JP2000305406A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device being excellent in energy efficiency by improving the non-paper passing part temp. rise, preventing the pressure roller dirt from occurring, and minimizing the power consumption at the time other than the image forming time. SOLUTION: This fixing device is constituted so as to hold traveling film 65 in contact with a heating element 61 provided with a heating resistor, to hold the film 65 press contact with the heating element 61 by the pressure roller 7, and to fix the toner image carried on recording material made passing through between the film 65 abutted with the heating element 61 and the roller 7, and is provided with rollers 91 and 97 being freely held in contact or uncontact with regard to the pressure roller 7, and the roller 91 is provided with the temp. controlling function of the pressure roller, and moreover the roller 97 is provided with the cleaning function of the pressure roller 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer for forming an image by an electrostatic recording method, an electrophotographic method or the like, and a fixing device used in the image forming apparatus. .

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrostatic recording apparatus, an electrophotographic apparatus, etc., an unfixed image is fixed by fixing a fixing roller made of aluminum, iron or the like containing a halogen heater or the like to an elastic layer on a surface layer. The recording material having an unfixed image formed thereon is guided to the fixing nip formed by the pressure roller having the pressure roller, and the two rollers are rotationally driven to pinch and convey the recording material. Generally, fixing is performed.

However, in the fixing roller system, the time required to raise the surface of the fixing roller from room temperature to a temperature at which the fixing roller can be fixed takes several tens seconds to several minutes due to the heat capacity of the fixing roller and the pressure roller. Therefore, it is difficult to output an image immediately after turning on the power to the image forming apparatus.

Further, in order to quickly output an image when an image forming command is input, it is necessary to maintain the fixing roller temperature at a certain temperature while the apparatus is on standby. Although it does not directly contribute to the formation, there is a problem that energy must be consumed to improve usability.

To reduce power consumption during standby and to reduce the time from power-on to image output, Japanese Patent Laid-Open Publication No.
As disclosed in JP-A-313182, JP-A-2-157778, etc., at least a fixedly supported heater (heater) and a heat-resistant film (fixing film) conveyed while being pressed against the heater. A heater unit comprising: and a heat-resistant film of the heater unit, on the surface of the heat-resistant film, has a pressing member for bringing the recording material into close contact, by applying the heat of the heater to the recording material through the film to the recording material surface A fixing device of a film heat fixing system for fixing an unfixed image that has been formed has been proposed.

Referring to FIGS. 5, 6, and 7, an image forming apparatus using the conventional film-heating type fixing device will be schematically described. FIG. 5 is a schematic view of a laser beam printer (LBP) using an electrophotographic system, FIG. 6 is a schematic sectional view of the fixing device, FIG. 7 is a front view of a fixing heater, and shows a power supply and wiring to a CPU. FIG.

First, in FIG. 5, reference numeral 1 denotes a photosensitive drum (OPC) which is an image carrier having an organic photosensitive layer formed on a surface thereof;
Reference numeral 2 denotes a charging roller which is a charging member for uniformly charging the surface of the photosensitive drum, and 3 denotes a laser exposure for outputting a laser whose intensity is deviated in accordance with an image signal to form an electrostatic latent image on the photosensitive drum 1. The device 4 is a developing device for visualizing the electrostatic latent image as a toner image, and includes a developing sleeve, a developing blade, a one-component magnetic toner, and the like.

The recording material is stored in a cassette 11,
The sheet is fed by driving the sheet feeding roller 10 in accordance with the image forming signal, and is sent to the toner image transfer section after registration adjustment is performed by the registration roller 13.

Reference numeral 5 denotes a transfer roller for transferring the toner image onto the recording material 20, and reference numeral 8 denotes a cleaning blade for removing transfer residual toner remaining on the photosensitive drum 1.
After the transfer of the toner image, the recording material is sent to a fixing device including a fixing heater unit 6, a pressure roller 7, and the like, and is discharged after an unfixed toner image is fixed.

FIG. 6 is a diagram showing a cross section of a main part of the film heating type fixing device. Reference numeral 61 denotes a resistance heating element, a thermistor 605, and a ceramic substrate such as alumina or aluminum nitride.
A fixing heater having electrodes and the like; 62, a film guide made of PPS, liquid crystal polymer, etc .; 63, a reinforcing sheet metal for suppressing deflection of the film guide 62 and the heater 61 due to pressure; and 65, a polyimide resin with a filler dispersed therein This is a fixing film in which a primer layer and a fluororesin layer made of PTFE or PFA are formed on a heat-resistant film having a thickness of 30 to 100 μm, and a fixing heater unit 6 is composed of the above main components.

The temperature of the fixing heater 61 is controlled by taking an output of a temperature sensor such as a thermistor 605 adhered or pressed onto the heater into the CPU 100, and energizing the AC power supply 80 according to the value. The control is performed by driving the triac 85.

The pressure roller 7 includes a metal core 71 made of aluminum, iron, or the like, and an elastic layer 73 made of silicon rubber, fluorine rubber, or the like.
A release layer composed of a P coat, a coating of a PFA tube, and the like is formed.

The fixing heater unit and the pressure roller are pressed by a pressure unit (not shown) at a total pressure of 13 kgf to form a fixing nip. The recording material 20 is guided by the entrance guide 25 to the fixing nip, and is discharged by the paper discharge guide 26 in the paper discharge direction.

FIG. 7 is a front view of the fixing heater 61 and a diagram showing a wiring relationship among the CPU 100, the power supply 80, and the triac 85.

