coating layer 51c.
A tube is used.

Here, the fixing roller 51 and the pressing mechanism 5
The flow of the thermal energy in the fixing nip formed by the steps 2 and 3 will be described below.

The flow of heat energy in the fixing nip will be described below with reference to FIG.

First, the flow of thermal energy in the fixing nip entrance area Wa of the fixing device 50 will be described.

At the start of fixing, the fixing roller 51 and the first and third pressure rollers 52b and 52d are stored at a predetermined temperature, and the fixing nip entrance area Wa is maintained at a high temperature higher than the softening point of the toner.

The toner T on the sheet P conveyed to the fixing nip entrance area Wa is transferred to the heat insulating layer 5 of the fixing roller 51.
The thermal energy stored in 1b and the thermal energy stored in the first pressure roller 52b are applied. In the fixing nip entrance area Wa, heat energy sufficient to melt the toner T on the paper P is applied. Incidentally, the first pressure roller 52b is a fixing roller 5b.
1 through the pressure belt 52a,
While the paper P is being transported to the fixing nip entrance area Wa,
It is in a state where heat is sufficiently stored.

Further, in the fixing nip entrance area Wa, the third pressure roller 52d disposed between the first pressure roller 52b and the second pressure roller 52c is formed of a metal roller, And 51 via a pressure belt 51a. Thereby, the third pressure roller 52d is
The heat is stored by the heat from the fixing roller 51, and heat energy is applied to the toner T on the sheet P at the fixing nip entrance area Wa.

Next, the flow of thermal energy in the fixing nip exit area Wb of the fixing device 50 will be described.

The toner T on the sheet P conveyed to the fixing nip exit area Wb is cooled by releasing the heat accumulated in the fixing nip entrance area Wa via the metal pressure belt 52a. Thus, the toner T is solidified in the fixing nip entrance area Wb and is fixed on the paper P.

In the fixing device 50, the fixing nip entrance area Wa and the fixing nip exit area Wb of the fixing nip portion.
Is set so that the temperature of the toner has a temperature distribution shown in the graph of FIG. 4 in the fixing nip portion.

That is, the fixing nip inlet area Wa is set so that the temperature of the toner rises from room temperature to beyond the softening point T _{N of the} toner and reaches the peak temperature T _O at the boundary with the fixing nip outlet area Wb. It is a heat storage area. On the other hand, in the fixing nip exit area Wb, the toner temperature is equal to the peak temperature T.
_This is a heat radiation region set so as to cool from _O to a point exceeding the toner softening point _TN and further to exceeding the offset occurrence limit temperature _TG .

The above-mentioned offset occurrence limit temperature is a temperature at which the melted toner is cooled and solidified, and the cohesive force becomes larger than the adhesive force between the toner and the fixing roller.

However, since the softening point and offset limit temperature of the toner vary depending on the type of the toner, it must be set according to the toner.

In this embodiment, by controlling the surface temperature of the fixing roller 51 and changing the width of the fixing nip, the toner T on the sheet P passing through the fixing nip is changed.
As shown in FIG. 4, a fixing nip inlet area Wa as a heat storage area and a fixing nip outlet area Wb as a heat radiating area are formed.

Here, the operation of the fixing device 50 having the above configuration will be described below with reference to FIG.

In the fixing device 50, during the printing operation, the fixing roller 51 is moved in the direction of arrow A by a peripheral speed of 150 mm.
/ Sec, and the heating roller 53
Is heated.

At this time, the surface of the fixing roller 51 is heated at the heating nip Wc with the heated heating roller 53, and the surface temperature is detected by the thermistor 55. In the heating roller 53, the surface temperature of the fixing roller 51 is detected by a thermistor 55, and energization of the heater lamp 54 is controlled by an energization control circuit (not shown) based on the detection signal.

That is, the surface temperature of the fixing roller 51 is controlled to a predetermined temperature (180 ° C. in the present embodiment) based on the detection signal from the thermistor 55.

At this time, the heat energy from the fixing roller 51 is transferred to the first pressing roller 52 via the pressing belt 52a.
It flows into b. Then, after the first pressure roller 52b reaches a predetermined temperature, that is, after a predetermined amount of heat is accumulated,
The paper P is transported to the fixing nip.

