JP2003345175A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a hot offsetting when regular sized recording material is printed after printing of a small sized recording material. <P>SOLUTION: In the constitution in which a heater of a heat fixing device is provided with a plurality of heating resistive layers and the heating resistive layer with the great heat generation value on an end part is positioned on the downstream side, when the regular sized recording material is printed within a specified time after printing the small sized recording material, the energizing to the heating resistive layer with the great heat generation value at the end part is reduced. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a printer or a facsimile using an electrophotographic method, and particularly, an unfixed toner is removed by a heat resistance layer through a heat resistant fixing film. The present invention relates to a fixing device that heats and fixes a recording sheet.

[0002]

2. Description of the Related Art Conventionally, many electrophotographic copying machines, printers, etc. do not supply electric power to a heating roller fixing system of a contact heating type which has good thermal efficiency and safety as a fixing means or a heating fixing device at the time of standby. , A method of suppressing power consumption as low as possible, more specifically, an energy-saving type film heating method in which a toner image on a recording material is fixed through a thin film between a heater unit and a pressure roller.

One of the heat fixing methods by the film heating method
Examples are JP-A-63-313182 and JP-A-2-15.
It is proposed in Japanese Patent No. 7878, Japanese Patent Application Laid-Open No. 4-44075, Japanese Patent Application Laid-Open No. 4-204980, and the like. FIG. 7 shows a schematic configuration of an example of the film heating method. That is, FIG.
1, a heating member (heater, hereinafter referred to as a heater) 2 fixed and supported by a stay holder (support) 1, and a heat-resistant thin film (hereinafter referred to as a fixing film) 3 sandwiched between the heaters 2 are described later. The elastic pressure roller 4 has a nip portion (fixing nip portion) having a predetermined nip width formed by the pressing means and is brought into pressure contact. The heater 2 is heated / controlled to a predetermined temperature by being energized. The fixing film 3 is conveyed in the direction of the arrow while being in close contact with and sliding on the heater 2 surface in the fixing nip portion by the rotational force of the drive transmission means (not shown) or the pressure roller 4, and is in the shape of a cylinder or an endless belt. Alternatively, it is a roll-wound end-shaped member.

The heater 2 is heated to a predetermined temperature and temperature-controlled,
In the state where the fixing film 3 is conveyed and moved in the direction of the arrow, when a recording material having an unfixed toner image as a heated material formed thereon is introduced between the fixing film 3 and the pressure roller 4 in the fixing nip portion. The recording material is brought into close contact with the surface of the fixing film 3 and is conveyed while being held together with the fixing film 3 in the fixing nip portion. In this fixing nip portion, the recording material / toner image is heated by the heater 2 via the fixing film 3, and the toner image on the recording material is heat-fixed. The recording material portion that has passed through the fixing nip portion is separated from the surface of the fixing film 3 and conveyed.

The fixing film 3 has a considerably small thickness of 20 to 70 μm in order to efficiently apply the heat of the heater 2 to the recording material as the material to be heated in the fixing nip portion.
The fixing film 3 is a film base layer 3a, as shown in FIG.
The conductive primer layer 3b and the release layer 3c have a three-layer structure, and the film base layer 3a side is the heater side,
The release layer 3c is on the pressure roller side. Film base layer 3a
Is a highly insulating polyimide, polyamideimide, PEE
K, etc., having heat resistance and high elasticity, and having a flexible thickness of about 15 to 60 μm.

Further, the film base layer 3a maintains mechanical strength such as tear strength of the entire fixing film 3. The conductive primer layer 3b is formed as a thin layer having a thickness of about 2 to 6 μm and is partially exposed on the surface of the fixing film.
In order to prevent electrostatic offset and the like, a conductive brush (not shown) is in contact with the conductive primer layer exposed on the surface of the fixing film, and a bias having the same polarity as the toner is applied during printing. The releasable layer 3c is a toner offset prevention layer for the fixing film 3 and has a good releasability.
Fluorine resin such as A, PTFE, FEP, etc.
It is formed so as to cover about m. Also, the fixing film 3
In order to reduce surface charge-up and prevent electrostatic offset, the releasable layer has a specific resistance of 10 ³ Ωcm-10.
A conductive member such as carbon black of about ⁶ Ωcm is mixed.

