JP2001117399A - Image heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device and an image forming device capable of preventing a pressurizing rotary body from being soiled, and also, capable of preventing a defective image caused by the soil of the pressurizing rotary body. SOLUTION: As for the image heating device provided with a heating rotary body 12 which is heated by a heating means 17 and the pressurizing rotary body 13 which comes into press contact with the rotary body 12 so as to form a nip A, and for holding and carrying a recording material K with an image T carried by the nip A and processing the image T by heating, the peripheral length Df of the rotary body 12 is made longer than the peripheral length Dr of the rotary body13. After the rotation of the rotary body 12 is activated, the rotary body 12 heating operation is started, and also, the heating operation is started before the rotary body 12 is rotated by the amount of a peripheral length difference Δ D between the rotary body 12 and the rotary body 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus and an image forming apparatus used as an electrophotographic copying machine, a laser beam printer or the like.

[0002]

2. Description of the Related Art For example, a heat fixing device in an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile, etc., that is, an image forming process means such as electrophotography, electrostatic recording, magnetic recording, etc. Indirect (transfer) or direct image forming and carrying on the surface of recording material (transfer sheet, printing paper, electrofax sheet, electrostatic recording sheet, etc.) using an agent (toner) As a heating device for thermally fixing an unfixed developer image on a recording material surface, a heat roller type device has been generally used in the past.

[0003] This heating device of the heating roller type is a pressing nip portion (fixing roller) of a heating roller (fixing roller) heated by a built-in heat source such as a halogen heater to maintain a predetermined temperature, and an elastic roller pressed against the heating roller. Fixing nip)
The recording material is introduced into the recording medium, and is nipped and conveyed, and the unfixed developer image on the recording material surface is thermally fixed by the heat of the heating roller.

Recently, a heating device of a film heating type has been proposed and put into practical use (Japanese Patent Laid-Open No. 63-313).
182, JP-A-1-263679, JP-A-2-15778, JP-A-4-44075-44
No. 083, JP-A-4-204980-204984
No.).

In this heating apparatus, a material to be heated is brought into close contact with a heating member fixedly supported by a supporting member via a heat-resistant thin-walled film material, and the film material is slid and moved to the heating member to heat the heating member. Is applied to a material to be heated via a film material, and can be used as an apparatus for thermally fixing an unfixed toner image as a permanently fixed image on the surface of a recording material carrying the image. Further, for example, it can be widely used as a device for heating a recording material carrying an image to improve the surface properties such as gloss and the like, a device for performing a hypothetical deposition process, and a device for heating a sheet-shaped material to be heated.

[0006] Such a film heating type heating device has a heating element having a low heat capacity with a rapid temperature rise, for example, a ceramic substrate having an insulating property and a good thermal conductivity, and provided on the surface of the substrate. A so-called ceramic heater having a basic structure of a resistance heating layer that generates heat by energization can be used,
In addition, since a thin film having a low heat capacity can be used as the film material, the temperature of the heating body rises in a short time, and there is no need to supply power to the heating body during standby. Even when the recording medium is immediately passed, the heating element can be sufficiently heated to a predetermined temperature before the recording material reaches the fixing portion, so that the wait time can be reduced (quick start property: operated on demand), The present invention has advantages such as power saving and a reduction in temperature rise in the apparatus such as an image forming apparatus, which is effective.

[0007]

In such a heating apparatus, it is ideal that all of the toner on the recording material is heated and melted and fixed on the surface of the recording material. There are toners in an offset state, toners that are excessively melted, toners electrostatically adhering to a fixing roller and a fixing film, and the like (hereinafter, referred to as offset toners). These offset toners transfer from the fixing film fixing roller to the pressure roller at the nip and accumulate, thereby causing pressure roller contamination. Conventionally, the heating roller, the fixing film, and the surface layer of the pressure roller used in the fixing device as a measure for preventing contamination of the pressure roller have PTFs having high release properties.
Fluororesin layer such as E, PFA, FEP, LTV, RT
It was common to use a silicone rubber layer such as V.

However, this release layer does not completely eliminate toner contamination. In such a state, if toner contamination adheres to the toner contact surface side of the heating rotator such as the fixing roller and the fixing film, the heating rotator is constantly heated to the toner melting temperature during image formation, so Is in a molten state, and when the next recording material arrives, it mixes with the toner image on its surface and moves to the recording material, or moves to the pressure roller between the papers, so that the heating rotator is continuously There is no state of being dirty.

