JP3586178B2 - Organic positive temperature coefficient thermistor and manufacturing method thereof - Google Patents

Description

【００４０】
すなわち、表１のＲ−Ｔ特性測定後の変形の欄に示すように、電極にめっきや蒸着膜のみを施した場合（比較例）は、素体との熱膨張係数の違いから、熱膨張収縮の応力により素体や電極の変形やしわ、亀裂等の発生があるが、実施例１〜６のように、本発明の電極シートを素子に接合することにより、その多孔質構造で応力を緩和すると共に、電極膜のアンカー効果が高まり、これらの問題が改善され、しわや亀裂の発生が無くなるものと考えられる。
【００４１】
実施例１〜６のＲ−Ｔ特性測定の結果はそれぞれ図３、図４に示す通りであり、いずれも所望のＰＴＣ特性が得られることが判明した。また、図４中の下段に示す比較例の特性図から判るように、素体に単に電極をめっきにより付けた場合には初期抵抗値が大となる。
【００４２】
（電極シートの組成について）
電極シートを作製する際の有機ポリマー、低分子有機化合物、導電性フィラーの組成を変化させて初期抵抗値、成形性を観察した結果を表２に示す。ここで、有機ポリマーと低分子有機化合物との比は、１：１および１：２（体積比）とし、それぞれの場合について、導電性フィラーの混合率（ｖｏｌ％）を５〜１００の範囲で変化させた。また、他のサンプルの作製条件は実施例１と同様に作製した。
【００４３】
表２に示すように、サンプルの初期抵抗値は、導電性フィラーの添加量に大きく依存し、特に導電性フィラーが１０〜７０ｖｏｌ％で低抵抗を示し、１０ｖｏｌ％未満であると抵抗値が高くなり、一方７０ｖｏｌ％を超えるとサンプルを作製することが困難となった。従って、低分子有機化合物除去前の電極シートの導電性フィラーの含有率は１０〜７０ｖｏｌ％であることが好ましい。
【００４４】
【表２】

【図面の簡単な説明】
【図１】本発明によるサーミスタの断面構造を示す図であり、（Ａ）は低分子有機化合物除去前の電極シートの断面図、（Ｂ）はその低分子有機化合物を除去した後の状態を示す断面図、（Ｃ）は該電極を素体に接合した状態を示す断面図である。
【図２】（Ａ）は本発明によるサーミスタの電極の表面構造の一例を示す写真図、（Ｂ）はその断面構造を示す写真図である。
【図３】本発明の実施例１〜４における抵抗−温度特性図である。
【図４】本発明の実施例５、６および比較例における抵抗−温度特性図である。
【図５】（Ａ）は従来のサーミスタの一例を示す側面図、（Ｂ）はその熱膨張、収縮による電極および素体の変化を示す側面図である。
【符号の説明】
１：素体、３：有機ポリマー、４：低分子有機化合物、５：導電性フィラー、６：電極[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic positive temperature coefficient thermistor and a method for manufacturing the same, and more particularly, to an electrode and a method for manufacturing the same.
[0002]
[Prior art]
It is known that a conductive composition in which a conductive substance such as carbon black or metal powder is dispersed in an organic polymer such as polyethylene or polypropylene exhibits PTC characteristics. Such compositions are disclosed, for example, in U.S. Pat. Nos. 3,591,526 and 3,673,121. Further, as a method for forming these electrodes, a method of applying metal plating (Japanese Patent Publication No. 4-44401), a method of burying a reticulated electrode made of a metal (Japanese Patent Publication No. 2-160022), and a method of sputtering (Japanese Patent Application Laid-Open No. Sho 62-142). No. 85401).
[0003]
[Problems to be solved by the invention]
As shown in FIG. 5A, in an organic positive temperature coefficient thermistor in which an electrode 2 is joined to the front and back surfaces of a PTC element 1 having the above-described composition, when the electrode 2 is formed by metal plating as described above, Alternatively, when the electrode 2 is formed by sputtering, the thermal expansion and contraction of the PTC body 1 causes the body 1 to deform, the electrode 2 to be wrinkled or cracked, There is a problem that the resistance value increases due to reasons such as peeling from No. 1. On the other hand, when a mesh electrode is used as the electrode 2, there is a problem that the resistance does not decrease for the shape of the element body 1 and the resistance value is unstable.
