JP2024080415A - Thermal sensor wiring sheet - Google Patents

Abstract

[Problem] To inexpensively and easily manufacture and provide a wiring sheet for a thermal sensor that can be connected to a sensor so that it can be applied to a safety device in a thermal device to safely detect an overheating state before it becomes dangerously hot. [Solution] A wiring sheet for a thermal sensor 1 is composed of a non-conductive sheet body 2 and a wiring section 3 made of conductive ink formed on the sheet body 2, the wiring section 3 having a wiring main body 32 that forms a two-dimensional geometric shape drawn in one stroke between a pair of connection ends 31, 31, and a cutting line 4 is formed on the sheet body 2 that runs approximately parallel to the wiring main body 32, so that by partially cutting the sheet body 2 along the cutting line 4, it can be developed into a long, single strip. [Selected Figure] Figure 1

Description

The present invention relates to a wiring sheet for thermal sensors that can be used in safety devices in heating equipment such as water heaters and heat sources.

In water heaters and heat sources, heat detection sheets are known as components for detecting overheating. For example, a heat detection sheet for combustion appliances applied to gas water heaters and the like has been proposed in which a conductive ink layer is printed and arranged in a meandering shape or the like on a sheet-like insulating substrate, a fuse layer made of a metal or the like that melts at a predetermined temperature is polymerized and fixed on the conductive ink layer by electroplating, and the surfaces of these two layers are further covered with a cover coat (see Patent Document 1). The material of the conductive ink layer is not specified in the document, but it is known that the conductive ink layer is made of, for example, a paste of materials such as silver, copper, and carbon. The document gives examples of tin with a melting point of about 232°C and lead with a melting point of about 327°C as fuse layers. The document gives examples of polyester film as cover coats. A heat detection sheet with this configuration is inserted between the combustion chamber of the combustion equipment and the heating part and casing of the heat exchanger, and the fuse layer is incorporated into the combustion control circuit. If a crack or hole occurs anywhere in the heating part due to abnormal overheating, the fuse layer detects it and melts, cutting off the power to the combustion control circuit and closing the safety valve.

Additionally, thermal fuse wires that are installed on the outside of combustion chambers and heat exchangers are also known for use in safety devices for combustion appliances. These thermal fuse wires are configured by covering a series of filaments made of a low-temperature melting metal that is conductive and melts at a specified temperature with an insulating resin that has a similar melting point (see Patent Document 2). The same document gives an example of a low-temperature melting metal such as an alloy (made of tin, lead, and cadmium) with a melting point of 145°C, and an example of a resin such as nylon elastomer with a melting point of 160°C. In safety devices that use such thermal fuse wires, the inside of the device's main case becomes abnormally overheated due to heat released from damaged areas such as cracks in the combustion chamber or heat exchanger, causing the abnormally overheated part of the wire, which is made of low-temperature melting metal, to reach its melting point and begin to melt. The resin covering the wire also begins to melt at about that temperature, causing the molten wire to become enveloped in the same molten resin and its tip to become spherical, causing it to separate and break. This cuts off the wire's electrical continuity, detects the abnormal overheating, and stops the combustion of the combustion device.

Japanese Utility Model Application Publication No. 4-57045 Japanese Utility Model Application Publication No. 5-52537 Japanese Patent Application Laid-Open No. 11-241903

However, in a thermal detection sheet such as that in Patent Document 1, the temperature at which the fuse layer melts is high, about 232°C if the material is tin, and about 327°C if the material is lead, and the melting point is even higher at around 1000°C if silver or copper is used for the conductive ink layer. Therefore, even if the resin of the cover coat melts off first around the overheated area, the fuse layer and the conductive ink layer remain connected, and unless the device is abnormally overheated to a very high temperature, the current flow to the combustion control circuit will not be cut off, which is dangerous. Even if a different material is used for the conductive ink layer and the current flow is cut off by the melting of the fuse layer as described in the same document, the temperature around the overheated area will reach the melting point of the fuse layer. Moreover, by the time the current flow to the combustion control circuit is cut off, the equipment around the overheated area, and ultimately the entire combustion equipment, will have been seriously damaged to the point that it cannot be repaired. Furthermore, even with a thermal fuse wire like that in Patent Document 2, the melting point of the low-melting metal that makes up the wire is 145°C, and the melting point of the resin that covers it is 160°C, so the wire and resin melt and break only when the area around the overheated point reaches a relatively high temperature, and there is the same risk of overheating to a high temperature range and damage to surrounding equipment and the entire combustion appliance as in Patent Document 1.