The stay holder 1 is made of, for example, a heat-resistant plastic member, holds the heater 2 and also serves as a conveyance guide for the fixing film 3. Therefore, in order to enhance slidability with the fixing film 3, grease having high heat resistance is interposed between the fixing film 3 and the outer peripheral surface of the heater 2 and the stay holder 1. The pressing member 4 includes an elastic layer formed by molding silicon rubber or a sponge elastic layer 7 formed by foaming silicon rubber on the outside of the core metal 6, and a PTFE, PFA, FEP, or the like similar to the fixing roller on the outer layer thereof. The moldable layer 8 is formed in a tube shape or by coating coating.

A ceramic heater is generally used as the heater 2 as a heating member. For example, on the surface of a ceramic substrate (surface facing the fixing film 3) of electrical insulation, good thermal conductivity, and low heat capacity, such as alumina, along the length of the substrate (direction perpendicular to the drawing), the silver palladium (Ag / Pd)
An energization heating resistance layer such as Ta2N is formed by screen printing or the like, and the heating resistance layer forming surface is covered with a thin glass protective layer. In this ceramic heater 2, when the energization heating resistance layer is energized, the energization heating resistance layer generates heat and the entire heater including the ceramic substrate / glass protective layer is rapidly heated. This temperature rise of the heater 2 is detected by the temperature detection means 5 installed on the back surface of the heater and fed back to an energization control unit (not shown). The energization control unit controls the power supply to the energization heating resistance layer so that the heater temperature detected by the temperature detection unit 5 is maintained at a predetermined substantially constant temperature (fixing temperature).

That is, the heater 2 is heated and temperature-controlled to a predetermined fixing temperature. Here, the heating resistance layer pattern of the heater is as shown in FIG. The heating resistance layer 15a on the upstream side has almost the same length as the maximum width of the recording material, the heating resistance layer 15b on the downstream side is longer than the heating resistance layer 15a, and the resistance value is reduced by narrowing the resistance layer width at the end. Since the height is high, the amount of heat generated at the end portion becomes large when energized.

Further, the energization ratio of the downstream heating resistor layer 15b to the heating resistor layer 15a is variable, and the temperature distribution in the longitudinal direction of the heater is changed by varying the energization ratio in accordance with the number of heat-fixed recording materials. To make it uniform. That is, in the initial stage of printing from a state where the heat fixing device is sufficiently cooled, heat is taken from the end portion, so that the energization ratio of the heating resistance layer 15b having a large heat generation amount at the end portion is set high and the heat is applied to the end portion. Even if there is a heat escape, it is possible to obtain sufficient fixability. On the contrary, when the heat fixing device is sufficiently heated, on the contrary, in order to prevent the heat deterioration of the fixing member due to the increase of the heat generation amount in the non-sheet passing area, the heat generating resistance layer 15b is provided.
The energization ratio is low.

[0011]

In the above heating resistance layer pattern, when the recording material having a wide width passes within a predetermined time after the recording material having a narrow width passes through the heat fixing device, the heating resistance layer 15b is energized. The control is as shown in FIG. That is, when a recording material having a narrow width passes through the heat fixing device, the area through which the recording material passes is sufficiently smaller than the length of the heating resistance layer. Only 15a is energized to adjust the temperature to a predetermined temperature.

After that, when a wide recording material passes, the energization heating resistance layer 15b having a large amount of heat generation at the end is energized in order to satisfy the end fixability according to the normal control. However, as shown in FIG. 10, the temperature distribution in the fixing nip when the recording material of the normal size is passed after the recording material of the small size is passed, the end temperature is high due to the temperature rise in the non-sheet passing portion. In addition to the temperature rise in the non-sheet passing portion, the energization heat generation resistance layer 15 has a large amount of heat generation at the end when printing a wide recording material.
It is considered that lighting of b is the cause.

FIG. 11 shows the heater temperatures at the central portion and the end portions when printing a normal size recording material after printing a small size recording material. The edge temperature rises to 240 ° C. or higher during normal size printing due to the influence of the temperature increase in the non-sheet passing area due to printing of small size recording material. The temperature range where hot offset and improper fixing do not occur is as shown in FIG. 10. When the temperature difference between the paper passing area and the non-paper passing area of the small-sized recording material becomes large, it does not pass through the paper passing area of the small-sized recording material. At the same time, it becomes impossible to obtain a good image without hot offset and fixing failure in the paper area.

