Planar heating element and water-based paint

Abstract

To provide a planar heating element that has excellent moldability during thermoforming, is less susceptible to cracks occurring in a heat generating layer during thermoforming, and is less susceptible to delamination between a substrate and the heat generating layer during thermoforming.SOLUTION: A planar heating element 1 includes at least a heat generating layer 2 and a thermoplastic sheet substrate 3 supporting the heat generating layer 2, the heat generating layer 2 includes a carbon nanotube component, a dispersant component, and a binder component, the carbon nanotube component includes multi-walled carbon nanotubes, the dispersant component includes a carboxymethyl cellulose component, the binder component includes a polyurethane resin, the polyurethane resin has a glass transition temperature in the range of 50.0°C or lower, and the heat generating layer 2 has a content of the polyurethane resin in the range of 60.0 mass% or more and 95.0 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sheet heating element having excellent thermoformability and a water-based coating material used for forming the heat-generating layer of the sheet heating element. [Background technology]

[0002] Unlike conventional heaters that use electric heating wires, sheet heating elements are capable of generating heat uniformly across the entire surface of the heating layer, have a fast heating rate, are less susceptible to problems such as a wire break causing the element to stop generating heat, consume low power, and are thin and flexible, making them suitable for a wide range of applications.

[0003] When using such a sheet-shaped heating element to heat an object to be heated, it is necessary to place the sheet-shaped heating element as close to the object to be heated as possible in order to improve heating efficiency; however, if the object has a complex shape, attempting to bring the sheet-shaped heating element into close contact with the complex shape of the object to be heated can result in wrinkles in the sheet-shaped heating element, making it impossible to place the sheet-shaped heating element in close contact with the object to be heated.

[0004] Possible methods for solving such problems include first thermoforming the sheet heating element into the shape of the object to be heated by vacuum forming, and then laminating and adhering the object to be heated and the sheet heating element, or, if the object to be heated is a resin molded product, integrally molding the resin molded product (the object to be heated) and the sheet heating element by insert molding. However, when a general sheet heating element such as that in Patent Document 1 is thermoformed by the methods described above, there are problems such as the heating layer of the sheet heating element being unable to withstand the stretching distortion and heat during the thermoforming process and cracks occurring in the heating layer, delamination occurring between the substrate and heating layer of the sheet heating element after thermoforming, and molding defects occurring because the substrate and heating layer do not stretch properly during thermoforming depending on the materials of the substrate and heating layer of the sheet heating element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-133047 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a sheet heating element having excellent thermoforming processability. More specifically, an object of the present invention is to provide a sheet heating element having excellent formability during thermoforming, in which cracks are unlikely to occur in the heating layer due to thermoforming, and in which delamination is unlikely to occur between the substrate and the heating layer due to thermoforming. [Means for solving the problem]

[0007] As a result of investigations conducted by the present inventors to solve the above-mentioned problems, it was found that a sheet heating element with excellent thermoforming processability can be obtained by using a sheet heating element having at least a heating layer and a thermoplastic sheet substrate supporting the heating layer, wherein the heating layer contains a carbon nanotube component, a dispersant component, and a binder component, wherein the carbon nanotube component contains multi-walled carbon nanotubes, the dispersant component contains a carboxymethyl cellulose component, and the binder component contains a polyurethane resin, wherein the polyurethane resin has a glass transition temperature in the range of 50.0°C or less, and the content of the polyurethane resin in the heating layer is in the range of 60.0% by mass or more and 95.0% by mass or less.

[0008] In order to obtain the above-mentioned sheet heating element, it is at least necessary to form a heating layer having excellent thermoforming processability. For this purpose, The planar heating layer may be formed using an aqueous paint for forming a heating layer of a planar heating element having at least a heating layer and a thermoplastic sheet substrate supporting the heating layer, the aqueous paint comprising a carbon nanotube component, a dispersant component, a binder component, and water, the carbon nanotube component comprising multi-walled carbon nanotubes, the dispersant component comprising a carboxymethyl cellulose component, and the binder component comprising a polyurethane resin, the polyurethane resin having a glass transition temperature in the range of 50.0°C or lower, and the content of the polyurethane resin in the solid matter of the aqueous paint after drying is in the range of 60.0% by mass or more and 95.0% by mass or less. Effect of the Invention

[0009] The sheet heating element can be molded into any shape by thermoforming. If the object to be heated is a resin molded product, the object to be heated and the sheet heating element can be molded integrally by insert molding or other methods. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a sheet heating element of the present invention. [Diagram 2] FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a sheet heating element of the present invention. [Diagram 3] FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a sheet heating element of the present invention. [Figure 4] FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a sheet heating element of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The planar heating element according to the first aspect of the present invention comprises at least a thermoplastic sheet substrate and a heating layer, the heating layer being provided on at least one side of the thermoplastic sheet substrate. The heating layer contains a carbon nanotube component, a dispersant component, and a binder component. The carbon nanotube component contains multi-walled carbon nanotubes, the dispersant component contains a carboxymethyl cellulose component, and the binder component contains a polyurethane resin having a glass transition temperature in the range of 50.0°C or lower. The content of the polyurethane resin in the heating layer is in the range of 60.0% by mass or more and 95.0% by mass or less.

[0012] The present invention also includes an aqueous paint for forming the heat generating layer of the sheet heating element of the first invention described above. The aqueous paint of the second invention of the present invention contains a carbon nanotube component, a dispersant component, a binder component, and water. The carbon nanotube component contains multi-walled carbon nanotubes, the dispersant component contains a carboxymethyl cellulose component, and the binder component contains a polyurethane resin having a glass transition temperature in the range of 50.0°C or lower. The content of the polyurethane resin in the solid content of the aqueous paint after drying is in the range of 60.0 mass% or more and 95.0 mass% or less.

[0013] The sheet heating element and the water-based paint will be described in more detail below.

[0014] <<Surface heating element>> As shown in Fig. 1, the sheet heating element 1 of the present invention comprises at least a thermoplastic sheet substrate 3 and a heating layer 2, and the heating layer 2 is provided on at least one side of the thermoplastic sheet substrate 3. The sheet heating element 1 comprises an electrode layer 4 for passing electricity through the heating layer 2 during normal use (Fig. 2). In addition, the sheet heating element 1 may be provided with a protective layer 5 to cover the surface of the heating layer 2 of the sheet heating element 1 for various protection purposes (Fig. 3), or a protective layer 5 may be provided as the outermost layer of the sheet heating element 1 to cover the entire surface (Fig. 4).

[0015] <Heat generating layer and water-based paint for forming the heat generating layer> The heat generating layer of the sheet heating element of the present invention contains a carbon nanotube component, a dispersant component, and a binder component. Such a heat generating layer can be formed by applying an aqueous paint containing a carbon nanotube component, a dispersant component, a binder component, and water to at least one side of a thermoplastic sheet substrate by various known methods, and then drying the paint. In addition to the essential components described above, the heat generating layer and the aqueous paint may further contain other components such as various known additives, as necessary.

[0016] (Carbon nanotube component) Carbon nanotubes (abbreviated as CNT (carbon nanotube)) are conductive carbon materials in which a six-membered ring network composed of carbon atoms is formed into a single-layer or multi-layer cylindrical body. Among carbon nanotubes, those with a single layer of cylinders are called single-walled carbon nanotubes (abbreviated as SWCNT (single-walled carbon nanotube)), and those with multiple layers of cylinders are called multi-walled carbon nanotubes (abbreviated as MWCNT (multi-walled carbon nanotube)). Note that hereafter in this specification, "carbon nanotubes" may be referred to as "CNT".

[0017] The carbon nanotube component (abbreviation: CNT component) of the present invention refers to single-walled CNT and multi-walled CNT.

