Planar heating element

Abstract

The present invention addresses the problem of providing a planar heating element of which the resistance value is easily increased in a short time after reaching a certain temperature and which has a high resistance value after temperature increase. The planar heating element comprises: a substrate; a pair of electrodes disposed on the substrate; and a PTC resistor disposed on the substrate and between the pair of electrodes. The PTC resistor contains conductive particles, a binder resin, and a wax. The wax includes a natural wax, and / or a polyolefin-based wax in which the number of melting peaks is 1 or 2 as observed in a DSC curve obtained by raising the temperature from 25°C to 150°C at a temperature raising rate of 10°C / min using a differential scanning calorimeter.

Description

Planar heating element

[0001] The present disclosure relates to a sheet heating element.

[0002] To remove frost and dew from automobile door mirrors, heaters are often installed on the rear surface of the mirror. These heaters often use planar heating elements with PTC (positive temperature coefficient) characteristics, which do not require expensive temperature control devices.

[0003] A sheet heating element with PTC characteristics typically has a pair of electrodes and a resistor with PTC characteristics (also referred to herein as a "PTC resistor") disposed between the electrodes. A known PTC resistor is one containing a crystalline resin and conductive particles (see, for example, Patent Document 1). In a sheet heating element with such a PTC resistor, when a voltage is applied between the electrodes, electricity flows through the PTC resistor, causing its temperature to rise. Meanwhile, as the temperature of the sheet heating element (PTC resistor) rises, the crystalline resin contained therein thermally expands, increasing the distance between the conductive particles and increasing the resistance value. The resistance value then rises sharply near the softening temperature or melting point of the crystalline resin, making it difficult for electricity to pass through. In other words, the temperature of the sheet heating element is controlled so as not to exceed a certain level.

[0004] JP 2012-227081 A

[0005] However, conventional sheet heating elements containing PTC resistors with a crystalline resin binder have problems in that they do not yet exhibit sufficient thermal expansion when heated, and it takes time for the resistance to increase even after the temperature reaches a certain level. There is also a need to further increase the resistance of sheet heating elements after heating.

[0006] Therefore, an object of the present disclosure is to provide a sheet heating element whose resistance value is likely to increase in a short time after reaching a certain temperature, and whose resistance value after temperature rise is high.

[0007] One embodiment of the present disclosure provides a sheet heating element having a substrate, a pair of electrodes arranged on the substrate, and a PTC resistor arranged on the substrate and between the pair of electrodes, wherein the PTC resistor contains conductive particles, a binder resin, and a wax, and the wax contains a naturally occurring wax and / or a polyolefin wax in which the number of melting peaks observed is one or two in a DSC curve obtained by heating from 25°C to 150°C at a heating rate of 10°C / min using a differential scanning calorimeter.

[0008] According to the present disclosure, a planar heating element can be obtained that has a resistance value that easily increases in a short time after reaching a certain temperature and has a high resistance value after the temperature rises.

[0009] Fig. 1 is a plan view showing an example of the structure of a sheet heating element of the present disclosure. Fig. 2A is a DSC curve of the polyolefin wax used in Examples A-1 and A-2, and Fig. 2B is a DSC curve of the ultra-high molecular weight polyethylene used in Comparative Examples A-2 and A-3.

[0010] In this specification, a numerical range indicated by "to" means a numerical range including the numerical values ​​written before and after "to".

[0011] The structure of the sheet heating element 100 of the present disclosure will be described. As shown in the plan view of Fig. 1, the sheet heating element 100 has a substrate 1, a pair of electrodes 21, 22 arranged on the substrate 1, and a PTC resistor 3 arranged between the pair of electrodes 21, 22. However, the structure of the sheet heating element 100 is not limited to this structure, and it may also have, for example, a conductive coating (not shown) arranged on the electrode 2.

[0012] The substrate 1 is not particularly limited as long as it is an insulating substrate on which the electrodes 21, 22 and the PTC resistor 3 can be laminated, and may be appropriately selected depending on the application of the sheet heating element 100. Specific examples of the substrate 1 include resin films, such as polyester films.

[0013] The pair of electrodes 21, 22 may have a structure including main electrodes 21 a, 22 a and comb-shaped electrodes 21 b, 22 b. The electrodes 21, 22 may be made of any material that can conduct electricity. The electrodes 21, 22 are typically made of metal, such as aluminum.