That is, as shown in FIG. 10, when the fixing temperature is set so as to satisfy the fixing property of the paper passing area in the small size, over-fixing occurs in the non-paper passing area in the small size, and hot offset occurs. (Fig. 10).
Further, when the fixing temperature is set so that the hot offset does not occur in the non-sheet passing area in the small size, the fixing failure occurs in the sheet passing area in the small size (FIG. 10).

[0015]

In order to solve the above problems, the present invention provides an image forming apparatus characterized by the following.

The recording material on which the unfixed image is formed is passed through a fixing nip formed by pressing a pressure member and a heating member against each other to heat-fix the unfixed image as a permanent image on the recording material. A heating heater disposed in the heating and fixing device has a plurality of energization heating resistance layers, and at least 1
When the recording material with a narrow width is printed in a book having a larger amount of heat generation at the end portion of the energization heating resistance layer than the central portion and the wide recording material is printed within a predetermined time, the above-mentioned amount of heat generation at the end portion is used. The image forming apparatus is characterized in that the energization ratio to the energization heating resistance layer having a large number is smaller than usual. As described above, it is possible to reduce the temperature difference between the center and the end by suppressing the energization of the energization heating resistance layer that has a large amount of heat generation at the end and reduce the amount of heat generated at the end, and it is possible to prevent hot offset and secure the fixability. It will be possible.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) An embodiment of the present invention will be described below. First, FIG. 1 is a block diagram of an image forming apparatus according to the present invention.

In FIG. 1, 19 is a photosensitive drum,
A photosensitive material such as OPC, amorphous Se, or amorphous Si is formed on a cylindrical base such as aluminum or nickel. The photosensitive drum 19 is rotationally driven in the direction of the arrow, and its surface is first uniformly charged by a charging roller 20 as a charging device. Next, the laser beam 21, which is ON / OFF controlled according to the image information, is reflected by the polygon mirror rotating in the scanner unit and scanning exposure is performed on the sightseeing drum to form an electrostatic latent image. This electrostatic latent image is developed and visualized by the developing device 22. As a developing method, a jumping developing method, a two-component developing method,
The FEED developing method or the like is used, and image exposure and reversal development are often used in combination.

The visualized toner image is transferred from the photosensitive drum 19 onto the recording material P conveyed at a predetermined timing by a transfer roller 23 as a transfer device. Here, the sensor 24 detects the leading edge of the recording material so that the image forming position of the toner image on the photosensitive drum 19 and the writing start position of the leading edge of the recording material match, and the timing is adjusted.
The recording material P conveyed at a predetermined timing is the photosensitive drum 1.
9 and the transfer roller 23 are nipped and conveyed with a constant pressing force.
The recording material P to which the toner image is transferred is conveyed to the fixing device 25 and fixed as a permanent image. On the other hand, transfer residual toner remaining on the photosensitive drum 19 is removed from the surface of the photosensitive drum 19 by the cleaning device 26.

Further, a width sensor that operates when the recording material has a predetermined width or more is provided in the conveying path before the recording material is developed. The control can be changed automatically.

FIG. 2 shows the structure of the heat fixing device 25 according to the present invention. In FIG. 2, the fixing member 27 is composed of the following members. Reference numeral 14 is a fixing film having a small heat capacity. In order to reduce the heat capacity and improve the quick start property, the total film thickness is 100 μm or less, and in this embodiment, it is 60 μm. Further, in order to prevent offset and ensure separability of the recording material, PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer), FEP is used on the surface layer.
(Tetrafluoroethylene / hexafluoropropylene copolymer), ETFE (ethylene / tetrafluoroethylene copolymer), CTFE (polychlorotrifluoroethylene), PVDF (polyvinylidene fluoride) and other fluororesins, silicone resin, etc. It is a mixture of heat-resistant resins having good properties or a single coating.

