Polymer-based conductive composite material and overcurrent protection element

Abstract

The present invention discloses a polymer-based conductive composite material and an overcurrent protection element prepared therefrom. The polymer-based conductive composite material comprises a polymer substrate and a conductive filler of a graphene-like two-dimensional layered structure dispersed in the polymer substrate, the polymer substrate accounts for 20%-75% of the volume fraction of the polymer-based conductive composite material, and the conductive filler accounts for 25%-80% of the volume fraction of the polymer-based conductive composite material. The conductive filler has outstanding weather resistance, good processing performance, and excellent conductivity. The overcurrent protection element prepared by the polymer-based conductive composite material comprises at least two metal electrode foils, and the polymer-based conductive composite material is tightly combined with the metal electrode foils. The overcurrent protection element prepared by the polymer-based conductive composite material has low room temperature resistivity, outstanding weather resistance and good processability.

Description

Technical Field

[0001] The present invention relates to a polymer-based conductive composite material and an overcurrent protection element, and specifically to a polymer-based conductive composite material with low room temperature resistivity, outstanding weather resistance and good processability, and an overcurrent protection element prepared therefrom. Background Art

[0002] Polymer-based conductive composite materials can maintain a low resistance value at normal temperature and have the characteristic of being sensitive to temperature changes. That is, when overcurrent or overtemperature occurs in the circuit, its resistance will instantly increase to a high resistance value, making the circuit in a disconnected state to achieve the purpose of protecting circuit components. Therefore, polymer-based conductive composite materials can be connected to the circuit as a material for current sensing elements. Such materials have been widely used in electronic circuit protection components.

[0003] Polymer-based conductive composite materials are generally composed of polymers and conductive fillers, and the conductive fillers are uniformly distributed in the polymer matrix macroscopically. The polymer is generally polyolefin and its copolymer, such as polyethylene or ethylene-vinyl acetate copolymer, and the conductive filler is generally carbon black, metal powder or conductive ceramic powder. For polymer-based conductive composite materials with carbon black as conductive filler, due to the special aggregate structure of carbon black and the polar groups on its surface, the adhesion of carbon black to the polymer is good, so it has good resistance stability. However, the conductivity of carbon black itself is limited and cannot meet the requirements of low resistance. Polymer-based conductive composite materials with metal powder as conductive filler have extremely low resistance, but because metal powder is easily oxidized, it is necessary to encapsulate the conductive composite material to prevent the resistance increase caused by oxidation of metal powder in the air, and the volume of the encapsulated overcurrent protection element cannot be effectively reduced, which is difficult to meet the requirements of miniaturization of electronic components. In order to obtain lower resistance and overcome the drawback of metal powder being easily oxidized, the industry gradually tends to use metal carbide, metal nitride or metal boride ceramic powder (such as titanium carbide) as conductive filler for low-resistance polymer-based conductive composite materials, and such materials have made great progress. However, due to the high hardness of metal carbides, metal nitrides or metal borides, a series of problems will be brought to production and processing (such as severe wear of mechanical parts and high processing costs). Strong shearing during processing will cause the polymer molecular chain to break, resulting in reliability degradation. This situation becomes more and more obvious in the long-term production process and when the area of ​​overcurrent protection components is further reduced (such as 1210, 1206, 0805, 0603 and other sizes). Therefore, it is necessary to develop conductive fillers with low resistivity, excellent oxidation resistance, excellent weather resistance and good processing performance. Summary of the invention

[0004] The object of the present invention is to provide a polymer-based conductive composite material.

[0005] Another object of the present invention is to provide an overcurrent protection element prepared from the above polymer-based conductive composite material, which has low room temperature resistivity, outstanding weather resistance and good processability.

[0006] To achieve the above object, the present invention discloses a polymer-based conductive composite material, which comprises:

[0007] A polymer substrate, which accounts for 20% to 75% of the volume fraction of the polymer-based conductive composite material;

[0008] Conductive filler with a graphene-like two-dimensional layered structure, an average particle size of 0.1 μm to 20 μm, a particle size distribution range of 0.01 μm to 100 μm, and a volume resistivity of less than 1×10 -3 Ω.cm, accounting for 25% to 80% of the volume fraction of the polymer-based conductive composite material, and dispersed in the polymer matrix. The molecular formula of the conductive filler with a layered structure is: M n+1 AX n ,in,

[0009] The element M is one of the transition metal elements Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta;

[0010] The X element is carbon or nitrogen; 1≤n≤3 and is an integer.

