JPH0794260A - Heater and fixing device - Google Patents

Abstract

PURPOSE:To obtain a heater and a fixing device of using this heater wherein a change of temperature can be decreased in any location of a long narrow band-shaped resistance heating unit. CONSTITUTION:A band-shaped thick film PTC heating unit 3 and a heater H of providing an electrode 21 added along both sides in a lengthwise direction of this heating unit 3 are provided in a surface of an insulating substrate 1. Accordingly, since this heater has a characteristic of controlling a current by increasing also a resistance value when a temperature rises, a heater of improving a quality, capable of self controlling a temperature with no particular control unit required in the outside and also capable of preventing generation of improper contrast, fixing unevenness, etc., of a copying image by obtaining almost uniform heating temperature distribution along the lengthwise direction of the heater, can be provided. In a fixing device for a copying machine or the like, mounting a single heater, having a PTC resistance heating unit of length matched with a width of the largest paper capable of copying, is only required, to play also an effect capable of reducing a cost of the fixing device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater used for toner fixing of office automation equipment such as copiers, facsimiles and printers of computers, and a fixing device using the heater.

[0002]

2. Description of the Related Art In the light, thin, short, and small flows of electronic equipment, in order to increase the density of circuit boards, miniaturization and multifunctionalization of constituent boards and parts are actively underway.

In an electronic copying machine, for example, a toner image formed on the surface of a photosensitive drum is transferred onto a copy sheet, and then this copy sheet is passed while being pinched between a heater and a pressure roller to heat the heater. The copying paper is heated to melt and fix the toner.

As a conventional fixing device, a heat roller in which a tubular infrared light bulb or a rod-shaped heater is arranged in the center of a hollow roller is used, and at least one of a pair of upper and lower rollers is pressed as this heat roller. There is a heat roller fixing method in which a toner image is melted and fixed by passing an unfixed copy paper between the roller and the roller.

This heat roller fixing system has a problem in that copying paper is indirectly heated from a heater through a roller and therefore it takes a long time to start, and it requires constant preheating and consumes a large amount of electric power.

Therefore, instead of the heat roller fixing method, a fixing method of a plate heater, which is excellent in terms of thermal efficiency, weight, size, cost, etc., has been developed and put into practical use. The heater used for the fixing method of this plate heater is
Silver / palladium alloy (Ag / Pd) powder, water glass (inorganic binder), water-soluble organic binder, etc. on a slender heat-resistant / electrically insulating substrate made of alumina ceramics etc. The strip-shaped resistance heating element is formed by printing and applying a paste mixed with the above, and the strip-shaped both ends of this resistance heating element are widened, and a film made of a good conductor such as silver (Ag) is formed on this portion to form a terminal. And the surface of this resistance heating element is covered with a vitreous overcoat layer.

The pressure roller is a roller having a rotating shaft parallel to the heater, the surface of which is made of a heat resistant elastic material, and is adapted to rotate while lightly contacting the overcoat layer of the heater. Then, when the copy sheet is supplied between the heater and the pressure roller, the copy sheet is conveyed while sliding on the surface of the overcoat layer of the heater by the rotation of the pressure roller, and the heat of the heater causes the copy sheet to move on the copy sheet. The toner is heated and melted and fixed.

The fixing system having such a structure has the advantages that the startability is good and the power consumption is saved even if the heater is not preheated, and the fixing device can be made compact.

The resistance heating element of the plate heater insulates the paste of silver-palladium alloy powder, which is a material of the resistance heating element, so that a uniform amount of heat is obtained at a predetermined current value over the entire length in the longitudinal direction. The thick film is printed on the flexible substrate so that the width and thickness are constant.

However, the heat generation temperature distribution along the length of the heat generating portion of the resistance heating element may not be uniform. The reason for this is that the paste material, which becomes the resistance heating element, squeezes out from the printing mask, oozes out and adheres to an undesired portion, or the mask is bent, so that it is located at a predetermined position on the substrate. When the resistance value was measured after firing, there were cases where a high resistance value partly occurred because the pattern could not be printed or the printed thick film was scratched during the process.

When such a heater is energized from both end portions in a strip shape, if the resistance value at each part of the resistance heating element is uniform, the distribution of heat generation temperature along the longitudinal direction is also uniform. If there is a part with a high resistance value in the middle part, the heat generation temperature of this part will be high, and conversely if there is a part with a low resistance value, the heat generation temperature of this part will be low, and the high temperature part In some rare cases, the toner cannot be fixed uniformly in the copying machine.

