Lower curie point positive temperature coefficient polymer composite material, preparation method and application thereof

Abstract

The application discloses a lower Curie point positive temperature coefficient polymer composite material and a preparation method and application thereof, and belongs to the polymer positive temperature coefficient thermistor material. The lower Curie point positive temperature coefficient polymer composite material is prepared from fatty acid, random copolymer and conductive filler. Specifically, the fatty acid is used as a phase change material, and the random copolymer is used as a composite material support. The polymer thermistor obtained by the technical scheme has the advantages of low room temperature resistance, poor repeatability and obvious NTC effect of the PTC material with a Curie temperature in the normal temperature range, and the lower Curie point positive temperature coefficient polymer composite material has low low-temperature resistivity, low Curie temperature and high PTC strength. The polymer thermistor has better reliability and stability, and has a wide application prospect in the fields of circuit protection and integrated circuits.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer positive temperature coefficient thermistor materials (PPTC materials), and particularly relates to a polymer composite material with a low Curie point positive temperature coefficient, its preparation method, and its application. Background Technology

[0002] PTC (Positive Temperature Coefficient) materials are thermistors exhibiting a positive temperature coefficient effect. The resistivity of PTC materials remains essentially constant or changes only slightly at low temperatures; however, when the temperature exceeds the Curie temperature, the resistivity of PTC materials increases sharply with increasing temperature—a phenomenon known as the PTC effect. In contrast to the PTC effect is the NTC (Negative Temperature Coefficient) effect, which is the effect of decreasing resistivity with increasing temperature. The NTC effect is generally avoided when using positive temperature coefficient materials. At normal temperatures, conductive particles form a low-resistance conductive network within the matrix. However, when the temperature rises above the device's operating temperature, whether due to high current flowing through the device or increased ambient temperature, the grains in the matrix melt and form an amorphous state. During this melting process, the increase in volume separates the conductive particles on the conductive chains, resulting in a nonlinear increase in the resistance of the PTC device by three or more orders of magnitude. The research and development of PTC materials are quite extensive, but the research and application of PTC materials are mainly limited to the high-temperature field. This is mainly because the Curie temperature of widely used polymer-based PTC composite materials is generally high (50-300℃), which makes it difficult to meet the requirements of use in the room temperature range.

[0003] Patent CN116959825A discloses a thermistor and a self-feedback flexible microheater, along with their preparation method and applications. The heater has a Curie temperature of 35°C, but its room temperature resistivity is high and its PTC strength is low. In the field of high-temperature PTC materials, patent CN118271724A discloses a polymer-based PTC material with high room temperature conductivity and its preparation method. This polymer-based composite material has extremely low room temperature resistivity and a PTC strength exceeding 7.38. In the field of low-temperature PTC materials, patent CN117736525A uses a hydrothermal method to prepare a porous carbon metal oxide / polyvinylidene fluoride conductive composite material. This material has low room temperature resistivity and a Curie temperature around 30°C, but its PTC strength is not high.

[0004] Currently, some researchers have prepared a series of polymer-based PTC materials with room temperature Curie temperatures using materials such as paraffin or EVA as matrix materials. However, these materials still suffer from problems such as high low-temperature resistivity and poor PTC repeatability, which present some drawbacks in practical applications. Similarly, some researchers have prepared low Curie temperature PTC materials using a melt method. Although these materials have low Curie temperatures and low room temperature resistivity, the uniformity of mixing remains a significant challenge. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a polymer composite material with a low Curie point positive temperature coefficient, its preparation method, and its applications. The composite material uses fatty acids as the phase change material and LDPE as the supporting material to overcome the problems of existing PTC materials, such as high Curie temperature, high room temperature resistivity, poor repeatability, and susceptibility to the NTC effect.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A polymeric composite material with a low Curie point positive temperature coefficient comprises the following raw materials in mass percentage: fatty acids 38.46-76.25%, random copolymers 12.82-47.65%, and conductive fillers 4.69-23.08%.

[0008] Furthermore, the fatty acid is one or more of myristic acid, palmitic acid, stearic acid, and n-alkane acid derivatives.

[0009] Furthermore, the random copolymer is one or more of polyvinylidene fluoride, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ultra-high molecular weight polyethylene.

[0010] Furthermore, the conductive filler is a carbon-based conductive particle; the carbon-based conductive particle is one or both of carbon black and graphite powder.