That is, in the fixing nip entrance area Wa between the fixing roller 51 and the pressing mechanism 52, the sheet P carrying the image formed with the unfixed toner T from the image forming apparatus 20 is formed.
Is transported from the direction of arrow D to the fixing nip exit area Wb after the first pressure roller b stores heat.

The fixing nip entrance area W of the fixing nip portion
The paper P conveyed to a is subjected to the heat energy from the fixing roller 51, the first and third pressure rollers 52b and 52d, and the pressure of the fixing nip. As a result, the toner T electrostatically attached to the sheet P is melted by heat. Then, the heat-fused toner T on the sheet P conveyed to the fixing nip exit area Wb of the fixing nip portion is applied with pressure, is cooled and solidified, and is completely hot-pressure fixed on the sheet P.

After fixing, the paper P is separated from the fixing roller 51 along the surface of the pressure roller 52,
Peeled from 2.

As described above, if the transfer timing of the sheet P to the fixing nip portion is set after the first pressure roller 52b made of the heat storage material is stored by the heat from the fixing roller 51, Before the sheet P is conveyed to the fixing nip portion, the sheet P can be sufficiently heated.

As a result, the unfixed toner on the sheet P is
Since the toner can be reliably melted from the fixing nip entrance area Wa, when the toner is a color, it is possible to eliminate poor color development due to insufficient temperature and to provide a high quality color image.

The following table compares the results of experiments on the presence or absence of offset and the warm-up time between the external heating type fixing device of the present embodiment and a conventional internal heating type fixing device. It is shown in FIG.

[0129]

[Table 1]

From Table 1, in the internal heating method, the surface temperature of the fixing roller at the exit of the fixing nip is 163 ° C., which is higher than the melting point (105 ° C.) which is the softening point of the toner, and offset occurs. On the other hand, in the external heating method, the surface temperature of the fixing roller at the exit of the fixing nip is 90 ° C. which is lower than the melting point (105 ° C.), which is the softening point of the toner, due to the self-cooling action, and no offset occurs. Further, it can be seen that the warm-up time in the external heating system is significantly shorter than that in the internal heating system.

Further, the external heating method is different from the internal heating method in that the difference between the inlet temperature and the outlet temperature in the fixing nip portion,
That is, the width of the temperature drop is large. As a result, the melted toner is sufficiently cooled in the fixing nip, so that the occurrence of offset can be reduced.

Therefore, in order to surely reduce the offset, it is understood that it is necessary to increase the temperature drop while securing the softening point of the toner. As a method of increasing the range of the temperature drop, it is conceivable to enhance the heat radiation effect in the fixing nip portion.

In order to enhance the heat radiation effect of the fixing nip, for example, as shown in FIG.
What is necessary is just to form the minute ventilation holes 52e ... of 0.2-0.3 mm in diameter.

Since a large number of air holes 52e are formed in the pressure belt 52a, high-temperature air that has settled in the fixing nip outlet area Wb is positively discharged to the outside of the pressure belt 52a, and convection currents are discharged. Pressurizing belt 5 with increased heat transfer coefficient
2a can be improved and stabilized, and the cooling effect of the toner T can be enhanced.

As a result, the heat radiating effect in the heat radiating region of the press contact portion can be enhanced, so that the fixing nip inlet region Wa
Is reliably cooled and solidified in the fixing nip exit area Wb. As a result, the toner T can be completely fixed on the paper P, so that the offset can be surely eliminated.

However, if the ratio of the total area of the ventilation holes per unit area is increased, the pressure holes 5
Although the cooling effect of 2a is enhanced, it is necessary to form it so as not to impair the pressing force required for fixing.

As described above, the fixing device 50 having the above-described structure is used.
In the fixing nip entrance area Wa, a fixing roller 51 whose temperature has been adjusted to a predetermined temperature, and a metal first pressure roller 5 storing heat energy flowing from the fixing roller 51 are stored.
2b and the third pressure roller 52d, heat energy actively flows into the paper P, and the toner T on the paper P reaches a temperature T ₀ higher than the softening point T _N and has a high-temperature molten state sufficient to develop color. Becomes Accordingly, it is possible to sufficiently cope with a toner that melts at a high temperature and develops a color, such as a color toner.

