A PPTC nanocoating material for room temperature thermal control and its preparation method

Abstract

This invention discloses a PPTC nano-coating material for room-temperature thermal control and its preparation method, comprising the following components in parts by weight: 100 parts low-melting-point paraffin wax, 60-150 parts conductive filler, 3-8 parts dispersant modifier, 0.1-0.8 parts low-temperature initiator, 1-3 parts emulsifier, and 200-300 parts deionized water. The raw materials are widely available, and the preparation method is simple and feasible. It produces a dispersion emulsion with a particle size of 100-300 nm. The resulting nano-coating exhibits a Curie temperature of 50-70℃ and a PTC strength of 3-5, demonstrating strong PTC and nano-effects, good coatability, and stability. It can be applied to fields such as thermosensitive, antistatic, and electric heating films, thus broadening its application range.

Description

Technical Field

[0001] This invention belongs to the technical field of composite PTC materials for thermal control, specifically relating to a PPTC nano-coating material for room temperature thermal control and its preparation method. Background Technology

[0002] Polymer conductive composites (PPTCs) exhibit a positive temperature coefficient, demonstrating rapid response to current and temperature. At room temperature, the resistivity of PPTC remains essentially constant or changes only slightly. However, when overcurrent or overtemperature occurs in a circuit, and the temperature rises to a specific transition temperature (Curie temperature) of the PPTC, its resistivity rapidly increases within a narrow temperature range of a few to a dozen degrees Celsius. Based on these properties, PPTCs have wide applications in circuit protection and electric heater technology, making the manufacture of high-strength PPTC materials of significant importance.

[0003] Currently, PPTC materials are mainly used in PTC components. The most widely used PPTC material is a conductive polymer component made of polyethylene as the base material, filled with conductive materials such as conductive carbon black, graphene, and carbon fiber. There is a demand for PPTC materials as conductive coatings, which show great promise in circuit protection, especially in electric heater technology. Conductive coating materials are required to have characteristics such as overheat protection, strong heat dissipation capacity, and simple manufacturing process.

[0004] Conductive coatings, applied using coating and printing processes, offer advantages such as uniform heating, high thermal efficiency, and low electromagnetic radiation, making them a next-generation high-efficiency electrothermal and protection technology. Researchers have conducted a series of studies on this technology. For example, patent document CN108738170A discloses a graphene nano-coated PTC electric heater and its manufacturing method. This involves uniformly mixing graphene nanopowder and liquid resin to form a mixture, coating it onto the surface of a heat sink, and then curing it to prepare the electric heater. The coating thickness is 1-10 micrometers. Patent document CN108912990A discloses a water-based PTC nano-carbon electrothermal coating and its preparation method, composed of conductive carbon materials, polymer micropowder, additives, water-based binder resin, and water. The polymer micropowder undergoes hydrophilication treatment and is then dispersed in the binder resin system through high-speed shearing to form a uniform and stable resin dispersion slurry. The ground and dispersed nano-carbon conductive slurry and various additives are mixed with this slurry, and after defoaming, the finished coating is obtained. However, the conductive coatings in these patent documents are all at the micrometer level and do not achieve nano-scale coating.

[0005] Paraffin wax is a mixture of hydrocarbons extracted from certain distillates of petroleum, shale oil, or other bituminous mineral oils, with solid alkanes as its main component. Paraffin wax is amorphous but possesses a distinct crystalline structure, thus it can be used in composite PTC materials for thermal control. For example, patent document CN103594214A discloses a room-temperature thermal control composite PTC material made from graphite powder or carbon black, paraffin wax or alkane substances, and low-density polyethylene. The preparation method involves melting and mixing paraffin wax or alkane substances with low-density polyethylene under vacuum at a temperature of 130–170°C, and stirring until homogeneous; then adding graphite powder or carbon black, and stirring and mixing homogeneously under vacuum at 130–170°C to obtain a mixture; finally, pressing the mixture into a mold to obtain a rod-shaped room-temperature thermal control composite PTC material. However, this document uses polymer molding methods such as compression molding, which are not suitable for conductive coating materials. Patent document CN109294465A discloses a flexible polymer-based PTC material for room-temperature thermal control and its preparation method. This material comprises an ethylene-octene block copolymer, a paraffin phase change matrix, and conductive filler graphite powder or conductive carbon black. The mass ratio of the block copolymer to the phase change matrix is ​​(20:80) to (40:60). The flexible polymer-based PTC material exhibits a Curie temperature of -10 to 40°C, demonstrates good flexibility, and can be fabricated into thin films, making it suitable for active temperature control in electronic devices and other room-temperature thermal control applications. However, while this material is suitable for extrusion and can be used to prepare flexible thin-film PTC, it is not suitable for coating or the preparation of nano-coatings.

