JP2003295683A - Image forming device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent toner accumulation in the thermistor portion by soft on-demand fixing and prevent the fixing roller from being damaged. A thermistor is provided downstream of a heater on a fixing roller and upstream of a fixing nip in soft-on-demand fixing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic printer, a copying machine, and a heat fixing device used in an electrostatic recording device.

[0002]

2. Description of the Related Art Conventionally, in a fixing device provided in an image forming apparatus adopting an electrophotographic system, an electrostatic recording system, etc., a recording material carrying an unfixed toner image is pressed against each other to rotate a fixing roller. A heat fixing device of a so-called heat roller type is widely used in which a permanent image is fixed on a recording material by passing through a nip portion formed by a pressure roller and a pressure roller. FIG. 10A shows a schematic configuration of the heat roller type heat fixing device. The fixing roller 60 is provided with a heating body 62 such as a halogen lamp in a hollow cored bar 61 made of aluminum or stainless steel, and a releasable layer 63 such as a fluororesin for preventing toner offset on the outer surface.
It is equipped with.

Further, the pressure roller 50 has an elastic layer formed of silicone rubber or the like or a sponge elastic layer 52 formed by foaming silicone rubber on the outside of the core 51.
Further, on the outer layer thereof, a releasable layer 53 such as a fluororesin similar to the fixing roller 60 is formed. Further, in the case of an image forming apparatus using a high speed machine or color toner, in order to sufficiently satisfy the fixing property of the toner, as shown in FIG.
By providing the elastic layer 64 having a thickness of about mm, the toner is wrapped on the surface of the fixing roller which is softened, thereby improving the heat transfer efficiency to the recording material and the toner.

However, while reduction in power consumption is strongly desired as one of environmental problems in recent years, high image quality and high-speed image output are desired due to market needs.
Therefore, in order to meet such demands for reduction of power consumption and high speed / high image quality, various improvements have been made to the above heat roller type heat fixing device.

First, for the purpose of shortening the temperature rising time of the fixing roller 60 and reducing the power consumption, a heating element 62 is arranged on the outer surface of the fixing roller 60 and the pressure roller 50 as shown in FIG. An example of a heat fixing device having low power consumption and high thermal efficiency by heating only the outer surface is disclosed in JP-A-10-301.
No. 417 / Japanese Patent Laid-Open No. 11-073050. The heating element 62 arranged on the outer surface of the fixing roller 60 is roughly classified into one in contact with the fixing roller 60 and one in non-contact with the fixing roller 60. High propagation efficiency. Also, the heating element 6
2 is a type in which a halogen lamp 66 is provided in the hollow cored bar 65, or a heating resistance layer via an insulating layer 67 such as an organic resin such as polyimide or glass on the inner surface of the hollow cored bar 65 as shown in FIG. There is a heat roller type with 68.

On the other hand, a method in which electric power is not supplied to the heating and fixing device during standby, so that power consumption is kept as low as possible,
More specifically, an example of a heat fixing method by a film heating method for fixing a toner image on a recording material through a thin film having a small heat capacity between a heater unit and a pressure roller is disclosed in Japanese Patent Laid-Open No. Sho 63-63.
-313182, JP-A-2-157878, JP-A-4-44075, and JP-A-4-20498
0 publication etc. FIG. 8 shows a schematic configuration of an example of the film heating method. That is, in FIG. 7, a heater 71 having a heating resistance layer formed on a ceramic plate such as alumina or aluminum nitride is a stay holder (support) 7.
Heat-resistant thin film of polyimide or the like fixed to No. 2 and adhered to the heater 71 (hereinafter referred to as a fixing film)
73 and the pressure roller 5 that is pressed against the film with the film sandwiched therebetween.
Has 0. The fixing film 73 is brought into close contact with the heater 71 surface at the fixing nip portion by the rotating force of the pressure roller 50.
While sliding, it is transported in the direction of the arrow. The temperature of the heater 71 is detected by a temperature detecting means 74 installed on the back surface of the heater and fed back to an energization control unit (not shown) to heat and regulate the heater temperature to a constant temperature (fixing temperature). Various image forming apparatuses such as printers and copiers that use such a film heating type fixing device eliminate the need for preheating during standby and shorten the wait time due to high heating efficiency and rising speed. It has many advantages over the conventional method of heating and fixing using a heat roller or the like.

