JP4462271B2 - PTC element - Google Patents

Description

  The present invention relates to a PTC element.

As a conventional PTC element, for example, as described in Patent Document 1, a metal member (electrode) bonded to the front and back of a sheet body (PTC element body) of a polymer conductive composition is known. Yes.
JP 2005-11847 A

  However, when a conventional PTC element receives a thermal history after a long period of time after manufacture, the PTC element body deteriorates and the room temperature resistance value is greatly increased. When the room temperature resistance value increases, the rate of change in resistance between non-operation and operation decreases, so that the PTC element may not function normally. In the conventional PTC element, it is considered that oxygen enters from the surroundings into the PTC element body after a long period of time after manufacture. When the PTC element receives a thermal history in this state, the resin and conductive particles in the PTC element body are oxidized by oxygen that has entered, and this oxidation causes the PTC element body to deteriorate and increase the room temperature resistance value. it is conceivable that.

  Therefore, an object of the present invention is to provide a PTC element in which the deterioration of the PTC element body is sufficiently suppressed when it receives a thermal history after a long period of time since its manufacture.

  A PTC element according to the present invention includes a PTC element body including a polymer matrix and conductive particles, a first main surface bonded to the PTC element body, and a second main surface facing the first main surface. And a protective layer covering a second outer surface excluding the first outer surface joined to the first main surface of the electrode among the outer surfaces of the PTC element body, and the protective layer includes a second layer of the electrode It extends to the main surface and covers only the peripheral portion in the vicinity of the second outer surface of the second main surface.

  In the PTC element of the present invention, the protective layer covers the second outer surface of the PTC element body, that is, the exposed surface of the PTC element body. The exposed surface of the PTC element body is covered with a protective layer, so that it does not come into contact with outside air. Since the protective layer extends to the second main surface of the electrode, the interface between the PTC element body and the electrode, which is located between the exposed surface of the PTC element body and the second main surface of the electrode, is also included in the protective layer. It will be covered. Therefore, the interface between the PTC element body and the electrode is not exposed to the outside air.

  The protective layer covers only the peripheral portion in the vicinity of the exposed surface of the PTC element body in the second main surface of the electrode. Thus, the protective layer formed in the comparatively narrow range is rising by the effect of surface tension. Therefore, the peripheral edge portion of the second main surface is covered with a sufficiently thick protective layer. When the peripheral portion of the second main surface is covered with a sufficiently thick protective layer, the vicinity of the peripheral portion of the second main surface, that is, the vicinity of the interface between the electrode and the PTC element body is also sufficiently thick. It will be covered with a protective layer. Therefore, the possibility that the vicinity of the interface between the electrode and the PTC element body is exposed to the outside air can be significantly suppressed.

  A PTC element body that is not in contact with outside air not only on the exposed surface but also in the vicinity of the interface with the electrode has extremely good gas barrier properties and is difficult to oxidize. By making the PTC element body difficult to oxidize, it is possible to sufficiently suppress the deterioration of the PTC element body when it is subjected to a thermal history after a long period of time since its manufacture. Further, by forming the protective layer so as to extend to the second main surface of the electrode, the adhesion between the protective layer and the electrode can be improved. As a result, the protective layer is difficult to peel off, and the PTC element body can be reliably protected.

  In the PTC element of the present invention, when viewed from the second main surface side of the electrode, the shortest distance from the end portion of the protective layer located on the second main surface to the most protruding portion of the PTC element body is 1 mm. It is preferable that it is less than. In this case, the vicinity of the interface between the electrode and the PTC element body is more reliably protected by the protective layer. As a result, since the PTC element body is less likely to be oxidized, it is possible to further suppress the deterioration of the PTC element body when subjected to a thermal history after a long period of time since the manufacture.

  According to the present invention, it is possible to provide a PTC element in which the deterioration of the PTC element body when the thermal history is received after a long period of time has been sufficiently suppressed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  FIG. 1 is a perspective view of a PTC element according to this embodiment. As shown in FIG. 1, the PTC element 1 includes a PTC element body 10, a pair of electrodes 12 and 14, and a protective layer 20. The electrodes 12 and 14 have first main surfaces 120 and 140, and the first main surface 120 and a part of the first main surface 140 are opposed to each other. Opposing portions of the first main surfaces 120 and 140 are joined to the PTC element body 10. As a result, the electrodes 12 and 14 sandwich the PTC element body 10. The electrodes 12, 14 are second main surfaces 121, 141 facing the first main surfaces 120, 140, and side surfaces located between the first main surfaces 120, 140 and the second main surfaces 121, 141. 122, 142.