[0011] This invention also provides a method for preparing the aforementioned low Curie point positive temperature coefficient polymer composite material, comprising the following steps:

[0012] The random copolymer was dissolved in xylene and stirred until homogeneous to obtain the solution.

[0013] The solvent, fatty acid and conductive filler are stirred evenly to obtain a solution mixture.

[0014] The solution mixture is dried in a vacuum oven to obtain the mixture;

[0015] The mixture is molded to obtain a polymer composite material with a low Curie point positive temperature coefficient.

[0016] Furthermore, during the preparation of the solvent, the stirring speed is 300-900 rpm and the heating temperature is 60-120℃; during the preparation of the solution mixture, the stirring speed is 300-900 rpm, the time is 0.5-5h, and the heating temperature is 60-120℃.

[0017] Furthermore, the drying temperature is 60-100℃.

[0018] The present invention also provides an application of the aforementioned low Curie point positive temperature coefficient polymer composite material in the preparation of positive temperature coefficient materials.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects:

[0020] The low Curie point positive temperature coefficient polymer composite material of this application uses random copolymers as the supporting matrix of the composite material. Since random copolymers have a large melting point and high viscosity, the conductive filler plays the role of forming a conductive network structure. After the fatty acid melts and destroys the conductive network, it can prevent the flow of molten fatty acid and prevent the conductive network from reforming, thereby effectively weakening the NTC effect. At the same time, due to the addition of low melting point fatty acids, the material resistance of the low Curie point positive temperature coefficient polymer composite material can undergo a large abrupt change near the melting point of fatty acid phase change material, thereby achieving a low Curie temperature and a very high PTC strength.

[0021] The low Curie point positive temperature coefficient polymer composite material prepared by this invention has a Curie temperature close to human body temperature (38-43℃), and at the same time has a very low room temperature resistivity and a high PTC strength, which makes up for the shortcomings of current PTC materials with Curie temperatures in the room temperature range, such as high room temperature resistance, low PTC strength and obvious NTC effect.

[0022] The low Curie point positive temperature coefficient polymer composite material prepared by this invention has a Curie temperature close to human body temperature, and has good application prospects in electronic devices that come into frequent contact with the human body.

[0023] This invention uses a solution method for preparation, which is simple, easy to control in terms of production conditions, uses inexpensive raw materials, and has low production costs, making it a promising candidate for industrial application. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 The thermal resistance diagram of the low Curie point positive temperature coefficient polymer composite material in Example 3;

[0026] Figure 2 A comparison diagram of the thermal resistance of the low Curie point positive temperature coefficient polymer composites of Example 3 and Comparative Example 3.

[0027] Figure 3 This is a comparison chart of the low Curie point positive temperature coefficient thermal resistance of polymers in Examples 1, 2, 4, and Comparative Example 1. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] This invention provides a method for preparing a polymer composite material with a low Curie point positive temperature coefficient. The composite material includes a polymer matrix and a conductive filler uniformly distributed within the polymer matrix. In some preferred embodiments, the polymer matrix comprises a random copolymer and a fatty acid. The specific preparation method includes the following steps:

[0034] (1) Dissolve the random copolymer in xylene and stir until homogeneous to obtain the solution;

[0035] (2) Stir the solvent, fatty acid and conductive filler evenly to obtain a solution mixture;

[0036] (3) The solution mixture is dried in a vacuum oven to obtain a mixture;

[0037] (4) The mixture is molded to obtain a polymer composite material with a lower Curie point positive temperature coefficient.

[0038] In some preferred embodiments, step (1) involves stirring at a speed of 500-800 rpm, preferably at 500 rpm until dissolved. The stirring is performed under heating conditions at a temperature of 70-110°C. When the stirring temperature is below 60°C, the random polymer is difficult to dissolve in xylene. When the stirring temperature is above 120°C, the phase change material and solvent will exhibit a certain degree of volatilization due to the excessively high temperature, which is not conducive to processing. Therefore, the preferred temperature is 80-85°C.

[0039] In some preferred embodiments, in step (2), the stirring speed is 400-900 rpm (preferably 500-800 rpm) and the time is 0.5-3 h (preferably 10-60 min). The stirring is carried out under heating conditions, and the heating temperature is 60-110℃ (preferably 80-83℃).

[0040] In some preferred embodiments, step (2) involves two steps of mixing: first, mixing at a temperature of 80-85°C and a speed of 500 rpm for 5-10 minutes, and then adjusting the speed to 800 rpm and mixing for 30-120 minutes to obtain a solution mixture.

