JP2005064090A - Polymer ptc element and its producing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer PTC element capable of sustaining sufficient reliability for long term use, and to provide its producing process. <P>SOLUTION: Carbon black having conductivity enhanced through heat treatment, at least one kind of carbon black not subjected to heat treatment, and a crystalline polymer as a bonding material are kneaded and molded to produce a sheet-like polymer PTC composition 2. Crosslinked bonding material and an intermediate layer 3 of carbon black are arranged on the opposite sides of the polymer PTC composition 2 and an electrode 4 is fixed thereto. Reliability is enhanced for long term use through action of the intermediate layer 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a PTC element having a positive temperature characteristic in which resistance rapidly increases when reaching a specific temperature range, that is, a so-called PTC (Positive Temperature Coefficient) characteristic, and in particular, a crystalline polymer is filled with conductive powder. The present invention relates to a polymer PTC element having a structure in which an electrode is provided on a molded body made of a PTC composition, and a method for producing the same.

PTC elements exhibiting positive temperature characteristics in which electrical resistance increases rapidly in a specific temperature range are frequently used as heaters that automatically control temperature, self-recovery overcurrent protection elements, and the like. As a composition used for the PTC element, ceramic-based PTC compositions such as barium titanate (BaTiO ₃ ) to which a small amount of yttrium oxide (Y ₂ O ₃ ) is added, conductive particles such as carbon black are used as crystalline polymers. Polymer PTC compositions dispersed therein are known.

  A PTC element using a ceramic PTC composition uses a sudden increase in resistance at the Curie point. However, since the resistivity in a steady state is as high as about 100 Ω · m, a comparison of several A is possible. Large current cannot flow. This means that a PTC element using a ceramic PTC composition is difficult to use as an overcurrent protection element. In addition, the ceramic PTC composition has a problem that many steps are required to form and process into a desired shape, and the impact resistance is poor.

  On the other hand, a polymer PTC element using a polymer PTC composition is suitable for an overcurrent protection element because of its low resistivity at room temperature, has excellent impact resistance, and is easy to mold and process. .

  In a polymer PTC element, the principle of causing a switching operation in which the resistivity rapidly increases as the temperature rises is based on the conductivity that forms a network at room temperature by utilizing the large thermal expansion at the crystalline melting point of the crystalline polymer. This is by separating the particles. For this reason, when the heat is excessively generated by a current exceeding the specified value, the resistivity rapidly increases at a temperature near the crystalline melting point, and when the temperature returns to room temperature, the network of conductive particles is re-formed, and the resistivity is also increased. descend.

  A general method for producing a polymer PTC element is to use a roll or the like to disperse conductive particles in a crystalline polymer to obtain a polymer PTC composition, which is then formed into a sheet with a hot press or a roll. However, there is a dry method in which an electrode made of a metal foil or the like is pressure-bonded and then punched into a required shape.

  Further, as a method for obtaining a sheet of the polymer PTC composition, there is a wet method in which a film is formed using a paste in which conductive powder is dispersed in a crystalline polymer solution. In this case, a metal foil constituting the electrode is used. There is also a method in which a film is formed on the substrate and the film formation sides are opposed to be integrated.

  As described above, in the polymer PTC composition, a crystalline polymer is used as a binder, and a typical one is high density polyethylene (hereinafter referred to as HDPE). HDPE is superior in terms of price and moldability, and is widely used in polymer PTC compositions. However, since HDPE permeates water molecules, the electrode and polymer PTC composition can be used over a long period of time. There is a problem that peeling occurs at the interface with the substrate, and the resistivity is increased or the characteristics are degraded.

  A technique for coping with such a problem is disclosed in Patent Document 1 below. The technique disclosed in Patent Document 1 is to provide a water vapor barrier layer on the surface of the polymer PTC element where the polymer PTC composition is exposed. However, this method still has insufficient reliability.

  In addition, as described above, carbon black is used as the conductive powder. However, when the conductivity of the conductive powder is improved, the conductivity as the polymer PTC composition does not decrease even when the filling amount is reduced. There is still room for consideration in this regard.