[0014] The method for producing the electrodes 21 and 22 is not particularly limited. For example, aluminum foil formed in a pattern may be attached to the substrate 1, or a metal layer placed on the substrate 1 may be patterned by cutting it out using a blade or the like.

[0015] Furthermore, the thickness of the PTC resistor 3 in such a sheet heating element 100 is preferably 10 μm or more, and more preferably 20 to 80 μm. If the thickness of the PTC resistor 3 is 10 μm or more, a sufficient amount of heat can be generated. On the other hand, if the thickness is 80 μm or less, the thickness of the sheet heating element 100 becomes thin, making it easier to apply to various uses. The PTC resistor 3 will be described in detail later.

[0016] When using the sheet heating element 100, the terminals 4 connected to the electrodes 21 and 22 are arranged on the substrate 1, and the terminals 4 are connected to external electrodes. Then, by applying a voltage between the electrodes 21 and 22, the temperature of the PTC resistor 3 can be raised to a desired temperature.

[0017] The sheet heating element 100 can be used for a wide variety of purposes, such as heaters for defogging door mirrors in automobiles, heaters for defogging cameras inside automobile rear-end collision prevention devices, heaters for defogging millimeter-wave radar inside automobile rear-end collision prevention devices, antenna covers, thermistors, heaters for preventing pipeline freezing, floor heating, heated seats for chairs, heated seats for handrails, etc. The PTC resistor 3 included in the sheet heating element 100 will be described in detail below.

[0018] (Regarding the PTC Resistor) As described above, PTC resistors in conventional planar heating elements primarily utilize the thermal expansion and recrystallization of crystalline resins to impart PTC characteristics. However, this method results in a low increase in resistance after a certain temperature is reached, and the degree of increase in resistance is also small. In contrast, the PTC resistor 3 in the planar heating element 100 of the present disclosure contains a specific polyolefin wax or natural wax in addition to conductive particles and a binder resin. In the PTC resistor 3, these waxes melt near their melting points when the temperature rises. The volume increase due to melting of these waxes is significantly greater than that of general resins. Furthermore, because they melt easily, the resistance increases significantly in a short period of time. Therefore, the planar heating element of the present disclosure exhibits a greater change in resistance at a desired temperature and a higher resistance value after heating than conventional planar heating elements.

[0019] Hereinafter, the PTC resistor will be described separately for a case where it contains a polyolefin wax (first embodiment) and a case where it contains a naturally occurring wax (second embodiment).

[0020] (1) PTC Resistor of First Aspect The PTC resistor of the first aspect comprises a polyolefin wax which exhibits one or two melting peaks in a differential scanning calorimeter (hereinafter also referred to as "DSC") curve when the DSC curve is created by heating from 25°C to 150°C at a heating rate of 10°C / min, a binder resin, and conductive particles. Each component will be described below.

[0021] Polyolefin wax: In this specification, wax refers to an organic substance that is solid or semi-solid at room temperature and melts without decomposition upon heating. Furthermore, polyolefin wax refers to a wax containing 50% by mass or more of an olefin-derived component. The polyolefin wax used in this embodiment has one or two melting peaks observed in the DSC curve when heated from 25°C to 150°C at a heating rate of 10°C / min by DSC. It is more preferable that one melting peak is observed. In this specification, a melting peak in a DSC curve refers to an endothermic peak whose absolute value of the peak height is 0.5 mW or more, and does not include noise whose height is less than 0.5 mW. Note that all DSC curves in this specification are values ​​obtained using 5 mg of sample.

[0022] In this specification, the peak height is defined as a value calculated as follows. First, in the DSC curve, the falling and rising positions of the line in the downward convex region (region where endothermic reaction occurs) are confirmed. If both can be confirmed, they are connected with a line, which is used as the baseline. Note that in this specification, a baseline is drawn only for large mountain-shaped regions where the rising and falling powers exceed 1 mW. For example, as shown in FIG. 2B, if a single large mountain-shaped region (downward convex region) contains small peaks (B, C, and D) with rising or falling powers of 1 mW or less, only one baseline is drawn for the large mountain-shaped region. Furthermore, as shown in FIG. 2B, if there are two or more large mountain-shaped regions (downward convex regions), a baseline is drawn for each of them (two in FIG. 2B). On the other hand, as shown in FIG. 2A, if either the rising or falling position of the line in the downward convex region cannot be confirmed, a linear baseline is drawn along the base of the side where the rising or falling position can be confirmed.