[0007]

However, even the above-described conventional heating and fixing apparatus achieves excellent performance in shortening the temperature rising time at startup, reducing power consumption, high speed and high image quality. Things are very difficult. For example, when considering a film heating method, it is very excellent in shortening the rise time and reducing the power consumption, but there are the following problems when the speed is increased. First, since an organic heat-resistant resin such as polyimide is used for the fixing film, the heat conductivity is poor, and it is impossible to supply a sufficient amount of heat to the recording material when speeding up. In other words, even if the heat heater generates as much heat as possible without causing any practical problems, the heat is insulated by the thin film and cannot be efficiently transferred onto the recording material and the toner.

Further, as a problem that appears remarkably when the speed is increased, there is image deterioration. Even if the unfixed toner image formed on the recording material has high image quality, the image is often deteriorated due to the heat fixing device. In particular, in the above-mentioned film heating method, since the fixing film is driven to rotate by the rotational drive of the pressure roller, there is a problem that the speed of the film is delayed with respect to the rotational speed of the pressure roller with the increase in speed, and It leads to deterioration. Also, when heat-fixing a recording material with rough surface irregularities, the surface of the metal tube, etc. is hard, so the contact with the concave part of the paper becomes poor, and sufficient heat cannot be transferred to the recording material, and the toner image surface becomes rough. To do. Such a problem is also a problem that occurs in a heat roller type heat fixing device, and it does not have an elastic layer on the surface as shown in FIG. 10A, and only a release layer is provided on a metal cored bar. With the fixing roller (hard roller), the roughness of the image remarkably appears as the speed increases.

Considering the above problems, it is an essential condition to have an elastic layer as a fixing roller in order to cope with high speed. If a heat fixing device that can handle higher speeds is selected based on this condition, the heat roller type heat fixing device with a conventional elastic layer will have an overwhelmingly long temperature rising time for the fixing roller and supply power even during standby. The power consumption is large because of the need for the configuration, which is disadvantageous to the environment and market needs.

Further, in the method of heating the surface of the fixing roller from the outside as shown in FIG. 11, the heating time is shortened and the power saving is improved as compared with the conventional heat roller method, but the film heating method is used. Performance is inferior to those of. One of the causes is that when the heating member for heating the surface of the fixing roller (hereinafter referred to as a heat roller) has a halogen heater or the like in a hollow core metal as shown in FIG. 11, the core metal is a halogen heater. Since the temperature is raised by the radiant heat of the heat roller, it takes time to warm the heat roller itself.

Further, as shown in FIG. 9, in the heat roller having the heating resistance layer 68 on the inner surface of the metal pipe 65 via the insulating layer 67, the heat roller rises earlier than the type in which the temperature is raised by the halogen heater. With such a roller-shaped heating member, heat can be supplied to the fixing roller only in the nip portion formed by pressure contact between the heat roller 62 and the fixing roller 60, and the portions other than the nip portion are in contact with each other. Since the heat is dissipated to the outside air, the heat supply becomes inefficient. If the heating and fixing process speed is slow, the heat on the surface of the fixing roller, which is lost by the passage of the recording material, can be compensated by the heat supply from the heat roller, but as the speed increases, the heat supply from the heat roller It is thought that it will not be enough in time. Therefore, the method of externally heating the fixing roller with the roller-shaped heater is considered to have a limit in increasing the speed. Further, the pressure roller 50 shown in FIG. 10 also stores heat via the fixing roller 60, which is a cause of delaying the rising temperature rising time.

From the above, a heat fixing device capable of high-speed and high-quality image output while maintaining reduction of power consumption and shortening of temperature rising time is not possible with the structure proposed hitherto. is there. In order to solve the above problems, the present applicant has filed an invention characterized by the following.