JP 2002-064004 A

  Accordingly, an object of the present invention is to provide a polymer PTC by a simple method in a polymer PTC element having a structure in which an electrode is provided on a sheet-like molded body made of a PTC composition in which a crystalline polymer is filled with conductive powder. To provide a polymer PTC element that exhibits sufficient reliability when used for a long period of time by improving the electrical conductivity of the composition and the heat resistance and moisture resistance of the polymer PTC element, and a method for producing the same. is there.

  In order to solve the above-mentioned problems, the present invention has been made as a result of studying the structure of the interface between the polymer PTC composition and the electrode and improving the characteristics of carbon black used as the conductive powder.

  That is, the present invention provides 5 to 50% by weight of a first conductive powder containing at least one kind of heat-treated carbon black and non-heat-treated carbon black, and 95 to 50% by weight of crystallinity. A sheet-like molded body of a polymer PTC composition comprising a first binder containing a polymer and at least 50 to 90% by weight of carbon black not subjected to heat treatment disposed on both sides of the sheet-shaped molded body A second conductive powder containing one type, an intermediate layer made of 10 to 50% by weight of a second binder containing a crystalline polymer, and a pair of electrodes arranged facing the outside of the intermediate layer It is a polymer PTC element characterized by having.

  In addition, the present invention provides the polymer PTC element, wherein the first conductive powder and the second conductive powder have an average particle diameter of 5 to 300 nm.

  Further, the present invention is characterized in that at least a part of the carbon black contained in the first conductive powder is heat-treated at a temperature range of 500 to 1500 ° C. for 2 to 20 hours. It is a manufacturing method of a molecular PTC element.

  The present invention also provides the method for producing the polymer PTC element, wherein the second binding material is subjected to a crosslinking treatment.

  Further, the present invention is characterized in that the crosslinking treatment is performed by adding a crosslinking agent to the second binder and performing a heat treatment at a temperature range of 85 to 200 ° C. for 1 to 240 hours. It is a manufacturing method of a polymer PTC element.

  The conductivity of a carbon material such as carbon black is derived from π electrons. Carbon black is classified into channel black, furnace black, lamp black, and thermal black depending on the production method. Among them, carbon black, carbon single bond and hydroxyl groups that do not contribute to the development of conductivity, moisture, and other low Contains molecular weight impurities. Accordingly, the heat treatment can remove low molecular weight components and increase π electrons due to the progress of the dehydrogenation reaction, thereby improving the conductivity.

  For the above reasons, in the present invention, the carbon black used as the conductive powder is subjected to heat treatment. The heat treatment temperature is in the range of 500 to 1500 ° C. and the heat treatment time is 2 to 20 hours. The temperature and time of the heat treatment are insufficient, and the above temperature and time do not show a difference in effect compared to the heat treatment in the above temperature range and time range, and the cost required for the treatment. This is because of the increase.

  In addition, when the polymer compound that permeates moisture is subjected to a crosslinking treatment, the amount of moisture permeation may be reduced. In the present invention, in order to utilize this, the interface of the polymer PTC composition with the electrode is reduced. An intermediate layer is formed by subjecting a nearby portion to a crosslinking treatment. Examples of the crosslinking method of the polymer material include a method of irradiating radiation such as an electron beam and a method of heating by adding a crosslinking agent such as an organic peroxide, but does not require a large-scale facility. In the case of the present invention, the latter is suitable because it is suitable for the crosslinking treatment of only a certain part of the molded body.

  In that case, it is necessary to appropriately set the conditions for the crosslinking treatment depending on the decomposition rate of the crosslinking agent used. In the present invention, the temperature is set in the range of 85 to 200 ° C., and the time is set in the range of 1 to 240 hours. The reason for this is that, from the decomposition rate of a commonly used crosslinking agent, crosslinking is insufficient at the following temperature and time, and at the above temperature and time, the influence of the reaction such as thermal decomposition of the polymer compound itself. This is because the characteristics of the polymer PTC element deteriorate.

  Next, the best mode for carrying out the present invention will be described.

  In the present invention, as described above, heat-treated carbon black is used as the conductive powder. As described above, the preferable range of the heat treatment condition is that the temperature is 500 to 1500 ° C. and the time is 2 to 20 hours. As a matter of course, the higher the processing temperature, the shorter the processing time, and in order to verify this, when heat treatment was performed at temperatures of 400 ° C., 500 ° C., 1000 ° C., 1500 ° C. for 2-20 hours, The change in resistance of carbon black was determined. The carbon used was a mixture of thermal black having an average particle diameter of 300 nm and channel black having an average particle diameter of 10 nm by 50% by weight.

