JP2000131977A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image of high quality by suppressing the excessive rise of the temperature of a non-paper passing part as for an image forming device whose copying speed is high and preventing a high temperature offset caused by the excessive rise of the temperature. SOLUTION: The fixing device 60 is provided with a heater (heating body) 1 equipped with a plurality of heating layers (heating resistor) 3 firmly supported on an aluminum substrate (fixed member) 2, a thermistor (safety member) 5 for blocking the power supply in contact with one surface of the heater 1 when a temperature becomes equal to or exceeding a prescribed temperature, a fixing film (heat resistant film) 6 which is carried in press contact with the other surface of the heater 1, and a pressure roller (pressing member) 9 for bringing a recording material P in tight contact with the other surface of the heater 1 with the fixing film 6 interposed, and by imparting the heat of the heater 1 to the recording material P through the fixing film 6, the unfixed image T formed on the surface of the recording material P is heated and fixed. In this case, the heat generation distribution is made different among the plurality of heating layers 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fixing device for an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, as a means for fixing a visible image on recording paper in an image forming apparatus, a method using a heat roller is known. It has disadvantages such as a longer time to reach (so-called warm-up).

Therefore, a fixing device using a heat-resistant film has been proposed (see Japanese Patent Application Laid-Open No. 63-313182). The fixing device includes a thin heat-resistant film, a driving roller for driving the heat-resistant film, a heating element fixed and supported so as to rub against the inner peripheral surface of the heat-resistant film, and a heat-resistant film. And a pressing member disposed so as to be in contact with the outer peripheral surface of the heating member and press against the heating body via the film.

The heat-resistant film and the pressure member are driven to rotate at the same speed as the conveying speed of the recording material at least at the time of image fixing, and a heating element and a pressure member formed via the heat-resistant film are formed. The recording material is nipped and conveyed in the fixing nip portion to apply thermal energy of a heating element to the developed image (unfixed toner image) on the recording material to soften and melt the developed image, and further fix the recording material to the fixing nip. The visible image is cooled and solidified by being discharged from the printing section to be fixed on the recording material.

In such a film fixing method, since the warm-up is very short, it is not necessary to raise the temperature of the heating body in advance (so-called standby temperature control), and energy saving can be realized.

Here, if a cleaning member having a low heat capacity is brought into contact with the pressure roller, the residual toner is removed from the pressure roller, and contamination of the recording material by the pressure roller is prevented.
That is, not only is the pressure roller cleaned by bringing the cleaning member made of a material having high thermal conductivity into contact with the pressure roller, but also the temperature distribution is made uniform by suppressing excessive temperature rise in the non-paper passing portion. In addition, it is possible to improve the durability of the fixing film and the pressure roller, prevent the offset, stabilize the deviation control of the fixing film, and the like.

[0007]

However, the film fixing method can only cope with a copying speed up to a certain value.
If the copying speed exceeds a certain value, the temperature of the non-sheet passing portion rises sharply, and the toner to be fixed peels off the recording material and adheres to the fixing film, which stains the recording material and degrades the image. there were.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and an object thereof is to suppress an excessive temperature rise in a non-sheet passing portion of an image forming apparatus having a high copying speed, and to reduce a high-temperature offset associated therewith. It is an object of the present invention to provide a fixing device capable of preventing the occurrence of a satisfactory image.

[0009]

In order to achieve the above object, an invention according to claim 1 includes a heating element having a plurality of heating resistors fixedly supported by a fixing member, and a heating element having a plurality of heating resistors. A security member that contacts and cuts off current at a certain temperature or more, a heat-resistant film that is conveyed while being pressed against the other surface of the heating element, and a recording material that passes through the heat-resistant film to the other side of the heating element. A pressure member that is brought into close contact with one surface of the recording material, and applying heat of the heating element to the recording material via the heat-resistant film to heat and fix an unfixed image formed on the recording material surface. In addition, the heat generation distribution of the plurality of heat generation resistors is made different.

A second aspect of the present invention is characterized in that, in the first aspect of the present invention, at least one heat generation distribution of the plurality of heat generating resistors is made higher at the center in the longitudinal direction.

According to a third aspect of the present invention, in the first aspect of the present invention, at least one heat generation distribution of the plurality of heat generating resistors is made higher at both ends in the longitudinal direction.

