JP4170980B2 - POLYMER PTC ELEMENT AND POLYMER PTC ELEMENT - Google Patents

Description

  The present invention relates to a polymer PTC element body and a polymer PTC element which are used as a temperature sensor and an overcurrent protection element and have a PTC (Positive Temperature Coefficient) characteristic in which a resistance value increases as the temperature rises.

  Conventionally, a PTC thermistor element utilizes a PTC characteristic (positive resistance-temperature characteristic), for example, a self-control heating element, a temperature sensor, a current limiting element, an overcurrent protection element (for example, an overcurrent of a lithium ion battery). As a protection element), it is used for circuit protection of electronic equipment.

When this PTC thermistor element is used for the above applications, mainly,
(1) Low room temperature resistance value during non-operation (2) Large rate of change between room temperature resistance value during non-operation and resistance value during operation (3) Amount of change in resistance value when repeatedly operated (Difference between the initial resistance value and the resistance value after repeated operation) is small (4) Excellent low-speed shut-off characteristics (5) Low heat generation temperature of the element (6) Miniaturization, weight reduction, and low cost It is required to have characteristics such as

  As such a PTC thermistor element, an element having a thermistor body made of a ceramic material has been conventionally used, and this type of PTC thermistor element is particularly preferable among the above required characteristics (1) to (6). The characteristics of (4), (5) and (6) were not preferable.

Therefore, in recent years, a polymer PTC thermistor element (hereinafter also referred to as a polymer PTC element) having characteristics superior to those of a PTC thermistor element using the ceramic material has been developed. This polymer PTC element uses a thermistor body in which conductive fine particles such as C, Ni, and Cu are dispersed in a crystalline polymer (thermoplastic resin), and is disclosed in Patent Document 1 and Patent Document 2 below. Has been. The increase in the resistance value in this polymer PTC element is considered to be because the crystalline polymer melts and expands as the ambient temperature increases, and the conductive path constructed by the conductive fine particles is broken.
US Pat. No. 3,243,753 US Pat. No. 3,351,882 JP 2004-88079 A US Pat. No. 5,378,407 Japanese Patent Laid-Open No. 5-470503 Japanese Examined Patent Publication No. 62-16523 JP-A-1-231284 Japanese Patent Laid-Open No. 3-132001 Japanese Patent Laid-Open No. 9-27383 Japanese Patent Laid-Open No. 11-168005

The inventors have disclosed a polymer PTC element that realizes further improvement in characteristics (2) and (3) among the above required characteristics in Patent Document 3. As a result of repeated research on the technology, it was confirmed that Ni ₃ C was generated in the kneaded product after the heat-kneading of the crystalline polymer and Ni powder shown in Patent Document 3 above. The present inventors discovered that the amount of Ni ₃ C produced has a correlation with the amount of change in operating temperature and the room temperature resistance value during non-operation.

  This operating temperature is a temperature at which the resistance value of the PTC thermistor element suddenly increases. The PTC thermistor element has an operating temperature at the initial stage of use and after repeated operation, as in (1) to (6) above. It is required that it does not change much. Further, it is preferable that the resistance value (room temperature resistance value) when not operating as an overcurrent protection element is as low as possible.

  Accordingly, the present invention has been made to solve the above-described problems, and is a polymer PTC element body and a polymer that have a low resistance value during non-operation and that suppress an operation temperature change due to repeated operation-non-operation. An object is to provide a PTC element.

The polymer PTC element body according to the present invention is produced by heat-kneading a thermoplastic resin and Ni powder, and the peak of the (002) plane of Ni ₃ C within an X-ray diffraction angle range of 30 to 60 degrees. the ratio to the peak intensity _{I B} of (200) plane of the Ni intensity _{I a (I} a / _{I B)} is being in the range of from 0.0030 to 0.0621.

