Polypropylene conductive composite material, preparation method and application thereof, and cable holder

Abstract

The invention provides a polypropylene conductive composite material as well as a preparation method and application thereof and a cable bracket, and belongs to the technical field of polypropylene composite materials. The polypropylene conductive composite material is prepared from the following components in percentage by mass: 40 to 86.4 percent of polypropylene matrix, 0.5 to 3 percent of modified or unmodified carbon nanotube, 1 to 10 percent of conductive carbon black, 1 to 5 percent of micron-sized SiO2, 0.1 to 5 percent of nano-sized SiO2, 10 to 50 percent of reinforced fiber material and 1 to 10 percent of additive. According to the invention, the carbon nanotubes, the conductive carbon black, the micron-sized SiO2, the nano-sized SiO2, the reinforced fiber material and the auxiliary agent are added into the polypropylene matrix according to a certain mass fraction, so that the bending strength, the conductivity and the weather resistance of the polypropylene conductive composite material can be remarkably improved, and the polypropylene conductive composite material can be used for preparing a cable bracket in an outdoor high-voltage environment.

Description

Technical Field

[0001] The present application relates to the technical field of polypropylene composite materials, and in particular to a polypropylene conductive composite material, a preparation method thereof, an application thereof, and a cable bracket. Background Art

[0002] Cable supports, among the structural components of power equipment, primarily provide stable mechanical support, ensuring electrical safety and reliable operation of the power system, and thus play a vital role in power equipment. When the cable is in operation, the alternating magnetic field generated by the core current generates an induced potential in the metal protective layer. If the grounding is interrupted due to poor or damaged grounding, the induced voltage cannot be discharged, resulting in a floating potential. In outdoor high-voltage power environments, the cable sheath is prone to aging and damage, leading to the formation of a floating potential and posing a personal safety risk. Therefore, cable supports must have excellent mechanical properties, electrical conductivity, anti-static properties, and weather resistance.

[0003] Cable supports are often constructed of metal (such as steel and stainless steel) or thermosetting composite materials (such as fiberglass reinforced plastic). Metal supports are susceptible to moisture, corrosion, and electrochemical erosion in outdoor high-voltage transmission environments, resulting in high maintenance costs. Additional treatment is also required for anti-static and electromagnetic interference control. While traditional fiberglass reinforced plastic supports offer a certain level of insulation and mechanical strength in outdoor high-voltage transmission environments, their electrical conductivity and anti-static properties are insufficient, making them prone to localized corona or flashover. Furthermore, they experience severe interface aging in high-humidity, high-UV environments, leading to rapid performance degradation. With the continuous upgrade of high-voltage transmission lines, the requirements for long-span, high-tower installations are increasing. Cable supports must not only be strong and lightweight, but also conductive and static-dissipating to reduce the risk of partial discharge and creepage failures, thereby extending their service life.

[0004] Polypropylene composite materials have the advantages of high chemical stability, weather resistance and strong UV resistance, and are widely used in cable brackets. However, most polypropylene composite materials currently on the market use ordinary glass fiber and carbon black filling. Their conductivity is often insufficient and a certain conductivity can only be achieved when a high carbon black filling amount is used. However, this will significantly reduce toughness and fatigue life, making it difficult to meet the stringent requirements of the high-voltage power industry.

[0005] Therefore, there is an urgent need for a polypropylene composite material with high toughness, excellent electrical properties and long weather resistance. Summary of the Invention

[0006] Based on this, the main purpose of this application is to provide a polypropylene conductive composite material, its preparation method, application and cable bracket. The polypropylene conductive composite material adopts a polypropylene matrix, modified or unmodified carbon nanotubes, conductive carbon black, micron-level SiO2, nano-level SiO2, reinforcing fiber materials and additives to improve the toughness, conductive properties and weather resistance life of the polypropylene conductive composite material.

[0007] In a first aspect, the present application provides a polypropylene conductive composite material, comprising the following components in weight fractions:

[0008] 40-86.4% polypropylene matrix, 0.5-3% modified or unmodified carbon nanotubes, 1-10% conductive carbon black, 1-5% micron-sized SiO2, 0.1-5% nano-sized SiO2, 10-50% reinforcing fiber materials and 1-10% additives.

[0009] In some embodiments, the modified carbon nanotubes include one or more of acid-treated carbon nanotubes, plasma-treated carbon nanotubes, and maleic anhydride-grafted polypropylene-modified carbon nanotubes.

