JP2003280442A - Image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation in fixed image quality which is caused by offset, trailing, fixing failure, etc., which result from the speed-up and life prolongation of an image heating device of a film heat system. <P>SOLUTION: In the image heating device of the film heat type, a heating body 1 has heating elements h1 and h2 constituted of resistors arranged parallel to each other in the direction in which a recording material is transported. The heating elements h1 and h2 can be energized and driven independently of each other, and have control circuits 100 and 101 which control so that the ratio of the amounts of heat emitted by the heating elements is variable. The control circuits make the above ratio between the heating elements h1 and h2 variable in a period when the recording material is transported while being put between the film and pressure member of a nip and before and after the period. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a fixedly supported heating element, a film that slides on the heating element, and a pressure member that forms a nip with the heating element via the film. The recording material carrying the image is nipped and conveyed between the film of the nip and the pressure member to heat the image on the recording material by the heat from the heating body through the film,
The present invention relates to a film heating type image heating apparatus.

This device is an electrophotographic copying machine, printer,
A fixing device (fixer) in an image forming apparatus such as a fax, that is, a recording material (electrofax) using a toner made of a heat-meltable resin by an appropriate image forming process means such as electrophotography, electrostatic recording, magnetic recording, etc. Seat
Recording that carries an unfixed toner image corresponding to the target image information that is formed on the surface of the electrostatic recording sheet, transfer material sheet, printing paper, etc. by a direct method or an indirect (transfer) method. It can be used as a device for heating, pressing and fixing processing as a permanently fixed image on the material surface.

Further, it can be used as an apparatus for heating a recording material carrying an image to modify the surface properties of gloss and the like, an assumed attachment apparatus, and the like.

[0004]

2. Description of the Related Art Conventionally, in many image forming apparatuses such as electrophotographic copying machines and printers, a contact heating type heat roller fixing method which is excellent in thermal efficiency and safety as an image fixing means, an energy saving type and an on-demand type. The film heating method of is adopted.

A fixing device of a film heating type is disclosed in, for example, Japanese Patent Laid-Open No. 63-313182 and Japanese Patent Laid-Open No. 2-15787.
8, 4-44075-44083, 4-204980
It is proposed in Japanese Patent No. 204984.

FIG. 6 is a schematic configuration diagram of an example thereof. The apparatus of this example is a pressure roller drive type (tensionless) film heating type fixing device (fixing device) using a cylindrical film.

Reference numerals 6 and 6'indicate a fuser upper frame and a fuser lower frame, respectively. Reference numeral 8 is a heating assembly arranged on the fixing device upper frame 6 side, and 4 is an elastic pressure roller (pressing rotary member) as a pressing member arranged on the fixing device lower frame 6'side.

The pressure roller 4 includes a core metal 4c and an elastic layer 4
b and a surface layer 4c, which is a composite layer roller, and both ends of the cored bar 4c are rotatably supported by the lower frame 6'of the fixing device via bearings.

The heating assembly 8 is a heating body (heater).
1, an assembly including a heater holder 2, a cylindrical fixing film (rotating body for heating) 3, a metal stay 5, and the like.

The heating element 1 is a low heat capacity member such as a ceramic heater having a length in a direction orthogonal to the recording material passing direction.

The heater holder 2 is a heat-resistant / heat-insulating / rigid member having a substantially semicircular cross-section gutter shape whose longitudinal direction is perpendicular to the recording material sheet feeding direction. A heater fitting groove is formed along the length of the heater holder in the substantially central portion on the lower surface side of the heater holder 2, and the heating element 1 is fitted and fixedly held in this groove.

The cylindrical fixing film 3 is loosely fitted on the heater holder 2 which holds the heating element 1 fixedly. The fixing film 3 has a film thickness of 100 μm or less, more preferably 40 μm or less and 20 μm or more, in order to reduce the heat capacity and improve the quick start property, PTFE, PFA, PPS having heat resistance, releasability, and durability.
Single layer film or a base layer film 3 such as polyimide, polyamideimide, PEEK, PES as shown in the figure.
PTF with the conductive primer layer 3b sandwiched on the surface of c
Releasable layer 3 made of fluorine resin such as E, PFA, FEP
It is composed of a composite layer film in which a is coated or formed into a tube.

The metal stay 5 is a U-shaped rigid member having a downward cross section and having a length in a direction orthogonal to the recording material passing direction, and is inserted inside the heater holder 2.