In FIG. 1, reference numeral 100 denotes a CPU for processing signals from various sensors in the printer and control signals from external devices.

The fixing heater 61 has a thickness of 0.635 mm.
Alumina substrate 601, resistance heating elements 602 and 603 made of Ag, Pd and the like formed on the surface thereof by screen printing to a thickness of about 10 μm, and the resistance heating element 60
2 and 603 in series, an electrode 612 of the resistance heating element 602, an electrode 613 of the resistance heating element 603, a thermistor 605 bonded to the back surface with a heat-resistant resin, and a conductive pattern. Electrodes 614, 615, etc. for detecting the thermistor resistance.
The surface of the resistance heating element is coated with a glass having a thickness of about 30 to 80 μm as a protective layer and an electric insulating layer.

After the A / D conversion, the resistance value of the thermistor is taken into the CPU 100, and based on the value, the triac 90 is driven through a control circuit (not shown), and the wave number control, the phase control, or the , The temperature control is performed.

By adopting the above main structure, the heat fixing method of the film (hereinafter referred to as a fixing film method) has a significantly lower heat capacity than the conventional fixing roller method.
The time required to elevate the fixing nip from room temperature to the feasible temperature can be reduced to 10 seconds or less. Therefore, there is no need to energize the fixing heater and to preheat the fixing member during standby, thereby consuming the apparatus. The power can be greatly reduced.

Further, since the thermal energy generated by the fixing heater can be directly transmitted to the transfer material via a fixing film having a low heat capacity, the thermal efficiency is improved as compared with the fixing roller system, and even when the paper is passed, Sufficient fixing is possible with less power consumption.

However, the fixing film method has the following problems.

First, a first problem is related to a temperature rise in the non-sheet passing portion. In the fixing film system, a recording material shorter than the longitudinal width of the resistance heating element, for example, a longitudinal width 31
B4 size paper, LGL for resistance heating element of about 0mm
When a size paper, an envelope, a postcard, or the like is passed, the temperature of the paper passing section where the temperature control element (thermistor, etc.) is disposed is 15
Although the so-called fixing temperature of about 0 to 200 ° C. is maintained, in the non-sheet passing portion, heat generated by the resistance heating element is not taken away by the recording material. There is a problem that the temperature is significantly higher than the temperature of the paper passing portion.

This problem is caused by increasing the printing speed,
It becomes more serious as the output of the heating element per unit length is increased.

Although the occurrence of this problem is basically the same in the fixing roller system, there is an air layer between the heater and the fixing roller, and heat is transmitted by radiation as compared with the fixing film system. Since the fixing roller made of aluminum or iron has higher heat conductivity and is thicker than the fixing film or the film guide made of heat-resistant resin, the heat conductivity in the longitudinal direction becomes larger, so that the fixing roller and the film guide are almost the same. Comparing the printing speeds of the above devices, the problem is more serious in the fixing film system.

The second problem is related to pressure roller contamination. At the time of fixing, it is preferable that all of the toner on the recording material is fixed on the recording material. However, a toner layer having an arbitrary area and a thickness distribution in a range of about 0 to 100 μm is preferably formed on the transfer material. In the fixing nip, it is difficult to completely soften and melt completely uniformly.If the melting is partially insufficient and the adhesion to the recording material is insufficient, a cold offset occurs and the melting becomes excessive. In this case, hot offset occurs, and it is difficult to completely eliminate them.

Further, when the fixing roller and the fixing film are charged by friction between the rollers and the recording material, the toner may be electrostatically offset. The offset toner is transferred to the recording material or the toner on the recording material and is discharged, or transferred to the pressure roller, or accumulates on the fixing roller or the fixing film as it is, thereby causing image contamination. , Fusing roller,
It may cause fouling of the fixing film and the pressure roller.

Usually, the fixing roller, the fixing film,
The pressure roller is designed to minimize the offset,
After being coated with a fluororesin coat or tube such as PTFE, PFA, FEP with excellent release properties, the fixing temperature is
The cold offset and the hot offset are set so as to fall within a level that cannot be visually confirmed on the recording material.

However, if image formation is repeated for thousands or tens of thousands of sheets for the above-described reason, even if the amount of offset toner per sheet is small, it is accumulated on the fixing roller, the fixing film, and the pressure roller. However, this reduces the releasability of the roller or the film, causing a paper jam or suddenly adhering to the recording material.

Further, in the image forming apparatus employing the fixing film system, the time interval between print jobs becomes several minutes or more and the number of jobs becomes small compared with the fixing roller system for the reasons described above. The pressure roller surface temperature decreases.

In particular, when the number of prints performed in one job is about 1 to 3 sheets, the configuration of the pressure roller is also inconvenient, but generally the maximum temperature is 60 to 90 ° C. When the job is completed, the temperature of the pressure roller decreases toward room temperature.

The offset toner adhering to the fixing roller or the fixing film has a high temperature at the time of fixing on the roller surface or the film surface. Therefore, at least the toner adhering to the roller surface or the film surface is melted in the fixing nip, and the recording material While the toner is easily transferred to the toner image on the recording material, the toner transferred from the fixing film to the surface of the pressure roller, the surface of the pressure roller does not become so hot, and almost no Since there is no toner, there is a problem that the toner is not easily transferred to the recording material and is easily accumulated.

In particular, as a filler for a recording material, calcium carbonate, which has high whiteness and stiffness and is low in cost, is used.
When so-called charcoal paper used at about 15% is used, the releasability of the pressure roller is reduced, and the pressure roller dirt becomes worse.

