Patent Publication Number: US-10782638-B2

Title: Heater and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the priority of Japanese Patent Application No. 2019-003779, filed on Jan. 11, 2019, the entire content of which is incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a heater and an image forming apparatus. 
     BACKGROUND 
     For example, there is known a heater used to fix toner in copying machines, facsimiles, and the like and to delete printing in a rewritable card reader and the like. The heater generates heat from a resistance heating element formed on one surface of a substrate by power supplied from an electrode for power supply. Further, a thermistor is disposed on the other surface of the substrate. The heater is adjusted to an appropriate temperature while the supply of power is controlled on the basis of a temperature detected by the thermistor. 
     Since such a heater contains lead as a component constituting the thermistor, there has been a demand for designing the thermistor in consideration of the environment. 
     A problem to be solved in the disclosure is to provide a heater and an image forming apparatus which are contrived in consideration of the environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating a heater according to an embodiment, seen from a first surface side of a substrate. 
         FIG. 2  is a plan view illustrating the heater according to the embodiment, seen from a second surface side of the substrate. 
         FIG. 3  is a diagram showing a result of a peeling test for a thermistor. 
         FIG. 4  is a diagram showing a relationship between a sheet resistance kg/□ and content mass % of ruthenium contained in the thermistor. 
         FIG. 5  is a cross-sectional view illustrating a fixing device of the embodiment that uses the heater according to the embodiment. 
         FIG. 6  is a cross-sectional view illustrating an image forming apparatus of the embodiment that uses the heater according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A heater  1  according to an embodiment to be described below includes a substrate  11 , a resistance heating element  12 , and a thermistor  16 . The substrate  11  includes a first surface  11   a  and a second surface  11   b  located on the side opposite to the first surface  11   a . The resistance heating element  12  is disposed on the first surface  11   a . The thermistor  16  is disposed on the second surface  11   b  and does not contain lead. 
     Further, the thermistor  16  according to the embodiment to be described below contains manganese, cobalt, and any one or both of copper and nickel. 
     Further, in the thermistor  16  according to the embodiment to be described below, the mass content becomes larger in order of the manganese, the cobalt, and any one or both of the copper and the nickel. 
     Further, in the thermistor  16  according to the embodiment to be described below, the mass contents of the manganese and the cobalt are larger than the mass contents of other components. 
     Further, in the thermistor  16  according to the embodiment to be described below, the sum of mass contents of the manganese, the cobalt, the copper, and the nickel is 50 mass % or more and 70 mass % or less. 
     Further, the thermistor  16  according to the embodiment to be described below contains ruthenium of 2 mass % or more and 15 mass % or less. 
     Further, a copying machine  100  which is an image forming apparatus according to the embodiment to be described later includes the heater  1  which heats a passing medium and a pressing roller  203  which presses a medium in a heating state and heats and presses the medium by the pressing roller  203  so that a toner image adhering to the medium is fixed. 
     Embodiments 
     The heater according to the embodiment will be described with reference to the drawings.  FIG. 1  is a plan view illustrating the heater according to the embodiment, seen from the first surface side of the substrate.  FIG. 2  is a plan view illustrating the heater according to the embodiment, seen from the second surface side of the substrate. Additionally, in order to easily understand the description,  FIGS. 1 and 2  illustrate a three-dimensional orthogonal coordinate system having a Z axis in which the first surface side of the substrate is a positive direction and the second surface side thereof is a negative direction. 
     The heater  1  according to the embodiment is mounted on electronic apparatuses and mainly heats a medium such as paper passing through the electronic apparatuses. The heater  1  includes, as illustrated in  FIG. 1 , the substrate  11 , the resistance heating element  12 , a first conductor  13 , a power-supply electrode  14 , and a coating layer  15 . Further, the heater  1  includes, as illustrated in  FIG. 2 , a plurality of thermistors  16 , a second conductor  17 , and a coating layer  18 . 
