HEATER, AND IMAGE FORMING APPARATUS

A heater includes: a substrate; a heating element, provided on a first surface of the substrate and extending in a longitudinal direction of the substrate; a protection part, provided on the first surface, extending in the longitudinal direction of the substrate, and covering the heating element; and at least one relaxation part, provided on a second surface of the substrate facing the first surface. A coefficient of thermal expansion of the protection part and a coefficient of thermal expansion of the at least one relaxation part are different from a coefficient of thermal expansion of the substrate. A material of the at least one relaxation part is the same as a material of the protection part, or a main component of the material of the at least one relaxation part is the same as a main component of the material of the protection part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Japan Application No. 2021-066851, filed on Apr. 12, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

An embodiment of the disclosure relates to a heater and an image forming apparatus.

Related Art

An image forming apparatus such as a copying machine or a printer is provided with a heater for fixing a toner. Generally, such a heater includes an elongated substrate, a heating element provided on one surface of the substrate and extending in a longitudinal direction of the substrate, and a protection part covering the heating element.

The substrate is made of a material having heat resistance, insulation properties, and high thermal conductivity. For example, the substrate is made of ceramics such as aluminum oxide, a metal core substrate in which a surface of a metal plate is coated with an insulating material, or the like.

The protection part is made of a material having heat resistance, insulation properties, high thermal conductivity, and high chemical stability. For example, the protection part is made of ceramics, glass, or the like.

Here, the material of the substrate and the material of the protection part may be different from each other. When the material of the substrate and the material of the protection part are different from each other, thermal stress may be generated due to a difference in coefficient of thermal expansion between the materials, and warpage my occur in the heater. In this case, the larger the difference in coefficient of thermal expansion between the substrate and the protection part, the more likely warpage is to occur.

When warpage occurs in the heater, there is a risk that a distance between the heater and an object to be heated may vary, and uneven heating may occur in the object to be heated.

Accordingly, it has been desired to develop a technique capable of suppressing the occurrence of warpage in the heater.Patent Document 1: Japanese Patent Laid-open No. 2007-240606

SUMMARY

The disclosure provides a heater in which the occurrence of warpage can be suppressed, and also provides an image forming apparatus.

A heater according to an embodiment includes: a substrate; a heating element, provided on a first surface of the substrate and extending in a longitudinal direction of the substrate; a protection part, provided on the first surface, extending in the longitudinal direction of the substrate, and covering the heating element; and at least one relaxation part, provided on a second surface of the substrate facing the first surface. A coefficient of thermal expansion of the protection part and a coefficient of thermal expansion of the at least one relaxation part are different from a coefficient of thermal expansion of the substrate. A material of the at least one relaxation part is the same as a material of the protection part, or a main component of the material of the at least one relaxation part is the same as a main component of the material of the protection part.

According to an embodiment of the disclosure, a heater in which the occurrence of warpage can be suppressed, as well as an image forming apparatus, can be provided.

DESCRIPTION OF THE EMBODIMENTS

An embodiment is hereinafter illustrated with reference to the drawings. In each drawing, similar components are assigned the same reference numerals and detailed description thereof will be omitted as appropriate. Arrows X, Y, and Z in each drawing represent three directions orthogonal to each other. For example, the longitudinal direction of a substrate is set as the X direction, the lateral direction (width direction) of the substrate is set as the Y direction, and a direction perpendicular to a surface of the substrate is set as the Z direction.

FIG. 1is a schematic front view for illustrating a heater1according to the present embodiment.

FIG. 1is a view of the heater1from a side where a heating part20and a protection part40are provided.

FIG. 2is a schematic back view for illustrating the heater1.

FIG. 2is a view of the heater1from a side where a relaxation part50is provided.

FIG. 3is a schematic sectional view of the heater1inFIG. 1along line A-A.

As shown inFIG. 1toFIG. 3, the heater1includes, for example, a substrate10, the heating part20, a wiring part30, the protection part40, and the relaxation part50.