This polymer PTC body is produced by heat-kneading a thermoplastic resin and Ni powder. The inventors have found that during the heat-kneading, the carbon in the thermoplastic resin reacts with the Ni powder to produce Ni ₃ C. Then, the X-ray diffraction angle 30 to 60 degrees, the ratio for the Ni ₃ C peak intensity ratio of Ni (Ni ₃ (200 of Ni peak intensity _{I A} of C of (002) plane) surface of the peak intensity _{I B} If (I _A / I _B )) is within the range of 0.0030 to 0.0621 , the amount of Ni ₃ C contained in the polymer PTC element is a suitable amount, and the polymer PTC element The inventors newly found that the resistance value during non-operation becomes low, and that the change in operating temperature due to repeated operation-non-operation is significantly suppressed.

A polymer PTC element according to the present invention includes a pair of electrodes opposed to each other and a polymer PTC element body disposed between the pair of electrodes. The polymer PTC element body is obtained by heating and kneading a thermoplastic resin and Ni powder. made Te, and, within the scope of X-ray diffraction angle 30 to 60 degrees, Ni ₃ C of (002) plane peak intensity _I ratio to the peak intensity _{I B} of (200) plane of Ni _{a (I} a / I _B ) is in the range of 0.0030 to 0.0621 .

This polymer PTC element includes a pair of electrodes, and a polymer PTC element produced by heating and kneading a thermoplastic resin and Ni powder. The inventors have found that when the polymer PTC element body is prepared by heating and kneading, carbon in the thermoplastic resin reacts with Ni powder to produce Ni ₃ C. Then, the X-ray diffraction angle 30 to 60 degrees, the ratio for the Ni ₃ C peak intensity ratio of Ni (Ni ₃ (200 of Ni peak intensity _{I A} of C of (002) plane) surface of the peak intensity _{I B} If (I _A / I _B )) is within the range of 0.0030 to 0.0621 , the amount of Ni ₃ C contained in the polymer PTC element is a suitable amount, and the polymer PTC element The inventors newly found that the resistance value during non-operation becomes low, and that the change in operating temperature due to repeated operation-non-operation is significantly suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the resistance value at the time of non-operation and the polymer PTC element | base_body and polymer PTC element with which the operating temperature change by repetition of operation | movement non-operation was suppressed are provided.

  Hereinafter, with reference to the accompanying drawings, a mode that is considered to be the best in carrying out a polymer PTC element body and a polymer PTC element according to the present invention will be described in detail. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  As shown in FIG. 1, a polymer PTC element (hereinafter simply referred to as a PTC element) 10 includes a pair of electrodes 12A and 12B facing each other and a polymer PTC element disposed between the pair of electrodes 12A and 12B. And a body (hereinafter simply referred to as a PTC element body) 14.

  Each electrode 12A, 12B has, for example, a sheet-like shape, and the material, dimensions, and the like are not particularly limited as long as they have conductivity that functions as an electrode of the PTC element 10.

  The PTC element body 14 is a molded body mainly composed of a thermoplastic resin and Ni powder. Hereinafter, a procedure for producing the PTC element body 14 will be described with reference to FIG.

  First, when producing the PTC element body 14, the thermoplastic resin and Ni powder as raw materials are weighed in a necessary amount (S10) and mixed so that they are uniformly mixed (S12). And the obtained mixture is heat-kneaded as a heat treatment (S14).

  The kneading operation may be performed by using a known kneading technique, using a kneading means such as a kneader, an extruder, a mill, or the like, and a temperature equal to or higher than the melting point of the thermoplastic resin (preferably 5 to 40 ° C. higher than the melting point) ) For about 10 to 120 minutes.

  By adjusting the melting / kneading conditions such as the melting / kneading temperature and kneading time in this kneading, the degree of dispersion (dispersion state) of the Ni powder in the PTC body 14 can be adjusted. At the time of the adjustment, it is necessary to find out so-called proper melting and kneading conditions by, for example, performing the same sample multiple times of melting and kneading. Therefore, as a technique for finding out such appropriate conditions, the inventors have found a method for confirming and controlling the dispersion of Ni powder in the kneaded material by the magnetization of the kneaded material, which is disclosed in Patent Document 3 above. However, the method was also used for producing the PTC element body 14.

  The kneaded product obtained as described above is molded into a sheet shape having a predetermined thickness by roll molding or press molding (S16), and Ni, Cu, Au, etc. are formed on both sides of the obtained sheet-shaped molded body. The electrode sheet made of is thermocompression bonded (S18). In addition, before this thermocompression bonding, both surfaces of the sheet-shaped molded body are roughened by sintering or etching Ni powder, so that the electrode sheet is firmly bonded to the sheet-shaped molded body. .