[0018] The CNT component of the present invention contains at least multi-walled CNTs. The lower limit of the average fiber diameter of the multi-walled CNTs is in the range of 1 nm or more, and more preferably in the range of 5 nm or more. The upper limit of the average fiber diameter of the multi-walled CNTs is in the range of 80 nm or less, and more preferably in the range of 30 nm or less. If the average fiber diameter of the multi-walled CNTs is within the above range, the dispersion state of the multi-walled CNTs in the heat generating layer and the aqueous paint is made uniform, the high conductivity of the heat generating layer is ensured, and more advantageous effects tend to be obtained in terms of improving the durability of the heat generating layer.

[0019] The average fiber diameter of the multi-walled CNTs can be determined, for example, from an image of the surface of the heat generating layer of the planar heating element taken with a scanning electron microscope (SEM). The average fiber diameter of the multi-walled CNTs can be determined by measuring the fiber diameters of any multiple multi-walled CNTs (in other words, the width of the observed fibers) in the SEM image of the surface of the heat generating layer, and averaging the fiber diameters of any 10 multi-walled CNTs. The SEM image used to measure the fiber diameter of the multi-walled CNTs may be subjected to image analysis processing as necessary.

[0020] The lower limit of the average fiber length of the multi-walled CNTs may be in the range of 1 μm or more, and more preferably in the range of 5 μm or more. On the other hand, the upper limit of the average fiber length of the multi-walled CNTs may be in the range of 1000 μm or less, more preferably in the range of 500 μm or less, and most preferably in the range of 100 μm or less. If the average fiber length of the multi-walled CNTs is in the above range, it is easy to ensure high dispersibility of the multi-walled CNTs in the heat generating layer and the aqueous paint, and it tends to be easy to ensure higher electrical conductivity.

[0021] The CNT component may contain single-walled CNTs to the extent that the effect of the present invention is not impaired. When the CNT component contains single-walled CNTs, it is advantageous in terms of increasing the electrical conductivity of the heat generating layer. However, it is preferable that the ratio of multi-walled CNTs in the CNT component is high. The content ratio of multi-walled CNTs in the CNT component is 80.0 mass% or more, and more preferably 90.0 mass% or more, and the CNT component may be composed of only multi-walled CNTs.

[0022] The upper limit of the content of the CNT component in the heating layer of the sheet heating element of the present invention and the content of the CNT component in the solid content of the aqueous paint after drying may be in the range of 25.0% by mass or less, and more preferably in the range of 22.0% by mass or less. If the content of the CNT component is in the above range, gelation of the aqueous paint tends to be suppressed and higher dispersibility tends to be easily ensured, and since the binder component is relatively increased, it tends to be easy to suppress the occurrence of cracks in the heating layer due to thermoforming processing and the occurrence of delamination between the substrate and the heating layer due to thermoforming processing. In addition, the lower limit of the content of the CNT component in the heating layer of the sheet heating element and the content of the CNT component in the solid content of the aqueous paint after drying may be in the range of 3.0% by mass or more, and more preferably in the range of 5.0% by mass or more. If the content of the CNT component is in the above range, the surface resistivity of the heating layer of the sheet heating element does not become too large, and it is possible to make the sheet heating element generate heat uniformly.

[0023] (Other conductive carbon materials) The heat generating layer and the aqueous coating material of the sheet heating element of the present invention may contain a conductive carbon material other than the CNT component, as long as the effect of the present invention is not impaired. Examples of the other conductive carbon material include carbon black, graphite, amorphous carbon, and carbon fibers other than CNT. Such conductive carbon materials may be used alone or in combination of two or more.

[0024] The ratio of the CNT component in the entire conductive carbon material contained in the heating layer and the aqueous paint of the sheet heating element of the present invention may be, for example, 60.0 mass % or more, more preferably 90.0 mass % or more, and most preferably 100.0 mass %. When the ratio of the CNT component is in such a range, the heating layer can ensure high conductivity, and it becomes easier to suppress the occurrence of cracks in the heating layer due to thermoforming processing and the occurrence of delamination between the substrate and the heating layer due to thermoforming processing.

[0025] (Binder component) The binder component of the present invention is the main component of the heat generating layer of the sheet heating element and the solid content of the aqueous paint after drying, and in the heat generating layer, refers to organic polymer compounds such as various resins and various elastomers that maintain the dispersion state of the CNT components and greatly affect various properties of the heat generating layer during thermoforming processing. The binder component of the present invention may be composed of one type of organic polymer compound, or may be composed of a mixture of two or more types of organic polymer compounds. Note that the organic polymer compound used as the binder component in the present invention refers to an organic polymer compound having a number average molecular weight of at least 5000.

[0026] The binder component of the present invention contains at least a polyurethane resin. As the polyurethane resin, it is preferable to use a thermoplastic polyurethane resin. As a result of examining the binder component used in the heat generating layer of the sheet heating element of the present invention, the present inventors have found that, compared with the case where other resins are used as the binder component, when a thermoplastic polyurethane resin is used as the binder component, the sheet heating element has excellent moldability during thermoforming processing, and the occurrence of cracks in the heat generating layer due to thermoforming processing tends to be reduced, and the occurrence of delamination between the substrate and the heat generating layer due to thermoforming processing also tends to be reduced.

[0027] The thermoplastic polyurethane resin used as the binder component of the present invention as described above is preferably a polyurethane resin (segmented polyurethane) having at least a soft segment consisting of a polymer polyol and a diisocyanate, etc., and a hard segment consisting of a short-chain diol and a diisocyanate, etc., in its molecular structure. When the temperature of such a polyurethane resin exceeds the glass transition temperature, it exhibits elastomeric properties, and at that time, the stress against deformation is significantly smaller than that of other resins, so that it is considered to be advantageous in suppressing the occurrence of cracks in the heat generating layer due to thermoforming processing and in suppressing the occurrence of delamination between the substrate and the heat generating layer due to thermoforming processing. Furthermore, when such polyurethane resins reach or exceed their glass transition temperature, the soft segments in the polyurethane resin begin to plasticize first. However, the melting point of the hard segments is much higher than the glass transition point of the soft segments. Therefore, if an appropriate molding temperature is set during thermoforming, it is possible to change the shape of the sheet heating element by thermoforming while maintaining the dispersion of the CNT components in the heating layer without completely melting or overly softening the heating layer of the sheet heating element. Furthermore, the molding temperature can be set over a wide range, so it is believed that using a polyurethane resin as the binder component of a sheet heating element will have an advantage in terms of formability when thermoforming the sheet heating element.

[0028] The polymer polyol component constituting the polyurethane resin used as the binder component of the present invention is not particularly limited, and can be, for example, various known polyol components such as polypropylene glycol, polytetramethylene glycol, polyester polyol, polycaprolactone polyol, polycarbonate polyol, etc., but is not limited thereto. The polymer polyol component constituting the polyurethane resin may be one type of polymer polyol, or two or more types of polymer polyols may be used in combination.

[0029] As a result of intensive research by the present inventors, it was found that when a polycarbonate-based polyurethane resin using polycarbonate polyol or polycarbonate diol as a macropolyol component is used as a binder component of the heat generating layer, the occurrence of cracks in the heat generating layer due to thermoforming processing and the occurrence of delamination between the substrate and the heat generating layer due to thermoforming processing tend to be suppressed compared to when a polyurethane resin composed of other polyol components is used. Therefore, it is more preferable to use a polycarbonate-based polyurethane resin as the polyurethane resin used as the binder component of the heat generating layer of the present invention.

[0030] The diisocyanate component constituting the polyurethane resin used as the binder component of the present invention is not particularly limited, and examples thereof include diphenylmethane diisocyanate (abbreviation: MDI), toluene diisocyanate (abbreviation: TDI), hexamethylene diisocyanate (abbreviation: HDI), dicyclohexylmethane 4,4'-diisocyanate (abbreviation: H 12 Various known diisocyanate components such as, but not limited to, isophorone diisocyanate (abbreviation: IPDI) can be used. The diisocyanate component constituting the polyurethane resin may be one type of diisocyanate component, or two or more types of diisocyanate components may be used in combination.

