CN112210176A - Polyvinylidene fluoride-based conductive composite material and PTC element - Google Patents
Polyvinylidene fluoride-based conductive composite material and PTC element Download PDFInfo
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Abstract
The invention discloses a polyvinylidene fluoride-based conductive composite material and a PTC element. The polyvinylidene fluoride-based conductive composite material uses a polyvinylidene fluoride (PVDF) matrix, has a Positive Temperature Coefficient (PTC) effect, has a resistivity of not more than 10 omega-cm at an ambient temperature of 25 ℃, and comprises: the PVDF is a first component polymer and accounts for 20-70% of the volume fraction of the polyvinylidene fluoride-based conductive composite material; irradiating crosslinked fluorine-containing polymer in advance, wherein the volume fraction is 1-20%; the volume fraction of the conductive filler is 25-80%. The invention also discloses a PTC element prepared by using the polyvinylidene fluoride-based conductive composite material and a preparation method thereof. The PTC element prepared from the polyvinylidene fluoride-based conductive composite material has outstanding resistance reproducibility, good voltage resistance and environmental reliability.
Description
Technical Field
The invention relates to a polyvinylidene fluoride-based conductive composite material and a PTC element, in particular to a polyvinylidene fluoride-based conductive composite material and a PTC element which have outstanding resistance reproducibility, good voltage resistance and environmental reliability and a preparation method thereof.
Background
The resistance and the temperature of the polymer-based conductive composite material obtained by blending the polymer and the conductive filler generally have a nonlinear relation, the interval between conductive particles is increased due to the thermal expansion of the polymer matrix along with the increase of the temperature, so that the volume resistivity of the material is increased, and when the external temperature is close to the melting point of the polymer matrix, the thermal expansion of the matrix is most remarkable, and the interval between the conductive particles is sharply increased, so that the volume resistivity of the conductive composite material is increased by several orders of magnitude, namely the PTC (positive temperature coefficient of resistance) effect is generated. The polymer conductive composite material has a plurality of applications in the fields of electronic circuit protection elements, heaters, sensors and the like.
One very typical application of PTC protection elements is in the field of electronics in the automotive field. Generally, in the field of vehicle mounting, it is desirable that a PTC protection element includes: the ability to work normally in an environment range of-40 to 125 ℃; the voltage grade is more than or equal to 26V, and larger voltage-resistant grade allowance (vehicle-mounted rated voltage: 12V for passenger vehicles and 24V for commercial vehicles) is required; good environmental reliability, and can meet the AEC-Q200 standard; the PTC protection element has a protection characteristic directly related to the resistance, and after the PTC protection element is restored by a plurality of consecutive trigger operations, the greater the rate of change in resistance, the greater the attenuation of the characteristic of the PTC protection element, and the shorter the life thereof, and therefore, it is desirable that the PTC protection element have a smaller rate of change in resistance, i.e., good PTC resistance reproducibility. The resistance change rate of the PTC protection element under a completely ideal state is close to zero, but the resistance change rate of the current vehicle-mounted PTC protection element which is actually commercialized reaches more than 30% after triggering once, and is generally not less than 80% after 10000 times of continuous triggering actions, so that the development of the PTC protection element for further reducing the resistance change rate has very urgent practical significance.
U.S. patent No. 5451919 provides a polyvinylidene fluoride-based conductive composite material having good PTC characteristics and a PTC device made of the material.
Disclosure of Invention
The invention aims to: provided is a polyvinylidene fluoride-based conductive composite material having excellent PTC characteristics and resistance reproducibility.
Yet another object of the present invention is to: provided is a PTC element using the polyvinylidene fluoride-based conductive composite material. And the number of the first and second groups,
yet another object of the present invention is to: a method for preparing the PTC element is provided.