[0004]
In view of the above problems, the present invention provides an organic positive temperature coefficient thermistor which eliminates thermal expansion and contraction of the elementary body, deformation of the elementary body due to shrinkage, generation of wrinkles and cracks in the electrode, and obtains a stable resistance value, and a method of manufacturing the same. The purpose is to provide.
[0005]
[Means for solving the problem, functions and effects]
The organic positive temperature coefficient thermistor according to claim 1, which has an element having a PTC characteristic in which a conductive substance is dispersed in an organic polymer, and has at least a pair of electrodes on front and back surfaces of the element. ,
An electrode having a porous structure comprising an organic polymer and a conductive filler is provided .
The organic positive temperature coefficient thermistor according to claim 2 is the method according to claim 1, wherein
The porous structure of the electrode was realized by removing the low-molecular organic compound with an organic solvent or water from a molded article formed by mixing an organic polymer, a conductive filler, and a low-molecular organic compound into a sheet. characterized in that <br/> that one.
[0006]
As described above, by forming the entire electrode into a porous structure including the organic polymer and the conductive filler, the electrode expands and contracts in accordance with the thermal expansion and contraction of the element body, thereby alleviating the stress. Also, generation of wrinkles and cracks in the electrode is prevented. In addition, as described above, by relaxing the stress, the bonding of the electrode to the element body is maintained in a good state, and the resistance value is stabilized. A thermistor with such characteristics is useful for short-circuiting the charge / discharge circuit of a battery, locking a small motor typified by an automobile door lock motor, and preventing overcurrent due to short-circuiting of a telephone communication circuit or information equipment. is there.
[0007]
Organic PTC thermistor according to claim 3, in claim 1 or 2,
A part of the electrode is embedded in the surface of the element body by thermocompression bonding.
[0008]
By embedding a part of the electrode by thermocompression bonding as described above, the electrode is firmly joined to the element body, and the resistance value is further stabilized.
[0009]
The organic positive temperature coefficient thermistor according to claim 4 is the method according to any one of claims 1 to 3,
The organic polymer constituting the elementary body is polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl chloride, polyvinyl acetate, an ionomer resin, or a copolymer thereof, a polymer selected from the group of thermoplastic elastomers,
The conductive filler, carbon black, graphite, carbon fiber, conductive whisker, conductive ceramic powder, or nickel, copper, gold, silver, iron, that one or more of the metal particles of chromium Features.
[0010]
By selecting such a material, it is possible to obtain a thermistor having more effective characteristics in terms of durability and resistance value stability.
[0011]
The method of manufacturing an organic positive temperature coefficient thermistor according to claim 5 , comprising a body having a PTC property in which a conductive substance is dispersed in an organic polymer, and having at least a pair of electrodes on the front and back surfaces of the body. A method for manufacturing a thermistor,
Mixing the organic polymer, conductive filler and low molecular weight organic compound to form a sheet,
By removing the low-molecular-weight organic compound from the sheet-like molded product with an organic solvent or water, an electrode sheet material is obtained,
The electrode sheet material is thermocompression-bonded to a material having PTC characteristics to obtain a thermistor material.
[0012]
According to such a manufacturing method, a thermistor having excellent characteristics according to claim 1 can be obtained.
[0013]
The method for manufacturing an organic positive temperature coefficient thermistor according to claim 6 is the method according to claim 5 , wherein
The content of the conductive filler in the sheet-like molded product for an electrode is 10 to 70 vol%.