[0031] The short-chain diol component constituting the polyurethane resin used as the binder component of the present invention is not particularly limited, and may be, for example, any of various known glycols such as 1,3-butanediol, 1,4-butanediol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, etc., but is not limited thereto. The short-chain diol component constituting the polyurethane resin may be one type of short-chain diol component, or two or more types of short-chain diol components may be used in combination.

[0032] The glass transition temperature of the polyurethane resin used as the binder component of the present invention must be at least in the range of 50.0°C or less, more preferably in the range of 30.0°C or less, and most preferably in the range of 0.0°C or less. If the glass transition temperature of the polyurethane resin is in the above range, the moldability during thermoforming of the sheet heating element is good, the occurrence of cracks in the heating layer due to thermoforming processing can be suppressed, and the occurrence of delamination between the substrate and the heating layer due to thermoforming processing can be suppressed. If the molding temperature during thermoforming processing is lower than the glass transition temperature of the polyurethane resin, thermoforming of the polyurethane resin is difficult, and thermoforming becomes possible only when the molding temperature is equal to or higher than the glass transition temperature of the polyurethane resin. In practice, the molding temperature is preferably equal to or higher than the softening temperature at which the polyurethane resin begins to plasticize significantly. Since the softening temperature is higher than the glass transition temperature, the lower the glass transition temperature, the lower the softening point, and the lower the stress against deformation and distortion of the heat generating layer of the planar heat generating layer during thermoforming. This is thought to be advantageous in suppressing cracks in the heat generating layer caused by thermoforming and suppressing delamination between the substrate and the heat generating layer caused by thermoforming. The lower limit of the glass transition temperature of the polyurethane resin is not particularly limited, but may be in the range of -90.0°C or higher. The glass transition temperature of the polyurethane resin in the present invention refers to the glass transition temperature measured by differential scanning calorimetry according to JIS K7121 (1987), and when the polyurethane resin has multiple glass transition temperatures, it refers to the glass transition temperature that appears at the lowest temperature.

[0033] The melting point of the polyurethane resin used as the binder component of the present invention may be 190.0°C or higher, and more preferably 230.0°C or higher. The higher the molding temperature at which thermoforming is possible, the more various thermoforming processes can be handled, but thermoforming cannot be performed at a temperature at which the resin used in the heat generating layer of the sheet heating element or the thermoplastic sheet substrate is completely dissolved. The molding temperature suitable for the sheet heating element of the present invention depends on the various thermal properties of the binder component of the heat generating layer of the sheet heating element and the thermoplastic sheet substrate, so it cannot be particularly limited, but if the melting point of the polyurethane resin is above the above range, it is significant in that it can be used for thermoforming of sheet heating elements using various thermoplastic sheet substrates and can be used for various thermoforming processing methods. The upper limit of the melting point of the polyurethane resin is not particularly limited, but it may be in the range of 300.0°C or lower. The melting point in the present invention refers to the melting peak temperature measured by differential scanning calorimetry according to JIS K7121 (1987), and when there are multiple melting peaks of the polyurethane resin, it refers to the melting peak temperature that appears at the highest temperature.

[0034] Other thermal properties of the polyurethane resin used as the binder component of the present invention include a softening temperature measured by a temperature rise method using a high-temperature flow tester (Shimadzu Corporation: CFD-500D) under conditions of a temperature rise rate of 3°C / min, a load of 98.0N, a diameter of the inner hole of the die of 1.0mm, and a length of the inner hole of the die of 2.0mm, in the range of 170.0°C or less, and more preferably in the range of 100.0°C or less. The softening temperature was measured in the range of 40.0°C or more and 210.0°C or less. If the softening temperature measured using a polyurethane resin flow tester is in the above range, it has excellent moldability during thermoforming processing, suppresses the occurrence of cracks in the heat generating layer due to thermoforming processing, and tends to suppress the occurrence of delamination between the substrate and the heat generating layer due to thermoforming processing. The lower limit of the softening temperature is not particularly limited, but it is preferably in the range of 40.0°C or more from the viewpoint of the environmental preservation of the heat generating layer.

[0035] The elongation at break of the polyurethane resin used as the binder component of the present invention may be in the range of 50.0% or more, more preferably in the range of 100.0% or more, and most preferably in the range of 300.0% or more. If the elongation of the polyurethane resin is in the above range, it has excellent moldability during thermoforming processing, tends to suppress the occurrence of cracks in the heat generating layer due to thermoforming processing, and tends to suppress the occurrence of delamination between the substrate and the heat generating layer due to thermoforming processing. Note that the elongation at break in the present invention refers to the elongation at break of JIS K6251 (2017).

[0036] When the elongation at break of the polyurethane resin used as the binder component of the present invention is in the range of 100.0% or more, the 100% modulus value of the polyurethane resin may be in the range of 40.0 MPa or less, more preferably in the range of 30.0 MPa or less, and most preferably in the range of 10.0 MPa or less. If the 100% modulus value of the polyurethane resin is in the above range, it tends to suppress the occurrence of cracks in the heat generating layer due to thermoforming processing, and to suppress the occurrence of delamination between the substrate and the heat generating layer due to thermoforming processing. The 100% modulus value of the polyurethane resin in the present invention refers to the tensile stress at a specified elongation when the elongation of the test piece is 100.0% in JIS K6251 (2017).

[0037] The binder component of the present invention contains at least a polyurethane resin having the above-mentioned properties, but may contain only one type of polyurethane resin having the above-mentioned properties, or may contain two or more types of polyurethane resin having the above-mentioned properties. Furthermore, the binder component may contain "other binder components" other than the polyurethane resin having the above-mentioned properties as necessary.

[0038] (Other binder components) Examples of other binder components contained in the binder component of the present invention include, but are not limited to, polyurethane resins other than polyurethane resins having the above-mentioned properties, acrylic resins, acrylic-styrene copolymers, polyester resins, polyamide resins, fluorine-based resins, olefin-based resins (polyolefin resins, olefin-based copolymers, etc.), polyvinyl alcohol resins, vinyl chloride-based resins, various thermoplastic elastomers, styrene-butadiene rubber, silicone rubber, etc. As the other binder components as described above, it is more preferable to use thermoplastic binder components from the viewpoint of moldability. As the binder component of the present invention, only one type of the other binder components may be used, or two or more types may be used in combination. The other binder components are added to the binder component with the purpose of improving the dispersibility of the binder component in the aqueous paint, the film-forming property of the heat generating layer of the sheet heating element, and the adhesion of the heat generating layer of the sheet heating element to the substrate.

[0039] (Crosslinking agent) Various known aqueous crosslinking agents may be added to the binder component of the present invention as necessary within the range that does not impair the effects of the present invention. The aqueous crosslinking agent is added for the purpose of improving or modifying various physical properties of the coating film of the heat generating layer, or improving the adhesion between the heat generating layer and the substrate. Examples of such aqueous crosslinking agents include, but are not limited to, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, carbodiimide-based crosslinking agents, aziridine-based crosslinking agents, and oxazoline-based crosslinking agents. In the present invention, when an aqueous crosslinking agent is added to the water-based paint and the heat generating layer, the aqueous crosslinking agent, the crosslinked product of the aqueous crosslinking agent and the binder component, and the self-crosslinked product of the aqueous crosslinking agent are each regarded as a binder component, regardless of their molecular weight.

[0040] The form of the raw materials for the above-mentioned various binder components used as the binder components of the present invention may be an aqueous resin in which the various binder components are dispersed, emulsified, or dissolved in a dispersion medium or solvent mainly composed of water, and the form of the raw materials is not particularly limited.