On the other hand, in the fixing nip exit area Wb, the toner T heated to a temperature equal to or higher than the softening point in the fixing nip entrance area Wa is radiated through a metal pressure belt 52a.
The temperature becomes lower than the softening point, and it is cooled and solidified. Since the cohesive force of the toner during cooling and solidification becomes extremely large,
The toner T has reduced adhesion to the fixing roller 51,
The image is completely fixed on the sheet P.

Further, unlike the related art, oil for preventing offset is not required, and as a result, a complicated oil application mechanism is not required, so that the cost of the apparatus can be reduced. Further, since there is no need to perform an operation for preventing offset such as oil application on the fixing roller 51, the life of the fixing roller 51 can be extended.

As described above, the fixing nip entrance area Wa
, The pressure belt 52a is made of a metal belt having excellent heat conductivity, a small heat capacity, and a high heat radiation cooling effect, and the first and third pressure rollers 52b and 52d are made of a metal having a high heat storage effect. By using a roller, heat energy can be stably supplied to the toner T of the sheet P conveyed to the fixing nip entrance area Wa. Therefore, the temperature change in the fixing nip entrance area Wa becomes stable.

[Embodiment 2] Another embodiment of the present invention will be described below. still,
For convenience of description, members having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 6, in the fixing device according to the present embodiment, the core material 51a of the fixing roller 51 is a hollow aluminum roller, the heat insulating layer 51b is a silicone rubber foam, and the coating layer 5
1c is composed of PFA.

By making the center of the fixing roller 51 hollow, the fixing roller 51 itself can be easily cooled,
The cooling effect of the toner T in the fixing nip exit area Wb is enhanced.

Further, as a means for cooling the fixing roller 51, for example, a fan may be disposed inside the core member 51a to forcibly cool the fixing nip exit area Wb of the fixing roller 51.

A heat pipe may be used in place of the fan. In this case, although not shown, a heat pipe is arranged in the width direction of the core member 51a so that heat accumulated inside the fixing roller 51 is released to the outside via the heat pipe.

As described above, according to the fixing device having the above-described structure, by providing each means for forcibly cooling the fixing roller 51 for applying thermal energy to the toner,
The heat radiation effect of the fixing nip exit area Wb can be enhanced. At this time, energization of the heat roller 54 of the heating roller 53 is controlled so that the heat storage effect in the fixing nip entrance area Wa does not decrease.

Therefore, the fixing device having the above-described configuration has a configuration in which the heat radiation effect of the fixing nip exit area Wb is enhanced, so that the toner T can be reliably cooled and solidified in the fixing nip exit area Wb. As a result, offset can be prevented, and defective fixing of toner and the like can be reduced, so that a high-quality image can be formed.

In the second embodiment, in order to enhance the heat radiation effect of the fixing nip exit area Wb, the fixing roller 5
1 to enhance the cooling effect. However,
In order to enhance the heat radiation effect of the fixing nip exit area Wb,
For example, a configuration may be adopted in which the cooling effect of the pressurizing mechanism 52 itself is enhanced, and this will be described in Embodiments 3 and 4 below.

[Embodiment 3] Still another embodiment of the present invention will be described below. For convenience of description, members having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 7, the fixing device according to the present embodiment has a configuration in which a fan 56 is disposed as a cooling means at a position corresponding to the fixing nip exit area Wb inside the pressure belt 52a. . That is, the fixing device is configured to enhance the cooling effect of the pressing mechanism 52 itself in order to enhance the heat radiation effect of the fixing nip exit area Wb.

As described above, by disposing the fan 56 at a position corresponding to the fixing nip exit area Wb inside the pressure belt 52a, the heat radiation characteristics of the pressure belt 52a can be improved. As a result, the toner T on the sheet P conveyed to the fixing nip exit area Wb can be effectively cooled.

As means for cooling the pressure belt 52a,
In addition to the fan 56 described above, the following method is conceivable.

A method of cooling the pressure belt 52a using a low-temperature member cooled by a heat pipe.

A method in which the inside of the pressure belt 52a is colored black to perform radiation cooling.

A method in which an air inlet is provided so that external wind enters the fixing nip outlet area Wb of the pressure belt 52a.