On the other hand, since the pressure roller has a lower temperature than the heating rotator, it does not always exist in a completely melted state on the moved toner contamination pressure roller. In particular, in an on-demand type fixing device using a fixing film, the pressure roller is not heated except at the time of paper passing, so that the temperature hardly rises and rises to only about 100 ° C. at the maximum. For this reason, the toner stain transferred to the pressure roller by offset as described above hardly melts on the pressure roller. Further, since the toner image on the surface of the recording material does not come into contact with the pressure roller side, dirt is rarely carried to the toner image, and once dirt is accumulated, the dirt is accumulated. When toner stains on the pressure roller accumulate, the releasability of the pressure roller decreases, so that the recording material (especially when the recording material is an OHP film) is wound around or accumulated on the pressure roller. There is a problem that the recording medium is smudged at once by the toner stain.

In particular, recently, printers using the electrophotographic system have been widely used all over the world, and accordingly, recording materials used in the printers have been diversified.

[0011] For example, in the European market, the recording material has a high degree of whiteness and is preferred, and CaCO ₃ is often used as a filler for the recording material. However, C
When aCO ₃ adheres to the pressure roller, the releasability of the pressure roller deteriorates, and the toner stain on the pressure roller is accelerated and aggravated. The adhesion of CaCO _{3 to} the pressure roller becomes more severe in a low humidity environment. Further, the toner contamination of the pressure roller becomes more severe in a low temperature environment.

For example, in an environment of 15 ° C./10%, CaCO ₃
When the paper passing durability is increased by using a recording material containing 10% to 15%, the pressure roller starts to be stained when the number of sheets passed from 1,000 to 2,000, and the toner is stained on the recording material with almost the same number of sheets. It becomes bad.

Accordingly, the present invention provides a method for preventing a rotating rotary member from being stained.
It is another object of the present invention to provide an image heating apparatus capable of preventing an image defect associated therewith and an image forming apparatus provided with the same.

[0014]

An image heating apparatus and an image forming apparatus having the same according to the present invention have the following features to solve the above-mentioned problems.

[1]: A recording material having an image and having a heating rotator heated by a heating means and a pressure rotator for forming a nip by mutually pressing the heating rotator. In the image heating apparatus which heats an image by nipping and transporting the nip, the circumference Df of the heating rotator is the circumference D
r, and after the rotation of the heating rotator is started, the heating of the heating rotator is started, and the heating rotator determines the difference in the circumferential length ΔD between the heating rotator and the pressing rotator. An image heating apparatus wherein heating is started before rotation is performed.

[2]: A heating rotator heated by a heating means, and a pressure rotator for forming a nip having a width N in the rotation direction by pressing against the heating rotator with each other. In an image heating apparatus in which an image is heated by nipping and transporting a held recording material in the nip, the circumference Df of the heating rotator is made larger than the circumference Dr of the pressing rotator to rotate the heating rotator. After starting, the heating of the heating rotator is started,
And an image heating apparatus which starts heating before the heating rotator rotates by a length d obtained by subtracting a nip width N from a circumferential difference ΔD between the heating rotator and the pressing rotator. .

[3] The image heating apparatus according to [1] or [2], wherein heating by the heating means is started after the rotating body has rotated by a distance equal to or greater than the nip width N.

[4]: A heating rotator to be heated by the heating means and a pressure rotator for forming a nip having a width N in the rotation direction by mutually pressing the heating rotator, In an image heating apparatus that heats an image by nipping and transporting a held recording material through the nip, the peripheral length Df of the heating rotator is made larger than the peripheral length Dr of the pressing rotator. The heating by the heating means is not performed from the end of the rotation of the body until the next heating treatment, and the rotating body is rotated by a predetermined distance when the temperature detected by the temperature detecting means of the apparatus becomes equal to or lower than a predetermined temperature TP. An image heating device characterized by the above-mentioned.

[5] The image heating apparatus according to [4], wherein the predetermined distance is equal to or less than a circumferential length difference ΔD between the heating rotating body and the pressing rotating body.

[6]: The predetermined distance is not less than the nip width N and not more than the length d obtained by subtracting the nip width N from the circumferential length difference ΔD between the heating rotating body and the pressing rotating body. ]
An image heating device according to claim 1.

[7]: When the heating process is started, when the detected temperature of the temperature detecting means is higher than the predetermined temperature TP and when the detected temperature is lower than the predetermined temperature TP, the heating rotating body or the pressing rotating body is changed. The image heating apparatus according to [4], [5] or [6], wherein the time difference from the start of rotation to the start of heating of the heating means is different.

[8] The image heating apparatus according to any one of [4] to [7], wherein the predetermined temperature TP is equal to or lower than the softening point of the toner forming the image.

[0023]

[9]: any one of [4] to [8], wherein the temperature detecting means is provided in the heating rotator and is also used as a temperature detecting means for controlling the temperature of the heating means. An image heating device according to claim 1.