[0041] The lower limit of the polyurethane resin content in the heat generating layer of the sheet heating element of the present invention and the polyurethane resin content in the solid content of the aqueous paint after drying must be in the range of 60.0 mass% or more, and more preferably in the range of 65.0 mass% or more. If the polyurethane resin content is in the above range, the heat forming process of the sheet heating element is excellent, and the occurrence of cracks in the heat generating layer due to the heat forming process and the occurrence of delamination between the base material and the heat generating layer due to the heat forming process can be suppressed. On the other hand, the upper limit of the polyurethane resin content in the heat generating layer of the sheet heating element and the polyurethane resin content in the solid content of the aqueous paint after drying must be in the range of 95.0 mass% or less, and more preferably in the range of 90.0 mass% or less. If the polyurethane resin content is in the above range, it is possible to secure the minimum amount of CNT components necessary for the heat generating layer to generate heat uniformly, and the surface resistivity of the heat generating layer of the sheet heating element does not become too large.

[0042] The lower limit of the binder component content in the heat generating layer of the sheet heating element of the present invention and the binder component content in the solid content of the aqueous paint after drying may be in the range of 60.0% by mass or more, and more preferably in the range of 65.0% by mass or more. If the binder component content is in the above range, the coating property of the aqueous paint becomes good, making it easier to form a uniform heat generating layer coating, and it becomes easier to suppress the occurrence of cracks in the heat generating layer due to the thermoforming process of the sheet heating element and the occurrence of delamination between the substrate and the heat generating layer due to the thermoforming process. On the other hand, the upper limit of the binder component content in the heat generating layer of the sheet heating element and the binder component content in the solid content of the aqueous paint after drying may be in the range of 95.0% by mass or less, and more preferably in the range of 90.0% by mass or less. If the binder component content is in the above range, it is possible to secure the minimum amount of CNT components necessary for the heat generating layer to generate heat uniformly, and the surface resistivity of the heat generating layer of the sheet heating element does not become too large.

[0043] (Dispersant component) The dispersant component of the present invention refers to various dispersant components used to uniformly disperse CNT components and other components in the aqueous paint, thereby improving the dispersibility of CNTs and maintaining and stabilizing the dispersed state of the paint itself.

[0044] As a result of the inventors' investigation into the dispersant components to be used in the present invention, it has been found that it is possible to disperse the CNT components and binder components more uniformly in the aqueous paint and maintain the dispersed state of the aqueous paint more stably, thereby not only ensuring high electrical conductivity of the heating layer of the planar heating element, but also providing excellent heat resistance due to a melting point of approximately 300°C and possessing properties that cause little adverse effect on the heating layer during thermoforming processing, and therefore it is essential to use at least a carboxymethyl cellulose component as the dispersant component of the present invention.

[0045] The carboxymethyl cellulose component in the present invention refers to carboxymethyl cellulose and carboxymethyl cellulose salts. Hereinafter, in this specification, "carboxymethyl cellulose (abbreviation: CMC (carboxymethyl cellulose))" may be referred to as "CMC".

[0046] The aqueous coating material of the present invention preferably contains a CMC salt from the viewpoint of easily obtaining a more uniformly dispersed state of the CNT components and the binder components. The CMC salt functions as a dispersant or a viscosity modifier in the aqueous coating material. Examples of the CMC salt include an alkali metal salt of CMC and an ammonium salt of CMC. Examples of the alkali metal salt include a potassium salt and a sodium salt. When an ammonium salt of CMC is used in the aqueous coating material, the heat generated during hot air drying of the aqueous coating material causes ammonia to be released from the ammonium salt of CMC, which is converted into a water-insoluble CMC, and therefore the water resistance of the heat generating layer can be further improved. The heat generating layer of the present invention may contain a CMC salt as a CMC component, may contain CMC, or may contain both a CMC salt and CMC.

[0047] The dispersant component of the present invention may contain other dispersants in addition to the CMC component. The other dispersants are not particularly limited as long as they can improve the dispersibility of the CNT component, improve the maintenance stability of the dispersibility of the water-based paint, and adjust the viscosity of the water-based paint, and various known anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic (nonionic) surfactants, polymer dispersants, etc. can be appropriately used. As the other dispersants, only one type of dispersant from the various dispersants described above may be used, or two or more types of dispersants may be used in combination.

[0048] Examples of the anionic surfactant include carboxylates, sulfonates, sulfates, and phosphates. More specifically, examples include higher fatty acid salts, alkyl ether carboxylates, alkyl sulfonates, styrene sulfonates, alkyl sulfates, alkyl ether sulfates, alkyl naphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, alkyl ether phosphates, polyoxyethylene alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl phosphates, polyoxyethylene glycerol fatty acid esters, etc., but are not limited thereto.

[0049] Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. More specifically, they include, but are not limited to, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl beef tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecyl benzyl triethyl ammonium chloride.

[0050] Examples of amphoteric surfactants include amino acid salts and betaines. Specific examples include, but are not limited to, sodium cocoamphoacetate, sodium lauroamphoacetate, sodium cocoamphodiacetate, cocamidopropyl betaine, lauramidopropyl betaine, cocobetaine, lauryl betaine, lauryl hydroxysultaine, etc.

[0051] Specific examples of nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers.

[0052] Specific examples of polymer dispersing agents include, but are not limited to, salts of cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethylhydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, carboxymethyl cellulose, etc.), polyacrylates, polyacrylamides, acrylamide-acrylic acid copolymers, polystyrene sulfonates, salts of naphthalenesulfonate-formaldehyde condensates, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile polymers, and the like.

[0053] As a result of further investigation by the present inventor, the present inventor found that, although the use of a CMC component alone as a dispersant component of the aqueous paint of the present invention can sufficiently improve the dispersibility of the CNT component and the binder component in the aqueous paint, the use of an anionic dispersant in addition to the CMC component can further improve the maintenance and stability of the dispersibility of the aqueous paint. Therefore, when a CMC component is used as a dispersant component of the present invention, it is more preferable to use an anionic dispersant in combination. In addition, the anionic dispersant in the present invention refers to an anionic surfactant and an anionic polymer dispersant in which the hydrophilic group is ionized to an anion when the dispersant is dissolved in water.

[0054] The lower limit of the content of the dispersant component of the present invention may be in the range of 20.0 parts by mass or more relative to 100.0 parts by mass of the CNT component, and is preferably in the range of 30.0 parts by mass or more. When the lower limit of the content of the dispersant component is in the above range, it is expected to suppress gelation of the water-based paint, improve the dispersibility of the CNT component in the water-based paint, and improve the coatability of the water-based paint. On the other hand, the upper limit of the content of the dispersant component may be in the range of 200.0 parts by mass or less relative to 100.0 parts by mass of the CNT component, more preferably in the range of 100.0 parts by mass or less, and even more preferably in the range of 80.0 parts by mass or less. When the content of the dispersant component is in the above range, it is expected to suppress the decrease in water resistance of the heat generation layer of the sheet heating element, the occurrence of cracks in the heat generation layer due to thermoforming processing, and the occurrence of delamination between the substrate and the heat generation layer due to thermoforming processing.

[0055] The lower limit of the content of the CMC component in the dispersant component of the present invention may be at least 10.0 parts by mass or more relative to 100.0 parts by mass of the dispersant component, and more preferably 20.0 parts by mass or more. On the other hand, the upper limit of the content of the CMC component in the dispersant component is not particularly limited, but may be 100.0 parts by mass or less relative to 100.0 parts by mass of the dispersant component, and more preferably 80.0 parts by mass or less. When the content of the CMC component in the dispersant component is in the above range, it is expected to have an effect of improving the dispersibility of the CNT component in the aqueous paint and the coatability of the aqueous paint.

[0056] (Other Ingredients) In addition to the above-mentioned essential components contained in the heat generating layer and the water-based paint of the sheet heating element of the present invention, they may further contain other components such as various known additives as necessary within the range that does not impair the effects of the present invention. Examples of additives include, but are not limited to, defoamers, viscosity adjusters, leveling agents, ultraviolet absorbers, ultraviolet curing agents, antioxidants, etc.

