JPH05152056A - Manufacture of ptc heating body - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing a PTC heating body undergoing a small secular change in conductivity CONSTITUTION:A first crystalline polymer, a second polymer not completely compatible with the first polymer and having a melting point or thermal deformation temperature higher than the melting point of the first polymer, and conductive particles are kneaded, thereby preparing a molded material. This material is used to manufacture a PTC heating body. The molded product after preparation is thermally treated at a temperature equal to or lower than the melting point or thermal deformation temperature of the second polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a heating element, and more particularly to a PTC (Positive TPE) having a positive temperature coefficient of resistance.
The present invention relates to a method for manufacturing an heating element.

[0002]

2. Description of the Related Art One of the heating elements that generate heat when energized is a PTC heating element whose resistance value increases as the temperature rises (that is, has a positive temperature coefficient of resistance). The electric heater using the PTC heating element naturally has a self-temperature control function that the resistance value increases as the temperature rises, the current decreases, the heat generation amount is suppressed, and the one-way temperature rise is prevented. Therefore, it is known as a useful and safe heater. As a material for manufacturing such a PTC heating element, a conductive particle-dispersed crystalline polymer in which conductive particles are dispersed in a crystalline polymer is known. Examples of the crystalline polymer include polyethylene, ethylene-vinyl acetate copolymer, ionomer, and polyvinylidene fluoride, and examples of the conductive particles include carbon black fine powder and graphite fine powder.

This conductive particle-dispersed crystalline polymer is PT
The reason why the C characteristic is exhibited is as follows. When the temperature of the conductive particle-dispersed crystalline polymer rises to the melting point of the crystalline polymer, a large volume increase occurs as the crystals melt. This increase in volume causes breakage of the conductive chains generated by the contact between the dispersed conductive particles and expansion of the spacing between the conductive particles. The breakage of the conductive chains and the expansion of the spacing between the conductive particles cause a decrease in the conductive action of the conductive particles, resulting in a sharp increase in the resistance value.

However, the above-mentioned conductive particle-dispersed crystalline polymer has a large change in conductivity (resistance value) with time,
There is a problem that the conductivity deviates from the initial value.
The reason for this is considered as follows. That is,
Since the crystalline polymer and the conductive particles have different surface energies, the conductive particles in the polymer tend to agglomerate and stabilize, and are also obtained by kneading the molten crystalline polymer and the conductive particles. With conductive particle-dispersed crystalline polymers, it is difficult to manufacture conductive particles in a stable dispersed state in the crystalline polymer.Therefore, when used in a heater, it is possible to dissolve and recrystallize the crystals. During the repetition, the conductive particles move in an attempt to reach a stable dispersed state, the dispersed state of the conductive particles gradually changes, and the conductive action of the conductive particles fluctuates, resulting in PTC heat generation. The electrical conductivity of the body will change significantly over time.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a method for producing a PTC heating element, from which a PTC heating element with a small change in electrical conductivity over time can be obtained.

[0006]

SUMMARY OF THE INVENTION The present invention is a crystalline first
And a molding material obtained by kneading a conductive polymer with a second polymer which is not completely compatible with the first polymer and has a melting point or heat distortion temperature higher than that of the first polymer. In the method for producing a PTC heating element according to claim 1, after forming into a molded product, heat treatment is performed at a temperature not lower than the melting point of the first polymer and not higher than the melting point or heat distortion temperature of the second polymer. It is a body manufacturing method.

Now, the process of the present invention will be described.
As a means for solving the above-mentioned problems, the inventors have found that the crystalline first polymer is not completely compatible with the first polymer, and the melting point or heat distortion temperature is higher than the melting point of the first polymer. P containing high second polymer and conductive particles
It has been found that it is effective to use a TC heating element molding material, and the application is filed as Japanese Patent Application No. 3-88881. The PTC heating element obtained by using the PTC heating element molding material by the present inventors realizes a fine mutual continuous structure by matching the melt viscosity of the first polymer and the second polymer, and An alloy material in which conductive particles are unevenly distributed in the region of the first polymer from the combination and blending amount of the first polymer and the second polymer,
Since the conductive particles are unevenly distributed in the region of the first polymer and the region of the first polymer is isolated by the second polymer having high heat resistance, the movement of the conductive particles is restricted and the conductivity is reduced. It is a stable PTC heating element.