The substrate10has a shape resembling a plate and extending in one direction (for example, X direction). The substrate10has a planar shape of, for example, an elongated rectangle. The substrate10has a thickness that can be set to, for example, about 0.5 mm to 1.0 mm. Planar dimensions of the substrate10can be appropriately changed depending on the size or the like of an object (for example, paper) to be heated.

The substrate10is made of a material having heat resistance, insulation properties, and high thermal conductivity. The substrate10is made of, for example, ceramics such as aluminum oxide or aluminum nitride, crystallized glass (glass ceramics), or a metal core substrate.

The metal core substrate has, for example, a metal plate made of stainless steel or the like, and an insulating layer covering a surface of the metal plate. The insulating layer can be formed of, for example, an inorganic material such as ceramics. The metal core substrate including the metal plate has higher thermal conductivity than ceramics or the like. Hence, if the substrate10is made of the metal core substrate, the occurrence of in-plane distribution in the temperature of the heater1can be suppressed.

The heating part20converts applied electric power into heat (Joule heat). The heating part20can be provided on a surface10a(corresponding to an example of a first surface) of the substrate10.

The heating part20includes, for example, a heating element21and a heating element22. Although the case where the heating element21and the heating element22are provided is illustrated as an example, the number or size of the heating element can be appropriately changed depending on the size or the like of the object to be heated. Multiple kinds of heating elements that are different in length, width, shape or the like can also be provided. That is, it is sufficient that at least one heating element be provided.

The heating element21and the heating element22are, for example, provided side by side at a predetermined distance from each other in the Y direction (lateral direction of the substrate10). The heating element21and the heating element22have, for example, a form extending along the X direction (longitudinal direction of the substrate10).

Dimensions (lengths) of the heating element21and the heating element22in the X direction can be set, for example, substantially the same. In this case, the center of each of the heating element21and the heating element22is preferably located on a straight line1a. That is, each of the heating element21and the heating element22is preferably provided so as to be axisymmetric with the straight line1aas the axis of symmetry.

When the heater1is attached to an image forming apparatus100, for example, the straight line1ais made to overlap a center line of a conveyance path of the object to be heated. In this way, even if a change occurs in a dimension of the object to be heated in a direction orthogonal to a conveyance direction, it becomes easy to substantially uniformly heat the object to be heated.

Electrical resistance values of the heating element21and the heating element22can be set substantially the same or different. For example, by setting the dimension (length) in the X direction, the dimension (width) in the Y direction, and the dimension (thickness) in the Z direction substantially the same between the heating element21and the heating element22, the electrical resistance values of the heating element21and the heating element22can be set substantially the same. By changing at least one of these dimensions, the electrical resistance values can be set different. By changing a material, the electrical resistance values can be set different.

The electrical resistance value per unit length of the heating element21can be set substantially uniform in the X direction. For example, the dimension (width) in the Y direction and the dimension (thickness) in the Z direction of the heating element21can be set substantially constant. A planar shape of the heating element21can be set, for example, a substantially rectangular shape extending along the X direction (longitudinal direction of the substrate10).

The electrical resistance value per unit length of the heating element22can be set substantially uniform in the X direction. For example, the dimension (width) in the Y direction and the dimension (thickness) in the Z direction of the heating element22can be set substantially constant. A planar shape of the heating element22can be set, for example, a substantially rectangular shape extending along the X direction (longitudinal direction of the substrate10).

The heating element21and the heating element22can be formed using, for example, ruthenium oxide (RuO2), silver-palladium (Ag—Pd) alloy, or the like. The heating element21and the heating element22can be formed, for example, by applying a paste-like material on the substrate10by using a screen printing method or the like and curing the same by using a firing method or the like.

The wiring part30is provided, for example, on the surface10aof the substrate10on which the heating part20(heating element21and heating element22) is provided.

The wiring part30includes, for example, a terminal31, a terminal32, a wire33, a wire34, and a wire35.