[0023] Then, a line perpendicular to the X-axis is drawn from each peak top of the melting peak of the DSC curve (A in FIG. 2A, and B, C, D, and E in FIG. 2B), and the distance from the intersection of the perpendicular line with the baseline to the peak top is defined as the height of each peak.

[0024] The absolute value of the melting peak height in the DSC curve obtained by the above method is preferably 5 mW or more. When the absolute value of the melting peak height is 5 mW or more, many polyolefin waxes tend to melt at the melting peak temperature. When there are two melting peaks in the DSC curve, it is sufficient that the absolute value of the height of either one of them is 5 mW or more.

[0025] The melting peak in the DSC curve of the polyolefin wax is preferably in the range of 80° C. to 150° C., more preferably in the range of 90° C. to 140° C., and even more preferably in the range of 100° C. to 130° C. This provides a PTC resistor that shows an increase in resistance value at 80° C. to 150° C.

[0026] The weight-average molecular weight of the polyolefin wax example is preferably 1,000 to 1,500,000, more preferably 3,000 to 20,000. When the weight-average molecular weight of the polyolefin wax is within this range, it is likely to have a melting peak within the above temperature range. The weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0027] The PTC resistor may contain only one type of the polyolefin wax, or may contain two or more types. Examples of polyolefin waxes include olefin homopolymers, copolymers of two or more types of olefins, and copolymers of olefins and monomers other than olefins. More specific examples of polyolefin waxes include polyethylene waxes such as low-density polyethylene wax, medium-density polyethylene wax, and high-density polyethylene wax, polypropylene wax, polybutene wax, ethylene-propylene copolymer wax, and ethylene-propylene-butene copolymer wax. Alternatively, oxidized polyolefin waxes obtained by oxidizing these waxes using known methods may be used. Among these, polyethylene waxes are preferred from the viewpoints of availability and PTC characteristics.

[0028] The amount of polyolefin wax in the PTC resistor is preferably 6% by mass or more and 24% by mass or less, and more preferably 12% by mass or more and 20% by mass or less. When the amount of polyolefin wax in the PTC resistor is 6% by mass or more, the PTC magnification of the PTC resistor is further increased, and the rate of increase in the resistance value after the PTC resistor has reached a constant temperature after heating is likely to be further increased. On the other hand, when the amount is 24% by mass or less, the amount of conductive particles is sufficiently large relative to the PTC resistor, and the PTC characteristics are likely to be further improved.

[0029] Binder Resin: The binder resin may be any resin capable of binding the polyolefin wax and the conductive particles described below, and binding them to a substrate or the like, but it is preferable that the binder resin does not prevent the volume change caused by melting the polyolefin wax. Furthermore, the binder resin itself may expand with increasing temperature, contributing to an increase in the resistance value of the PTC resistor. The PTC resistor may contain only one type of binder resin, or may contain two or more types.

[0030] Examples of the binder resin include known thermoplastic resins. Specific examples include thermoplastic polyurethane resins, polyester resins, polyacrylate resins, polysiloxane resins, vinyl halide resins, vinylidene resins, polyimide resins, phenoxy resins, polyether resins, polyketone resins, polyvinyl butyral resins, polyvinylpyrrolidone resins, polyacrylate resins, SEBS resins (styrene-ethylene-butylene-styrene copolymers) and their hydrogenated products, and SEPS resins (styrene-ethylene-propylene-styrene copolymers) and their hydrogenated products. Among these, SEBS resins and hydrogenated SEPS resins are preferred because they are easily deformable and do not interfere with the volume change of the polyolefin wax.

[0031] The amount of binder resin in the PTC resistor is preferably 6% by mass or more and 30% by mass or less, and more preferably 15% by mass or more and 28% by mass or less. When the amount of binder resin in the PTC resistor is 6% by mass or more, it becomes easier to print conductive resins, polyolefin waxes, and compositions containing the binder resin, and the fixation after printing becomes good. Furthermore, the strength of the PTC resistor is likely to be further increased. On the other hand, when the amount of binder resin is 30% by mass or less, the amount of conductive particles becomes sufficiently large relative to the amount of conductive particles, and the PTC characteristics are likely to be further improved.

[0032] Conductive particles There are no particular limitations on the conductive particles as long as they are conductive. －６ / °C or less, and －６ / °C or less is more preferred. The thermal expansion coefficient of the conductive particles can be determined from the material of the conductive particles. The PTC resistor may contain only one type of conductive particles or may contain two or more types of conductive particles.