According to a fourth aspect of the present invention, in the first, second, or third aspect, the power ratio supplied to the plurality of heating resistors is switched in accordance with the size of the recording material.

[0013]

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

<First Embodiment> FIG. 1 is a schematic configuration diagram of a main part of an image forming apparatus provided with a fixing device according to the present invention, and FIG. 2 is a schematic configuration diagram of a fixing device according to the present invention.

The image forming apparatus shown in FIG. 1 is an electrophotographic copying apparatus of a fixed original platen / moving optical system / rotating drum type / transfer type. In this copying apparatus, an original 19 is placed on a fixed original table glass 20. When a copy start key (not shown) is pressed after setting necessary copying conditions, the photosensitive drum 39 is driven to rotate at a predetermined peripheral speed in the direction of the arrow (clockwise).

The light source 21 (22 is a reflection shade) and the first mirror 23 move at a predetermined speed V from the home position on the left side of the glass to the right side of the glass along the lower surface of the platen glass 20, and the second mirror 24 and the third mirror 25
By moving at a speed of / 2, the downward image surface of the placed original 19 on the original platen glass 20 is illuminated and scanned from the left side to the right side, and the original surface reflected light of the illumination scan light is fixed to the image forming lens 29 and fixed. Image formation exposure (slit exposure) is performed on the surface of the rotating photosensitive drum 39 via the fourth to sixth mirrors 26, 27, 28.

The surface of the rotating photosensitive drum 39 is uniformly charged to a predetermined positive or negative potential by the primary charger 30. When the charged surface is exposed to light, the surface of the photosensitive drum 39 is placed on the surface of the photosensitive drum 39. An electrostatic latent image having a pattern corresponding to the image is sequentially formed. Then, the electrostatic latent image formed on the surface of the photosensitive drum 39 is visualized as a toner image by the developing roller 32 of the developing device 31.

On the other hand, a recording material P is fed by a paper feed roller 51, and the recording material P is introduced into a transfer section between the photosensitive drum 39 and the transfer charger 34 at a predetermined timing through a guide 33 and transferred. Upon receiving the corona, the photosensitive drum 39 comes into contact with the photosensitive drum 39, and the toner image on the photosensitive drum 39 side is sequentially transferred to the upper surface thereof.

The recording material P that has passed through the transfer section is sequentially separated from the surface of the photosensitive drum 39 while being subjected to charge removal of the back surface by the charge removing needle 35, and is conveyed to the transport section 38 and the entrance guide 10.
The toner image is fixed to the fixing device 60 as described below, and is fixed to a toner image, as described later, and discharged out of the apparatus as an image formed product.

Incidentally, the surface of the photosensitive drum 39 after the transfer is cleaned and removed by the cleaning blade 37 of the cleaning device 36, and the photosensitive drum 39 is repeatedly subjected to image formation.

The moving optical members 21 to 25 that have moved on the outward path as described above are set to move on the return path when they arrive at a predetermined end point on the outward path, and return to the initial home position until the start of the next copy cycle. The process waits (hereinafter, this process is referred to as an optical system back process). If a plurality of copies (for example, 100 copies) is designated before the copy start key is pressed, a microcomputer (not shown hereafter) (not shown) is used after the optical system back process is completed.
) Is repeated at predetermined intervals.

Next, the fixing device 60 mounted on the image forming apparatus according to the present embodiment will be described in detail with reference to FIG.

In FIG. 2, 100 is a heating means, 200
Is a pressing means, and 6 is an endless belt-shaped fixing film. The fixing film 6 is a heating roller fixedly disposed below the left driving roller 7 and the right driven roller 8 and between these two rollers 7, 8. It is stretched between the body and the low heat capacity linear heater 1.

The driven roller 8 also serves as a tension roller for applying tension in the direction in which the fixing film 6 is stretched outward. The fixing film 6 is coated with silicone rubber or the like to increase the friction coefficient. With the rotation in the direction, the motor is rotated clockwise at a predetermined peripheral speed without wrinkles, meandering, and speed delay.