On the other hand, when considering the case where carbon paste is used for the conductive ink layer in Patent Document 1, since carbon has a low electrical resistivity, in order to increase the resistance of the conductive ink layer, it is necessary to print a very long serpentine pattern, which requires the use of a considerably large sheet-like insulating substrate. Therefore, in this document, the sheet-like insulating substrate of a size that matches the installation position must be made larger the larger the combustion appliance, and even if silk screen printing as exemplified in this document is adopted, a large printing machine is required, which increases the manufacturing cost.

In the field of measures to prevent abnormal overheating in water heaters and heat sources, the above-mentioned heat detection sheets and thermal fuse wires have been used for many years despite the various problems mentioned above.

The present invention was made in consideration of these problems, and aims to provide a wiring sheet for a thermal sensor that can detect abnormal overheating at a safer, lower temperature than conventional methods and can be manufactured at low cost, particularly in the field of measures to prevent abnormal overheating in water heaters and heat sources.

That is, the thermal sensor wiring sheet according to the present invention is used in connection with a sensor that detects abnormal overheating in a heating device, and comprises a non-conductive sheet body and a wiring section made of conductive ink printed on one side of the sheet body. The wiring section has a wiring main body that presents a geometric figure (a shape drawn in one stroke, so to speak) that spreads in a plane and is drawn without interruption or overlapping by a line that extends continuously between a pair of connection ends that are electrically connected to the sensor that detects abnormal overheating, and the sheet body has a cutting line formed that passes near the wiring main body and extends approximately parallel to the wiring main body, and the sheet body can be partially cut along the cutting line so that it can be unfolded into a long strip.

With a thermal sensor wiring sheet of this configuration, a long wiring section can be formed by printing a single line of conductive ink on a single sheet body in one stroke, and the sheet body can be partially cut along the cutting line to form a long strip-shaped wiring sheet. Therefore, if a relatively compact sheet body is prepared without using a large sheet-like insulating substrate as in the past, it is easy to increase the resistance of the conductive ink layer by the length of the wiring section formed by printing on it, and it is possible to simplify the manufacturing process and reduce manufacturing costs. In addition, a thermal sensor wiring sheet developed into a strip can be easily constructed as a safety device for detecting abnormal overheating by wrapping it around the main body (the device inside the exterior case) of a heating device such as a water heater or heat source device and connecting both connection ends to a sensor. In other words, if abnormal overheating occurs due to malfunction or partial damage of the main body of the heating device, the stretching of the sheet body causes the wiring section made of conductive ink to stretch, changing its electrical resistance value, and this change can be detected by a sensor to trigger the cutting off of electricity and fuel supply to the heating device. This can ensure safety before the danger of electricity being cut off due to the belt-shaped sheet body and wiring section melting or burning at high temperatures or before adverse effects occur to the main body of the heating device.

Here, as a sensor using a conductive material, a strain sensor in which the electrical resistance value changes as the film stretches, for the purpose of safety inspection of buildings and structures, is known in which conductive particles are dispersed in a polymeric film and molded into a sheet or other shape (Patent Document 3). However, such sensors have not been expected to be used as thermal sensors in safety devices for heating equipment. The present invention focuses on this point, and as a result of intensive research, it has been discovered that when a wiring sheet for a thermal sensor having the above-mentioned configuration is created, if the sheet body is partially cut along the cutting line to form a long strip, and a conductive ink is used for the wiring portion that becomes long as a result, it can be used inexpensively and appropriately as a safety device for heating equipment.