[0033] Examples of conductive particles include carbon-based particles such as graphite, carbon black, carbon nanotubes, and graphene; metal-based particles such as nickel powder, copper powder, silver powder, and tungsten powder; etc. Among these, nickel powder, silver powder, tungsten powder, and graphite are preferred because they have high affinity with the above-mentioned polyolefin wax and binder resin, and are less likely to precipitate in the composition for producing a PTC resistor.

[0034] The shape of the conductive particles is not particularly limited, and may be, for example, spherical, irregular, tubular, rod-like, flat, crushed, etc. The specific surface area of ​​the conductive particles is 5 m ２ The specific surface area is a value measured by a gas adsorption method.

[0035] The size of the conductive particles is selected appropriately depending on the type of conductive particles, etc. For example, when the conductive particles are spherical or similar in shape, the average particle diameter is preferably 30 μm or less, and more preferably 1 μm or more and 10 μm or less. When the average particle diameter is 30 μm or less, the PTC magnification of the PTC resistor tends to be better. The average particle diameter is a value measured by a laser diffraction / scattering method, and is the median (D50) in the cumulative particle size distribution.

[0036] The content of conductive particles in the PTC resistor is preferably 45% by mass or more and 80% by mass or less, more preferably 50% by mass or more and 70% by mass or less, and even more preferably 55% by mass or more and 67.5% by mass or less. When the amount of conductive particles in the PTC resistor is 45% by mass or more, the PTC characteristics tend to be more stable. On the other hand, when the amount of conductive particles in the PTC resistor is 80% by mass or less, the amount of the polyolefin wax and binder resin increases, and the resistance value when heated tends to increase.

[0037] Others In addition to the polyolefin wax, binder resin, and conductive particles, the PTC resistor may contain other components as needed, provided that the purpose and effect of the present invention are not impaired. Examples of other components include various additives such as antioxidants and flame retardants.

[0038] - Method for Manufacturing PTC Resistor The PTC resistor of this embodiment can be manufactured by applying a composition containing the polyolefin wax, the binder resin, the conductive particles, and, if necessary, a solvent, and then heating and curing the composition.

[0039] The type of solvent is not particularly limited as long as it can uniformly dissolve or disperse the polyolefin wax, binder resin, conductive particles, etc. However, the boiling point of the solvent is preferably 100° C. or higher, more preferably 100 to 330° C., and even more preferably 150 to 250° C. When the boiling point of the solvent is within this range, the storage stability of the composition is improved and the composition is easier to apply.

[0040] The solvent is appropriately selected depending on the type of polyolefin wax, the type of binder resin, etc. Examples of the solvent include alcohols, ketones, esters, glycol esters, glycol ethers, ethers, aromatic hydrocarbons, and mixtures thereof, with terpineol, butyl carbitol acetate, tetralin, toluene, and mixtures thereof being preferred.

[0041] The amount of the solvent is appropriately selected depending on the desired viscosity of the composition, and is usually preferably about 20 to 70 parts by mass, and more preferably 25 to 65 parts by mass, per 100 parts by mass of the total amount of the composition (ink). When the amount of the solvent is within this range, the viscosity of the composition (ink) tends to fall within the desired range.

[0042] The preferred viscosity of the composition is appropriately selected depending on the method for forming the PTC resistor. For example, when the composition is printed by screen printing and then cured to obtain a PTC resistor, the viscosity of the composition is preferably 100 to 400 dPa·s. This viscosity is a value measured at 25°C using a cylindrical rotational viscometer (manufactured by Rion Co., Ltd.). When the viscosity of the composition is within this range, the composition can be applied to a desired thickness and can form a film without unevenness.

[0043] The method for preparing the composition is not particularly limited, and the polyolefin wax, resin binder, conductive particles, and solvent may be mixed at once, or the resin binder and solvent may be mixed first, and then the polyolefin wax and conductive particles may be mixed.

[0044] The method for applying the composition is not particularly limited, and examples thereof include screen printing, roll coating, and application with a dispenser.

[0045] The composition can be cured by heating it to about 100 to 200° C. The heating time is preferably about 1 to 30 minutes. Heating the composition to this extent removes the solvent in the composition.