Reference numeral 9 denotes a pressing roller having a rubber elastic layer having good releasability, such as silicone rubber, which is one of the components constituting the pressing means. Between the heater 1 and the lower surface of the heater 1 by a biasing means such as a spring.
The recording material P is rotated counterclockwise in the forward direction in the conveying direction of the recording material P while being brought into opposing pressure contact with a contact force of Kg / cm. still,
The diameter of the end portion in the longitudinal direction of the pressure roller 9 is set to be larger than the diameter of the central portion in the longitudinal direction by about 50 to 500 μm, so that a force pulling the recording paper P toward the end portion in the fixing nip acts. This prevents wrinkles from occurring on the recording paper P.

Reference numeral 13 denotes a cleaning roller which is a cleaning means provided so as to be in pressure contact with the pressure roller 9;
The cleaning roller 13 is made of an aluminum rod, and is opposed to and pressed by a biasing means supporting member such as a spring with a contact force of, for example, 200 to 2000 g / cm.

Since the endless fixing film 6 which is rotationally driven is repeatedly subjected to heat fixing of a toner image, the fixing film 6 generally has a heat resistance of 100 μm and has excellent releasability and durability. Below, preferably 40 μm
The following thin films are used: As an example, a 20 μm thick polyimide, polyetherimide, polyethersulfone, polyetheretherketone, or other high heat-resistant resin, or a thin endless belt made of nickel, SUS, or other metal is used to form an outer peripheral surface of PTFE (tetrafluoroethylene resin). , PF
A (low-surface-energy resin such as tetrafluoroethylene / perfluoroalkylvinylether copolymer resin) or a release coating layer obtained by adding a conductive material such as carbon black to these resins to a total thickness of 10 μm and a total thickness of 30 μm Endless belt. Note that the fixing film 6 may be endless.

The heater 1 having a low heat capacity has a thickness of 1.0 μm, a width of 10 mm, and a length of 340 mm in the longitudinal direction on an alumina substrate 2 made of a resistance material such as silver palladium or ruthenium oxide having a thickness of 10 μm and a width of 1.0 mm. The heat generating layer 3 is formed by coating to a thickness of 0 mm, and a protective layer 4 made of glass or the like having a thickness of 10 μm is further formed thereon in consideration of the slidability with the fixing film 6. It is fixed and supported.

The heater support 11 heat-insulates and supports the heater 1 with respect to the fixing device 60 and the image forming apparatus, and is made of a material having high heat insulation, high heat resistance and high rigidity, for example, PPS (polyphenylene). Sulfide), P
It is made of a high heat-resistant resin such as EEK (polyetheretherketone) and liquid crystal polymer, or a composite material of these resins with ceramics and metal.

The heating layer 3 of the heater 1 is energized from both ends in the longitudinal direction.
The MPU controls the energization according to the temperature detected by a thermistor 5 such as an NTC thermistor, which is bonded, pressed or integrally formed on the back surface of the substrate 2 with a thermally conductive silicone rubber adhesive or the like.

FIG. 3 is a diagram showing a pattern of the heat generating layer 3 in the conventional fixing device (a view in which the heater 1 is viewed from the sheet feeding side). It is formed in a straight line along the longitudinal direction of the substrate. Reference numerals 3a and 3b denote current-carrying electrodes (input terminals) provided on the left end of the heat generating layer 3 and made of a good conductive material such as silver.

E is the effective total length of the heat generating layer 3. This is the maximum size recording material that can be supplied to the apparatus and used and is A3 size (width 297 mm), and is set to a length corresponding to the width of the recording material. ing.

5a is within the minimum paper passing area c (width 105m).
m) is a thermistor as a temperature detecting element provided in FIG. At the time of fixing, the MPU controls the heater drive circuit (not shown) so that the detection output of the thermistor 5a becomes a predetermined constant value, and controls the energization to the heat generating layer 3.

Reference numeral 5b denotes a thermistor which is a temperature detecting element provided outside the minimum paper passing area c. The thermistor 5b is provided outside the paper passing area d of the B4 plate (width 257 mm) in the maximum paper passing area e. Have been.