According to the study of the present inventors, the adhesion of calcium carbonate to the pressure roller tends to increase in a low humidity environment, and the toner and calcium carbonate stain on the surface of the pressure roller deteriorate in a low temperature environment. I do.

[0033]

As a countermeasure against the above two problems, a metal roller made of aluminum or iron, or a roller coated with a resin on the metal roller is pressed against the pressure roller to prevent the pressure roller from passing. A method has been proposed and implemented in which the temperature rise of the paper portion is reduced, and at the same time, the toner or the like adhered to the pressure roller is adhered to the metal roller and used as a cleaning roller.

Further, the cleaning roller is configured to be able to be separated from the pressure roller, and is appropriately separated and pressed according to the number of prints and the temperature from temperature detecting means such as a fixing roller. For example, when starting the heater,
There has been proposed a method in which the cleaning roller is separated from the pressure roller, and when the temperature of the heating member is sufficiently stabilized, the cleaning roller is pressed against the pressure roller (Japanese Patent Laid-Open No. 6-175520).

According to the study of the present inventors, however, the offset toner adhered to the fixing film or the fixing roller may be removed when the temperature difference between the temperature of the fixing film or the fixing roller and the temperature of the pressure roller is large in the fixing nip. In the case of a fixing film type fixing device, in the pre-rotation when the pressure roller temperature starts image formation from about room temperature, especially in an environment where the room temperature is relatively low at 15 ° C. or less, the pressure roller The result that it is easy to transfer is obtained.

Therefore, in the means and configuration as in the above-mentioned conventional example, the toner stains on the pressure roller and the cleaning roller must be appropriately melted and adhered to the cleaning roller before the toner stains from the cleaning roller. There is a problem in that the film is peeled off, and the stain is electrostatically attached to the pressure roller, then transferred to the recording material, and becomes an image stain.

In actual use, continuous printing of several tens of sheets, preferably 40 to 50 sheets or more is required to make the toner stain on the cleaning roller in a molten state, but such a print command is periodically issued. Is relatively rare in a medium-speed (4 to 50 ppm) image forming apparatus. In particular, in an apparatus of the 20 ppm class or less, most of the print commands are actually completed with one to three output.

Therefore, the conventional image forming apparatus having the cleaning roller in the fixing device has a memory for accumulating the number of prints, and performs a post-process (post-process) for each predetermined number of prints. Rotation)
It is necessary to perform post-processing such as extending the power supply to the heater and idling of the fixing device, and increasing the temperature of the cleaning roller to melt and fix the stained toner.

In general, the pressing force, the outer diameter, the torsional strength (the end is easier to twist) at the center and the end of the pressure roller,
Because the surface temperature, etc. are different, the end part is
The rubbing and deviation from the recording material (especially charcoal paper and talc paper) are increased, and the temperature is also lowered. Therefore, the amount of dirt tends to increase. The number of ends is larger than that of the part, and the pressing force concentrates on the increased part, for example, A3
In an apparatus capable of passing paper, if B4 paper, LGL paper, or the like is continuously passed in a state in which toner stains are accumulated, the toner stains on the cleaning roller due to the increase in the temperature of the non-sheet passing portion and the concentration of the pressing force. However, there is also a problem that the toner is re-transferred (backflow) to the pressure roller and the fixing film, and the recording material is stained.

The object of the invention according to the present invention is to solve the above-mentioned problems, that is, to greatly improve the temperature rise in the non-paper passing portion, not to cause pressure roller contamination, and to have excellent thermal efficiency. An object of the present invention is to provide an image forming apparatus which is excellent in energy efficiency while minimizing power consumption except during image formation.

[0041]

A first configuration of a fixing device for realizing the object of the invention according to the present application is such that a heating element having a heating resistor is brought into contact with a moving film, and the film is pressed by a pressing means. In a fixing device that is brought into pressure contact with the heating element to fix a toner image carried on a recording material passing between the film that is in contact with the heating element and the pressure means onto the recording material, Has at least two rotatable rollers that can freely contact and separate from the roller.

According to a second configuration of the fixing device for realizing the object of the invention according to the present application, in the first configuration, the one roller has a heat conductivity of 50 W / m / K or more, the other roller has a thermal conductivity of 1 W / m / K at a portion in contact with the pressing means.
It is as follows.

A third configuration of the fixing device for realizing the object of the present invention according to the present application is any one of the above configurations, further including a scraper that comes into contact with the other roller and removes a deposit on the surface.

According to a fourth configuration of the fixing device for realizing the object of the invention according to the present application, in the fixing device of the first or second configuration, the one roller and the other roller can be rotated. By attaching to a lever member and rotating the lever member, both rollers are selectively brought into contact with the pressing means, and both rollers are separated from each other so as to be in a non-contact state.

According to a fifth configuration of the fixing device for realizing the object of the invention according to the present application, in the third configuration, the one roller and the other roller are attached to a rotatable lever member. The scraper is attached to the lever member, and by rotating the lever member, both rollers are selectively brought into contact with the pressing means, and both rollers are separated from each other so as to be in a non-contact state. It is.

According to a sixth configuration of the fixing device for realizing the object of the invention according to the present application, in any one of the above configurations, the one roller is formed of any one of iron, aluminum, and copper. .

According to a seventh aspect of the present invention, there is provided a fixing device according to any one of the first to fifth aspects, wherein the other roller comprises a phenol resin, an epoxy resin, a polyimide resin, It is formed of any of polyphenyl sulfide.