     The substrate  11  has heat resistance and insulation and is formed in an elongated rectangular shape in the embodiment. The substrate  11  is a flat plate which is formed of, for example, ceramics such as alumina or aluminum nitride, glass ceramics, or heat resistant composite materials. The substrate  11  has a thickness corresponding to a space where the heater  1  is attached and the thickness is, for example, about 0.5 mm to 1.0 mm. Additionally, the shape of the substrate  11  is not limited thereto as long as a longitudinal direction (an X-axis direction) and a width direction (a Y-axis direction) intersecting the longitudinal direction are provided. For example, a recess, a protrusion, a chip, or the like may be formed on the outer periphery. 
     The resistance heating element  12  is electrically connected to the first conductor  13  and is provided on the first surface  11   a  of the substrate  11  in the thickness direction (the Z-axis direction). The resistance heating element  12  generates heat when power is supplied thereto. The resistance heating element  12  is a heating element pattern which is formed of a heating element paste of, for example, a silver-palladium type, a graphite type, or a ruthenium oxide type. In the embodiment, the resistance heating element  12  is disposed in the X-axis direction. A resistance heating element  12   a  and a resistance heating element  12   b  included in the resistance heating element  12  are disposed so as to be separated from each other in the Y-axis direction. The resistance heating elements  12   a  and  12   b  are respectively disposed in a band shape in the longitudinal direction so that the length of the heater  1  in the width direction is uniform. 
     The first conductor  13  is used to supply power to the resistance heating element  12  and is provided on the first surface  11   a  of the substrate  11 . The first conductor  13  is, for example, a conductor pattern which is formed on the first surface  11   a  by a conductor paste such as silver (Ag). The first conductor  13  of the embodiment is electrically connected to the resistance heating element  12  in the X-axis direction which is the longitudinal direction of the heater  1  (the substrate  11 ). A conductor  13   a , a conductor  13   b , and a conductor  13   c  of the first conductor  13  are provided so as to be separated from one another in the X-axis direction and the resistance heating elements  12   a  and  12   b  are respectively disposed therebetween. The conductor  13   a  is formed in the longitudinal direction of the resistance heating element  12   a , one end portion thereof is electrically connected to an electrode  14   a , and the other end portion thereof is electrically connected to one end portion of the resistance heating element  12   a . The conductor  13   b  is formed in the longitudinal direction of the resistance heating element  12   b , one end portion thereof is electrically connected to an electrode  14   b , and the other end portion thereof is electrically connected to one end portion of the resistance heating element  12   b . The conductor  13   c  is electrically connected to each of the other end portions of the resistance heating elements  12   a  and  12   b . That is, the first conductor  13  is electrically connected in the longitudinal direction of the resistance heating element  12 . The power-supply electrode  14  is electrically connected to the first conductor  13  and is provided on the first surface  11   a  of the substrate  11 . As illustrated in  FIG. 1 , a pair of the electrodes  14   a  and  14   b  included in the power-supply electrode  14  is provided at the end portion of the substrate  11  in the X-axis direction. The pair of electrodes  14   a  and  14   b  is respectively electrically connected to the conductors  13   a  and  13   b  so that a current flows to the conductors  13   a  and  13   b . Additionally, in  FIG. 1 , the pair of electrodes  14   a  and  14   b  is provided at one end portion of the substrate  11 , but the pair of electrodes  14   a  and  14   b  may be respectively provided at both end portions or the other end portion. In general, the pair of electrodes  14   a  and  14   b  is formed on the first surface  11   a  of the substrate  11  so as to be respectively integrated with the conductors  13   a  and  13   b , but the pair of electrodes  14   a  and  14   b  and the conductors  13   a  and  13   b  may be formed respectively separately. Further, the pair of electrodes  14   a  and  14   b  is disposed on the first surface  11   a  provided with the conductors  13   a  and  13   b  in the substrate  11 , but the pair of electrodes  14   a  and  14   b  may be disposed on the second surface  11   b  on the side opposite to the surface provided with the conductors  13   a  and  13   b . In this case, the pair of electrodes  14   a  and  14   b  is respectively electrically connected to the conductors  13   a  and  13   b  through a through-hole formed in the substrate  11 . 
