JP2003332026A - Heating element and heat-fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a fixing failure at the end of paper. <P>SOLUTION: The heating element support side surface of a heater end is provided with irregularities to prevent the drop of temperature at a fixing nip end part when using a material of high heat conductivity for a heater base. <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 an image forming apparatus using an electrophotographic process such as a copying machine, a laser printer and a facsimile.

[0002]

2. Description of the Related Art For convenience, a laser printer using a transfer type electrophotographic process will be described as an example.

In the above printer, an electrophotographic photosensitive member, which is generally a rotary drum type, is rotationally driven at a predetermined peripheral speed (process speed), and the surface of the rotary photosensitive drum is charged to a predetermined polarity and potential by a charging means. Then, the charged surface is scanned and exposed by the laser beam outputted from the laser scanner section, which is modulated corresponding to the time-series electric digital pixel signal of the target image information. To form an electrostatic latent image. The electrostatic latent image is developed as a toner image by the developing device, and the toner image is transferred from the paper feeding unit side to the transfer unit of the rotary photosensitive drum on the paper fed at a predetermined timing by the transfer unit. Then, the paper on which this toner image (unfixed image) has been transferred is introduced into the fixing means, and the toner image is fixed on the paper as a permanently fixed image and output as an image formed product.

Conventionally, the roller heating method shown in FIG. 2 has been often used as the fixing means.

The fixing roller 20 has a structure in which a roller having a heat-resistant release layer such as PFA formed on the surface of a hollow cylindrical core metal such as aluminum is heated from the inner surface by a halogen heater 21. Based on the temperature detected by 22, the heater is turned on / off by a control circuit (not shown) to maintain a predetermined temperature.

The paper P on which the toner image T is placed passes through the pressure contact portion (nip portion) with the pressure roller 23 that is pressed against the fixing roller 20, and the toner image T is melted and fixed.

However, in the heat roller heating type fixing device, the heat capacity of the fixing roller is large, and a halogen heater as a heat source is energized to raise the fixing roller from a room temperature state to a predetermined fixing temperature to bring it into a temperature control state. Since it takes a considerable amount of time, the first print time (hereinafter referred to as FPT), which is the time required from receiving the print signal to discharging the first sheet, becomes long.

Further, the roller heating type fixing device has a problem that it consumes a large amount of electric power because the energy efficiency is poor because the electric energy is once converted into light.

In order to solve the problem of the roller heating method, a film heating type heating and fixing device has been proposed in which heat is applied from a heating body to paper through a resin film having a small heat capacity to heat the paper. JP-A-63-3131
No. 82, Japanese Patent Laid-Open No. 2-157878.

This film heating type heat fixing device is
A heating body, a heating body support that supports the heating body, a film that adheres to the heating body, and this film,
And a pressure roller that presses the paper against the heating element side.
According to this method, the heat capacity of the entire fixing device is small, and the paper faces the heating element with only the film sandwiched between them, so that heat can be efficiently applied to the paper, and toner is fixed with low power consumption. It is possible to do.

[0011]

In the film fixing device, the heating body is formed of an electrically insulating substrate, a resistance heating layer formed thereon, and a heat resistant protective glass layer formed thereon. However, it is effective to use a material having high thermal conductivity in order to prevent damage to the electrically insulating substrate. In other words, by using a material with high thermal conductivity for the substrate, the temperature distribution in the substrate becomes more uniform, and the stress in the substrate caused by the difference in thermal expansion during the fixing operation is reduced, resulting in damage to the substrate. Can be prevented.

However, the thermal conductivity of the substrate is 30 W /
When a material of m · K or more is used, heat escapes to the heating body support that supports the heating body from the back side, especially at the end of the heating body where the resistance heating layer is not formed. The temperature at the end is greatly reduced compared to the heating body of No. When such a heating element is used in the fixing device, the temperature distribution of the fixing device during the fixing operation decreases at the edges, so when the paper with the maximum width that can be passed is passed through, the fixing at the edges There is a problem that sex deteriorates.

In order to improve the deterioration of the fixing property at the end portion, the width of the resistance heating element formed on the heater substrate is made narrower at the end portion in the longitudinal direction of the heater substrate than at the central portion, so that There is a method for improving the fixing property at the end by increasing the amount of heat generation.

