JPH03182089A - Heater and fixing device - Google Patents

Abstract

PURPOSE:To keep the fusion cutting characteristics for a long period of time by installing a conductive member to be fusion cut at a certain temp. on a heater base board, and covering part of the surface of conductive member with a heat resistant protection film having a low oxygen permeation factor. CONSTITUTION:A current-fed heat emitting resistance body 23 is linearly printed on the undersurface of the base board 22 of heater 21. A thermistor 24 is put in close contact with the oversurface of this base board 22 in its center, and a fuse 35 is put in close contact in the neighborhood of this thermistor 24. The outer surface of the fuse is covered with a protection film 36 consisting of Si resin. A control circuit 39 controls a switching element 38 properly in conformity to the heater 21 temp. information given by a temp. sensing element 24, and current feed to electrodes 23a, 23b of the resistance body 23 is controlled. Alumina base board 22 of the heater gets momentarily uniform temp. specified, and the fuse 35 attains equal temp. instantly. The Si resin film 36 protects the fuse from degradation due to oxidation, etc. Fuse will blow at overrising of the temp. to cause deformation of the Si resin film 36, and dividing into two pieces is made on electrodes 34a, 34b. Thus the current feed is shut.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heater in which a substrate is provided with a current-carrying heating element. More specifically, the present invention relates to a means (safety device) for preventing excessive temperature rise of the heater.

The present invention also relates to a fixing device using the heater.

(Prior Art) For convenience, an image heating fixing device in an image forming apparatus such as an electrophotographic copying machine, a printer, or a fax machine, that is, an electrophotographic
The surface of a recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, printing paper, etc.) is coated with a toner made of heat-meltable resin or the like by an appropriate image forming process such as electrostatic recording or magnetic recording. Direct method or indirect method (
An example of an image fixing device will be described in which an unfixed toner image corresponding to target image information formed by a transfer method is heat-fixed as a permanently fixed image on the surface of a recording material carrying the image.

Image heat fixing devices of various types and configurations, such as a heat roller type, a hot plate type, a belt fixing type, and a flash fixing type, have been known and are in practical use.

Recently, a heating element (thermal heater, hereinafter referred to as "heater") that is fixedly supported, a heat-resistant film (fixing film) that is conveyed while being in pressure contact with the heater, and a method that brings the recording material into close contact with the heater through the film have been developed. A fixing device (film heating method) that has a pressure member and heats and fixes an undefined blue image formed and carried on the surface of the recording material by applying heat from a heater to the recording material through the film. ) has been devised.

For example, Japanese Patent Application Laid-Open No. 63-3131 related to the applicant's previous proposal
The method, device, etc. disclosed in Publication No. 82 belongs to this category, and includes a thin heat-resistant film (sheet), a means for moving the film, and a device fixedly supported on one side of the film with the film inside. a heater, and a pressure member disposed on the other side facing the heater to bring the image-bearing surface of the recording material to which the image is to be fixed into close contact with the heater through the film, and the film has at least When performing image fixing, the recording material to be image-fixed is conveyed and introduced between the film and the pressure member, and is moved at the same speed in the forward direction, and the heater and the pressure member are connected with the moving film in between. By passing through a fixing nip formed by pressure contact, the visible image-bearing surface of the recording material is heated by the heater through the film, and thermal energy is applied to the visible image (unfixed toner image) to soften it. This is a heating means/device that basically melts the toner and then separates the film and recording material, or separates the film and recording material after the toner has cooled and solidified.

These film heating type fixing devices include heat roller type, hot plate type, belt fixing type, flash fixing type,
In comparison with other heat fixing devices such as oven fixing systems, ■ A low heat capacity heating element can be used as the heater, which saves power and shortens wait time (quick start); Since the separation point can be set separately, offsets can be prevented, and various drawbacks of other systems can be solved, and this is an effective method.

The heater as a heating element is formed by baking and attaching a low heat capacity current-carrying heating resistor in the form of a wire or band to an insulating substrate (base material) with low heat capacity and heat resistance and good thermal conductivity such as ceramic. Low heat capacity of the embodiment is used,
When the resistor is energized, the heater heats the surface to the required fixing temperature (for example, about 1,808 m
The temperature rapidly rises to around C).

The heat-resistant film in contact with this heater also has a small heat capacity, and the thermal energy from the heater side is effectively transferred to the recording material that is in pressure contact with the heat-resistant film through the heat-resistant film, so that the image can be thermally fixed well. Ru.