Here, among the above or other methods,
The case will be described below with reference to FIG.
FIG. 8A is a schematic plan view of the fixing device shown in FIG. 7 as viewed from above.

As shown in FIG. 8 (b), the low-temperature member used in this embodiment is composed of a substantially plate-shaped SUS 61 and a heat pipe 62 penetrating the SUS 61.

As shown in FIG. 8A, the SUS 61 extends in the width direction of the pressure belt 52a at a position corresponding to the fixing nip exit region Wb inside the pressure belt 52a. The SUS 61 is configured such that one end thereof protrudes from the width direction of the pressure belt 52a.
It is formed longer than the width of a.

The SUS 61 is provided close to the pressure belt 52a, and heat energy flows from the pressure belt 52a. And SUS
Thermal energy is transmitted through a heat pipe 62 inside 61.

The fixing device is provided with a fan 63 for cooling the SUS 61 protruding from the pressure belt 52a. By blowing air to the protruding portion of the SUS 61 by the fan 63, the heat pipe 62 can be cooled and the entire SUS 61 can be cooled.

As a result, the pressure belt 52a can be effectively cooled at the position corresponding to the fixing nip exit area Wb, so that an offset due to a temperature drop in the fixing nip exit area Wb can be prevented.

[Embodiment 4] FIGS. 9 to 1 show still another embodiment of the present invention.
1 will be described below. Note that, for convenience of explanation, members having the same functions as those of the above-described embodiments are given the same symbols, and descriptions thereof are omitted.

As shown in FIG. 9, the fixing device according to the present embodiment is located at a position corresponding to the fixing nip exit area Wb inside the pressure belt 52a, as in the fixing device according to the third embodiment. A fan 56 is provided. further,
A sensor 57 for detecting the temperature of the pressure belt 52a is provided inside the pressure belt 52a immediately before the pressure belt 52a separates from the fixing roller 51 (in the vicinity of the fixing nip exit area Wb). The rotation of the fan 56, that is, the cooling capacity is controlled based on the detection signal.

More specifically, the sensor 57 and the fan 56
Are connected to the control circuit 17 as shown in FIG.
Based on the detection signal of the sensor 57, the control circuit 1
7 controls the rotation of the fan 56.

Here, the rotation control of the fan 56 will be described below with reference to the flowchart shown in FIG.

First, when the power of the laser printer is turned on and the warming-up of the fixing device or the like is performed, the control circuit 17 sets the rotation speed of the fan 56 to M, and drives the fan 56 at this rotation speed M. (S1). In this case, to detect the temperature T ₁ of the fixing nip exit area Wb near the pressure belt 52a.

[0167] Then, the temperature T ₁ is equal to or larger than a predetermined temperature Tα (S2). Here, the temperature T ₁
Is equal to or higher than the predetermined temperature Tα, the fixing nip exit area W
It is determined that the temperature T ₁ of the pressure belt 52a near the point b has risen to a value close to the toner offset occurrence limit temperature, and the rotational speed of the fan 56 is increased by a predetermined number α from M.
+ Α (S3), and the fan 56
Is driven to rotate.

[0168] Next, the temperature T ₁ is equal to or smaller than a predetermined temperature T [beta (S4). Here, if the temperature T ₁ is equal to or lower than the predetermined temperature Tβ, the fixing nip exit area Wb
It is determined that the temperature T _{1 of the} nearby pressure belt 52a has dropped unnecessarily, and the rotation speed of the fan 56 is changed from M + α to M
Is set (S5), and the fan 56 is driven to rotate at this rotation speed M.

As described above, the rotation speed of the fan 56 is set to the temperature T _{1 of the} pressure belt 52a near the fixing nip exit area Wb.
, The temperature of the fixing nip exit area Wb can be kept constant.

Generally, toner is colored by being melted. Therefore, it is necessary to sufficiently melt the toner in the fixing nip entrance area Wa. Further, in order to fix the toner on the paper, it is necessary to sufficiently cool the toner and increase its cohesive force.

Therefore, if the temperature of the fixing nip exit area Wb is too high, the toner cannot be completely solidified and will not be completely fixed on the paper, resulting in an offset. On the other hand, if the temperature of the fixing nip exit area Wb becomes too low, the temperature of the fixing nip entrance area Wa may also decrease. In this case, since the sheet moves to the fixing nip exit area Wb without sufficiently melting the toner in the fixing nip entrance area Wa, there occurs a problem that the toner cannot be sufficiently developed.