     The coating layer  15  is a protection layer and covers the resistance heating element  12  and the first conductor  13  provided on the first surface  11   a  of the substrate  11 . The coating layer  15  is formed in a band shape in the embodiment. Since the coating layer  15  covers the resistance heating element  12  and the first conductor  13 , it is possible to prevent the resistance heating element  12  and the first conductor  13  from being directly exposed to the atmosphere. Accordingly, it is possible to suppress the resistance heating element  12  and the first conductor  13  from being damaged and broken due to an external interference (for example, mechanical, chemical, and electrical interference). 
     The thermistor  16  is a temperature detection element for detecting the temperature of the substrate  11 . As illustrated in  FIG. 2 , the thermistor  16  is provided at a plurality of positions of the second surface  11   b  of the substrate  11  in the longitudinal direction of the substrate  11 . That is, the thermistor  16  is disposed at the center and both end sides of the substrate  11  in the longitudinal direction of the substrate  11 . In this way, it is possible to detect a temperature at a plurality of positions in the longitudinal direction of the substrate  11  by the plurality of thermistors  16  in the heater  1 . The thermistor  16  is a printed thermistor which is directly disposed on the second surface  11   b  of the substrate  11 . For this reason, it is possible to obtain faster temperature sensing and superior temperature control response as compared with a so-called chip thermistor. Further, the thermistor  16  has a high degree of freedom in size or arrangement as compared with the chip thermistor. Additionally, detailed characteristics or compositions of the thermistor  16  will be described below. 
     The second conductor  17  is a band-shaped thermistor conductor which corresponds to a plurality of conductors supplying power to the plurality of thermistors  16 . As illustrated in  FIG. 2 , the second conductor  17  includes a connection portion  17   a  which is connected to the thermistor  16 , a linear conductive portion  17   b  which extends in the longitudinal direction (the X-axis direction) of the substrate  11 , and an electrode portion  17   c  which is connected to each terminal member (not illustrated) supplying power. Further, the second conductor  17  electrically connects the thermistors  16 . 
     The connection portion  17   a  includes a portion which extends in the width direction (the Y-axis direction) of the substrate  11  and is connected to one end portion of the conductive portion  17   b . Since the connection portion  17   a  extends in this way, the position of the conductive portion  17   b  with respect to the width direction of the substrate  11  is adjusted. The conductive portion  17   b  extends to the end portion of the substrate  11  in the longitudinal direction (the X-axis direction) of the substrate  11 . A plurality of the conductive portions  17   b  are arranged at intervals in the width direction of the substrate  11 . 
     The electrode portion  17   c  is formed at the other end portion of the conductive portion  17   b  extending to the end portion of the substrate  11  in the longitudinal direction (the X-axis direction). The electrode portion  17   c  is formed at the end portions of the substrate  11  in the longitudinal direction with a gap interposed therebetween in the longitudinal direction of the substrate  11 . The electrode portion  17   c  supplies power to the thermistor  16  through a terminal member (not illustrated) by the connection to the terminal member connected to a power-supply unit (not illustrated) of an electronic apparatus such as an image forming apparatus. 
     The coating layer  18  is a protection layer which coats the thermistor  16  and the second conductor  17  provided on the second surface  11   b  of the substrate  11 . The material of the coating layer  18  can be the same as that of the coating layer  15 . In the embodiment, the coating layer  18  is formed in a band shape so as to cover the entire substrate  11  in the width direction (the Y-axis direction). Further, both ends of the substrate  11  in the longitudinal direction (the X-axis direction) without the coating layer  18  in the second conductor  17  are the electrode portions  17   c.    
     The number and arrangement of the resistance heating elements  12  or the thermistors  16  of the heater  1  and the configurations of the first conductor  13  and the second conductor  17  are not limited to the configurations illustrated in  FIGS. 1 and 2  and may be changed in response to the application or performance of the heater  1 . 