The heating assembly 8 described above comprises a pressure roller 4
Of the metal stay 5 with the heating element 1 side facing downward and in parallel with the pressure roller 4 and incorporated in the fuser upper frame 6 side. By pressing and urging, the heating body 1 is pressed against the pressure roller 4 via the fixing film 3 against the elasticity of the pressure roller 4 at a total pressure of about 40 to 147 N (4 to 15 kgf). The heating body 1 and the pressure roller 4 form a fixing nip portion N having a predetermined width via the fixing film 3.

The pressure roller 4 is rotationally driven in the counterclockwise direction indicated by an arrow at a predetermined peripheral speed by a driving means (not shown). As the pressure roller 4 is driven to rotate, the inner surface of the cylindrical fixing film 3 faces downward in the fixing nip portion N due to the frictional force between the pressure roller 4 and the fixing film 3 in the fixing nip portion N. The heater holder 2 is driven to rotate clockwise around the outer circumference of the heater holder 2 while sliding in close contact with the surface. The heater holder 2 also functions as a film guide member for the rotating fixing film 3. Further, between the heating body 1 and the fixing film 3, between the fixing film 3 and the heater holder 2,
Heat-resistant grease is interposed between them to reduce friction,
The driving torque of the pressure roller 4 is lowered and the smooth rotation of the fixing film 3 is ensured.

The heating element 1 is quickly heated by power supply to rise to a predetermined fixing temperature, and the temperature is adjusted to the predetermined fixing temperature.

Then, the pressure roller 4 is rotationally driven, the fixing film 3 is driven to rotate accordingly, and the heating body 1 is supplied with electric power so that the heating body 1 rises to a predetermined fixing temperature and is temperature-controlled. 3, a recording material P carrying an unfixed toner image t is introduced between the fixing film 3 and the pressure roller 4 in the fixing nip N of the fixing device from an image forming mechanism (not shown) along the fixing entrance guide 7. Then, the fixing nip portion N is nipped and conveyed. In the process in which the recording material P is nipped and conveyed through the fixing nip portion N, the unfixed toner image t on the recording material P is heated on the surface of the recording material P by the heat from the heating body 1 via the fixing film 3 and the nip pressure. It is fixed. The recording material P exiting the fixing nip portion N is separated from the surface of the fixing film 3 and discharged and conveyed along the paper discharge guide 7 '.

When a fixing film having a three-layer structure including the above-mentioned conductive primer layer 3b is used as the fixing film 3, a region where the conductive primer layer 3b is exposed is provided at the end of the fixing film as shown in FIG. The conductive rubber ring 4d is fitted to the pressure roller core 4c through the resistor 4e at the end of the pressure roller side opposite to the primer layer surface, and the conductive rubber ring 4d is pressed against the conductive primer layer 3b. Therefore, the primer layer 3b of the fixing film 3
Is grounded by resistance, so that the potential of the fixing film 3 is stabilized, and the electrostatic adverse effect on the charged toner image t on the recording material P is less likely to occur.

As described above, various image forming apparatuses such as printers using the above fixing device eliminate the need for preheating during standby due to high heating efficiency and rising speed, and elimination of waiting time ( It has many advantages such as on-demand), and in particular, the method of driving the cylindrical film with the conveying force of the pressure roller can be realized at low cost. It is expected to be introduced into machines.

FIG. 8 is a structural model view of the heating element 1,
(A) is a plan view of the front side of the heating body, (b) is a partially cutaway plan view of the back side of the heating body, and (c) is c in (b).
It is a cross-sectional enlarged model figure which follows the c line.

Reference numeral 1a is a heater substrate. Alumina (Al
₂ O ₃ ), aluminum nitride (AlN), silicon carbide (S
It is a horizontally long and thin member having high insulation, good thermal conductivity, and low heat capacity such as iC) and having the longitudinal direction in the direction orthogonal to the recording material conveyance direction. The heater 1 of this example uses aluminum nitride (AlN) as the heater substrate 1a.

H1 and h2 are first heat-generating resistors
And the second parallel two-row heating element, and the heater substrate 1a
It is formed and provided along the length of the substrate on one surface side. Each heating element h1 ・ h2 is silver paradium (Ag / Pd) ・ T
It is prepared by forming a pattern by screen printing or the like using an energization heating resistor paste such as a ₂ N and firing it. The first and second heating elements h1 and h2 have the same material, length L, widths w1 and w2, thickness and the like, and have the same resistance value.

Reference numerals 1b and 1c denote first and second power supply electrode portions, which are electrically connected to one end portions of the first and second heating elements h1 and h2, respectively. Reference numeral 1d is a connecting electrode portion that electrically connects the other end portions of the first and second heating elements h1 and h2. First and second power feeding electrode portion 1b
The portion 1c and the connecting electrode portion 1d are formed and prepared by forming a pattern on the surface of the heater substrate 1a by screen printing using a conductive paste such as silver (Ag) and firing.