The terminals31and32are provided, for example, in the vicinity of one end of the substrate10in the X direction. The terminals31and32can be provided side by side in the X direction. The terminals31and32are electrically connected to, for example, a power supply or the like, via a connector and a wire or the like.

The wire33is provided, for example, on a side of the substrate10where the terminal31is provided in the X direction. The wire33has a form extending in the X direction. The wire33is electrically connected to the terminal31and an end of the heating element21on the terminal31side.

The wire34is provided, for example, in the vicinity of an end of the substrate10opposite the side where the terminals31and32are provided in the X direction. An end of the heating element21opposite the wire33side and an end of the heating element22opposite the wire35side are electrically connected to the wire34.

The wire35is provided, for example, on a side of the substrate10where the terminal32is provided in the X direction. The wire35has a form extending in the X direction. The wire35is electrically connected to the terminal32and an end of the heating element22on the terminal32side.

The wiring part30(terminals31,32and wires33to35) is formed using a material containing, for example, silver or copper. For example, the terminals31,32and the wires33to35can be formed, for example, by applying a paste-like material on the substrate10by using a screen printing method or the like and curing the same by using a firing method or the like.

The protection part40is provided, for example, on the surface10aof the substrate10on which the heating part20is provided. The protection part40has, for example, a form extending along the X direction (longitudinal direction of the substrate10). The protection part40covers the heating part20(heating elements21and22) and a portion (wires33to35) of the wiring part30. In this case, the terminals31and32can be exposed from the protection part40.

The protection part40has, for example, a function of insulating the heating part20and a portion of the wiring part30, a function of transmitting the heat generated in the heating part20, and a function of protecting the heating part20and a portion of the wiring part30from an external force or a corrosive gas or the like. The protection part40is made of a material having heat resistance, insulation properties, high chemical stability, and high thermal conductivity. The protection part40is made of, for example, ceramics, glass, or the like. In this case, the protection part40can also be made using glass to which a filler containing a material having high thermal conductivity, such as aluminum oxide, is added. The thermal conductivity of the glass to which the filler is added can be set to, for example, 2 [W/(m K)] or more.

The heater1may further be provided with a detector detecting a temperature of the heating part20(heating elements21and22). The detector can be set as, for example, a thermistor. The detector can be provided on at least one of the surface10aof the substrate10on which the heating part20is provided and a surface10b(corresponding to an example of a second surface) of the substrate10opposite the side where the heating part20is provided. For example, a wire and a terminal electrically connected to the detector are provided on the surface of the substrate10on which the detector is provided. For example, the detector and the wire can be covered by the protection part40, and the terminal can be exposed from the protection part40.

Here, as mentioned above, the substrate10is made of, for example, ceramics such as aluminum oxide or aluminum nitride, crystallized glass (glass ceramics), or a metal core substrate. On the other hand, the protection part40is made of, for example, ceramics, glass, or glass to which a filler is added.

Hence, the substrate10may have a coefficient of thermal expansion different from that of the protection part40. During use of the heater1, when the heater1generates heat, the substrate10and the protection part40are heated. During manufacture of the heater1, when the protection part40is fired, the substrate10and the protection part40are heated. Hence, during use or manufacture of the heater1, thermal stress may be generated due to a difference in coefficient of thermal expansion between the materials, and warpage my occur in the heater1.

In this case, if the substrate10has a short length in the lateral direction (width direction, for example, Y direction), or the substrate10has a long length in the longitudinal direction (for example, X direction), or the substrate10has a small thickness, warpage is likely to occur in the heater1. In a metal core substrate, since a metal plate serves as a base, the coefficient of thermal expansion of the metal core substrate is greater than that of an inorganic material such as ceramics or crystallized glass. Hence, if the substrate10is a metal core substrate, since a difference in the coefficient of thermal expansion increases, there is a risk that warpage may be relatively likely to occur in the heater1, or relatively large warpage may occur in the heater1.