A heating heater 15 is provided inside the fixing film 14 to heat the nip portion for melting and fixing the toner image on the recording material. The heater 15 for heating is made of, for example, Ag / Pd (silver-palladium), RuO2, Ta2N, etc. along the longitudinal direction on the surface of a highly insulating ceramic substrate such as alumina or a heat-resistant resin substrate such as polyimide, PPS or liquid crystal polymer. The energization heating resistance layer is formed by screen printing to have a thickness of about 10 μm and a width of 1
It is a member for electrical heating formed by coating in a linear or strip shape of about 5 mm. Alternatively, it is a heater for heating a metal made by sequentially laminating an insulating layer and an electric heating resistance layer on the opposite side of the fixing nip on the metal substrate, and the metal substrate may have a shape in which the fixing nip side is curved.

The pattern of the energization heating resistance layer has a shape as shown in FIG. That is, the heating resistance layer 15 on the upstream side
a is 1 mm longer than the maximum width of the recording material that can be passed, and the amount of heat generated is constant in the longitudinal direction, whereas the heat generation resistance layer 15b on the downstream side is sufficiently larger than the maximum width of the recording material that can be passed. The length is very long, and the amount of heat generation is increased by narrowing the resistance layer width at the end and increasing the resistance value. The heat generating resistance layers 15a and 15b can be independently heated by being supplied with power from a power source (not shown) from the electrode portions 15c to 15e. Further, the power supply for power supply (not shown) to each energization heating resistance layer is independent, and the energization ratio to the energization heating resistance layers 15a and 15b can be changed.

In addition, each of the energization heating resistance layers 15a,
The resistance value ratio of 15b was formed to be 2: 3. As a result, when the energization heat generating resistance layer is energized at the same energization ratio, the heat generation ratio of the energization heat generation resistance layer 15a on the upstream side and the energization heat generation resistance layer 15b on the downstream side is 3: 2.

FIG. 4 shows the results of measuring the temperature distribution of the heater width for heating by energization of the respective energization heating resistance layers 15a and 15b. The horizontal axis in the figure indicates the position within the nip, where the nip center is 0, the upstream side is negative, and the downstream side is positive. The thermistor for temperature control is located 1.2 mm downstream from the center of the nip.

As shown in FIG. 4, the temperature distribution is substantially uniform across the width of the heater for heating when only the upstream side heating resistor layer 15a is energized, and when both 15a and 15b are energized. It is stable near the position. On the other hand, when electricity is supplied only to the energization heating resistance layer 15b located on the downstream side, there is a temperature peak on the downstream side of the nip, and the temperature change near the thermistor arrangement is large.

In each case, the temperature control temperature was shaken to confirm the fixability and the hot offset margin.
Almost no margin was obtained by energizing only the energization heating resistance layer 15b on the downstream side. From the above, when having multiple energization heating resistance layers and controlling multiple energization heating resistance layers at different energization rates, it is better to place the heating resistance layer with a lower energization rate on the downstream side for control. Since the temperature distribution is small and stable control can be performed, a margin of fixability and hot offset can be obtained.

A temperature detecting element 28 such as a thermistor for detecting the temperature of the heater for heating, which is raised in accordance with the heat generation of the energization heating resistance layer, is arranged between the two energization heating resistance layers on the back surface of the substrate. By appropriately controlling the duty ratio, the wave number, etc. of the voltage applied to the energization heating resistance layer from the electrode portions 15c to 15e at the end portions in the longitudinal direction in accordance with the signal of the temperature detecting element 28 provided, The temperature controlled in the fixing nip is kept substantially constant, and heating necessary for fixing the toner image on the recording material is performed. DC energization from the temperature detection element 28 to the temperature control unit (not shown) is achieved by a connector (not shown) via the DC energizing unit (not shown) and the DC electrode portions 15c to 15e.

Electric power is supplied to the heating heater 15 through connectors (not shown) provided at both ends of the heating heater. In addition, a protective layer such as a thin glass coat and a fluororesin layer capable of withstanding sliding friction with the fixing film 14 is provided on the surface of the energization heating resistance layer of the heater 15 for heating. Alternatively, when AlN (aluminum nitride), which has excellent wear resistance and good thermal conductivity, is used as the substrate, an energization heat generating resistance layer is formed on the side opposite to the fixing nip with respect to the substrate. Is also good.