According to an eighth aspect of the present invention, there is provided a fixing device according to any one of the above aspects, wherein a temperature detecting means for detecting a temperature of the heating element, and a sheet passing direction of the recording material. Controlling a size detection unit for detecting a length in a direction perpendicular to the recording medium, a driving unit for causing the plurality of rollers to contact and separate the pressurizing unit from the continuous number of sheets of the recording material, and controlling the driving unit Control means for controlling the temperature of the heating element, the width of the recording material in a direction orthogonal to the paper passing direction, and the number of continuous paper passing of the recording material as input information. Is controlled.

A ninth configuration of the fixing device for realizing the object of the invention according to the present application is the eighth configuration, wherein the control means is configured to control the temperature of the heating element at the start of energization to the heating element to a predetermined temperature. If it is lower than this, the driving means is driven so that the other roller is brought into contact with the pressure means at the time of pre-rotation.

A tenth configuration of the fixing device for realizing the object of the invention according to the present application is the ninth configuration, wherein the control unit is configured to control the recording material to have a width equal to or greater than a predetermined width, and In the case of paper, the other roller is brought into contact with the pressing means at the time of post-rotation.

An eleventh configuration of the fixing device for realizing the object of the invention according to the present application is the ninth configuration, wherein the control unit is configured to control a large number of sheets when the width of the recording material is smaller than a predetermined width. In the case of paper passing, the one roller is brought into contact with the pressing means from the middle number of the paper passing, and the driving means is controlled so as to separate the one roller from the pressing means at the time of post-rotation. It is like that.

A twelfth structure of the fixing device for realizing the object of the invention according to the present application is the eighth structure, wherein the control means controls the heating element temperature at the start of energization to the heating element to a predetermined temperature. If the width of the recording material is not less than a predetermined width and is not a small number of sheets, the driving is performed so that the one roller and the other roller are separated from the pressing unit. The means is driven.

A seventh configuration of the fixing device for realizing the object of the invention according to the present application is the eighth configuration, wherein the control unit is configured to control the heating element temperature at the start of energization to the heating element to a predetermined temperature. If the width of the recording material is greater than or equal to a predetermined width and a small number of sheets are passed, the other roller is brought into contact with the pressing unit at the time of pre-rotation, and is separated at the time of post-rotation. Thus, the driving means is driven.

A fourteenth configuration of the fixing device for realizing the object of the invention according to the present application is the eighth configuration, in which the control means controls the heating element temperature at the start of energization to the heating element to a predetermined temperature. If the width of the recording material is equal to or less than a predetermined width and a large number of sheets are passed, the one roller is brought into contact with the pressing unit from the middle of the sheet passing, and post-rotation is performed. The driving means is driven so as to be separated at times.

An image forming apparatus that achieves the object of the present invention according to the present application includes a fixing device having any one of the above-described configurations.

In the above-described configuration, when the heating element rises from a substantially room temperature state to a fixing temperature, a roller having a heat conductivity of 1 W / m / K or less is used as a cleaning roller and a pressure unit. To the pressure roller.

Here, by setting the thermal conductivity of the cleaning roller to 1 W / m / K or less, the surface temperature can be raised to the softening point of the toner with a relatively small amount of heat, and the cleaning roller can be more effectively applied to the pressure roller. The transferred toner stain can be collected.

In other words, it is preferable that the cleaning roller is set to have a low thermal conductivity and a small heat capacity, thereby minimizing the power loss when the temperature of the heating element is raised. It becomes possible.

When a command to continuously feed a recording material having a width narrower than the longitudinal width of the heating element is input to the image forming apparatus, the temperature detection data and the content of the command (paper size, number of sheets, etc.) are used. Simulate or measure the temperature rise in the non-sheet passing area, and if the value is different from the job being executed, if images of different paper sizes are formed, the occurrence of hot offset, the occurrence of paper wrinkles, the pressure roller The heat conduction roller can be pressed against the pressure roller only when it is determined that a problem arises in consideration of the heat resistance of the surface layer, the heat resistance of the film guide, and the like.

As a result, it is possible to effectively use the power consumed by the heating element and to reduce the non-sheet passing temperature rise as compared with a configuration in which the heat conduction roller is constantly pressed against the pressure roller.

[0061]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. This embodiment will be described by taking as an example a case where the present invention is applied to an electrophotographic LBP.

In the image forming process of the LBP according to the present invention, the process excluding the fixing is similar to that described in the above-mentioned conventional example, and the description is omitted. Note that the LBP in the present embodiment has a peripheral speed of the photosensitive drum of 115 mm /.
sec, and continuous printing of 24 sheets of A4 paper per minute is possible.

FIG. 1 is a diagram showing a fixing device used in the image forming apparatus according to the present embodiment. In the figure, the same members as those described in the conventional example are denoted by the same reference numerals.

In the figure, reference numeral 91 denotes φ1 made of aluminum.
4mm heat conductive roller, heat conductivity is 240W
/ M / K. Reference numeral 97 denotes a Φ8 mm cleaning roller made of styrene acrylic.
It is about 0.2 W / m / K. The heat transfer roller 91 and the cleaning roller 97 are arranged in parallel with the pressure roller 7 and can be in contact with each other.

Reference numeral 93 denotes an arm rotatable about the Z portion as a support shaft. For example, a pair of arms (only the near side is shown in the drawing) are provided on the near side and the back side of the fixing device, and at the upper end between the pair of arms 93. The roller shaft is rotatably supported by the heat conducting roller 91, and the roller shaft is rotatably supported between the lower portions of the pair of arms 93 by the cleaning roller 97.