From the above, as described above, by keeping the temperature of the fixing nip exit area Wb constant, the heat storage effect in the fixing nip entrance area Wa and the heat radiation effect in the fixing nip exit area Wb are always kept constant. Can be kept. Therefore, a high-quality image can always be obtained.

Further, in order to enhance the cooling effect of the toner T, the cooling effect of the pressure belt 52a and the cooling effect of the fixing roller 51 may be enhanced. For this purpose, in addition to providing the fan 56 inside the pressure belt 52a as described above, the core member 51a of the fixing roller 51 may be formed of a hollow aluminum roller as in the second embodiment.

As described above, in each of the above embodiments, since the fixing nip portion is formed by the pressure contact between the pressure belt 52a and the fixing roller 51, the width of the fixing nip portion is set between the rollers. It can be wider than the width of the fixing nip formed. Accordingly, the toner can be sufficiently melted and cooled and solidified in the fixing nip portion, so that even if the paper P passes through the fixing nip portion at high speed, stable fixing without offset can be performed. Therefore, it is possible to cope with high-speed printing.

Further, since the fixing device of the present invention employs an external heating system for heating the surface of the fixing roller 51 from the outside, the time required for the fixing nip to reach a predetermined temperature is greatly reduced. be able to.

Further, in the external heating system, compared to the fixing device of the internal heating system, the heating is performed by an amount corresponding to the heat capacity necessary for fixing the surface of the fixing roller 51 from the outside, so that the heat efficiency is excellent and the warm-up time is shortened. can do. Further, since the boundary temperature between the heat insulating layer 51b made of rubber and the core material 51a can be kept low, the heat insulating layer 51b is hardly peeled off, and the life of the fixing roller 51 can be greatly improved.

[0177]

As described above, the fixing device according to the first aspect of the present invention is stretched by the fixing roller whose surface is heated from the outside and the plurality of pressure rollers arranged in parallel with the fixing roller. A pressure belt for pressing the outer peripheral surface of the fixing roller, and conveying the recording material on which the unfixed toner image is formed to a pressure contact portion formed by the fixing roller and the pressure belt. In the fixing device, the toner is thermally melted and fixed to the press contact portion, from the upstream side in the conveying direction of the recording material, a heat storage area set to a temperature equal to or higher than the softening point of the toner, and cooling and solidifying the melted toner. And a heat radiation area set at a temperature required for the heat treatment.

Therefore, it is not necessary to apply the oil for preventing offset to the fixing roller in order to prevent the offset after the fixing, so that various problems caused by the oil for preventing offset can be solved. In particular, since a mechanism for applying the oil for preventing offset is not required, the apparatus can be simplified, and an image forming apparatus such as a printer including the fixing device can be provided at low cost.

As described above, in the fixing device according to the second aspect of the present invention, in addition to the configuration of the first aspect, the pressing belt is formed of a material having thermal conductivity and a plurality of pressing rollers are provided. Among them, at least one pressure roller is arranged to be in contact with the fixing roller via the pressure belt in the heat storage area.

Therefore, in addition to the effect of the structure of the first aspect, the heat easily accumulates on the pressure roller in contact with the fixing roller via the pressure belt, and the recording material conveyed into the heat storage area. Since the thermal energy from the fixing roller and the thermal energy from the pressure roller flow into the upper toner, the toner is in a high-temperature melting state. As described above, in the heat storage area, there is an effect that thermal energy can be efficiently supplied to the toner on the recording material.

As described above, in the fixing device according to the third aspect of the present invention, in addition to the configuration of the second aspect, the pressing roller that is disposed in contact with the fixing roller via the pressing belt is made of a heat storage material. Configuration.

Therefore, in addition to the effect of the structure of claim 2, the pressure roller that is arranged in contact with the fixing roller via the pressure belt can store the heat energy flowing from the fixing roller. In the heat storage area of the fixing section, the high temperature state can be maintained with a small amount of heat energy. Accordingly, the energy required to heat the fixing roller is reduced, and an effect is provided that an economical fixing device can be provided.

