JP2000122463A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image failure such as hot offset, and a temperature rise of the inside of a device by providing a controller for causing a heater to generate heat so that the temperature of a nip once reaches the softening point of the toner or above after a fixing process is finished and setting the temperature of the nip at the time according to the heating condition of a roller. SOLUTION: A fixing device is composed of a ceramic heater (hereinafter referred to as heater) 20 for heating toner, a fixing film 25 incorporating the heater 20, a pressure roller 26 as other fixing rotary body, made to abut against the fixing film 25, a temperature control means 27 for controlling the temperature of the heater 20, and a rotation control means 28 for controlling the carrying of a recording material P. The fixing device heats toner on the recording material P by the heater 20 while sandwiching and carrying the recording material P with a fixing nip N by the rotation of the pressure roller 26 in the direction of the arrow R26. In this case, the feed of the recording material P is controlled by controlling the rotation of the pressure roller 26 by the rotation control means 28, and the temperature of the heater 20 is also controlled by the temperature control means 27.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a laser printer, a facsimile, and the like.

[0002]

2. Description of the Related Art For example, as a fixing device used in an image forming apparatus such as a copying machine, a printer, and a facsimile,
There is a heat roller type.

This heat roller type heat fixing device includes a heat roller (fixing roller) heated by a built-in heat source such as a halogen heater and maintained at a predetermined temperature, and an elastic pressure roller pressed against the heat roller. The recording material is introduced into the press-contact nip portion (fixing nip portion) and is nipped and conveyed to thermally fix an unfixed toner image on the surface of the recording material.

Recently, a heat fixing device of a film heating type has been put into practical use (for example, JP-A-63-313182, JP-A-1-263679, JP-A-2-57878, and JP-A-4,578). -44075-44083, JP-A-4-204980-204984, etc.).

[0005] The heat fixing device of this film heating type is
It has a heating element fixedly supported by a support member, a heat-resistant film that moves while contacting the heating element, and a pressure roller that forms a nip with the heating element via the film. The toner image is heated and fixed by nipping and conveying the recording material carrying the toner image at the nip.

[0006] This film heating type heat fixing device is
Not only can it be used as a device for thermally fixing an unfixed toner image as a permanent fixed image on the recording material surface, for example,
It can be widely used as a device for modifying a surface property by heating a recording material carrying a toner image, a device for performing a temporary deposition process, and a device for performing a sheet-like heated process.

In such a film heating type heating apparatus, a heating element having a high heat-up rate and a low heat capacity, for example, a ceramic substrate having an insulating property and a good thermal conductivity, and a surface provided on the surface of the substrate are provided. It is possible to use a so-called ceramic heater having a resistance heating layer that generates heat by energization as a basic component, and a thin film having a low heat capacity can be used as a film material. There is no need to supply power to the heating element during standby, and even if the recording medium as the material to be heated is immediately passed, the heating element is sufficiently heated to a predetermined temperature until the recording material reaches the fixing nip. And shorten the wait time
(Quick start property: Operate on demand), power saving is possible, and further, there is an advantage that temperature rise in the apparatus of the image forming apparatus main body can be suppressed, and the effect is effective.

[0008] Here, the unfixed toner carried on the surface of the recording material is ideally heated and melted appropriately and fixed on the surface of the recording material. If toner or toner in a hot offset state that is excessively melted is present, these toners are transferred to a fixing roller or a fixing film in contact with the recording material surface.

When the temperature of the upper and lower rotating bodies is the same, such offset toner transfers to the one having poor releasability.
When the upper and lower temperatures are different, the lower the temperature, the more easily the toner solidifies, so that the toner tends to transfer to the lower temperature. In particular, in a fixing device having a low heat capacity such as a film heating system, since the power supply to the heating body is not performed in a print waiting (standby) state, the pressure roller is cooled. Therefore, when printing is started from this state, the heating body and the film are warmed by the energization but the pressure roller is kept cold, so that the toner sandwiched between the nips is transferred to the pressure roller when the film and the pressure roller rotate. When such toner accumulates, the hardness of the rotating body changes, and the releasability of the surface changes, which has various adverse effects on the fixability.

Therefore, in order to prevent accumulation of toner stains, a fixing roller or a fixing film used in a fixing device and a pressure roller (hereinafter referred to as “fixing rotating body”).
In consideration of the releasability from the toner, the surface layer of
Fluororesin layer such as PFA / FEP, LTV / RT
Generally, a release layer made of a silicone rubber layer such as V is provided.