[0057] (How to make water-based paint) The water-based paint of the present invention is prepared by mixing and dispersing the material of the heat generating layer and the dispersion medium by various known stirring mixers and dispersers. In this case, it is preferable to prepare a CNT dispersion in advance by mixing and dispersing the CNT component, the dispersant component, and the dispersion medium, and then mix and disperse the prepared CNT dispersion with other materials of the heat generating layer such as the binder component to prepare the water-based paint, but there is no particular limitation on the method of preparing the water-based paint. In addition, as the dispersion medium, only water may be used, or a mixture of water and a hydrophilic organic solvent may be used. The hydrophilic organic solvent refers to a hydrophilic organic solvent that is liquid at room temperature (about 25°C), and examples thereof include, but are not limited to, alcohol-based solvents such as methanol, ethanol, 1-propanol, etc., glycol-based solvents such as ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol, ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether, and N-methylpyrrolidone.

[0058] (How to make the heating layer) The heat generating layer of the sheet heating element of the present invention is formed by applying a predetermined amount of the above-mentioned water-based paint of the present invention to a substrate by various known coating methods or printing methods, and then drying with hot air. Various known coating methods include, for example, gravure coating, bar coating, roll coating, kiss coating, comma coating, lip coating, and slot die coating, and various known printing methods include, but are not limited to, silk screen printing. When the water-based paint is applied to a substrate by gravure coating or silk screen printing and then dried with hot air to form a heat generating layer, it is possible to partially adjust the amount of water-based paint applied per unit area by providing a pattern on the gravure roll plate or a pattern on the screen printing mesh plate, and partially control the heat generation amount at any location of the heat generating layer of the sheet heating element. The formed heat generating layer may be heat treated as necessary.

[0059] The lower limit of the thickness of the heat generating layer of the sheet heating element of the present invention is not particularly limited, but may be in the range of 1.0 μm or more, more preferably in the range of 3.0 μm or more, and even more preferably in the range of 10.0 μm or more. If the thickness of the heat generating layer is in the above range, it is easy to keep the variation in the surface resistivity of the heat generating layer within a moderate range, and it is easy to control the surface resistivity of the heat generating layer relatively low, so that it is easy to ensure stable heat generation. On the other hand, the upper limit of the thickness of the heat generating layer is not particularly limited, but may be in the range of 100.0 μm or less, more preferably in the range of 50.0 μm or less, and most preferably in the range of 30.0 μm or less, from the viewpoints of the flexibility of the sheet heating element, the space saving of the sheet heating element, and the manufacturing cost.

[0060] The lower limit of the surface resistivity of the heat generating layer of the sheet heating element of the present invention is not particularly limited, but may be at least 1.0Ω / □ or more, and preferably 10.0Ω / □ or more. On the other hand, the upper limit of the surface resistivity of the heat generating layer is not particularly limited, but may be 3000.0Ω / □ or less, preferably 1000.0Ω / □ or less, more preferably 600.0Ω / □ or less, and most preferably 300.0Ω / □ or less. When the upper and lower limits of the surface resistivity of the heat generating layer are in the above-mentioned range, the entire heat generating layer can be heated more uniformly, and the temperature of the heat generating layer can be easily controlled within an appropriate range. The surface resistivity of the heat generating layer can be measured in accordance with JIS K7194 (1994) using a low resistivity meter (Loresta AX MCP-T370, manufactured by Mitsubishi Chemical Analytec Co., Ltd.). The correction factor (RCF) during measurement is set to RCF=4.235.

[0061] The sheet heating element of the present invention may be partially stretched when it is thermally processed and shaped, and at that time the heating layer is also stretched at the same time. From the viewpoint of uniformly heating the heating layer, it is preferable that the change in the surface resistivity of the heating layer when the sheet heating element is stretched is as small as possible.

[0062] Regarding the sheet heating element of the present invention, when the sheet heating element is stretched to a stretching rate S of 50.0%, the rate of change R in the surface resistivity of the heating layer of the sheet heating element before and after stretching may be in the range of 1000.0% or less, more preferably in the range of 600.0% or less, and most preferably in the range of 300.0% or less. The sheet heating element was stretched by setting a sheet heating element sample having a size of 50.0 mm wide x 80.0 mm long in a tensile tester installed in a thermostatic chamber, setting the temperature of the thermostatic chamber to a suitable molding temperature for the sheet heating element sample to be stretched, and after the temperature of the sheet heating element sample itself reached the set temperature, pulling the sheet heating element sample in the length direction with the tensile tester under conditions of a chuck distance of 50.0 mm and a pulling speed of 50.0 mm / min. The surface resistivity of the heating layer of the sheet heating element sample before and after stretching was measured at the center of the sheet heating element sample.

[0063] The stretch ratio S of the sheet heating element is a value calculated by the following formula (1) when the chuck distance of the sheet heating element sample before stretching is L0 and the chuck distance of the sheet heating element sample after stretching is L1. S(%)=(L1-L0) / L0×100...Equation (1)

[0064] The rate of change R in the surface resistivity of the heating layer of the sheet heating element before and after stretching is a value calculated using the following formula (2), where the surface resistivity of the heating layer of the sheet heating element sample before stretching is R0, and the surface resistivity of the heating layer of the sheet heating element sample after stretching is R1. R(%)=(R1-R0) / R0×100...Equation (2)

[0065] <Thermoplastic sheet substrate> The substrate used in the sheet heating element of the present invention may be a thermoformable thermoplastic sheet-like material that uses a thermoplastic material as a raw material in whole or in part from the viewpoint of formability during thermoforming of the sheet heating element, and the structure, type and properties of the thermoplastic material are not particularly limited, and can be selected appropriately in consideration of the required performance according to the application of the sheet heating element, molding conditions, etc. In the present invention, such a substrate is referred to as a thermoplastic sheet substrate.

[0066] The thermoplastic sheet substrate of the present invention is not particularly limited in structure as long as a thermoplastic material is used as a raw material, and may be, for example, a resin film or resin sheet using a thermoplastic material, a fiber sheet such as a nonwoven fabric, knitted fabric, woven fabric, or paper using a thermoplastic material, or a laminate of these.

[0067] Examples of the thermoplastic material used in the thermoplastic sheet substrate of the present invention include polyester resin, polycarbonate resin, acrylic resin, olefin resin, polyamide resin, polyurethane resin, fluorine resin, cellulose resin, vinyl acetate resin, vinyl chloride resin, vinyl acetate resin, and various other thermoplastic elastomers. Only one type of the thermoplastic material may be used in the thermoplastic sheet substrate, or two or more types may be used in combination.

[0068] The content of the thermoplastic material used in the thermoplastic sheet substrate in the thermoplastic sheet substrate is not particularly limited, and there is no problem as long as the thermoforming process is possible, but for example, it is sufficient to be in the range of 20.0 mass% or more, more preferably in the range of 50.0 mass% or more, and most preferably in the range of 80.0 mass% to 100.0 mass%. If the content of the thermoplastic material in the thermoplastic sheet substrate is in the range of 50.0 mass% or more, it is preferable to select and use a thermoplastic material whose melting point or liquefaction point is higher than the molding temperature during the thermoforming process of the planar heating element.

[0069] As the thermoplastic sheet substrate of the present invention, it is more preferable to use a resin film or sheet made of a thermoplastic material from the viewpoints of ease of forming a heat generating layer of uniform thickness and ease of thermoforming processing.