In the copying machine, several kinds of copy papers having different paper widths can be used, and the length of the heating portion of the resistance heating element is set to the maximum size paper which can be fixed. When copying with a smaller size paper than the paper of No. 2, the heat generated by the paper facing the copy paper is deprived of heat and the temperature drops, but the heat generated in the area where the copy paper does not pass rises and is overheated. In some cases, it is impossible to apply a uniform temperature to a large-sized copy sheet that passes through, which causes uneven fixing. Further, it is possible to prevent the fixing unless the temperature of each part of the heat generating part becomes uniform, but this is not preferable because the copying speed (number of sheets / per hour) is lowered.

As a means for preventing this, a dedicated heater having a different heating section length is used for each copy sheet size, and the width of each heating element middle section of one heater is adjusted to the maximum size sheet. It is possible to derive the leader line from the portion and switch and use it, but it may be costly because a large number of heaters are required or the number of processing steps is increased to derive the leader line.

[0014]

SUMMARY OF THE INVENTION The present invention eliminates the above-mentioned problems and provides a heater capable of reducing the temperature change in any part of a strip-shaped elongated resistance heating element, and a fixing device using this heater. The purpose is to

[0015]

A heater according to claim 1 of the present invention is characterized in that a PTC heating element having a belt-like thick film is formed on the surface of an insulating substrate.

A heater according to a second aspect of the present invention is characterized in that a strip-shaped thick film PTC heating element and electrodes are provided along both longitudinal sides of the heating element on the surface of an insulating substrate.

The heater according to claim 3 of the present invention is characterized in that a strip-shaped thick film PTC heating element is formed on the surface of an insulating substrate and a thermistor for temperature detection is provided on the back surface of the substrate.

According to a fourth aspect of the present invention, in the heater of the present invention, a strip-shaped thick film PTC heating element and electrodes are provided along both sides of the heating element in the longitudinal direction on the surface of the insulating substrate, and a temperature is provided on the back surface of the substrate. The feature is that a thermistor for detection is provided.

According to a fifth aspect of the present invention, the fixing device is characterized in that the pressure roller and the heater according to the first to fourth aspects are arranged to face each other.

[0020]

Since the PTC having a positive temperature characteristic is used as the resistance heating element, even if the film width or the film thickness of the PCT changes, heat is generated according to the resistance value of that portion, and the temperature distribution in the elongated heating element is not uniform. It is possible to obtain a predetermined temperature distribution with high accuracy without generating equilibrium. Further, in the case where the thermistor for temperature detection is provided on the substrate, when the PCT heating element abnormally generates heat, it is possible to prevent the ignition etc. without causing the control circuit to operate and causing the overcurrent to flow.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a plan view in which a middle portion of a heater H of the present invention is cut away, and FIG. 2 is an enlarged cross-sectional side view of a portion cut along line XX in FIG. In the figure, reference numeral 1 denotes a substrate made of a heat-resistant and electrically insulating material such as alumina (Al ₂ O ₃ ) ceramics,
A pair of electrodes 21 and 26 are formed on the surface of the substrate 1 along the longitudinal direction with a gap therebetween, and a PC is formed on the surface of the substrate 1 between the electrodes 21 and 26 extending in the longitudinal direction.
The T resistance heating element 4 is a vitreous overcoat layer which covers the entire surface of the resistance heating element 3 and the surfaces of the electrodes 21 and 26.

The electrodes 21, 26 are made of a material such as silver (A
g), silver-platinum alloy (Ag / Pt), gold (Au),
A thick film is formed by screen-printing a paste prepared by kneading a good conductive metal such as platinum (Pt) and firing it.
Wide terminal portions 22 and 27 made of the same material are formed at one end. Further, the PTC resistance heating element 3 is formed by kneading a paste containing, for example, a powder of tungsten (W), nickel (Ni), platinum (Pt) or the like as a main component, for both electrodes 21 and 2.
It is formed by screen-printing on the surface of the substrate 1 between 6 and firing.

After this, the strip-shaped PTC resistance heating element 3
The vitreous overcoat layer 4 is formed on the surface of the substrate 1 and the portions where the electrodes 21 and 26 are connected to the strip portions. This overcoat layer 4 is formed by PbO (55-85 Wt%) containing lead oxide (PbO) as a main component.
_{-B 2 O 3 (5~15Wt%)} - SiO 2 (10~30
Wt%) glass powder is kneaded with nitrocellulose (organic binder) in an organic solvent to apply a glass paste manufactured by Tanaka Kikinzoku International Co., Ltd. to form a continuous coating film with no gaps. And after drying,
Baking at about 700 ° C. for about 8 minutes, thickness 15 μm to 30 μ
m glass layer.