[0011] The polymer substrate is one of polyethylene, chlorinated polyethylene, oxidized polyethylene, polyvinyl chloride, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, polystyrene, polycarbonate, polyamide, polyethylene terephthalate, polybutylene terephthalate, polyphenylene ether, polyphenylene sulfide, polyoxymethylene, phenolic resin, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, polytrifluoroethylene, polyvinyl fluoride, maleic anhydride grafted polyethylene, polypropylene, polyvinylidene fluoride, epoxy resin, ethylene-vinyl acetate copolymer, polymethyl methacrylate, ethylene-acrylic acid copolymer and a mixture thereof; wherein the polyethylene includes high-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene and the like.

[0012] The volume fraction of the polymer matrix in the conductive composite material is between 20% and 75%, preferably between 25% and 70%, and more preferably between 30% and 65%.

[0013] The conductive filler with a layered structure is one of Sc2C, Ti2C, V2C, Cr2C, Zr2C, Nb2C, Mo2C, Ti2N, Hf2C, Ta2C, V2N, Zr2N, Hf2N, Ti3C2, V3C2, Ta3C2, Ti4N3, V4C3, Nb4N3, Ta4C3, Ti4C3 and a mixture thereof.

[0014] The average particle size of the conductive filler having a graphene-like two-dimensional layered structure is 0.01 μm to 100 μm, preferably 0.05 μm to 50 μm, and more preferably 0.1 μm to 20 μm.

[0015] The average particle size and particle size distribution of the conductive filler are measured using a laser particle size tester.

[0016] The volume resistivity of the conductive filler having a layered structure is less than 1×10 -3 Ω.cm, preferably less than 5×10 -3 Ω.cm, the best is less than 1×10 -2 Ω.cm.

[0017] The volume fraction of the conductive filler with a layered structure in the polymer-based conductive composite material is between 25% and 80%, preferably between 30% and 75%, and more preferably between 35% and 70%.

[0018] The polymer-based conductive composite material may contain other components, such as antioxidants, radiation crosslinking agents (often referred to as radiation accelerators, crosslinking agents or crosslinking accelerators, such as triallyl isocyanurate), coupling agents, dispersants, stabilizers, non-conductive fillers (such as magnesium hydroxide, calcium carbonate), flame retardants, arc inhibitors or other components. These components usually account for at most 15% of the total volume of the polymer-based conductive composite material, such as 10% by volume.

[0019] The overcurrent protection element prepared using the above-mentioned polymer-based conductive composite material comprises two metal electrode foils, between which a polymer-based conductive composite material layer is sandwiched to form an overcurrent protection chip with a "sandwich" structure, and the metal electrode foil is tightly combined with the polymer-based conductive composite material layer.

[0020] The volume resistivity of the overcurrent protection element is less than 0.02Ω.cm at 25°C, and it has outstanding weather resistance and good processability.

[0021] The polymer-based conductive composite material and the overcurrent protection element prepared from the polymer-based conductive composite material of the present invention can be prepared according to the following method:

[0022] The polymer substrate and the conductive filler are placed in a mixing device and melt-mixed at a temperature above the melting temperature of the polymer. The mixing device can be an internal mixer, an open mixer, a single screw extruder or a twin screw extruder. The melt-mixed polymer is then processed into a sheet by extrusion molding, compression molding or calendering. In general, the thickness of the polymer sheet is 0.01-3.0 mm, preferably 0.05-2.0 mm, and more preferably 0.1-1.0 mm for the convenience of processing.

[0023] The forming method of the composite product is to composite metal electrode foil on both sides of the polymer sheet. The method of composite metal electrode foil on both sides of the polymer sheet includes compression molding or directly pressing the electrode sheet with the polymer through a roller after the polymer is extruded from the sheet die and is still in a molten state. The composite sheet can be processed into a surface mount overcurrent protection element through a series of PCB processes such as etching, lamination, drilling, copper plating, tinning and scribing, or it can be divided into individual components and then connected to other metal parts to be processed into SMT or strip overcurrent protection elements. The metal electrode foil is tightly combined with the polymer-based conductive composite material layer. The thickness of the metal electrode foil is generally at most 0.3 mm, preferably at most 0.2 mm, and in particular at most 0.1 mm, for example, 0.035 mm. Materials suitable for metal electrode foil include nickel, copper, zinc and their composites, such as copper foil, nickel foil, single-sided nickel-plated copper foil, double-sided nickel-plated copper foil, etc.