  The actual resistance was measured by preparing a polymer PTC composition having a composition of 40% by weight of carbon black and 60% by weight of HDPE, forming a sheet to a thickness of 1 mm, cutting it to a size of 5 mm × 10 mm, and attaching an electrode. The specific resistance was calculated using the attached sample. FIG. 2 summarizes the results and is a graph showing the relationship between the heat treatment time and the specific resistance.

  According to the results shown in FIG. 2, when the processing temperature is 500 ° C. or higher, a sudden change in resistance is observed when the processing time is 2 hours or longer, and a significant decrease in resistance is observed after 15 hours or longer. I can't understand. On the other hand, under the condition of 400 ° C., it can be seen that even when the treatment time reaches 20 hours, the rate of decrease in resistance is about 5%, and the effect of heat treatment is hardly seen.

  From the above results, the heat treatment condition is preferably 500 ° C. or higher in terms of temperature. However, although no particular data is shown, a change in properties such as a change in average particle diameter becomes obvious at a temperature of 1500 ° C., which is not preferable. Therefore, the preferable range of temperature is 500-1500 degreeC.

  In terms of time, as described above, the effect of the heat treatment clearly appears in 2 hours or more, and even if 15 hours or more have elapsed, an increase in the effect cannot be expected, so the preferred range is 2 to 20 hours. .

  In the present invention, the average particle size of carbon black used as the conductive powder is 5 to 300 nm. In order to verify the preferable range of the average particle diameter of carbon black, a polymer PTC composition using channel black heat-treated at 1000 ° C. for 10 hours was prepared, and the relationship between the average particle diameter and specific resistance was determined. In this case, too, a polymer PTC composition in which carbon black and HDPE are mixed at a weight ratio of 40/60 is cut into a thickness of 1 mm, molded into a sheet of 5 mm × 10 mm, and an electrode is attached. Samples were used.

  FIG. 3 summarizes the results and is a graph showing the relationship between the average particle diameter of carbon black and the specific resistance. As is apparent from this graph, when the average particle size of the carbon black is outside the above range, the specific resistance is remarkably increased, which makes it unpractical as a polymer PTC element. Therefore, the average particle size of the carbon black powder needs to be 5 to 20 nm.

  In the present invention, the second binder constituting the intermediate layer is chemically cross-linked using a cross-linking agent. Here, it is preferable to use a general organic peroxide as a crosslinking agent. Examples of the organic peroxide include hydroperoxide, dialkyl peroxide, peroxy ester, diacyl peroxide and the like.

  Here, the main polymer compound used for the binder is HDPE, and considering that the temperature for kneading and molding is 120 to 140 ° C., a crosslinking agent having an appropriate decomposition rate in this temperature range is desirable, It is desirable to select a cross-linking agent that has a half-life of about 10 hours in this temperature range. A peroxide that meets such conditions is a dialkyl peroxide, particularly dicumyl peroxide.

  If the kneading temperature and molding temperature are higher than that of HDPE, a crosslinking agent having a half-life of 10 hours may be used in the region of 140 ° C. or higher, and vice versa. What is necessary is just to use the crosslinking agent in the area | region whose temperature which becomes a period for 10 hours is 120 degrees C or less. That is, it can be appropriately selected depending on the polymer compound used as the binder.

  Next, the present invention will be described in more detail based on specific examples.

  First, furnace black and thermal black were mixed to have an average particle size of 85 nm and heat-treated at 1100 ° C. for 12 hours to prepare a conductive powder for a polymer PTC composition. The conductive powder and HDPE were weighed and kneaded so as to have a weight ratio of 40/60 to obtain a polymer PTC composition.

  Next, the polymer PTC composition, the conductive powder, and HPDE were weighed and mixed to a weight ratio of 60/40, and further, 100 parts by weight of the mixture of the conductive powder and HDPE. 1.6 parts by weight of dicumyl peroxide was added. Note that the conductive powder used here was not heat-treated. This mixture was kneaded at 130 ° C. for 15 minutes using a roll to obtain a composition for an intermediate layer.