[0041] In some preferred embodiments, in step (3), the drying temperature in the vacuum oven is 60-100°C, preferably 80-90°C for 4-12 hours.

[0042] The low Curie point positive temperature coefficient polymer composite material prepared using the above method has a Curie temperature of 38-43℃. Specifically, it comprises the following raw materials by mass percentage: fatty acids 38.46-76.25%, random copolymers 12.82-47.65%, and conductive fillers 4.69-23.08%. When the mass percentage of random copolymers is less than 12.82% and the mass percentage of fatty acids is greater than 76.25%, the synthesized positive temperature coefficient polymer material, due to the insufficient amount of random copolymers, cannot maintain its shape after heating and is prone to collapse. When the mass percentage of random copolymers is greater than 47.65% and the mass percentage of fatty acids is less than 38.46%, the excessive mass percentage of random copolymers prevents the conductive network of the positive temperature coefficient polymer material from being completely destroyed during heating, resulting in a weaker PTC effect at lower temperatures. A mass ratio of random copolymer to phase change material of approximately 1:3 achieves better results.

[0043] In some preferred embodiments, the fatty acid is one or more of myristic acid, palmitic acid, stearic acid, and n-alkane acid derivatives, preferably palmitic acid or stearic acid. These fatty acids contribute to a more uniform dispersion of the conductive filler within it, a denser conductive mesh, and lower filler density and room temperature resistance of the conductive filler.

[0044] In some preferred embodiments, the random copolymer is polyvinylidene fluoride or high-density polyethylene (HDPE, with a density of 0.941-0.960 g / cm³). 3 Low-density polyethylene (LDPE, density 0.91-0.93 g / cm³) 3 Linear low-density polyethylene (LLDPE, with a density of 0.918-0.935 g / cm³) 3 ) and ultra-high molecular weight polyethylene (UHMWPE, density 0.920-0.964 g / cm³) materials. 3 One or more of the following, preferably LDPE. These random copolymers act as supporting materials in positive temperature coefficient polymers, ensuring that the material does not collapse when the ambient temperature reaches the melting point of fat-sized acids, and also providing excellent electrical and temperature response properties for positive temperature coefficient polymers.

[0045] In some preferred embodiments, the conductive filler is carbon-based conductive particles; the carbon-based conductive particles are carbon black or graphite powder. These conductive fillers serve to form a conductive network structure.

[0046] Unless otherwise specified, "room temperature" in this invention refers to 20-30℃.

[0047] All raw materials used in the following embodiments and comparative examples of this invention are commercially available products well known to those skilled in the art. LDPE, LLDPE, HDPE, EVA12, EVA18, conductive carbon black, and graphite powder were purchased from Shanghai Titan Technology Co., Ltd. (Adamas); xylene and stearic acid were purchased from Shanghai Titan Technology Co., Ltd. (Greagent).

[0048] The technical solution of the present invention will be further illustrated by the following embodiments.

[0049] Example 1

[0050] A method for preparing a polymer composite material with a low Curie point positive temperature coefficient, the specific steps of which are as follows:

[0051] (1) Dissolve 3.6g LDPE in 36mL xylene, set the oil bath temperature to 80℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0052] (2) Add 3.6g palmitic acid and 2.16g graphite to the above-mentioned solvent, mix for 10 minutes at 80℃ and 500rpm, then adjust the speed to 800rpm and mix for 60 minutes to obtain the solution mixture.

[0053] (3) Pour the solution mixture into an evaporating dish, dry it in a vacuum oven at 80°C for 6 hours to evaporate the xylene, and then cool it to room temperature to obtain the mixture;

[0054] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC1.

[0055] Example 2

[0056] A method for preparing a polymer composite material with a low Curie point positive temperature coefficient, the specific steps of which are as follows:

[0057] (1) Dissolve 1.2g LDPE in 12mL xylene, set the oil bath temperature to 80℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0058] (2) Add 6g palmitic acid and 2.16g graphite to the above-mentioned solvent, mix for 10 minutes at 80℃ and 500rpm, then adjust the speed to 800rpm and mix for 30 minutes to obtain the solution mixture.

[0059] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 80°C for 6 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0060] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC2.