As described above, the fixing device according to the fourth aspect has an external
A fixing roller whose surface is heated from a portion,
Stretched by a plurality of pressure rollers arranged in parallel,
A pressure belt that presses the outer peripheral surface of the fixing roller,
In the pressure contact portion formed by the fixing roller and the pressure belt,
By conveying the recording material on which the unfixed toner image is formed,
To a fixing device that melts and fixes the toner on the recording material by heat.
The pressing portion may be located on the upstream side in the conveying direction of the recording material.
Heat storage region set at a temperature equal to or higher than the softening point of the toner
And set the temperature to cool and solidify the melted toner
The heat radiation area is formed in order, and the pressure belt is
It is formed of a material having thermal conductivity, and
At least one pressure roller among the pressure rollers is as described above.
Contact the fixing roller via the pressure belt in the heat storage area
It is arranged, and the fixing roller is
The pressure roller that is placed in contact is made of heat storage material.
The transfer timing of the recording material to the pressure contact part is
Pressure roller accumulates heat from the fixing roller
This is the configuration that has been set after it has been performed.

Therefore, the effect of the configuration according to claim 3 is attained.
Before the recording material is conveyed to the pressure contact
Since it can be in a heated state, it is undecided on the recording material
Make sure that the toner is melted from the entrance area
Can be. If As a result, the toner over was the color,
It is possible to eliminate poor color development due to insufficient temperature,
The effect is that color images can be provided.
You.

As described above, in the fixing device of the fifth aspect , in addition to the configuration of the second , third, or fourth aspect , the pressure roller existing in the heat radiation area is made of a heat insulating material.

Therefore, in addition to the effects of the second , third and fourth aspects, the thermal energy flowing from the pressure belt is not accumulated in the pressure roller in the heat radiation area, so that the molten toner on the recording material is effectively reduced. This has the effect of being able to be cooled and solidified.

The fixing device according to the sixth aspect of the present invention, as described above, has the structure of any one of the first to fifth aspects, in which the surface of the fixing roller is externally provided on the upstream side in the recording material conveyance direction of the pressing portion. In this configuration, a heating roller for heating is provided.

Therefore, in addition to the effect of any one of the first to fifth aspects, the fixing roller is heated by the heating roller from the upstream side of the pressing portion in the recording material conveyance direction. It is possible to reduce heat loss between the pressure contact portion and the pressure contact portion. Accordingly, the fixing roller can be heated to a temperature required for melting the toner with a small amount of energy, so that the energy required for the fixing device can be reduced.

As described above, the fixing device according to the seventh aspect of the present invention has a configuration in which the pressure belt has a large number of ventilation holes in addition to the configuration of any one of the first to sixth aspects.

Therefore, in addition to the effect of any one of the first to sixth aspects, high-temperature air stagnating in the heat-dissipating region of the press-contact portion is positively discharged to the outside of the belt to increase the convective heat transfer coefficient. The heat radiation performance of the pressure belt can be improved and stabilized, and the cooling effect of the toner can be enhanced. Thus, the heat radiation effect in the heat radiation area of the press contact portion can be enhanced, so that the toner melted in the heat storage area can be reliably cooled and solidified in this heat radiation area. As a result, the toner can be completely fixed on the recording material, so that the offset can be surely eliminated.

[0191] Further, in addition to any one of the claims 1 to 7, the pressure belt, also be a structure comprising a metal
it can.

Therefore, in addition to the effect of any one of the first to seventh aspects, the heat energy from the fixing roller in the heat storage area can be efficiently placed in contact with the fixing roller via the pressure belt. Can be transmitted to the pressure roller. Further, heat energy from the fixing roller in the heat radiation area can be efficiently released to the outside of the pressure belt. Therefore, at the pressure contact portion between the fixing roller and the pressure belt, a stable temperature change can be given to the toner, so that there is an effect that the fixing can be stably performed without offset.

The fixing device according to the invention of claim 8 is, as described above, in addition to the structure of any one of claims 1 to 7 , the fixing roller has a structure in which the central portion has a hollow structure.