1e is a heat-resistant glass coating layer,
It is formed so as to cover the first and second two parallel heating elements h1 and h2 and the connecting electrode pattern 1d. The heat-resistant glass coating layer 1e is patterned by screen printing or the like on the surface of the heater substrate 1a using glass paste,
It is formed by firing and is provided to protect and insulate the first and second two parallel heating elements h1 and h2 and the connecting electrode portion 1d.

Reference numeral 1f is a thermistor as a heating element temperature detecting element, which is arranged in contact with the surface of the heat-resistant glass coating layer 1e at the substantially central portion in the longitudinal direction of the heating element 1.

In the heating element 1 of this example, the surface of the heater substrate 1a opposite to the heating element forming surface side is the heating element surface side, and this heating element surface side is the film sliding surface. That is, the heating element 1 is fixedly held by exposing the surface of the heater substrate 1a opposite to the heating element forming surface to the outside and fitting it into the heater fitting groove of the heater holder 2.

Reference numeral 101 denotes a power supply circuit for the heating body 1, which supplies power between the first and second power supply electrode portions 1b and 1c. As a result, the first and second heating elements h1 and h2 generate heat, and the temperature of the entire heating element is rapidly raised. Then, the temperature rise of the heating element 1 is detected by the thermistor 1f, and the detected temperature information is input to the control circuit 100. The control circuit 100 controls the amount of electric power supplied from the power supply circuit 101 to the heating body 1 so that the heating body temperature detected by the thermistor 1f is maintained at a predetermined constant temperature.

[0028]

In order to prevent the deterioration of the quality of a fixed image due to offset, tailing, defective fixability, etc. in the case of considering speeding up and extending the life of the film heating type fixing device. There is a need for further improvement.

As a means for controlling the potential of the surface of the fixing film, which is the surface of the rotating body, like the fixing device of the conventional example (FIGS. 6 to 8) described above, the fixing film is passed from the pressure roller core metal 4c through the conductive rubber ring 4d. By charging the surface to a potential having a polarity opposite to that of the toner, the fixed image quality such as offset and tailing has been improved.

However, even if the potential of the film surface is controlled by such a method, a high fixing temperature is required to secure the fixing property as the speed of the apparatus increases.
A problem is that the margin of fixed image quality such as offset and trailing is reduced.

In the offset, the surface of the pressure roller is covered with a fluororesin coat or a tube having a good releasability,
Since the toner itself tends to be negatively charged by rubbing the paper or film, if the toner has the same negative polarity as the pressure roller, the toner before the fixing nip on the paper repels the pressure roller to the film side. This is a phenomenon in which the toner is transferred to the film side because the transfer force acts, or the viscosity of the toner is lost due to the high fixing temperature and it is difficult for the toner to remain on the paper.

Trailing is a phenomenon in which water vapor is generated on the upstream side of fixing and unfixed toner is deviated to the downstream side with respect to the recording material conveying direction and fixed immediately before the fixing nip.

Further, durability is required in accordance with the prolongation of life, but if the fixing speed is increased or the fixing temperature is raised,
There is also a problem that members such as a film and a roller are damaged during the durability, the releasability of the surface is deteriorated, and the fixed image quality such as offset and tailing is easily deteriorated.

When dirt is accumulated on the film or the roller member, the recording paper may be easily soiled at the time of fixing.

The heating element 1 of the conventional fixing device as described above.
In the case where the heat generation ratio of the first heating element h1 on the upstream side in the recording material conveyance direction and the second heating element h2 on the downstream side, which are arranged in parallel along the recording material conveyance direction, is 1: 1, It has been possible to simplify the structure of the heating element and the control circuit without independently driving the plurality of heating elements h1 and h2.

That is, as described above, the first heating element h1 on the upstream side and the second heating element h2 on the downstream side are the first and second heating elements.
The power supply electrode portions 1b and 1c are simultaneously energized. The heating element h1 on the upstream side and the heating element h on the downstream side
Since each 2 has the same length and width and the same resistance value,
The calorific values of the upstream side and the downstream side are the same.

However, if an attempt is made to increase the speed of the fixing device with such a configuration, the quality of the fixed image such as offset becomes a problem when the fixing temperature becomes high.

FIG. 9 shows the conventional heating element structure shown in FIG. 8 in which the heat generation ratios of the heating elements h1 and h2 on the upstream side and the downstream side are the same, the fixing device is temperature-controlled, and the paper (recording material) is FIG. 6 is a diagram showing temperature distributions in the width direction of the heating body before the sheet enters the fixing nip portion N and when the sheet enters the fixing nip portion N. 24 fixing devices
The temperature is controlled to 220 ° C. by the thermistor 1f at a speed of ppm (transport speed of about 150 mm / sec).