The purpose of the invention is realized by the following technical scheme: a polyvinylidene fluoride-based conductive composite material takes polyvinylidene fluoride (PVDF) as a matrix, has Positive Temperature Coefficient (PTC) effect, has resistivity of not more than 10 omega cm at an ambient temperature of 25 ℃, and comprises:
a) the PVDF is a first component polymer and accounts for 20-70% of the volume fraction of the polyvinylidene fluoride-based conductive composite material, preferably 25-65%, and more preferably 30-60%;
b) the pre-irradiation crosslinked fluorine-containing polymer is a second component polymer, and is one or a mixture of more than two of Polytetrafluoroethylene (PTFE) which is irradiated and crosslinked with a dose of 0-200 Mrads, polyvinylidene fluoride which is irradiated and crosslinked with a dose of 3.2-200 Mrads, Fluorinated Ethylene Propylene (FEP) which is irradiated and crosslinked with a dose of 3.2-200 Mrads, and tetrafluoroethylene-ethylene copolymer (ETFE) which is irradiated and crosslinked with a dose of 3.2-200 Mrads, wherein the volume fraction of the polyvinylidene fluoride-based conductive composite material is 0.5-30%, preferably 1-20%, and the second component polymer is dispersed in the first component polymer;
c) and the conductive filler accounts for 25-75% of the volume fraction of the polyvinylidene fluoride-based conductive composite material, preferably 30-70%, and is dispersed in the first component polymer.
The invention adopts the fluorine-containing polymer which is irradiated and crosslinked in advance as the second component polymer, has the characteristics of no flow or small fluidity in the melt processing process, and the conductive filler can not enter the second polymer body, so that the resistance stability, the voltage level, the weather resistance and the like are more excellent.
Furthermore, the particle size of the second component polymer is 10 nm-20 μm, preferably 5 nm-15 μm, and the blending effect with PVDF is better.
The conductive filler can be one or a combination of more than two of carbon black, carbon fiber, carbon nano tube, graphite, graphene, ceramic powder, ceramic fiber, metal powder and metal fiber, and carbon black is preferred.
The invention also provides a PTC element prepared from the polyvinylidene fluoride base conductive composite material, which consists of a polyvinylidene fluoride base conductive composite material sheet and metal electrodes tightly connected to two surfaces of the composite material sheet, wherein the thickness of the polyvinylidene fluoride base conductive composite material sheet is 0.01-3.00 mm, preferably 0.05-2.5 mm, the polyvinylidene fluoride base conductive composite material sheet is divided into single PTC elements with plane shapes, the PTC elements are provided with two surfaces vertical to the current flowing direction, and the resistivity of the PTC elements is not more than 10 omega at 25 ℃.
The PTC element has outstanding resistance reproducibility, good voltage resistance and environmental reliability.
On the basis of the scheme, the PTC element is of a sheet structure in a square shape, a triangular shape, a circular shape, a ring shape, a polygonal shape or other irregular shapes.
The invention also provides a preparation method of the PTC element prepared from the polyvinylidene fluoride-based conductive composite material, which comprises the following steps:
1) mixing a first component polymer polyvinylidene fluoride, a second component polymer which is irradiated and crosslinked in advance and a conductive filler at a temperature higher than the melting temperature of the first component polymer polyvinylidene fluoride, for example, putting the mixture into an internal mixer, an open mill, a double-screw extruder or a single-screw extruder at 250 ℃ for melt mixing; then processing the mixed polymer composite material into a polyvinylidene fluoride-based conductive composite material sheet with the thickness of 0.01-3.0 mm in an extrusion molding, compression molding or calendaring molding mode, wherein the preferable thickness is 0.05-2.5 mm, and more preferably 0.1-2.0 mm for the convenience of processing;
2) tightly connecting metal electrodes to the upper surface and the lower surface of the polyvinylidene fluoride base conductive composite material sheet in a roller or flat plate hot pressing mode to form a PTC sheet;
3) the PTC sheet is punched, cut or cut by laser into single PTC elements, the PTC elements are sheet-shaped, namely, the PTC elements have two surfaces which are vertical to the flowing direction of current, and the distance between the two surfaces is not more than 3.0mm, preferably not more than 2.5mm, more preferably not more than 2.0mm, and the PTC elements are prepared;
4) the PTC element is subjected to a cross-linking and/or heat treatment.