[0046] (2) PTC Resistor of Second Aspect The PTC resistor of the second aspect contains a naturally occurring wax, a binder resin, and conductive particles. Each component will be described below.

[0047] Naturally Originated Wax In this specification, wax refers to an organic substance that is solid or semi-solid at room temperature (25°C) and melts without decomposition when heated. Naturally Originated Wax refers to plant-based wax derived from plants or animal-based wax derived from animals. Furthermore, plant-based wax refers to wax made from plants. Animal-based wax refers to wax derived from animals. A PTC resistor may contain only one type of naturally Originated Wax, or may contain two or more types. There are no particular restrictions on the type of naturally Originated Wax contained in a PTC resistor, but a PTC resistor is typically required to increase in resistance at temperatures between 40°C and 100°C. Therefore, the melting point of the naturally Originated Wax is preferably between 40°C and 100°C, and more preferably between 50°C and 90°C.

[0048] The wax ester content of the naturally occurring wax is preferably 10% by mass or more. When the wax ester content is 10% by mass or more, the melting point of the naturally occurring wax tends to fall within the above range. Furthermore, melting near the melting point tends to proceed in a shorter time.

[0049] Here, the wax ester component refers to an ester in which a higher fatty acid and a higher monohydric alcohol are bonded in a 1:1 ratio. The wax ester component is, for example, an ester of a higher fatty acid having from 10 to 50 carbon atoms and a higher monohydric alcohol having from 10 to 50 carbon atoms. The total number of carbon atoms constituting the wax ester component is preferably from 20 to 100, and more preferably from 30 to 50.

[0050] The naturally occurring wax may further contain free saturated fatty acids (the above-mentioned higher fatty acids) and free alcohols (the above-mentioned higher monohydric alcohols). The amount of free saturated fatty acids is preferably 20% by mass or less relative to the total mass of the naturally occurring wax. On the other hand, the amount of free alcohols is more preferably 15% by mass or less relative to the total mass of the naturally occurring wax.

[0051] The iodine value of the naturally occurring wax is preferably 80 or less, more preferably 30 or less, and even more preferably 25 or less. The iodine value represents the amount of unsaturated bonds in the hydrocarbon chains of the components contained in the naturally occurring wax. The iodine value, i.e., the amount of unsaturated double bonds, in the naturally occurring wax is preferably small. If the amount of unsaturated double bonds is large, the naturally occurring wax is less likely to melt even when the temperature of the PTC resistor rises. In other words, if the iodine value exceeds 80, the resistance value is less likely to increase when the temperature rises. In contrast, if the iodine value is 80 or less, the naturally occurring wax is more likely to melt when the temperature of the PTC resistor rises, and the resistance value is more likely to increase.

[0052] Examples of the plant-based wax, which is one type of naturally occurring wax, include candelilla wax, carnauba wax, rice wax, Japan wax wax, hydrogenated jojoba wax, etc. Among these, carnauba wax, candelilla wax, and rice wax are preferred from the viewpoints of easy availability and ease of increasing the PTC multiplier.

[0053] On the other hand, examples of animal waxes, which are a type of naturally occurring wax, include beeswax and lanolin wax.

[0054] The amount of naturally occurring wax in the PTC resistor is preferably 5% by mass or more and 50% by mass or less, and more preferably 7% by mass or more and 40% by mass or less. When the amount of naturally occurring wax in the PTC resistor is 5% by mass or more, the resistance value of the PTC resistor when the temperature rises is likely to be further increased. On the other hand, when the amount is 50% by mass or less, the amount of conductive particles described below becomes sufficiently large relatively, and the PTC characteristics of the PTC resistor are likely to be further improved.

[0055] Binder Resin: The binder resin may be any resin capable of binding the naturally occurring wax and the conductive particles described below, and binding them to a substrate or the like, but it is preferable that the binder resin does not prevent the volume change of the naturally occurring wax caused by melting. Furthermore, the binder resin itself may expand with increasing temperature, contributing to an increase in the resistance value of the PTC resistor. The PTC resistor may contain only one type of binder resin, or may contain two or more types. The binder resin is the same as the binder resin of the PTC resistor of the first embodiment.

[0056] The amount of binder resin in the PTC resistor of this embodiment is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less. When the amount of binder resin in the PTC resistor is 5% by mass or more, it becomes easier to print conductive resins, naturally occurring waxes, and compositions containing the binder resin, and the fixation after printing becomes good. Furthermore, the strength of the PTC resistor is likely to be further increased. On the other hand, when the amount of binder resin is 50% by mass or less, the amount of conductive particles becomes sufficiently large relative to the amount of conductive particles, and the PTC characteristics are likely to be further improved.