The arm 93 is urged clockwise by a spring (not shown) so that the heat transfer roller 91 always contacts the pressure roller 7. As a result, the cleaning roller 97 is urged in a direction that always separates from the pressure roller 7.

Reference numeral 98 denotes a cam member which is provided below the arm 93 and abuts against a cam follower (not shown). The cam member has a rotating shaft at an eccentric position Y and is driven to rotate clockwise and counterclockwise by a motor M, respectively.

That is, by the rotation of the cam member 98, the arm 93 rotates counterclockwise against the spring force of the spring, and separates the heat transfer roller 91 from the pressure roller 7. Further, the cleaning roller 97 and the heat transfer roller 91 can be separated from the pressure roller 7 by the rotation position of the arm 93.

In this embodiment, the roller unit 9 is constituted by the heat conduction roller 91, the cleaning roller 97, the arm 93, the cam member 98, the motor M, and the like.

A motor M for rotating the cam 95
Is controlled by the CPU 101 via a control circuit (not shown), and is controlled based on image data from an external device, the temperature of the fixing heater, and the like.

The above-mentioned coil spring (not shown) is fixed to a part of the fixing device frame (not shown) from the support shaft position Z of the arm 93 to a part of the cleaning roller 97 side.
A rotational moment acts on the arm 93 in the direction of the arrow F1, and the rotation of the cam 95 enables the cleaning roller 97 and the heat transfer roller 91 to be in pressure contact with the pressure roller and to be separated therefrom.

FIG. 1 shows a state in which the cleaning roller 97 is in contact with the pressure roller 7 at a pressure F2.

By rotating the cam 95, the arm 9
FIG. 2 shows a state in which the heat conductive roller 91 is rotated clockwise by the spring force of the coil spring, and the heat conductive roller 91 is brought into contact with the pressing roller 7 at a pressure F3.

The position of the support shaft Z depends on the shape of the arm 93, but in this embodiment, the two rollers 9 are used.
1 and 97, the outer diameter of the heat transfer roller 91 is larger than the radius of the heat transfer roller 91, and is located farther from the surface of the pressure roller 7;
In addition, the arm 93 is arranged at a position closer to the surface of the pressure roller 7 than the shorter one of the rotation radii of the arm 93 around the support shaft position Z.

By controlling the driving of the motor M with the above structure, the cam 95 is rotated, and one of the two rollers 93 and 97 is pressed against the pressure roller.
Alternatively, both can be separated from the pressure roller.

FIG. 3 is a flowchart showing the control of the roller unit 9 in the LBP according to the present embodiment.

In FIG. 3, first, it is determined whether or not the temperature of the pressure roller and the heater unit has dropped to about room temperature, and whether or not the resistance value of the temperature control thermistor 605 of the fixing heater is 50 ° C. or less. (S1).

If the temperature of the fixing heater is 50 ° C. or more, it is determined whether the width of the recording material conveyed to the fixing device is narrow or long (S2). It is determined whether or not there is (S3).

If it is determined in step S3 that the number of continuous sheets passed is 5 or more, the cleaning roller (abbreviated as cleaning R in FIG. 3) is brought into contact with the pressure roller during the pre-rotation of the fixing device. Then, while the cleaning roller is in contact with the pressure roller, the fixing process of continuous paper passing is performed (S
5), end (S6).

This is because, since the length of the recording material is close to the length of the heating element, the temperature rise in the non-sheet passing portion does not pose a problem. Since the surface temperature of the pressure roller is expected to approach or exceed the temperature at which the toner is softened, the job is executed in a contact state in order to fix and fix the toner attached to the cleaning roller.

In this case, since the number of jobs is five or more, in this embodiment, the surface temperature of the pressure roller at the time of post-rotation becomes 100 ° C. or more, and the toner offset to the fixing film is removed by the pressure roller and the cleaning roller. Even when the toner is transferred to the roller, the surface viscosity of the toner increases, so that the toner is fixed on the cleaning roller, and the pressure roller and the back of the paper are not stained.

In S2, if it is determined that the width of the recording material to be subjected to the fixing process is narrow, it is determined whether or not the continuous number of sheets is equal to or more than 20 (S7). In steps S8 and S9, the cleaning roller is brought into contact with the pressure roller during the pre-rotation of the fixing device to perform the continuous paper fixing process, and the heat transfer roller is brought into contact with the pressure roller from the twentieth sheet to perform the fixing process. I do. Then, after the post-rotation, the heat conduction roller is separated from the pressure roller (S10), and the process ends (S11).

That is, this processing (S1 → S2 → S7 →
According to S8 → S9 → S10 → S11), the longitudinal width is LT
When more than 20 sheets of paper having a width of less than R are passed, the temperature of the non-sheet passing portion of the heater rises, thereby increasing the surface temperature of the pressure roller and the cleaning roller, and the surface temperature of the non-sheet passing portion. The possibility of greatly exceeding the temperature (about 160 ° C.) increases.

If the cleaning roller is in contact with the pressure roller greatly exceeding the melting temperature of the toner, the viscosity of the toner adhered on the cleaning roller becomes too low, and the toner re-transfers to the pressure roller, thereby soiling the recording paper. Therefore, in the present embodiment, when the width of the narrow paper is 20 sheets or more, the cleaning roller is separated and the heat conductive roller is contacted to prevent the toner on the cleaning roller from being re-transferred to the pressure roller. In addition, since the temperature of the non-sheet passing portion of the pressure roller is reduced by the contact of the heat conduction roller, it is possible to reduce thermal damage to the pressure roller.