[0014]
If the content of the sheet-like conductive filler for an electrode is less than 10 vol%, sufficient conductivity cannot be obtained, and if it exceeds 70 vol%, moldability deteriorates.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
As an example, a thermistor to which the present invention is applied is one in which the electrodes 2 are formed on the front and back surfaces of the element body 1 as shown in FIG. The electrodes 2 may be provided not only in pairs but also in pairs. In order to obtain a body 1 having PTC characteristics, an organic polymer and a conductive substance are mixed and formed into a sheet. Examples of the organic polymer for forming the element body include polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl chloride, polyvinyl acetate, an ionomer resin, or a copolymer thereof, or a polymer selected from the group of thermoplastic elastomers. Used.
[0016]
Examples of the conductive substance in the element body 1 include carbon black and graphite such as furnace black and acetylene black, or carbon fibers, conductive whiskers, conductive ceramic powder or nickel, copper, gold, silver, iron, and chromium. One or more of the metal particles such as described above are used.
[0017]
Such an organic polymer and a conductive substance are kneaded by a kneading machine such as a Banbury mixer or a mixing roll at, for example, 120 to 250 ° C. for 15 to 60 minutes, and then formed into a sheet or film by a heating roll or a hot press. I do. In this case, although it is not always necessary, since the fluidity of the polymer after the expression of PTC is suppressed and the resistance value is stabilized, the electron beam and its efficiency are increased as disclosed in US Pat. No. 3,269,862. For this purpose, electron beam crosslinking with the addition of a crosslinking assistant may be performed, or chemical crosslinking may be performed. Further, as disclosed in Japanese Patent Publication No. 11575/1992, after a silane compound is grafted onto an organic polymer in the presence of a free radical generator, it is contacted with water or an aqueous catalyst in the presence of a silanol condensation catalyst. For example, by performing a method such as water crosslinking, the fluidity of the polymer after the expression of PTC is suppressed, and the resistance value is stabilized.
[0018]
The electrode sheet according to the present invention is bonded to both main surfaces of the thus obtained sheet-like molded body for a body by thermocompression bonding. There is no restriction on the material of the conductive filler of the electrode sheet, and one or more of carbon fibers, conductive whiskers, conductive ceramic powder or metal particles such as nickel, copper, gold, silver, iron, and chromium are used. Can be The electrode sheet is composed of a thermoplastic organic polymer such as polyethylene, a low molecular weight organic compound compatible with the organic polymer such as paraffin wax, and the conductive filler. Since the low molecular weight organic compound has a relatively low molecular weight and needs to be removed in a later step, it must be soluble in an organic solvent or water.
[0019]
An electrode sheet is prepared as follows using such an organic polymer, a low molecular weight organic compound, and a conductive filler. As shown in FIG. 1 (A), the organic polymer 3, the low molecular weight organic compound 4, and the conductive filler 5 are kneaded by a kneader such as a Banbury mixer or a mixing roll at a temperature equal to or higher than the melting point of the organic polymer. It is formed into a sheet by a hot press or the like so as to have a desired thickness.
[0020]
Next, the low-molecular-weight organic compound 4 was removed with an organic solvent or water that dissolves the low-molecular-weight organic compound 4, and as shown in FIG. 1B, the portion filled with the low-molecular-weight organic compound 4 became a cavity. An electrode sheet 6 having a porous structure is obtained. Such an electrode sheet 6 has a structure in which the conductive filler 5 contained therein is exposed and a large number of holes are formed in a cave shape up to the inside of the sheet. Therefore, both main surfaces of the element body 1 made of a PTC molded product When thermocompression bonding is performed, the anchor effect with the surface of the molded body is much larger than that of the conventional structure, so that the bonding strength of the electrode sheet, the stabilization of the element body 1 and the reduction in resistance can be achieved.
[0021]
At this time, if the diameter of the entrance portion of the hole of the electrode sheet is as small as less than 0.1 μm, the anchor effect at the time of thermocompression bonding cannot be obtained, and the element body cannot be stabilized and the resistance cannot be reduced. The mixing ratio between the organic polymer 3 and the low molecular weight organic compound 4 and the conductive filler 5 and the particle size of the conductive filler 5 must be set so that the diameter of the pores on the surface of the electrode sheet is at least 0.1 μm or more. . For these reasons, the preferred content of the conductive filler 5 in the electrode sheet containing the low molecular weight organic compound 4 is 10 to 70 vol%. The preferred average particle size of the conductive filler 5 is 0.05 μm to 500 μm. If the average particle size is less than 0.05 μm, it is difficult to obtain PTC characteristics.