[0011] Further, as the applicant previously proposed,
After the printing is completed and the rotation of the rotating body is stopped, the toner in the fixing nip portion is heated to a temperature higher than the temperature at which the toner softens (FIG. 6), and the respective toners are combined by melting so that the toner is easily transferred. By cooling by natural heat radiation, it is fixed to the fixing film (fixing roller). At the end of printing, the pressure roller is also warm, so that the fused toner is attached to the film with poor releasability by cooling.

By rotating the fixing rotator in such a state, it is easy to hold the toner on the fixing film and the fixing roller by bonding even in a situation where it is difficult to hold the toner individually. Then, the transfer of the nip portion toner to the pressure roller can be reduced. (When the fixing rotator is rotated, by lowering the nip temperature below the softening point of the toner, the amount of toner fixed on the fixing film side can be further increased.)

When printing is started in a state where the toner is fixed on the fixing film side, the temperature of the paper entering the nip is room temperature, so that a temperature difference occurs between the surface of the fixing film and the paper.
Therefore, the toner held in the nip portion between the fixing film and the fixing roller adheres to the paper and is discharged to the extent that it is invisible to the naked eye. Therefore, even if the toner adheres to the pressure roller, if the toner is heated and cooled in the nip after the printing, the toner is transferred to the film and can be removed by the recording material at the time of printing.

Since the surface of the film or the surface of the pressure roller stopped at the nip position after printing is usually different every time printing is completed, dirt can be discharged over the entire circumference of the pressure roller by repeating printing. This makes it possible to prevent accumulation of dirt such as toner on the pressure roller.

[0015]

However, in the above-described example, the nip portion is always heated at a constant temperature (about 5 seconds) after printing, so that intermittent printing is performed one after another as shown in FIG. The nip is heated almost continuously every time.

Since the temperature of the pressure roller rises due to this heating, the toner in the nip portion is not sufficiently cooled, so that the toner cannot be discharged onto the paper. Further, various problems such as an image defect such as a hot offset and a temperature rise in the apparatus occur.

[0017]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a heater maintained at a controlled temperature during a fixing process, a film moving in contact with the heater, and a nip with the heater via the film. And a pressure roller for forming a toner image, and a fixing device that heats and fixes the toner image on the recording material while nipping and conveying the recording material at the nip.
The heater is controlled to generate heat so that the temperature of the nip is once higher than the softening point of the toner, and the temperature of the nip at this time is set according to the degree of warming of the pressure roller.

Further, the printer has a heater, a fixing roller heated by the heater and maintained at a temperature controlled during the fixing process, and a pressure roller forming a nip with the fixing roller. In a fixing device that heats and fixes a toner image on a material, after the fixing process is completed, the nip has a control to generate heat so that the temperature of the nip temporarily becomes equal to or higher than the softening point of the toner. It is set according to the degree of warming of the pressure roller.

(Operation) According to the present invention, it is possible to optimize the temperature in the stop nip by performing heating after adjusting the temperature of the fixing rotating body. This makes it possible to optimize the amount of transfer of the toner of the pressure roller to the fixing film / fixing roller, and to prevent accumulation of toner stain on the fixing rotating body without leaving the toner adhered to the pressure roller. Therefore, it is possible to prevent the recording material from wrapping around the fixing rotator or to prevent the toner stain accumulated on the fixing rotator from fouling the recording material at a stretch, and to prevent abnormal temperature rise of the fixing rotator to obtain a good image. Output. Further, it is possible to reduce power consumption and eliminate problems such as temperature rise in the machine.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows an image forming apparatus provided with a fixing device of the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a laser beam printer as an example of an image forming apparatus.

First, the configuration of a laser beam printer (hereinafter, referred to as an "image forming apparatus") will be described with reference to FIG.

The laser beam printer shown in FIG. 1 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed in a direction of an arrow R1 by a driving unit (not shown).

Around the photosensitive drum 1, a charging roller (charging device) 2, an exposing unit 3, a developing device 4, a transfer roller (transfer device) 5, and a cleaning device 6 are arranged substantially in order along the rotation direction. Have been.

A paper feed cassette 7 containing a sheet-like recording material P such as paper is disposed below the apparatus main body M, and is arranged in order from the upstream side along the conveyance path of the recording material P.
A paper feed roller 15, a transport roller 8, a top sensor 9, a transport guide 10, a fixing device 11, a transport roller 12, a paper discharge roller 13, and a paper discharge tray 14 according to the present invention are arranged.