In S7, if the number of continuous sheets passed is 20
If not, the process proceeds to S4.

When the number of sheets is 5 or less, the reason why the cleaning roller is separated after the post-rotation is that the surface temperature of the pressure roller and the cleaning roller does not warm up in the JOB of 5 sheets or less, so This is because there is a high possibility that the offset toner is retransferred to the recording material (paper).

If the number of sheets is five or more, the surface temperature of the cleaning roller approaches the toner melting temperature, so that when the offset toner adheres to the cleaning roller, it does not transfer again to the pressure roller and the recording material.

When the continuous paper feeding is performed for 20 sheets or more, the toner viscosity on the cleaning roller is significantly reduced. Therefore, the cleaning roller is separated from the pressure roller.

Further, in S3, the number of continuous sheets passed is 5
If it is determined that the number is not more than the number of sheets, the cleaning roller is brought into contact with the pressure roller during the pre-rotation and post-rotation of the fixing device (S12), and the fixing process is performed (S13). Release from the roller (S14) and end (S15).

That is, this processing (S1 → S2 → S12)
According to -S15), since the number of jobs is five or less, the surface temperature of the pressure roller and the cleaning roller does not reach a temperature at which the toner melts and is completely fixed on the cleaning roller. Therefore, after the offset toner is deposited on the cleaning roller in the pre-rotation and post-rotation,
It is separated from the pressure roller to prevent re-transfer of the contaminated toner from the cleaning roller surface to the pressure roller and the recording material in the next job.

On the other hand, in S1, the temperature of the heater becomes 50
If the temperature is not lower than ° C, it is determined whether the width of the recording material to be subjected to the fixing process is wide or narrow (S16). If the width is wide, it is determined whether or not the number of continuous sheets passed is 5 or more (S17).

If it is determined in step S17 that the number of continuous sheets passed is 5 or more, both the cleaning roller and the heat transfer roller are separated from the pressure roller and brought into a non-contact state (S18).
The fixing process is performed (S19), and the process ends (S20).

That is, this processing (S1 → S16-S2)
According to 0), in this case, the pressure roller temperature starts a job from 50 ° C. or higher, and there is no need to raise the temperature of the non-paper passing portion. Since the surface temperature of the pressure roller reaches 100 ° C. or higher, the surface of the offset toner has a high viscosity, adheres to paper, and does not spread to the pressure roller. Therefore, both the cleaning roller and the heat conduction roller are brought into non-contact.

In S16, if it is determined that the width of the recording material is narrow, it is determined whether or not the continuous number of sheets is equal to or more than 20 (S21). After that, the heat conduction roller is brought into contact with the pressure roller, and subsequently, the fixing process is executed (S23), and the heat conduction roller is released during the post-rotation of the fixing device (S24), and the process ends (S25).

That is, this processing (S1 → S16 → S2)
According to 1 to S25), when outputting 20 or more narrow papers, the toner on the cleaning roller is re-transferred to the pressure roller and the paper due to the temperature rise in the non-paper passing portion.
The cleaning roller is separated from the first sheet, and the heat conduction roller is brought into contact with the sheet to reduce the temperature rise in the non-sheet passing portion.

In S21, the number of continuous sheets passed is 2
If the number of sheets is not zero or more, the process proceeds to S18. If the number of sheets is 20 or less, the temperature of the non-sheet passing portion of the pressure roller and the cleaning roller does not reach a temperature at which the toner is completely melted and re-transferred to the paper. Therefore, the heat transfer roller is not brought into contact with the pressure roller. Also, by outputting 5 to 19 sheets,
Do not touch the cleaning roller.

In S17, the number of continuous paper passing is 5
If the number is not more than one, in S26, the cleaning roller is brought into contact with the pressure roller at the time of post-rotation to perform a fixing process (S27), and after the post-rotation of the fixing device, the cleaning roller is separated from the pressure roller (S28). The process ends (S29).

That is, this processing (S17 → S26-S
According to 29), since the number of jobs is 5 or less, the surface temperature of the pressure roller does not rise to about 100 ° C.
According to the study by the present inventors, the toner used in the present embodiment does not have a sufficiently high viscosity on the toner surface at 100 ° C. or lower. Therefore, when the offset toner is transferred to the pressure roller, it adheres to paper (recording material). Force is weak and tends to remain on the pressure roller surface.

In this case, in the next job, the toner on the cleaning roller is transferred to the pressure roller and further transferred to the paper, thereby soiling the back of the paper. Therefore, the cleaning roller is separated by post-rotation. .

As described above, according to the present embodiment, when the energization of the fixing heater is started by the start of the pre-rotation, the offset toner on the fixing film is easily transferred to the pressure roller 7. It is determined whether or not the cleaning roller 97 is brought into contact with the pressure roller 7 during the pre-rotation.

Further, when the specified job is executed, it is determined whether or not the temperature rise of the non-sheet passing portion of the heater unit and the pressure roller becomes a problem based on the paper size and the number of prints specified in the job. It is determined whether the heat conduction roller 91 is pressed against the pressure roller.

Furthermore, the difference between the temperature of the heater unit and the pressure roller when the specified paper size and the number of prints are fixed and the temperature drop in the subsequent post-rotation are estimated. It is determined whether the cleaning roller 97 needs to be brought into contact with the pressure roller.