Heater temperature control has an energization control configuration in which the heater temperature is detected by a temperature sensing element, and the energization to the energized heating resistor is controlled based on the temperature detection information, thereby controlling the temperature of the heater to a predetermined fixing temperature. Be taken.

(Problems to be Solved by the Invention) By the way, in the above-described heater, when the heater is energized to generate heat, there is a possibility that the temperature of the heater may rise abnormally due to an abnormality in the energization control device (heater runaway). . Abnormal temperature rise of the heater may cause smoke or ignition of combustible materials near the heater. Conventionally, in order to prevent such excessive temperature rise problems, a temperature fuse made of a material with a predetermined melting point, or a thermostat made of a material that deforms at a predetermined temperature, was placed in contact with the heating part of the heater. These elements are placed close to each other, and when the heater reaches a predetermined temperature or higher, these elements cut off the current supply.

However, in the above-mentioned conventional example, an element such as a temperature fuse or a thermostat is placed close to or in contact with the temperature raising part of the heater, so that there is a large difference in thermal response depending on the installation conditions of the element. Therefore, in order to operate at a predetermined temperature, the installation conditions of the element (contact area, proximity distance, etc.) had to be strictly inspected.

Further, even when these elements are brought into contact, it is impossible to prevent minute air layers from forming on the contact surfaces, resulting in poor thermal response.

Therefore, it is difficult to prevent smoke, ignition, etc. from occurring when the heater runs out of control by using the above-mentioned element in a low heat capacity heater that rapidly increases temperature, such as those used in film heating type fixing devices. It is.

Furthermore, Japanese Patent Application Laid-Open No. 63-160128 proposes a safety circuit that short-circuits with a conductor or resistor that melts at high temperatures; The disadvantage was that the resistor would undergo denaturation such as oxidation, making it difficult to melt during overheating. The present invention also prevents abnormal temperature rise troubles of the heater using a safety element, solves the problem of delayed response, and prevents deterioration in reliability due to deterioration of the safety element over time. The purpose is to improve the safety and reliability of devices that use heaters.

(Means for Solving the Problems) The present invention provides a heater in which a current-carrying heating element is provided on a substrate, in which a metal having a predetermined melting point is melted at a predetermined temperature or higher to interrupt the current-carrying circuit of the current-carrying heating element. A conductive member is formed on the substrate of the heater, and at least a part of the surface of the conductive member is covered with a heat-resistant protective film having a low oxygen permeability.

In the above, the oxygen permeability of the heat-resistant protective film is 5 x 10
It is preferable that the pressure is −8 m·Pa or less.

Further, the present invention is a fixing device characterized in that the heater described above is used as a heat fixing member.

(Function) - The conductive member made of a metal with a predetermined melting point used as a safety element can be made into a thin, narrow strip shape, etc. to reduce its heat capacity, and it can be formed and provided in close contact with the substrate of the heater. As a result, even if the heater is of a type with a low heat capacity and changes in temperature rapidly, the conductive member can raise and lower the temperature in substantially real time without response delay in response to the temperature changes, and the heater can maintain a predetermined temperature. When the temperature rises above the temperature, it is immediately fused and the energizing circuit is cut off, making it possible to eliminate abnormal temperature rise of the heater due to response delay.

■In addition, at least part of the surface of the conductive member listed in L is coated with a heat-resistant protective film with low oxygen permeability to keep it isolated from the outside air, thereby preventing thermal oxidation at high temperatures and room temperature oxidation over time. Degeneration due to progression and the resulting change in fusing characteristics are prevented. This prevents oxidation of the conductor member, maintains the desired fusing characteristics over a long period of time, and improves reliability.

(2) By improving the safety and reliability of the heater as described above, the safety and reliability of the device using the heater is improved.

(Example) (1) Configuration example of a fixing device (Figs. 8 and 9) Fig. 8 shows a film heating type fixing device 1 using a heater according to the present invention.
1 shows a schematic configuration of an example of No. 1.

Reference numeral 25 designates an endless belt-shaped fixing film, which includes a driving roller 26 on the left side, a driven roller 27 on the right side, and a low heat capacity linear heating heater that is fixedly supported and disposed below both rollers 26 and 27. body 21 and drive roller 2
A guide roller 26a disposed below the four members is suspended between the four members parallel to each other.