  The electrodes 12 and 14 are made of a conductive material such as metal and are formed to a thickness of about 0.1 mm. As the conductive material constituting the electrodes 12 and 14, Ni or Ni alloy is preferable. Moreover, it is preferable that at least a portion in contact with the PTC element body 10 in the first main surfaces 120 and 140 is roughened. When this portion is roughened, the electrodes 12 and 14 are more strongly fixed to the PTC element body 10 by the anchor effect. Leads (not shown) are connected to the electrodes 12 and 14. Charges can be discharged or injected from the electrodes 12 and 14 to the outside through the connected leads.

  Between the first main surface 120 of the electrode 12 and the first main surface 140 of the electrode 14, the PTC element body 10 having a positive resistance temperature characteristic is disposed. The PTC element body 10 includes a polymer matrix and conductive particles. More specifically, in the PTC element body 10, conductive particles are dispersed in a polymer matrix. Here, the polymer matrix may be a thermoplastic resin or a cured product of a thermosetting resin. However, when the polymer matrix is a crystalline or amorphous thermoplastic resin, the effect of the present invention can be obtained. More noticeable. In the present specification, the “thermoplastic resin” includes those in which polymer chains in the thermoplastic resin are crosslinked.

  When the PTC element body 10 contains a low-molecular organic compound described later, it is preferable that the melting point or softening point of the thermoplastic resin constituting the polymer matrix is higher than the melting point of the low-molecular compound. Thereby, the flow by the melting | fusing of the low molecular organic compound at the time of operation | movement and the deformation | transformation of the PTC element | base_body 10 can be prevented. The melting point or softening point of the thermoplastic resin is more preferably 30 ° C. or more higher than the melting point of the low molecular compound, and more preferably in the range of 30 ° C. or more and 110 ° C. or less. Moreover, it is preferable that melting | fusing point or softening point of a thermoplastic resin is 70 to 200 degreeC. Thereby, the flow of the low molecular organic compound during the operation and the deformation of the PTC element body 10 can be more reliably prevented.

  As for the molecular weight of the thermoplastic resin, the weight average molecular weight Mw is preferably about 10,000 to 5,000,000. Moreover, it is preferable that the melt flow rate defined by ASTM D1238 of a thermoplastic resin is 0.1-30 g / 10min.

  Examples of the thermoplastic resin suitable as the polymer matrix include polyolefin (for example, polyethylene), one or more olefins (for example, ethylene, propylene), and one or more olefinically unsaturated monomers containing polar groups. Copolymer (eg ethylene-vinyl acetate copolymer), polyvinyl halide or polyvinylidene halide (eg polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride), polyamide (eg 12-nylon), polystyrene, Examples include polyacrylonitrile, thermoplastic elastomer, polyethylene oxide, polyacetal, thermoplastic modified cellulose, polysulfones, and polymethyl (meth) acrylate. Among these, polyolefin is preferable, and among polyolefin, polyethylene is particularly preferable.

  More specific examples of the thermoplastic resin include high-density polyethylene (for example, “Hi-Zex 2100JP” (trade name, manufactured by Mitsui Petrochemical), “Marlex 6003” (trade name, manufactured by Philippe)), low-density polyethylene (for example, LC500 (trade name, manufactured by Nippon Polychem), “DYNH-1” (trade name, manufactured by Union Carbide), medium density polyethylene (for example, “2604M” (trade name, manufactured by Gulf)), ethylene-ethyl acrylate Copolymer (for example, “DPD6169” (trade name, manufactured by Union Carbide)), ethylene-acrylic acid copolymer (for example, “EAA455” (trade name, manufactured by Dow Chemical)), hexafluoroethylene-tetrafluoroethylene copolymer (for example, , "FEP100" (trade name, manufactured by DuPont)), Li polyvinylidene fluoride (for example, "Kynar461" (trade name, manufactured by Penbaruto Co., Ltd.)), and the like.