In particular, when the sheet body is rectangular, the wiring section has a pair of connection ends disposed near two adjacent corners of the sheet body, the wiring body has a plurality of straight lines substantially parallel to one of the opposing sides of the sheet body, and a plurality of connecting parts connecting the adjacent straight lines, and is formed into a geometric figure that meanders between the pair of connection ends, and further, the cutting line is formed linearly in the sheet body in an area that does not reach the connecting parts from one of the other opposing sides perpendicular to the aforementioned opposing sides between the straight lines of the adjacent wiring body. By configuring in this way, for example, if a sheet body of a normal silk screen printing size (such as A4 size) is applied, there is no need to make special settings when printing conductive ink on the sheet body, and printing can be achieved at low cost, and the completed thermal sensor wiring sheet can be easily transported. Furthermore, by partially cutting the thermal sensor wiring sheet of the present invention along the cutting line, a sufficiently long strip-shaped wiring sheet can be easily obtained, which makes it easy to install (wrap) it around the main body of the heating device. For example, even during inspection or replacement work, if the thermal sensor wiring sheet is brought to the installation site of the heating device in its sheet form before being partially cut, workers can unfold it into a strip on the spot and easily install it.

The conductive ink applied to the thermal sensor wiring sheet of the present invention is preferably a mixture of an insulating material with carbon paste as the main component. The carbon paste is composed of carbon particles such as graphite, carbon black, and carbon graphite, as well as an appropriate insulating material and solvent. As mentioned above, carbon has a low electrical resistivity, so in order to increase the resistance of the conductive ink layer, it must be printed in a very long, meandering pattern, but with the thermal sensor wiring sheet of the present invention, even if the sheet body is relatively small, a long pattern of the wiring body can be formed by printing with conductive ink, so that a sufficiently high electrical resistance can be obtained. Examples of insulating materials include phenolic resin, polyvinyl chloride, silicon polymer, polyethylene terephthalate (PET), acrylic resin, polyvinyl acetate, and various amorphous polymers (non-crystalline polymers), and can be selectively applied from materials that adhere to the material of the sheet body.

The sheet body may be made of a sheet-like material selected from synthetic resin, cloth, and synthetic or artificial leather. In the present invention, when the sheet body is partially cut along the cutting lines and unfolded into a strip, the sheet body may be bent depending on how the cutting lines are formed (i.e., how the wiring body is patterned). Therefore, it is desirable to use a material for the sheet body that is not easily damaged or broken when bent.

According to the present invention, without using a large, costly sheet as in the past, a sheet body on which a wiring portion is formed in a single stroke shape with conductive ink by normal printing can be partially cut along a cutting line to be expanded into a long strip, which can be wrapped around the main body of a heating device and the connection ends provided at both ends of the wiring portion connected to a safety device sensor, thereby inexpensively and easily configuring a safety device. In particular, the present invention utilizes the property that when abnormal overheating occurs in the heating device, the strip-shaped sheet body and conductive ink expand due to heat, changing the electrical resistance value of the wiring portion. If the change is detected by a sensor and the supply of electricity and fuel to the heating device is cut off, a heating device and its safety device can be provided that can ensure safety appropriately before the risk of fire or damage to the heating device occurs.

FIG. 1 is a plan view showing a thermal sensor wiring sheet according to an embodiment of the present invention. FIG. 4 is a plan view showing a state in which the thermal sensor wiring sheet according to the embodiment is partially cut along the cutting lines and developed into a strip shape. FIG. 13 is an explanatory diagram showing a state in which the thermal sensor wiring sheet according to the embodiment is unfolded into a strip shape and wrapped around and attached to the main body of a heating device.

One embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the thermal sensor wiring sheet 1 according to this embodiment has a sheet body 2 made of a PET (polyethylene terephthalate) film that is rectangular in plan view, and a wiring section 3 is formed by silk screen printing conductive ink in a meandering geometric shape on one side of the sheet body 2, and a cut section 4 is further formed on the sheet body 2 along the wiring section 3.

In this embodiment, the sheet body 2 is an example of an A4 size (210 mm x 297 mm) PET film that can be printed on a general silk screen printing device without any special settings, but a PET film of a different size can also be used.