However, in this case, since the paper is optimized only for the wide paper, when the narrow paper such as a postcard is continuously passed, the area where the paper is not passed (non-passing portion) In (), heat is not taken by the paper, so that the fixing device and the pressure roller at the position corresponding to the non-sheet passing portion may be heated more than necessary and may be damaged.

[0015]

SUMMARY OF THE INVENTION Therefore, according to the present invention, a fixing failure is prevented at the edge of a paper when a wide paper is passed, and a rise in a non-paper passing portion is performed when a small size paper is passed. Both prevention of temperature,
It is a heating body and a heating device characterized by the following constitution for the purpose of providing a fixing device capable of ensuring a good fixing property over the entire surface of paper.

(1) In a heating device having a heating body having a resistance heating layer formed on an electrically insulating substrate and a heating body support for supporting the heating body, a heating body support at an end of the heating body A heating body characterized in that unevenness is provided on the pressure contact surface of.

(2) The heating element according to (1), characterized in that it has at least two or more types of uneven shapes in the longitudinal direction of the heating element.

(3) A heat fixing device using the heating element described in (1) or (2).

(Operation) By adopting the configuration as described in (1), it is possible to suppress the temperature drop at the end of the fixing device and to make a uniform temperature distribution in the fixing nip longitudinal direction.

By adopting a configuration such as (2),
As compared with (1), it is possible to more effectively suppress the temperature decrease at the end portion of the fixing device and obtain a uniform temperature distribution in the longitudinal direction of the fixing nip portion.

By adopting the configuration as described in (3), it is possible to provide a heat fixing device which eliminates fixing failure at the edge of the paper, is always stable, and has good fixability over the entire surface of the paper.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. 1, 3, 5, and 6.

The heat fixing device shown in FIG. 1 to which the present invention is applied is a heating body 1, a heating body support 4 for supporting the heating body 1, and a heating body 1 and a heating body support 4 which are fitted onto the heating body 1. It has an endless heat-resistant film 3 and a pressure roller 5 that forms a nip by sandwiching the heat-resistant film between the heating body 1.

Here, the film 3 is fitted on the outer circumference of the heating body 1 and the heating body support 4 with a margin so that the inner circumferential length of the film 3 is fitted. Therefore, the film 3 is guided by the heating body 1 and the heating body support 4 to rotate. The pressure roller 5 is composed of an aluminum cored bar 5a and a heat resistant elastic layer 5b provided around the cored bar 5a.

As shown in FIG. 3, the heating element 1 of the present embodiment has a heater substrate 1a, a resistance heating element pattern 1b provided along the longitudinal direction of the heater substrate, and a resistance heating element arrangement surface. The surface protective layer 1c and the temperature measuring element 2 are included.

The heater substrate 1a is a laterally long and thin plate having a length in a direction (fixing film width direction) orthogonal to the transport movement direction of the heat resistant film 3, and has a length 270.
A substrate (thermoelectric power: 95 W / mK) having a heat resistance, an electrical insulation property, and a low heat capacity, which is formed of an aluminum nitride ceramic having a width of 7 mm, a width of 7 mm, and an original size of 1 mm. 50m from each end of the heater board in the longitudinal direction
As shown in FIG. 3, the contact surface with the heater support is provided with a groove-shaped concave shape over m. The pitch of this concave shape is 0.5
mm and the depth is 0.3 mm.

On the surface of the heater base 1a, silver palladium (AgPd) having a thickness of 10 is formed as an electric resistance material paste.
The resistance heating element pattern 1b was formed by applying a screen-printing to a strip having a width of μm and a width of 0.95 mm and baking it. Further, in order to protect the resistance heating element pattern 1b and ensure insulation, a glass paste having a thickness of about 40 μm was applied by screen printing and baked to form a heat resistant glass layer.

Electrodes (not shown) for energizing the resistance heating element pattern are provided at the ends of the heating element 1.

Further, the temperature measuring element 2 (chip type thermistor)
Was bonded to the electrode provided on the heater substrate 1a with a heat-resistant conductive adhesive.

The heating element 1 is connected to the resistance heating element pattern 1b,
The surface of the heater substrate on which the surface protection eyebrow 1c is formed (referred to as the front surface)
Was exposed downward and was fitted into a groove provided along the longitudinal direction of the heating body support to be fixedly supported. Further, a heat resistant film was fitted outside and pressed against a pressure roller to form a fixing device.