This glass has a melting point of about 600.degree.
The temperature of the paste-like coating material forming the TC resistance heating element 3 is lower than the firing temperature, and the glass paste is used as the resistance heating element 3 in the above-mentioned strip shape.
Then, the coating is applied to a portion to be coated in the longitudinal direction of the substrate 1 including the electrodes 21 and 26 provided on both sides of the heating element 3, dried, and then fired. When the glass paste melted by this firing flows over the resistance heating element 3 and the electrodes 21, 26 and reaches the substrate 1, the heating is stopped when these surfaces reach a flat and even surface.

Such a heater H has terminal portions 2 on both sides.
When electricity is applied from 2 and 27, the PTC resistance heating element 3 in the narrow strip portion excluding the terminal portions 22 and 27 generates heat. Since the PTC resistance heating element 3 has a positive temperature characteristic, the current decreases when the resistance value increases due to heat generation, and the current is limited and the temperature decreases when a portion having a higher temperature than the other occurs, and conversely,
Since a large amount of current flows in the portion where the resistance value is low, the temperature of this portion rises, that is, the opposing electrode 2
Since the current is self-controlled in accordance with the temperature over almost the entire area between Nos. 1 and 26, no special control device is required and a uniform temperature distribution can be obtained over the entire length of the heating element 3.

In a normal device or the like, the heater H having the above-mentioned configuration can sufficiently control the temperature. However, in the case where temperature conditions such as a chemical reaction are particularly severe and a finer range of temperature control is required, the temperature control shown in FIGS. The heater H may have a structure as shown in FIG.

FIG. 3 is a plan view in which a long intermediate portion of the heater H is cut away, FIG. 4 is a rear view of the heater H in FIG. 3, and FIG. 5 is an enlarged view of a portion cut along the line YY in FIG. It is a sectional side view. 3 to 5, the same parts as those in FIGS. 1 and 2 described above are designated by the same reference numerals, and the description thereof will be omitted.
The heater H is provided with a thermistor 7 for temperature detection on the surface opposite to the surface on which the resistance heating element 3 is formed, that is, on the back surface side of the substrate 1.

In the figure, reference numerals 81 and 86 denote two wire conductors formed on the back surface side of the substrate 1, which are made of the same material as the electrodes 21 and 26, and the thermistor 7 is attached between the wire conductors 81 and 86. . The electric power is supplied to the heater H from both upper and lower sides of the substrate 1 on one end side, and the other terminal portion 27 is formed on the back surface side of the substrate 1 and is electrically conductive through the through hole 28. . The terminal portions 82 and 87 of the wiring conductors 81 and 86 are formed on the front surface side of the substrate 1 and are electrically conductive through the through holes 83 and 88.

This thermistor 7 uses a semiconductor having a large negative temperature coefficient of electric resistance. When the temperature of the thermistor 7 is increased by absorbing the energy of infrared rays, the resistance value greatly changes and the heat of infrared rays is conducted. It is a sensor that consists of a thermal detection element that measures the strength of infrared rays by converting it into a large or small body resistance value.

The characteristics of the thermistor 7 are that the detection sensitivity is substantially constant regardless of the wavelength of the incident light, that it can be used at room temperature during operation, that it is easy to make, and that it is inexpensive.
Further, since the thermistor 7 must receive the heat radiation to raise the temperature of the element and reduce the resistance value, the thinner the film thickness and the smaller the heat capacity, the better the sensitivity and response.

The structure and attachment of the thermistor 7 will be described in detail with reference to FIG. The thermistor 7 is a plate-shaped base 71 made of alumina ceramics (Al ₂ O ₃ ) or the like.
And an oxide of manganese, cobalt, nickel or the like (MnO ₂ ,
Co ₃ O _4, the thermosensitive portion 7 of a thin film made of a mixture of NiO)
2 and electrode portions 73, 73 made of a platinum (Pt) layer formed on both sides of the heat sensitive portion 72 so as to be connected to the heat sensitive portion 2.

The thermistor 7 is attached such that the heat-sensitive portion 72 is in contact with or close to the back surface of the substrate 1, and the electrode portions 73 and 73 are used for the wiring conductors 81 and 86, respectively. Glass (inorganic binder)
They are joined via a conductive adhesive 9 mixed with a water-soluble organic binder.