[0024] The stability of the performance of the overcurrent protection element can usually be improved by crosslinking and / or heat treatment. The crosslinking can be chemical crosslinking or radiation crosslinking, for example, using a crosslinking accelerator, electron beam irradiation or Co 60 The irradiation dose required for the overcurrent protection element is generally less than 1000 kGy, preferably 1-500 kGy, and more preferably 1-200 kGy. The heat treatment can be annealing, thermal cycling, high and low temperature alternation, such as +85°C / -40°C high and low temperature alternation. The annealing temperature environment can be any temperature below the decomposition temperature of the polymer substrate, such as high temperature annealing above the melting temperature of the polymer substrate and low temperature annealing below the melting temperature of the polymer substrate.

[0025] The overcurrent protection element of the present invention has a resistivity at 25° C. of less than 0.1Ω.cm, preferably less than 0.05Ω.cm, and most preferably less than 0.02Ω.cm. Therefore, the overcurrent protection element of the present invention has a very low resistance at 25° C., for example, 1.0 mΩ-20 mΩ.

[0026] The advantages of the present invention are: the polymer-based conductive composite material has low resistivity, excellent weather resistance, and is easy to process. The overcurrent protection element prepared from the polymer-based conductive composite material has low room temperature resistivity, excellent weather resistance, and reduced processing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of an overcurrent protection element;

[0028] Figure 2 This is a schematic diagram of an overcurrent protection component with metal pins. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below through specific examples.

[0030] Comparative Example

[0031] The composition of the conductive composite material for preparing the overcurrent protection element is shown in Table 1, wherein polymer 1 is 44 parts by weight of high-density polyethylene, with a melting temperature of 131°C and a density of 0.954 g / cm 3 ; Polymer 2 is 6 parts by weight of high-density polyethylene, with a melting temperature of 134°C and a density of 0.954 g / cm 3 ; The conductive filler is 50 parts by weight of spherical TiC with an average particle size of 3.0 μm;

[0032] The preparation process of the overcurrent protection element is as follows: the temperature of the internal mixer is set at 180°C and the speed is 30 rpm, the polymer is first added and internally kneaded for 3 minutes, and then the conductive filler is added and internally kneaded for 15 minutes to obtain a polymer-based conductive composite material. The melt-mixed polymer-based conductive composite material is rolled through an open mill to obtain a polymer-based conductive composite material 11 with a thickness of 0.20-0.25 mm.

[0033] like Figure 1 Schematic diagram of an overcurrent protection element. A layer of polymer-based conductive composite material 11 is placed between two metal electrode foils 12 that are symmetrical in the upper and lower parts. The metal electrode foil 12 is tightly bonded to the polymer-based conductive composite material layer 11. The polymer-based conductive composite material 11 and the metal electrode foil 12 are tightly bonded together by a hot pressing method. The hot pressing temperature is 180°C. Preheat for 5 minutes, then hot press at a pressure of 5MPa for 3 minutes, then hot press at a pressure of 12MPa for 10 minutes, and then cold press on a cold press for 8 minutes. Use a mold to punch it into a single component of 3*4mm. Finally, connect two metal pins 13 to the surfaces of the two metal electrode foils 12 by a reflow soldering method to form an overcurrent protection element, such as Figure 2 shown.

[0034] Example 1

[0035] A polymer-based conductive composite material, the polymer material is the same as that in the comparative example, the conductive filler is composed of 25 parts by weight of Ti2C having a two-dimensional layer structure and 25 parts by weight of TiC, the mixing and sheeting, the overcurrent protection element and the protection element with two metal pins are prepared in the same manner as in the comparative example 1, and the formula of the polymer-based conductive composite material and the electrical properties of the overcurrent protection element of this embodiment are shown in Table 1.

[0036] Example 2

[0037] A polymer-based conductive composite material, the polymer material is the same as that in the comparative example, the conductive filler is composed of 50 parts by weight of Ti2C having a two-dimensional layer structure and 50 parts by weight of TiC, the mixing and sheeting, the overcurrent protection element and the protection element with two metal pins are prepared in the same manner as in the comparative example 1, and the formula of the polymer-based conductive composite material and the electrical properties of the overcurrent protection element of this embodiment are shown in Table 1.

[0038] Table 1 shows the resistance test data of the overcurrent protection elements made of the polymer-based conductive composite materials of the comparative example and Examples 1 to 2 after being triggered under the condition of 6V / 50A and placed in a temperature environment of 25°C for 1 hour.