Regarding the above-described heat fixing device of the present embodiment, a comparison of the fixing property at the edge of the paper is made in comparison with the heat fixing device using the conventional heating body having no groove on the contact surface with the heating body support. I went.

The fixing property is such that a halftone image having a printing rate of 50% is printed on a paper having a letter size of 90 g / m ² , passed through each heating fixing device, and then 10 g / cm ^{2 in} the vertical direction by a non-woven cloth. It was determined by comparing the difference in image density before and after rubbing under pressure (density reduction rate).

Here, the density reduction rate is an index for evaluating whether the fixing property is good or bad from the change in the image density when the image is rubbed with a predetermined pressure, and is defined by the following formula.

Density reduction rate = (Image density before rubbing−Image density after rubbing) / Image density before rubbing × 100 [%] As can be seen from the above equation, the lower the density lowering rate, the better the fixability.

Table 1 shows the results of the fixability depending on the distance from the edge of the paper when the fixing is performed by both heating and fixing devices.

[0036]

[Table 1]

As shown in Table 1, when the fixing device of the conventional example is used, if the distance from the edge of the paper is more than 25 mm, the density decrease rate is 10% or less and there is no problem in fixing property, but within 20 mm. Is more than 10% within the range of, and within 10 mm, the fixability is judged to be extremely poor 2
It exceeds 0%.

On the other hand, when the fixing device of the present embodiment is used, the density decrease rate exceeds 10% within the range of 15 mm from the edge of the paper, but there is no area exceeding 20%. It can be seen that the fixing property at the edge portion of the paper is greatly improved as compared with the fixing device.

This is because the contact area is reduced by making the surface of the end portion of the heating body, which is the surface in contact with the heating body support, groove-like, so that the amount of heat escaping to the heating body support at the heating body end is reduced. It is considered that this is because the temperature of the fixing nip portion could be made more uniform in the paper region.

Therefore, in the above-mentioned heating and fixing device, the pressure roller is rotated at a peripheral speed of 72 mm / s to supply power to the resistance heating element so that the temperature of the temperature measuring element becomes constant at 190 ° C., and power supply is started. After 10 seconds from the above, a polyimide sheet provided with a plurality of thermocouples was passed through the fixing nip in the longitudinal direction of the nip, and the temperature distribution in the longitudinal direction in the fixing nip was measured based on the detected temperature at that time.

The results are shown in FIGS. 5 and 6, respectively. In the heating element in the figure, for convenience, only the heater substrate and the heating element are shown.

As a result of measuring the temperature distribution in the fixing nip portion using the conventional heating and fixing device, the temperature at the edge of the paper passing area is lowered as shown in FIG. 5, and the temperature T2 at the edge of the paper passing area is measured.
And the temperature difference between the central portion and the temperature T1 is about 15 [deg. ]
Met.

On the other hand, in the case of the heat fixing device of the present embodiment shown in FIG. 6, the temperature T3 at the end of the sheet passing area and the temperature T1 at the center are measured, and as a result, the difference between them is 8 [deg. It can be seen that the temperature drop at the edge of the paper is suppressed as compared with the conventional heat fixing device.

That is, by providing unevenness on the surface of the end of the heating body facing the support of the heating body and reducing the contact area, the heat escape to the support of the heating body at the end of the heating body is reduced, It has become possible to reduce uneven temperature distribution in the fixing nip portion in the longitudinal direction. This allows
It has become possible to obtain good fixing property over the entire area of the passed paper without providing an additional member.

(Second Embodiment) In the above-described first embodiment, the groove-shaped concave portion is uniformly provided on the contact surface of the end portion of the heating body with the heating body support, but in this embodiment, In order to further enhance the effect of suppressing the escape of heat at the end of the heating element, the pitch of the concave shape in the region where the resistance heating elements do not overlap is made large.

In the first embodiment, by providing the concave portion at the end portion of the heating body, the temperature drop at the end portion of the sheet passing area of the heat fixing device can be suppressed as compared with the conventional case, but the central portion can be suppressed. Could not be improved to the same level as. On the other hand, in order to suppress the temperature decrease at the end of the paper passing area of the heat fixing device, it is considered effective to increase the pitch of the concave shape to further reduce the contact area.