[0006] In recent years, with the rapid development of the electronic furniture industry, the requirements for thermal control materials suitable for home use have also increased. PPTC materials, as active thermal control systems for heating resistors, have gradually become mainstream. Currently, in the field of room temperature heating resistors, high Curie temperature, low PTC strength, and a lack of nano-coatings have become significant obstacles to the development of this field. Therefore, it is necessary to optimize the performance of room temperature PPTC materials and develop room temperature thermal control PPTC nano-coated materials. Summary of the Invention

[0007] The purpose of this invention is to provide a PPTC nano-coating material for room temperature thermal control and its preparation method, so as to solve the problem that the existing PPTC materials cannot maintain a high PTC effect while realizing a nano-coating, and obtain a PPTC nano-coating with both low Curie temperature and high PTC strength.

[0008] This invention is achieved through the following technical solution:

[0009] The present invention discloses a PPTC nano-coating material for room temperature thermal control, characterized in that it is made of components comprising the following parts by weight:

[0010] 100 parts low-melting-point paraffin, 60-150 parts conductive filler, 3-8 parts dispersant modifier, 0.1-0.8 parts low-temperature initiator, 1-3 parts emulsifier, and 200-300 parts deionized water;

[0011] The low-melting-point paraffin wax has a melting point of 45–65°C. It is obtained from lubricating oil fractions obtained by crude oil distillation through solvent refining, solvent dewaxing, or wax freeze crystallization and pressing to produce a wax paste. This paste is then further refined through solvent deoiling or sweating deoiling to obtain flaky or needle-like crystals, such as Kunlun brand No. 58 paraffin wax from China Petroleum & Chemical Corporation. In the cured PPTC nano-coating material, the low-melting-point paraffin wax accounts for 30%–70% of the total mass.

[0012] The conductive filler has a specific surface area of ​​10–3000 m². 2 / g of conductive carbon black, graphite powder, graphene powder, and carbon nanotube powder; in the cured PPTC nano-coating material, the conductive filler accounts for 30% to 70% of the total mass;

[0013] The dispersing modifier is an ethylene-vinyl acetate copolymer with a melt index (MI) of 200-400 g / 10 min and a vinyl acetate (VAc) content of 25%-33%; the low-temperature initiator is one of the azo radical initiators, such as azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate; the emulsifier is one or more of the long-chain alkyl sulfonate surfactants, such as sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, and sodium hexadecylbenzenesulfonate.

[0014] The present invention discloses a method for preparing a PPTC nano-coating material for room temperature thermal control, characterized by comprising the following steps:

[0015] (1) The dispersant modifier, low-temperature initiator and conductive filler are added to the low-melting-point paraffin at a temperature of 55-70°C and stirred to mix evenly. Then, the mixture is dispersed evenly by ultrasonication to obtain a composite conductive material.

[0016] (2) The emulsifier is added to the deionized water and dissolved into a transparent state to obtain an emulsion;

[0017] (3) While stirring, pour the emulsion into the composite conductive material at a temperature of 55-70°C to make it completely uniform, and obtain a nanoemulsion with an average particle size of 100-300 nm.

[0018] (4) The nanoemulsion is coated into a coating of 300-800 nm and cured at 70-90 °C to obtain nano PPTC coating material.

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

[0020] Based on the PTC effect mechanism, this invention uses low-melting-point paraffin as a base material and ethylene-vinyl acetate copolymer as a dispersant modifier. The raw materials are widely available, and the preparation method is simple and feasible. By optimizing the emulsification conditions, a dispersion emulsion with a particle size of 100-300 nm is prepared, which can be coated into a nano-coating. The obtained nano-coating exhibits a Curie temperature of 50-70℃ and a PTC strength of 3-5, demonstrating strong PTC and nano-effects, as well as good coatability and stability. It can be applied to fields such as thermosensitive, antistatic, and electric heating films, thus broadening its application range. Attached Figure Description

[0021] Figure 1 Example 1 uses a laser particle size analyzer to determine the particle size and distribution of particles in an emulsion.

[0022] Figure 2 This is a graph showing the change of resistivity ρ with temperature T in Example 1.

[0023] Figure 3 Example 2 uses a laser particle size analyzer to determine the particle size and distribution of particles in the emulsion.