  Then, a crosslinking process is performed (S20). As a crosslinking method, a known crosslinking method such as radiation crosslinking, chemical crosslinking with an organic peroxide, or water crosslinking by grafting a silane coupling agent and condensation reaction of silanol groups can be used. Next, by cutting the sheet-shaped molded body to which the electrode sheet is attached into individual element shapes (S22), the electrode sheet becomes the electrodes 12A and 12B, and the sheet-shaped molded body becomes the PTC element body 14, 1 is completed.

  The thermoplastic resin used in the method for producing the PTC element body 14 described above is preferably a crystalline polymer, and its melting point is preferably in the range of 70 to 170 ° C.

  Specific examples of this thermoplastic resin include (1) polyolefin (eg, polyethylene), (2) at least one olefin (eg, ethylene, propylene), and at least one polar group-containing olefinically unsaturated monomer. (3) vinyl halide and vinylidene polymers (for example, polyvinyl chloride, polyvinyl fluoride, polyvinylidene fluoride), (4) ) Polyamide (eg 12-nylon), (5) polystyrene, (6) polyacrylonitrile, (7) thermoplastic elastomer, (8) polyethylene oxide, polyacetal, (9) thermoplastic modified cellulose, (10) ) Polysulfones, (11) Polymethyl (meth) Kurire - door, and the like.

  More specifically, (1) high density polyethylene [for example, trade name: Hi-Zex 2100JP (manufactured by Mitsui Chemicals), Marlex 6003 (manufactured by Philippe), etc.], (2) low density polyethylene [for example, trade name: LC500 ( Nippon Polychem Co., Ltd.), DYMH-1 (Union Carbide Co., Ltd.), etc.], (3) Medium density polyethylene [eg, trade name: 2604M (Gulf Co., Ltd.), etc.], (4) Ethylene-ethyl acrylate copolymer -[E.g., trade name: DPD6169 (manufactured by Union Carbide)], (5) ethylene-acrylic acid copolymer [e.g., trade name: EAA455 (made by Dow Chemical Co., Ltd.)], (6) hexafluo Ethylene-tetrafluoroethylene copolymer [for example, trade name: FEP100 (manufactured by DuPont), etc.], (7) Polyvinylil Nfuruoraido [for example, trade name: Kynar461 (Penbaruto Co., Ltd.), etc.], and the like.

  As the thermoplastic resin, only one kind of the above-described resins may be used, or two or more kinds may be used in combination, or those having a structure in which different kinds of thermoplastic resins are cross-linked may be used. .

  In the present embodiment, a polymer (mixed polyethylene) in which (1) high density polyethylene and (2) low density polyethylene are mixed to broaden the base (distribution region) of the molecular weight distribution is used. The mixing ratio was 5 to 50 wt% for high density polyethylene and 50 to 95 wt% for low density polyethylene.

  If necessary, an antioxidant for preventing thermal deterioration of the mixed polyethylene (crystalline polymer) can be added. Examples of such antioxidant include phenols. , Organic sulfurs, phosphites and the like. Furthermore, as a low melting point component, polyethylene or polypropylene having a lower molecular structure can be added and mixed in the same manner. However, polyethylene, polypropylene, and the like having a low molecular structure are deformed in the PTC element 10 due to repeated expansion and contraction in the operation-non-operation of the PTC element 10, and may cause segregation in some cases. Must be determined.

  In addition, it is preferable that the molecular weight of a thermoplastic resin is 100,000-5 million in the weight average molecular weight Mw, More preferably, it is 200,000-2 million. When the weight average molecular weight Mw of the thermoplastic resin is smaller than the above range, problems such as rapid deterioration of the polymer and increase in device characteristics over time and characteristic variations occur. On the other hand, when the weight average molecular weight Mw of the thermoplastic resin is larger than the above range, it is not suitable for the practical temperature range of general electronic components.