The fixing roller has an elastic layer, a heating member that contacts the fixing roller from the outer surface to form a heating nip portion, and a pressing member that presses the fixing roller to form the fixing nip portion. The recording material on which the unfixed toner image is formed is nipped and conveyed in the fixing nip portion to perform heat fixing. The heater provided in the heating member has a plate shape with a low heat capacity and rubs against the heating nip portion to generate heat.
The pressing member has a low heat capacity thin film and a stay holder for externally fitting the thin film. The heater forming the pressing member is formed in a curved shape so as to extend along the outer diameter of the fixing roller. The outer surface of the fixing roller is provided with a means for detecting the surface temperature. An oil application mechanism for applying oil to the outer surface of the fixing roller is provided.

In the above-mentioned application, the surface temperature detection of the fixing roller is provided upstream of the heating member in the rotating direction of the fixing roller. This is because the temperature of the fixing roller is directly controlled by providing the surface temperature detecting element on the fixing roller. However, since the toner is after the fixing nip, the toner that is offset at the fixing nip and adheres to the fixing roller collects on the temperature detecting element. There is. When the toner accumulates, the toner that solidifies when it cools damages the fixing roller immediately after the operation starts,
There may be an error in the detected temperature.

An object of the present invention is to provide a fixing device capable of stably controlling the fixing temperature control and obtaining good fixing property.

[0016]

In order to solve the above problems, the invention according to the present application is characterized by the following.

The fixing roller has an elastic layer, a heating member that contacts the fixing roller from the outer surface to form a heating nip portion, and a pressure member that presses the fixing roller to form the fixing nip portion. In a heat fixing device that performs heat fixing by nipping and transporting a recording material on which an unfixed toner image is formed in a nip portion, a temperature detecting unit in contact with an outer surface of a fixing roller is provided downstream of a heating member in a rotating direction of the fixing roller. Installed upstream from the fixing nip.

In this structure, the temperature immediately before the fixing nip is controlled so that the fixing roller rushes into the fixing nip at the optimum temperature, so that the nip temperature at the time of fixing is always kept constant. As a result, even if the toner is offset on the film at the fixing nip, the offset toner is stopped by the heater so that it does not reach the temperature detecting element. Therefore, even if a contact-type temperature detecting element is used instead of a non-contact type as the temperature detecting element, the toner accumulated in the contact portion spills and stains the image, or the toner accumulated in the detecting portion cools and solidifies on the fixing roller. Since there is no scratch, there is an advantage that there is no image defect due to it. By the way, since the toner accumulated in the heater is heated and melted, there is no fear of damaging the fixing roller.

In the present invention, the temperature in the vicinity of the fixing nip where the actual fixing operation is performed can be temperature-controlled, and the toner is not accumulated in the temperature detecting element, so that there is no error in the detected temperature and stable fixing is performed. You can get sex.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) An embodiment according to the present invention will be described below. First, FIG. 1 is a configuration diagram of an image forming apparatus according to the present invention. In FIG. 1, reference numeral 1 is a photosensitive drum, which is OPC, amorphous Se, or amorphous Si.
Is formed on a cylindrical base made of aluminum or nickel. The photosensitive drum 1 is rotationally driven in the direction of the arrow, and its surface is first uniformly charged by a charging roller 2 as a charging device. Next, scanning exposure is performed by the laser beam 3 whose ON / OFF is controlled according to the image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a developing method, a jumping developing method, a two-component developing method, an FEED developing method, or the like is used, and image exposure and reversal developing are often used in combination.

The visualized toner image is transferred from the photosensitive drum 1 onto the recording material P conveyed at a predetermined timing by a transfer roller 5 as a transfer device. Here, the sensor 8 detects the leading edge of the recording material so that the image forming position of the toner image on the photosensitive drum 1 and the writing start position of the leading edge of the recording material match, and the timing is adjusted. The recording material P conveyed at a predetermined timing is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressure. The recording material P to which the toner image is transferred is conveyed to the fixing device 6 and fixed as a permanent image. On the other hand, transfer residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

FIG. 2 shows the structure of the heat fixing device 6 according to the present invention. In FIG. 2, the fixing roller 10 is composed of the following members. An elastic layer (solid rubber layer) formed of silicone rubber on the outside of the core bar 11 made of aluminum or iron, or an elastic layer (sponge rubber layer) formed by foaming silicone rubber to have a more heat insulating effect, Alternatively, an elastic layer (cellular rubber layer) with enhanced heat insulation by dispersing air bubbles in the silicone rubber layer by some method
It consists of 12. However, if the heat capacity of the fixing roller 10 is large and the thermal conductivity is large even a little, the heat received from the outer surface is easily absorbed, and the surface temperature hardly rises.