  Next, the polymer PTC composition was preformed to obtain a sheet having a thickness of 850 μm. Moreover, the composition for intermediate | middle layers was preformed and it was set as the sheet | seat with a thickness of 110 micrometers. And the composition for intermediate | middle layer is arrange | positioned on both surfaces of the preformed sheet | seat of a polymeric PTC composition, Furthermore, the electrode which consists of copper foil with a thickness of 100 micrometers is arrange | positioned on both surfaces of the outer side of an intermediate | middle layer, 160 degreeC The hot pressing was performed under the condition of 50 minutes. At this time, in order to adjust the thickness of the polymer PTC element after pressing, a spacer having a thickness of 120 μm was interposed.

  Then, the sheet | seat with which the polymer PTC composition, the intermediate | middle layer, and the electrode were integrated was cut | disconnected to the magnitude | size of 5 mm x 10 mm, the lead wire was attached, and the polymer PTC element of the Example was obtained. Further, this polymer PTC element was held in a thermostatic bath maintained at 120 ° C. for 7 days to promote the crosslinking reaction.

  FIG. 1 is a cross-sectional view of a polymer PTC element 1 of this example. However, the lead wire is omitted. In FIG. 1, 2 is a polymer PTC composition, 3 is an intermediate layer, and 4 is an electrode. For comparison, a polymer PTC element of a comparative example in which the intermediate layer 3 in FIG. 1 was replaced with the polymer PTC composition 2 was also prepared.

  These polymer PTC elements were kept in a constant temperature and humidity chamber having a temperature of 85 ° C. and a relative humidity of 85% for 100 hours to perform a high temperature and high humidity test. Then, the temperature dependence of resistance was evaluated about the polymer PTC element of the Example and the comparative example. FIG. 4 is a graph showing the temperature dependence of resistance in the polymer PTC elements of Examples and Comparative Examples. In FIG. 4, the solid line is the result of the example, and the broken line is the result of the comparative example.

  In the results shown in FIG. 4, when the example and the comparative example are contrasted, in the comparative example, the rise of the resistance accompanying the temperature rise is steeper than the example, but the high temperature region of 110 ° C. or higher, that is, The resistance after the switching operation is seen to be up and down, and a state of lack of stability is seen. On the other hand, the example has extremely stable resistance after the switching operation, and exhibits excellent characteristics as a polymer PTC element.

  As described above, according to the present invention, a polymer PTC element having an intermediate layer subjected to a crosslinking treatment between the electrode and the polymer PTC composition can be obtained, and the polymer for long-term use can be obtained. The reliability of the PTC element can be improved. Thereby, further application development of the polymer PTC element becomes possible.

Sectional drawing of the polymer PTC element of a present Example. The graph which showed the relationship between heat processing time and a specific resistance. The graph which shows the relationship between the average particle diameter of carbon black, and a specific resistance. The graph which shows the temperature dependence of resistance in the polymer PTC element of an Example and a comparative example.

Explanation of symbols

1 Polymer PTC Device 2 Polymer PTC Composition 3 Intermediate Layer 4 Electrode

Claims (5)

5 to 50% by weight of a first conductive powder containing at least one kind of heat-treated carbon black and non-heat-treated carbon black, and 95 to 50% by weight of a first polymer containing a crystalline polymer A sheet-like molded body of a polymer PTC composition comprising the above-mentioned binder, and a second one containing at least one carbon black of 50 to 90% by weight that has not been subjected to heat treatment, disposed on both sides of the sheet-shaped molded body It has a conductive powder, an intermediate layer made of a second binder containing 10 to 50% by weight of a crystalline polymer, and a pair of electrodes arranged to face the outside of the intermediate layer. Polymer PTC element. 2. The polymer PTC device according to claim 1, wherein the first conductive powder and the second conductive powder have an average particle diameter of 5 to 300 nm. 3. The heat treatment is performed on at least a part of the carbon black contained in the first conductive powder at a temperature range of 500 to 1500 ° C. for 2 to 20 hours. 4. Manufacturing method of polymer PTC element. The method for producing a polymer PTC element according to claim 1, wherein the second binding material is subjected to a crosslinking treatment. 5. The polymer according to claim 4, wherein the crosslinking treatment is performed by adding a crosslinking agent to the second binder and performing a heat treatment in a temperature range of 85 to 200 ° C. for 1 to 240 hours. A method for manufacturing a PTC element.

Images