[0057] Conductive Particles The conductive particles are not particularly limited as long as they are particles having conductivity, and are the same as the conductive particles of the PTC resistor of the first embodiment described above.

[0058] The content of conductive particles in the PTC resistor of this embodiment is preferably 45% by mass or more and 80% by mass or less, and more preferably 50% by mass or more and 70% by mass or less. When the amount of conductive particles in the PTC resistor is 45% by mass or more, the PTC characteristics tend to be more stable. On the other hand, when the amount of conductive particles in the PTC resistor is 80% by mass or less, the amount of the naturally occurring wax and binder resin increases, and the resistance value when heated tends to be higher.

[0059] Others In addition to the naturally occurring wax, binder resin, and conductive particles, the PTC resistor may contain other components as needed, provided that the purpose and effect of the present invention are not impaired. Examples of other components include various additives such as antioxidants and flame retardants.

[0060] Manufacturing Method of PTC Resistor The PTC resistor of this embodiment can be manufactured by applying a composition containing the naturally occurring wax, the binder resin, the conductive particles, and optionally a solvent, and then heating and curing the composition.

[0061] The type of solvent is not particularly limited as long as it can uniformly dissolve or disperse the above-mentioned naturally occurring wax, binder resin, conductive particles, etc. However, the boiling point of the solvent is preferably 100° C. or higher, more preferably 100 to 330° C., and even more preferably 150 to 250° C. When the boiling point of the solvent is within this range, the storage stability of the composition is improved and the composition is easier to apply.

[0062] The solvent is appropriately selected depending on the type of naturally occurring wax, the type of binder resin, etc. Examples of the solvent include alcohols, ketones, esters, glycol esters, glycol ethers, ethers, aromatic hydrocarbons, and mixtures thereof, with terpineol, butyl carbitol acetate, tetralin, toluene, and mixtures thereof being preferred.

[0063] The amount of the solvent is appropriately selected depending on the viscosity of the desired composition (ink), and is usually preferably about 40 to 90 parts by mass, and more preferably 40 to 85 parts by mass, per 100 parts by mass of the total amount of the composition (ink). When the amount of the solvent is within this range, the viscosity of the composition tends to fall within the desired range.

[0064] The preferred viscosity of the composition is appropriately selected depending on the method for forming the PTC resistor. For example, when the composition is printed by screen printing and then cured to obtain a PTC resistor, the viscosity of the composition is preferably 100 to 400 dPa·s. This viscosity is a value measured at 25°C using a cylindrical rotational viscometer (manufactured by Rion Co., Ltd.). When the viscosity of the composition is within this range, the composition can be applied to a desired thickness and can form a film without unevenness.

[0065] The method for preparing the composition is not particularly limited, and the naturally occurring wax, resin binder, conductive particles, and solvent may be mixed at once, or the resin binder and solvent may be mixed first, and then the naturally occurring wax and conductive particles may be mixed.

[0066] The method for applying the composition is not particularly limited, and examples thereof include screen printing, roll coating, and application with a dispenser.

[0067] The composition can be cured by heating it to about 100 to 200° C. The heating time is preferably about 1 to 30 minutes. Heating the composition to this extent removes the solvent in the composition.

[0068] Specific examples of the present invention will be described below, but the scope of the present invention should not be construed as being limited by these examples.

[0069] [First Aspect] 1. Preparation of Materials The following compounds were prepared as materials for producing a PTC resistor.

[0070] (Polyolefin-based components) Polyethylene wax (CERAFLOUR 961 manufactured by BYK) Ultra-high molecular weight polyethylene (MIPERON PM-200 manufactured by Mitsui Chemicals)

[0071] (Binder resin) SEBS resin (styrene-ethylene-butylene-styrene block copolymer, Tuftec 1913, manufactured by Asahi Kasei Corporation) Hydrogenated SEPS resin (hydrogenated styrene-ethylene-propylene-styrene block copolymer, Septon 2002, manufactured by Kuraray Co., Ltd.)

[0072] (Conductive particles) PWSH: crushed carbon (graphite, manufactured by Eitan Co., Ltd.) PG11: spherical carbon (graphite, manufactured by Eitan Co., Ltd.) ICB: spherical carbon (graphite, manufactured by Nippon Carbon Co., Ltd.)