The driven roller 27 is an endless belt-shaped fixing film 2.
It also serves as the tension roller for fixing film 25.
is a transfer material sheet serving as a recording material carrying on its upper surface an unfixed toner image Ta that is conveyed clockwise at a predetermined circumferential speed as the drive roller 26 is rotated in the clockwise direction, that is, from the image forming section (9) side. It is rotated at the same circumferential speed as the conveyance speed of P without wrinkles, meandering, or speed delays.

Reference numeral 28 denotes a pressure roller having a rubber elastic layer of silicone rubber or the like with good mold releasability as a pressure member. The rollers are pressed against each other by a biasing means with a total contact pressure of, for example, 4 to 7 kg, and are rotated forward and counterclockwise in the conveyance direction of the transfer material sheet P.

Endless belt-shaped fixing film 25 that is rotatably driven
Because it is used repeatedly to heat and fix toner images, it has excellent heat resistance, releasability, and durability, and has a total thickness of 1100 mm.
A thin one having a thickness of Atm or less, preferably 40 Atm or less is used.

For example, polyimide, polyetherimide, PE5-PF
A (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin) single-layer film or composite layer film of a heat-resistant resin such as A (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin), for example, a 20 μm thick film, at least on the image contact side. Resin) A 10 μm thick releasable coating layer made of a fluororesin such as PAF with a conductive material added.

The low heat capacity linear heating body 21 as a heater in this example is a horizontally elongated heater holder having rigidity, high heat resistance, and heat insulation properties and whose longitudinal direction is in the transverse direction of the fixing film (direction perpendicular to the running direction of the fixing film 25). 30, and a heater board 22, which is integrally attached and held on the lower surface side of the holder along the longitudinal length of the holder, and is equipped with a current-carrying heating resistor 23, a temperature measuring element 24 as a means for detecting the temperature of the heater 21, etc. I have it.

The heater holder 30 ensures the overall strength of the heater 21,
It also maintains insulation, such as PP5 (polyphenylene sulfide), PAI (polyamideimide), P
It can be composed of highly heat-resistant resins such as I (polyimide), PEEK (polyetheretherketone), and liquid crystal polymers, and composite materials of these resins and ceramics, metals, glass, etc.

As an example, the heater board 22 has a thickness of 1.0 mm and a width of 10 m.
It is an alumina substrate with a length of 240 mm. Also, there are composite substrates and the like containing this.

The energizing heating resistor 23 is made of, for example, A g / P d, Ru 02T along the longitudinal direction approximately at the center of the lower surface of the substrate 22.
It is a linear or band-shaped low heat capacity current-carrying heating element made by coating (screen printing, etc.) an electrical resistance material such as a2N to a width of 1.0 mm.

The temperature measuring element 24 is a low heat capacity temperature measuring resistor such as a thermistor or a PT film provided on the upper surface of the substrate 22 (the surface opposite to the side on which the resistor 23 is provided).

In this example, the temperature of the substrate 22 is detected by the temperature measuring element 24 as the temperature of the heater 21.

Electricity is applied to the heating resistor 23 from both longitudinal ends thereof to generate heat over the entire length of the resistor. Electricity is DCl
The heater 21 is heated to a predetermined fixing temperature (for example, 1808 C ) is controlling the temperature side. Pulse width is approximately 0
．． 5~5+n5ec. Instead of DC current, the heater may be controlled to a predetermined temperature by repeating 0N10FF with AC current.

The fixing film 25 is not limited to an endless belt shape.
As shown in the figure, the fixing film 25 with an end wound around the feed-out shaft 41 is passed between the heater 21 and the pressure roller 28, and under the guide roller 26a, and then placed on the take-up shaft 41.
It may be configured such that the transfer material sheet P is stopped at the feed-out shaft 41 side and travels from the take-up shaft 42 side at the same speed as the conveyance speed of the transfer material sheet P.

(2) Fixing execution operation The image forming apparatus performs image forming operation in response to the image forming start signal, and the transfer material sheet P conveyed from the image forming section (9) side to the fixing device 11 is guided by a guide 29 and temperature-controlled. The unfixed toner enters between the fixing film 25 and the pressure roller 28 at the pressure contact portion N (fixing nip) between the heater 21 and the pressure roller 28, and the unfixed toner image surface is moved at the same speed as the conveyance speed of the sheet P. The fixing nip N between the heater 2I and the pressure roller 28 is pressed tightly against the lower surface of the fixing film 25 that is moving in the same direction, and the fixing film 24 is overlapped with the fixing film 24 without causing surface misalignment or wrinkles. It passes while receiving.