On the basis of the scheme, in the step 2), in order to ensure that the metal electrode plate and the polyvinylidene fluoride-based conductive composite material sheet are firmly compounded, the metal electrode can be tightly connected to the upper surface and the lower surface of the sheet in a roller or flat plate hot pressing mode when the polyvinylidene fluoride-based conductive composite material sheet is still in a molten state to obtain a composite sheet;
in the step 4), the PTC element is subjected to crosslinking and/or heat treatment, the PTC element is generally stable in characteristics by means of crosslinking and/or heat treatment, the crosslinking can be performed by chemical or high-energy ray irradiation crosslinking, the irradiation crosslinking of the PTC element is generally not more than 100Mrads, preferably 1-50 Mrads, and more preferably 3.2-32 Mrads; the heat treatment may be annealing, thermal cycling, high and low temperature alternation, such as 135 deg.C/40 deg.C high and low temperature alternation.
The invention has the advantages that: the polyvinylidene fluoride-based conductive composite material has good conductivity, and the PTC element prepared from the polyvinylidene fluoride-based conductive composite material has outstanding resistance reproducibility, good voltage resistance and environmental reliability.
The invention is described in further detail below with reference to the figures and the specific embodiments.
Drawings
FIG. 1 is a schematic view showing the structure of a PTC element according to the present invention;
FIG. 2 is a schematic view of a PTC element including a metal conductive pin according to the present invention;
the reference numbers in the figures illustrate:
11-polyvinylidene fluoride-based conductive composite sheet;
12. 13-upper and lower metal electrodes;
14. 15-upper and lower metal conductive pins.
Detailed Description
Example 1
A PTC element of polyvinylidene fluoride-based conductive composite material is prepared by the following steps:
a polyvinylidene fluoride-based conductive composite material takes PVDF as a matrix, has PTC effect and is prepared by the following steps:
a) the PVDF is a first component polymer, the melting temperature of the PVDF is 173 ℃, the density of the PVDF is 1.8g/cm3, and the volume fraction of the PVDF is 54%;
b) the pre-irradiation crosslinked fluoropolymer is the second component polymer,
the second component polymer is polytetrafluoroethylene PTFE which is not subjected to irradiation crosslinking, the particle size is 120nm, and the density is 2.16 g/cm3The volume fraction is 6 percent;
c) the conductive filler is carbon black, and the volume fraction is 40%.
2, preparing a polyvinylidene fluoride-based conductive composite material sheet:
the temperature of an internal mixer is 250 ℃, the rotating speed is 30 r/min, the polyvinylidene fluoride of the first component polymer is firstly added for internal mixing for 3min, the PTFE of the second component polymer and the conductive filler with the weight of 1/2 are added for internal mixing for 5min, the PTFE of the second component polymer and the conductive filler with the other weight of 1/2 are added, the internal mixing is continued for 10min, the material is discharged, and the obtained material is thinned through a pulling sheet by a open mill to prepare a sheet with the thickness of 0.30-0.34 mm.
And 3, covering metal foils on the upper surface and the lower surface of the sheet to be used as metal electrodes, performing hot-press molding by using a vacuum press, wherein the temperature of the vacuum press is 220 ℃, preheating is performed for 5min, the hot-press pressure is 10MPa, the hot-press time is 8min, the cold-press pressure is 10MPa, and the cold-press time is 10min, and a single PTC element with the size of 12 multiplied by 8mm is formed by stamping a die and consists of a polyvinylidene fluoride base conductive composite material sheet 11 and upper and lower metal electrodes 12 and 13, as shown in figure 1.
And 4, performing electron beam radiation crosslinking on the PTC element by 16M, connecting the upper metal pin 14 and the lower metal pin 15 to the surfaces of the upper metal electrode 12 and the lower metal electrode 13 respectively by a reflow soldering method, and finally performing cold and hot impact for 6 times under the conditions of 135 ℃/1h to 40 ℃/1h to obtain the final PTC element.
The electrical properties of the PTC elements of this example are shown in Table I, and the finished resistance R0Is 20.2; resistance reproducibility (R)10000-R0/R0) 100% to 36.6%; weather resistance (R)1000h@85℃/85%RH-R0)/R0100% to-1.0%; withstand voltage capability (R)36V/50A-R0)/R0100% is 58.9%.