  The above thermoplastic resins are used alone or in combination of two or more. In addition, the polymer matrix is preferably composed of only a thermoplastic resin, but in some cases, may contain an elastomer, a cured product of a thermosetting resin, or a mixture thereof.

  The conductive particles contained in the PTC body 10 are not particularly limited as long as they exhibit PTC characteristics when combined with a polymer matrix, but Ni is particularly preferable as the material. When Ni particles are used as the conductive particles, the protective layer 20 is particularly useful because the PTC element body 10 is likely to be deteriorated by oxidation.

  It is preferable that a plurality of spike-like protrusions (usually 10 to 500) are formed on the surface of the conductive particles. In this case, it is preferable that the height of the spike-like protrusion is typically about 1/3 to 1/50 of the particle diameter.

  The conductive particles may be a powder in which primary particles are individually present, but preferably form chain-like secondary particles in which about 10 to 1000 primary particles are connected. As an example of the former, there is “INCOType 123 nickel powder” (trade name, manufactured by Inco Corporation), which is a spherical Ni particle having spike-like protrusions. The average particle diameter of the Ni particles is about 3 to 7 μm, the apparent density is about 1.8 to 2.7 g / cm 3, and the specific surface area is about 0.34 to 0.44 m 2 / g. Examples of conductive particles forming chain-like secondary particles include “INCO Type 255 Nickel Powder”, “INCO Type 270 Nickel Powder”, “INCO Type 287 Nickel Powder” or “INCO Type 210 Nickel Powder” which are filamentary Ni particles. "(The above-mentioned trade name, manufactured by Inco Corporation), INCO Type 255, 270 and 287 are particularly preferable. The apparent density of these filamentous Ni particles is about 0.3 to 1.0 g / cm 3 and the specific surface area is about 0.4 to 2.5 m 2 / g.

  The average particle size (value measured by the fish-subsieve method) of the primary particles constituting the filament Ni particles is preferably 0.1 μm or more, more preferably 0.5 μm or more and 4.0 μm or less, and 1.0 μm or more 4 More preferably, it is 0.0 μm or less. Furthermore, filamentous Ni particles in which primary particles having an average particle diameter of not less than 1.0 μm and not more than 4.0 μm are connected to primary particles having an average particle diameter of not less than 0.1 μm and less than 1.0 μm. May be combined at a ratio of 50% by mass or less of the entire conductive particles.

  The content ratio of the conductive particles in the PTC element body 10 can be determined as appropriate so that the PTC characteristics are exhibited. Specifically, the content ratio of the conductive particles is preferably 20 to 50% by volume with respect to the entire volume of the PTC element body 10.

  The PTC element body 10 preferably further contains a low-molecular organic compound in addition to the polymer matrix and the conductive particles. As the low molecular organic compound in this case, a crystalline compound having a molecular weight of 1000 or less is preferably used. This low molecular organic compound is preferably solid at room temperature (about 25 ° C.). The low molecular organic compound preferably has a melting point (mp) of 40 to 100 ° C.

  Preferred specific examples of the low molecular weight organic compound include hydrocarbons (for example, alkane-based linear hydrocarbons having 22 or more carbon atoms), fatty acids (for example, alkane-based linear hydrocarbon fatty acids having 22 or more carbon atoms). Fatty acid esters (for example, methyl esters of saturated fatty acids obtained from saturated fatty acids having 20 or more carbon atoms and lower alcohols such as methyl alcohol), fatty acid amides (for example, saturated fatty acid primary amides or oleic acid amides having 10 or less carbon atoms) , Unsaturated fatty acid amides such as erucic acid amide), aliphatic amines (for example, aliphatic primary amines having 16 or more carbon atoms), higher alcohols (specifically, n-alkyl alcohols having 16 or more carbon atoms). It is done. The low molecular organic compound is used alone or in combination of two or more depending on the operating temperature.

  In addition, a low molecular organic compound can be used in the state of the wax or fats and oils which contain these as a component. Examples of the wax containing these low-molecular organic compounds include natural waxes such as plant waxes, animal waxes, and mineral waxes, including petroleum waxes such as paraffin wax and microcrystalline wax. Moreover, what is called fat or solid fat is mentioned as fats and oils containing these low molecular organic compounds.