Such a heater H is energized with a circuit configuration as shown in FIG. That is, when the terminals 22 and 27 are energized via the temperature control circuit T, the electrodes 21 and 2 are
A current flows through the PTC resistance heating element 3 via 6 and the resistance heating element 3
Heats up. Further, the signal current also flows through the thermistor 7.

Due to the heat generated by the resistance heating element 3, the substrate 1 also receives heat and its temperature rises, and this heat is transmitted to the heat-sensitive portion 72 in the central portion of the thermistor 7 attached to the back surface of the substrate 1 and the heat-sensitive portion. The resistance value of 72 is changed. This heat sensitive part 72
The change in the resistance value of the terminal portion 8 is changed through the wiring conductors 81 and 86.
2, 87, and outputs this to the temperature control circuit T to determine whether or not it is in an appropriate temperature range, and adjusts the temperature by adjusting the power applied to the resistance heating element 3 by, for example, phase control. . It should be noted that this temperature adjustment is not limited to phase control of electric power, but may be adjusted to a predetermined temperature range by controlling voltage or current.

With such a structure, the thermistor 7 can accurately receive the temperature of the back surface of the heater H, detect the change in the resistance value thereof with accuracy, and feed this back to the temperature control circuit T for proper detection. The temperature can be controlled. Since the PTC resistance heating element 3 has the same heat generation temperature in any portion, accurate temperature detection can be performed regardless of the location of the thermistor 7. Further, the PTC resistance heating element 3 has a characteristic of self-controlling the current according to the temperature, but the primary temperature control is finely controlled by the thermistor 7, and the secondary temperature such as runaway of the resistance heating element 3 is controlled. The PTC resistance heating element 3 can be controlled by utilizing its own characteristics, and has an effect of preventing accidents such as ignition due to overheating of the heater H.

7 and 8 show an example of a fixing device such as a copying machine or a facsimile in which the heater H is incorporated. Since the heater H portion in the drawing is the same as that of the above embodiment, its description is omitted. . In the figure, R is a pressure roller, and a heat-resistant elastic material such as a silicone rubber roller 53 is fitted on the surface of a cylindrical roller body 52 having rotary shafts 51 protruding from both end surfaces. A fixing heater H is juxtaposed to face the rotary shaft 51 of the pressure roller R, and the rubber roller 5 is provided.
3 is lightly elastically contacted with the surface of the glass coat layer 4 directly above the PTC resistance heating element 3 of the heater H. Reference numeral 6 denotes a connector made of a phosphor bronze plate or the like and provided with elasticity, and contacts the terminal portions 22 and 27 of the heater H to supply power to the PTC resistance heating element 3. Further, P indicates a copy sheet.

This fixing device is provided in, for example, a copying machine, and a predetermined voltage or current is applied to the heater H through the connector 6. Then, the PTC resistance heating element 3 that has generated heat
The copy paper P is pinched between the surface of the glass coat layer 4 and the rubber roller 53, and the copy paper P is conveyed in the direction of the arrow by the rotation of the pressure roller R to fix the toner.

Since such a fixing device uses the heater H capable of obtaining a substantially uniform heat irradiation distribution along the three axes of the PTC resistance heating element, the occurrence of image contrast defects and fixing unevenness for fixing. It can be prevented.

When a copy paper P having a width much narrower than that of the PTC resistance heating element 3 is passed, the temperature of the portion of the PTC resistance heating element 3 in contact with the paper P decreases, but the resistance value becomes low immediately. As the current increases and the temperature rises again, and when the temperature of the portion that does not come into contact with the paper P rises, the resistance value increases and the current is controlled, so that the heating element 3 does not suffer from overheating.

The present invention is not limited to the above embodiment,
For example, the material of the heat-resistant / insulating substrate is not limited to alumina ceramics, but may be other ceramics, glass, a synthetic resin member having high heat resistance such as polyimide resin, or a metal whose surface is subjected to insulation treatment such as glass coating. .

In the above embodiment, the PT formed on the substrate
The material of the C resistance heating element is barium titanate (BaTi).
O ₃ ) may be formed by adding at least one of rare earth oxides such as yttrium oxide (Y ₂ O ₃ ), neodymium oxide (Nd ₄ O ₇ ) and antimony oxide (Sb ₂ O ₃ ). Instead, it may be appropriately selected according to the heat generation temperature and the condition of the heater to be used. The number of strip-shaped resistance heating elements formed on the substrate is not limited to one, and a plurality of resistance heating elements may be formed.