[0010] In some embodiments, the reinforcing fiber material includes one or more of carbon fiber, basalt fiber, and glass fiber.

[0011] In some embodiments, the auxiliary agent includes one or more of a dispersing agent, an antioxidant, a UV stabilizer, a UV absorber, a flame retardant, a coupling agent, and an anti-aging additive.

[0012] In some embodiments, the coupling agent includes a silane coupling agent.

[0013] In some embodiments, the dispersing aid includes one or more of a dispersant and a compatibilizer.

[0014] In some embodiments, the compatibilizer includes maleic anhydride grafted polypropylene.

[0015] In a second aspect, the present application provides a method for preparing the polypropylene conductive composite material according to the first aspect, comprising the following steps:

[0016] Premixing modified or unmodified carbon nanotubes, conductive carbon black, micron-sized SiO2, nano-sized SiO2 and part or all of the additives to prepare a premixed masterbatch;

[0017] The premixed masterbatch and the remaining components are melt-extruded to prepare a polypropylene conductive composite material.

[0018] In some embodiments, premixing includes grind premixing or melt blending.

[0019] In some embodiments, the step of melt-extruding the premixed masterbatch and the remaining components includes: putting the premixed masterbatch and the remaining components into an extruder for melt extrusion; the parameter settings of the extruder include: the front section temperature is 190-200°C, the middle section temperature is 210-220°C, and the rear section temperature is 210-220°C.

[0020] The third aspect of the present application provides use of the polypropylene conductive composite material described in the first aspect or the polypropylene conductive composite material prepared by the preparation method described in the second aspect in preparing a cable bracket.

[0021] In a fourth aspect of the present application, a cable bracket is provided, wherein the raw materials include the polypropylene conductive composite material described in the first aspect or the polypropylene conductive composite material prepared by the preparation method described in the second aspect.

[0022] Compared with traditional technologies, this application has at least the following beneficial effects:

[0023] This application significantly improves the flexural strength, electrical conductivity, and weather resistance of a polypropylene conductive composite material by adding a certain mass fraction of modified or unmodified carbon nanotubes, conductive carbon black, micron-sized SiO2, nano-sized SiO2, reinforcing fiber materials, and additives to a polypropylene matrix. The composite material can be used to manufacture cable supports for outdoor high-voltage environments. The use of micron-sized and nano-sized SiO2 reduces the agglomeration of the modified or unmodified carbon nanotubes, improving the flexural strength, electrical conductivity, and weather resistance of the polypropylene conductive composite material. DETAILED DESCRIPTION

[0024] Below in conjunction with embodiment and example, the application is further described in detail These embodiment and example are only used to illustrate the application and are not used to limit the scope of the application, and the purpose of providing these embodiment and example is to make the understanding of the disclosure of the application more thorough and comprehensive. It should also be understood that the application can be implemented in many different forms and is not limited to the embodiment and example described herein. Those skilled in the art can make various changes or modifications without violating the connotation of the application, and the equivalent form obtained also falls within the protection scope of the application. In addition, in the description below, a large amount of specific details are given in order to provide a more complete understanding of the application, and it should be understood that the application can be implemented without one or more of these details.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] To address the problem that polypropylene composite materials currently available on the market have insufficient conductivity due to low amounts of conductive carbon black, while high amounts significantly reduce toughness and fatigue life, making them unable to meet the stringent requirements of the high-voltage power industry, this application uses a polypropylene matrix to add a certain mass fraction of modified or unmodified carbon nanotubes, conductive carbon black, micron-sized SiO2, nano-sized SiO2, reinforcing fiber materials, and additives to prepare a polypropylene composite material with high toughness, high conductivity, and long weather resistance.

[0027] In a first aspect, the present application provides a polypropylene conductive composite material, comprising the following components in weight fractions:

[0028] 40-86.4% polypropylene matrix, 0.5-3% modified or unmodified carbon nanotubes, 1-10% conductive carbon black, 1-5% micron-sized SiO2, 0.1-5% nano-sized SiO2, 10-50% reinforcing fiber materials and 1-10% additives.

[0029] This application uses a composite of micron-sized SiO2 and nano-sized SiO2 to reduce the agglomeration of carbon nanotubes, and together with carbon nanotubes, conductive carbon black, reinforcing fiber materials and additives as fillers for the polypropylene matrix, it can significantly improve the toughness, conductivity and weather resistance of the polypropylene conductive composite material.

[0030] In some embodiments, in the polypropylene conductive composite material, the mass fraction of the polypropylene matrix is ​​40-86.4%, which can be 40%, 45%, 50%, 55%, 58%, 58.4%, 58.9%, 59%, 59.4%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 75%, 78%, 80%, 85% or 86.4%.

[0031] In some embodiments, the mass fraction of modified or unmodified carbon nanotubes in the polypropylene conductive composite material is 0.5-3%, and can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 2%, 2.5% or 3%.

[0032] In some embodiments, the modified carbon nanotubes include one or more of acid-treated carbon nanotubes, plasma-treated carbon nanotubes, and maleic anhydride-grafted polypropylene-modified carbon nanotubes.

[0033] In some embodiments, the polypropylene conductive composite material uses modified carbon nanotubes, which are modified by surface functionalization and / or graft polymerization to significantly improve their dispersibility and achieve effective volume conductive paths at lower filling amounts.

[0034] In some embodiments, the mass fraction of conductive carbon black in the polypropylene conductive composite material is 1-10%, which can be 1%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0035] In some embodiments, the mass fraction of micron-sized SiO2 in the polypropylene conductive composite material is 1-5%, and can be 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 3%, 4% or 5%.

[0036] In some embodiments, the particle size of the micron-sized SiO2 is 1-20 μm, and may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 11.5 μm, 15 μm, or 20 μm.

[0037] In some embodiments, the particle size of the micron-sized SiO2 is 1-2 μm.

[0038] In some embodiments, the average particle size of the micron-sized SiO 2 is 1.5 μm.

[0039] In some embodiments, the mass fraction of nano-SiO2 in the polypropylene conductive composite material is 0.1-5%, and can be 0.1%, 0.5%, 0.8%, 0.85%, 0.9%, 0.95%, 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0040] In some embodiments, the particle size of nano-SiO2 is 50-200 nm, which can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm.

[0041] In some embodiments, the particle size of nano-SiO2 is 50-100 nm.

[0042] In some embodiments, the particle size of nano-SiO2 is 50-200 nm.

[0043] In some embodiments, the average particle size of the nano-sized SiO2 is 100 nm.

[0044] In some embodiments, in the polypropylene conductive composite material, the mass fraction of the reinforcing fiber material is 10-50%, which can be 10%, 15%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 35%, 40%, 45% or 50%.

[0045] In some embodiments, the reinforcing fiber material includes one or more of carbon fiber, basalt fiber, and glass fiber.

[0046] In some embodiments, the glass fibers include E-glass fibers, which can be chopped fibers or continuous fibers. The chopped fibers can have a length of 3-6 mm, such as 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, or 6 mm.

[0047] In some embodiments, in the polypropylene conductive composite material, the mass fraction of the additive is 1-10%, and can be 1%, 2%, 3%, 4%, 5%, 5.6%, 6%, 7%, 8%, 9% or 10%.

[0048] In some embodiments, the auxiliary agent includes one or more of a dispersing agent, an antioxidant, a UV stabilizer, a UV absorber, a flame retardant, a coupling agent, and an anti-aging additive.

[0049] In some embodiments, the coupling agent includes a silane coupling agent.

[0050] In some embodiments, the dispersing aid includes one or more of a dispersant and a compatibilizer.

[0051] In some embodiments, the compatibilizer includes maleic anhydride grafted polypropylene.

[0052] In a second aspect, the present application provides a method for preparing the polypropylene conductive composite material according to the first aspect, comprising the following steps:

[0053] Premixing modified or unmodified carbon nanotubes, conductive carbon black, micron-sized SiO2, nano-sized SiO2 and part or all of the additives to prepare a premixed masterbatch;

[0054] The premixed masterbatch and the remaining components are melt-extruded to prepare a polypropylene conductive composite material.

[0055] This application utilizes the dual effects of micron-scale SiO2 (physical grinding) on ​​carbon nanotube aggregates and nano-scale SiO2 (exfoliation) on fine carbon nanotube clusters to initially construct a relatively uniform carbon nanotube-conductive carbon black-SiO2 composite network, resulting in a premixed masterbatch with low agglomeration. By incorporating modified or unmodified carbon nanotubes, conductive carbon black, micron- and nano-scale SiO2, and reinforcing fiber materials into a polypropylene matrix, along with specific additives, a polypropylene conductive composite material with high flexural strength, high electrical conductivity, a low conductivity threshold, and excellent weather resistance is prepared through a melt extrusion process.