  Low molecular organic compounds or waxes and fats and oils containing them can be obtained as commercial products. Examples of commercially available paraffin wax include “Tetracosane C24H50” (mp 49-52 ° C.), “Hexatriacontane C36H74” (mp 73 ° C.), “HNP-10” (trade name, manufactured by Nippon Seiwa Co., Ltd., mp 75 ° C.). “HNP-3” (trade name, manufactured by Nippon Seiwa Co., Ltd., mp 66 ° C.)). Examples of commercially available microcrystalline waxes include “Hi-Mic-1080” (trade name, manufactured by Nippon Seiwa Co., Ltd., mp 83 ° C.), “Hi-Mic-1045” (trade name, manufactured by Nippon Seiwa Co., Ltd., mp 70). ° C), “Hi-Mic 2045” (trade name, manufactured by Nippon Seiwa Co., Ltd., mp 64 ° C.), “Hi-Mic 3090” (trade name, manufactured by Nippon Seiwa Co., Ltd., mp 89 ° C.), “Selatta 104” (trade name, Nippon Oil Refinery, mp 96 ° C.) and “155 Micro Wax” (trade name, Nippon Oil Refinery, mp 70 ° C.). Examples of commercially available fatty acids include behenic acid (Nippon Seika, mp 81 ° C.), stearic acid (Nippon Seika, mp 72 ° C.), and palmitic acid (Nippon Seika, mp 64 ° C.). Examples of commercially available fatty acid esters include arachidic acid methyl ester (manufactured by Tokyo Chemical Industry, mp 48 ° C.). Examples of commercially available fatty acid amides include oleic acid amide (Nippon Seika Co., Ltd., mp 76 ° C.).

  The PTC element 1 includes a protective layer 20. The protective layer 20 covers the exposed surface (second outer surface) 100 of the PTC element body 10. The exposed surface 100 of the PTC element body 10 refers to a portion of the outer surface of the PTC element body 10 excluding the surface (first outer surface) that joins the first main surfaces 120 and 140 of the electrodes 12 and 14.

  The protective layer 20 extends to the second main surfaces 121 and 141 of the electrodes 12 and 14. More specifically, the protective layer 20 covers not only the exposed surface 100 of the PTC element body 10 but also the side surfaces 122 and 142 of the electrodes 12 and 14 and the first main surfaces 120 and 140. It extends to 14 second main surfaces 121 and 141. However, the portions of the side surfaces 122 and 142 of the electrodes 12 and 14 and the first main surfaces 120 and 140 that are covered with the protective layer 20 are portions located around the exposed surface 100 of the PTC element body 10. Further, the second main surfaces 121 and 141 of the electrodes 12 and 14 are covered with the protective layer 20 only in the peripheral portion near the exposed surface 100 of the PTC element body 10.

  FIG. 2 is a side view of the PTC element 1 as viewed from the second main surface 121 side of the electrode 12. 3 is a cross-sectional view of the PTC element 1 taken along line III-III in FIG. 1, and FIG. 4 is a cross-sectional view of the PTC element 1 taken along line IV-IV in FIG. As shown in FIG. 3, the protective layer 20 extends from the peripheral portion of the second main surface 121 of the electrode 12 to the first main surface 140 of the electrode 14, and the peripheral edge of the second main surface 141 of the electrode 14. The portion extends from the first main surface 120 of the electrode 12. Further, as shown in FIG. 4, it extends from the peripheral portion of the second main surface 121 of the electrode 12 to the peripheral portion of the second main surface 141 of the electrode 14.

  As shown in FIG. 2, when the PTC element 1 is viewed from the second main surfaces 121 and 141 side of the electrodes 12 and 14, the end portion 200 of the protective layer 20 located on the second main surfaces 121 and 141. The shortest distance W from the most protruding portion of the PTC element body 10 to the PTC element body 10 is preferably less than 1 mm. Hereinafter, W will be described more specifically. As shown in FIGS. 3 and 4, when the exposed surface 100 of the PTC element body 10 is aligned with the side surfaces 122 and 142 of the electrodes 12 and 14, the end portion of the protective layer 20 located on the second main surface 141. The shortest distance from 200 to the side surfaces 122 and 142 of the PTC element body 10 corresponds to W. On the other hand, as shown in FIG. 5, when the exposed surface 100 of the PTC element body 10 protrudes from the first main surfaces 120 and 140, the protective layer 20 positioned on the second main surfaces 121 and 141. The shortest distance from the end portion 200 to the most protruding portion of the exposed surface 100 of the PTC element body 10 corresponds to W.