Example 2
A PTC element of a polyvinylidene fluoride based conductive composite similar to example 1 but having a formulation different from the second component polymer, was prepared by the following steps:
a polyvinylidene fluoride-based conductive composite material takes PVDF as a matrix, has PTC effect and is prepared by the following steps:
a) the PVDF is a first component polymer, the melting temperature of the PVDF is 173 ℃, the density of the PVDF is 1.8g/cm3, and the volume fraction of the PVDF is 54%;
b) the second component polymer is cross-linked polyvinylidene fluoride irradiated by 32Mrads dose, and the density of the alkene is 1.8g/cm3The grain diameter is 1 mu m, and the volume fraction is 6 percent;
c) the conductive filler is carbon black, and the volume fraction is 40%.
2, polyvinylidene fluoride-based conductive composite sheet preparation, 3, PTC element preparation and 4, the final PTC element was the same as in example 1.
The electrical properties of the PTC element of this example are shown in table one: finished resistor R0Was 17.3, resistance reproducibility (R)10000-R0/R0) 100% to 32.4%; weather resistance (R)1000h@85℃/85%RH-R0)/R0100% to-0.6%; withstand voltage capability (R)36V/50A-R0)/R0100% is 65.3%.
Example 3
A PTC element of a polyvinylidene fluoride based conductive composite similar to example 1, except that the second component polymer was prepared by the following steps:
a polyvinylidene fluoride-based conductive composite material takes PVDF as a matrix, has PTC effect and is prepared by the following steps:
a) the PVDF is a first component polymer, the melting temperature of the PVDF is 173 ℃, the density of the PVDF is 1.8g/cm3, and the volume fraction of the PVDF is 54%;
b) the second component polymer is:
irradiating a mixture of crosslinked polyvinylidene fluoride with a dose of 32Mrads and crosslinked tetrafluoroethylene-ethylene copolymer with a dose of 16Mrads, wherein the crosslinked polyvinylidene fluoride with the dose of 32Mrads has a density of 1.8g/cm3, a particle size of 1 μm and a volume fraction of 2%; the density of the tetrafluoroethylene-ethylene copolymer which is irradiated and crosslinked by 16Mrads is 1.8g/cm3, the particle size is 1.5 mu m, and the volume fraction is 4 percent;
c) the conductive filler is carbon black, and the volume fraction is 40%.
2, polyvinylidene fluoride-based conductive composite sheet preparation, 3, PTC element preparation and 4, the final PTC element was the same as in example 1.
The electrical properties of the PTC element of this example are shown in table one: finished resistor R0Is 16.4; resistance reproducibility (R)10000-R0/R0) 100% to 32.9%; weather resistance (R)1000h@85℃/85%RH-R0)/R0100% to-1.2%; withstand voltage capability (R)36V/50A-R0)/R0100% was 62.8%.
Example 4
A PTC element of a polyvinylidene fluoride based conductive composite similar to example 1, except that the second component polymer was prepared by the following steps:
a polyvinylidene fluoride-based conductive composite material takes PVDF as a matrix, has PTC effect and is prepared by the following steps:
a) the PVDF is a first component polymer, the melting temperature of the PVDF is 173 ℃, the density of the PVDF is 1.8g/cm3, and the volume fraction of the PVDF is 56%;
b) the pre-irradiation crosslinked fluoropolymer is the second component polymer,
the second component polymer is polytetrafluoroethylene PTFE which is not subjected to irradiation crosslinking, the particle size is 120nm, and the density is 2.16 g/cm3The volume fraction is 4%;
c) the conductive filler is carbon black, and the volume fraction is 40%.
2, polyvinylidene fluoride-based conductive composite sheet preparation, 3, PTC element preparation and 4, the final PTC element was the same as in example 1.
The electrical properties of the PTC element of this example are shown in table one: finished resistor R0Is 18.2; resistance reproducibility (R)10000-R0/R0) 100% to 34.6%; weather resistance (R)1000h@85℃/85%RH-R0)/R0100% to-1.6%; withstand voltage capability (R)36V/50A-R0)/R0*100%61.5%。
Example 5
A PTC element of polyvinylidene fluoride based conductive composite material similar to example 2, except that the second component polymer was prepared by the following steps:
a polyvinylidene fluoride-based conductive composite material takes PVDF as a matrix, has PTC effect and is prepared by the following steps:
a) the PVDF is a first component polymer, the melting temperature of the PVDF is 173 ℃, the density of the PVDF is 1.8g/cm3, and the volume fraction of the PVDF is 56%;
b) the second component polymer is: irradiating the crosslinked polyvinylidene fluoride by using a dose of 32Mrads for 4 percent;
c) the conductive filler is carbon black, and the volume fraction is 40%.