As described above, according to the present embodiment, by controlling the roller unit 9, the toner offset on the surface of the fixing film is transferred to the surface of the pressure roller 7 in the pre-rotation or post-rotation. Only when the possibility is high, the cleaning roller 97 can be brought into contact, so that there is no need to apply unnecessary heat to the cleaning roller.

In the case where the surface of the pressure roller rises in the non-sheet-passing area when the narrow paper is continuously passed, the cleaning roller 97 is not brought into contact with the pressure roller. Can be reduced,
Therefore, it is possible to select a resin-based material based on surface energy, adhesion, and the like so that the toner collecting ability is improved.

The heat transfer roller 91 is brought into contact with the pressure roller 7 only when the non-sheet passing portion of the pressure roller 7 and the heater unit starts to heat up and the amount of heat becomes partially excessive. This allows excess heat to be directed to the necessary parts, thereby making it possible to use power more efficiently.

As for the cleaning roller, a polyimide resin, an epoxy resin, a silicone sponge and a polyimide tube-coated roller have a thermal conductivity of 1 or more.
It was confirmed that the use of a roller having a ratio of W / m / K or less allows the adhered toner to be collected well.

On the other hand, when a glass roller or a metal roller having a thermal conductivity of more than 1 W / m / K is used, since the temperature of the cleaning roller surface does not become sufficiently high due to the heat of the previous rotation, the viscosity and adhesion of the toner However, there were problems such as insufficient collection on the surface of the cleaning roller and transfer from the surface of the cleaning roller to the recording material.

Table 1 shows the result of comparing the difference in the occurrence of image stains depending on the material of the cleaning roller.

[0109]

[Table 1]

[0110] The image stain was determined by comparing an image with a printing rate of 7% with 2%.
After output of 500 sheets per page / 30 seconds, evaluation was made on the smear on the image output after stopping for 30 minutes.

In this embodiment, the heat conductive roller 91 is an aluminum roller having a heat conductivity of about 240 W / m / K, but the heat conductivity of iron, brass, etc. is 50 to 150 W.
/ M / K, the effect of reducing the temperature rise in the non-sheet passing portion can be recognized.

For example, if the number of continuous LGL-size sheets is 20 or less, the hot offset (LGL) generated when the LD roller-size sheets are output after the temporary stoppage is performed.
In the non-sheet passing portion) can be suppressed within an allowable level.

Table 2 shows the difference in temperature between the non-sheet passing portion and the sheet passing portion and the difference in the level of hot offset due to the difference in the material of the heat transfer roller 91. In addition, by using a material having a higher thermal conductivity than aluminum, such as copper, the effect of reducing the temperature rise in the non-paper passing portion can be further enhanced.

[0114]

[Table 2]

The temperature rise in the non-sheet passing portion is measured by measuring the temperature difference between the sheet passing portion and the non-sheet passing portion on the surface of the pressure roller when continuously passing 20 sheets of LGL size paper.
After passing 20 sheets of paper, the hot offset generated on the LD roller paper when one sheet passed through the LD roller size after a temporary stop was examined.

As described above, by adopting the above-described configuration, an image forming apparatus which effectively collects toner stains adhering to the pressure roller, reduces the temperature rise in the non-sheet passing portion, and uses power more efficiently. Can be provided.

The driving sequence of the roller unit 9 described with reference to FIG. 2 is an example. For example, the temperature detected by the thermistor is divided into several stages different from the embodiment, and the cleaning roller The contact of the rollers may be controlled, or the temperature sensor may be brought into direct contact with the non-paper passing area of a member such as a heater or a pressure roller, and the contact of the two rollers may be performed based on the output. Controlling is also included in the scope of the present invention. (Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. In the figure, the same members as those in the first embodiment are denoted by the same reference numerals.

The present embodiment is characterized in that the scraper 94 is brought into contact with the cleaning roller 97.

The scraper 94 is a 1.5 mm thick L
A stainless steel sheet having a thickness of 0.2 mm is spot-welded on a L-shaped sheet metal. The free length of the stainless sheet is 4 mm, and both ends of the L-shaped sheet metal are connected to arms 9.
3, and the free end (edge) of the stainless steel sheet is in contact with the cleaning roller at the counter.

With the above-described characteristic configuration of the present embodiment, the offset toner transferred from the fixing film to the pressure roller is cleaned during the pre-rotation and post-rotation as described in the first embodiment. After the transfer to the roller 97, the scraper 94 scrapes off the cleaning roller surface, so that the cleaning roller surface may adhere to the cleaning roller surface as very thin dirt. It will be stable for a long time.

As a result, the amount of toner stains adhering to the heat conductive roller 91 is reduced, and stable performance can be exhibited for a long period of time.

In this embodiment, the scraper edge is brought into contact with the cleaning roller in the counter direction. However, even if the scraper edge is brought into contact with the edge in the forward direction, a scraping effect can be obtained. In a cleaning roller having a high frictional resistance on the surface such as a felt layer, a nonwoven fabric layer, or a surface layer in which an edge is caught, the rotation resistance of the cleaning roller is lower than that of the counter. There is a stable advantage.

Further, not only the edge contact but also the application of pressure even when the belly is touched makes it difficult for the adhered toner to be peeled off from the cleaning roller, thereby contributing to the improvement and stability of the cleaning force of the roller.

The performance of the roller unit 9 can be improved and stabilized even when the scraper 94 is not limited to the cleaning roller but is brought into contact with a heat conductive roller.