Reference numeral 17 denotes a heat insulating stay holder for holding the heater 15 for heating and for preventing heat radiation in the direction opposite to the nip, which is a liquid crystal polymer, phenol resin, PPS, PEE.
The fixing film 14 is loosely fitted outside with a margin, and is rotatably arranged in the direction of the arrow. Since the fixing film 14 rotates while rubbing against the heating heater 15 and the heat insulating stay holder 17 inside, the frictional resistance between the heating heater 15 and the heat insulating stay holder 17 and the fixing film 14 must be kept small. Therefore, a lubricant such as heat resistant grease is interposed on the surfaces of the heating heater 15 and the heat insulating stay holder 17. This allows the fixing film 14 to rotate smoothly.

The pressing member 18 is composed of an elastic layer 30 formed by foaming heat-resistant rubber such as silicone rubber or fluororubber or silicone rubber on the outside of the cored bar 29, on which PFA, PTFE, FEP or the like is formed. The releasable layer 31 may be formed. The pressure member 18 is sufficiently pressed in the direction of the fixing member 27 by pressure means (not shown) from both ends in the longitudinal direction so as to form a nip portion necessary for heat fixing.

The above is the configuration of the heat fixing device. The recording material P is appropriately supplied by a supply means (not shown) and is formed by the heating member 27 and the pressing member 18 along the heat resistant fixing inlet guide 32. It is transported into the fixing nip. Thereafter, the recording material P discharged from the fixing nip is guided by a heat-resistant fixing discharge guide (not shown) and discharged onto a discharge tray (not shown).

When a small-sized recording material passes through the fixing nip, since the width of the recording material is sufficiently smaller than the width of the heating resistance layer, only the heating resistance layer 15a is energized and the paper is not passed. Part temperature rise is reduced. However, the temperature of the non-sheet passing area becomes higher as the number of prints of the small size recording material increases as shown in FIG. On the other hand, since the paper passing area is kept constant by the temperature detecting element, the temperature difference between the paper passing area and the non-paper passing area becomes large. Therefore, in the case of printing the normal size recording material after passing the small size recording material, energization control to the heating resistance layer 15b is performed as shown in the table below depending on the number of small size recording materials printed.

[0034]

[Table 1]

The energization ratio here is the energization ratio of the heat generating resistance layer 15b having a large amount of heat generation at the end portion on the downstream side to the energization of the heat generating resistance layer 15a on the upstream side having a constant amount of heat generation over the length. That is, the larger the energization ratio, the greater the degree of energization to the heating resistance layer 15b, which has the larger amount of heat generation at the ends, and the greater the amount of heat generation at both ends in the longitudinal direction.

As described above, by reducing the energization ratio of 15b as the number of prints of the small-sized recording material increases, it is possible to suppress the heat generation at the end portion and reduce the temperature difference between the paper passing area and the non-paper passing area. By setting the temperature to the optimum value, it is possible to obtain a good image without hot offset and fixing failure. Further, by decreasing the energization ratio of the heating resistance layer 15b as the number of prints of the small-sized recording material increases, it is possible to perform control according to the temperature rise state in the non-sheet passing area.

After printing the com # 10 size recording material under the control of the energization ratio of the heating resistance layer 15b as shown in Table 1, the LTR size recording material was printed and the fixability and hot offset were evaluated. The fixability was measured with bond paper having poor fixability, and the hot offset was evaluated with thin paper which is likely to be hot offset.
After 5 seconds, 5 sheets were printed and evaluated.

As a comparative example 1, the energization ratio of the heating resistance layer 15b is 100% regardless of the number of printed small size recording materials.
Then, in order to satisfy the fixing property in the small size sheet passing area, the fixing temperature was set to a normal setting, and as Comparative Example 2, the energization ratio of the heating resistance layer 15b was set to 100% regardless of the number of printed sheets of the small size recording material. Then, in order to suppress the hot offset in the small size non-sheet passing area, the fixing temperature and the hot offset were evaluated in the same manner for the fixing temperature lower than the normal setting by 20 ° C.

The results are shown below. First, the heating heater temperature measurement result during the first printing of the normal size recording material after passing the small size recording material is shown.

[0040]

[Table 2]

Further, the evaluation results of fixability and hot offset at this time are shown below.