     In the heater  1  according to the embodiment, the sheet resistance of the thermistor  16  disposed on the second surface  11   b  of the substrate  11  can be 100 kΩ/□ to 10000 kΩ/□. The resistance value of the thermistor  16  is generally a high value of the order of kΩ/□ or more, but in the range of the sheet resistance, for example, the measurement can be performed without any influence on the resistance measurement accuracy. Accordingly, desirable thermistor performance is obtained. Further, the thermistor  16  can set the B constant to −2700 K or less. Here, the “B constant” is a physical property value that indicates the sensitivity of the thermistor  16  with respect to a temperature change. When the thermistor  16  has such a physical property value, the temperature of the substrate  11  can be accurately detected. 
     Further, the thermistor  16  according to the embodiment does not contain lead (Pb). For this reason, it is possible to provide the heater  1  with the thermistor  16  in consideration of the environment. Here, a “case in which lead is not contained” means that the content of lead measured by an electron probe microanalyzer (EPMA) JXA-8200 (manufactured by JEOL Ltd.) is a detection limit or less after the thermistor  16  disposed on the second surface  11   b  is cut in the thickness direction of the substrate  11 . Further, the contents and mass contents of the components in the thermistor  16  to be described later can be also measured similarly to the content of the lead. 
     Further, the thermistor  16  according to the embodiment contains manganese, cobalt, and any one or both of copper and nickel and does not contain lead. For this reason, it is possible to provide the heater  1  with the thermistor  16  capable of accurately detecting the temperature of the substrate  11  in consideration of the environment. 
     Further, in the thermistor  16  according to the embodiment, mass contents become larger in order of manganese, cobalt, and any one or both of copper and nickel and lead is not contained. For this reason, it is possible to provide the heater  1  with the thermistor  16  capable of accurately detecting the temperature of the substrate  11  in consideration of the environment. 
     Further, in the thermistor  16 , the mass contents of manganese and cobalt are larger than the mass contents of other components. For this reason, it is possible to provide the heater  1  with the thermistor  16  capable of accurately detecting the temperature of the substrate  11  in consideration of the environment. 
     Further, in the thermistor  16  according to the embodiment, the sum of mass contents of manganese, cobalt, copper, and nickel is 50 mass % or more and 70 mass % or less. When the sum of mass contents is smaller than 50 mass %, the B constant exceeds −2700 K and hence the thermistor  16  cannot accurately detect the temperature of the substrate  11 . Meanwhile, when the sum of mass contents exceeds 70 mass %, the contents of other components contained in the thermistor  16 , for example, glass mixed to be bound to the substrate  11  decreases, so that the adhesion strength is affected. Alternatively, the amount of conductive materials for controlling the resistance decreases, so that the resistance increases. 
     Further, the thermistor  16  according to the embodiment contains ruthenium of 2 mass % or more and 15 mass % or less. Since the sheet resistance of the thermistor  16  is out of the range of 100 kΩ/□ to 10000 kΩ/□ when the content of ruthenium is smaller than 2 mass % or larger than 15 mass %, the temperature of the substrate  11  cannot be accurately detected. 
     Here, a relationship between the physical property of the thermistor  16  and the sum of mass contents of manganese, cobalt, and copper will be described. The physical property of the thermistor  16 , particularly, the occurrence of peeling was tested by changing the sum of mass contents of manganese, cobalt, and copper. The test was performed on the thermistor  16  of which the sum of mass contents of manganese, cobalt, and copper was changed to 60 mass %, 65 mass %, 70 mass %, 75 mass %, and 80 mass % so as to visually check the occurrence of pattern peeling when a pin with epoxy resin adhesive (area ϕ 2 mm) on one side was bonded to the thermistor  16  and was pulled horizontally. Additionally, observing no pattern peeling is demanded as a result of the peeling test. 
     The test result is shown in  FIG. 3 . In  FIG. 3 , a “case without the pattern peeling” is expressed by “◯” and a “case with the pattern peeling” is expressed by “x”. As obvious from  FIG. 3 , it was proved that no pattern peeling occurred when the sum of mass contents of manganese, cobalt, and copper was 60 mass %, 65 mass %, and 70 mass %, that is, the sum of mass contents of manganese, cobalt, and copper is 70 mass % or less and hence no problem occurred in the thermistor  16 . Meanwhile, since the pattern peeling occurred when the sum of mass contents of manganese, cobalt, and copper exceeded 70 mass %, that is, the sum of mass contents of manganese, cobalt, and copper was 75 mass % and 80 mass %, a problem was found in the thermistor  16 . From the description above, the sum of mass contents of manganese, cobalt, and copper is desirably 70 mass % or less. 