[0056] The present application significantly reduces the amount of filler used by pre-dispersing carbon nanotubes in conjunction with reasonable fillers, thereby ensuring the conductive properties while taking into account the toughness and processability of the material.

[0057] In some embodiments, part / all of the additives are 0-10% by mass of the additives in the polypropylene conductive composite material.

[0058] In some embodiments, premixing includes grind premixing or melt blending.

[0059] In some embodiments, after the premixing step, a solvent is added for ultrasonic dispersion to prepare a premixed masterbatch.

[0060] In some embodiments, the step of melt-extruding the premixed masterbatch and the remaining components includes: putting the premixed masterbatch and the remaining components into an extruder for melt extrusion; the parameter settings of the extruder include: the front section temperature is 190-200°C, the middle section temperature is 210-220°C, and the rear section temperature is 210-220°C.

[0061] In some embodiments, the step of melt-extruding the premixed masterbatch and the remaining components includes: feeding the premixed masterbatch and the remaining components into a twin-screw extruder for melt extrusion; the parameters of the twin-screw extruder are set as follows: a front section temperature of 190-200°C, a middle section temperature of 210-220°C, and a rear section temperature of 210-220°C. Different temperatures are set in the front, middle, and rear sections of the twin-screw extruder, with the front section (190-200°C) providing sufficient shearing and mixing space, and the rear section (210-220°C) moderately raising the temperature to protect the reinforcing fiber material.

[0062] In some embodiments, kneading blocks or toothed elements are provided in the front / middle high shear dispersion zone of the twin-screw extruder to moderately increase shear strength and further break up residual agglomerates in the premixed masterbatch of carbon nanotubes, conductive carbon black, and micron-sized SiO2 and nano-sized SiO2, preventing severe shear damage in the rear section and making the overall conductive network more stable. Vacuum exhaust ports can also be provided in the front / middle high shear dispersion zone to remove solvent residues or volatile low-molecular weight substances, thereby improving the surface cleanliness and interfacial bonding strength of the filler. Micron-sized SiO2 and nano-sized SiO2 regulate melt viscosity and interfacial bonding, slowing down slippage or peeling between the reinforcing glass fiber material and the matrix, and achieving high strength and high toughness of the polypropylene conductive composite material.

[0063] In some embodiments, a conveying element with a large pitch and shallow tooth depth is used in the low-shear fiber-preserving zone in the rear section of the twin-screw extruder, and a small number of reverse threads / tangential blocks can be arranged to flexibly disperse the reinforcing fiber material and prevent excessive breakage of the reinforcing fiber material. The multi-scale SiO2 can also form a certain physical or chemical adsorption layer with the surface of the reinforcing fiber material in the rear section of extrusion, thereby reducing the slippage of the reinforcing fiber material and improving the mechanical properties of the system.

[0064] In some embodiments, the twin-screw extruder controls the feed rates of the polypropylene matrix, premixed masterbatch, reinforcing fiber material, and additives / remaining additives respectively through a quantitative feeding device or a frequency conversion system to ensure that there is sufficient but not excessive mixing time in each functional section.

[0065] In some embodiments, a staged feeding method is adopted, where the premixed masterbatch is fed first, and then the reinforcing fiber material is fed.

[0066] In some embodiments, a staged feeding method is used. The premixed masterbatch, polypropylene matrix, and additives / remaining additives are added to the extruder in the front or middle section of the twin-screw extruder. The residual agglomerates are further crushed and homogenized by the high shear kneading unit to strengthen the conductive network. In the back section of the twin-screw extruder, the reinforcing fiber material is introduced through the side feed or the back section feed port and dispersed in the lower shear zone to maximize the retention of fiber length and achieve the reinforcement effect. It is understood that if flame retardants or other nanoparticles are required in this application, they can be introduced through the side feed or the back section feed port to avoid mutual interference with the dispersion of carbon nanotubes.

[0067] The preparation method described in this application has the following advantages:

[0068] Significantly reduces carbon nanotube agglomeration and enhances the conductive network: The "physical grinding / exfoliation" of multi-scale SiO2 (micron-scale SiO2 and nano-scale SiO2) enables the carbon nanotubes to be well dispersed during pre-mixing. The subsequent extrusion process further maintains and improves the conductive path, reduces the amount of filler, and optimizes the dispersion efficiency of the conductive filler through physical isolation to achieve high conductivity.