[0042]

[Table 3]

As shown in FIG. 6, in the first embodiment, the heater temperature is in a region where neither fixing failure nor hot offset occurs in both the paper passing area and the non-paper passing area in a small size, so that neither fixing failure nor hot offset occurs. A good image can be obtained. On the other hand, in Comparative Example 1,
Regarding the paper passing area in the small size, a good image without fixing failure and hot offset can be obtained as in the present embodiment, but in the non-paper passing area in the small size, the temperature rise during printing of the small size recording material. Because of this, hot offset has occurred.

On the other hand, in Comparative Example 2, in the non-sheet passing area in the small size, although the temperature was raised during the printing of the small size recording material, the fixing set temperature was lowered by 20 ° C. from the normal during the printing of the normal size recording material. Fixing failure,
Although a good image without hot offset can be obtained, the fixing temperature is 20 ° C. lower even in the paper passing area in a small size where the temperature has not risen, so that fixing failure occurs.

As described above, in the case of printing a normal size recording material after printing a small size recording material, the heating ratio of the end portion is suppressed by reducing the energization ratio to the heating resistance layer 15b having a large amount of heat generation at the end portion, and the hot portion is heated. The offset could be prevented.

(Embodiment 2) In Embodiment 2, the overall structure of the image forming apparatus and the heat fixing apparatus is the same as that of Embodiment 1 described above, and the repetitive description will be omitted.

As shown in FIG. 5, the temperature of the non-sheet passing area is high immediately after printing the small-sized recording material, and if a medium-sized recording material is printed at this time, hot offset occurs, but When a certain amount of time elapses after printing the recording material, the temperature difference between the paper passing area and the non-paper passing area becomes small, and hot offset does not occur even if the normal size recording material is printed at this time. In addition, when a certain amount of time has passed after the printing of the small-sized recording material is completed, the first embodiment is performed.
As described above, if the energization ratio to the heating resistance layer 15b having a large amount of heat generation at the end is reduced, the fixing property at the end may be deteriorated.

Therefore, the second embodiment is characterized in that the power supply to the heating resistance layer 15b having a large amount of heat generation at the end is changed depending on the time from the end of printing of the small size recording material to the start of printing of the normal size recording material. As shown in the table below, the energization of the energization heating resistance layer 15b having a large amount of heat generation at the end is changed depending on the number of prints of the small size recording material and the interval from the end of printing of the small size recording material to the start of printing of the normal size recording material.

[0049]

[Table 4]

As described above, when the interval from the end of printing of the small-sized recording material to the start of printing of the normal-sized recording material becomes large, the end portion fixability is improved by increasing the amount of electricity supplied to the heating resistance layer 15b having a large end portion heat generation amount. Satisfactory, it was possible to obtain a good image without hot offset.

(Third Embodiment) In the third embodiment, the overall structure of the image forming apparatus and the heat fixing device is the same as that of the first embodiment.

The non-sheet passing portion is heated by the printing of the small-sized recording material, and immediately thereafter, the heat generating resistance layer 15 having a large amount of heat generation at the end portion.
When a normal size recording material is printed with the energization ratio to b kept at 100%, hot offset occurs in the non-paper passing area of the small size recording material. However, the hot offset does not occur when several normal size recording materials are printed. The following table shows that the energization ratio of the heating resistance layer 15b, which generates a large amount of heat at the end, is 10 seconds after printing a predetermined number of small-sized recording materials.
It represents the number of sheets in which hot offset occurred when printing a normal size recording material at 0%.

[0053]

[Table 5]

Further, the heat generating resistance layer 15 having a large amount of heat generation at the end portion.
If a normal size recording material is continuously printed with the energization ratio to b reduced, the fixability of the end portion deteriorates. Therefore, in the present embodiment, in the printing of the normal size recording material after the printing of the small size recording material, the number of prints for the small size recording material is large so that the control for reducing the energization ratio to the heating resistance layer 15b having a large amount of heat generation at the end is performed. As much as possible, the heat generation resistance layer 15 having a large amount of heat generation at the end portion
It is characterized in that the number of sheets to be controlled to reduce the energization ratio to b is increased as the time from the end of printing of the small size recording material to the start of printing of the normal size recording material is increased. Further, it is characterized in that the ratio of energization to the heat generating resistance layer 15b having a large amount of heat generation at the end is increased by increasing the number of prints of the normal size recording material.