W is the width j of the energizing heating resistor 23 provided on the lower surface of the heater, and the resistor 23 is located within the width area where the lower surface of the heater 21 and one surface of the pressure roller 28 are in mutual pressure contact, that is, in the fixing nip. It exists within a width area of N. The toner image bearing surface of the sheet P receives heat from the heater 21 via the fixing film 25 while passing through the fixing nip N while being in close contact with the fixing film, and the toner image is melted at a high temperature and the sheet 11
Apply a softened adhesive stopper to the surface.

In the case of this example device, the sheet P which is the recording material and the standard film 2
Separation from the sheet P is performed at the time the sheet P passes through the fixing nip N and comes out.

At the time of separation, the temperature of the toner Tb is higher than the glass transition point of the toner. Therefore, at this time of separation, the bonding force (adhesive force) between the sheet P and the fixing film 25 is small, so the sheet P is The sheet P is always smoothly separated without causing almost any toner offset to the surface of the film 25, and without causing a jam due to the sheet P being stuck to the surface of the fixing film 25 due to poor separation.

Since the toner Tb at a temperature higher than the glass transition point has appropriate rubber characteristics, the toner image surface upon separation does not follow the fixing film surface but has an appropriate uneven surface. Since the toner is maintained and cooled and solidified, excessive image gloss does not occur on the fixed toner image surface, resulting in a high quality image.

The sheet P separated from the fixing film 25 is guided by a guide 43, and while reaching the paper ejection roller pair (44), the temperature of the toner Tb, which is higher than the glass transition point, is lowered by natural temperature drop (natural cooling).
Then, the temperature reaches the glass transition temperature F and solidifies Tc, and the sheet P on which the image has been fixed is outputted onto the tray.

(3) How many layers of fuse structure (Figs. 1 to 3) Fig. 1 is a energization control circuit diagram of the heater 21, Fig. 2 (a) is a cutaway plan view of the fuse portion of the heater 21, and the same figure ( 3(b) is a cross-sectional view, and FIGS. 3(a) and 3(b) are a plan view and a cross-sectional view, respectively, with the fuse blown.

As described above, below the substrate 22 of the heater 21 (referred to as the heater surface), an energizing heat generating resistor 23 is formed in a linear or band shape along the longitudinal direction approximately at the center thereof. 23a
- 23b is the first and second silver electrode portions for electrical conduction provided at both ends of the resistor 23; Since this heater surface is a sliding surface with the film 25, a protective layer 20 made of glass or the like is formed on this surface to protect the surface.

Reference numeral 24 designates, for example, a thermistor as a temperature measuring element provided in close contact with the substantially central portion of the upper surface of the substrate 22 (referred to as the rear surface of the heater).

35 is the upper surface of the substrate 22, and the temperature measuring element 24 is
A conductive member (fuse member) made of a metal such as Sn that melts at a predetermined temperature and is formed in close contact with the substrate surface in the vicinity of the fuse. 34a and 34b are the fuse members 35
'fJ1 and a second current-carrying silver electrode were provided to be electrically connected to both ends of the long strand.

The entire outer surface of the fuse member 35 is coated with a protective film 36 made of silicone resin as a heat-resistant protective film with a low oxygen permeability.

As shown in FIG.
energizing type Vi23a, first energizing electrode 34a of fuse member 35, fuse member 35, second energizing electrode 34b of fuse member 35, power source 37, switching element 38 such as power FEF, energizing heating resistor 23 The second current-carrying electrodes 23b are successively connected in series.

39 is a control circuit including a microcomputer, which collects temperature information of the heater 21 detected by the temperature measuring element 24 (element 2).
The switching element 38 is controlled according to the output of 4).

During fixing, the switching element 38 is appropriately controlled by the control circuit 39 according to the temperature information of the heater 21 detected by the temperature measuring element 24, and the electrodes 23a and 2 at both ends of the energized heating resistor 23 are controlled.
The power supply to the heater 3b is controlled, and the alumina substrate 22 of the heater, which has good thermal conductivity and a small heat capacity, instantly reaches a substantially uniform fixing temperature (approximately 180''C in this example).