A material having a heat capacity as low as possible and a low thermal conductivity and a high heat insulating effect is more advantageous for the rise time of the surface temperature of the fixing roller. Here, the solid rubber of the silicone rubber has a thermal conductivity of 0.25 to 0.29 W / m ·
K, sponge rubber / cellular rubber 0.11-0.16W /
m · K, and sponge rubber / cellular rubber shows a value about half that of solid rubber. Further, the specific gravity relating to the heat capacity is about 1.05 to 1.30 for solid rubber and about 0.75 to 0.85 for sponge rubber / cellular rubber. Therefore, a preferable form of the elastic layer has a thermal conductivity of about 0.15 W.
A sponge rubber layer or a foam rubber layer having a specific gravity of 0.85 or less and having a high heat insulation effect is preferable.

Further, the smaller the outer diameter of the fixing roller 10 is, the more the heat capacity can be suppressed. However, if the outer diameter is too small, the heating nip is hard to obtain, so that the proper diameter is required. As for the wall thickness of the elastic layer, if it is too thin, the heat will escape to the metal cored bar, so that an appropriate thickness is required. In consideration of the above, in this embodiment,
In order to form a proper heating nip and to suppress the heat capacity, an elastic layer is formed using foam rubber with a wall thickness of 4 mm,
A fixing roller having an outer diameter of 20 mm was used. Further, the cored bar 11 may be a hollow cored bar as described in the conventional example of FIG. On the elastic layer described above, the fluororesin release layer 13 such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP) is formed. The release layer 13 may be either coated on the tube or coated on the surface with a paint.

The heating member 20 is composed of the following members. A heating heater 21 heats the surface of the fixing roller 10. The heater 21 for heating is, for example, Ag / Pd (silver palladium), RuO ₂ , T on the surface of a highly insulating ceramic substrate such as alumina or aluminum nitride along the longitudinal direction.
a ₂ N etc. energization heating resistance layer by screen printing etc.
It is a member for electric heating that is formed by coating in a linear or strip shape having a thickness of about 10 μm and a width of about 1 to 5 mm. It is preferable to provide a protective sliding layer on the surface of the heater 21 for heating so that the release layer of the fixing roller 10 does not wear due to rubbing. As an example, perfluoroalkoxy resin (P
FA), polytetrafluoroethylene resin (PTF
E), tetrafluoroethylene-hexafluoropropylene resin (FEP), ethylene tetrafluoroethylene resin (ETFE), polychlorotrifluoroethylene resin (CTEF), polyvinylidene fluoride (PVD)
A fluorine resin layer such as F) may be coated alone or in a mixture, or a dry coating lubricant made of graphite, diamond-like carbon (DLC), molybdenum disulfide or the like, or a protective layer such as a glass coat may be used.

Reference numeral 22 is a heat insulating stay holder for holding the heater 21 for heating. Pressure is applied to the fixing roller 10 by a pressing means (not shown), and a heating nip N is formed between the heating heater 21 and the fixing roller 10 by the applied pressure. The heat insulating stay holder 22 has a role of preventing heat radiation in a direction opposite to the heating nip N, and is made of liquid crystal polymer, phenol resin, PPS, PEEK, or the like.

Further, a temperature detecting element 23 such as a thermistor for detecting the temperature of the fixing roller 10 is provided.
Is disposed downstream of the heater 22 and upstream of the fixing nip M. By appropriately controlling the duty ratio, the wave number, etc. of the voltage applied to the energization heating resistance layer from the electrode portion (not shown) at the end portion in the longitudinal direction of the heater 21, in accordance with the signal of the temperature detecting element 23, The heater 21 is caused to generate heat to heat and control the surface of the fixing roller 10. The thermistor is a heat-resistant elastic material such as ceramic paper or a leaf spring, and is appropriately pressed to contact and press the fixing roller 10. DC energization from the temperature detection element 23 to the temperature control unit (not shown) is achieved by a connector (not shown) via a DC energizing unit (not shown) and a DC electrode unit.