[0125]

As described above, according to the present invention,
In a use environment in which the number of output sheets in one print job is small and the time interval between jobs is several minutes or more, it is possible to improve the contamination of the pressing means such as the pressing roller, which becomes conspicuous, and to generate heat. Paper with a width narrower than the body width (for example, 310 m
It is possible to reduce the temperature rise in the non-sheet passing portion, which is a problem when a 210 mm width paper is continuously passed through the m width heating element.

In particular, based on the output from the heating element temperature detecting means and the content of the print job, a cleaning roller having a thermal conductivity of 1 W / m / K or less and a thermal conductivity of 50 W / m
/ K or more heat conductive rollers can be in contact with the pressure roller,
Eliminating toner stains adhering to the surface of the pressure roller, preventing the stains from being transferred to the recording material paper again, and reducing the temperature rise in the non-sheet passing portion and efficient use of electric power. Will be possible.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation state of a roller unit in the fixing device of FIG.

FIG. 3 is a flowchart illustrating operation control of a roller unit in the fixing device according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a fixing device according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a conventional example of a laser beam printer.

FIG. 6 is a view for explaining a conventional film heating type fixing device.

FIG. 7 is a front view and a schematic wiring diagram of a fixing heater of a conventional film heating type fixing device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photosensitive drum 2 charging roller 4 developing device 6 heater unit 7 pressure roller 61 fixing heater 62 fixing film guide 65 fixing film 91 heat transfer roller 97 cleaning roller 94 scraper 101 CP
U

Claims (15)

[Claims] 1. A heating element having a heating resistor is brought into contact with a moving film, and the film is brought into pressure contact with the heating element by pressing means. A fixing device for fixing a toner image carried on a recording material passing through the recording material to the recording material, wherein at least two of the fixing devices are capable of freely contacting and separating from the pressing means.
A fixing device comprising two rotatable rollers. 2. One of the rollers has a thermal conductivity of 50 W / m / K or more at a portion in contact with the pressure roller,
2. The fixing device according to claim 1, wherein the other roller has a thermal conductivity of 1 W / m / K or less at a portion in contact with the pressing unit. 3. 3. The fixing device according to claim 1, further comprising a scraper that comes into contact with the other roller to remove attached matter on the surface. 4. The one roller and the other roller are attached to a rotatable lever member, and by rotating the lever member, both rollers are selectively brought into contact with the pressing means. The fixing device according to claim 1, wherein the two rollers are separated from each other so as to be in a non-contact state. 5. The two rollers are selectively attached by attaching the one roller and the other roller to a rotatable lever member, attaching the scraper to the lever member, and rotating the lever member. 4. A fixing device according to claim 3, wherein said fixing device is brought into contact with said pressure means, and both rollers are separated from each other so as to be in a non-contact state. 6. The fixing device according to claim 1, wherein the one roller is formed of one of iron, aluminum, and copper. 7. The fixing device according to claim 1, wherein the other roller is formed of any one of phenol resin, epoxy resin, polyimide resin, and polyphenyl sulfide. 8. A temperature detecting means for detecting a temperature of the heating element, a size detecting means for detecting a length of the recording material in a direction orthogonal to a paper passing direction, and A drive unit for causing the plurality of rollers to contact and separate from the pressing unit, and a control unit for controlling the drive unit, wherein the control unit controls the temperature of the heating element and the temperature of the recording material. The fixing device according to any one of claims 1 to 7, wherein the driving unit is controlled using a width in a direction orthogonal to a sheet passing direction and a continuous sheet number of the recording material as input information. 9. When the temperature of the heating element at the start of energization to the heating element is lower than a predetermined temperature, the control means causes the other roller to contact the pressing means at the time of pre-rotation. 9. The fixing device according to claim 8, wherein the driving unit is driven. 10. The control means, when the width of the recording material is equal to or greater than a predetermined width and a small number of sheets are passed, causes the other roller to contact the pressure means during post-rotation. The fixing device according to claim 9, wherein: 11. When the width of the recording material is equal to or less than a predetermined width, and when a large number of sheets are passed, the control unit applies the one roller to the pressing unit from the middle of the number of sheets passed. The fixing device according to claim 9, wherein the driving unit is controlled such that the one roller is brought into contact with the roller and the one roller is separated from the pressing unit during the post-rotation. 12. The control unit according to claim 1, wherein the heating element temperature at the start of energization of the heating element is higher than a predetermined temperature, and the width of the recording material is equal to or larger than the predetermined width and a small number of sheets are not passed. 9. The fixing device according to claim 8, wherein the driving unit is driven such that the one roller and the other roller with respect to the pressing roller are separated from the pressing unit. 13. The control device according to claim 1, wherein the heating element temperature at the start of energization of the heating element is higher than a predetermined temperature, and the width of the recording material is equal to or more than the predetermined width and a small number of sheets are passed. 9. The fixing device according to claim 8, wherein the driving unit is driven so that the other roller is brought into contact with the pressing unit at the time of pre-rotation and separated at the time of post-rotation. 14. The control unit according to claim 1, wherein the heating element temperature at the start of energization of the heating element is higher than a predetermined temperature, and the width of the recording material is equal to or smaller than the predetermined width and a large number of sheets are passed. 9. The method according to claim 8, wherein the one of the rollers having a temperature control function is brought into contact with the pressurizing unit based on the number of sheets in the middle of the sheet passing, and the driving unit is driven so as to be separated at the time of post-rotation. 3. The fixing device according to claim 1. 15. An image forming apparatus comprising the fixing device according to claim 1. Description: