JP2003257704A - Ptc composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a PTC composite material which is suitably used for forming a current-limiting device or the like that restrains an accidental current, practically satisfiable enough in heat resistance, resistance-returning properties, withstand voltage properties, and initial (room temperature) resistance. <P>SOLUTION: This PTC composite material contains a conductive filler 1, an insulating filler 2, and a thermosetting resin 3. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a PTC composite material. More specifically, a PTC composite material having heat resistance, resistance recovery, withstand voltage, and initial (room temperature) resistance that is suitable for practical use, such as a current limiting element that suppresses fault current, and is sufficiently satisfactory for practical use. Regarding

[0002]

2. Description of the Related Art PTCR (Positive tem)
performance coefficient of r
Esistence) materials (hereinafter referred to as “PTC materials”) have the property of rapidly increasing the electrical resistance value at a specific temperature, and therefore are used as current limiting devices for suppressing fault current in breakers, for example. Conventionally, as such a PTC material, barium titanate-based ceramics whose electric characteristics change at the Curie point is best known. However, since the initial (room temperature) resistivity is high, conduction loss is large and manufacturing is difficult. Due to the high cost, PTC materials made of other substances have been sought.

As a result, a PTC characteristic similar to that of barium titanate-based ceramics was found in a composite material including a polymer as a base material and a conductive material as an additive. For example,
When conductive particles such as carbon are mixed with crystalline polymer such as polyethylene, which is an insulator, a conductive path is formed in the polymer matrix at a specific mixing ratio, resulting in a sharp decrease in electrical resistance. An insulator-conductor transition is triggered.

In the composite material produced with such a mixing ratio, the thermal expansion of the crystalline polymer constituting the composite material is much larger than that of the conductive particles, so that the temperature rises and the melting temperature of the crystalline polymer increases. When it reaches the vicinity, it will expand rapidly. Due to this expansion, the conductive particles forming the conductive path in the crystalline polymer are separated from each other, and as a result, the conductive path is cut and the PTC characteristic in which the electric resistance sharply increases is exhibited. become.

However, when an organic material such as a polymer is used as a base material, there is a problem that the operation cannot be maintained if the high temperature state due to the accident current continues for a long time because the heat resistance is low.

In order to solve such a problem, in particular, in order to improve the shape retention property at the time of temperature rise and the reliability of the operating characteristics, the crystalline polymer of the thermoplastic resin, the conductive filler, and An organic PTC composite material characterized by comprising an insulating filler is proposed (Japanese Patent Laid-Open No. 10-270204).

[0007]

However, in the organic PTC composite material described in JP-A-10-270204, the conductive filler and the insulating filler are thermoplastic (that is, heat softening) crystals. Since it is fixed by a crystalline polymer, its heat resistance is low. By heating the device above the melting point of the crystalline polymer, the initial (room temperature) resistance value increases (resistive resistance is poor) and an insulating filler is used. The initial (room temperature) resistance value increases due to the addition of
There is a problem that they are not always sufficiently satisfactory in terms of resistance recovery, voltage resistance, and initial (room temperature) resistance value.

The present invention has been made in view of the above problems, and has heat resistance that is sufficiently satisfactory for practical use.
It is an object of the present invention to provide a PTC composite material having resistance recoverability, withstand voltage property, and initial (room temperature) resistance value.

[0009]

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides the following PTC composite material.

[1] A PTC composite material containing a conductive filler, an insulating filler, and a thermosetting resin.

[2] The particle size of the conductive filler is 2
The PTC composite material according to [1] above, which has a thickness of about 50 μm.

[3] The particle size of the conductive filler is 5
The PTC composite material according to [1], wherein the PTC composite material is about 20 μm.

[4] The conductive filler is silicided
Libden (MoSi₂), Tungsten silicide (WS
i₂), Titanium boride (TiB₂), Zirconium boride
(ZrB ₂), Molybdenum (Mo), tungsten
(W), nickel (Ni), and stainless alloy
The at least one filler selected from the group
The PTC composite material according to any one of [1] to [3].

[5] Any one of the above [1] to [4], wherein the thermosetting resin is at least one resin selected from the group consisting of a phenol resin, an epoxy resin, a urea resin, and a urethane resin. The PTC composite material described.

[6] The insulating filler is at least one filler selected from the group consisting of cristobalite phase SiO ₂ , tridymite phase SiO ₂ , cristobalite phase AlPO ₄ , and tridymite phase AlPO ₄ . The PTC composite material according to any one of [5].

[7] On a set of linear conductive filler rows in which a plurality of thermosetting resins, insulating fillers, and linear conductive fillers are juxtaposed in parallel on the same plane, A conductive material formed by stacking another plurality of sets of the linear conductive filler rows so that the longitudinal directions of the linear conductive filler rows adjacent to each other in the vertical direction are alternately orthogonal to each other to form a cross beam shape. P characterized by containing and
TC composite material.

[8] The conductive filler is molybdenum silicide (MoSi ₂ ), tungsten silicide (WS)
i ₂ ), molybdenum (Mo), tungsten (W), nickel (Ni), and the PTC composite material according to the above [7], which is at least one filler selected from the group consisting of stainless alloys.

[9] The PTC composite material according to [7] or [8], wherein the linear conductive filler has a wire diameter of 20 to 500 μm.

[10] The insulating filler is cristobalite phase SiO ₂ , tridymite phase SiO ₂ , cristobalite phase AlPO ₄ , and tridymite phase AlPO _4.
The PTC composite material according to any one of the above [7] to [9], which is at least one filler selected from the group consisting of:

[11] In any one of the above [7] to [10], wherein the thermosetting resin is at least one resin selected from the group consisting of phenol resin, epoxy resin, urea resin, and urethane resin. The PTC composite material described.

[0021]

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is an explanatory view schematically showing one embodiment of the PTC composite material of the present invention.

As shown in FIG. 1, the PT of the present embodiment
The C composite material includes a conductive filler 1 and an insulating filler 2.
And a thermosetting resin 3 are included.

As the conductive filler 1 used in the present embodiment, for example, molybdenum silicide (MoS) is used.
i ₂ ), tungsten silicide (WSi ₂ ), titanium boride (TiB ₂ ), zirconium boride (ZrB ₂ ), molybdenum (Mo), tungsten (W), nickel (Ni)
And at least one filler selected from the group consisting of stainless steel alloys can be cited as a suitable example. Of these, fillers of metal silicides such as molybdenum silicide (MoSi ₂ ) and tungsten silicide (WSi ₂ ) are preferable.

The conductive filler 1 is used to impart conductivity to the insulating filler 2 described later.

The particle size of the conductive filler 1 is 2 to 50 μm.
The thickness is preferably m, more preferably 5 to 20 μm. When it is more than 50 μm, the withstand voltage is lowered, and it may be difficult to uniformly disperse the conductive filler in the composite, and when it is less than 2 μm, sufficient PTC characteristics should be ensured. You may not be able to That is, the PTC material usually has the following characteristics.
It is required that the jump rate (resistance value after operation / initial (room temperature) resistance value (times)) is large. The content of the filler 1 may be reduced or the particle size of the conductive filler 1 may be increased, but when the content of the conductive filler 1 is reduced, the initial (room temperature) resistance value increases,
The conduction loss will increase. By specifying the particle size of the conductive filler 1 to be 2 μm or more as described above, the PTC can be maintained at a low initial (room temperature) resistance value.
The characteristics can be sufficiently secured. As a result, the contact resistance can be reduced, and the jump rate can be improved while preventing the initial (room temperature) resistance value from increasing.

The content of the conductive filler 1 used in the PTC composite material of the present embodiment is preferably 10 to 50% by volume, more preferably 20 to 35% by volume. If it exceeds 50% by volume, sufficient PTC characteristics may not be ensured, and if it is less than 10% by volume, a small initial (room temperature) resistance value may not be obtained.

Further, as the insulating filler 2 used in the present embodiment, for example, cristobalite phase Si
O ₂ , tridymite phase SiO ₂ , cristobalite phase Al
Preferable examples include at least one kind of filler selected from the group consisting of PO ₄ and tridymite phase AlPO ₄ . Of these, cristobalite phase SiO ₂ is preferable.

Here, the cristobalite is quartz,
A type of polymorph of SiO ₂ mineral with tridymite (scaly silica), which has a property of rapidly expanding as the crystal structure changes from alpha (tetragonal) to beta (cubic) around 230 ° C. Inflatable material.
Therefore, although cristobalite itself is an insulator, for a material in which a conductive material is mixed at a predetermined ratio to cause an insulator-conductor transition, when cristobalite thermally expands as the temperature rises, the formed conductivity is increased. The path was cut,
PTC characteristics can be expressed.

Cristobalite has a melting point of 17
It is as high as 30 ° C., has excellent heat resistance as compared with a polymer which is an organic material, and is not damaged by melting or the like even when exposed to a high temperature for a long time, and therefore, it is suitable as a base material of a PTC composite material. Cristobalite can be obtained by calcining quartz at a high temperature, but can be obtained by calcining at a lower temperature in the presence of an alkali metal or an alkaline earth metal that stabilizes cristobalite. In the present invention, PTC can be obtained by using a cristobalite crystal structure or a tridymite crystal structure with a low transition temperature as disclosed in JP 2001-237104 A as a base material.
The temperature at which the characteristic develops can be controlled to a desired temperature.

The content of the insulating filler 2 with respect to the thermosetting resin 3 used in the PTC composite material of the present embodiment is 50: by volume ratio (insulating filler: thermosetting resin).
It is preferably 50 to 95: 5. If the volume ratio of the insulating filler 2 is less than 50:50, the thermal expansion amount may decrease and the jump rate may decrease, and if it exceeds 95: 5, the conductive filler 1 and the insulating filler formed by the thermosetting resin 3 may be used. The adhesive force with 2 may be weakened and the resistance to resistance may deteriorate.

As the thermosetting resin 3 used in the present embodiment, for example, phenol resin, epoxy resin,
At least one resin selected from the group consisting of urea resins and urethane resins can be mentioned. Of these, a phenol resin is preferable because it has high heat resistance.

With such a configuration, the heat resistance, the resistance recovery property, the withstand voltage property, which are sufficiently satisfactory in practical use,
In addition to having an initial (room temperature) resistance value, it is possible to secure a jump rate of three digits.

FIG. 2 is an explanatory view schematically showing another embodiment of the PTC composite material of the present invention.

As shown in FIG. 2, the PT of the present embodiment
The C composite material is a thermosetting resin 4 and an insulating filler 8
And a plurality of linear conductive fillers 5 arranged in parallel on the same plane on a set of linear conductive filler rows 6 that are adjacent to each other in the vertical direction.
And a conductive material 7 constituted by laminating a plurality of other sets of the linear conductive filler rows 6 so that the longitudinal directions thereof are alternately crossed to form a cross shape.

Here, the thermosetting resin 4, the insulating filler 8 and the linear conductive filler 5 in the PTC composite material of the present embodiment are the same as those used in the embodiment shown in FIG. 1, respectively. Any thing can be used.

The wire diameter of the linear conductive filler 5 is preferably 20 to 500 μm. 20 μm
When it is less than 500 μm, the strength of the wire is weak and the wire is easily cut, which may make the manufacturing difficult. When it exceeds 500 μm, sufficient withstand voltage may not be obtained.

With this configuration, it is possible to ensure heat resistance, resistance recovery, withstand voltage, and initial (room temperature) resistance that are sufficiently satisfactory for practical use, and to secure a jump rate of three digits. You can

Hereinafter, a method for manufacturing the PTC material of this embodiment will be described.

The conductive filler, the insulating filler, and the thermosetting resin are weighed and sufficiently mixed in a revolving orbital mill, and then integrally molded with an electrode by a hot press to a desired thickness. A desired shape is cut out from the obtained molded body to obtain a PTC element. Further, when using a linear conductive filler, they are first laminated alternately so that they cross each other, and while keeping this state, the insulating filler and the thermosetting resin that are sufficiently mixed in a rotation revolution mill. A mixture of and is poured around a linear conductive filler and hot pressed to produce a PTC element. In this case, the electrode may be integrally formed with the electrode at the time of hot pressing, or the uppermost metal wire and the lowermost metal wire may be used as the electrode. When the heat treatment is performed again after the molding, the resin is more sufficiently cured and the resistance recoverability can be improved.

[0041]

EXAMPLES Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

Examples 1 to 48 MoSi ₂ having an average particle size of 1 to 55 μm, cristobalite having an average particle size of 0.8 μm, and a phenol resin (thermosetting resin) in volume% are shown in Table 1. After being weighed and mixed in a revolving orbital mill, it was integrally molded with a Ni foil electrode so as to have a thickness of 0.5 mm by a hot press. The volume ratio of cristobalite and phenolic resin is 8
It was set to 0:20. 3mm square PT from the obtained pellets
The C element was cut out, and the resistance value at 25 ° C. and 300 ° C. and the withstand voltage due to self-heating by energization were measured. The results are shown in Tables 1 and 2.

Comparative Example In Example 23, a PTC element was produced by thermoforming using thermoplastic polyethylene as a resin for fixing MoSi ₂ and cristobalite. A PTC element of 3 mm square was cut out from the obtained pellet, and the temperature was kept at 25 ° C for 30
The resistance value at 0 ° C. and the resistance recovery rate after holding at 300 ° C. for 5 minutes were measured. The results are shown in Table 3.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

From Table 1 and Table 2, when the particle size of the conductive filler (MoSi ₂ ) is as small as 1 μm as in Examples 43 to 48, the resistance jump (jump rate) tends to be small, and conversely, As in Examples 1 to 5, it can be seen that as the resistance increases, the resistance jump increases but the withstand voltage decreases. In addition, from Table 3, it can be seen that the resistance recovery rate after the thermal cycle is increased in the comparative example using the thermoplastic polyethylene instead of the thermosetting phenol resin. Therefore, by using the thermosetting resin, It can be seen that the heat resistance is improved.