2, polyvinylidene fluoride-based conductive composite sheet preparation, 3, PTC element preparation and 4, the final PTC element was the same as in example 1.
The electrical properties of the PTC element of this example are shown in table one: finished resistor R0Is 15.2; resistance reproducibility (R)10000-R0/R0) 100% to 34.2%; weather resistance (R)1000h@85℃/85%RH-R0)/R0100% to-0.7%; withstand voltage capability (R)36V/50A-R0)/R0100% is 60.5%.
Example 6
A PTC element of polyvinylidene fluoride based conductive composite material similar to example 3, except that the second component polymer was prepared by the following steps:
a polyvinylidene fluoride-based conductive composite material takes PVDF as a matrix, has PTC effect and is prepared by the following steps:
a) the PVDF is a first component polymer, the melting temperature of the PVDF is 173 ℃, the density of the PVDF is 1.8g/cm3, and the volume fraction of the PVDF is 56%;
b) the second component polymer is:
irradiating a mixture of crosslinked polyvinylidene fluoride with a dose of 32Mrads and crosslinked tetrafluoroethylene-ethylene copolymer with a dose of 16Mrads, wherein the crosslinked polyvinylidene fluoride with the dose of 32Mrads has a density of 1.8g/cm3, a particle size of 1 μm and a volume fraction of 1%; the density of the tetrafluoroethylene-ethylene copolymer which is irradiated and crosslinked by 16Mrads is 1.8g/cm3, the particle size is 1.5 mu m, and the volume fraction is 3 percent;
c) the conductive filler is carbon black, and the volume fraction is 40%.
2, polyvinylidene fluoride-based conductive composite sheet preparation, 3, PTC element preparation and 4, the final PTC element was the same as in example 1.
The electrical properties of the PTC element of this example are shown in table one: finished resistor R0Is 21.4; resistance reproducibility (R)10000-R0/R0) 100% to 35.0%; weather resistance (R)1000h@85℃/85%RH-R0)/R0100% to-1.4%; withstand voltage capability (R)36V/50A-R0)/R0100% is 56.1%.
Comparative example 1
The procedure for preparing the polyvinylidene fluoride-based conductive composite and the PTC element was the same as in example 1, except that no second component polymer was added, and the matrix fraction of the first component polymer, polyvinylidene fluoride, was 60%.
The electrical properties of the PTC element of this comparative example are shown in table one: finished resistor R0Is 17.2; resistance reproducibility (R)10000-R0/R0) 100% 271.5%; has a weather resistance of (R)1000h@85℃/85%RH-R0)/R0100% to-4.7%; withstand voltage capability is NA (R)36V/50ABreakdown).
Comparative example 2
The procedure for producing a polyvinylidene fluoride-based conductive composite and a PTC element was the same as in example 1, except that the second component polymer added was a tetrafluoroethylene-ethylene copolymer which was not radiation-crosslinked, and the density of the tetrafluoroethylene-ethylene copolymer which was not radiation-crosslinked was 1.8g/cm3, the particle diameter was 1.5 μm, and the volume fraction was 6%.
The electrical properties of the PTC element of this comparative example are shown in table one: finished resistor R0Is 18.3; resistance reproducibility (R)10000-R0/R0) 100% to 134.4%; the weather resistance is-4.9%; withstand voltage capability (R)36V/50A-R0)/R0100% of NA (R)36V/50ABreakdown).