The conductive particles are unevenly distributed in the region of the first polymer because
The difference in surface energy between the second polymer and the conductive particles is the main cause, and the difference in surface energy between the conductive particles and the first polymer is smaller than the difference in surface energy between the conductive particles and the second polymer. As a driving force, the conductive particles migrate to the region of the first polymer during kneading. Table 1 shows the surface tension of the raw material. That is, for example, when polyethylene is used as the first polymer, polypropylene is used as the second polymer, and carbon black is used as the conductive particles, from the surface tension values in Table 1, the carbon black is mixed in the polyethylene phase having a small difference in surface tension during kneading. It will shift.

[0009]

[Table 1]

The inventors of the present invention have made earnest studies in an attempt to further improve the stability of the electric conductivity of the PTC heating element obtained by using the PTC heating element molding material by further reducing the change with time of the electric conductivity. As a result, the present invention has been achieved.

The present invention will be specifically described below. Examples of the crystalline first polymer used in the present invention include polyethylene, polypropylene, polymethylpentene, EVA (ethylene-vinyl acetate resin), EEA (ethylene-ethyl acrylate resin), and EMA (ethylene-methyl acrylate resin). Examples thereof include ethylene copolymer polymers, ionomers, polyvinylidene fluoride, polyamides and polyesters. On the other hand, as the second polymer which is not completely compatible with the first polymer, polyethylene, polypropylene, polymethylpentene, ethylene copolymer (EVA, EEA, EMA, etc.), ionomer, polyvinylidene fluoride, polyamide, Examples thereof include crystalline polymers such as polyester, and amorphous polymers such as PMMA (polymethylmethacrylate), polystyrene, polycarbonate, polysulfone, polyvinyl chloride and copolymers thereof.

The second polymer used in the present invention, which is not completely compatible with the first polymer, means a polymer which is almost incompatible with the first polymer or a first polymer. It is a polymer that is compatible with a small amount or partially and forms a polymer alloy that is not a compatible system with the first and second polymers. Regarding such a polymer alloy, (“Polymer alloy-basic and applied-”; edited by Japan Society of Polymer Science, 1981),
(“Polymer Alloy”; edited by The Society of Polymer Science, Japan, Takashi Inoue, Toshio Nishinishi, 1988), (“Polymer Blend”; published by CMC, 1979). It is needless to say that the crystalline polymer does not have to be in a crystalline state over the entire region, and an amorphous portion may coexist. Further, it is known that the crystalline polymer that is actually commercially available does not have such high crystallinity under ordinary molding conditions. For example, nylon 6-6
Is 30 to 35%, polypropylene is 50 to 70%, polyethylene is 65 to 90%, PBT (polybutylene terephthalate) is 25 to 35%, and PET (polyethylene terephthalate) is about 15 to 20%.

It is important that the second polymer used in the present invention has a melting point or heat distortion temperature higher than the melting point of the first polymer, and a specific combination of the first polymer and the second polymer is used. Examples include the combinations shown in Table 2.

[0014]

[Table 2]

The blending ratio of the first polymer and the second polymer is not particularly limited, but 10 parts by weight of the entire polymer is used.
When the amount is 0 parts by weight, the amount of the first polymer is preferably in the range of 20 parts by weight or more and 80 parts by weight or less in order to realize the mutual continuous structure of the first polymer and the second polymer. Further, in the present invention, a third polymer component such as a polymeric compatibilizer may be added as long as it does not impair the object of the present invention.

The conductive particles used in the present invention include powdery or fiber-like particles made of carbon, graphite and metal, and fine carbon black powder is usually used. The amount of conductive particles added is not particularly limited, but is preferably 1 to 40 parts by weight with respect to 100 parts by weight of the polymer. The reason for this is that if the amount is less than 1 part by weight, the intended current does not flow, and if it exceeds 40 parts by weight, the intended self-temperature control function cannot be obtained.