[10]: The heating rotator is an endless film (preferably a seamless and endless film.
An endless film may be joined by joining end pieces.)
Characterized by [1] to

The image heating apparatus according to any one of [9].

[11] The image heating apparatus according to any one of [1] to [10], wherein the pressing rotary member is a pressing roller.

[12] The image heating apparatus according to any one of [1] to [11], wherein the circumferential length difference ΔD between the heating rotating body and the pressing rotating body is longer than the nip width N. .

[13] The image according to any one of [1] to [12], wherein the releasability of the outer peripheral surface of the pressurizing rotary body is higher than that of the outer peripheral surface of the heating rotary body. Heating equipment.

[14] The image heating apparatus according to any one of [1] to [13], wherein the heating process is a process of thermally fixing the image on a recording material.

[15]: In an image forming apparatus having an image forming means for forming an image on a recording material and an image heating means for heating the image on the recording material, [1] to [14] An image forming apparatus comprising the image heating device according to any one of [14] and [14].

<Operation> In the conventional image heating apparatus, generally, the driving of the rotating body and the heating of the heating means are started at the same time. In this case, however, the heated rotating body is heated first, and the contamination existing in the nip is removed. While the adhesive force with the source is weakened, the pressurizing rotator remains in a cold state, and the adhesive force with the dirt source remains unchanged. For this reason, when the rotation is started, the source of dirt present in the nip almost adheres to the pressure rotating body side.

Therefore, according to the configuration [1], there is no temperature difference between the heating rotator and the pressing rotator at the start of rotation, and a source of dirt can be attached to the heating rotator. Further, the portion on the heating rotator to which the source of the dirt has adhered does not overlap with the source of the dirt attached to the pressing rotator when reaching the nip after one rotation, and passes through the nip once on the outer peripheral surface of the pressing rotator. As a result, the source of dirt is less likely to be transferred to the pressing rotator again, so that the dirt on the pressing rotator can be prevented.

According to the configuration of [2], in addition to the configuration of [1], the upper limit of the distance over which the rotating body rotates between the start of rotation of the rotating body and the start of heating of the heating means is further limited.
When the entire area on the heating rotator to which the dirt source having the same width as the nip width adheres reaches the nip after one rotation, it contacts the portion of the outer peripheral surface of the pressure rotator that has once been heated through the nip. Therefore, dirt on the pressure rotating body can be more reliably prevented.

According to the configuration [3], in addition to the configurations [1] and [2], the lower limit of the moving distance of the rotating body at the start of the heat treatment is limited, so that the nip exists at the start of the heat treatment. The source of dirt can be adhered to the heating rotator over the entire nip width, so that dirt on the pressure rotator can be more reliably prevented.

According to the configuration [4], by moving the source of dirt present in the nip when the temperature becomes equal to or lower than the predetermined temperature TP, regardless of slipping of the rotating body in a low temperature environment, etc. The source of dirt can be reliably adhered to the heating rotator side.

According to the configuration of [5], in addition to the configuration of [4], the upper limit of the moving distance of the rotating body at the start of the heating process is limited, so that the portion on the heated rotating body to which the source of dirt has adhered. But,
When the nip is reached after one rotation, it comes into contact with the portion of the outer peripheral surface of the pressure rotating body that has once passed through the nip and has been warmed, making it difficult for the source of dirt to transfer to the pressure rotating body again, and more reliably pressurizing. Dirt on the rotating body can be prevented.

According to the configuration of [6], in addition to the configuration of [4], by limiting the upper and lower limits of the moving distance of the rotating body at the start of the heat treatment, the source of dirt having the same width as the nip width can be reduced. When the entire area of the adhered heating rotator reaches the nip after one rotation, it comes into contact with the portion of the outer peripheral surface of the pressure rotator that has once been heated through the nip, so that the source of dirt is again generated by the pressure rotator. And it is possible to more reliably prevent the pressurized rotating body from being stained.

According to the configuration [7], the source of dirt can be stably and efficiently fixed to the heating rotator without being influenced by the surrounding environment, and the dirt on the pressure rotator can be more reliably prevented. .

According to the configuration [8], the toner can be more strongly adhered to the heating rotator by rotating the rotator after the toner forming the image is cooled to the softening point or lower, and the pressing rotator is It is possible to reduce the amount of transfer to the rotator, and it is possible to more reliably prevent the pressurized rotating body from being stained.

[0039]

According to the configuration [9], the temperature detecting means is also used for controlling the temperature of the heating means, and the apparatus can be simplified.