[0070] When a resin film or a resin sheet is used as the thermoplastic sheet substrate of the present invention, the thermoplastic material used in the resin film or the resin sheet is preferably, for example, an acrylic resin, an olefin resin, a polyamide resin, a polyester resin, a polyurethane resin, a polycarbonate resin, a vinyl chloride resin, various elastomers, etc., from the viewpoint of ease of thermoforming processing, but is not limited thereto. Furthermore, from the viewpoint of the relationship with the appropriate molding temperature during the thermoforming processing of the heat generating layer of the planar heating element of the present invention and the shape retention after molding, it is more preferable to use a resin film or a resin sheet using an acrylic resin, a polyester resin, or a polycarbonate resin. The thermoplastic material may be used in the resin film or the resin sheet by one type, or may be used in combination of two or more types. In addition, such a resin film and a resin sheet may have a single layer structure or a multilayer structure, and are not particularly limited. The content of the thermoplastic material in these resin films and resin sheets is at least in the range of 50.0% by mass or more, and preferably in the range of 70.0% by mass or more, but is usually in the range of 90% by mass to 100% by mass.

[0071] When a resin film or a resin sheet is used as the thermoplastic sheet substrate of the present invention, more suitable resin films and resin sheets are specifically described. A resin film or a resin sheet using at least one resin selected from the group consisting of amorphous polyethylene terephthalate resin (abbreviation: A-PET), glycol-modified polyethylene terephthalate resin (abbreviation: PET-G), polymethyl methacrylate resin (abbreviation: PMMA), and polycarbonate resin (abbreviation: PC) is preferably used as the thermoplastic sheet substrate of the present invention, and a resin film or a resin sheet using at least one resin of amorphous polyethylene terephthalate resin or glycol-modified polyethylene terephthalate resin is most preferably used as the thermoplastic sheet substrate of the present invention. The resin film and the resin sheet using the resin may be a single layer film or a single layer sheet using any one of the above resins, or a laminate film or a laminate sheet consisting of two or more layers in which layers using any two or more of the above resins are laminated. Examples of such laminated films and sheets include GAG ​​films and GAG sheets having a layered structure in which a layer of amorphous polyethylene terephthalate resin is sandwiched between layers of glycol-modified polyethylene terephthalate resin.

[0072] When a resin film or a resin sheet is used as the thermoplastic sheet substrate of the present invention, the surface of the thermoplastic sheet substrate on which the heat generating layer is provided may be subjected to a surface treatment such as a corona treatment or various adhesion enhancing treatments as necessary. By performing the surface treatment, the adhesion between the thermoplastic sheet substrate and the heat generating layer is improved, and problems such as delamination can be suppressed.

[0073] The thickness of the thermoplastic sheet substrate of the present invention is not particularly limited, and the thickness may be appropriately selected depending on the application and required performance. The lower limit of the thickness of the thermoplastic sheet substrate may be 6.0 μm or more, more preferably 10.0 μm or more, and even more preferably 100.0 μm or more. On the other hand, the upper limit of the thickness may be 600.0 μm or less, and preferably 300.0 μm or less. The thinner the thickness of the thermoplastic sheet substrate, the more flexible it is, and the better it tends to be in terms of space saving, but the thinner it is, the more easily it is deformed by the heat of drying when applying and drying an aqueous paint, and the more difficult it tends to be to mold and handle during thermoforming processing.

[0074] <Electrode layer> A sheet heating element usually has an electrode layer for passing electricity through the heating layer when in use. The electrode layer is provided so as to be in direct contact with the heating layer, since it has the role of passing electricity through the heating layer and causing the heating layer to generate heat. The electrode layer is usually provided on top of the heating layer provided on the thermoplastic sheet substrate, as shown in Figure 2, but it may also be provided between the thermoplastic sheet substrate and the heating layer.

[0075] Regarding the shape and arrangement of the electrode layer, for example, if the heating layer is rectangular when viewed from above, the electrode layer is provided on each of a pair of opposing peripheral parts of the rectangular peripheral part, and although the shape is not particularly limited, it is usually strip-shaped. The shape, arrangement, and thickness of the electrode layer are not particularly limited because they are designed and examined mainly for the purpose of uniformly heating the heating layer of the planar heating element and improving the heating efficiency, and are therefore greatly influenced by the shape and heating properties of the heating layer, and therefore there is no particular limit to the shape, arrangement, or thickness, and they need to be set appropriately and arbitrarily.

[0076] As the electrode layer, various known electrode layers can be used. For example, the electrode layer can be formed by applying or printing a conductive paste containing conductive particles such as silver or conductive fibers by various known coating methods or printing methods, and drying or curing the paste. The resin component contained in the electrode layer is not particularly limited, and examples thereof include thermoplastic resins, thermoplastic elastomers, thermosetting resins, photocurable resins, UV curable resins, and electron beam curable resins. However, it is preferable to select and use a material having thermoformability, such as the binder component of the heat generating layer of the present invention or the thermoplastic material used in the thermoplastic sheet substrate.

[0077] <Protective layer> The sheet heating element of the present invention may be provided with a protective layer to cover the surface of the heat generating layer of the sheet heating element for various protection purposes (FIG. 3), or may be provided with a protective layer as the outermost layer of the sheet heating element to cover the entirety (FIG. 4). Examples of various protection purposes include providing a protective layer to protect the heat generating layer and electrode layer from scratches and to make them waterproof, providing an insulating protective layer for the purpose of preventing electric leakage from the heat generating layer and electrode layer of the sheet heating element, and providing a moisture-proof protective layer to prevent performance changes of the heat generating layer due to moisture, etc.

[0078] The material constituting the protective layer is not particularly limited, and examples thereof include thermoplastic resins, thermoplastic elastomers, thermosetting resins, photocurable resins, UV curable resins, and electron beam curable resins, but it is preferable to select and use a material having thermoformability, such as the thermoplastic material used in the binder component of the heat generating layer of the present invention or the thermoplastic sheet substrate. The method of forming the protective layer may be, for example, by applying a coating material made of the various resins and elastomers described above so as to cover the surface of the heat generating layer, by laminating a film or sheet made of each of the resins on the surface of the heat generating layer, or by laminating a film or sheet made of each of the resins on the outermost layer of both sides of the planar heat generating element, or by laminating and sealing, but is not limited to these methods.

[0079] The thickness of the protective layer is not particularly limited, but may be, for example, in the range of 1.0 μm or more and 300.0 μm or less, and more preferably in the range of 3.0 μm or more and 200.0 μm or less.

[0080] <About thermoforming processing> The main object of the present invention is to provide a sheet heating element with excellent thermoforming processability, specifically, to provide a sheet heating element with excellent formability during thermoforming, in which cracks are unlikely to occur in the heating layer due to thermoforming, and in which delamination is unlikely to occur between the substrate and the heating layer due to thermoforming. To explain each element of the object of the present invention in detail, in the present invention, "thermoforming" mainly refers to so-called sheet forming molding, in which a sheet-like material is pressed against a mold in an open space to be thermoformed, such as vacuum forming, but also includes a special method, such as molding molding, such as so-called insert molding, in which a sheet-like material is inserted into an enclosed space inside a mold and thermoformed, and other resin is injected and integrated at the same time, and the main object of the present invention is to provide a sheet heating element suitable for each thermoforming process.

[0081] The "moldability during thermoforming" in the above-mentioned problem of the present invention will be specifically explained. Thermoforming in an open space such as vacuum forming cannot apply a large force to the sheet heating element itself during thermoforming, as compared with molding, and is therefore more susceptible to the thermomechanical properties of the material of the sheet heating element, that is, the ease of thermoforming is easily affected by the thermomechanical properties of the material of the sheet heating element. From this point of view, the more specific meaning of "moldability during thermoforming" in the problem of the present invention means the ease of thermoforming in vacuum forming.

[0082] To give a more specific explanation of the "sheet heating element in which cracks are unlikely to occur in the heat generating layer due to thermoforming processing and in which delamination is unlikely to occur between the substrate and the heat generating layer due to thermoforming processing" in the above-mentioned problem of the present invention, it at least means that after the sheet heating element is stretched to an elongation ratio of 50.0% using a tensile testing machine under conditions of a stretching speed of 50.0 mm / min when the temperature of the sheet heating element is 110°C, cracks are unlikely to occur in the heat generating layer and delamination is unlikely to occur between the substrate and the heat generating layer.