  The protective layer 20 is formed of a cured product of an epoxy resin composition containing an epoxy resin and a thiol-based curing agent. As the epoxy resin in the epoxy resin composition forming the cured product of the protective layer 20, one obtained by a method such as a one-step method, a two-step method, an oxidation method, etc. can be used without particular limitation. Preferred are glycidyl ethers of aromatic amines and those having a polar group or generating a polar group upon curing. Specific examples of suitable epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, glycidylated aliphatic amines such as tetraglycidyl m-xylenediamine, and aromatic amines such as tetraglycidyldiaminodiphenylmethane. There are glycidized products and aminophenol type epoxy resins.

  As the thiol-based curing agent, any thiol compound having two or more thiol groups can be used without particular limitation. Specific examples of suitable thiol-based curing agents include aliphatic polythioesters such as pentaerythritol tetrathioglycolate and trimethylolpropane tristhiopropionate, aliphatic polythioethers, and aromatic ring-containing polythioethers. As understood by those skilled in the art, the amount of the thiol-based curing agent in the epoxy resin composition is appropriately determined in consideration of the equivalent ratio with the epoxy resin.

  The epoxy resin composition preferably further contains an amine compound having a secondary amino group or a tertiary amino group. As this amine compound, aromatic amine and aliphatic amine, amine-epoxy adduct, imidazole, imidazole adduct and the like are preferably used.

  In addition to the above components, the epoxy resin composition includes fillers such as silica, mica and talc particles, inorganic salts such as magnesium hydroxide and aluminum hydroxide, other curing agents or curing accelerators such as carboxylic acid and phenol, A solvent for the purpose of adjusting the viscosity of the resin composition may further be contained.

  Then, the manufacturing method of the PTC element 1 which has the structure mentioned above is demonstrated.

  When the polymer matrix in the PTC element body 10 includes a thermoplastic resin, the PTC element 1 includes, for example, a step of kneading a mixture containing a thermoplastic resin and conductive particles to obtain a kneaded material containing these. A step of forming the kneaded material into a sheet to form a PTC element body 10 in which conductive particles are dispersed in a polymer matrix containing a thermoplastic resin, and a pair of electrodes 12 for the PTC element body 10. , 14 are fixed by thermocompression bonding, and a manufacturing method is provided that includes forming a protective layer 20 that integrally covers the exposed surface of the PTC element body 10 and the portions of the electrodes 12, 14 located around the exposed surface 100. Can be obtained.

  The step of obtaining the kneaded product can be performed while heating the mixture obtained by mixing the respective components to a temperature equal to or higher than the melting point or softening point of the thermoplastic resin (preferably a temperature higher by 5 to 40 ° C. than the melting point or softening point). . Alternatively, it is possible to disperse the conductive particles in the thermoplastic resin without heating by adding a solvent that dissolves the thermoplastic resin and kneading the mixture with a reduced viscosity. The kneading can be performed by a known method such as a mill, a pressure kneader, or a twin screw extruder.

  The obtained kneaded material is formed into a sheet shape by a method such as hot pressing to form the PTC element body 10. At this stage, the PTC element body 10 may be cut into a predetermined size by punching or the like.

  The pair of electrodes 12 and 14 are fixed to the PTC element body 10 by hot pressing a sandwiched body in which the PTC element body 10 is sandwiched between the pair of electrodes 12 and 14. After fixing the electrodes 12 and 14, it is preferable to crosslink the thermoplastic resin in the polymer matrix by irradiation or the like. This cross-linking improves the stability of the PTC element 1 against heat.

  The protective layer 20 adheres the above-mentioned epoxy resin composition to the exposed surface 100 and the first main surfaces 120 and 140, the second main surfaces 121 and 141, and the side surfaces 122 and 142 of the PTC element body 10. It is formed by heating the epoxy resin composition which is being heated to advance the curing reaction. The method for attaching the epoxy resin composition is not particularly limited. For example, a method of transferring the epoxy resin composition to the surfaces of the PTC element body 10 and the electrodes 12 and 14 using a jig, a dip coating method, and a spray coating method. Further, a screen printing method, a dispenser printing method, or the like can be used. In addition, after making an epoxy resin composition melt | dissolve or disperse | distribute to a solvent and making it adhere to PTC body 10 grade | etc., You may remove a solvent by drying. In this case, drying and curing can be performed simultaneously or continuously.