  Moreover, as Ni powder used for the manufacturing method of the PTC element | base_body 14 mentioned above, the normal Ni powder marketed is mixed with single powder or other kinds of conductive powder (C, WC, Fe, etc.) It can also be used as a powder. Ni powder is a conductive fine particle suitable for downsizing and low power consumption of the PTC element 10, and is excellent in economy. Conductive powders other than Ni powder are not very suitable for use in the PTC element 10 because of their strong catalytic action, too high resistance, and poor economic efficiency.

The Ni powder preferably has a specific surface area obtained by the BET 1-point method in the range of ¹ to 20 m ² · g ⁻¹ . The Ni powder is preferably Ni powder obtained by [Ni (CO) ₄ → Ni + 4CO]. This is because the Ni powder produced by the decomposition reaction can control the particle size and particle shape within a suitable range depending on the reaction conditions.

  And it is preferable to contain this Ni powder with the content rate of 75-90 wt% with respect to the said thermoplastic resin (mixed polyethylene). Here, when the Ni powder content is less than 75 wt%, the PTC element 10 has a high operating resistance, and it is difficult to produce a PTC element body 14 at a practical level. On the other hand, when the Ni powder content exceeds 90 wt%, it becomes difficult to partially agglomerate the Ni powder in the PTC element 10 and a short circuit due to overcurrent is likely to occur. The situation that it does not sufficiently function as an element is invited.

The inventors have now discovered that Ni ₃ C is produced when the thermoplastic resin described above and Ni powder are heated and kneaded. Such generation of Ni ₃ C is due to the reaction between C in the thermoplastic resin and Ni in the Ni powder due to the action of heat and (shear) pressure during kneading as in the generation model shown in FIG. It is believed that there is. That is, in the thermoplastic resin in which radicals are generated in a side chain as shown in FIG. 3A, Ni ions are substituted with radical hydrogen ions as shown in FIG. 3B. Then, when the radical substituted with the Ni ions moves (see FIG. 3C), the radical is separated as Ni ₃ C as shown in FIG. By such a separation of radical transfer and Ni 3 _C are repeated, one after another Ni 3 _C in a thermoplastic resin is produced during kneading. That is, during the heat-kneading, the polymer molecular structure is changed to lower molecular weight, and Ni ₃ C is gradually generated.

We, the amount of the thus Ni 3 _C, which has been generated is, the effects on the PTC element 10 was subjected to various experiments. The amount of Ni ₃ C produced was determined by determining the peak intensity ratio of Ni ₃ C / Ni using an X-ray diffractometer. This particular, the peak intensity of the _Ni 3 C (002) plane as the peak intensity of the Ni ₃ C, employing a peak intensity of Ni (200) surface as the peak intensity and Ni.

As a result, Ni ₃ C produced in the PTC element body 14 is an unstable substance, and the amount of Ni ₃ C produced is greatly involved in the behavior of the temperature-resistance curve (RT curve) of the PTC element 10. It became clear to do. This is considered to be because Ni ₃ C is a factor that adversely affects the thermal characteristics and electrical characteristics of the PTC element 10 by accelerating the degradation of the resin by chain attacking the resin.

Therefore, we repeated further experiments, the range as a result, Ni ₃ C peak intensity ratio to the peak intensity _{I B} of Ni peak intensity _{I A} of _(I A / _{I B)} is 0.001 to 0.100 It was found that the temperature-resistance curve of the PTC element 10 would be good if it was within the range. That is, if the peak intensity ratio I _A / I _B is within the above range, an overcurrent is passed through the PTC element 10 to bring the PTC element into an operating state, and then normalize the current to return the PTC element 10 to a non-operating state. After the operation / non-operation state change is repeated 1000 times, the rate of change of the operating temperature after 1000 times of operation to the original operating temperature (operating temperature change rate) can be suppressed to 20% or less. It was found that the room temperature resistance value was low (for example, 50 mΩ or less). Thus, even after the operation / non-operation state change is repeated 1000 times, the PTC element whose operation temperature change rate is 20% or less and the room temperature resistance value during non-operation is 50 mΩ or less. If it is 10, it can be said that it is an excellent element having high reliability.

Incidentally, the peak intensity ratio I _{A /} I _B is in the case of less than 0.001, the room-temperature resistance is increased at the time of non-operation, utility as an overcurrent protection element decreases. On the other hand, if the peak intensity ratio I _{A /} I _B is more than 0.100, the operation - there is a problem such as repeated by operating temperature change rate and resistance change rate of the non-operation increases.