According to the configuration [10], the heating rotator is a film having a small heat capacity, and is easily heated and cooled. Therefore, it is possible to melt the source of the dirt and lower the softening point or less in a short time. The time required for control can be shortened.
Therefore, it is possible to efficiently prevent the pressure rotating body from being stained, and
User friendly and energy saving.

According to the configuration [12], the lower limit of the circumferential length difference between the heating rotator and the pressing rotator is limited, so that the dirt source having the same width as the nip width adheres to the heating rotator. When the whole area reaches the nip after one rotation, it does not overlap with the source of the dirt attached to the pressure rotary body side, so that the dirt on the pressure rotary body can be more reliably prevented.

According to the structure [13], most of the dirt sources existing in the nip can be attached to the heating rotating body when the rotating body starts rotating.

According to the configuration [15], it is possible to prevent the pressurized rotating body from being stained, and to prevent image defects accompanying the contamination.

[0044]

FIG. 1 is a cross-sectional view of an image forming apparatus using the present invention.

At the start of printing, first, the sheet feeding cassette 1
(Recording material) K is fed from the printer, the top sensor 2 provided in the middle of the conveyance path recognizes the leading end of the paper K, and an image is formed on the photosensitive drum 5 in synchronization with this.

The photosensitive drum 5 is uniformly charged by the charging roller 4. After this, the laser optical system 3
A latent image is formed by scanning and exposing the photosensitive surface with light L from the light source, and a visible image, that is, a toner image is formed by selectively attaching toner to an exposed portion of the latent image by the developing device 6. . The toner image on the photosensitive drum 5 is the paper K
In synchronization with this, the photosensitive drum 5 and the transfer roller 9 reach an opposing portion (transfer portion), and when a voltage having a polarity opposite to that of the toner is applied from the transfer roller 9 side, the toner is attracted and transferred onto paper. . The toner and paper dust remaining on the photosensitive drum 5 are removed by the cleaner 7.

These laser optical system 3, charging roller 4,
The toner image formed on the paper by the image forming means including the photosensitive drum 5, the developing device 6, the transfer roller 9, and the like is fixed on the paper by applying heat and pressure by a fixing device (image heating means) 8. .

FIG. 2 is a sectional view of a fixing device (image heating device) used in the present embodiment. In this method, heating is performed by a ceramic heater (heating means) 17 from the inside through a cylindrical film formed of a heat-resistant resin such as polyimide.

The ceramic heater 17 is formed by printing a resistor pattern 2 on a heat-resistant substrate 19 such as alumina by printing.
0, a glass layer 21 is formed. Ceramic heater 1
A thermistor (temperature detecting means) 18 is attached to the back surface of 7. The temperature of ceramic heater 17 is set to thermistor 1
The heat is adjusted by controlling the energization of the ceramic heater 17 by the triac (registered trademark: gate control type semiconductor switch) 11 by the CPU 10.

Reference numeral 16 denotes a heater holder formed of a heat-resistant resin or the like. A fixing film (heating rotator) 12 coated with heat-resistant grease (not shown) on the inner surface thereof is loosely fitted thereto, and is pressed by a pressure spring (not shown). Pressure is applied to the pressure roller side. Reference numeral 13 denotes a pressure roller (pressure rotating body) which is formed on a metal core 14 by a heat-resistant elastic release layer 15 such as silicone rubber.
Is provided. In this embodiment, the fixing film 12 has an outer diameter of φ25, and the pressing roller 13 has a roller diameter of φ19. A is a nip portion formed by the fixing film 12 and the pressure roller 13. In the present embodiment, in particular, the hardness of the pressure roller and the pressure spring are adjusted, and the nip width N is set to 5 mm. Further, a stepping motor (not shown) is used as a driving source of the fixing device of the present embodiment.

When the paper K carrying the unfixed toner image T by the image forming means is introduced into the nip A,
With the heat from the heater 17 via the film 12 and the pressure from the pressure spring being applied, the toner image T is conveyed by the rotation of the pressure roller 13, and the toner image T is fixed on the paper K (heat treatment).

In such an apparatus, the source of dirt on the pressure roller is, as shown in FIG. 3 (a), the offset toner present in a fog-like size of invisible size on the stopped film after printing is completed. W and paper dust P are mainly generated by mixing in the nip between the pressure roller 13 and the film 12 as shown in FIG. Heater 1 is placed in a state where a mixture M in which toner W and paper powder P are mixed is sandwiched in a nip.
If the start of energization is performed without delaying the start of driving of the pressure roller 13, the temperature of the film 12 rises more rapidly than that of the pressure roller 13. The mixture M becomes weaker, and all of the mixture M is transferred to the pressure roller side, and accumulation of the mixture causes pressure roller contamination.