[0022]
If it is necessary to attach a metal lead terminal electrode to the electrode after thermocompression bonding of the electrode sheet to the element body 1, the surface of the electrode sheet is further subjected to chemical plating, electroplating, or vacuum return plating such as evaporation or sputtering. Form a film. When such a metal film is formed, the adhesion strength to the lead terminal electrode can be easily obtained.
[0023]
After thermocompression bonding of the electrode sheet having a porous structure to both sides of the sheet-like PTC molded article as described above, processing to a desired size by punching or cutting, and further, if necessary, soldering a metal lead wire, and then Alternatively, the terminal may be molded with an insulating resin as an exterior, or a conductive adhesive may be applied to the electrode, and then another terminal made of metal may be adhered. Hereinafter, specific examples of the present invention will be described.
[0024]
(Example 1)
[Production of sheet-like PTC molded product]
As shown in Japanese Patent Publication No. 11575/1992, a silane coupling agent (KBC1003 manufactured by Shin-Etsu Chemical Co., Ltd.) was used for high-density polyethylene (hereinafter referred to as HDPE) (HY540 manufactured by Mitsui Chemicals, Inc.) as an organic polymer. 10 parts by weight based on 100 parts by weight of the polymer, and 2,5 dimethyl-2,5 (t-butylpaoxin) hexyne-3, which is an organic peroxide for radicalizing the polymer, was also added to 1 part by weight. The mixture was heated and kneaded at 150 ° C. for 1 hour in a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.), and a grafted resin was prepared with a twin screw extruder.
[0025]
Next, 30 vol% of filamentary nickel powder (# 255 manufactured by INCO) was added to the grafted resin, mixed, and kneaded at 150 rpm for 1 hour at a rotation speed of 25 rpm to obtain a PTC composition. At 150 ° C. and 2.94 MPa to obtain a sheet molded product having a thickness of about 1 mm.
[0026]
The obtained sheet for elementary body was immersed in water at 60 ° C., and 5 parts by weight of dibutyltin dilaurate as a crosslinking catalyst was added as a catalyst and left for 8 hours, and then dried at 60 ° C. for 12 hours by a vacuum dryer. Crosslinking was completed.
[0027]
[Preparation of electrode sheet]
50 vol% of filamentary nickel powder (# 110, manufactured by INCO) as a conductive filler of the electrode sheet, 20 vol% of HDPE as an organic polymer (HY540, manufactured by Mitsui Chemicals, Inc.), and ethylene homopolymer as a low molecular weight organic compound ( 30 vol% of Nippon Seiro Wax Co., Ltd.) was heated and kneaded at 150 ° C. for 30 minutes using a Labo Plastomill, and then hot-pressed at 150 ° C.-2.94 MPa with a hot press to obtain a thickness of about 0.1 mm. An electrode sheet molded product was obtained.
[0028]
The obtained electrode sheet molded product was cut into a size of 50 mm × 100 mm, immersed in toluene, washed with an ultrasonic cleaner at 20 Hz for 1 hour to completely remove ethylene homopolymer, and then washed with acetone in 25%. The resultant was immersed at 10 ° C. for 10 minutes to replace toluene with acetone, and the solvent was completely evaporated at 60 ° C. for 8 hours using a vacuum dryer to obtain an electrode sheet.
[0029]
[Preparation of sample]
The element body sheet prepared as described above is overlapped so as to be sandwiched between two electrode sheets, preheated at 150 ° C. for 3 minutes by a hot press, and then hot pressed at 150 ° C.-2.94 MPa. A 0.5 mm thick sample sheet was obtained. Furthermore, electroless plating of 1-2 μm was applied to both electrode surfaces of this sample sheet. Then, this sample sheet was punched into a size of 10 mφ to obtain a sample.
[0030]
(Example 2)
A sample was produced under the same conditions as in Example 1 except that flake-like nickel powder (manufactured by INCO / HCA-1) was used as the conductive filler.