Next, the operation of the above-described image forming apparatus will be described.

The photosensitive drum 1 rotated and driven in the direction of arrow R1 by a driving means (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by a charging roller 2.

On the surface of the charged photosensitive drum 1, an image exposure L based on image information is performed on the surface of the photosensitive drum 1 by an exposure unit 3 such as a laser optical system, and the charge of the exposed portion is removed to form an electrostatic latent image. You.

The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing roller 4a, and applies a developing bias to the developing roller 4a to
By applying toner to the upper electrostatic latent image, development (visualization) as a toner image is performed.

The toner image is transferred onto a recording material P such as paper by a transfer roller 5. The recording material P is stored in a paper feed cassette 7, fed and transported by a paper feed roller 15 and a transport roller 8, and transferred via a top sensor 9 to a transfer nip between the photosensitive drum 1 and the transfer roller 5. Transported to the department. At this time, the leading end of the recording material P is detected by the top sensor 9, and the recording material P is synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P.

The recording material P carrying the unfixed toner image on the surface by the transfer is conveyed to a fixing device 11 along a conveyance guide 10, where the unfixed toner image is heated and pressurized to be applied to the surface of the recording material P. Be established. The fixing device 11 will be described later in detail.

The recording material P after fixing the toner image is transported by a transport roller.
12. A discharge tray on the upper surface of the apparatus main body M by a discharge roller 13.
Conveyed and ejected on 14.

On the other hand, the photosensitive drum 1 after the transfer of the toner image
Toner remaining on the surface without being transferred to the recording material P (hereinafter referred to as “transfer residual toner”) is removed by the cleaning blade 6a of the cleaning device 6 to prepare for the next image formation.

By repeating the above operations, images can be formed one after another.

Next, an example of the fixing device 11 according to the present invention will be described in detail with reference to FIG. Note that FIG. 3 is a longitudinal sectional view along the conveying direction of the recording material P (the direction of arrow K).

The fixing device 11 shown in FIG. 1 includes a ceramic heater (hereinafter referred to as a “heater”) 20 as a heating element for heating the toner, a fixing film (fixing rotating body) 25 and a fixing film 25 including the heater 20. A pressure roller 26 as another fixing rotator abutted on the recording medium P, a temperature control means 27 for controlling the temperature of the heater 20, and a rotation control means 28 for controlling the conveyance of the recording material P are constituted as main constituent members. ing.

The heater 20 is made of a heat-resistant base material 20 such as alumina.
Form a resistor pattern 20b on a by, for example, printing,
Its surface is covered with a glass layer 20c, and is long in the left-right direction perpendicular to the recording material P conveyance direction (the direction of arrow K).
That is, it is formed longer than the width of the recording material P. The heater 20 is a heater holder 2 attached to the apparatus main body M.
Supported by two.

The heater holder 22 is a semicircular member made of heat-resistant resin, and also functions as a guide member for guiding the rotation of the fixing film 25.

The fixing film 25 is formed of a heat-resistant resin such as polyimide in a cylindrical shape, and encloses the heater 20 and the heater holder 22 described above. The fixing film 25 is pressed against the heater 20 by a pressure roller 26 to be described later, whereby the back surface of the fixing film 25 comes into contact with the lower surface of the heater 20.

The fixing film 25 is formed by the arrow R of the pressure roller 26.
The recording material P is rotated in the direction of the arrow R25 as the recording material P is transported in the direction of the arrow K by the rotation in the 26 direction. The left and right ends of the fixing film 25 are regulated by guide portions (not shown) of the heater holder 22 so that the fixing film 25 does not come off in the longitudinal direction of the heater 20.

A heater is provided on the inner surface of the fixing film 25.
Grease is applied to reduce sliding resistance between the heater 20 and the heater holder 22.

The pressure roller 26 is provided on the outer peripheral surface of the metal core 26a with a heat-resistant release layer having elasticity such as silicone rubber.
A fixing nip N is formed between the fixing film 25 and the fixing film 25 by pressing the fixing film 25 against the heater 20 from below by the outer peripheral surface of the release layer 26b. Assuming that the width (nip width) of the fixing roller N in the rotation direction of the pressure roller 26 is a, the nip width a is set to such an extent that the toner on the recording material P can be suitably heated and pressed. Have been.