As shown in FIG. 9, when the fixing temperature becomes high and the speed is increased, the electric power of the heating elements h1 and h2 on the upstream side and the downstream side is increased in the conventional heating element structure (FIG. 8). When the ratio is the same, the temperature distribution is flat before paper throwing, but the temperature distribution of the heater substrate becomes higher on the downstream side during paper feeding, and high temperature offset occurs especially on the downstream side of the fixing nip. It will be easier.

The present invention is intended to solve the above problems in a film heating type image heating apparatus in order to stably obtain a good heated image such as a fixed image over the life of the apparatus.

[0041]

The present invention is an image heating apparatus having the following configuration.

(1) A fixedly supported heating body, a film that slides on the heating body, and a pressure member that forms a nip with the heating body via the film, and an image is formed. In an image heating device that heats an image on a recording material by heat from the heating body through the film by sandwiching and transporting the carried recording material between the film in the nip and the pressure member,
The heating element has a heating element composed of a plurality of resistors arranged side by side along the recording material conveyance direction, and each heating element can be independently energized and driven. The control circuit has a variable amount ratio, and the control circuit controls the plurality of heating elements before and after the recording material is nipped and conveyed between the film in the nip and the pressure member. An image heating device characterized in that the heat generation ratio is variable.

That is, according to the present invention, as a means for solving the above problem, a plurality of heating elements arranged in parallel along the longitudinal direction are provided, and the heating value ratio of each heating element is controlled to be variable to ensure good fixing property. However, it is intended to improve fixed image quality such as offset and tailing.

The heat generation amount ratio of the plurality of heat generating elements is made variable before and after the recording material is conveyed to the apparatus. More specifically, the heat generation amount ratio of the upstream heat generating element is changed during paper feeding. The temperature distribution in the width direction of the heater substrate during paper passing can be made flat by increasing the heat generation ratio between the sheets.

This is because when the paper enters the fixing nip during the paper passing, the heat of the heater substrate on the upstream side is taken away to warm the paper. On the other hand, since the paper is sufficiently warmed on the downstream side of the nip, the amount of heat given to the paper by the heater substrate on the downstream side is small. The temperature distribution is flat. Unlike the case of passing the paper, the paper is not conveyed between the sheets, so that it is not necessary to increase the heat generation ratio in the upstream as in the case of passing the paper.

According to the present invention, the temperature on the downstream side of the nip can be lowered, the offset generated when the downstream side of the nip is high can be eliminated, and a good or stable heated image can be obtained throughout the life of the apparatus. be able to.

(2) A fixedly supported heating element, a film that slides on the heating element, and a pressure member that forms a nip with the heating element through the film, and an image is formed. In an image heating device that heats an image on a recording material by heat from the heating body through the film by sandwiching and transporting the carried recording material between the film in the nip and the pressure member,
The heating element has a heating element composed of a plurality of resistors arranged side by side along the recording material conveyance direction, and each heating element can be independently energized and driven. An image heating apparatus comprising: a control circuit having a variable amount ratio, wherein the control circuit varies the heat generation amount ratio of the plurality of heating elements according to the changed device setting heating temperature.

That is, a fixing device in which a device-set heating temperature such as a fixing temperature is made variable is characterized in that the heat generation amount ratio of a plurality of heating elements is made variable by the device-set heating temperature. When the temperature is high, hot offset is likely to occur, so the offset can be reduced by reducing the heat generation amount ratio on the downstream side.

[0049]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> 1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this example is a laser beam printer using an electrophotographic process.

Reference numeral 11 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) which is an image bearing member, and is an OPC,
It is formed by forming a layer of a photosensitive material such as amorphous silicon on a cylinder-shaped substrate such as aluminum or nickel, and is rotationally driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow.

The photosensitive drum 11 is
With a charging roller 12 as a charging device,
It is uniformly charged to the electric potential.

Next, the laser beam scanning exposure 13a by the laser scanner unit 13 as an exposure device is received. The laser scanner unit 13 is turned ON / O in response to the time series electric digital image signal of the target image information.
The FF-controlled laser beam is output to scan and expose the rotary photosensitive drum 11. As a result, an electrostatic latent image corresponding to the scanning exposure pattern is formed on the photosensitive drum 1.