[0031]
(Example 3)
A sample was produced under the same conditions as in Example 1 except that WC powder (manufactured by Tokyo Tungsten Co., Ltd./WC05N) was used as the conductive filler.
[0032]
(Example 4)
A sample was produced under the same conditions as in Example 1 except that a non-oxidized ceramic conductive powder (TICM # 100, manufactured by Nippon Shinkin Co., Ltd.) was used as the conductive filler.
[0033]
(Example 5)
A sample was produced under the same conditions as in Example 1 except that a filamentary nickel powder (manufactured by INCO / # 210) was used as the conductive filler.
[0034]
(Example 6)
A sample was produced under the same conditions as in Example 1 except that a filamentary nickel powder (manufactured by INCO / # 255) was used as the conductive filler.
[0035]
(Comparative example)
An element was produced in the same manner as in Example 1, and an electrode was produced by a method described in Japanese Patent Publication No. 4-44001 without using an electrode sheet. Specifically, the PTC composition was immersed in a chromic acid mixture (high chromium mixture), etched at 60 ° C. for 15 minutes, washed with water, and dried at 100 ° C. for 1 hour by a vacuum dryer. Furthermore, it was immersed in a plating bath using an aqueous solution of hydrochloric acid 0.06 ml / l to form a cathode, and on the other hand, a phosphoric copper-containing plate was used as an anode to perform electroplating with a thickness of 1 to 2 μm.
[0036]
(Observation of microstructure)
FIG. 2A shows a photograph of the surface of the electrode manufactured according to Example 1, and FIG. 2B shows a photograph of a cross section thereof. As can be seen from these figures, the electrodes according to the invention show a porous structure.
[0037]
(Characteristic measurement)
[Initial resistance value] The initial resistance value of each sample was measured by a four-terminal method using a digital multimeter.
[Electrode adhesion strength] A peeling test was carried out using an adhesive tape (Sony Chemical T4000) to check the electrode adhesion strength. Here, the peeling test refers to whether the electrode is adhered to the adhesive surface when the adhesive tape is attached so that the entire electrode portion of the sample is in close contact, and then the tape is peeled off instantaneously. This is a method of checking the adhesion strength of the sheet.
[Resistance-Temperature (RT) Characteristics] The resistance-temperature characteristics of each sample from room temperature of 25 ° C to 140 ° C were measured.
[Presence of Deformation after Resistance-Temperature (RT) Characteristics] For each sample, the presence or absence of deformation after resistance-temperature characteristics measurement was observed.
[0038]
(Evaluation)
As shown in the results of the initial resistance value and the peeling test in Table 1, in the case of the conventional plating only (Comparative Example), the adhesion between the electrode and the element was weak and the resistance value was high. On the other hand, in the case of Examples 1 to 6 of the present invention, by joining the electrode sheet before forming the plating or vapor-deposited film on the sheet-like PTC molded product serving as the elementary body, the initial resistance value is reduced, and the thermal expansion, It has been found that stress relaxation occurs when thermal stress is applied due to shrinkage, and there is a reinforcing effect such as deformation of the element body, electrode deformation and crack prevention.
[0039]
[Table 1]

[0040]
That is, as shown in the column of deformation after measurement of RT characteristics in Table 1, when only plating or a vapor-deposited film was applied to the electrode (Comparative Example), the thermal expansion coefficient was different from that of the element body. Deformation, wrinkles, cracks, etc. of the elementary body and the electrode may occur due to the shrinkage stress. However, as in Examples 1 to 6, by joining the electrode sheet of the present invention to the element, the stress is reduced by the porous structure. It is considered that these effects are alleviated, the anchor effect of the electrode film is enhanced, these problems are improved, and wrinkles and cracks are eliminated.
[0041]
The results of the RT characteristic measurement of Examples 1 to 6 are as shown in FIGS. 3 and 4, respectively, and it was found that the desired PTC characteristic was obtained in each case. Further, as can be seen from the characteristic diagram of the comparative example shown in the lower part of FIG. 4, when the electrode is simply plated on the element body, the initial resistance value becomes large.