[0073] A DSC curve was obtained for the polyolefin component in the range of 25°C to 150°C at a heating rate of 10°C / min using a DSC. The number of melting peaks and the absolute values ​​of the melting peak heights were determined. These results are shown in Table 1. Furthermore, the DSC curves for the polyethylene wax used in Examples A-1 and A-2 are shown in Figure 2A, and the DSC curves for the ultra-high molecular weight polyethylene used in Comparative Examples A-2 and A-3 are shown in Figure 2B.

[0074] The average particle diameter D50 of the conductive particles was measured by a laser diffraction / scattering method. The thermal expansion coefficient was measured using a literature value. The specific surface area was measured by a gas adsorption method. The results are shown in Table 1.

[0075] 2. Fabrication of PTC Resistors Each PTC resistor was fabricated according to the following procedure. [Example A-1] 8.0 parts by mass of hydrogenated SEPS resin and 51.0 parts by mass of an organic solvent (terpineol) were mixed at 100°C for 1 hour using a stirrer to prepare a varnish. This varnish was mixed with 9.0 parts by mass of polyolefin wax (polyethylene wax) and 32.0 parts by mass of conductive particles (spherical carbon) and crushed using a crusher to obtain the desired screen printing ink. A substrate equipped with a pair of comb-shaped electrodes was prepared, and the ink described above was printed between the comb-shaped electrodes by screen printing. The substrate was then heated to 150°C to prepare a sheet heating element having the desired PTC resistor.

[0076] Comparative Example A-1 A sheet heating element having a PTC resistor was produced in the same manner as in Example A-1, except that a paste was produced with the composition shown in Table 1 without using polyolefin wax.

[0077] [Example A-2 and Comparative Examples A-2 and A-3] A sheet heating element having a PTC resistor was produced in the same manner as in Example A-1, except that the organic solvent and the type and amount of each component were changed as shown in Table 1.

[0078] [Evaluation] The sheet heating elements produced in Examples A-1 and A-2 and Comparative Examples A-1 to A-3 were subjected to the following tests. The results are shown in Table 1.

[0079] (Measurement of Temperature Rise Rate) The sheet heating element was heated in a room temperature environment (25°C), and the temperature when it stabilized and the time it took to reach that temperature were determined. This was determined using the following formula: (stable temperature - initial temperature) / (time until stabilization).

[0080] (Measurement of Sheet Resistance) The sheet resistance of each sheet heating element was measured by the two-terminal method or the four-terminal method.

[0081] (Determination of Maximum PTC Magnification) The resistance value of each sheet heating element was measured when the temperature was raised from -40°C to 120°C. The maximum resistance value and the minimum resistance value were then determined, and the ratio of these (maximum resistance value / minimum resistance value) was calculated as the maximum PTC magnification. The measurement of each resistance value was performed using the two-terminal method or the four-terminal method.

[0082] (Determining the maximum PTC magnification in a room temperature environment) The resistance value of the sheet heating element at 25°C was measured immediately after production. Next, the temperature of the sheet heating element was changed from -40°C to 120°C, and then returned to 25°C, and the resistance value was measured again. The ratio of these values ​​(resistance value at 25°C after the temperature change / resistance value at 25°C before the temperature change) was calculated as the maximum PTC magnification in a room temperature environment.

[0083] (Evaluation) A maximum PTC magnification of 100 times or more was evaluated as ◯, and a maximum PTC magnification of less than 100 times was evaluated as x.

[0084]

[0085] As shown in the table above, the sheet heating elements using PTC resistors containing polyolefin wax (Examples A-1 and A-2) had a much higher maximum PTC magnification and a faster temperature rise rate than the sheet heating elements using PTC resistors that did not contain polyolefin wax (Comparative Examples A-1 to A-3).

[0086] [Second Aspect] 1. Preparation of Materials The following compounds were prepared as materials for producing a PTC resistor.