In the electrostatic latent image, a toner image is formed on the photosensitive drum 11 by the developing device 14, and a toner image is formed from the paper feeding portion 17 in the transfer nip portion T formed by the photosensitive drum 11 and the transfer roller 15 as the transfer device. The recording material (transfer material) P is sequentially transferred to the transfer nip portion T at a predetermined control timing.

The paper feeding unit 17 is a cassette paper feeding unit, and the recording materials P stacked and accommodated therein are fed to a paper feeding roller 18 (not shown).
One sheet is separated and fed in cooperation with the sheet separating member, and is fed to the transfer nip portion T at a predetermined timing through a sheet path 19 including a registration roller 20.

The recording material P, to which the toner image has been transferred at the transfer nip portion T, has the toner on the recording paper fixed by the fixing device 21, and is discharged to the discharge detail 23 outside the machine through the sheet path 22.

On the other hand, the transfer residual toner on the photosensitive drum 11 after the toner image is transferred onto the recording material P is cleaned by the cleaning device 1.
The photosensitive drum 1 which has been removed from the surface of the photosensitive drum 1 by 6 and whose surface has been cleaned is repeatedly used for image formation.

2) Fixing Device 21 FIG. 2 is a schematic configuration diagram of the fixing device 21. The device of this example is
This is a pressure roller drive type (tensionless) film heating type on-demand fixing device using a cylindrical film, similar to the fixing device of the conventional example shown in FIGS. The same components and parts as those of the fixing device of FIGS. FIG. 3 shows a heating body 1.
9 is a structural model diagram of the above, and the same components and parts as those of the heating element 1 of FIG.

In the fixing device 21 of this embodiment, 24 ppm is used.
In the present embodiment, the fixing device shown in the conventional example is mounted on an image forming apparatus of (A4 lengthwise paper passing speed of 150 msec).
In order to prevent deterioration of the quality of the fixed image such as tailing, the heat generation ratio of the plurality of heat generating elements is made variable before and after the recording material is conveyed to the fixing device. The heat generation ratio is switched by distinguishing when the paper is in the fixing nip and when it is not, by the flag sensor on the recording paper conveyance between the transfer and the fixing.

That is, in the fixing device 21 of the present embodiment, the heating element 1 includes the first and second heating elements h1 and h2 on the upstream side and the downstream side of the connecting electrode portion 1d of the heating element 1 shown in FIG.
The third heating electrode section 1g (FIG. 3) common to the first heating element on the upstream side by supplying power from the power feeding circuit 101 between the first and third feeding electrode sections 1b and 1g. h1 is independently energized, and power is supplied from the power feeding circuit 101 between the second and third power feeding electrode portions 1c and 1g to independently power the second heating element h2 on the downstream side. Each heating element h1 · h can be energized
The energization ratio of No. 2 can be changed, and the heat generation amount ratio of the heating elements h1 and h2 can be made variable on the upstream side and the downstream side. Since the upstream heating element h1 and the downstream heating element h2 have the same length and width and the same resistance value, when the upstream and downstream heating elements have the same energization ratio, the upstream side and the downstream side Have the same calorific value.

By making the heat generation amount ratio of the upstream heating element h1 higher than the heat generation amount ratio between the sheets during paper passing, it is possible to prevent the temperature on the downstream side of the fixing nip portion from becoming high during paper passing. Therefore, the temperature distribution in the width direction of the heater substrate can be made flat.

This is because, during the passage of the paper, if the paper rushes into the fixing nip portion N, the heat of the heater substrate on the upstream side is taken away to warm the paper. On the other hand, since the paper is sufficiently warmed on the downstream side of the nip, the amount of heat given to the paper by the heater substrate on the downstream side is small. The temperature distribution is flat.

Since the paper is not conveyed between the sheets, unlike the case of passing the sheet, it is not necessary to raise the heat generation ratio in the upstream as in the case of passing the sheet.

In this embodiment, the heat generation ratio (electric power ratio) of the heat generating element during paper feeding is: upstream side: downstream side = 2: 1 power ratio of heat generating element between papers: upstream side: downstream side = 1: 1.

FIG. 4 shows the temperature distribution in the width direction of the substrate during sheet passing when the heating element structure shown in FIG. The figure shows XEROX 4024 LTR (75 g basis weight paper)
After passing through the paper, the temperature distribution on the back side of the substrate of the heating element was observed with a thermoviewer. Measurement is at room temperature (23 ℃ / 5
The fixing control temperature is 220 ° C. at 0% RH).