[0042]
(About composition of electrode sheet)
Table 2 shows the results of observing the initial resistance value and moldability by changing the composition of the organic polymer, the low molecular weight organic compound, and the conductive filler when preparing the electrode sheet. Here, the ratio of the organic polymer to the low molecular weight organic compound is 1: 1 and 1: 2 (volume ratio), and in each case, the mixing ratio (vol%) of the conductive filler is in the range of 5 to 100. Changed. The other samples were manufactured in the same manner as in Example 1.
[0043]
As shown in Table 2, the initial resistance value of the sample greatly depends on the amount of the conductive filler added. In particular, the conductive filler has a low resistance at 10 to 70 vol%, and has a high resistance value at less than 10 vol%. On the other hand, if it exceeds 70% by volume, it becomes difficult to prepare a sample. Therefore, the content of the conductive filler in the electrode sheet before the removal of the low-molecular organic compound is preferably 10 to 70 vol%.
[0044]
[Table 2]

[Brief description of the drawings]
FIG. 1 is a view showing a cross-sectional structure of a thermistor according to the present invention, wherein (A) is a cross-sectional view of an electrode sheet before a low-molecular organic compound is removed, and (B) is a state after the low-molecular organic compound is removed. FIG. 2C is a cross-sectional view showing a state where the electrode is joined to a body.
2A is a photograph showing an example of a surface structure of an electrode of a thermistor according to the present invention, and FIG. 2B is a photograph showing a sectional structure thereof.
FIG. 3 is a resistance-temperature characteristic diagram in Examples 1 to 4 of the present invention.
FIG. 4 is a resistance-temperature characteristic diagram in Examples 5 and 6 of the present invention and a comparative example.
FIG. 5A is a side view showing an example of a conventional thermistor, and FIG. 5B is a side view showing changes in electrodes and element bodies due to thermal expansion and contraction thereof.
[Explanation of symbols]
1: elementary body, 3: organic polymer, 4: low molecular organic compound, 5: conductive filler, 6: electrode

Claims (6)

An organic positive temperature coefficient thermistor having a PTC element body in which a conductive substance is dispersed in an organic polymer, and having at least a pair of electrodes on the front and back surfaces of the element body,
An organic positive temperature coefficient thermistor comprising an electrode having a porous structure comprising an organic polymer and a conductive filler . In claim 1,
The porous structure of the electrode was realized by removing the low-molecular organic compound with an organic solvent or water from a molded article formed by mixing an organic polymer, a conductive filler, and a low-molecular organic compound into a sheet. organic PTC thermistor according to claim in which <br/> that one. In claim 1 or 2,
An organic positive temperature coefficient thermistor, wherein a part of said electrode is embedded in the surface of said element body by thermocompression bonding. In any one of claims 1 to 3,
The organic polymer constituting the elementary body is polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl chloride, polyvinyl acetate, an ionomer resin, or a copolymer thereof, a polymer selected from the group of thermoplastic elastomers,
The conductive material is carbon black, graphite, carbon fiber, conductive whiskers,
An organic positive temperature coefficient thermistor comprising conductive ceramic powder or at least one of nickel, copper, gold, silver, iron and chromium metal particles. A method for producing an organic positive temperature coefficient thermistor having a PTC element body in which a conductive substance is dispersed in an organic polymer, and having at least a pair of electrodes on the front and back surfaces of the element body,
A mixture of an organic polymer, a conductive filler and a low molecular organic compound is formed into a sheet,
By removing the low-molecular-weight organic compound from the sheet-like molded product with an organic solvent or water, an electrode sheet material having a porous structure including an organic polymer and a conductive filler is obtained.
A method for producing an organic positive temperature coefficient thermistor, characterized by obtaining said thermistor material by thermocompression bonding said electrode sheet material to a material having PTC characteristics. In claim 5,
The method for producing an organic positive temperature coefficient thermistor, wherein the content of the conductive filler in the electrode sheet-shaped molded product is 10 to 70 vol%.

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