JPH08234611A - Fixing heater, fixing device and image forming device - Google Patents

Abstract

PURPOSE: To optionally change a temp. distribution and to effectively prevent nonuniform fixing by forming a resistance heating element on the inner and outer faces of a substrate. CONSTITUTION: The insulating roller 22 having a fixing heater 21 is formed into a cylinder with alumina (Al2 O3 ) ceramics etc., as a heat-resistant and electrical insulating material and made freely rotatable. A paste prepared by kneading the powder of Ag-Pd alloy with the glass powder (inorg. binder) and an org. binder is printed on almost the entire inner face 22a of the insulating roller 22 and fired to form a thick-film internal resistance heating element 23a by thick-film printing, etc. Meanwhile, an annular external resistance heating element 23b having pratically the same composition is partially (selectively) formed on an appropriate region, e.g. the intermediate part in the axial direction, of the outer face of the shell of the insulating roller 22 by thin-film printing, etc. In this case, a high-temp. part is formed at the part where the external resistor 23b is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing heater, a fixing device, and an image forming apparatus suitable for a roller type in which a substrate made of a heat-resistant and electrically insulating material is formed into a roller shape.

[0002]

2. Description of the Related Art Generally, in an electronic copying machine, a copy sheet on which a toner image is formed is passed between a roller type fixing heater and a pressure roller, either directly or indirectly through a heat-resistant sheet while being pressed. The toner on the copy sheet is heated and melted by the heating of the fixing heater to be fixed.

As a conventional roller type fixing heater of this type, there is one having a structure as shown in FIG. 5, for example. The fixing heater 1 is a body outer surface 2a of a rotatable insulating roller 2 which is a base formed in a cylindrical shape from alumina (Al ₂ O ₃ ) ceramics which is a heat resistant and electrically insulating material.
The resistance heating element 3 is formed by printing and coating a low antibody paste mainly containing silver / palladium alloy (Ag / Pd) or the like on almost the entire surface and baking the paste.

The pair of left and right electrodes 4a, 4 are electrically connected to the outer surfaces of both ends of the insulating roller 2 in the axial direction so as to partially overlap the both ends of the resistance heating element 3 in the vertical direction.
b is formed by thick film printing, and these electrodes 4a, 4
Power is supplied to b to energize the resistance heating element 3 to generate heat. A joint portion between the electrodes 4a and 4b and the resistance heating element 3 and the entire outer surface of the resistance heating element 3 are covered with a vitreous overcoat layer 15.

However, in such a conventional fixing heater 1, since the resistance heating element 3 is formed almost entirely on the outer surface 2a of the insulating roller 2, the temperature distribution is almost uniform. It is impossible to arbitrarily change the temperature distribution by providing a high temperature part and a low temperature part. For this reason, when a heat absorbing body such as a thermal fuse is connected to the resistance heating body 3, the temperature of the connecting portion is locally lowered, which causes a problem of local fixing unevenness.

Therefore, it is conceivable to form a spiral resistance heating element 13 on the outer surface 12a of the insulating roller 12 like the fixing heater 11 shown in FIG. 6 to change the temperature distribution arbitrarily. In FIG. 6, reference numerals 14a and 14b are a pair of electrodes, and 15 is an overcoat layer.

[0007]

However, in such a fixing heater 11, since the area of the resistance heating element 13 per unit area of the insulating roller 12 is small, the total amount of heat generation is small and a predetermined temperature is obtained. However, there is a problem in that the insulating roller 12 becomes large and heavy.

Therefore, in order to partially increase the film thickness of the resistance heating element 3 of the fixing heater 1 shown in FIG. 5, a multi-layer is partially formed and a low temperature portion is selectively formed to obtain an arbitrary temperature distribution. It is possible to get it.

However, this increases the number of steps for forming the resistance heating element 3 in multiple layers and increases the protruding height of the multilayer portion, so that relatively large irregularities are formed on the outer surface thereof. Therefore, the unevenness formed on the top surface of the overcoat layer 4 laminated on the resistance heating element 3 is likely to increase. The top surface of the overcoat layer 4 is a portion that is lightly elastically contacted with a pressure roller (not shown) to press the copy sheet (not shown). Therefore, when a large uneven surface is formed on the overcoat layer 4, the uneven surface is formed. As a result, unevenness may occur in the pressing force of the copy sheet brought into pressure contact, resulting in uneven heating and uneven fixing.