It can be seen that the temperature distribution just before the paper rush is almost flat in the substrate. About half of the paper (about 13 from the tip
The temperature distribution at the time of entry is low on the upstream side and high on the downstream side. This is room temperature (about 23 ℃)
Because the paper that was left for a while entered the fixing nip part,
This is because the heat of the heater substrate was used to warm the paper. On the other hand, on the downstream side of the nip, the paper is warmed to some extent on the upstream side, so there is less heat absorbed by the paper than on the upstream side, and the heater is overheated on the downstream side. Target temperature 220
It is higher than (℃).

In FIG. 4, the power ratio between the upstream side and the downstream side is 1: 1,
Approximately 13 from the front edge of the paper while passing 2: 1 and 3: 1
The substrate temperature distribution of about 0 mm is shown.

It can be seen that as the heat generation ratio on the upstream side increases, the temperature on the upstream side rises and the temperature distribution becomes flat when the ratio is 2: 1.

It is not desirable that the temperature on the upstream side becomes too high as compared with the temperature on the downstream side because tailing is likely to occur.

Table 1 below shows the results of evaluation of the fixability, offset, and trailing image when the heat generation ratio of the upstream and downstream heating elements was made variable and the power ratio between papers was made the same as the power ratio during paper feeding. Indicates.

[0070]

[Table 1]

The fixing property is evaluated based on the density reduction rate when a halftone image is printed and fixed and rubbed with sillbon paper.

As for the offset, the presence or absence of the offset image of the film cycle when the halftone image is printed is confirmed,
An evaluation was performed.

The tailing is evaluated by observing the degree of image scattering when a fine line image is printed and fixed.

In the table, ◯ is a good level, Δ is an acceptable level, and X is a defective level.

It is advantageous for the fixing property that the heat generation ratio on the upstream side is large. It is considered that this is because the amount of heat required to heat the toner and the paper and fix them on the paper is larger on the upstream side than on the downstream side.

Further, it is advantageous that the offset also has a large power ratio on the upstream side. This is because the temperature on the downstream side of the nip can be prevented from increasing and the high temperature offset can be reduced.

According to the present embodiment, it can be seen that the fixing, offset, and trailing can be set at the allowable levels. The heat generation ratio between the upstream side and the downstream side between the sheets is 1: 1.

By doing so, the temperature distribution in the substrate can be kept flat even between the sheets as shown in FIG.

If the power ratio is set to 2: 1 between sheets as in the case of sheet passing, the temperature on the upstream side rises. Even at the time of passing the paper, the temperature history remains particularly at the front end of the paper, and tailing is likely to occur at the front end of the paper.

In Table 2 below, the heat generation ratio during paper passing is on the upstream side:
In the case where the downstream side is 2: 1 and the electric power between the sheets is variable, the result of tailing evaluation is shown. The apparatus, method, and evaluation criteria used for evaluation are the same as in Table 1.

[0081]

[Table 2]

In order to prevent tailing from occurring even at the leading edge of the paper, it is desirable that the temperature distribution during the paper interval is also flat. According to this embodiment, the power is supplied so that the temperature distribution during the paper interval is also flat. (The amount of heat generation) The ratio is changed.

The power ratio between the sheets in FIG. 4 is upstream: downstream =
If there is a temperature higher than the target controlled temperature (220 ° C.) as in the case of 3: 1, the calorific value of the entire device also increases and the temperature becomes higher.

In such a case, the stress on the pressure roller, the film, the grease, etc., which are the parts of the fixing device, becomes large, and the durability margin of the device disappears. It is desirable to change the power ratio so that

Further, as shown in FIG. 4, when the heat generation ratio upstream: downstream is 3: 1, or 2: 1, there are more portions where the target temperature exceeds 220 ° C. than in the case of 1: 1. However, the amount of heat generated by the entire device increases, which is not desirable from the viewpoint of energy saving.

Further, when it is difficult to heat the fixing device in a low temperature environment or when the fixing device is used in an area where the supply voltage is lower than the rated value of the device, the electric power may be insufficient and the target temperature control temperature for fixing may not be reached. There is also.

According to this embodiment, the temperature on the downstream side of the fixing nip can be lowered, the offset generated when the downstream side of the nip is high can be eliminated, and a stable and good fixed image can be obtained throughout the life of the fixing device. You can

<Second Embodiment> The present embodiment is characterized in that a fixing device having a variable fixing temperature is used, and the heat generation ratio of a plurality of heating elements is made variable according to the fixing temperature.

As a means for changing the fixing temperature, the apparatus has the following three fixing temperature tables, and the user can change the fixing temperature by selecting a desired fixing temperature table.

.. Normal mode: A temperature control table suitable for printing standard paper in a standard environment (normal temperature and humidity environment). The fixing temperature is fixed at 200 (° C.) from the cold state of the fixing device.