The wiring section 3 is composed of a pair of connection ends 31, 31 set near two adjacent corners of the sheet body 2, and a wiring main body 32 that electrically connects these connection ends 31, 31. The wiring main body 32 is formed so that it has a meandering shape over the entire surface of the sheet body 2 as a whole, by a plurality of straight line parts 33, 33... extending parallel to the short sides 21, 21 of the sheet body 2, and a plurality of connecting parts 34, 34... that connect the ends of the straight line parts 33, 33 that are alternately adjacent near the long sides 22, 22 of the sheet body 2 in a curved shape. The conductive ink that constitutes the wiring main body 32 uses a carbon paste in which carbon particles are mixed with a small amount of insulating material. The carbon particles can be selected from graphite, carbon black, carbon graphite, etc., and the insulating material can be selected from materials such as phenol resin, polyvinyl chloride, silicon polymer, polyethylene terephthalate (PET), acrylic resin, polyvinyl acetate, and various amorphous polymers (non-crystalline polymers). When selecting an insulating material, it is preferable to place particular emphasis on its affinity (adhesion) with the sheet body 2, and in this embodiment, polyvinyl chloride, for example, is used.

The cut section 4 is a cut made by a cutter in a straight line extending from the long side 22 on the side where the connecting section 34 is not provided to just before the connecting section 34 located near the long side 22 facing parallel to the short side 21 at the intermediate position of the adjacent straight section 33 of the wiring section 3 in the sheet main body 2. The presence of the cut section 4 allows the sheet main body 2 to be partially cut at each cut section 4 and developed into a long strip as shown in FIG. 2. When the sheet main body 2 is developed into a strip, the sheet main body 2 is partially folded (folded back) in the area including each connecting section 34. In this embodiment, 12 straight sections 33 of the wiring section 3 are set at approximately equal intervals, and 11 cut sections 4 are set correspondingly. With this configuration, the sheet main body 2 has a length of about 2 m when developed into a strip, and the connection ends 31, 31 of the wiring section 3 are positioned at both ends.

When using the thermal sensor wiring sheet 1 in this strip-like state, as shown in FIG. 3, it is wound around the main body part X of the heating device (the device inside the exterior case, shown by imaginary lines in the figure), and the connection ends 31, 31 at both ends are connected to the sensor (not shown) on the main body part X side. For example, in the case of a No. 24 water heater, which has the largest hot water supply capacity (and the largest physical size of the device) among gas water heaters widely used in Japan, the length of one revolution in the width and depth directions is about 1 m, so when the thermal sensor wiring sheet 1 of this embodiment is deployed in a strip-like shape of about 2 m and wound around the main body part X of this No. 24 water heater, it will be wound two times. Since the sheet main body 2 is a flexible strip-like shape, there is no problem even if the thermal sensor wiring sheet 1 in the wound state is twisted or turned inside out as long as there is no break in the wiring part 3.

The sensor is configured to detect the current and voltage values flowing through the wiring portion 3 of the thermal sensor wiring sheet 1. When the main body portion X of the heating device becomes overheated, the sheet main body 2 expands due to the heat, causing the wiring portion 3 to expand as well, resulting in a change in the electrical resistance of the wiring portion 3 (in this embodiment, the resistance value increases). By utilizing this property, if the sensor detects this change as a change in the current or voltage value, it is set to cut off the supply of electricity and fuel to the main body portion X, allowing it to function as a safety device to prevent overheating in the heating device.

In the case of the wiring sheet 1 for heat sensors of this embodiment, the wiring section 3 can be formed by silk-screen printing conductive ink on the sheet body 2 of A4 size, which is a standard printing size, so that the manufacturing cost of the wiring sheet 1 for heat sensors is not increased and storage and transportation are easy. In addition, the wiring section 3 is formed in a meandering shape over the entire area of one side of the sheet body 2, and multiple cut sections 4 are provided parallel to the straight section 33 in the wiring section 3 and the short side 21 of the sheet body 2, so that the cut sections 4 can be easily arranged and formed, and the sheet body 2 can be partially cut at the cut sections 4 and unfolded to easily deform the wiring sheet 1 for heat sensors into a long strip shape. In addition, since the wiring section 3 itself is formed long on the sheet body 2, the electrical resistance value of the wiring section 3 made of carbon paste is also increased.

When manufacturing the heating equipment, the thermal sensor wiring sheet 1 can be assembled into a safety device simply by wrapping it around the main body and connecting the connection ends 31, 31 to the sensor. In addition, the safety device can be easily replaced on the spot by workers at the installation site of the heating equipment.