Therefore, the present invention has been made in consideration of such circumstances, and its object is to provide a fixing heater capable of arbitrarily changing the temperature distribution with a simple structure and effectively preventing uneven fixing. It is to provide a fixing device and an image forming apparatus.

[0011]

The present invention is configured as follows in order to solve the above-mentioned problems.

A fixing heater according to a first aspect of the present invention includes a base body formed of a heat-resistant electric insulating material in a cylindrical shape; formed on the inner surface and the outer surface of the base body, partially on one of the inner and outer surfaces thereof, and the other. Resistance heating element formed almost entirely on one side;
Have.

According to a second aspect of the fixing heater, the resistance heating element according to the first aspect is partially formed on the outer surface of the substrate.
The inner surface is almost entirely formed.

According to a third aspect of the fixing heater, the resistance heating element according to the first aspect is partially formed on the inner surface of the base,
The outer surface is formed almost entirely.

A fixing heater according to a fourth aspect is a fixing heater according to the first aspect.
3. An electrode formed on each of both axial end portions of the base body according to any one of 3 above and electrically connected to the entire circumference of each axial end portion of the resistance heating element.

The invention according to claim 5 of the present application is the same as claim 1.
4. The fixing heater according to any one of items 1 to 4; a conveying sheet that can travel in a direction intersecting the longitudinal direction of the fixing heater; and the fixing heater is pressed against the fixing heater via the conveying sheet. And a pressure roller that applies heat from the fixing heater to the toner forming the image of the fixing target through the conveyance sheet and that conveys the fixing target. Is characterized by.

According to a sixth aspect of the present invention, toner is attached to the electrostatic latent image formed on the medium to form a reverse image, and the reverse image is transferred to a fixing target to form a predetermined image. And a fixing device according to a fifth aspect of the present invention.

[0018]

In each of the first to fourth aspects of the present invention, since the resistance heating element is formed on both the inner surface and the outer surface of the substrate, it is possible to increase the temperature and accordingly reduce the size and weight.

An arbitrary temperature distribution can be obtained by partially (selectively) forming a resistance heating element on the inner surface or the outer surface of the substrate to form a high temperature portion. This allows
For example, by connecting a heat absorber such as a thermal fuse to the high temperature portion, it is possible to prevent the temperature of the connection portion from being locally lower than that of the other portion, and to flatten the temperature distribution. Therefore, it is possible to effectively prevent local unevenness in fixing due to such local temperature decrease.

Since the portion where the resistance heating element is partially formed does not have to be a multi-layer, the step of forming the multi-layer can be omitted and the thickness of the partial resistance heating element can be reduced. Therefore, it is possible to suppress an increase in the unevenness of the surface due to the formation of the multi-layer resistance heating element, and to effectively prevent the uneven fixing due to these unevenness.

According to the fourth aspect of the invention, since the electrodes are electrically connected to the entire circumference of the end portion of the resistance heating element, both the increase and the certainty of the current passing from the electrode to the resistance heating element are achieved. be able to.

According to a fifth aspect of the present invention, the fixing device to which the toner adheres is conveyed while being pressed against the fixing heater and the pressure roller of the first to fourth aspects through a conveying sheet, and the fixing heater heats the fixing heater. The toner is melted and fixed. Since this fixing device includes the fixing heater according to any one of claims 1 to 4, the fixing device exhibits the effects of the fixing heater according to claims 1 to 4.

An image forming apparatus according to a sixth aspect of the present invention includes the fixing device according to the fifth aspect, and therefore, the operation of the fixing device is achieved.

[0024]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4, the same or corresponding parts are designated by the same reference numerals.

FIG. 1 is a perspective view of an embodiment of the fixing heater of the present invention. In the drawing, the fixing heater 21 includes an insulating roller 22 and a heat-resistant and electrically insulating material such as alumina (Al).
₂ O ₃ ) It is formed into a cylindrical shape from ceramics or the like to form a rotatable roller. The dimensions of this insulating roller 22 are, for example, a shaft length of 360 mm, an outer diameter of 15 mm, and an inner diameter of 11 mm.
mm.

The insulating roller 22 is printed with a paste prepared by kneading silver-palladium alloy (Ag.Pd) powder with a glass powder (inorganic binder) and an organic binder on almost the entire inner surface 22a. By applying and firing, the thick-film inner resistance heating element 23a is formed by, for example, thick-film printing.