Therefore, in addition to the effect of any one of claims 1 to 7 , since the center of the fixing roller is hollow, heat energy from the surface of the fixing roller is not accumulated inside the fixing roller. It is possible to eliminate the influence of the internal heat storage on the heat radiation area of the press contact portion. Thereby, there is an effect that the cooling effect of the toner in the heat radiation region of the press contact portion can be enhanced.

According to the ninth aspect of the present invention, as described above, in addition to any one of the first to eighth aspects, the vicinity of the recording material outlet at the pressure contact portion of the pressure belt with the fixing roller is cooled. This is a configuration in which cooling means is provided.

Therefore, in addition to the effect of any one of the first to eighth aspects, the provision of the cooling means for cooling the vicinity of the recording material outlet of the pressure contact portion of the pressure belt allows the pressure belt to be cooled. Can be forcibly cooled. As a result, it is possible to increase the convective heat transfer coefficient of the pressure belt, improve and stabilize the heat radiation performance of the pressure belt, and enhance the effect of cooling the toner in the heat radiation area.

According to a tenth aspect of the present invention, as described above,
A fixing roller having a surface heated from the outside, and the fixing roller
Stretched by multiple pressure rollers arranged in parallel with
A pressure belt for pressing the outer peripheral surface of the fixing roller.
And a press contact portion formed by the fixing roller and the pressure belt.
The recording material on which the unfixed toner image is formed
Fixing device for fusing and fixing toner to the recording material by heat
The press-contact portion is located on the upstream side in the conveying direction of the recording material.
From the heat storage area set to a temperature above the softening point of the toner
And set the temperature to cool and solidify the melted toner
The heat radiation area is formed in order,
Cooling that cools the vicinity of the recording material exit at the pressure contact portion with the fixing roller
A pressurizing means is provided, in the vicinity of the recording material outlet of the press contact portion.
Temperature detecting means for detecting the temperature of the pressure belt of the
Cooling of the cooling means based on the detection information of the temperature detecting means.
Cooling control means for controlling the capacity
is there.

Therefore, in addition to the effect of the ninth aspect,
In other words, the cooling capacity of the cooling means is
Is controlled based on the temperature of the pressure belt immediately
The temperature in the heat radiating area of the insulation displacement
You can. Thereby, the toner in the heat radiation area
The cooling effect can be stabilized.
I do.

In the fixing device according to the eleventh aspect of the present invention, as described above, in addition to the constitution of the ninth or tenth aspect, the cooling means is provided in a region surrounded by the pressure belt and the pressure roller. Configuration.

Therefore, in addition to the effect of the ninth or tenth aspect, the cooling means can forcibly discharge the hot air that has settled in the area surrounded by the pressure belt and the pressure roller. There is an effect that the cooling effect of the pressure belt can be further enhanced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a fixing device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a laser printer including the fixing device shown in FIG.

FIG. 3 is an explanatory diagram showing a flow of thermal energy in a fixing nip portion of the fixing device shown in FIG.

FIG. 4 is a graph showing a temperature distribution of toner in a fixing nip portion of the fixing device shown in FIG.

FIG. 5 is a schematic plan view showing an example of a pressure belt provided in the fixing device shown in FIG.

FIG. 6 is a schematic configuration diagram of a fixing device according to another embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a fixing device according to still another embodiment of the present invention.

FIG. 8 is an explanatory diagram illustrating an example of a cooling unit for cooling the pressure belt in the fixing device illustrated in FIG. 7;

FIG. 9 is a schematic configuration diagram of a fixing device according to still another embodiment of the present invention.

FIG. 10 is a block diagram illustrating cooling control in a control circuit provided in the fixing device illustrated in FIG. 9;

FIG. 11 is a flowchart showing a flow of cooling control in the control circuit shown in FIG. 10;

FIG. 12 is a schematic configuration diagram of a conventional fixing device.

FIG. 13 is a schematic configuration diagram of a conventional fixing device.