The rotation control means 28 includes a motor 29 for rotating the pressure roller 26 and a CPU 30 for controlling the rotation of the motor 29.
And As the motor 29, for example, a stepping motor or the like can be used. In addition to continuously rotating the pressure roller 26 in the direction of arrow R26, it is also possible to intermittently rotate the pressure roller 26 by a predetermined angle. That is, the recording material P can be fed stepwise while the rotation and the stop of the pressure roller 26 are repeated.

The temperature control means 27 includes a thermistor (temperature detecting element) 21 attached to the back surface of the heater 20 and a CPU 23 which controls the triac 24 based on the temperature detected by the thermistor 21 and controls the energization of the heater 20. Having.

As described above, the fixing device 11 includes a pressure roller
The toner on the recording material P is heated by the heater 20 while the recording material P is nipped and conveyed at the fixing nip portion N by the rotation in the direction of the arrow R26 at 26. At this time, the rotation of the pressure roller 26 is controlled by the rotation control means 28 so that the feeding of the recording material P can be appropriately controlled.
Thus, the temperature of the heater 20 can be appropriately controlled.

Next, the details of the present invention will be described below.

In the control shown in FIGS. 5 and 6, since the heating is performed at a constant temperature after the end of printing regardless of the state of the fixing rotator, the nip portion is appropriately heated in the morning and the toner adheres to the fixing film. However, if the nip is heated to the same temperature as in the morning after the fixing rotator has been warmed after printing several sheets, the nip becomes difficult to cool and the toner hardly adheres to the fixing film. Further, as shown in FIG. 5, by repeatedly heating the nip portion, the fixing unit becomes hot and hot offset occurs.

In this embodiment, as shown in FIG. 3, the temperature of the fixing device (the temperature of the heater) at the start of printing is detected, and
When the temperature is below 5 ° C, the post-heating becomes 200 ° C. When the temperature is above 105 ° C,
The post-heating is characterized by reaching 180 ° C. As a result, the temperature of the pressure roller is maintained at an appropriate level even when the post-heating is performed every time such that intermittent print signals are successively input, and the toner in the nip portion can be sufficiently cooled. Therefore, it is possible to discharge the toner onto the paper, and it is also possible to prevent problems such as an image defect such as hot offset and a temperature rise in the apparatus.

In the case of continuous printing, the heating is performed after the continuous printing is completed.

For example, in an environment of a temperature of 23 ° C. and a humidity of 60%, CaC
When O ₃ is carried out for one print to (post-heating entering time) sheet feeding durability test in the mode 25 seconds using 10-15% inclusive recording material, hot offset occurs in the sheet passing number of conventional 50 sheets Although the pressure roller was dirty, no hot offset or pressure roller contamination was observed even with 20,000 sheets passed according to the present embodiment.

According to this embodiment, problems such as image defects and temperature rise in the apparatus are prevented, and accumulation of toner stains on the fixing rotating body is prevented, whereby the winding of the recording material around the fixing rotating body and the fixing rotating body are prevented. This makes it possible to prevent such a problem that the toner stain accumulated in the recording medium at once blows the recording material.

(Second Embodiment) In the second embodiment, as shown in FIG. 4, the temperature of the fixing rotating body at the start of printing is detected, and the post-heating temperature is determined based on the detected temperature. This makes it possible to change the temperature of the post-heating from the first state in the morning to the state in which the pressure roller is sufficiently warmed, and it is possible to always keep the fixing rotator at an optimum temperature, which causes contamination. The toner can be efficiently discharged onto paper.

For example, in an environment of a temperature of 23 ° C. and a humidity of 60%, CaCO 3
When a paper-passing durability test is performed in a mode in which post-heating is performed every time using a recording material containing 10 to 15%, hot offset has occurred in the past 50 sheets and the pressure roller was dirty. According to the present embodiment, no generation of hot offset, contamination of the pressure roller, etc. was observed even when the number of sheets passed 50,000. Of course, the optimal temperature control temperature varies depending on the model, such as the heat capacity of the fixing device, and the heating time can be controlled according to the state of the fixing rotator.

According to the present embodiment, problems such as an image defect and a rise in temperature inside the apparatus are prevented from occurring, and furthermore, accumulation of toner contamination on the fixing rotating body is prevented. This makes it possible to prevent such a problem that the toner stain accumulated in the recording medium at once blows the recording material. Further, it is possible to prevent abnormal temperature rise of the fixing rotator and to output a good image, to reduce power consumption, and to eliminate problems such as temperature rise in the apparatus.