On the other hand, on the outer surface of the body of the insulating roller 22, a ring-shaped outer surface resistance heating element 23b having a similar composition to that of the above composition is partially (selectively) formed at an appropriate portion thereof, for example, an intermediate portion in the axial direction. Form).

On the outer surface of the body of the insulating roller 22, silver or silver / platinum (Ag / Pt) is formed at both ends in the axial direction.
A pair of electrodes 24a and 24b made of a good conductor film such as an alloy or silver / palladium alloy (Ag / Pd) is formed by thick film printing or the like. The electrodes 24a and 24b are electrically connected to a pair of left and right wiring conductors 25a and 25b made of a good conductor formed on the outer surface 22b of the insulating roller 22 by thick film printing or the like.

The wiring conductors 25a and 25b are electrically connected by laminating the outer ends of the wiring conductors 25a and 25b so as to overlap with the inner ends of the electrodes 24a and 24b in the up-down direction and electrically connecting the inner ends. The external resistance heating element 23b is laminated and electrically connected to both ends in the axial direction of the outer surface resistance heating element 23b so as to partially overlap each other in the vertical direction. The pair of electrodes 24a and 24b are electrically connected to the internal resistance heating element 23b either directly or via an internal wiring conductor (not shown).

The outer surfaces of the wiring conductors 25a and 25b and the outer surfaces of the joints with the electrodes 24a and 24b are
The outer surface of the outer resistance heating element 23b and its wiring conductors 25a,
An overcoat layer 26 of a glass film having electrical insulation and smoothness is entirely laminated on the outer surface of the joint with 25b. As a result, it is possible to improve mechanical strength such as abrasion resistance and impact resistance, protect corrosion from sulfide and oxidation, and electrically insulate the pressure roller and the like.

FIG. 2 shows the fixing heater 2 constructed as described above.
1 shows the temperature distribution in the axial direction of 1, and the external resistance heating element 23
The high temperature portion 27 is formed at the portion where b is formed.

Therefore, if a heat absorber such as a temperature fuse (not shown) is connected to the high temperature portion 27 by adhering it to the high temperature portion 27, even if the temperature of the high temperature portion 27 decreases due to the heat absorption,
Since they cancel each other out, the temperature becomes almost the same as the other parts, and the temperature distribution becomes uniform. As a result, it is possible to effectively prevent uneven fixing due to variations in temperature distribution.

Since the inner and outer resistance heating elements 22a and 22b are formed on both the inner surface and the partially outer surface of the insulating roller 22, respectively, the temperature can be increased.
This makes it possible to reduce the size and weight of the insulating roller 22.

Further, the external resistance heating element 22b can be formed by one layer, and it is not necessary to form it by multiple layers. Therefore, the multi-layer forming process can be omitted, and the thickness of the outer resistance heating element 22b can be reduced to lower the protrusion height. Therefore, the protrusion can cause unevenness on the top surface of the overcoat layer 26. Can be suppressed. Therefore, it is possible to effectively prevent the uneven fixing due to the large unevenness on the top surface of the overcoat layer 26.

Further, a pair of left and right wiring conductors 25a and 25b
The axial end portion of the external resistance heating element 23b and each electrode 24a,
Since it is electrically connected to the outer surface of the external resistance heating element 23b from each of the electrodes 24a and 24b, it is possible to increase the conduction current and ensure the conduction.

In the above embodiment, the resistance heating element 22
Is formed almost entirely (solid coating) on the inner surface 22a of the insulating roller 22, while it is partially formed on the outer surface 22b, the opposite, that is, the resistance heating element 22 is formed on the outer surface 22b.
b is formed almost entirely (solid coating), while the inner surface 22
It may be partially (selectively) formed on a.

FIG. 3 shows the construction of an embodiment of an electronic copying machine 31 which is a kind of the image forming apparatus of the present invention. The copying machine 31 has a casing 32 and a copy sheet P in a cassette 33. And an image forming unit 34 that forms a toner image corresponding to an image of an original document (not shown) and a fixing device 35 that fixes the toner image on the copy sheet P.

The fixing device 35 is constructed, for example, as shown in FIG. 4, and faces the pressure roller 36 to face the fixing heater 2.
The fixing heaters 21 are rotatably supported by the casing 32 and elastically contact the silicone rubber layer 37 of the pressure roller 36.