The fuse member 35 is formed in close contact with the heater board 22, and since the heat capacity of the fuse member 35 itself is extremely small, the temperature of the fuse member 35 becomes approximately isothermal in real time with the temperature of the heater board 22, that is, the heater 21. .

When the circuit runs out of control, i.e., switching element 38, check t! A
If the element 24, control circuit 39, etc. malfunction and the temperature control function does not work, the heater 21 may become overheated (above ISO'C) due to continuous or excessive power being supplied to the energized heating resistor 23. Then, in response to the excessive temperature rise of the heater 21, the fuse member 35 also turns on the heater 21 in real time without substantial delay.
It is heated almost isothermally. And the fuse member 3
5 is a predetermined temperature, in this example it is 235°C which is the melting point of Sn.
When it reaches this point, it instantly melts down (Fig. 3 (a) and (b)), cutting off the current flow to the energizing heating resistor 23.
Even if flammable materials such as paper are near the heater, it will not emit smoke or catch fire.

Here, the melting phenomenon of the Sn fuse member 35 will be described in detail.

During normal use of the heater, the Sn fuse member 35 is coated with a heat-resistant and elastic protective layer 36 made of silicone resin treated to make it air-impermeable (see FIG. 2(a)).
(b)) is a good conductor without being modified by oxidation, etc., and the heater 21 is heated to 180°C with a controlled current.
will be maintained.

When the heater 21 reaches 235° C., which is the melting point of Sn, during excessive temperature rise, the Sn fuse member 35 melts and becomes a liquid state. Sn in liquid state has Ag due to surface energy.
A force that tries to gather in a hemispherical shape on the electric currents 34a and 34b acts, deforming the elastic silicone resin film 36,
As shown in FIGS. 3(a) and (b), the electrodes 34a and 34a on both t4A sides
It splits into two on 34b and ruptures. As a result, the power to the heater is cut off, and smoke, fire, and damage to the device can be prevented when the heater runs out of control.

According to experiments, when the fixing process is performed for more than 50 hours without the heat-resistant insulating film 36 (180°C state), the surface of the Sn fuse member 35 is oxidized and the temperature is 250"
There were cases where it did not melt even when exposed to high temperatures of C or higher,
The device with the protective film 36 has a maximum usage time of 10
Even after 0 hours of use, it melted when the temperature was too high.

Furthermore, forming the protective film 36 on the Sn fuse member 35 with a flux such as zinc chloride is advantageous because the flux dissolves tin oxide that is generated by a small amount of 0□ passing through the protective film 36. , can withstand longer-term use. As described above, by forming the elastic protective film 36 on the surface of the 4F member 35 made of a low melting point metal provided on the same substrate 22 as the heater, the conductive member 35 will not be denatured during normal use. When the conductive member 35, which is a low melting point metal, melts when the heater runs out of control, the elastic protective film 36 deforms and the molten metal splits into two, thereby cutting off the current flow. In other words, this embodiment enables a safety device that is small, inexpensive, and has excellent responsiveness.

(4) Fuse configuration example
A thin anti-corrosion layer 36a made of gold or the like is formed on the electrical member 35 as a heat-resistant protective film with a low oxygen permeability.
Figure (a)) In other words, Ag electrodes 34a and 34b with a pattern printed on the alumina substrate 22 of the heater have a width of 1.5 mm.
"A thin Au film 36a (1000λ or less) is formed by sputtering or other means after short-circuiting with a PB fuse member 35 having a thickness of 0.2 mm and a melting point of 320°C.The formation of the Au thin film 36a is as follows. This is performed after surface oxides are removed from the surface of the pb fuse member 35 by polishing or chemical means.

With this configuration, the thin gold film 36a is formed on the surface of the PB fuse member 35, so that it does not oxidize and can be used as a good conductor during normal use. In addition, when the heater temperature rises to 320''C during an abnormality, the PB fuse member 35 melts as shown in FIG. 4(b), ruptures the Auvi film 36a and separates the electrode 34a.

It is divided into two parts and gathered on 34b.

Forming the thin film layer 36a with a thickness of 10 μm or less in this manner is sufficient for preventing oxidation, and also easily ruptures when the low melting point metal used as the fuse member 35 melts, preventing the metal from dividing into two. This is a safety device that operates stably.

(5) Example of Fuse Configuration (Fig. 5) In this embodiment, a portion of the low melting point metal serving as the fuse member 35 is coated with a rigid protective film 36b such as glass. That is, as shown in FIG. 5(a), 23
For example, the LPD method (Liquid Phase
A rigid glass coat 36b is applied as a protective film using the same method.