[0083] The suitable molding temperature during thermoforming depends on the thermal properties of the thermoplastic material used in the thermoplastic sheet substrate of the sheet heating element and the binder component of the heating layer of the sheet heating element. For example, if the molding temperature is lower than the glass transition temperature of the various thermoplastic compositions of the sheet heating element (polyurethane resin, which is the main component of the thermoplastic material of the thermoplastic sheet substrate and the binder component of the heating layer), thermoforming cannot be performed, and the molding temperature is required to be at least higher than the glass transition temperature of the various thermoplastic compositions of the sheet heating element. Furthermore, by setting the molding temperature to a temperature higher than the softening temperature of the various thermoplastic compositions of the sheet heating element, the plasticity of the various thermoplastic compositions of the sheet heating element becomes better, and the moldability of the thermoforming process tends to be good. On the other hand, if the molding temperature is higher than the melting point or liquid point (JIS K0064 (1992)) of the various thermoplastic compositions of the sheet heating element, the various thermoplastic compositions melt or become liquid, so that the thermoplastic sheet substrate of the sheet heating element and the heating layer of the sheet heating element melt, causing molding defects, or the conductivity of the heating layer changes significantly. Therefore, the suitable molding temperature during thermoforming processing of the sheet-shaped heating element must at least be equal to or higher than the glass transition temperature of the various thermoplastic compositions of the sheet-shaped heating element and lower than the melting point or liquid point of the various thermoplastic components of the sheet-shaped heating element, and it is more preferable that the molding temperature be equal to or higher than the softening point of the various thermoplastic compositions of the sheet-shaped heating element and lower than the melting point or softening point of the various thermoplastic compositions of the sheet-shaped heating element. EXAMPLES

[0084] EXAMPLES Next, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0085] <Preparation of water-based paint for heat generating layer> Water-based paints were prepared by dispersing and mixing the CNT component, binder component, dispersant component, and dispersion medium component shown in Table 1 in the blending ratios shown in Tables 3 and 4 below.

[0086] [Table 1]

[0087] <Formation of heating layer> The water-based paint prepared above was applied by bar coating to one surface of a thermoplastic sheet substrate shown in Table 2 so that the heat generating layer after drying would be 15 μm thick, and the heat generating layer was formed by drying with hot air in a hot air dryer at a set temperature of 80° C. for 6 minutes, to produce each of the planar heating elements evaluated in the Examples and Comparative Examples. The thermoplastic sheet substrate used was a GAG sheet (thickness 250 μm) in which amorphous polyethylene terephthalate resin (A-PET) and glycol-modified polyethylene terephthalate resin (PET-G) were laminated in the order PET-G / A-PET / PET-G.

[0088] [Table 2]

[0089] <Various evaluation methods> The sheet heating elements and water-based paints evaluated in the Examples and Comparative Examples prepared as described above were evaluated in various ways by the methods described below, and the results are shown in Tables 3 to 5. In the following evaluations, for those given ratings A to C or A to D, it is preferable to give them a rating of A or B in order to solve the problems of the present invention.

[0090] (Evaluation of paint dispersibility) The prepared water-based paint was placed in a glass storage bottle, capped, and left to stand for one week. After leaving the bottle to stand, the paint adhering to the inner wall of the glass bottle was visually inspected to evaluate the dispersion state of the water-based paint according to the following criteria. A: There are absolutely no aggregates in the water-based paint. B: A small amount of aggregates can be confirmed to be present in the water-based paint. C: It can be confirmed that a large amount of aggregates are present in the water-based paint.

[0091] (Evaluation of Coatability) The prepared water-based paint was applied to a thermoplastic sheet substrate by bar coating, and the appearance was visually inspected, and the coatability of the water-based paint was evaluated according to the following criteria. A: No repelling or uneven application of water-based paint is observed. B: Water-based paint repelling and / or uneven application is slightly observed in some areas. C: Water-based paint repelling and / or uneven application is observed in some areas. D: Cracks and / or uneven application of water-based paint are clearly visible over the entire surface.

[0092] (Evaluation of cracks in the heat generating layer after stretching) The sheet heating element thus produced is cut to a size of 50.0 mm wide x 80.0 mm long to produce a sheet heating element sample. The sheet heating element sample is set in a tensile tester installed in a thermostatic chamber, and the temperature of the thermostatic chamber is set to 110°C. After the temperature of the sheet heating element sample itself reaches 110°C, the sheet heating element sample is pulled in the length direction by the tensile tester under the conditions of a chuck distance of 50.0 mm and a pulling speed of 50.0 mm / min, and the sheet heating element is stretched until the stretch ratio S of the sheet heating element reaches 50.0% (actually, the chuck distance of 50.0 mm becomes 75.0 mm). The heat generating layer of the sheet heating element after the stretching is visually observed, and the cracks in the heat generating layer after the stretching are evaluated according to the following criteria. This evaluation was performed using three sheet heating element samples. A: There are no cracks at all in the heating layer. B: Very fine cracks may occasionally occur in some parts of the heating layer. C: Small cracks always occur throughout the heating layer. D: Numerous clear cracks are constantly present throughout the heating layer.

[0093] (Measurement of surface resistivity before and after stretching) The surface resistivity of the heating layer at the center of each sheet heating element of the sheet heating element sample (width 50.0 mm x length 80.0 mm) before stretching and the sheet heating element sample after stretching prepared in the above (evaluation of cracks in the heating layer after stretching) was measured using a low resistivity meter (Mitsubishi Chemical Analytech Co., Ltd., Loresta AX MCP-T370 type) in accordance with JIS K7194 (1994). The correction factor (RCF) during the measurement was set to RCF = 4.235. This measurement was performed using three sheet heating element samples, and the average of the measured values ​​was taken as the surface resistivity of each sample. Note that when the evaluation of cracks in the heating layer of the sheet heating element sample after stretching was C or D, the surface resistivity was not measured.

[0094] (Calculation of the rate of change in surface resistivity) The rate of change R in the surface resistivity of the heating layer of the sheet heating element before and after stretching can be calculated using the following formula (3), where the surface resistivity of the heating layer of the sheet heating element sample before stretching is R0, and the surface resistivity of the heating layer of the sheet heating element sample after stretching is R1. R(%)=(R1-R0) / R0×100...Equation (3)

[0095] (Evaluation of delamination before stretching) The heat generating layer of the sheet heating element thus prepared was cut into a grid of 100 squares spaced 2 mm apart, and a commercially available adhesive tape was applied to the cut portions, and then one end of the adhesive tape was pulled in a direction at an angle of 45° to the surface of the heat generating layer, and the adhesive tape was peeled off in one go. The number of squares in which peeling of the heat generating layer was observed at this time was determined. This evaluation was performed using three sheet heating element samples, and the average number of squares in which peeling of the heat generating layer was observed was calculated. Based on this average value, evaluation was performed according to the following criteria, and used as an index of interlayer peeling between the heat generating layer and the thermoplastic sheet substrate before stretching. A: No peeling was observed in the heating layer of any of the 100 squares. B: Peeling is observed in the heating layer in squares 1 to 9. C: Peeling is observed in the heating layer in 10 or more squares.

[0096] (Evaluation of delamination after stretching) The stretched sheet heating element sample prepared in the above (evaluation of cracks in the heat generating layer after stretching) was used, and the center of the stretched sheet heating element sample was cut into a grid of 100 squares at intervals of 2 mm, and a commercially available adhesive tape was applied to the cut portion, and then one end of the adhesive tape was pulled in a direction at an angle of 45° to the surface of the heat generating layer, and the adhesive tape was peeled off in one go. The number of squares in which peeling of the heat generating layer was observed at this time was calculated. This evaluation was performed using three sheet heating element samples, and the average number of squares in which peeling of the heat generating layer was observed was calculated, and based on this average value, evaluation was performed according to the following criteria, which was used as an index of interlayer peeling between the heat generating layer and the thermoplastic sheet substrate after stretching. A: No peeling was observed in the heating layer of any of the 100 squares. B: Peeling is observed in the heating layer in squares 1 to 9. C: Peeling is observed in the heating layer in 10 or more squares.