Examples 49 to 73 After alternately laminating Ni wires so as to cross each other, the wires were filled with a mixture of cristobalite and phenol resin, which were sufficiently mixed in a rotation orbital mill, and heat-press molded to obtain PT.
A C element was produced. The volume ratio of cristobalite to phenol resin was 80:20. The withstand voltage was evaluated by the self-heating of electricity when the uppermost and lowermost metal wires were used as electrodes. Initial diameter (room temperature) with wire diameter, wire material, number of layers and parallel
Table 4 shows the relationships among the resistance, the thickness, and the withstand voltage. In this embodiment, Ni wires are laminated, but W wires may be laminated.

[0049]

[Table 4]

From Table 4, it can be seen that the one in which the linear conductive fillers are regularly laminated has a lower initial (room temperature) resistance than the one in which the conductive filler particles are randomly dispersed (Examples 1 to 48). I understand. This is because the laminated linear conductive fillers surely contact each other,
This is because all the conductive fillers conduct electricity. Also,
From Table 4, it can be seen that as the wire diameter increases, the withstand voltage tends to decrease. This is because when the wire diameter is large, the temperature difference inside the element during heat generation by energization becomes large, and there is a time lag in cutting the conductive filler contact points of each wire, and a voltage is intensively applied to each cutting point. This is because arc discharge is likely to occur because they are not shared. In addition, as in Examples 72 and 73, N is used as the conductive filler material.
It can be seen that the withstand voltage becomes higher when W is used than when i is used. This is because the use of W having a melting point higher than that of Ni can suppress the occurrence of arc discharge.

[0051]

As described above, according to the present invention, the heat resistance, the resistance recoverability, the withstand voltage, and the initial resistance, which are suitable for use in the current limiting element for suppressing the fault current, can be sufficiently satisfied in practical use. A PTC composite material having a (room temperature) resistance value can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory view and a partially enlarged view schematically showing an embodiment of a PTC composite material of the present invention.

FIG. 2 is a perspective view schematically showing another embodiment of the PTC composite material of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Conductive filler, 2 ... Insulating filler, 3 ... Thermosetting resin, 4 ... Thermosetting resin, 5 ... Linear conductive filler, 6 ... Linear conductive filler row, 7 ... Conductive material, 8 ...
Insulating filler.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toru Hayase             2-56, Sudacho, Mizuho-ku, Nagoya-shi, Aichi             Inside Hon insulator Co., Ltd. F-term (reference) 5E034 AA07 AB01 AC10 AC18 AC19

Claims (11)

[Claims] 1. A conductive filler and an insulating filler,
PTC containing a thermosetting resin
Composite material. 2. The particle size of the conductive filler is 2 to 50.
The PTC composite material according to claim 1, which has a thickness of μm. 3. The particle size of the conductive filler is 5 to 20.
The PTC composite material according to claim 1, which has a thickness of μm. 4. The conductive filler is molybdenum silicide (MoSi ₂ ), tungsten silicide (WSi ₂ ), titanium boride (TiB ₂ ), zirconium boride (Zr).
B ₂ ), molybdenum (Mo), tungsten (W), nickel (Ni), and at least one filler selected from the group consisting of stainless alloys. 5. The thermosetting resin is a phenol resin,
5. At least one resin selected from the group consisting of epoxy resins, urea resins, and urethane resins.
7. The PTC composite material according to any one of 1. 6. The insulating filler is at least one filler selected from the group consisting of cristobalite phase SiO ₂ , tridymite phase SiO ₂ , cristobalite phase AlPO ₄ , and tridymite phase AlPO ₄ . PTC composite material in any one. 7. A set of linear conductive fillers formed by arranging a plurality of thermosetting resins, insulating fillers, and linear conductive fillers in parallel on the same plane. And a conductive material formed by laminating another plurality of sets of the linear conductive filler rows so that the longitudinal directions of the linear conductive filler rows that are adjacent to each other are alternately orthogonal to each other in a cross beam shape. A PTC composite material comprising: 8. The conductive filler is molybdenum silicide (MoSi ₂ ), tungsten silicide (WSi ₂ ), molybdenum (Mo), tungsten (W), nickel (N).
The PTC composite material according to claim 7, which is at least one filler selected from the group consisting of i) and a stainless alloy. 9. The wire diameter of the linear conductive filler is 20.
The PTC composite material according to claim 7 or 8, which has a thickness of ˜500 μm. 10. The insulating filler is cristobalite.
Ito phase SiO₂, Tridymite phase SiO₂, Cristoborough
Ito phase AlPO_Four, And tridymite phase AlPO _FourEmpty
At least one filler selected from the group
Item 10. A PTC composite material according to any one of items 7 to 9. 11. The thermosetting resin is at least one resin selected from the group consisting of a phenol resin, an epoxy resin, a urea resin, and a urethane resin.
10. The PTC composite material according to any one of 10 to 10.