Incidentally, the recording material P on which the unfixed toner image T is transferred to the upper surface by the image forming operation described above.
Are guided by a guide 10 shown in FIG.
And enters the fixing nip portion between the heater 1 and the pressure roller 9 formed through the fixing film 6.
The fixing nip portion N in an overlapping state together with the fixing film 6 without causing surface deviation, wrinkles and deviation.
(See FIG. 2) while receiving a narrow pressure, the toner image carrying surface of the recording material P is pressed against the surface of the fixing film 6 and passes through the fixing nip portion N in a state where the heat is applied to the fixing film 6. 6, the toner image T is melted at a high temperature and becomes an image Ta softened and adhered to the surface of the recording material P.

In the fixing device 60 according to the present embodiment, the separation of the recording material P from the fixing film 6 is performed when the recording material P passes through the fixing nip N and is separated. At this point, the temperature of the molten toner Ta is still higher than the glass transition point of the toner. Since the toner Ta at a temperature higher than the glass transition point at this separation point has an appropriate rubber property, the toner image surface at the time of separation has an appropriate uneven surface property without following the surface of the fixing film 6. However, since the surface property is maintained and solidified by cooling, excessive image gloss is not generated on the surface of the fixed toner image Tb, and high quality image is obtained. While the recording material P separated from the fixing film 6 is guided by the paper ejection guide 12 shown in FIG. 1 and reaches the paper ejection roller pair 15, the temperature of the toner Ta higher than the glass transition point naturally lowers (natural cooling). As a result, the temperature becomes lower than the glass transition point, and the toner Ta solidifies to form an image Tb (see FIG. 2).

In the present embodiment, since the heat capacity of the heat generating layer 3 and the substrate 2 of the heater 1 is small, and these are heat-insulated and supported by the heater support 11, the surface temperature in the fixing nip N of the heater 1 is increased. Is to raise the temperature to a sufficiently high temperature relative to the melting point of the toner in a short time, and it is not necessary to raise the temperature of the heater 1 in advance (that is, to adjust the so-called standby temperature). Can be.

With the above configuration, when an image was formed on a small-size sheet at a rate of 30 sheets per minute for only 10 minutes, the temperature of the non-sheet passing portion (both ends) rose to nearly 300 ° C. Further, when an image was formed on a large-sized paper immediately, a part of the toner on both ends of the paper was not fixed on the paper, and the fixing film 6 was not removed.
When the fixing film 6 has made one rotation, it is fixed on the paper and a good image cannot be obtained (hereinafter, this phenomenon is called a high-temperature offset).

Therefore, in the present embodiment, as shown in FIG. 3, of the two heating layers 3A and 3B of the heater 1, the heating layer 3A on the side where the recording paper enters (hereinafter referred to as the upstream side). The width t1 of the central portion was made narrower than the width t2 of both ends (t1 <t2) in order to increase the heat generation distribution at the central portion in the longitudinal direction and lower it at both ends. As a result, the temperature of the non-sheet passing portion when the small-size paper was flown was about 250 ° C., and the temperature could be suppressed to about 50 ° C. lower than that of the sheet having the same heat generation distribution. In FIG. 3, reference numeral 101 denotes a power supply.

<Embodiment 2> However, since the method of Embodiment 1 alone could not cope with the high-temperature offset, in the present embodiment, the power supplied to the heat generating layers 3A and 3B shown in FIG. Control, and 3
The control is performed in different cases as follows.

First, in order to shorten the time required to reach the minimum temperature required for fixing the toner (hereinafter, referred to as warm-up), the power supplies 102, 1
03 is supplied at a ratio of 1: 1. Thereafter, when a large-size recording sheet is supplied, only the downstream heating layer 3B is supplied. When a small-size recording sheet is supplied, only the upstream heating layer 3A is supplied. It turned on electricity. As a result, the temperature of the non-sheet passing portion was about 200 ° C., and a good image could be obtained without high-temperature offset.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG.

In the present embodiment, similarly to the first embodiment, the heat generation distribution at the central portion in the longitudinal direction of the heat generation layer 3A on the upstream side of the two heat generation layers 3A and 3B is made high, and the heat distribution is made lower at both ends. The width t1 of the portion is smaller than the width t2 of both ends (t1 <t
2) In addition to the setting, the width t of the center portion is set so that the heat generation distribution at both ends of the heat generation layer 3B on the downstream side is high and the center portion is low.
3 is set wider than the width t4 of both ends (t3> t4),
The heat generation distribution of the upstream and downstream heat generating layers 3A and 3B is made equal to that of the conventional one.