The present invention is not limited to the above-mentioned embodiment. For example, in the above-mentioned embodiment, the wiring portion 3 is formed in a meandering manner so as to have 12 straight portions 33 on the sheet body 2 of A4 size, and the sheet body 2 is unfolded by partially cutting at the cut portions 4 between the adjacent straight portions 33, 33. However, for example, the width of the band when unfolded becomes narrower, but if the cut portions 4 are provided between twice as many straight portions 33 (24 portions) and the adjacent straight portions 33, 33, or if the width of the band when unfolded is not changed and the cut portions 4 are provided between 24 straight portions 33 and the adjacent straight portions 33, 33 on the sheet body 2 of A3 size, the length of the band unfolded after partial cutting can be about 4 m. For example, the size of the sheet body 2 and the number of straight portions 33 and cut portions 4 in the wiring portion 3 having a meandering shape can be appropriately changed as necessary.

In addition, not only the size but also the shape of the sheet body 2 can be adopted as long as the wiring part 3 can be printed without special changes or settings on a printing device such as a normal silk screen printer, in consideration of reducing printing costs. The material of the sheet body 2 is not limited to PET, and can be selected from other materials such as synthetic resin, cloth, synthetic or artificial leather, and can be used in the form of a sheet or film. In particular, in the present invention, considering that the property of the wiring part 3 made of conductive ink that expands due to heat and changes in electrical resistance value is used for overheat detection, it is desirable to select a material that does not melt or burn at the expected overheat temperature in the main body of the heating device and that expands moderately, and considering the printing pattern of the wiring part 3 that will be folded when unfolded, it is desirable to select a material that will not break the wiring part 3 or damage the sheet body 2 itself due to folding.

In addition, the printing pattern of the wiring main body 32 on the sheet main body 2 in the wiring section 3 is not limited to the serpentine shape of the above-mentioned embodiment, but may be any geometric figure that has a planar spread and is drawn without interruption or overlap by a line that extends continuously between a pair of connection ends 31, 31, that is, any geometric figure that can be drawn in a single stroke, such as a zigzag shape or a spiral shape. In accordance with such a geometric shape of the wiring main body 32, the cut portion 4 may be formed in the vicinity of the wiring main body 32 so as to be approximately parallel to it.

The specific configuration of each part is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention.

The thermal sensor wiring sheet of the present invention is useful in the field of safety devices for heating equipment such as water heaters and heat sources, helping to reduce costs, improve work efficiency, and prevent damage to or loss of equipment.

1... Heat sensor wiring sheet 2... Sheet body 3... Wiring portion 4... Cutting portion 31... Connection end portion 32... Wiring body portion 33... Straight portion 34... Connection portion X... Heating device (main body portion)

Claims (4)

A wiring sheet for a thermal sensor used in connection with a sensor that detects abnormal overheating in a heating device,
A non-conductive sheet body;
a wiring portion formed by printing on one surface of the sheet body and made of a conductive ink;
the wiring portion has a wiring main body portion presenting a geometric figure having a planar extent drawn by a line continuously extending between a pair of connection ends electrically connected to the sensor without interruption or overlapping,
forming a cutting line in the sheet body, the cutting line passing near the wire main body and extending substantially parallel to the wire main body;
A wiring sheet for a thermal sensor, characterized in that the sheet body is partially cut along the cutting lines so that it can be developed into a single long strip. The sheet body has a rectangular shape,
In the wiring portion, the pair of connection ends are disposed near two adjacent corners of the sheet body, and the wiring main body is formed into a geometric shape having a plurality of straight line portions substantially parallel to one opposing side of the sheet body and a plurality of connecting portions connecting adjacent straight line portions, and meandering between the pair of connection ends;
The wiring sheet for thermal sensors as described in claim 1, wherein the cutting line is formed linearly in a region of the sheet body that does not extend from one side of the other opposing side that is perpendicular to the opposing side between adjacent straight line portions and does not reach the connecting portion. The thermal sensor wiring sheet according to claim 1 or 2, wherein the conductive ink is a mixture of carbon paste as the main component and an insulating material. 4. The thermal sensor wiring sheet according to claim 1, wherein the sheet body is in the form of a sheet made of a material selected from the group consisting of synthetic resin, cloth, and synthetic or artificial leather.

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