In order to avoid this process, in the present embodiment, when the fixing device is raised to the fixing temperature, the heating of the pressure roller 13 is started after the driving of the pressure roller 13 is started. That is, it starts from driving the motor. FIG. 4 shows this sequence as a flowchart.

As shown in the figure, when printing is started in response to a print signal from the operation unit or other equipment (S1), first, the motor is started, and at the same time, the timer in the CPU is initialized (S2). A timer is started (S3). It is C whether or not this timer has exceeded t1 time.
The determination is made by the PU (S4), and if YES, energization of the heater is started (S5). Accordingly, the start of energization of the heater 17 is delayed by t1 sec with respect to the start of driving of the motor.

Before the heating, the pressing roller 1 is heated.
When the film 12 and the film 12 are displaced from each other, there is almost no temperature difference between the film 12 and the pressure roller 13.
The mixture M of the toner and the paper powder formed in the nip as shown in FIG. 5A has an invisible size, and mainly has lower releasability than the pressure roller as shown in FIG. 5B. Attaches on film. Then, the fixing portion X of the mixture M on the film has moved a distance d outside the nip at time t1.

However, not all of the mixture M is taken to the film side, and about 10% of the entire mixture M remains on the pressure roller side. This portion is shown as a fixing portion Y in FIG.

The present invention is further characterized in that the surface temperature of the pressure roller which is pressed when the fixing portion X of the mixture M on the film passes through the nip again increases.

More specifically, heating is started after the rotation of the film 12 is started and before the film 12 rotates by the circumferential length difference ΔD with the pressure roller 13. In the present embodiment, the time difference t1 from the start of rotation of the film 12 to the start of heating is set to 0.3 sec.

The reason will be described below. In the stepping motor used in the present embodiment, the pressure roller rotates 8 mm during 0.3 sec from the drive ON of the motor. At this time, since the film is also driven and rotated by 8 mm, the energization of the heater 17 is started when the mixture M moves from the nip A to a position d = 8 mm downstream in the paper conveyance direction. Since this distance d is smaller than the circumference difference ΔD, the mixture M
From the position 8 mm downstream of the nip to the nip A again (70.5 mm), preferably the distance D until the tip of the mixture enters the nip A D = 65.5 mm (= φ25)
× 3.14-8-5), the circumferential length of the pressure roller 13 is made smaller.

The circumference of the pressure roller is 59.7 mm (= φ1
Since the film rotates 95.5 mm, the pressure roller rotates 5.8 mm for one rotation until the film rotates 65.5 mm. For this reason, as shown in FIG. 5C, the mixture passes through the nip A while overlapping the warm pressure roller surface that has once passed through the fixing nip A, so that the mixture is not easily transferred to the pressure roller. Even when the paper K is transferred to the scale, the amount is extremely small, and the surface is generally much rougher than the pressure roller 13 or the film 12 and is taken when the paper K having a lower temperature than the film 12 passes. 13 is no longer dirty.

The toner W adhered on the film
When the paper K enters the nip A, the mixture M presses against the paper K in a state where heat is applied from the film side, so that the mixture M is taken to the paper K and grows as a film stain. There was no.

Table 1 shows the relationship between the film moving distance d when the time difference t1 from the start of the film rotation to the start of the heating and the relationship between the pressure roller contamination and the endurance after the time t1. The results are shown in Table 2. Evaluation,
At room temperature (20 ° C.), paper containing 20% by weight or more of calcium carbonate was subjected to intermittent durability of 3 sheets / 20 minutes, and dirt on the pressure roller was observed.

[0063]

[Table 1]

[0064]

[Table 2]

As can be seen from Tables 1 and 2, the structure is such that the surface temperature of the pressure roller 13 to be pressed when the mixture M on the film passes through the nip A again is increased.
That is, the film movement distance d is the nip width N (= 5 mm)
And the peripheral length difference between the film and the pressure roller−nip width N = Df−Dp−N> d, that is, 13.8 mm> d
(Df = film circumference, Dp = pressure roller circumference) t1 = 0.3 sec (d = 8 m at this time)
In the case of m), the best result with respect to the pressure roller contamination is shown.

Further, the circumferential length difference between the film and the pressure roller = D
Even when the relationship of f-Dp> d, that is, 18.8 mm> d, is satisfied, a favorable result with respect to the contamination of the pressure roller is shown as compared with the related art.

As described above, it was possible to prevent the pressure roller from being stained in the fixing device and the image forming apparatus, and to prevent image defects caused thereby.