However, when the concave pitch is actually increased uniformly, the temperature drop at the end of the heating body can be suppressed, but the heat escape to the heating body support becomes extremely small,
At the position where the resistance heating element and the concave shape on the back surface thereof overlap, the temperature rises above the center of the fixing nip and the toner is excessively melted, so that a high temperature offset in which the excessively melted toner is not fixed occurs.

Therefore, in the present embodiment, in the longitudinal direction of the heating element, the concave pitch in the range of 25 mm from the end is 1.0 mm, the depth is 0.5 mm, and 25 mm to 5 mm from the end.
In the range of 0 mm, the pitch is 0.5 mm and the depth is 0.3 m.
The shape of m is a shape that more effectively prevents heat from escaping at the end. FIG. 4 is a diagram showing the heating element used in the second embodiment.

Actually, with respect to the heat fixing device using the heating element of the present embodiment, the fixing property at the edge of the paper was compared between the conventional heat fixing device and the heat fixing device of the first embodiment. . Table 2 shows a comparison result of fixing properties in the present embodiment.

[0050]

[Table 2]

The first embodiment has the effect of improving the fixability at the edge of the paper as compared with the case where the conventional fixer is used, but the fixability is completely equivalent to that at the center of the paper. I couldn't. On the other hand, in the present embodiment, the density decrease rate at the edge of the paper is also 10% or less, and the fixability at the edge of the paper is further improved as compared with the first embodiment. I found out that

Further, the temperature distribution in the longitudinal direction in the fixing nip portion was measured in the same manner as the method described in the first embodiment. FIG. 7 is a diagram showing the temperature distribution in the longitudinal direction of the nip portion of the heat fixing device using the heating element of the present embodiment.

It can be seen from FIG. 7 that the temperature distribution in the longitudinal direction of the nip portion is uniform in the aging fixing device using the heating element of the present embodiment.

As described above, by making the shape of the concave portion provided in the heating element plural, the amount of heat generated by the resistance heating element and the amount of heat escaping to the heating element support are balanced, and the entire surface of the paper is good. It has become possible to secure excellent fixability.

Here, the change of the pitch of the concave shape provided on the contact surface of the end portion of the heating element with the heating element support is set in two steps.
It is also possible to set this in two or more steps, or to change the pitch and depth of the concave shape independently or simultaneously.

[0056]

As described above, according to the present invention, heat is prevented from escaping from the end portion of the heating body, so that the contact portion (fixing nip portion) of the fixing device and the pressure roller in the longitudinal direction is prevented. By suppressing the temperature unevenness and reducing the difference in the temperature distribution within the paper passing area, it becomes possible to prevent defective fixing at the edge of the paper and ensure good fixability over the entire area of the paper.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a heat fixing device of the present invention.

FIG. 2 is a schematic cross-sectional view of a conventional roller heating type heat fixing device.

FIG. 3 is a diagram showing a shape of a heating body according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a shape of a heating body according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a temperature distribution in a fixing nip longitudinal direction of a conventional heat fixing device.

FIG. 6 is a diagram showing a temperature distribution in a fixing nip longitudinal direction of the heat fixing device according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a temperature distribution over a fixing nip longitudinal direction of a heat fixing device according to a second embodiment of the present invention.

[Explanation of symbols]

1 heating element 2 thermistor 3 film 4 Heated body support 5 pressure roller 5a core metal 5b elastic layer 6 thermistor P recording material T toner

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H033 AA03 BA25 BA26 BA27 BB30                       BE03                 3K058 AA65 AA71 BA18 DA01 GA03                       GA06

Claims (3)

[Claims] 1. A heating body having a resistance heating layer formed on an electrically insulating substrate, and a heating body support for supporting the heating body, wherein the electrically insulating substrate has a thermal conductivity of 30 W / m.・
A heating element having a temperature of K or more, characterized in that unevenness is provided on the pressure contact surface of the end portion of the heating element with the heating element support. 2. The heating element according to claim 1, wherein the heating element has at least two or more types of uneven shapes in the longitudinal direction of the heating element. 3. A heat fixing device comprising the heating element according to claim 1.