[0061] Example 3

[0062] A method for preparing a polymer composite material with a low Curie point positive temperature coefficient, the specific steps of which are as follows:

[0063] (1) Dissolve 1.2g LDPE in 12mL xylene, set the oil bath temperature to 83℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0064] (2) Add 3.6g palmitic acid and 1.2g graphite to the above-mentioned solvent, mix for 5 minutes at a temperature of 83℃ and a speed of 500rpm, then adjust the speed to 800rpm and mix for 60 minutes to obtain the solution mixture;

[0065] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 90°C for 12 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0066] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC3.

[0067] Example 4

[0068] A method for preparing a polymer composite material with a low Curie point positive temperature coefficient, the specific steps of which are as follows:

[0069] (1) Dissolve 1g LDPE in 10mL xylene, set the oil bath temperature to 85℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0070] (2) Add 3g of stearic acid and 1.2g of graphite to the above-mentioned solvent. Mix for 10 minutes at a temperature of 85℃ and a speed of 500rpm. Then adjust the speed to 800rpm and mix for 120 minutes to obtain the solution mixture.

[0071] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 80°C for 6 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0072] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC4.

[0073] Example 5

[0074] A method for preparing a polymer composite material with a low Curie point positive temperature coefficient, the specific steps of which are as follows:

[0075] (1) Dissolve 1.4g LDPE in 14mL xylene, set the oil bath temperature to 85℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0076] (2) Add 4.2g stearic acid and 1.2g graphite to the above-mentioned solvent, mix for 5 minutes at a temperature of 85℃ and a speed of 500rpm, then adjust the speed to 800rpm and mix for 100 minutes to obtain the solution mixture.

[0077] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 88°C for 5 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0078] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC5.

[0079] Comparative Example 1

[0080] A method for preparing a polymer composite material with a low Curie point positive temperature coefficient, the specific steps of which are as follows:

[0081] (1) Dissolve 1.3g EVA12 in 13mL xylene, set the oil bath temperature to 83℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0082] (2) Add 5.2g palmitic acid and 0.32g carbon black to the above-mentioned solvent, mix for 10min at a temperature of 83℃ and a speed of 500rpm, then adjust the speed to 800rpm and mix for 60min to obtain the solution mixture;

[0083] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 90°C for 4 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0084] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC6.

[0085] Comparative Example 2

[0086] A method for preparing a polymer composite material with a low Curie point positive temperature coefficient, the specific steps of which are as follows:

[0087] (1) Dissolve 3.25g EVA12 in 32.5mL xylene, set the oil bath temperature to 70℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0088] (2) Add 3.25g palmitic acid and 0.32g carbon black to the above-mentioned solvent. Mix for 15 minutes at 70℃ and 500rpm, then adjust the speed to 800rpm and mix for 30 minutes to obtain the solution mixture.

[0089] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 70°C for 12 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0090] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC7.

[0091] Comparative Example 3

[0092] A method for preparing a common PTC composite material (without fatty acids as a phase change material) includes the following steps:

[0093] (1) Dissolve 4.8g LDPE in 48mL xylene, set the oil bath temperature to 80℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0094] (2) Add 1.2g of graphite to the above-mentioned solvent, mix for 10min at 80℃ and 500rpm, then adjust the speed to 800rpm and mix for 60min to obtain the solution mixture.

[0095] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 80°C for 6 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0096] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC8.

[0097] Comparative Example 4

[0098] A method for preparing a common PTC composite material (without fatty acids as a phase change material) includes the following steps:

[0099] (1) Dissolve 4.8g of EVA12 in 48mL of xylene, set the oil bath temperature to 80℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0100] (2) Add 1.2g of graphite to the above-mentioned solvent, mix for 10min at 80℃ and 500rpm, then adjust the speed to 800rpm and mix for 60min to obtain the solution mixture;

[0101] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 80°C for 6 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0102] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC9.

[0103] Comparative Example 5

[0104] A method for preparing a common PTC composite material (without fatty acids as a phase change material) includes the following steps:

[0105] (1) Dissolve 6.5g EVA12 in 48mL xylene, set the oil bath temperature to 80℃ and the speed to 500rpm, and stir until the random copolymer is completely dissolved to obtain the solution;

[0106] (2) Add 0.98g of graphite to the above-mentioned solvent, mix for 10min at 80℃ and 500rpm, then adjust the speed to 800rpm and mix for 60min to obtain the solution mixture.

[0107] (3) Pour the solution mixture into an evaporating dish and dry it in a vacuum oven at 80°C for 6 hours to evaporate the xylene. After cooling to room temperature, the mixture can be obtained.