As described above, the inventors controlled the peak intensity ratio I _A / I _B (that is, the amount of Ni ₃ C generated) to the specific range, thereby reducing the resistance value during non-operation, The present inventors have found that a PTC element 10 in which a change in operating temperature due to repeated operation-non-operation is suppressed can be obtained. The amount of Ni ₃ C produced is controlled by, for example, selecting a suitable thermoplastic resin and optimizing kneading conditions.

In addition, the cross-linking treatment (S20 in FIG. 2) for the PTC element body 14 significantly suppresses the situation where Ni ₃ C generated during kneading increases in a large amount during device use and attacks the resin. Has been. However, if the degree of crosslinking is too high, the influence of Ni ₃ C can be suppressed, but the linear expansion coefficient changes, making it difficult to obtain the designed operating temperature. On the other hand, if the degree of cross-linking is low, the influence of Ni ₃ C becomes large, and Ni ₃ C promotes the deterioration of the resin, which adversely affects the change in the resistance value of the PTC element 10 with time. For this reason, in this embodiment, the optimum cross-linking conditions that can obtain the effect of suppressing the chain influence on the resin of Ni ₃ C are adopted.

As the thermoplastic resin, when using those obtained by incorporating a high-density polyethylene to low density polyethylene, in comparison with the thermoplastic resin containing no high-density polyethylene, it is possible to suppress the generation amount of Ni 3 _C described above It becomes easy.

Note that the PTC element can also be manufactured by methods other than those described above. For example, for PVDF, which is a crystalline polymer that can be dissolved in a solvent, after the PVDF is dissolved in the solvent, a metal powder or the like is added thereto, further mixed, and dried while making it into a sheet. A PTC element can be obtained by laminating and forming electrodes on the upper and lower surfaces. The PTC element obtained by this manufacturing method is a manufacturing method that does not involve heat and pressure, so that the above-mentioned Ni ₃ C is not generated. However, since it is necessary to maintain the solubility of the resin during the manufacturing process, the polymer crystallinity is low. Low. Accordingly, such a PTC element has a smaller change in resistance value during operation and non-operation than the above-described PTC element 10 using the PTC element body 14 obtained by kneading, and thus has a high reliability as a PTC element. poor.

  Hereinafter, in order to further clarify the effect of the present invention, description will be made using Examples and Comparative Examples.

  First, seven types of PTC element samples (samples 1 to 4 and comparative samples 11 to 13) shown in the table of FIG. 4 were prepared. That is, seven types of samples were prepared with different mixing ratios of low density polyethylene and high density polyethylene, Ni powder content, kneading conditions, and radiation crosslinking dose. As Ni powder, commercially available Ni powder (trade name: INCOType 210, 255, 270 nickel powder (manufactured by Inco)) was used. For kneading, a lab plast mill manufactured by Toyo Seiki Seisakusho was used.

  Then, the upper and lower surfaces of each of the seven types of PTC element samples were sandwiched between Ni foils (electrode sheets) having a thickness of 15 μm, and heat-pressed at 150 ° C. to thermally press the sample and the Ni foil. A 3 mm sample was obtained. This sample was sheared to a size of 3 × 6 mm, further subjected to radiation crosslinking treatment (crosslinking conditions are as shown in the table of FIG. 4), and seven types of PTC element samples (samples 21 to 24) as shown in the table of FIG. And samples 31 to 33) were obtained.

Then, in order to identify the amount of Ni ₃ C of each PTC element samples (content), using X-ray diffraction apparatus (manufactured by Rigaku Corporation), Ni ₃ in the range of diffraction angle (2 [Theta] angle) 30-60 degrees C (002) plane peak intensity I _A (2θ: around 41.9 °) and Ni (200) plane peak intensity I _B (2θ: around 51.9 °) were determined (see FIG. 6). These peak intensity ratios (I _A / I _B ) were calculated. As a result, the peak intensity ratios IA / IB of the samples 21 to 24 were in the range of 0.001 to 0.100, and the other samples (samples 31 to 33) were out of the range.