When warpage occurs in the heater1, there is a risk that a distance between the heater1and the object to be heated may vary, and uneven heating may occur in the object to be heated.

Accordingly, the heater1is provided with the relaxation part50.

As shown inFIG. 2andFIG. 3, the relaxation part50is provided on the surface10bof the substrate10facing the surface10a. When viewed from a direction (Z direction) perpendicular to the surface10a(10b) of the substrate10, at least a portion of the relaxation part50overlaps the protection part40.

At least one relaxation part50can be provided. If multiple relaxation parts50are provided, as shown inFIG. 2, the multiple relaxation parts50can be provided side by side in the longitudinal direction (X direction) of the substrate10.

The relaxation part50has a coefficient of thermal expansion different from that of the substrate10. If the coefficient of thermal expansion of the relaxation part50is different from the coefficient of thermal expansion of the substrate10, thermal stress is generated due to the difference in coefficient of thermal expansion between the materials during use or manufacture of the heater1.

However, since the relaxation part50is provided on the surface10bof the substrate10opposite the surface10aon which the protection part40is provided, the thermal stress generated by the substrate10and the protection part40can be canceled out by the thermal stress generated by the substrate10and the relaxation part50. If the thermal stress is canceled out, the occurrence of warpage in the heater1can be suppressed.

That is, if the relaxation part50is provided, the occurrence of warpage in the heater1can be suppressed.

In this case, the magnitude of the thermal stress generated by the substrate10and the relaxation part50is preferably set as equal as possible to the magnitude of the thermal stress generated by the substrate10and the protection part40. Hence, the coefficient of thermal expansion of the relaxation part50is preferably set the same as or close to the coefficient of thermal expansion of the protection part40. For example, a material of the relaxation part50can be set the same as a material of the protection part40. For example, a main component of the material of the relaxation part50can be set the same as a main component of the material of the protection part40. In this case, if the material of the relaxation part50is the same as the material of the production part40, the manufacturing process can be simplified, the productivity can be improved, the manufacturing cost can be reduced, and so on.

By changing at least one of planar dimensions and thickness of the relaxation part50, the occurrence of warpage can be suppressed, or the magnitude of warpage can be reduced. However, when a difference between the volume of the relaxation part50and the volume of the protection part40increases, the effect of canceling out the thermal stress is reduced. Hence, for example, if the material of the relaxation part50is the same as the material of the protection part40, or if the main component of the material of the relaxation part50is the same as the main component of the material of the protection part40, the volume of the relaxation part50is preferably set about the same as the volume of the protection part40. For example, in the case where the volume of the protection part40is set to V1 mm3and the volume of the relaxation part50is set to V2 mm3, preferably, “0.9≤V2/V1≤1.1”, and more preferably, “0.94≤V2/V1≤1.06”.

If multiple relaxation parts50are provided, by changing at least one of arrangement position, material, and volume (planar dimensions, thickness) of the multiple relaxation parts50, the occurrence of warpage can be suppressed or the magnitude of warpage can be reduced. The arrangement position, material, and volume of the multiple relaxation parts50can be appropriately determined by conducting an experiment or a simulation.

If multiple relaxation parts50are provided, as shown inFIG. 2, a space can be provided between each of the relaxation parts50. If the space is provided between each of the relaxation parts50, a jig60can be provided in the space when the heater1is manufactured. If the jig60is provided in the space, for example, when multiple relaxation parts50are fired, bending of the substrate10can be suppressed. Hence, when the heater1is manufactured, deformation of the heater1can be suppressed.

However, when a distance L between each of the relaxation parts50increases, the effect of canceling out the thermal stress is reduced. Hence, the distance L between each of the relaxation parts50is preferably set to 7 mm or less. For example, if the distance L is set to about 5 mm, reduction in the effect of canceling out the thermal stress can be suppressed, and arrangement of the jig60is facilitated.