The pressing member 30 has the following structure.
Reference numeral 33 is a sliding film, which has heat-resistant and thermoplastic polyimide, polyamide-imide, PEEK, PES, P
It is a resin film having a base layer of PS, PFA, PTFE, FEP or the like. Considering strength, etc., the film thickness
An appropriate range is 20 μm or more and less than 150 μm. In addition, PFA, PTFE, FEP, and
A heat-resistant resin having a good releasing property such as a silicone resin is mixed or coated alone. Further, 31 is a sliding plate provided inside the sliding film, and 32 is a heat insulating stay holder holding the sliding plate 31. The heat insulating stay holder 32 is pressed against the fixing roller by a pressing means (not shown), and a nip M necessary for fixing is formed between the sliding plate 31 and the fixing roller 10 via the sliding film 33. There is. The heat insulating stay holder 32 is formed of liquid crystal polymer, phenol resin, PPS, PEEK, or the like as a resin having heat insulating properties and heat resistance similar to the stay holder 22 of the heating member.

The sliding plate 31 is made of a material having a small friction with the sliding film 33 and a heat insulating property, such as a liquid crystal polymer, a phenol resin, or the like as the stay holder 32.
It is desirable to form it by PPS, PEEK, or the like, and coat the surface thereof with a sliding layer that reduces frictional resistance. An example thereof is the same as that of the sliding layer provided on the surface of the heater 21, and therefore description thereof is omitted. Here, the sliding plate 31 and the heat insulating stay holder 32 are treated as separate members, but they may be formed by integral molding and the sliding portion may be coated with the above-mentioned sliding layer, and the cost can be further reduced. Is possible. In addition, a small amount of a lubricant such as grease is interposed between the sliding film 33 and the sliding plate 31 in order to suppress the friction resistance.

In such a structure, the fixing roller 10
Is rotationally driven in the direction of the arrow from the end in the longitudinal direction through the cored bar 11 by rotational drive (not shown). As a result, the sliding film 33 is rotated outside the stay holder 32 in the direction of the arrow in the figure. The above is the configuration of the heat fixing device of the present embodiment, but the recording material P is appropriately supplied by the supply means (not shown), and is formed by the fixing roller 10 and the pressing member 30 along the heat resistant fixing inlet guide 15. And is conveyed into the fixing nip M. After that, the recording material P discharged from the fixing nip is guided by the heat-resistant fixing paper discharge guide 16, is sandwiched and conveyed by the paper discharge roller 17 and the paper discharge roller 18, and is discharged onto a discharge tray (not shown).

The apparatus of this embodiment has a process speed of 150 mm / sec and is capable of printing 25 sheets per minute. The resistance value of the heater is 12.5Ω
Then, the power when operated at a voltage of 100V is 800W.
Is. This is in the state of full energization, and it is set to 0, 2.5, every 2.5% by known wave number control or phase control.
5,7.5,10, ..., 95,97.5,100%
As described above, the energization power to the heater is controlled by controlling the energization duty. In this embodiment, the surface temperature of the fixing roller for fixing is 200 ° C. The fixing device is started up from room temperature so that the temperature becomes 200 ° C.

With respect to the fixing roller temperature T detected by the thermistor 23 at that time, the target temperature T1 is 20
To safely start up to 0 ° C, for example, set T1 to T + 1
The temperature is rewritten one after another and the temperature is raised like ℃ / 40 msec. 40 msec if the initial temperature of the fixing roller is 20 ° C
The target temperature T1 after that is 21 ° C., and the target temperature after 80 msec is 22 ° C. 20 ° C to 200 ° C
Even though the target temperature rises up to (200-20) x 0.0
It takes 4 = 7.2 seconds.

In the configuration of the present invention, since there is a distance from the heater to the thermistor, there is a time lag from the heating of the heater to the detection by the thermistor. In this embodiment, the distance is 10 mm, so the process speed is 150 mm / se.
The fixing roller rotating at c has a time lag of about 67 msec. Further, since the outer diameter of the fixing roller is 20 mm, it takes about 419 msec for one rotation of the fixing roller. In the present configuration, strictly speaking, the temperature rise of the fixing roller is not continuous, but the first and second rounds of the fixing roller ...
There is a characteristic that it rises like a staircase.