[0097] (Evaluation of moldability) The sheet heating element thus produced was actually vacuum molded using a vacuum molding machine, the appearance of the sheet heating element after molding was visually inspected, and the moldability of the sheet heating element during thermoforming was evaluated according to the following criteria: The molding temperature during vacuum molding was 110°C, and the sheet heating element to be thermoformed was heated to the above molding temperature before vacuum molding. A: The sheet heating element is formed uniformly and without any problems. B: There may be slight distortion in the heating layer, but overall it is molded without any problems. C: There is a clear large distortion or crack in the heating layer, and there is a problem with molding.

[0098] The following Tables 3 and 4 show the formulations of the water-based paints used in the examples and comparative examples of the present invention, the ratios of the various components in the heat generating layers formed with the water-based paints, and the results of various evaluations. Note that the abbreviation "TPU" in the tables stands for "thermoplastic polyurethane resin," and the abbreviations "PC," "Et," and "Es" stand for "polycarbonate," "ether," and "ester," respectively.

[0099] [Table 3]

[0100] [Table 4]

[0101] From the results of Tables 3 and 4, as in the sheet heating elements of Examples 1 to 11, a sheet heating element having at least a heating layer and a thermoplastic sheet substrate supporting the heating layer, the heating layer contains a carbon nanotube component, a dispersant component, and a binder component, the carbon nanotube component contains multi-walled carbon nanotubes, the dispersant component contains a carboxymethyl cellulose component, the binder component contains a polyurethane resin having a glass transition temperature of 50.0 ° C. or less, and the content of the polyurethane resin in the heating layer is in the range of 60.0 mass% to 95.0 mass% or less, the heat forming process is excellent in formability, the heat forming layer is unlikely to crack due to stretching associated with the heat forming process, and delamination between the thermoplastic sheet substrate and the heat forming layer is unlikely to occur due to stretching associated with the heat forming process. A sheet heating element was obtained. In addition, all of the aqueous paints for forming the heat forming layer at this time had excellent paint dispersibility and paint coating properties.

[0102] Furthermore, when no CMC component was added to the water-based paint as a dispersant component at all, as in Comparative Example 1, not only was the paint dispersibility in the water-based paint slightly reduced, but repelling occurred when the water-based paint was applied, and it was not possible to form a uniform heat-generating layer coating.

[0103] In addition, when a polyurethane resin having a glass transition temperature of more than 50.0°C was used as the binder component as in Comparative Example 2, the moldability during thermoforming was poor, cracks occurred in the heat generating layer due to the stretching associated with the thermoforming process, and delamination also occurred between the thermoplastic sheet substrate and the heat generating layer due to the stretching associated with the thermoforming process. In Comparative Examples 3 to 6, when no polyurethane resin having a glass transition temperature of 50.0°C or less was used as the binder component of the heat generating layer of the planar heating element, the moldability during thermoforming was poor, cracks occurred in the heat generating layer due to the stretching associated with the thermoforming process, and delamination occurred between the thermoplastic sheet substrate and the heat generating layer due to the stretching associated with the thermoforming process. The PVDF-based resin used as the binder component in Comparative Example 5 is the same as the PVDF-based resin used in the heat generating layer in the examples of Patent Document 1.

[0104] Furthermore, when the content of polyurethane resin having a glass transition temperature of 50.0° C. or less in the heat generating layer was below 60.0 mass % as in Comparative Examples 7 and 8, cracks occurred in the heat generating layer due to stretching accompanying the thermoforming process. [Industrial Applicability]

[0105] The sheet heating element of the present invention can be used for various applications requiring heating (for example, building materials, agricultural materials, vehicle materials, storage or display materials, components of electronic or electrical equipment, clothing, bedding, etc.) The sheet heating element of the present invention can be thermoformed and laminated into the same shape as the object to be heated, or can be molded integrally with the object to be heated by a method such as insert molding, and is therefore particularly suitable for use in heating objects having complex shapes or objects that do not require much installation space. [Explanation of symbols]

[0106] 1: Planar heating element 2: Heating layer 3: Thermoplastic sheet base material 4: Electrode layer 5:Protective layer

Claims

1. A sheet heating element including at least a heat generating layer and a thermoplastic sheet substrate supporting the heat generating layer, The heat generating layer includes a carbon nanotube component, a dispersant component, and a binder component, the carbon nanotube component comprises multi-walled carbon nanotubes; the dispersant component comprises a carboxymethyl cellulose component, the binder component comprises a polyurethane resin, The glass transition temperature of the polyurethane resin is in the range of 50.0° C. or less, The heat generating layer has a polyurethane resin content of 60.0% by mass or more and 95.0% by mass or less.

2. 2. The sheet heating element according to claim 1, wherein the polyurethane resin is a polycarbonate-based polyurethane resin.

3. 3. The sheet heating element according to claim 1, wherein the content of the binder component in the heat generating layer is in the range of 60.0% by mass or more and 95.0% by mass or less.

4. 3. The sheet heating element according to claim 1, wherein the polyurethane resin has a melting point of 190.0° C. or higher.

5. 2. The sheet heating element according to claim 1, wherein the polyurethane resin has an elongation at break of 50.0% or more.

6. 3. The sheet heating element according to claim 1, wherein the polyurethane resin has an elongation at break of 100.0% or more.

7. The sheet heating element according to claim 6, wherein the 100% modulus value of the polyurethane resin is in the range of 40.0 MPa or less.

8. 3. The sheet heating element according to claim 1, wherein the content of the dispersant component in the heat generating layer is in the range of 20.0 parts by mass to 200.0 parts by mass per 100.0 parts by mass of the carbon nanotube component.

9. 9. The sheet heating element according to claim 8, wherein the content of the carboxymethyl cellulose component in the dispersant component is in the range of 10.0 parts by mass or more and 100.0 parts by mass or less per 100.0 parts by mass of the dispersant component.

10. 3. The sheet heating element according to claim 1, wherein the content of carbon nanotube components in the heat generating layer is in the range of 3.0% by mass or more and 25.0% by mass or less.

11. 3. The sheet heating element according to claim 1, wherein the heat generating layer has a thickness in the range of 1.0 μm to 100.0 μm.

12. 3. The sheet heating element according to claim 1, wherein the surface resistivity of the heat generating layer is in the range of 3000.0 Ω / □ or less.

13. 3. The sheet heating element according to claim 1, wherein the rate of change R in the surface resistivity of the heat generating layer of the sheet heating element before and after stretching when the sheet heating element is stretched to a stretch ratio S of 50.0% is in the range of 1000.0% or less.

14. 3. The sheet heating element according to claim 1, wherein the thermoplastic sheet substrate is a resin film or sheet using at least one resin selected from the group consisting of acrylic resin, polyester resin, and polycarbonate resin.

15. 3. The sheet heating element according to claim 1, wherein the thermoplastic sheet substrate is a resin film or sheet using at least one of an amorphous polyethylene terephthalate resin and a glycol-modified polyethylene terephthalate resin.

16. A water-based paint for forming a heat generating layer of a sheet heating element including at least a heat generating layer and a thermoplastic sheet substrate supporting the heat generating layer, The water-based paint contains a carbon nanotube component, a dispersant component, a binder component, and water, the carbon nanotube component comprises multi-walled carbon nanotubes; the dispersant component comprises a carboxymethyl cellulose component, the binder component comprises a polyurethane resin, The glass transition temperature of the polyurethane resin is in the range of 50.0° C. or less, The content of the polyurethane resin in the solid matter of the aqueous coating material after drying is in the range of 60.0 mass % or more and 95.0 mass % or less.

17. 17. The water-based paint according to claim 16, wherein the urethane resin is a polycarbonate-based polyurethane resin.

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