In the present invention, P formed by kneading the above raw materials
A TC heating element molding material is used, and as a method for producing this PTC heating element molding material, the following method is exemplified. First, the second polymer is added to the first polymer and kneaded. At this time, a compatibilizer may be added to control or stabilize the phase-separated structure. Next, conductive particles are added and further kneaded to obtain a PTC heating element molding material. The order of introducing these raw materials is not limited to the above, and the first polymer and the conductive particles may be kneaded and then the second polymer may be added and kneaded. You may knead. In the production of the PTC heating element molding material, if necessary, a stabilizer, an antioxidant, a lubricant, a surfactant, a flame retardant, an inorganic filler (aluminum hydroxide, silica, etc.), a nucleating agent, etc. may be appropriately added. It may be added in stages.

In the present invention, P produced as described above
A PTC heating element is produced by molding using a TC heating element molding material, but the method of molding is not particularly limited, and for example, direct pressure molding or extrusion molding into a desired shape such as a sheet shape or a wire shape. You can use this method.

The feature of the present invention is that the obtained molded product is heat-treated at a temperature not lower than the melting point of the first polymer and not higher than the melting point or the heat distortion temperature of the second polymer.
By heat-treating the molded product under specific conditions in this way, the change over time in the electrical conductivity of the PTC heating element obtained is reduced, and the stability of the electrical conductivity is improved. The heat treatment time is not particularly limited, but it is preferable to perform the heat treatment for 30 seconds or more to ensure the effect of improving the stability of the electric conductivity.

Further, in the molding material used in the present invention, the kind of conductive particles used (for example, carbon black having different primary particle size, specific surface area, oil absorption, degree of graphitization, etc.) and the filling amount of conductive particles are used. By controlling the types and blending ratios of the first polymer and the second polymer, the electrical characteristics of the conductive paths (factors that affect the ease of conduction and the temperature at which resistance starts to increase) and the number of conductive paths Since the (factor that affects the resistance value of the PTC heating element) can be controlled independently, there is also an advantage that the PTC heating element can be easily designed.

[0021]

In the present invention, the crystalline first polymer and the second polymer, which is not completely compatible with the first polymer and has a melting point or a heat distortion temperature higher than the melting point of the first polymer, are electrically conductive. Since the molding material obtained by kneading the conductive particles is used, the obtained PCT heating element has the first polymer region in which the conductive particles are unevenly distributed and the second polymer region in which the first polymer is phase-separated. And are finely mixed. Therefore, the movement of the conductive particles is limited to the microscopic region due to the presence of the second polymer, the dispersed state of the conductive particles is hard to change, and the electric conductivity is stable.

Further, according to the present invention, after the molded product is formed, the heat treatment is performed at a temperature which is higher than the melting point of the first polymer and lower than the melting point or the heat distortion temperature of the second polymer. Agglomerates within the microscopic areas of the polymer. Therefore, in the molded product subjected to the above heat treatment, the dispersed state of the conductive particles is further unlikely to change, and the electric conductivity is further stabilized.

[0023]

EXAMPLES The present invention will be described below with reference to examples. Needless to say, the present invention is not limited to the following examples. (Examples 1 and 2 and Comparative Examples 1 and 2) Low-density polyethylene having MFR = 0.23 and melting point 122 ° C as the crystalline first polymer, and polypropylene having MFR = 2 and melting point 166 ° C as the second polymer. And carbon black having a particle size of 62 nm was used as the conductive particles. In addition, M
FR indicates the melt flow rate. A 1.8 (1) T-type intensive mixer (hand mixer) was used as a kneading machine, and the raw materials were blended in the proportions shown in Table 3 (% by weight).
Approximately 1 kg of the raw material blended in step 1 was kneaded under the following kneading conditions to obtain a molding material. Kneading conditions: rotation speed 120 rpm, heating temperature of mixer jacket 120 to 130 ° C., kneading time 6 minutes, and then using the obtained molding material, molding is performed under the conditions of 240 ° C. × 2 minutes and pressure of 10 seconds to form a sheet-like molded article. Got

[0024]

[Table 3]