  The curing conditions of the epoxy resin composition may be appropriately determined according to the type of thiol-based curing agent and the curing accelerator (tertiary amine, etc.) combined therewith, but are heated below the operating temperature of the PTC element 1. The protective layer 20 is preferably formed. When the protective layer 20 is formed by heating at a temperature exceeding the operating temperature, the resistance value of the PTC element 1 when the temperature is returned to room temperature is higher than the resistance value of the PTC element 1 before curing the epoxy resin. There is. Here, the operating temperature is a resistance value in a temperature region lower than a region showing the PTC characteristic in a resistance-temperature curve showing a change in resistance value when the temperature of the PTC element 1 is increased at a rate of temperature increase of 2 ° C./min. Is the temperature at the intersection of the tangent of the part where the resistance is almost constant and the tangent of the part where the resistance value rises rapidly as the temperature rises. Specifically, in the case of an epoxy resin composition using a thiol-based curing agent, it is preferable to form the protective layer 20 by heating to 50 to 90 ° C. In this case, the heating time is preferably 5 to 120 minutes.

  In the PTC element 1 manufactured in this way, the protective layer 20 covers the exposed surface 100 of the PTC element body 10. Therefore, the exposed surface 100 of the PTC element body 10 is not exposed to the outside air. The protective layer 20 covers the exposed surfaces 100 of the PTC element body 10 and the side surfaces 122 and 142 of the electrodes 12 and 14 and a part of the first main surfaces 120 and 140. The part is a part located around the exposed surface 100 of the PTC element body 10. Therefore, the interface between the electrodes 12 and 14 and the PTC element body 10 is covered with the protective layer 20 and is not exposed to the outside air.

  The protective layer 20 extends over the second main surfaces 121 and 141 of the electrodes 12 and 14. However, of the second main surfaces 121 and 141, only the peripheral portion near the exposed surface 100 of the PTC element body 10 is covered with the protective layer 20. Thus, the protective layer 20 formed in a relatively narrow range rises due to the effect of the surface tension and has a sufficient thickness. The protective layer 20 having a sufficient thickness at the peripheral portions of the second main surfaces 121 and 141 is sufficient even in the vicinity of the peripheral portions, that is, in the vicinity of the interface between the electrodes 12 and 14 and the PTC element body 10. It will have a thickness. As a result, the possibility that the vicinity of the interface between the PTC element body 10 and the electrodes 12 and 14 is exposed to the outside air can be further suppressed.

  Thus, the PTC element body 10 whose contact with the outside air is suppressed as much as possible by the protective layer 20 has extremely good gas barrier properties and is difficult to oxidize. By making the PTC element body 10 difficult to oxidize, it is possible to sufficiently suppress the deterioration of the PTC element body when it receives a thermal history after a long period of time since its manufacture.

  Further, by forming the protective layer 20 so as to extend over the second main surfaces 121 and 141 of the electrodes 12 and 14, the adhesion between the protective layer 20 and the electrodes 12 and 14 can be improved. As a result, it is difficult for the protective layer 20 to peel off, so that the PTC element body 10 can be reliably protected by the protective layer 20. Further, portions of the second main surfaces 121 and 141 other than the peripheral portion, that is, the central portions of the second main surfaces 121 and 141 are not covered with the protective layer 20. Therefore, it becomes easy to perform laser marking or the like on the central portions of the second main surfaces 121 and 141. Since the laser marking applied to this portion is not hidden by the protective layer 20, it can be easily distinguished from the appearance.

  Furthermore, it is preferable that the shortest distance W from the end portion 200 of the protective layer 20 located on the second main surfaces 121 and 141 to the most protruding portion of the PTC element body 10 is less than 1 mm. When the shortest distance W is less than 1 mm, the vicinity of the interface between the electrodes 12 and 14 and the PTC element body 10 is surely protected by the protective layer 20. As a result, since the PTC element body 10 becomes more difficult to be oxidized, it is possible to further suppress the deterioration of the PTC element body 10 when it receives a thermal history after a long period of time since its manufacture.