.. High mode: A temperature control table that is suitable for low temperature environments or when printing on thick paper and the fixability is not good. The temperature control temperature is higher than in normal mode. The temperature is 21 after the fixing device is cold.
It is fixed at 0 (° C).

.. Low mode: high temperature environment, thin paper, OH
The temperature control table is suitable for printing the P sheet, and the temperature control temperature is lower than in the normal mode. The fixing temperature is fixed at 190 (° C.) from the cold state of the fixing device.

The fixing device of this embodiment is a fixing device mounted on an image forming apparatus of 24 ppm (conveyance speed of 150 mm / sec) similar to that of the first embodiment. When the high mode is selected, high fixing is performed. The temperature is controlled by the temperature, and the energization ratio is higher in the power ratio on the upstream side than in the normal mode or low mode.

Energization ratio of the present embodiment (power ratio = heat generation ratio)
Is

[0095]

[Table 3]

As described in the first embodiment, by setting the power ratio of the upstream heating element h1 to the downstream heating element h2 to 2: 1, XEROX4024 (basis weight: 75 g) can be transferred to NN (normal temperature and normal humidity). In the case of printing in the environment), the fixed image quality such as fixability, offset, and trailing can be set to a level without problems.

However, rough paper (FO
X RVERBond Basis weight 90g Paper and Neenah CLASSICLaid Text
When printing a basis weight of 105 g paper or the like), a high fixing temperature is required to obtain good fixing properties. As described above, when the fixing temperature is high, high temperature offset is likely to occur. Therefore, in the case where a high temperature is required to obtain fixability as compared with plain paper (for example, XEROX4024 basis weight 75 g) like rough paper, in this embodiment, the temperature on the downstream side of the nip is prevented from becoming as high as possible. The power ratio between the upstream side and the downstream side of the high mode is 4: 1.

In the low mode, since the temperature control temperature is low, it is difficult for high temperature offset to occur.
The amount of electric power on the downstream side is the same as that on the upstream side, and there is no problem.

By doing so, it is possible to prevent high-temperature offset even when a high fixing temperature is required as compared with plain paper in order to obtain a good fixing property like rough paper.

<Third Embodiment> This embodiment is characterized in that a fixing device having a variable fixing temperature is used, and the heat generation amount ratio of a plurality of heat generating members is made variable according to the fixing temperature.

As a means for varying the fixing temperature, the apparatus has different fixing temperature tables as in the second embodiment, and the user can change the fixing temperature by selecting a desired fixing temperature table. In addition to the above, the image forming apparatus of the fixing device has means for detecting the outside air temperature, and the fixing temperature of the fixing device is set based on the detection result.

In this embodiment, the following three temperature control tables are prepared based on the outside air temperature detection results.

1) Low temperature environment mode: the outside air temperature detection result is 1
In the table of the temperature control temperature when the temperature is 9 ° C. or less, the temperature control temperature is set to be high. The fixing temperature is fixed at 200 (° C.) from the cold state of the fixing device.

2) Normal temperature environment mode: the outside air temperature detection result is 1
In the table of temperature control temperature at 9 to 30 ° C., the standard temperature control temperature is set. The fixing temperature is fixed at 205 (° C.) from the cold state of the fixing device.

3) High temperature environment mode: In the table of temperature control temperature when the outside air temperature detection result is 30 ° C. or higher, the temperature control temperature is set to be low. The fixing temperature is fixed at 195 (° C.) from the cold state of the fixing device.

In the present embodiment, when the low temperature environment mode is selected, the temperature is adjusted at a high fixing temperature, and the power supply ratio on the upstream side is higher than that in the normal mode or low mode.

The power ratio of this embodiment is

[0108]

[Table 4]

As described in the first embodiment, by setting the power ratio of the upstream side and the downstream side to 2: 1, XEROX4024
When printing (grammage of 75 g) with NN, the fixed image quality such as fixability, offset, and tailing can be set to a level without problems.

However, rough paper (FOX
RVERBond Basis weight 90g Paper and Neenah CLASSICLaid Text
When printing a basis weight of 105 g paper or the like), a high fixing temperature is required to obtain good fixing properties.

In the second embodiment, the temperature control temperature is changed by the user's setting, but in this embodiment, the apparatus main body detects the outside air temperature, and the fixing temperature is automatically set based on the detection result. Therefore, without bothering the user,
Good fixability can be obtained. In the low temperature environment mode, the fixing temperature is high.Therefore, if a higher temperature is required to obtain fixability than in the normal temperature environment mode, the temperature on the downstream side of the nip is set so that high temperature offset does not occur. In this embodiment, the power ratio between the upstream side and the downstream side is 4: 1 in the low temperature environment mode in order to prevent it from becoming as high as possible.
Further, in the high temperature environment mode, since the temperature control temperature is low, high temperature offset is less likely to occur.