In the case of such a heater, if it is kept in a high temperature state for a long time due to normal use, the surface layer 351 of the Sn fuse member 35 exposed to the air as shown by diagonal lines in FIG. 5(b) will oxidize after a long period of time. It will no longer melt at °C.

However, the surface layer 35 of the portion and end portion where the glass coat 36b is applied. Since it does not come into contact with oxygen, it will not oxidize, and if the temperature reaches 235°C or higher during excessive temperature rise, it will melt.
Due to the difference in wettability, these are Agden JJi34 a/3.
A force moving toward the 4b side acts and pushes out the oxide film toward both ends. Therefore, as shown in FIG. 5(C), the glass coating portion 36
b becomes hollow, and current flow between the electrodes 34a and 34b is cut off.

For example, when there is no coating (36b) as shown in FIG. 5(d), the entire surface layer of the Sn fuse member 35 is coated with an oxide film 351.
Therefore, even when the temperature rises excessively, it may not take 2 minutes.

As described above, this embodiment has a structure in which the fuse member 35 is easily divided into two parts when melted by applying the anti-oxidation coating 36b to at least a portion of the surface of the fuse member 35.

The protective film 36b may be a heat-resistant inorganic adhesive containing alumina or the like as a main component.

Furthermore, in a device in which the heater 21 is controlled at a temperature of 180° C. or lower, an epoxy sealing material that has been subjected to heat-resistant treatment may be used.

(6) Fuse configuration example (Fig. 6) In this example, a protective film having the same configuration as the fuse configuration example (2) in (5) above is formed of a heat-shrinkable material 36c, for example, PFA. Figure (a)). When such a material is used as a protective film, the PFA protective film 36
Due to the shrinkage of c, the melted Sn fuse member 35
(Fig. 6(b)).

(7) Other examples of energization control circuits (Fig. 7) In each of the above-mentioned circuits, a low melting point metal is inserted as a fuse member (conductive member) 35 in series with the heater energization circuit as in the circuit shown in Fig. 1. However, it does not necessarily have to be primary energization, and as shown in FIG. 7, a secondary current is passed from the secondary power source 37a to the low melting point metal member 35 to prevent the heater from running out of control. It is also possible to adopt a configuration in which the primary relay 40 is cut off because the heater energization is cut off, and the heater energization is prohibited.

With this configuration, the current flowing through the low melting point metal member 35 can be kept constant regardless of the heater salinity control, so that the low melting point metal member 35 can be more reliably blown out when the temperature rises.

For example, if the voltage applied to the low-melting point metal member 35 is set to 5V, the current flowing through the low-melting point metal member 35 is very small, making it possible to make the metal member 35 thin and thin. Therefore, it is possible to provide a safety device that is smaller in size, has faster response, and can easily cut off the heater current.

Further, for example, if the current applied to the low melting point metal member 35 is set to always be 3A or more, even if the low melting point metal member 35, which is a fuse member, does not completely part during melting, the metal member 35 may If the part becomes thinner, the resistance value of that part becomes higher, so the fuse member 3 cannot withstand the current.
5 is ruptured, that is, a safety device is created in which the fuse member 35 is reliably fused with the help of the electric current.

(8) Example of Image Forming Apparatus (FIG. 10) FIG. 10 shows a schematic configuration of an example of an image forming apparatus incorporating the fixing device 11 of FIG. 8 described above. The image forming apparatus of this example is an electrophotographic copying apparatus of a reciprocating document table type, a rotating drum type, and a transfer type.

100 is a device cabinet; 1 is a top plate 100a of the device cabinet;
This is a reciprocating type document mounting table made of a transparent plate member such as a glass plate disposed above, and is driven to reciprocate at a predetermined speed on the upper surface plate 100a of the machine casing in the right direction a and the left direction a' in the drawing, respectively. be done.

G is a document, which is placed by placing the image side to be copied facing down on the top surface of the document table 1 according to a predetermined placement standard, and placing the document pressure bonding plate 1a on top of it and pressing it down. .

Reference numeral 100b denotes a slit opening, which serves as a document illumination section, which is opened on the surface of the top plate 100a of the machine casing, with its periphery extending in a direction perpendicular to the direction of reciprocating movement of the document table 1 (direction perpendicular to the plane of the paper).