     Further, the same result as the thermistor  16  shown in  FIG. 3  could be obtained even in the thermistor  16  containing manganese, cobalt, and nickel and the thermistor  16  containing manganese, cobalt, copper, and nickel. From the description above, the sum of mass contents of manganese, cobalt, copper, and nickel is desirably 70 mass % or less. 
     Next, a relationship between the sheet resistance kΩ/□ and the content mass % of ruthenium contained in the thermistor  16  was tested. The test result is shown in  FIG. 4 . In  FIG. 4 , a horizontal axis indicates the content mass % of ruthenium and a vertical axis indicates the sheet resistance kΩ/□. Additionally, the sheet resistance kΩ/□ is a measurement result under the condition of 25° C. As obvious from  FIG. 4 , it was proved that the content of ruthenium when the sheet resistance of the thermistor  16  was in the range of 100 kΩ/□ to 10000 kΩ/□ was 2 mass % or more and 15 mass % or less. 
     As described above, the heater  1  according to the embodiment includes the substrate  11 , the resistance heating element  12 , and the thermistor  16 . The substrate  11  includes the first surface  11   a  and the second surface  11   b  located on the side opposite to the first surface  11   a . The resistance heating element  12  is disposed on the first surface  11   a . The thermistor  16  is disposed on the second surface  11   b  and does not contain lead. For this reason, it is possible to provide the heater  1  in consideration of the environment. 
     Further, the thermistor  16  according to the embodiment contains manganese, cobalt, and any one or both of copper and nickel. For this reason, it is possible to provide the heater  1  capable of accurately detecting the temperature of the substrate  11  in consideration of the environment. 
     Further, in the thermistor  16  according to the embodiment, mass contents become larger in order of the manganese, the cobalt, and any one or both of the copper and the nickel. For this reason, it is possible to provide the heater  1  capable of accurately detecting the temperature of the substrate  11  in consideration of the environment. 
     Further, in the thermistor  16  according to the embodiment, the mass contents of the manganese and the cobalt are larger than the mass contents of other components. For this reason, it is possible to provide the heater  1  capable of accurately detecting the temperature of the substrate  11  in consideration of the environment. 
     Further, in the thermistor  16  according to the embodiment, the sum of mass contents of the manganese, the cobalt, the copper, and the nickel is 50 mass % or more and 70 mass % or less. For this reason, it is possible to provide the heater  1  capable of accurately detecting the temperature of the substrate  11  in consideration of the environment. 
     Further, the thermistor  16  according to the embodiment contains ruthenium of 2 mass % or more and 15 mass % or less. For this reason, it is possible to provide the heater  1  capable of accurately detecting the temperature of the substrate  11  in consideration of the environment. 
     Configuration of Fixing Device 
     Next, a fixing device of the embodiment using the heater  1  of the embodiment will be described as an example with reference to the drawings.  FIG. 5  is a cross-sectional view illustrating the fixing device of the embodiment that uses the heater according to the embodiment. As illustrated in  FIG. 5 , a fixing device  200  has a configuration in which the heater  1  is provided in a bottom of a fixing film belt  201  wound on a support body  202  in a cylindrical shape. The fixing film belt  201  is formed of, for example, a resin material having heat resistance such as polyimide. The pressing roller  203  is disposed at a position facing the heater  1  and the fixing film belt  201 . The pressing roller  203  has a heat-resistant elastic material, for example, a silicone resin layer  204  formed on the surface thereof and can rotate around a rotation shaft  205  (a direction P in  FIG. 5 ) while being in press-contact with the fixing film belt  201 . 