  Here, in order to confirm that the PTC element body 10 becomes more difficult to be oxidized when the shortest distance W is less than 1 mm, the following experiment was performed. That is, a thermal shock test and a trip operation test were performed on the PTC element 1, and changes in the room temperature resistance value before and after the test were examined.

  First, several types of PTC elements 1 having different thicknesses T of the protective layer 20 were prepared, and a thermal shock test was performed. The thickness T of the protective layer 20 is the thickness at which the protective layer 20 is thinnest in the vicinity of the exposed surface 100 of the PTC element body 10 and the interface between the PTC element body 1 and the electrodes 12 and 14. Point to. Each prepared PTC element 1 was left in the air for 180 days after manufacture. Before conducting the thermal shock test, the room temperature resistance value of each prepared PTC element 1 was measured to confirm the initial value. After confirmation, each PTC element 1 was subjected to thermal shock at 100 ° C. for 5 hours. The room temperature resistance value of each PTC element 1 after applying the thermal shock was measured, and the change in the room temperature resistance value of each PTC element 1 before and after the thermal shock was examined. The results are shown in FIGS. Examples 1 to 13 are PTC elements 1 in which the thickness T (described as T_MIN in FIG. 6) of the protective layer 20 is 3 μm or more. Examples 14 to 20 are PTC elements 1 in which the thickness T (described as T_MIN in FIG. 6) of the protective layer 20 is less than 3 μm.

  In the PTC elements 1 of Examples 1 to 13, the amount of change in the room temperature resistance value (described as ΔR in FIG. 6) was 20 mΩ or less. On the other hand, in the PTC elements 1 of Examples 14 to 20, there were many cases where the amount of change in the room temperature resistance value was 50 mΩ or more. In the thermal shock test, it is known that the amount of change in the room temperature resistance value increases as the oxidation of the PTC element body 10 progresses. Therefore, it was found that when the thickness T of the protective layer 20 is 3 μm or more, the PTC element body 10 is more difficult to be oxidized.

  Next, several types of PTC elements 1 having different thicknesses T of the protective layer 20 were prepared, and a trip operation test was performed. Each prepared PTC element 1 was left in the air for 180 days after manufacture. Prior to the trip operation test, the room temperature resistance value of each PTC element 1 was measured to confirm the initial value. After confirmation, each PTC element 1 was connected to an electric circuit (power supply 6V, 20A) and tripped. The room temperature resistance value of each PTC element 1 after the trip operation was measured, and the change in the room temperature resistance value of each PTC element 1 before and after the trip operation was examined. The results are shown in FIGS. In addition, Examples 1-13 show the PTC element 1 whose thickness T (it describes as T_MIN in FIG. 8) of the protective layer 20 is 3 micrometers or more. Examples 14 to 20 show PTC elements 1 in which the thickness T of the protective layer 20 (described as T_MIN in FIG. 8) is less than 3 μm.

  In the PTC elements 1 of Examples 1 to 13, the resistance change amount (described as ΔR in FIG. 8) was often 5 mΩ or less. On the other hand, in the PTC elements 1 of Examples 14 to 20, there were many cases where the amount of change in the room temperature resistance value was 5 mΩ or more. Similar to the thermal shock test, it is known that the change amount of the room temperature resistance value also increases in the trip operation test according to the oxidation of the PTC element body 10. Therefore, from the result of the trip operation test, it was found that when the thickness T of the protective layer 20 is 3 μm or more, the PTC element body 10 is more difficult to be oxidized.

  Subsequently, several types of PTC elements 1 having different shortest distances W were prepared. And in each PTC element 1, the thickness T of the protective layer 20 was measured. The results are shown in FIG. 10 and FIG. Examples 21-31 show the PTC element 1 in which the shortest distance W is 50 μm or more and less than 1 mm. Examples 32 to 40 show the PTC element 1 having the shortest distance W of 0 mm and the PTC element 1 having a length of 1 mm or more.