In the above-described embodiments, the set temperature of the post-heating is set by the temperature of the pressure roller before the start of printing. However, when continuous printing is performed, the pressure roller gradually warms up. In order to keep the temperature suitable for the temperature, it is preferable to gradually lower the temperature controlled during fixing. Therefore, when the temperature control temperature during fixing is switched in this manner, the post-heating set temperature after completion of fixing may be set according to the fixing temperature during fixing.

In each of the above embodiments, the film heating method has been described. However, the present invention is also effective when applied to a heat roller method having a heating roller and a pressure roller.

[0057]

As described above, according to the present invention, by adjusting the temperature of the pressure roller, it is possible to eliminate problems such as image defects such as hot offset and temperature rise in the apparatus. Further, it is possible to effectively prevent accumulation of toner stains on the fixing rotator, prevent toner and paper dust from adhering to peripheral members of the fixing device, and prevent the recording material from wrapping around the fixing rotator and the fixing rotator. Image defects such as accumulated toner stains on the recording material at once can be eliminated. As a result, the grades of the fixing device members and the fixing device peripheral members conventionally used can be reduced (which also leads to cost reduction), and the durability life of the fixing device peripheral members can be extended. There are many more advantageous points than before, such as lower power consumption.

[Brief description of the drawings]

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

FIG. 2 is a longitudinal sectional view showing a schematic configuration of a fixing device according to the present invention.

FIG. 3 is a temperature control diagram during intermittent printing according to the first embodiment.

FIG. 4 shows a post-heating temperature with respect to a fixing rotator temperature at the start of printing according to the second embodiment.

FIG. 5 is an intermittent print temperature in the temperature control proposed by the applicant earlier.

FIG. 6 is a temperature control diagram of a fixing rotating body previously proposed by the applicant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging device (charging roller) 3 Exposure means 4 Developing device 5 Transfer device (transfer roller) 6 Cleaning device 7 Paper feed cassette 8 Transport roller 9 Top sensor 10 Transport guide 11 Fixing device 12 Transport roller 13 Discharge Roller 14 Discharge Tray 20 Heating Body (Ceramic Heater) 21 Temperature Sensing Element (Thermistor) 22 Heater Holder 23 CPU 24 Triac 25 Fixing Rotating Body (Fixing Film) 26 Fixing Rotating Body (Pressing Roller) 27 Temperature Control Means 28 Rotation control means 29 Motor 30 CPU 31 Conductive rubber ring 32 High voltage power supply N Fixing nip P Recording material

Claims (10)

[Claims] 1. A heater that maintains a controlled temperature during a fixing process, a film that moves while being in contact with the heater, and a pressure roller that forms a nip with the heater via the film. In a fixing device that heats and fixes a toner image on a recording material while nipping and conveying, after the fixing process is completed, a control is performed to cause the heater to generate heat so that the temperature of the nip temporarily exceeds the softening point of the toner. A fixing device wherein the temperature of the nip is set according to the degree of warming of the pressure roller. 2. The temperature of the nip at the time of the heat generation control is set according to the degree of warming of the pressure roller before raising the heater to a temperature control temperature in a fixing step. Fixing device. 3. The fixing device according to claim 1, wherein the nip temperature at the time of the heat generation control is set according to a temperature control temperature during a fixing process. 4. The fixing device according to claim 1, wherein the temperature of the nip is determined based on a temperature of the heater. 5. The fixing device according to claim 2, wherein the degree of warming of the pressure roller is determined based on a temperature of the heater. 6. A recording apparatus comprising: a heater; a fixing roller heated by the heater and maintained at a temperature controlled during a fixing process; and a pressure roller forming a nip with the fixing roller. In a fixing device that heats and fixes a toner image on a material, after the fixing process is completed, the nip has a control to generate heat so that the temperature of the nip temporarily becomes equal to or higher than the softening point of the toner. A fixing device, which is set according to the degree of warming of the pressure roller. 7. The nip temperature at the time of the heat generation control is set in accordance with the degree of warming of the pressure roller before raising the fixing roller to a temperature control temperature in the fixing step. The fixing device as described in the above. 8. The fixing device according to claim 6, wherein the temperature of the nip at the time of the heat generation control is set according to a temperature control temperature during a fixing process. 9. The fixing device according to claim 6, wherein the temperature of the nip is determined based on a temperature of the fixing roller. 10. The apparatus according to claim 7, wherein the degree of warming of the pressure roller is determined based on a temperature of the fixing roller.
3. The fixing device according to claim 1.