     In a toner fixing process, a toner image U 1  adhering onto a recording sheet (copy paper) M corresponding to a medium is heated and melted by the heater  1  through the fixing film belt  201  in a contact surface between the fixing film belt  201  and the silicone resin layer  204 . As a result, at least a surface portion of the toner image U 1  exceeds a melting point so as to be softened and melted. Then, the recording sheet M is separated from the heater  1  and is separated from the fixing film belt  201  on the sheet discharge side of the pressing roller  203  so that a toner image U 2  is solidified again while naturally thermally radiating and hence the toner image U 2  is fixed to the recording sheet M. 
     Configuration of Image Forming Apparatus 
     Finally, an image forming apparatus of the embodiment including the heater  1  of the embodiment will be described as an example with reference to the drawings.  FIG. 6  is a cross-sectional view illustrating the image forming apparatus of the embodiment that uses the heater according to the embodiment. Additionally, the image forming apparatus of the embodiment is configured as the copying machine  100 . As illustrated in  FIG. 6 , in the copying machine  100 , components including the fixing device  200  are provided inside a casing  101 . A document platen which is formed of a transparent material such as glass is attached to the upper portion of the casing  101  and a document M 1  corresponding to an object for reading image information therefrom is moved in a reciprocating manner on the document platen (in a direction Q in  FIG. 6 ) so as to scan the document M 1 . 
     A luminaire  102  having a light irradiation lamp and a reflection mirror is provided at an upper portion inside the casing  101 . The light irradiated from the luminaire  102  is reflected on the surface of the document M 1  on the document platen and is slit-exposed onto a photosensitive drum  104  by a short focus small diameter imaging element array  103 . In addition, the photosensitive drum  104  is rotatable (in a direction R in  FIG. 6 ). Further, a charger  105  is provided in the vicinity of the photosensitive drum  104  disposed inside the casing  101  and the photosensitive drum  104  is uniformly charged by the charger  105 . The photosensitive drum  104  is coated with, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer. An electrostatic image which is exposed by the short focus small diameter imaging element array  103  is formed on the charged photosensitive drum  104 . The electrostatic image is developed by toner formed of resin or the like which is softened and melted by the heating of the developer  106 , so that a toner image is formed. 
     The recording sheet M accommodated in a cassette  107  is transferred onto the photosensitive drum  104  by a feeding roller  108  and a pair of conveying rollers  109  rotating in a press-contact state at the upper and lower positions in synchronization with the toner image on the photosensitive drum  104 . Then, the toner image on the photosensitive drum  104  is transferred onto the recording sheet M by a transfer discharger  110 . Subsequently, the recording sheet M which is sent from the photosensitive drum  104  toward the downstream side is guided to the fixing device  200  by a conveying guide  111  so as to undergo a heating and fixing process (the above-described toner fixing process) and is discharged to a tray  112 . After the toner image is transferred, the toner remaining on the photosensitive drum  104  is removed by a cleaner  113 . 
     In the fixing device  200 , the heater  1  is installed so as to be pressed by the silicone resin layer  204  attached to the outer periphery of the pressing roller  203 . The heater  1  includes the resistance heating element  12  which is provided in the width direction of the recording sheet M orthogonal to the conveying direction of the recording sheet M so as to have an effective length according to the width (length) of the maximum sheet to be copied by the copying machine  100 , that is, a length larger than the width (length) of the maximum sheet. Then, the unfixed toner image on the recording sheet M sent between the heater  1  and the pressing roller  203  is melted by the heat generated from the resistance heating element  12  so that a copy image of characters, symbols, images, and the like appears on the recording sheet M. 
     Additionally, an example in which the heater  1  of the embodiment is applied as a fixing heater of an image forming apparatus such as the copying machine  100  has been described, but the application of the heater  1  is not limited. The heater  1  of the embodiment may be used as a heat source for heating or warming while being attached to devices such as household electric appliances, precision machines for business use and experiments, equipment for chemical reaction, and the like. 
     While embodiments of the invention have been described, these embodiments have been presented only by way of examples and are not intended to limit the scope of the invention. The embodiments can be embodied in a variety of other forms and various omissions, substitutions, and modifications in the form of the embodiments described herein can be made without departing from the gist of the invention. The embodiments or modifications included in the scope or gist of the invention are also included in the invention described in claims and its equivalent range.