<Embodiment 2> The embodiment 1 was very effective against pressure roller contamination when used in a normal environment. However, in a low-temperature environment of 0 ° C. or lower, the grease viscosity on the inner surface of the fixing film increases, causing the film 12 and the pressure roller 13 to slip, and
Even if the energization of the heater is delayed by 0.5 sec with respect to the driving of the pressure roller 13, the energization of the heater is started while the mixture of the toner W and the paper dust P stays in the nip, and the pressure roller is contaminated. was there.

The present embodiment provides an LBP (laser beam printer) that does not cause pressure roller contamination stably even in such an environment. That is, in the present embodiment, the start of energization of the heater is delayed by 0.3 sec with respect to the start of rotation of the pressure roller at the start of printing as shown in FIG.
When the temperature becomes lower than or equal to ° C., the main motor is driven by a pulse and step feed is performed once. This embodiment is different from the first embodiment in the control system such as the CPU for controlling the driving of the pressure roller and the heating control of the heating means, and the other configurations are substantially the same. Repetitive description is omitted by giving the same reference numerals to the elements.

Hereinafter, description will be made based on the flowchart of FIG.

First, in the present embodiment, when printing is started upon receiving a print signal (S10), the case of the first printing after the main power is turned on is distinguished from the case of other printing (S11).

In the case of the first printing after the main power is turned on,
This is exactly the same as the first embodiment. That is, the driving of the pressure roller 13 is started before the heater is energized, that is, the driving of the motor is started. At this time, the timer in the CPU is initialized at the same time (S12), and the timer is started (S13).

The CPU determines whether or not the timer has exceeded the time t1 (S14), and if YES, energizes the heater (S15). Accordingly, the start of energization of the heater 17 is delayed by t1 sec with respect to the start of driving of the motor.

As described above, in the low-temperature environment, the film becomes difficult to rotate. Therefore, if the control of the first embodiment is used, the source of the stain mainly adheres to the pressure roller side. However, it is rare that the main power is turned off every time printing is completed as a usual usage of LBP, and a plurality of prints are performed while the main power is turned on. Therefore, even if the source of dirt adheres to the pressure roller side at the time of the first printing after the main power is turned on, since the amount is small, the dirt comes off at the time of passing through the nip of the print paper or the like, so that no dirt is generated.

After the printing is completed (S18), the next print signal comes while monitoring whether or not the thermistor temperature (the temperature detected by the thermistor 18) has fallen below a predetermined temperature (a temperature at which the toner is considered to be hardened) TP ° C. (S19, S20), and when the thermistor temperature is lower than TP ° C., a pulse is sent to the main motor, and the pressure roller is stepped to stand by until the next print signal (S21, S22). .

Next, the case of the second or subsequent print after the main power is turned on will be described.

In the case of the second or subsequent print after the main power is turned on, it is determined in step S16 whether or not the thermistor temperature has become lower than the predetermined temperature TP ° C. after the previous print is completed. If above, step S
Proceeding to 12, the same startup as in the case of the first printing after the main power is turned on is performed.

When printing is started from a temperature lower than TP ° C., the CPU sends a pulse to the main motor when the temperature of the thermistor before the print signal comes below TP ° C. in steps S19 and S21. The pressure roller 13 is moved stepwise to move the film forming the nip portion and the pressure roller portion, whereby the mixture M of the toner and the paper powder mainly arrives on the film side with poor releasability. In this state, it is out of the nip A.
Therefore, in this case, the driving of the pressure roller 13 is started and the heater is turned on at the same time (S17). Note that TP is desirably set to a temperature at which the toner can be considered to be hardened.

As shown in Table 3, the test was conducted by changing the TP to several temperatures. When the TP was set at a temperature lower than the softening point 70 ° C. of the toner resin at which the softening of the toner began, good results were obtained. Obtained.

[0080]

[Table 3]

In this embodiment, one of the step motors is used.
Since the pressure roller and the film rotate about 8 mm in each step feed, the mixture M of toner and paper powder, which is a source of dirt, moves on the film 8 mm outside the nip. Then, in this state, the stopped state is maintained until the next print comes.

As described above, in each case, the heater is
In the case of N, the mixture M of toner and paper powder, which is a source of dirt, is located outside the nip and on the film 8 mm downstream in the paper transport direction.

Further, as in the first embodiment, the surface temperature of the pressure roller which is pressed when the mixture of the toner and paper powder on the film passes through the nip A again is increased.

That is, the distance 65.5 until the mixture M enters the nip A again from above the film 8 mm downstream of the nip.
mm (= φ25 × 3.14-8-5), the circumference of the pressure roller 13 is made smaller. Since the circumferential length of the pressure roller 13 is 59.7 mm (= φ19 × 3.14), the pressure roller rotates one rotation and 5.8 mm before the film rotates by 65.5 mm. For this reason, the mixture overlaps the warm pressure roller surface once passing through the fixing nip, and the nip A
, It is difficult to transfer to the pressure roller side.