  In the PTC elements 1 of Examples 21 to 31, the thickness T of the protective layer 20 was 3.2 μm or more. On the other hand, in the PTC element 1 of Examples 32 to 40, the thickness T of the protective layer 20 was 2.8 μm or less. From this result, it is understood that if the shortest distance W from the end portion 200 of the protective layer 20 to the exposed surface 100 of the PTC element body 10 is less than 1 mm, the thickness T of the protective layer 20 is 3 μm or more.

  From the above test results, if the shortest distance W from the end portion 200 of the protective layer 20 located on the second main surface 121, 141 to the exposed surface 100 of the PTC element body 10 is less than 1 mm, the protective layer 20 Since the thickness T was 3 μm or more, it was confirmed that the PTC element body 10 was less likely to be oxidized.

  By the way, when the second main surfaces 121 and 141 of the present embodiment are viewed, only the peripheral portion near the exposed surface 100 of the PTC element body 10 is covered with the protective layer 20. Here, not only the peripheral portion but also the case where the entire region overlapping the PTC element body 10 on the second main surfaces 121 and 141 is covered with the protective layer 20 will be considered. Covering the entire region overlapping the PTC element body 10 with the protection layer 20 means that in the PTC element 1 shown in FIG. 2, the protection layer 20 is arranged so that the shortest distance W is the same as the width or length of the PTC element body 10. It is to spread. It has been confirmed by the above-described test that the PTC element body 10 is easily oxidized when the shortest distance W is 1 mm or more. Therefore, in the above case, that is, when the entire region overlapping the PTC element body 10 on the second main surfaces 121 and 141 is covered with the protective layer 20, the PTC element body 10 is likely to be oxidized. Easy to understand. In addition, when the protective layer 20 is overlaid on the entire region of the second main surfaces 121 and 141 that overlap the PTC element body 10, the thickness T of the protective layer 20 increases, so the PTC element body 1 and the electrode 12. , 14 is less likely to be exposed, and oxidation of the PTC element body 10 is suppressed. However, in this case, since the convex portions due to the surface tension of the protective layer 20 are formed on the second main surfaces 121 and 141, the stability of the PTC element 1 at the time of mounting is deteriorated. Moreover, the dimension of the PTC element 1 will also become large. Furthermore, since the process of laminating the protective layer 20 occurs, the manufacturing cost may increase. From the above, it is said that overlaying the protective layer 20 on the entire region of the second main surfaces 121 and 141 that overlaps the PTC element body 10 is an effective means for preventing the oxidation of the PTC element body 10. It ’s hard.

It is a perspective view of the PTC element concerning this embodiment. It is a side view when the PTC element concerning this embodiment is seen from the 2nd principal surface side of an electrode. It is sectional drawing of the PTC element along the III-III line of FIG. It is sectional drawing of the PTC element along the IV-IV line of FIG. It is sectional drawing of the other PTC element which concerns on this embodiment. It is a table | surface which shows the result of a thermal shock test. It is a graph which shows the result of a thermal shock test. It is a table | surface which shows the result of a trip operation test. It is a graph which shows the result of a trip operation test. It is a table | surface which shows the relationship between the shortest distance W and thickness T. It is a graph which shows the relationship between the shortest distance W and thickness T.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... PTC element, 10 ... PTC element | base_body, 12, 14 ... Electrode, 20 ... Protective layer, 100 ... Exposed surface, 120, 140 ... 1st main surface, 121 141, second main surface, 122, 142, side surfaces, 200, end portions.

Claims (1)

A PTC element body including a polymer matrix and conductive particles;
A first main surface to be bonded to the PTC element body, said first have a second major surface opposite the major surface, said pair of electrodes opposed to each other in some so as to sandwich the PTC element body When,
A protective layer covering a second outer surface excluding a first outer surface joined to the first main surface of the electrode among the outer surfaces of the PTC element body,
The part of the one electrode that does not sandwich the PTC element body extends to one side, and the part of the other electrode that does not sandwich the PTC element body extends to the other,
The protective layer extends to the second main surface of the electrode, and covers only a peripheral portion of the second main surface near the second outer surface;
When viewed from the second main surface side of the electrode, the shortest distance from the end portion of the protective layer located on the second main surface to the most protruding portion of the PTC element body is 50 μm or more, 1 mm Is less than
A PTC element having a thickness of 3.2 μm or more and 20.8 μm or less where the protective layer is thinnest in the vicinity of the interface between the PTC element body and the electrode.

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