[0024] Figure 4 This is a graph showing the change in resistivity ρ with temperature T in Example 2.

[0025] Specific examples

[0026] The present invention will be further illustrated by examples below. The following description is only for explaining the present invention and does not limit the content. The technical solution of the present invention will be further described with reference to the accompanying drawings.

[0027] The raw materials used in the following examples are all commercially available products. Low-melting-point paraffin: Kunlun brand No. 58 paraffin from China Petroleum & Chemical Corporation; Ethylene-vinyl acetate copolymer: Sumitate KE-10 produced by Sumitomo Corporation of Japan, with an MI value of 300g / 10min and a VAc content of 28%; Conductive carbon black: Asahi F-200GS produced by Asahi Carbon Co., Ltd. of Japan, with a specific surface area of ​​55m². 2 / g; Graphene micro powder: C-09 produced by Hunan Keen New Material Technology Co., Ltd., with a specific surface area of ​​500m². 2 / g; Carbon nanotube powder: NFF22 grade produced by Nanjing Pioneer Nanomaterials Technology Co., Ltd., with a specific surface area of ​​1800 m². 2 / g.

[0028] Example 1

[0029] (1) Using the in-situ modification method, 4 parts of the dispersion modifier ethylene-vinyl acetate copolymer, 0.3 parts of the low temperature initiator azobisisobutyronitrile and 110 parts of conductive carbon black were added to 100 parts of low melting point paraffin at 60℃ and stirred for 5 minutes to make them uniformly mixed. Then, the dispersion was enhanced by ultrasound for 10 minutes to make them more dispersed, and a composite conductive material was obtained.

[0030] (2) Add 1.5 parts of sodium dodecylbenzenesulfonate emulsifier to 220 parts of deionized water to dissolve until transparent to obtain an emulsion;

[0031] (3) While stirring, slowly pour the emulsion into the composite conductive material in three portions, and continue stirring to make it completely uniform, so as to obtain a nano-emulsion with an average particle size of 247.4 nm. Figure 1 The paper demonstrates the use of a laser particle size analyzer to determine the particle size and distribution in nanoemulsions.

[0032] (4) The nano-PPTC coating material is coated to form a coating with a thickness of about 500 nm and cured at 75°C to obtain the nano-PPTC coating material. Figure 2 The graph shows the resistivity ρ of the coating material as a function of temperature T. The PTC strength value of the coating material is 3.22.

[0033] Example 2

[0034] (1) Using the in-situ modification method, 6 parts of the dispersion modifier ethylene-vinyl acetate copolymer, 0.6 parts of the low-temperature initiator azobisisobutyronitrile and 140 parts of conductive carbon black were added to 100 parts of low-melting-point paraffin at 55°C and stirred for 10 min to make them uniformly mixed. Then, the dispersion was enhanced by ultrasound for 10 min to make it more dispersed, and a composite conductive material was obtained.

[0035] (2) Add 2.5 parts of sodium dodecyl sulfonate emulsifier to 280 parts of deionized water and dissolve until transparent to obtain an emulsion;

[0036] (3) While stirring, slowly pour the emulsion into the composite conductive material in 4 portions, and continue stirring to make it completely homogeneous, to obtain a nano-emulsion with an average particle size of 295.7 nm. Figure 3 The paper demonstrates the use of a laser particle size analyzer to determine the particle size and distribution in nanoemulsions.

[0037] (4) The nano PPTC coating material is coated to form a coating with a thickness of about 600 nm and cured at 80 °C to obtain the nano PPTC coating material. Figure 4 The graph shows the resistivity ρ of the coating material as a function of temperature T. The PTC strength value of the coating material is 4.23.

[0038] Example 3

[0039] (1) Using the in-situ modification method, 7 parts of the dispersion modifier ethylene-vinyl acetate copolymer, 0.5 parts of the low-temperature initiator azobisisobutyronitrile and 80 parts of carbon nanotube powder were added to 100 parts of low-melting-point paraffin at 65°C and stirred for 8 minutes to make them uniformly mixed. Then, the dispersion was enhanced by ultrasound for 10 minutes to make them more dispersed, and a composite conductive material was obtained.

[0040] (2) Add 1.2 parts of emulsifier sodium cetylbenzenesulfonate to 230 parts of deionized water to dissolve until transparent to obtain an emulsion;

[0041] (3) While stirring, slowly pour the emulsion into the composite conductive material in 4 portions, and continue stirring to make it completely uniform, so as to obtain a nano-emulsion with an average particle size of 208.3 nm.