[0039] In Table 1,

[0040] R represents the resistance before the two metal pins 13 are welded on the surface of the two metal electrode foils 12 of the overcurrent protection element, that is, Figure 1 The resistance of the overcurrent protection element shown;

[0041] R0 represents the resistance after two metal pins 13 are welded on the surface of two electrode sheets 12 of the overcurrent protection element. Figure 2 Overcurrent protection element;

[0042] R1 represents the resistance value measured after the overcurrent protection element is continuously energized (6V / 50A) for 6 seconds and then placed in a temperature environment of 25°C for 1 hour;

[0043] R 100 It means the resistance value of the overcurrent protection element after it is continuously powered on (6V / 50A) for 6 seconds, then powered off for 60 seconds, and this cycle is repeated 100 times, and then placed in a temperature environment of 25°C for 1 hour;

[0044] High temperature and humidity R 1000h It indicates the resistance value of the overcurrent protection element after being placed in an environment of 85°C, 85%RH for 1000 hours and then placed in an environment of 25°C for 1 hour.

[0045] Thermal Shock R 200It indicates the resistance value of the overcurrent protection element after it is placed at 85℃ for 30 minutes, then transferred to -40℃ for 1 hour within 5 minutes, repeated 200 times, and then placed in a temperature environment of 25℃ for 1 hour.

[0046]

[0047] It can be seen from Table 1 that the overcurrent protection element in Example 1-2 has a lower processing torque. As the amount of two-dimensional layered Ti2C substitution increases, the machinability is significantly improved, and the maximum processing torque (Nm) is reduced from 87.8 to 44.2. The processing stability torque (Nm) is reduced from 56.3 to 28.4, which greatly reduces the difficulty and cost of processing. The resistance of the prepared element is less than 20 milliohms. After 100 current shocks, high temperature and high humidity, and high humidity environment experiments, the resistance change of the overcurrent protection element is better than that of the comparative example.

[0048] The polymer-based conductive composite material used in the overcurrent protection element of the present invention contains a conductive filler with a self-lubricating layered structure with low resistivity, has low room temperature resistivity and excellent weather resistance, does not need to be protected by encapsulation, and has excellent processing performance. Therefore, small-sized overcurrent protection elements with a thickness of 0.2mm-2.0mm and a current-carrying area of ​​1210, 1206, 0805, 0603, etc. can be prepared.

[0049] The content and features of the present invention have been disclosed above, however, the present invention described above is only briefly or only relates to a specific part of the present invention, and the features of the present invention may be more than what is disclosed herein. Therefore, the protection scope of the present invention should not be limited to the content disclosed in the embodiments, but should include the combination of all the contents embodied in different parts, as well as various substitutions and modifications that do not deviate from the present invention, and are covered by the claims of the present invention.

Claims

1. A polymer-based conductive composite material, characterized in that It contains: A polymer substrate, which accounts for 20% to 75% of the volume fraction of the polymer-based conductive composite material; Conductive filler with a graphene-like two-dimensional layered structure, an average particle size of 0.1 μm to 20 μm, a particle size distribution range of 0.01 μm to 100 μm, and a volume resistivity of no more than 1×10 -3 Ω.cm, accounting for 25% to 80% of the volume fraction of the polymer-based conductive composite material, and dispersed in the polymer matrix, and the conductive filler with a layered structure is Ti2C.

2. The polymer-based conductive composite material according to claim 1, characterized in that: The polymer substrate is: polyethylene, chlorinated polyethylene, oxidized polyethylene, polyvinyl chloride, butadiene- Propylene Nitrile copolymer, Propylene One of nitrile-butadiene-styrene copolymer, polystyrene, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, polytrifluoroethylene, polyvinyl fluoride, maleic anhydride grafted polyethylene, polypropylene, polyvinylidene fluoride, epoxy resin, ethylene-vinyl acetate copolymer, polymethyl methacrylate, ethylene-acrylic acid copolymer or a mixture thereof.

3. An overcurrent protection chip prepared according to the polymer-based conductive composite material according to any one of claims 1 to 2, which has a "sandwich" structure formed by sandwiching the polymer-based conductive composite material layer between two metal electrode foils, and the metal electrode foil and the polymer-based conductive composite material layer are tightly compounded.

4. The overcurrent protection chip according to claim 3, characterized in that: The two metal electrode foils are connected in series in the protected circuit through a conductive component to form a conductive path.

5. The overcurrent protection chip according to claim 3, characterized in that: The chip is prepared into a surface mounted overcurrent protection element through a PCB processing technology.

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