[0087] (Naturally derived waxes (plant waxes)) Carnauba wax: melting point 80°C to 86°C, iodine value 5 to 14, wax ester content 80 to 85% by mass Candelilla wax: melting point 68°C to 73°C, iodine value 5 to 14, wax ester content 80 to 85% by mass Rice wax: melting point 80°C, iodine value 7.4, wax ester content 93 to 97% by mass

[0088] (Vegetable oil) Castor oil: No melting point, iodine value 83-89, wax ester content 1.7%

[0089] (Other) Conductive particles (artificial graphite, average particle diameter D50 4 μm, specific surface area 5.0 m ２ / g, thermal expansion coefficient 6.0×10 －６ / °C) Binder resin: SEBS resin (styrene-ethylene-butylene-styrene block copolymer, Tuftec 1913, manufactured by Asahi Kasei Corporation) Solvent: terpineol

[0090] 2. Preparation of Sheet Heating Elements Containing PTC Resistors Sheet heating elements containing each PTC resistor were prepared according to the following procedure. [Example B-1] 4.9 parts by mass of SEBS resin and 63.5 parts by mass of an organic solvent (terpineol) were mixed in a stirrer at 100°C for 1 hour to prepare a varnish. This varnish was mixed with 11.5 parts by mass of a natural wax (carnauba wax) and 20.1 parts by mass of conductive particles (artificial graphite) and crushed in a crusher to obtain an ink for screen printing. A substrate equipped with a pair of comb-shaped electrodes was prepared, and the ink described above was printed between the comb-shaped electrodes by screen printing. The substrate was then heated to 150°C to prepare a sheet heating element having the desired PTC resistor.

[0091] Example B-2 A planar heating element having a PTC resistor was produced in the same manner as in Example B-1, except that the type of naturally occurring wax was changed to candelilla wax.

[0092] Example B-3 A sheet heating element having a PTC resistor was produced in the same manner as in Example B-1, except that the type of naturally occurring wax was changed to rice wax.

[0093] Comparative Example B-1 A sheet heating element having a PTC resistor was produced in the same manner as in Example B-1, except that castor oil was used instead of the naturally occurring wax.

[0094] [Evaluation] The resistance values ​​of the sheet heating elements produced in Examples B-1 to B-3 and Comparative Example B-1 were measured from 25°C to 120°C. The maximum PTC magnification was calculated as (maximum resistance value) / (resistance value at 25°C). The resistance values ​​were measured using the two-terminal method or the four-terminal method. The results are shown in Table 2. The evaluation was as follows: ◯ when the maximum PTC magnification was 100 times or more; △ when the maximum PTC magnification was 2 times or more but less than 100 times; and × when the maximum PTC magnification was less than 2 times.

[0095]

[0096] As shown in the table above, the sheet heating element using vegetable oil (Comparative Example B-1) did not have a sufficiently high PTC multiplier, but the sheet heating elements using PTC resistors containing naturally derived wax (Examples B-1 to B-3) all had extremely high maximum PTC multipliers. It was also confirmed that in Examples B-1 to B-3, the temperature stabilized in about one minute when heated from room temperature (25°C).

[0097] This application claims priority based on Japanese Patent Application No. 2023-046590, filed March 23, 2023. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

[0098] The PTC resistor of the present disclosure has a resistance that easily rises in a short time after reaching a certain temperature, and has a high resistance after the temperature rise, making it extremely useful for producing various sheet heating elements.

Claims

1. A substrate; a pair of electrodes disposed on the substrate; a PTC resistor disposed on the substrate and between the pair of electrodes; and the PTC resistor includes conductive particles, a binder resin, and a wax; The wax comprises a naturally occurring wax and / or a polyolefin wax in which the number of melting peaks observed is one or two in a DSC curve obtained by heating from 25°C to 150°C at a heating rate of 10°C / min using a differential scanning calorimeter; the binder resin contains at least one of a styrene-ethylene-butylene-styrene copolymer resin and a hydrogenated styrene-ethylene-propylene-styrene copolymer; Surface heating element.

2. The conductive particles have a thermal expansion coefficient of 20×10 －６ / °C or less, The sheet heating element according to claim 1 .

3. The conductive particles have an average particle size of 30 μm or less. The sheet heating element according to claim 1 .

4. The conductive particles have a specific surface area of ​​5 m ２ / g or less, The sheet heating element according to claim 1 .

5. the wax includes the polyolefin wax, The absolute value of at least one melting peak height in the DSC curve is 5 mW or more; The sheet heating element according to any one of claims 1 to 4.

6. The wax comprises a naturally occurring wax, The naturally occurring wax contains 10% by mass or more of a wax ester component. The sheet heating element according to any one of claims 1 to 4.

7. The naturally occurring wax has an iodine value of 80 or less. The sheet heating element according to claim 6.