In the energized state in this embodiment, the duty is determined by proportional control and integral control with respect to the difference between the actual fixing roller temperature T detected by the thermistor 23 and the target temperature T1.

(1) Proportional control The difference T1-T between the fixing roller temperature T and the target temperature T1 is set to 2.
The value obtained by multiplying by 5% is added to change the energization state as a new energization duty. That is, the current duty
Is duty0 and the new duty is duty1,
The duty is changed in the manner of duty1 = duty0 + (T1-T) × 2.5.

When starting from room temperature, first dut
The initial value of y0 is, for example, 40%. This initial value is 40%
Is maintained for 67 msec until the heating start portion of the fixing roller reaches the thermistor. Then, proportional control is started. That is, if the initial temperature of the fixing roller is 20 ° C., 40
The target temperature T1 after msec is 21 ° C., and the difference T1-T
Is 1 ° C, duty1 = duty0 + 2.5% = 40 + 2.5% =
Change the energization duty to the heater to 42.5%. This control is always performed. Specifically, in this embodiment, the control is performed every 40 msec, and the proportional control is performed about 10 times during the time of 419 msec for one rotation of the fixing roller. The temperature of the fixing roller gradually rises during this time due to the increase in the amount of heat generated by the heater, but the temperature of the fixing roller rises stepwise after 419 msec when the second round of the fixing roller reaches the thermistor.

In this embodiment, the target temperature change interval is 40 msec and the energization duty change range of the proportional control is 2.5% so that the energization control does not oscillate due to the time lag between the heater and the thermistor. If this is made too large, there is a risk that the feedback of the temperature detection will not be in time and the control will oscillate.

(2) Integral control When the relationship between the fixing roller temperature T and the target temperature T1 is maintained for a predetermined time or below, the duty is adjusted by 10%.

When T1> T, duty1 = duty0 + 10% When T1 <T, duty1 = duty0-10% In the present embodiment, the integral control is performed for each rotation of the fixing roller, that is, 41.
It goes every 9 msec. With this, the energization duty determined by the proportional control is corrected. The energization of the heater is controlled by the duty formula based on the above proportional control and integral control.

An experiment was carried out by printing an image forming apparatus using the heat fixing device described above. FIG. 3 shows a state in which the fixing device in the room temperature state is raised to the controlled temperature in the apparatus of this embodiment, and is a graph in which the detected temperature of the controlled temperature thermistor in contact with the fixing roller is monitored. According to the present invention, the thermistor temperature is 2 at the point indicated by A on the time axis of the figure.
Reach 00 ° C. The time was about 8 seconds.
The electric power supplied to the heater increases to about 600 to 800 W at 320 W at the start of energization. After reaching 200 ° C., the power is reduced and reduced to about 300 to 400 W.
In FIG. 3, the fixing roller temperature is 2 because the paper is not passed.
After reaching 00 ℃, overshoot and at point B, 2
It reached 20 ° C. In the fixing device of the present invention, the fixing operation can be started in about 8 seconds after the fixing device is started up, and in reality, the paper is fed at such a timing that the paper enters the fixing nip.

Next, FIG. 4 shows the temperatures at which the fixing device of the present invention reaches the target temperature-controlled temperature of 200 ° C. and paper is actually fixed by the paper rushing into the fixing device. The rising portion is the same as in FIG. 3, and the paper enters the fixing nip at the timing C when the fixing roller reaches 200 ° C. It is timing F when the trailing edge of the paper leaves the fixing nip. After the paper enters at the timing of C, the heat of the fixing roller is removed and the fixing roller cools. The detected temperature is slightly lowered at the timing D when the cooled portion passes through the heater and reaches the thermistor position. The electric power supplied to the heater during paper passing was about 600 W.

In the present invention, the idea is to control the temperature of the fixing roller toward the nip to a required temperature. Even if the paper actually enters the nip, the temperature of the fixing roller does not fluctuate greatly and the paper passes through the fixing device. The temperature was stable until the timing. When the paper with an unfixed image was fixed by the apparatus of the present invention, good fixing results were obtained.