[0108] (4) The mixture is pressed into a circular sample with a diameter of 10 mm and a thickness of 0.75 mm by a hot press and cooled to room temperature to obtain a low Curie point PTC composite material, denoted as PTC10.

[0109] Comparative Example 6

[0110] Same as Example 3, except that the amount of LDPE added is 0.3g, the amount of palmitic acid added is 3.7g, and the amount of graphite added is 1.2g. A low Curie point PTC composite material was obtained, denoted as PTC11.

[0111] Comparative Example 7

[0112] Same as Example 3, except that palmitic acid was replaced with tetradecyl alcohol by mass. A low Curie point PTC composite material was obtained, denoted as PTC12.

[0113] The compositional conditions of the low Curie point PTC composite material PTC1-12 prepared above are summarized, along with the corresponding low-temperature resistivity (ρ15℃), Curie temperature, and PTC strength (P=Lg(ρ15℃) of the PTC composite material PTC1-12). max / ρ min , ρ max ρ is the maximum resistivity of the material. min The material's minimum resistivity and other properties were tested, and the test results are shown in Table 1.

[0114] Table 1 is a comparison table of raw material composition, low-temperature resistivity, Curie temperature, and PTC strength for Examples 1-5 and Comparative Examples 1-7.

[0115]

[0116] As shown in Table 1, when the mass ratio of fatty acids to LDPE is 1:3, the composite material exhibits both low room temperature resistivity and high PTC strength. With increasing random copolymer mass percentage, the conductive network of the positive temperature coefficient polymer cannot be completely destroyed during heating due to the excessively large percentage of random copolymer. This results in a weaker PTC effect at lower temperatures, failing to achieve the desired low Curie temperature composite material. Simultaneously, the increased mass fraction of random copolymer makes it more difficult for conductive pathways to form in the composite material, leading to a higher room temperature resistivity. Conversely, insufficient random copolymer content causes the material to collapse easily after heating, preventing the achievement of higher resistivity and resulting in lower PTC strength.

[0117] Figure 1 The figure shows the temperature resistance of the low Curie point positive temperature coefficient polymer composite material in Example 3. As can be seen from the figure, the material exhibits a significant increase in resistance at 60°C and maintains good stability up to 80°C.

[0118] Figure 2 The graph shows a comparison of the temperature resistance of the low Curie point positive temperature coefficient polymer composites of Example 3 and Comparative Example 3. As can be seen from the graph, the composite material without the addition of phase change material not only has a higher room temperature resistance, but also a lower PTC strength than the composite material with the addition of phase change material.

[0119] Figure 3This is a comparison graph of the low Curie point positive temperature coefficient polymer thermal resistance of Examples 1, 2, 4, and Comparative Example 1. As can be seen from the graph, the composite material with EVA as the copolymer has a higher room temperature resistance and a slower heating rate compared to the composite material with LDPE as the copolymer.

[0120] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A polymer composite material with a low Curie point positive temperature coefficient, characterized in that, The raw materials include the following percentages by weight: fatty acids 38.46-76.25%, low-density polyethylene 12.82-47.65%, and conductive filler 4.69-23.08%; The fatty acid is one or more of myristic acid, palmitic acid and stearic acid; The mass ratio of low-density polyethylene to fatty acids is 1:

3.

2. A method for preparing a polymer composite material with a low Curie point positive temperature coefficient as described in claim 1, characterized in that, Includes the following steps: Low-density polyethylene is dissolved in xylene and stirred until homogeneous to obtain the solution; The solvent, fatty acid and conductive filler are stirred evenly to obtain a solution mixture. The solution mixture is dried in a vacuum oven to obtain the mixture; The mixture is molded to obtain a polymer composite material with a low Curie point positive temperature coefficient.

3. The method for preparing a low Curie point positive temperature coefficient polymer composite material according to claim 2, characterized in that, During the preparation of the solvent, the stirring speed is 300-900 rpm and the heating temperature is 60-120℃; during the preparation of the solution mixture, the stirring speed is 300-900 rpm, the time is 0.5-5h, and the heating temperature is 60-120℃.

4. The method for preparing a low Curie point positive temperature coefficient polymer composite material according to claim 2, characterized in that, The drying temperature is 60-100℃.

5. The application of the low Curie point positive temperature coefficient polymer composite material as described in claim 1 in the preparation of positive temperature coefficient materials.

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