Next, in Examples 1 and 2, the sheet-shaped molded product obtained above was heat-treated at 150 ° C. for 5 minutes to obtain a heat-treated molded product, and in Comparative Examples 1 and 2, the above-described molded product. The molded product obtained in 1. was not heat-treated, and the molded product in the state as it was was tested for electrical characteristics. In this electrical test, a test piece prepared by sticking aluminum foil with a conductive adhesive material on both sides of the above-mentioned sheet-shaped molded product as an electrode was used, and as a conductivity of the PTC heating element, a specific impedance in the thickness direction (100 Hz ) Was measured. First, 1 test piece as the first electrical test
Heat treatment was performed at 50 ° C. for 5 minutes, and the impedance before and after this heat treatment was measured while changing the temperature. The results are shown as a graph in FIGS. 1 and 2. The H.V. calculated using the impedance values before and after the heat treatment measured at 20 ° C. shown in FIGS. T. Is shown in Table 4. In addition, this H.264. T. Shows the impedance of the test piece before heat treatment at 150 ° C for 5 minutes at 20 ° C as "Z20
"Before treatment" and the impedance at 20 ° C of the test piece after heat treatment at 150 ° C for 5 minutes is "after Z20 treatment", the value calculated by the formula of Log (after Z20 treatment / before Z20 treatment) Yes, it is a value for evaluating the stability of impedance against heat treatment. Then, in addition to the above, the test piece was subjected to a second electrical test at 20 ° C.
The rate of change in impedance before and after standing for 00 hours was measured, and the obtained results are shown in Table 4.

[0026]

[Table 4] * 1: Value calculated by the formula of Log (after Z20 treatment / before Z20 treatment) * 2: Rate of change in impedance before and after leaving at 90 ° C for 2000 hours

Comparing FIG. 1 and FIG. 2 and comparing the thermal stability of impedances of Examples 1 and 2 and Comparative Examples 1 and 2 before and after heat treatment at 150 ° C. for 5 minutes, Example 1 shown in FIG. In Comparative Examples 1 and 2, the change in impedance before and after heat treatment is small and stable at any measurement temperature, while in Comparative Examples 1 and 2 shown in FIG. 2, the change in impedance before and after heat treatment is large at any measurement temperature. It turns out that it is unstable.

In addition, H.264 shown in Table 4 T. And 90 ° C, 2
From the numerical value of the rate of change in impedance before and after leaving for 000 hours, it is clear that the changes with time in impedance of Examples 1 and 2 are small, while the changes in impedance with time in Comparative Examples 1 and 2 are large. ..

Therefore, it was confirmed from the above results that the PTC heating element produced by the method of the present invention is stable with a small change in conductivity over time.

[0030]

The PTC heating element produced by the method of the present invention has a melting point or a heat distortion temperature of the first polymer which is not completely compatible with the crystalline first polymer. After forming a molded article by using a molding material obtained by kneading a higher second polymer and conductive particles, this molded article has a melting point of the first polymer or higher and a melting point or heat of the second polymer. Since it is obtained by performing heat treatment at a temperature equal to or lower than the deformation temperature, the conductive particles are aggregated and stabilized during the manufacturing process. As a result, the obtained PTC heating element has a small change in electric conductivity with time, and has stable electric conductivity. Therefore, according to the present invention, the change of the electric conductivity with time is small, and the electric conductivity is stable.
It is a useful method for manufacturing TC heating elements.

[Brief description of drawings]

FIG. 1 is a schematic diagram of Embodiments 1 and 2 of the present invention.
It is a graph which measured the intrinsic impedance (100 Hz) in the thickness direction before and after heat treatment at 0 ° C. for 5 minutes while changing the temperature.

2 is a graph of Comparative Examples 1 and 2 of the present invention, FIG.
It is a graph which measured the intrinsic impedance (100 Hz) in the thickness direction before and after heat treatment at 0 ° C. for 5 minutes while changing the temperature.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Sumita 2-4 Terao No. 13 Terao, Ayase City, Kanagawa Prefecture

Claims (2)

[Claims] 1. A crystalline first polymer and a second polymer and conductive particles which are not completely compatible with the first polymer and have a melting point or heat distortion temperature higher than that of the first polymer. In the method for producing a PTC heating element using a molding material obtained by kneading and, a molded product, after which the temperature is not less than the melting point of the first polymer and not more than the melting point or heat distortion temperature of the second polymer. PT characterized by heat treatment in
C Manufacturing method of heating element. 2. The method for producing a PTC heating element according to claim 1, wherein the first polymer is polyethylene, the second polymer is polypropylene, and the conductive particles are carbon black.