[Explanation of symbols]

 17 Control Circuit (Cooling Control Means) 50 Fixing Device 51 Fixing Roller 51a Core Material 52a Pressure Belt 52b First Pressure Roller (Pressure Roller) 52c Second Pressure Roller (Pressure Roller) 52d Third Pressure Roller ( Pressure roller) 52e Vent hole 53 Heating roller 56 Fan (cooling means) 57 Sensor (temperature detecting means) P Paper (recording material) T Toner Wa Fixing nip entrance area (heat storage area) Wb Fixing nip exit area (heat dissipation area)

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-303300 (JP, A) JP-A-5-341672 (JP, A) JP-A 8-202180 (JP, A) JP-A-5-202180 72926 (JP, A) Japanese Utility Model Showa 58-23350 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 13/20 G03G 15/20

Claims (11)

(57) [Claims] A fixing roller having a surface heated from the outside;
A pressure belt that is stretched by a plurality of pressure rollers arranged in parallel with the fixing roller and presses an outer peripheral surface of the fixing roller; and a pressure contact portion formed by the fixing roller and the pressure belt. A fixing device that heats and fixes the toner on the recording material by conveying the recording material on which the unfixed toner image is formed, wherein the press-contact portion is configured to soften the toner from the upstream side in the conveying direction of the recording material. A fixing device, wherein a heat storage region set at a temperature equal to or higher than a point and a heat radiation region set at a temperature at which a molten toner is cooled and solidified are sequentially formed. 2. The pressure belt is formed of a material having thermal conductivity, and at least one of the plurality of pressure rollers is configured to control the pressure belt in the heat storage area. The fixing device according to claim 1, wherein the fixing device is arranged to be in contact with the fixing roller via the fixing roller. 3. The fixing device according to claim 2, wherein the pressure roller, which is in contact with the fixing roller via a pressure belt, is made of a heat storage material. 4. A fixing roller having a surface heated from the outside,
A plurality of pressure rollers arranged in parallel with the fixing roller
Pressurizing belt for pressing the outer peripheral surface of the fixing roller.
And a belt formed by the fixing roller and the pressure belt.
Transport the recording material on which the unfixed toner image is formed
The toner is thermally fused to the recording material by
In the fixing device, the pressing portion is provided with a toner from an upstream side in a conveying direction of the recording material.
Heat storage area set to a temperature equal to or higher than the softening point
The heat radiation area set at the temperature to cool and solidify the toner
Are formed in order, and the pressing belt is formed of a material having thermal conductivity.
And at least one pressure roller among the plurality of pressure rollers.
Roller in the heat storage area via the pressure belt.
Roller, and is in contact with the fixing roller via a pressure belt.
The pressure roller is made of a heat storage material, and the transfer timing of the recording material to the pressing portion is controlled by the heat storage material.
The pressure roller consisting of
A fixing device characterized by being set after being heated
Place. 5. The pressure roller present in the heat radiation area,
5. A heat insulating material, wherein the heat insulating material is made of a heat insulating material.
The fixing device as described in the above. 6. A heating roller according to claim 1, wherein a heating roller for heating the surface of the fixing roller from the outside is provided upstream of the pressing portion in the recording material conveyance direction. Fixing device. 7. The fixing device according to claim 1, wherein the pressure belt has a large number of ventilation holes. 8. The fixing roller has a hollow structure at the center.
The method according to any one of claims 1 to 7, wherein
Fixing device. 9. A pressure contact of the pressure belt with the fixing roller.
Cooling means for cooling the vicinity of the recording material outlet
The method according to any one of claims 1 to 8, wherein
Fixing device. 10. A fixing roller whose surface is externally heated.
And a plurality of pressure rollers arranged in parallel with the fixing roller
And presses the outer peripheral surface of the fixing roller.
And a pressure belt.
Recording material on which an unfixed toner image is formed
The toner is thermally fused to the recording material by transporting
In the fixing device to be attached, the pressing portion is provided with a toner from an upstream side in a conveying direction of the recording material.
Heat storage area set to a temperature equal to or higher than the softening point
The heat radiation area set at the temperature to cool and solidify the toner
The recording material is formed at the pressure contact portion of the pressure belt with the fixing roller.
Cooling means for cooling the vicinity of the opening is provided, and detects the temperature of the pressure belt near the recording material outlet of the press contact portion.
Temperature detecting means, and the cooling means based on detection information of the temperature detecting means.
And cooling control means for controlling the cooling capacity of the
A fixing device characterized by the above-mentioned. 11. The fixing device according to claim 9 , wherein said cooling means is provided in a region surrounded by a pressure belt and a pressure roller.