  Furthermore, the room temperature resistance value of each PTC element sample when not operating was measured. As shown in the table of FIG. 5, the resistance values of Samples 21 to 24 and Samples 31 and 32 are 5 to 45 mΩ, which are advantageous for element miniaturization and lower power consumption of 50 mΩ or less. . However, the sample 33 showed a value far exceeding the practical level of 152 mΩ.

For each PTC element sample, operating temperatures (T ₁ , T ₁₀₀ , T ₅₀₀ , T ₁₀₀₀ ) were measured when the operating / non-operating state change was repeated once, 100 times, 500 times, and 1000 times. More specifically, as shown in FIG. 7, the temperature-resistance curve of the PTC element sample when the operation-non-operation state change is performed once, 100 times, 500 times, and 1000 times is created. the temperature was measured as the operating temperature in ² Omega. The resistance value was measured by a four-terminal method. Then, the operating temperature change rate (operating temperature change rate, (T ₁ −) after the operating / non-operating state change is repeated 1000 times with respect to the operating temperature when the operating / non-operating state change is performed only once. T ₁₀₀₀ ) / T ₁ × 100) was calculated for each PTC element sample.

As shown in the table of FIG. 5, the operating temperature change rate of Samples 21 to 24 and Sample 33 was 20% or less in absolute value of the operating temperature change rate. However, Samples 31 and 32 showed values of the operating temperature change rate of 25.9% and 30.9%, which exceeded the practical level, respectively. The graph of FIG. 8, the vertical axis of (the horizontal _axis, Ni 3 C / Ni peak intensity ratio in the graph of FIG. 8) a graph of the operating temperature (Fig. 8 peak intensity ratio _I A / _{I B} of each PTC element samples It is the graph which showed the relationship with).

From the experimental results shown above, in the PTC elements (samples 21 to 24) in which the amount of Ni ₃ C produced during heating and kneading is within the specific range, the operating temperature change rate in repeated operation-non-operation is It is clear that it is small and has a low room temperature resistance value and high reliability.

It is the figure which showed the polymer PTC element which concerns on embodiment of this invention. It is the flowchart which showed the procedure which produces the polymer PTC element shown in FIG. It is a diagram showing a generation model of Ni ₃ C. It is the table | surface which showed the structure and process conditions of each PTC element | base_body sample used for the Example of this invention. It is the table | surface which showed the measurement result of the PTC element sample obtained from each sample shown in FIG. It is the figure which showed the X-ray-diffraction result of the polymer PTC body based on the Example of this invention. It is the figure which showed the temperature-resistance curve of the sample which concerns on the Example of this invention. It is a graph which shows the measurement result of each PTC element sample shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Polymer PTC element, 12A, 12B ... Electrode, 14 ... Polymer PTC element | base_body.

Claims (4)

A thermoplastic resin and Ni powder produced is heated and kneaded, and, within the scope of X-ray diffraction angle 30 to 60 degrees, (200) of Ni peak intensity _{I A} of (002) plane of the Ni ₃ C surface the ratio of the peak intensity _{I B (I a / I B} ) is in the range of 0.0030 to 0.0621, the polymer PTC element body.   The thermoplastic resin includes mixed polyethylene obtained by mixing high-density polyethylene and low-density polyethylene, and the mixing ratio is 5 to 50 wt% for high-density polyethylene and 50 to 95 wt% for low-density polyethylene. 1. The polymer PTC element body according to 1. A pair of electrodes facing each other and a polymer PTC element body disposed between the pair of electrodes,
The polymer PTC body is prepared by heat-kneading a thermoplastic resin and Ni powder, and the peak intensity I _A of the (002) plane of Ni ₃ C within an X-ray diffraction angle range of 30 to 60 degrees. the ratio of the peak intensity _{I B} of (200) plane of the Ni _(I a / _{I B)} is in the range of .0030 to .0621, the polymer PTC element. The thermoplastic resin includes mixed polyethylene obtained by mixing high-density polyethylene and low-density polyethylene, and the mixing ratio is 5 to 50 wt% for high-density polyethylene and 50 to 95 wt% for low-density polyethylene. 3. The polymer PTC element according to 3.

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