The formulation compositions and electrical performance test results of the PTC elements of the present invention are shown in Table I. Wherein R0 represents the finished resistance of the PTC element;
r1 represents the resistance value of the PTC element after being electrified for 6s and deenergized for 60s at 16V/50A, electrified and deenergized for 1 time and then placed in an environment at 25 ℃ for at least 1 h;
r10000 represents the resistance value of the PTC element after being electrified for 6s and then continuously electrified for 10000 times under the condition of 16V/50A and being placed for at least 1h under the environment of 25 ℃;
r1000cycles represents the resistance value of the PTC element after being subjected to 1000cycles in a cold and hot impact environment at 125 ℃/60min to-40 ℃/60min and then being placed in an environment at 25 ℃ for at least 1 h;
r1000h @125 ℃ represents the resistance value of the PTC element after being placed in an environment of 125 ℃ for 1000 hours and then being placed in an environment of 25 ℃ for at least 1 hour;
r1000h @85 ℃/85% RH represents the resistance value of the PTC element after being placed in an environment with the temperature of 85 ℃ and the humidity of 85% RH for 1000h and then being placed in an environment with the temperature of 25 ℃ for at least 1 h;
R32V/50A is the resistance value of PTC after being maintained for 24 hours under the condition of 32V/50A electrification and then being placed in the environment at 25 ℃ for at least 1 hour;
R36V/50A is the resistance value after the PTC is subjected to voltage resistance maintenance for 24 hours under the condition of 36V/50A electrification and then is placed in an environment at 25 ℃ for at least 1 hour;
it is understood from examples 1 to 6 and comparative examples 1 to 2 that the conductive filler has the same volume fraction, but in examples 1 to 6, the polymer is divided into a first component polymer and a second component polymer, the second component polymer of examples 1 and 4 is Polytetrafluoroethylene (PTFE), the second component polymer of examples 2 and 5 is polyvinylidene fluoride crosslinked by irradiation of 32Mrads, and the second component polymer of examples 3 and 6 is a mixture of polyvinylidene fluoride crosslinked by irradiation of 32Mrads and tetrafluoroethylene-ethylene copolymer crosslinked by irradiation of 16 Mrads.
The resistance reproducibility, weather resistance and voltage resistance of the examples and the comparative examples are respectively considered to obtain a table I, and the resistance values of the PTC element after being electrified for 6S and deenergized for 60S at 16V/50A, and being electrified and deenergized for 1 time and 10000 times and then being placed in an environment at 25 ℃ for at least 1 hour are known from the table I, the resistance change rates of the examples 1-6 are small, and the obvious resistance reproducibility advantage is shown; in the weather resistance evaluation that the PTC element is respectively subjected to 1000cycles in a cold-hot impact environment of 125 ℃/60min to-40 ℃/60min, placed for 1000 hours at a high temperature of 125 ℃, placed for 1000 hours at a temperature of 85 ℃ and placed for 1000 hours in an environment of 85% RH humidity, the resistance change rate of the embodiments 1-6 is small, which shows that the PTC element has an obvious weather resistance advantage; the PTC elements are respectively maintained at 32V/50A and 36V/50A for 24h, wherein the comparative examples 1-2 have breakdown failure under the condition of 36V/50A voltage resistance, while the PTC elements of the examples 1-6 are normal, which shows that the PTC elements have higher voltage resistance.
Table one illustrates the following:
resistance R of PTC element finished product0；
Resistance reproducibility:
the PTC element is electrified for 6s and deenergized for 60s at 16V/50A, electrified for 1 time and 10000 times, and then placed in an environment at 25 ℃ for at least 1h to form a resistance R1And a resistance R10000The resistance change rate after 1 power on/off is as follows: (R)1-R0/R0) 100% of the total weight; the resistance change rate of 10000 times of power on/off is as follows: (R)10000-R0/R0)*100%；
Weather resistance:
the PTC element respectively carries out 1000 circulating resistances R in a cold-hot impact environment at 125 ℃/60min-40 ℃/60min1000cyclesAnd a resistance R placed at a high temperature of 125 ℃ for 1000h1000h@125℃A resistance R of 1000h placed in an environment with the temperature of 85 ℃ and the humidity of 85 percent RH1000h@85℃/85%RHThe rate of change of resistance is: performing 1000cycles (R) in a cold-hot impact environment at 125 ℃/60min-40 ℃/60min1000cycles-R0)/R0100%, resistance change rate (R) at 125 deg.C for 1000h1000h@125℃-R0)/R0100%, resistance change rate (R) of 1000h placed in 85 ℃ temperature and 85% RH humidity environment1000h@85℃/85%RH-R0)/R0*100%；