[0042] (4) The nano PPTC coating material is coated to form a coating with a thickness of about 700 nm and cured at 85°C to obtain the nano PPTC coating material; the PTC strength value of the coating material is 2.53.

[0043] Example 4

[0044] (1) Using the in-situ modification method, 4 parts of the dispersion modifier ethylene-vinyl acetate copolymer, 0.7 parts of the low temperature initiator azobisisobutyronitrile and 130 parts of graphene micro powder were added to 100 parts of low melting point paraffin at 70℃ and stirred for 10 min to make them uniformly mixed. Then, the dispersion was enhanced by ultrasound for 10 min to make it more dispersed, and a composite conductive material was obtained.

[0045] (2) Add 1.8 parts of sodium dodecylbenzenesulfonate emulsifier to 250 parts of deionized water to dissolve until transparent to obtain an emulsion;

[0046] (3) While stirring, slowly pour the emulsion into the composite conductive material in two portions, and continue stirring to make it completely homogeneous, to obtain a nano-emulsion with an average particle size of 263.5 nm. Figure 3 The paper demonstrates the use of a laser particle size analyzer to determine the particle size and distribution in nanoemulsions.

[0047] (4) The nano PPTC coating material is coated to form a coating with a thickness of about 650 nm and cured at 80 °C to obtain the nano PPTC coating material. The PTC strength value of the coating material is 3.86.

[0048] Example 5

[0049] (1) Using the in-situ modification method, 3 parts of the dispersion modifier ethylene-vinyl acetate copolymer, 0.4 parts of the low-temperature initiator azobisisobutyronitrile and 110 parts of conductive carbon black were added to 100 parts of low-melting-point paraffin at 58°C and stirred for 10 min to make them uniformly mixed. Then, the dispersion was enhanced by ultrasound for 10 min to make it more dispersed, and a composite conductive material was obtained.

[0050] (2) Add 2.1 parts of sodium dodecyl sulfonate emulsifier to 250 parts of deionized water to dissolve until transparent to obtain an emulsion;

[0051] (3) While stirring, slowly pour the emulsion into the composite conductive material in 4 portions, and continue stirring to make it completely uniform, so as to obtain a nano-emulsion with an average particle size of 253.6 nm.

[0052] (4) The nano PPTC coating material is coated to form a coating with a thickness of about 750 nm and cured at 85°C to obtain the nano PPTC coating material. The PTC strength value of the coating material is 3.43.

Claims

1. A PPTC nano-coating material for room temperature thermal control, characterized in that, It is made from the following components in parts by weight: 100 parts low-melting-point paraffin, 60-150 parts conductive filler, 3-8 parts dispersant modifier, 0.1-0.8 parts low-temperature initiator, 1-3 parts emulsifier, and 200-300 parts deionized water. The dispersing modifier is an ethylene-vinyl acetate copolymer with a melt index of 200-400 g / 10 min and a vinyl acetate content of 25%-33%; the low-temperature initiator is one of the azo radical initiators. The preparation method of the PPTC nano-coating material for room temperature thermal control includes the following steps: (1) The dispersant modifier, low-temperature initiator and conductive filler are added to the low-melting-point paraffin at a temperature of 55-70°C and stirred to mix evenly. Then, the mixture is dispersed evenly by ultrasonication to obtain a composite conductive material. (2) The emulsifier is added to the deionized water and dissolved into a transparent state to obtain an emulsion; (3) While stirring, pour the emulsion into the composite conductive material at a temperature of 55-70°C to make it completely uniform, and obtain a nanoemulsion with an average particle size of 100-300 nm. (4) The nanoemulsion is coated into a coating of 300-800 nm and cured at 70-90 °C to obtain nano PPTC coating material.

2. The PPTC nanocoating material according to claim 1, characterized in that, The low-melting-point paraffin wax has a melting point of 45–65°C; in the PPTC nano-coating material after curing, the low-melting-point paraffin wax accounts for 30%–70% of the total mass.

3. The PPTC nanocoating material according to claim 1, characterized in that, The conductive filler has a specific surface area of ​​10–3000 m². 2 / g of one or more of conductive carbon black, graphite powder, graphene powder, and carbon nanotube powder.

4. The PPTC nanocoating material according to claim 1, characterized in that, In the cured PPTC nano-coating material, the conductive filler accounts for 30% to 70% of the total mass.

5. The PPTC nanocoating material according to claim 1, characterized in that, The emulsifier is one or more of long-chain alkyl sulfonate surfactants.

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