The downward image surface of the document G set on the document platform 1 passes through the position of the slit opening 100b sequentially from the right side to the left side during the forward movement of the document platform 1 to the right side a. During the passage, the light from the lamp 3 is received through the slit opening 100b and the transparent original table 1, and the document is illuminated and scanned. The light reflected from the document surface of the illumination scanning light is imaged and exposed on the surface of the photosensitive drum 4 by the short focus and small diameter imaging element array 2.

The photosensitive drum 4 has a photosensitive layer such as a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer subjected to N treatment, and is driven to rotate clockwise as shown by an arrow around a central support shaft 4a at a predetermined circumferential speed. The charger 5 charges the battery with positive or negative polarity. By receiving image forming exposure (slit exposure) of the NN4 image on the F surface, electrostatic latent images corresponding to the image-forming exposed original images are sequentially formed on the surface of the photosensitive drum 4.

This electrostatic latent image is sequentially developed using a toner made of a resin or the like that softens and melts when heated by a developing device 6, and the developed toner image is transferred to a location where a transfer discharger 9 is provided as a transfer section. I will do it.

S is a cassette in which transfer material sheets P as recording materials are stacked and stored, and the sheets in the cassette are fed one by one by the rotation of the feeding roller 7, and then the toner on the drum 4 is transferred by the registration roller 8. When the leading edge of the image forming section reaches the transfer discharger 9, the leading edge of the transfer material sheet P also reaches the open position of the transfer discharger 9 and the photosensitive drum 4, and is synchronized so that they coincide. be sent. Then, the toner image on the photosensitive drum 4 side is sequentially transferred onto the surface of the fed sheet by the transfer discharger 9.

The sheet to which the toner image has been transferred in the transfer section is sequentially separated from the four surfaces of the photosensitive drum by a separating means (not shown) and transferred to the conveying device 1.
0, the unfixed toner image Ta carried thereon is guided to the aforementioned fixing device 11 and subjected to heat-fixing processing, and then passed through a guide 43 and an ejection roller 44 as an image-formed product (copy) to a paper ejection tray 12 outside the machine. is discharged to the top.

The surface of the photosensitive drum 4 after image transfer is cleaned by a cleaning device 13.
After removing residual contaminants such as residual toner from the transfer, the image is repeatedly used for image formation (effects of the invention) As described above, the present invention prevents the delay in response and aging of the fuse member by cutting off the current supply in response to excessive temperature rise of the heater. The heater and safety device can be configured to be small, low cost, and durable, improving the safety and reliability of the heater and devices using the heater. be able to.

[Brief explanation of drawings]

FIG. 1 is an energization control circuit diagram of a heater according to an embodiment. Figures 2 (a) and (b) are a partially cutaway plan view and cross-sectional view of the fuse section, respectively. Figure 3 (a) and (b) are a plan view and a cross-sectional view of the fuse section when it is cut, respectively. Surface diagram. FIGS. 4(a) and 4(b) are cross-sectional views of the respective fuse configuration examples before and after the fuse is blown. FIG. 5(a) is a partially cutaway side view of another fuse configuration example, FIG. 5(b) is a side view, FIG. 5(C) is a cross-sectional view of the state after the fuse is blown, ) is a cross-sectional view of one without an M film. FIGS. 6(a) and 6(b) are cross-sectional views of other fuse configuration examples before and after the fuse is blown. FIG. 7 is another energization control circuit diagram. FIG. 8 is a schematic diagram of the structure of a fixing device according to an embodiment. FIG. 9 is a schematic diagram of the configuration of another example of a fixing device. FIG. 10 is a schematic diagram of the configuration of an example of an image forming apparatus. 21 is a heater (low heat capacity linear heating element), 22 is a heater substrate, 23 is a current-carrying heating resistor, 24 is a thermometer T-125 is a fixing film, 35 is a fuse member, and 36 is a protective film.

Claims (3)

[Claims] (1) In a heater whose substrate is equipped with a current-carrying heating element,
A conductive member made of a metal having a predetermined melting point is formed on the substrate of the heater, and at least a portion of the surface of the conductive member is made of a low-oxygen material. A heater characterized by being covered with a heat-resistant protective film of transmittance. (2) Oxygen permeability of heat-resistant protective film 5×10^-^8ml/S・m・Pa The heater according to claim 1, characterized in that: (3) A fixing device characterized in that the heater according to claim 1 is used as a heat fixing member.