As shown in the table below, depending on the time from printing a small-sized recording material to printing a normal-sized recording material, the number of printed small-sized recording materials, and the number of printed normal-sized recording materials, the heat generation resistance layer 15b having a large amount of heat generation at the end portion is formed. By changing the energization, it is possible to obtain a good image without hot offset and without fixing failure.

[0056]

[Table 6]

[0057]

As described above, according to the present invention, the recording material on which an unfixed image is formed is passed through the fixing nip formed by pressing the pressure member and the heating member against each other, and A heating heater disposed in a heating and fixing device that heats and fixes an unfixed image on a recording material as a permanent image has a plurality of energization heating resistance layers, and at least one energization heating resistance layer has a central end heat generation amount. When printing a wide recording material after printing a narrow recording material in a larger area, make the energization ratio to the energization heating resistance layer with a large amount of heat generation at the end smaller than usual. Due to
A good image without hot offset could be obtained.

Furthermore, since the end portions are not heated more than necessary, the effect of improving the durability of the fixing member can be obtained. In addition, the heating and fixing device can be heated at any temperature by changing the energization ratio to the energization heating resistance layer having a large amount of heat generation at the end depending on the interval from the small size recording material print to the normal size recording material print. It was possible to prevent fixing failure and hot offset.

Further, the hot offset can be reliably prevented by changing the number of sheets for changing the energization ratio of the normal size recording material depending on the number of prints of the small size recording material and the interval from the print of the small size recording material to the printing of the normal size recording material. I was able to.

[Brief description of drawings]

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

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

FIG. 3 is a heating resistance layer pattern of a heater according to the present invention.

FIG. 4 is a temperature distribution in the transport direction in the heater nip according to the present invention.

FIG. 5: Result of heater temperature measurement in print mode according to the present invention

FIG. 6 is a conceptual diagram of a longitudinal temperature distribution in a heater according to the present invention.

FIG. 7 is a configuration diagram of a film heating type heat fixing device.

FIG. 8 is a sectional view of a fixing film in a conventional example.

FIG. 9 is a current-carrying ratio to the heating resistance layer in the conventional example.

FIG. 10 is a conceptual diagram of a temperature distribution in a longitudinal direction in a heater in a conventional example.

FIG. 11: Result of heater temperature measurement in print mode in a conventional example

[Explanation of symbols]

19 Photosensitive drum 20 charging roller 21 laser beam 22 Developing device 23 Transfer roller

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H033 AA03 AA09 BA11 BA12 BA25                       BA27 BE03 CA17 CA30 CA48                 3K058 AA13 AA22 BA18 CA12 CA22                       CB14 CE21 CE23 DA01 DA06                       GA06

Claims (4)

[Claims] 1. An unfixed image is formed on the recording material as a permanent image by passing the recording material on which the unfixed image is formed through a fixing nip formed by pressing a pressure member and a heating member against each other. In an image forming apparatus having a heating and fixing device for heating and fixing, the heating heater provided in the heating and fixing device has a plurality of energization heating resistance layers, and at least one energization heating resistance layer has an end portion heat generation amount in a central portion. It is larger and is formed on the downstream side in the recording material conveyance direction from one series of other energization heating resistance layers, and after printing a narrow recording material, a wide recording material is printed within a predetermined time. In this case, the image forming apparatus is characterized in that the energization ratio to the energization heating resistance layer having a large amount of heat generation at the end is made smaller than usual. 2. The image forming apparatus according to claim 1, wherein the energization ratio to the energization heating resistance layer having a large amount of heat generation at the end is changed according to the number of prints of the recording material having a narrow width. 3. The method according to claim 1, wherein the energization ratio to the energization heating resistance layer having a large amount of heat generation at the end portion is changed by the interval from the printing of the narrow recording material to the printing of the wide recording material. The image forming apparatus according to claim 2. 4. The number of sheets for performing control for reducing the energization ratio of the energization heating resistance layer having a large amount of heat generation at the end portion to a value smaller than usual, is increased as the number of printed sheets of narrow recording material is increased. The image forming apparatus described in 1, 2, or 3.