A print durability test was conducted using the apparatus of the present invention. As a result of the thermistor being provided downstream of the heater, all the toner stains can be dammed by the heater even when printing 100,000 sheets. There wasn't. In the comparative example in which the thermistor 101 shown in FIG. 5 is located downstream of the fixing nip and upstream of the heater, 5000
When the number of sheets was 1, dirt was accumulated, and when 10,000 sheets, the solidified toner was cooled and the fixing roller was damaged, resulting in an image defect. The results are shown in the table.

[0044]

[Table 1] As described above, by providing the temperature adjusting thermistor of the fixing roller downstream of the heater and upstream of the fixing nip, the temperature is controlled near the fixing nip. Therefore, stable temperature control of the fixing roller can be performed by a simple method. It was possible to obtain good fixing property without toner stain.

(Second Embodiment) In the present embodiment, when a special mode is provided for temperature control and a large amount of heat is required, such as thick paper, the corresponding position of the fixing roller where the leading edge of the paper enters the fixing nip is the heater. The feature is that the temperature control temperature is changed to a higher value at the timing of passing through. FIG. 6 shows a cross-sectional view of the fixing device of this embodiment when the thick paper is being fed.

FIG. 7 is a graph showing a temperature change of the thermistor 23 in the apparatus of the first embodiment when a fixing device reaches a fixing temperature of 200 ° C. and one thick paper is fixed by a solid line. At timing C in the graph, the temperature control temperature is increased by 10 ° C. and changed to 210 ° C. at the moment when the thick paper with the unfixed image enters the fixing nip is at the heater part. As a result, the electric power supplied to the heater is increased based on the above-described heater energization control, and the fixing roller temperature can be raised corresponding to the portion where the paper is fixed in advance. On the other hand, the graph shown by the dotted line is the one in which thick paper is fixed under the control of the first embodiment. Since it is thick paper, more heat is taken away than in the case shown in FIG. 4, and the amount of temperature decrease is large.

As in the present embodiment, by increasing the temperature control temperature in accordance with the fixing start timing when the thick paper is passed, it is possible to obtain a sufficient fixability. As described above, the contact type thermistor has been described so far, but a non-contact type thermistor can also obtain good results by installing it in the same position.

[0048]

As described above, according to the present invention, the temperature control of the fixing roller is provided downstream of the heater and upstream of the fixing nip, so that the thermistor does not collect toner stains and has a good fixing property. I was able to get

[Brief description of drawings]

FIG. 1 is a schematic view of an image forming apparatus according to the present invention.

FIG. 2 is a schematic view of a fixing device according to the present invention.

FIG. 3 is a diagram of thermistor sensed temperature according to the present invention.

FIG. 4 is a diagram of thermistor sensed temperature according to the present invention.

FIG. 5 is a schematic view of a fixing device according to a comparative example.

FIG. 6 is a schematic view of a fixing device according to the present invention.

FIG. 7 is a diagram of thermistor sensed temperature according to the present invention.

FIG. 8 is a schematic view of a fixing device according to a conventional example.

FIG. 9 is a schematic view of a fixing roller according to a conventional example.

FIG. 10 is a schematic view of a fixing device according to a conventional example.

FIG. 11 is a schematic view of a fixing device according to a conventional example.

[Explanation of symbols]

1 Photosensitive drum 2 ... Charging roller 3 ... Image exposure 4 ... Developer 5 ... Transfer roller 6 ... Fixer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Wataru Nihonyanagi             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Hiroto Hasegawa             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F term (reference) 2H033 AA18 BA25 BA26 BA30 BA32                       BB05 BB06 BB15 BB18 BB21                       BB23 BE03 CA03 CA07 CA28                       CA48

Claims (2)

[Claims] 1. A fixing roller having an elastic layer, a heating member fixedly arranged to come into contact with the fixing roller from an outer surface to form a heating nip portion, and a pressure member to come into pressure contact with the fixing roller to form a fixing nip portion. In a heat fixing device that has a member and performs heat fixing by sandwiching and transporting a recording material on which an unfixed toner image is formed in a fixing nip portion, a temperature detecting unit is fixed downstream from a heating member in a rotation direction of a fixing roller. An image forming apparatus having a fixing device provided upstream of the nip and detecting the temperature of the outer surface of the fixing roller. 2. The fixing device according to claim 1, wherein the temperature detecting means is in contact with the fixing roller.