Next, the image forming apparatus100provided with the heater1is illustrated.

In the following, a case where the image forming apparatus100is a copying machine is described as an example. However, the image forming apparatus100is not limited to a copying machine, and may be any apparatus provided with a heater for fixing a toner. For example, the image forming apparatus100can be set as a printer or the like.

FIG. 4is a schematic view for illustrating the image forming apparatus100according to the present embodiment.

FIG. 5is a schematic view for illustrating a fixing part200.

As shown inFIG. 4, the image forming apparatus100includes, for example, a frame110, an illumination part120, an imaging element130, a photosensitive drum140, a charging part150, a discharging part151, a development part160, a cleaner170, a storage180, a conveyance part190, the fixing part200, and a controller210.

The frame110has a box shape, inside which the illumination part120, the imaging element130, the photosensitive drum140, the charging part150, the development part160, the cleaner170, a portion of the storage180, the conveyance part190, the fixing part200and the controller210are stored.

A window111made of a light transmissive material such as glass can be provided on an upper surface of the frame110. A manuscript500to be copied is placed on the window111. A movement part that moves the position of the manuscript500can be provided.

The illumination part120is provided in the vicinity of the window111. The illumination part120includes, for example, a light source121such as a lamp, and a reflector122.

The imaging element130is provided in the vicinity of the window111.

The photosensitive drum140is provided below the illumination part120and the imaging element130. The photosensitive drum140is rotatably provided. For example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer is provided on a surface of the photosensitive drum140.

The charging part150, the discharging part151, the development part160and the cleaner170are provided around the photosensitive drum140.

The storage180includes, for example, a cassette181and a tray182. The cassette181is detachably attached to one side part of the frame110. The tray182is provided on a side part of the frame110opposite the side where the cassette181is attached. Paper510(for example, blank paper) before copying is stored in the cassette181. Paper511on which a copy image511ais fixed is stored in the tray182.

The conveyance part190is provided below the photosensitive drum140. The conveyance part190conveys the paper510between the cassette181and the tray182. The conveyance part190includes, for example, a guide191supporting the paper510to be conveyed, and conveyance rollers192to194conveying the paper510. The conveyance part190can be provided with a motor that rotates the conveyance rollers192to194.

The fixing part200is provided on a downstream side (tray182side) of the photosensitive drum140.

As shown inFIG. 5, the fixing part200includes, for example, the heater1, a stay201, a film belt202, and a pressure roller203.

The heater1is attached to a side of the stay201toward a conveyance line of the paper510. The heater1can be embedded in the stay201. In this case, the side of the heater1where the protection part40is provided is exposed from the stay201.

The film belt202covers the stay201provided with the heater1. The film belt202may contain a heat-resistant resin such as polyimide.

The pressure roller203is provided so as to face the stay201. The pressure roller203includes, for example, a core203a, a drive shaft203b, and an elastic part203c. The drive shaft203bprotrudes from an end of the core203aand is connected to a drive apparatus such as a motor. The elastic part203cis provided on an outer surface of the core203a. The elastic part203cis made of an elastic material having heat resistance. The elastic part203cmay contain, for example, a silicone resin.

The controller210is provided inside the frame110. The controller210includes, for example, a calculation part such as a central processing unit (CPU), and a storage part storing a control program. The calculation part controls operation of each element provided in the image forming apparatus100based on the control program stored in the storage part. The controller210may also include an operation part for a user to input a copying condition or the like, a display part displaying an operating state or an abnormality, or the like.

Since a known technique is applicable to the control of each element provided in the image forming apparatus100, detailed description thereof will be omitted.

Although several embodiments of the disclosure have been illustrated above, they are presented as examples and are not intended to limit the scope of the disclosure. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the disclosure. These embodiments or modifications thereof are included in the scope or gist of the disclosure, as well as in the scope of the disclosure described in the claims and the equivalent scope thereof. Each of the above-described embodiments can be implemented in combination with each other.