Further, although the electrode is formed along the longitudinal edge of the PTC resistance heating element, the electrode may be formed along the short side of the substrate, and the material thereof is not limited to that of the embodiment. Absent. Further, in the above embodiment, the resistance heating element is provided after the electrodes are formed on the substrate, but the present invention is not limited to this, and as shown in FIG.
First, the strip-shaped PTC resistance heating element 3 is formed on the surface of the substrate 1, and then the electrodes 21 and 26 are formed along the longitudinal direction of the heating element 3 and on both side edges thereof so as to overlap with each other. The heater H also has the same effect as the above embodiment.

Further, as described above, since the PTC resistance heating element has the same heating temperature in any part,
The thermistor may be arranged anywhere and its position may be determined in relation to the electrode, the terminal portion or other parts.

Further, the PTC resistance heating element and the glassy overcoat layer on the substrate are not essential, and when they are formed, the materials are not limited to those of the embodiment.

Further, in the above embodiment, the power supply to the PTC resistance heating element is performed by the elastic connector, but the present invention is not limited to this, and the socket structure or the one in which the lead wire is directly connected to the terminal portion may be used. Absent.

Furthermore, in the above-mentioned embodiment, the copy paper directly contacts the surface of the overcoat layer, but it may be indirect contact with a plastic sheet interposed for protection of the fixing heater and paper feeding. The heater of the present invention is O
The present invention can be put to various practical uses not only for fixing the equipment A but also in other fields.

[0047]

According to the present invention having the above-described structure, the resistance heating element formed on the substrate is the PTC. Therefore, if voltage and current are set and power is supplied, the resistance heating element is substantially uniform over its entire length. That is, it is possible to prevent the occurrence of defective contrast or uneven fixing in the copied image because the temperature can be controlled by the outside without a special control device and a substantially uniform heat generation temperature distribution can be obtained along the longitudinal direction. It is possible to provide a heater with improved performance.

Further, since this heater has the characteristic that the resistance value increases as the temperature rises and the current is controlled, even if a fixing device such as a copying machine is not provided with a heater suitable for each size, this heater can be used. It suffices to mount one heater having a PTC resistance heating element having a length corresponding to the paper width of the maximum paper that can be copied by the copying machine, and it is possible to reduce the cost of the fixing device.

Further, although this heater is a PTC resistance heating element and has the function of adjusting the current by itself, by providing a temperature detection sensor consisting of a thermistor, it becomes possible to carry out finer temperature control and the PCT heating element. In the case of abnormal heat generation, it also functions as an electrical safety device that can prevent ignition and the like without causing the control circuit to operate and causing an overcurrent to flow.

[Brief description of drawings]

FIG. 1 is a plan view showing an intermediate portion of a heater according to an exemplary embodiment of the present invention with a cutout.

2 is an enlarged cross-sectional view of a portion of the heater of FIG. 1 taken along line XX.

FIG. 3 is a plan view showing a notched intermediate portion of a heater according to another embodiment of the present invention.

FIG. 4 is a rear view of the heater H shown in FIG.

5 is an enlarged cross-sectional view of a portion of the heater of FIG. 4 taken along line YY.

FIG. 6 is a circuit diagram showing an example of an energization control circuit of the heater of the present invention.

FIG. 7 is a partially sectional front view showing an embodiment of the fixing device of the present invention.

FIG. 8 is a cross-sectional view of a portion cut along the line VV in FIG.

FIG. 9 is an enlarged transverse sectional view of a heater according to another embodiment of the present invention.

[Explanation of symbols]

 H: Heater R: Pressure roller P: Copy paper 1: Substrate 21, 26: Electrode 22, 27: Terminal part 3: PTC resistance heating element 4: Overcoat layer 7: Thermistor 81, 86: Wiring conductor

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takaaki Kanabe 3-3-9 Shimbashi, Minato-ku, Tokyo Toshiba Abu E. Co., Ltd.

Claims (5)

[Claims] 1. A heater characterized in that a PTC heating element having a belt-shaped thick film is formed on the surface of an insulating substrate. 2. A heater characterized in that a PTC heating element having a belt-shaped thick film and electrodes are provided along both sides of the heating element in the longitudinal direction on the surface of an insulating substrate. 3. A heater characterized in that a strip-shaped thick film PTC heating element is formed on the front surface of an insulating substrate and a thermistor for temperature detection is provided on the back surface of the substrate. 4. A PTC heating element having a strip-shaped thick film on the surface of an insulating substrate, electrodes are provided along both sides of the heating element in the longitudinal direction, and a thermistor for temperature detection is provided on the back surface of the substrate. And a heater. 5. A fixing device, wherein a pressure roller and the heater according to any one of claims 1 to 4 are arranged so as to face each other.