The power sources 104 and 105 for supplying electric power to the heat generating layers 3A and 3B are controlled so that the energization ratio of the upper and lower heating elements 3A and 3B is set to 1: 1 at the time of warm-up and large size, and at the time of small size. When the paper passing width is 220 mm or less, the power supply ratio of the heating layers 3A and 3B on the upstream and downstream sides is 10: 0, and the paper passing width is 22 mm.
When the thickness was 0 mm or more, image formation was performed with the current-carrying ratio of the heating layers 3A and 3B on the upstream and downstream sides being 7: 3.

As a result, as in the first embodiment, the temperature of the non-sheet passing portion at the time of the small size was suppressed to about 200 ° C., and the high-temperature offset did not occur. In addition, it was possible to eliminate the temperature unevenness occurring in the first embodiment at the time of warm-up and at the time of a small size having a width of 220 mm or more.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described with reference to FIG.

According to the studies by the inventors, it is known that unevenness in gloss of an image is less likely to occur when heating is performed on the downstream side. Therefore, in this embodiment, as shown in FIG.
The upper and lower patterns of the heat generating layers 3A and 3B are reversed to form the heat generating layers 3A and 3B.
A, 3B are controlled by controlling power supplies 106 and 107 for supplying power to the heat generation layers 3 upstream and downstream in warm-up and large size.
The energization ratio of A and 3B is 1: 1. When the paper size is small and the paper passing width is 220 mm or less, the energizing ratio of the upper and lower heat generating layers 3A and 3B is 0:10. Image formation was performed with the current-carrying ratio of the heat generating layers 3A and 3B being 3: 7.

As a result, as in the third embodiment, the temperature of the non-sheet passing portion at the time of small size is suppressed to about 200 ° C., so that high-temperature offset does not occur.
Temperature unevenness in a small size having a width of 220 mm or more could be eliminated. Further, gloss unevenness of the image can be suppressed, and a higher quality image can be provided.

[0049]

As is apparent from the above description, according to the present invention, a heating element having a plurality of heating resistors fixedly supported by a fixing member, and a heating element having a certain value which is in contact with one surface of the heating element. A security member that cuts off current at the temperature of, and a heat-resistant film that is conveyed while being pressed against the other surface of the heating element,
A pressure member for bringing the recording material into close contact with the other surface of the heating element via the heat-resistant film, and applying the heat of the heating element to the recording material via the heat-resistant film. In a fixing device that heats and fixes an unfixed image formed on a surface, the heat generation distribution of the plurality of heating resistors is made different, so that an excessive temperature rise in a non-sheet passing portion is suppressed in an image forming apparatus having a high copying speed. Thus, a good image can be obtained by preventing a high-temperature offset accompanying this.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a main part 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 diagram showing a pattern of a heater heat generating layer according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a pattern of a heater heat generating layer according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a pattern of a heater heat generating layer according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a pattern of a heater heat generating layer according to a fourth embodiment of the present invention.

FIG. 7 is a view showing a pattern of a conventional heater heating layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Low heat capacity linear heater (heating body) 2 Substrate (fixing member) 3A, 3B Heating layer (heating resistor) 6 Fixing film (heat resistant film) 9 Pressure roller (pressure member) 60 Fixing device 101-107 Power supply P recording material

Claims (4)

[Claims] 1. A heating element having a plurality of heating resistors fixedly supported by a fixing member, a security member abutting on one surface of the heating element to cut off electricity at a certain temperature or higher, and A heat-resistant film conveyed while being pressed against the other surface, and a pressing member for bringing the recording material into close contact with the other surface of the heating body via the heat-resistant film, the heat of the heating body In a fixing device for heating and fixing an unfixed image formed on a recording material surface by applying the recording material to the recording material via the heat-resistant film, the heat generation distributions of the plurality of heating resistors are made different. Fixing device. 2. The fixing device according to claim 1, wherein the heat generation distribution of at least one of the plurality of heat generating resistors is made higher at the center in the longitudinal direction. 3. The fixing device according to claim 1, wherein at least one heat distribution of the plurality of heat generating resistors is made higher at both ends in a longitudinal direction. 4. The fixing device according to claim 1, wherein a power ratio supplied to said plurality of heating resistors is switched according to a recording material size.