Further, even if the transfer to the scale is performed, the amount thereof is extremely small, and is generally taken when paper K having a surface property much coarser than that of the pressure roller 13 or the film 12 passes, so that the pressure roller 13 is not stained. . The mixture M of the toner and the paper powder adhering to the film is pressed against the paper K when the paper K enters the nip A while being heated from the film side. He did not grow as a film stain.

In the following, the relationship between the number of sheets passed and the contamination of the pressure roller was examined in a low-temperature environment (0 ° C.) for the configuration in which TP = 60 ° C. in the present embodiment, and very good results were obtained.
Table 4 shows the results. Table 4 shows the configuration of the first embodiment for comparison, the configuration not using the sequence shown in FIG.
That is, a configuration in which the driving of the pressure roller is started and the heater is turned on at the same time under any condition is described as a conventional example.

[0087]

[Table 4]

The results in Table 4 show that the present embodiment is very effective against pressure roller contamination even in a low temperature environment of 0 ° C. In this way, when the temperature is lower than 60 ° C., the operation of taking out the mixture M onto the film outside the nip A is always performed, so that the pressure roller can be reliably prevented from being stained even in a low temperature environment of 0 ° C. Could be obtained.

<Embodiment 3> The basic configuration of this embodiment is the same as Embodiment 2 except that the diameter of the film 12 is φ42.

Also in this embodiment, the mixture M of the toner and the paper powder, which is a source of the stain generated after the end of the printing, is always 8 m downstream of the nip at the start of the energization to the heating element 20 for the next printing.
m on the film.

The most significant feature of the present configuration is that the pressure roller operates between the fixing nip where the heating element is energized before the source of the dirt circulates again on the film and enters the fixing nip. Is passed twice.

As a result, the surface temperature of the pressure roller 13 became higher than that in the first and second embodiments, and the mixture M of toner and paper powder, which was a source of dirt, did not transfer to the pressure roller 13 at all. . Further, the mixture M of the toner and the paper powder adhering to the film is pressed against the paper K in a state where heat is applied from the film side when the paper K enters the nip A. He did not grow as a film stain.

As described above, it was possible to obtain a configuration in which contamination of the pressure roller and the like did not occur.

<Others> In the above embodiment, the apparatus of the film heating type has been described. However, the present invention is not limited to this, and the metal roller 26 including the halogen heater 25 as shown in FIG.
The same effect can be obtained when the present invention is applied to a heat roller type image heating device such as a device using a heating roller as a heating rotator or a device for electromagnetically heating a metal roller.

2. In the above-described embodiment, a so-called tensionless type apparatus has been described. However, the present invention is not limited to this, and as shown in FIG. 7B, the heater 17, the driving roller 12a, and the tension roller 12b are wound and stretched. The same effect can be obtained when the endless film 12 is used as a heating rotator and applied to an image heating apparatus of a system in which the film 12 is rotated by driving the drive roller 12a and the pressure roller 13 is driven.

3. In the above embodiment, the apparatus using the ceramic heater as the heating means has been described. However, the present invention is not limited to this, and the magnetic force generated by the exciting coil 23 acts on the magnetic body 24 as shown in FIG. A device that generates an induced current to generate heat in the magnetic body 24 by Joule heat, or a device that causes a magnetic force generated by an exciting coil to act on the film 12 having a heating layer made of a magnetic material to generate heat in the film itself. Similar effects can be obtained when the present invention is applied to an image heating apparatus using a heating means of an electromagnetic induction heating system.

4. In the above embodiment, the pressure roller is shown as the pressure rotating body. However, the present invention is not limited to this, and the present invention is configured such that the transport belt 13 is wound around the drive roller 13a and the driven roller 13b, and the film 12 and the transport belt are transported. The same effect can be obtained when the present invention is applied to an apparatus in which the nip A is formed by pressing the heater 17 and the guide member 13c with the belt 13 interposed therebetween.

[0098]

As described above, according to the present invention,
It is possible to provide an image heating apparatus capable of preventing contamination of a pressure rotating body and preventing an image defect associated therewith, and an image forming apparatus including the same.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus including a fixing device according to the present invention.

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

FIG. 3 is a conceptual diagram showing a state of generation of a mixture of toner and paper powder in a fixing nip.

FIG. 4 is a control flowchart of a print operation according to the first embodiment.

FIG. 5 is an explanatory diagram of a relationship between a mixture adhering position and a rotating state of a rotating body.

FIG. 6 is a control flowchart of a print operation according to the second embodiment.