Voltage resistance:
the PTC elements respectively have the voltage resistance maintained at 26V/50A for 24h and the resistance is R26V/50AAnd the resistance of the 24h under the withstand voltage of 36V/50A is R36V/50AThe resistance change rate of 24h maintained at 26V/50A is (R)26V/50A--R0)/R0100%, the withstand voltage under 36V/50A maintains the resistance change rate of 24h as (R)36V/50A-R0)/R0*100%，
Claims (6)
1. A polyvinylidene fluoride-based conductive composite material is characterized in that: polyvinylidene fluoride (PVDF) is used as a matrix, has Positive Temperature Coefficient (PTC) effect, has resistivity of not more than 10 omega cm at the ambient temperature of 25 ℃, and comprises:
a) the PVDF is a first component polymer and accounts for 20-70% of the volume fraction of the polyvinylidene fluoride-based conductive composite material;
b) irradiating a crosslinked fluoropolymer as a second component polymer in advance, wherein the second component polymer is one or a mixture of more than two of crosslinked Polytetrafluoroethylene (PTFE) irradiated at a dose of 0-200 Mrads, crosslinked polyvinylidene fluoride irradiated at a dose of 3.2-200 Mrads, crosslinked Fluorinated Ethylene Propylene (FEP) irradiated at a dose of 3.2-200 Mrads and crosslinked tetrafluoroethylene-ethylene copolymer (ETFE) irradiated at a dose of 3.2-200 Mrads, and accounts for 0.5-30% of the volume fraction of the polyvinylidene fluoride-based conductive composite, and the second component polymer is dispersed in the first component polymer;
c) and the conductive filler accounts for 25-75% of the volume fraction of the polyvinylidene fluoride-based conductive composite material, and is dispersed in the first component polymer.
2. The polyvinylidene fluoride-based conductive composite of claim 1, wherein: the particle size of the second component polymer is 10 nm-20 μm.
3. The polyvinylidene fluoride-based conductive composite of claim 1, wherein: the conductive filler can be one or a composition of more than two of carbon black, carbon fiber, carbon nano tube, graphite, graphene, ceramic powder, ceramic fiber, metal powder and metal fiber.
4. A PTC element prepared from the polyvinylidene fluoride-based conductive composite material according to any one of claims 1 to 3, which comprises a polyvinylidene fluoride-based conductive composite material sheet having a thickness of 0.01 to 3.00mm and divided into individual PTC elements having a planar shape, and metal electrodes closely attached to both surfaces of the composite material sheet, the PTC element having two surfaces perpendicular to a current flowing direction, and having a resistivity of not more than 10 Ω.
5. A PTC element prepared from polyvinylidene fluoride-based conductive composite material according to claim 4, wherein: the PTC element is a sheet structure with a square shape, a triangular shape, a circular shape, a ring shape, a polygonal shape or other irregular shapes.
6. A method for preparing a PTC element prepared from the polyvinylidene fluoride-based conductive composite according to claims 4 and 5, comprising the steps of:
1) mixing a first component polymer polyvinylidene fluoride, a second component polymer which is irradiated and crosslinked in advance and a conductive filler at a temperature higher than the melting temperature of the first component polymer polyvinylidene fluoride, and then processing the mixed polymer composite material into a polyvinylidene fluoride-based conductive composite material sheet with the thickness of 0.01-3.0 mm in an extrusion molding, compression molding or calendaring molding manner;
2) tightly connecting metal electrodes to the upper surface and the lower surface of the polyvinylidene fluoride base conductive composite material sheet in a roller or flat plate hot pressing mode to form a PTC sheet;
3) the PTC sheet is punched, cut or laser cut into single PTC elements, the PTC elements are sheet-shaped, namely two surfaces which are vertical to the flowing direction of current are arranged, and the distance between the two surfaces is not more than 3.0 mm;
the PTC element is subjected to a cross-linking and/or heat treatment.
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| CN102140194A (en) * | 2010-01-29 | 2011-08-03 | 比亚迪股份有限公司 | Material with positive temperature coefficient, preparation method thereof and thermosensitive resistor having same |
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| CN102140194A (en) * | 2010-01-29 | 2011-08-03 | 比亚迪股份有限公司 | Material with positive temperature coefficient, preparation method thereof and thermosensitive resistor having same |
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