The fixing heater 21 has a pair of electrodes 24.
Electrical resistance is generated through the connector with elasticity provided by phosphor bronze plate, etc. in contact with a and 24b.
2 generates heat and heats the overcoat layer 15. Therefore, between the outer surface of the overcoat layer 15 and the silicone rubber layer 37 of the pressure roller 36, the copy sheet P on which the toner image T is formed is pinched and heated by the fixing heater 21, so that the unfixed toner image is formed. T can be melted and fixed on the copy paper P.

Since the electronic copying machine 31 and the fixing device 35 are provided with the fixing heater 21 which can effectively prevent the fixing unevenness as described above, the fixing unevenness can be effectively prevented.

[0041]

As described above, according to the present invention, the resistance heating elements are formed on both the inner surface and the outer surface of the base body, so that it is possible to increase the temperature and accordingly reduce the size and weight.

An arbitrary temperature distribution can be obtained by partially (selectively) forming a resistance heating element on the inner surface or the outer surface of the substrate to form a high temperature portion. This allows
For example, by connecting a heat absorber such as a thermal fuse to the high temperature portion, it is possible to prevent the temperature of the connection portion from being locally lower than that of the other portion, and to flatten the temperature distribution. Therefore, it is possible to effectively prevent local unevenness in fixing due to such local temperature decrease.

Since the portion where the resistance heating element is partially formed does not have to be a multi-layer, the step of forming the multi-layer can be omitted and the thickness of the partial resistance heating element can be reduced. Therefore, it is possible to suppress an increase in the unevenness of the surface due to the formation of the multi-layer resistance heating element, and to effectively prevent the uneven fixing due to these unevenness.

According to the fourth aspect of the present invention, since the electrodes are electrically connected to the entire circumference of the end portion of the resistance heating element, both the increase and the certainty of the current flowing from the electrode to the resistance heating element are achieved. be able to.

According to a fifth aspect of the present invention, the fixing device to which the toner is adhered is conveyed while being pressed against the fixing heater and the pressure roller of the first to fourth aspects via a conveying sheet, and is heated by the fixing heater. The toner is melted and fixed. Since this fixing device includes the fixing heater according to any one of claims 1 to 4, the fixing heater according to any one of claims 1 to 4 has the effect.

An image forming apparatus according to a sixth aspect of the invention includes the fixing device according to the fifth aspect of the invention, so that the effect of the fixing device can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of a roll-type fixing heater of the present invention.

FIG. 2 is an axial temperature distribution chart of the embodiment shown in FIG.

FIG. 3 is an overall configuration diagram of an embodiment of an image forming apparatus of the present invention.

FIG. 4 is an overall configuration diagram of an embodiment of a fixing device of the present invention.

FIG. 5 is a perspective view of a conventional roll-type fixing heater.

FIG. 6 is a perspective view of another conventional roll-type fixing heater.

[Explanation of symbols]

 21 fixing heater 22 insulating roller 22a insulating roller inner surface 22b insulating roller outer surface 23a inner resistance heating element 23b outer resistance heating element 24a, 24b pair of electrodes 25a, 25b wiring conductor 26 overcoat layer 27 high temperature section 31 image forming apparatus 32 casing Body 33 Cassette 34 Image forming apparatus main body 35 Fixing device 36 Pressure roller

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H05B 3/10 0380-3K H05B 3/10 A

Claims (6)

[Claims] 1. A substrate formed of a heat-resistant electrically insulating material in a cylindrical shape; formed on an inner surface and an outer surface of the substrate,
And a resistance heating element formed on one part of the inner and outer surfaces thereof and substantially entirely on the other. 2. The fixing heater according to claim 1, wherein the resistance heating element is partially formed on the outer surface of the base and is almost entirely formed on the inner surface. 3. The fixing heater according to claim 1, wherein the resistance heating element is partially formed on an inner surface of the base and is substantially entirely formed on an outer surface. 4. An electrode formed on each axial end of the base body and electrically connected to the entire circumference of each axial end of the resistance heating element. The fixing heater according to item 1. 5. The fixing heater according to claim 1, a conveying sheet that can travel in a direction intersecting a longitudinal direction of the fixing heater, and a fixing sheet that faces the fixing heater via the conveying sheet. A pressure roller which is disposed so as to press the fixing heater, and which causes heat from the fixing heater to act on the toner forming the image of the fixing target through the conveying sheet and conveys the fixing target. A fixing device comprising: 6. A means for adhering toner to an electrostatic latent image formed on a medium to form a reverse image, and transferring the reverse image to a fixing member to form a predetermined image; An image forming apparatus comprising: a fixing device;