FIG. 7 is a diagram showing another configuration example of the image heating apparatus according to the present invention.

FIG. 8 is a diagram showing another configuration example of the image heating apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Paper feed cassette 2 Top sensor 3 Laser optical system 4 Charging roller 5 Photoreceptor drum 6 Developing device 7 Cleaner 9 Transfer roller 12 Film (heating rotator) 13 Pressure roller (pressing rotator) 17 Heater (heating means) 18 Thermistor (Temperature detecting means) 19 Base material 20 Resistor pattern (heating element) 21 Glass layer 23 Excitation coil 24 Magnetic body 25 Halogen heater 26 Metal roller A Nip K Paper W Offset toner P Paper powder M Mixture of toner and paper powder N Nip width X Adhered portion of mixture on heated rotator surface Y Adhered portion of mixture on pressurized rotator surface d Moving distance of adhering portion of mixture T Toner image

Claims (15)

[Claims] 1. A rotator heated by a heating means, and a pressure rotator for forming a nip by mutually pressing the rotator, and a recording material carrying an image is transferred to the nip. In the image heating apparatus which heats the image by nipping and transporting, the circumference Df of the heating rotator is made larger than the circumference Dr of the pressing rotator, and after the rotation of the heating rotator is started, the heating rotation An image heating apparatus, wherein heating of a body is started, and heating is started before the heating rotator rotates the circumference difference ΔD between the heating rotator and the pressing rotator. 2. A heating rotator heated by a heating means, and a pressure rotator for forming a nip having a width N in the rotation direction by mutually pressing the heating rotator, and carrying an image. In an image heating apparatus that heats an image by nipping and transporting a recording material in the nip, the circumference Df of the heating rotator is set to be larger than the circumference Dr of the pressing rotator to start rotation of the heating rotator. After that, heating of the heating rotator is started, and the heating rotator rotates by a length d obtained by subtracting a nip width N from a circumferential difference ΔD between the heating rotator and the pressing rotator. An image heating apparatus characterized in that heating is started during the period. 3. The image heating apparatus according to claim 1, wherein the heating by the heating means is started after the rotating body has rotated by a distance equal to or more than the nip width N. 4. A heating rotator heated by a heating means, and a pressure rotator for forming a nip having a width N in the rotation direction by mutually pressing the heating rotator, and carrying an image. In an image heating apparatus that heats an image by nipping and transporting a recording material at the nip, the circumference Df of the heating rotator is made larger than the circumference Dr of the pressing rotator, and After the rotation is completed, heating by the heating means is not performed until the next heating process, and the rotating body is rotated by a predetermined distance when the temperature detected by the temperature detecting means of the apparatus falls below a predetermined temperature TP. Image heating device. 5. The apparatus according to claim 4, wherein the predetermined distance is equal to or less than a circumference difference ΔD between the heating rotating body and the pressing rotating body.
An image heating device according to claim 1. 6. The method according to claim 4, wherein the predetermined distance is not less than a nip width N and not more than a length d obtained by subtracting the nip width N from a circumferential difference ΔD between the heating rotating body and the pressing rotating body. The image heating device according to claim 1. 7. When the heating process is started, when the temperature detected by the temperature detecting means is higher than a predetermined temperature TP and when the detected temperature is lower than the predetermined temperature TP, the rotation of the heating rotator or the pressurizing rotator is started. 7. The image heating apparatus according to claim 4, wherein a difference in time from when the heating unit starts heating is different. 8. The image heating apparatus according to claim 4, wherein the predetermined temperature TP is equal to or lower than a softening point of a toner forming the image. 9. The apparatus according to claim 4, wherein said temperature detecting means is provided in said heating rotator and is also used as a temperature detecting means for controlling the temperature of said heating means.
Item 10. The image heating device according to item 1. 10. The image heating apparatus according to claim 1, wherein the heating rotator is an endless film. 11. The image heating apparatus according to claim 1, wherein the pressing rotator is a pressing roller. 12. A circumferential difference Δ between a heating rotating body and a pressing rotating body.
The image heating apparatus according to any one of claims 1 to 11, wherein D is longer than a nip width N. 13. The releasability of an outer peripheral surface of a pressurizing rotary body is made higher than an outer peripheral surface of a heating rotary body.
13. The image heating apparatus according to any one of claims 12 to 12. 14. The image heating apparatus according to claim 1, wherein the heating process is a process for thermally fixing the image on a recording material. 15. An image forming apparatus comprising: an image forming means for forming an image on a recording material; and an image heating means for heating the image on the recording material, wherein the image heating means is provided. An image forming apparatus comprising the image heating device according to claim 1.