By doing so, good fixability can be obtained regardless of the operating environment of the apparatus, and high temperature offset can be prevented even when a high fixing temperature is required in the low temperature environment mode.

As the environment detecting means, in addition to the thermistor used in this embodiment, a means for detecting the outside air temperature by utilizing the environmental change of the resistance value of the transfer roller can be considered.

<Others> 1) Needless to say, the structures of the fixing device and the heating body are not limited to those of the embodiments.

2) The image heating apparatus of the present invention can be used not only as the fixing apparatus of the embodiment but also as an apparatus for heating a recording material carrying an image to modify the surface properties such as gloss and a hypothetical wearing apparatus. .

[0116]

As described above, according to the present invention, in the film heating type image heating apparatus, offset, tailing,
It is possible to provide an image heating apparatus that stably obtains a good heated image such as a fixed image throughout the life of the apparatus without deteriorating the quality of the fixed image due to poor fixing property.

[Brief description of drawings]

FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic configuration model diagram of a fixing device.

[Fig. 3] Structural model diagram of heating element

FIG. 4 is a temperature distribution diagram of a heating element along a recording material conveyance direction.

FIG. 5 is a temperature distribution diagram of a heating element along a recording material conveyance direction in a second embodiment.

FIG. 6 is a schematic configuration model diagram of a general conventional example of a film heating type fixing device.

FIG. 7 is an explanatory diagram of a grounding structure

FIG. 8: Structural model diagram of heating element

FIG. 9 is a temperature distribution diagram of the heating element along the recording material conveyance direction.

[Explanation of symbols]

1 ... Heating body (heater), 2 ... Heater holder, 3 ...
Fixing film, 3a ... Fixing release layer, 3b ... Conductive primer layer, 3c ... Base layer film, 4 ... Pressure roller,
5 ... Metal stay, 4a ... Releasing layer, 4b ... Heat resistant rubber layer, 4c ... Core bar, 4d ... Conductive rubber ring, 4e ...
Resistance, 6 ... Fusing upper frame, 6 '... Fusing lower frame,
7 ... Rotating guide, 7 '... Paper ejection guide, t ... Toner, 11 ... Image carrier, 12 ... Charging roller, 13 ...
Laser scanner unit, 13a ... Laser beam scanning exposure, 14 ... Developing device, 15 ... Transfer roller, 1
6 ... Cleaning installation, 17 ... Paper feeding unit, 18 ... Paper feeding roller, 19 ... Sheet path, 20 ... Registration roller,
21 ... Fixing device, 22 ... Sheet path, 23 ... Ejecting section, P ... Recording material, T ... Transfer nip section, h1 ... Upstream heating element, h2 ... Downstream heating Body, L ... Heating element length, w1,
w2 ・ ・ ・ Width of heating element

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiko Suzuki             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H033 AA01 AA09 AA20 AA30 BA11                       BA12 BA25 BA26 BA27 BA30                       BE03 CA07 CA27 CA48                 3K058 AA45 AA61 AA71 BA18 CA12                       CA22 CA61 CE02 CE13 CE19                       CE23 CE29 DA01 GA03 GA06

Claims (2)

[Claims] 1. An image bearing device comprising: a fixedly supported heating element; a film that slides on the heating element; and a pressure member that forms a nip with the heating element via the film. In the image heating device, the recording material is nipped and conveyed between the film in the nip and the pressure member to heat the image on the recording material by the heat from the heating body through the film, wherein the heating body is a recording unit. It has a heating element composed of a plurality of resistors arranged side by side along the material conveying direction, and each heating element can be independently energized and driven, and the heating value ratio of each heating element is variable. The control circuit has a control circuit configured to change the heat generation amount ratio of the plurality of heating elements before and after the recording material is nipped and conveyed between the film in the nip and the pressure member. An image heating device characterized by: 2. An image bearing device comprising: a fixedly supported heating element; a film that slides on the heating element; and a pressure member that forms a nip with the heating element through the film. In the image heating device, the recording material is nipped and conveyed between the film in the nip and the pressure member to heat the image on the recording material by the heat from the heating body through the film, wherein the heating body is a recording unit. It has a heating element composed of a plurality of resistors arranged side by side along the material conveying direction, and each heating element can be independently energized and driven, and the heating value ratio of each heating element is variable. An image heating apparatus having a control circuit as described above, wherein the control circuit changes the heat generation amount ratio of the plurality of heating elements according to the changed device setting heating temperature.