[0069] Ensure fiber reinforcement and fluidity control: Adding reinforcing fiber materials in the later stage can not only avoid excessive breakage but also form a stable rheological environment with the help of SiO2 to moderately increase the melt viscosity, thus achieving a good balance between mechanics and processing;

[0070] Multiphase synergy and scalability: SiO2 of different sizes works in synergy with carbon nanotubes and conductive carbon black fillers. Compatibilizers, flame retardants, antioxidants, UV stabilizers and other additives can be added as needed to create a multifunctional polypropylene conductive composite material with "mechanical-electrical-weathering" properties, suitable for demanding outdoor applications such as cable supports.

[0071] Compared with the traditional "one-time feeding" or single-size SiO2, the present invention first prepares a premixed masterbatch composed of multi-scale SiO2, carbon nanotubes and conductive carbon black, and then achieves optimal dispersion and fiber protection through multi-stage temperature control and segmented feeding, which has outstanding creativity and practical value; it has made significant breakthroughs in the dispersion efficiency of conductive fillers, fiber retention and overall rheological properties control, and prepared a polypropylene conductive composite material with high bending strength, excellent conductivity and aging resistance.

[0072] The third aspect of the present application provides use of the polypropylene conductive composite material described in the first aspect or the polypropylene conductive composite material prepared by the preparation method described in the second aspect in preparing a cable bracket.

[0073] Polypropylene conductive composite materials are used in outdoor high-voltage environments such as cable supports. Polypropylene conductive composite materials have excellent conductivity, anti-static, arc protection or bending strength properties. They can effectively disperse electric field stress in high-voltage and high-current impact environments, are not prone to local corona or creepage failure, and have little performance degradation during long-term outdoor service, meeting the life requirements of outdoor high-voltage cable supports.

[0074] The reinforcing effect of the reinforcing fiber material in this application is combined with the through-network of carbon nanotubes and conductive carbon black in the polypropylene matrix to improve the bending and impact strength of the polypropylene conductive composite material, and has high stability in high-voltage impact and thermal deformation environments. Furthermore, by adjusting the mass ratio of carbon nanotubes and conductive carbon black and the degree of compatibility with the polypropylene matrix, the bending strength and impact resistance of the conductive composite material can be improved. 3 -10 8 The volume resistance can be adjusted within the Ω·cm range to adapt to different power system requirements and avoid static electricity accumulation or localized excessive discharge.

[0075] In a fourth aspect of the present application, a cable bracket is provided, wherein the raw materials include the polypropylene conductive composite material described in the first aspect or the polypropylene conductive composite material prepared by the preparation method described in the second aspect.

[0076] The embodiments of the present application will be described in detail below with reference to the examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are preferably referred to the guidance provided in the present application, and can also be based on the experimental manuals or conventional conditions in this area, or according to the conditions recommended by the manufacturer, or with reference to experimental methods known in the art.

[0077] As an example, the sources of raw materials in the embodiment are as follows:

[0078] Polypropylene matrix: manufacturer: SK, South Korea, model BX3900;

[0079] Conductive carbon black: manufacturer TIMCAL, model ENSACO 350G;

[0080] E-glass fiber: manufacturer Chongqing International, model ECS305-4.5-K, chopped 4.5mm;

[0081] Carbon nanotubes: purchased from LG Chem, South Korea, model LUCAN CP 1002M;

[0082] Maleic anhydride grafted polypropylene: manufacturer: Israel Priram, model BONDYRAM®1001;

[0083] Antioxidant: BASF Antioxidant 1010.

[0084] Example 1

[0085] The polypropylene conductive composite material is composed of the following components in mass fractions:

[0086] 58.9% polypropylene (PP) matrix, 0.5% modified carbon nanotubes (acid treated), 3% conductive carbon black, 1.2% micron-sized SiO2 (particle size 1-2μm, average particle size 1.5μm), 0.8% nano-sized SiO2 (particle size 50-200nm, average particle size 100nm), 30% glass fiber (E glass fiber, chopped 4.5mm) and 5.6% additives (5% maleic anhydride grafted polypropylene, 0.2% BASF antioxidant 1010, 0.2% BASF antioxidant 168, 0.2% BASF UV absorber TINUVIN 326).

[0087] The preparation method of modified carbon nanotubes (acid treatment) is: modifying carbon nanotubes by acid treatment, specifically:

[0088] CNTs (carbon nanotubes) were treated in concentrated nitric acid at 60°C for 2 hours, and then washed with deionized water until the pH value of the solution returned to neutral; and dried at 110°C to obtain acid-treated carbon nanotubes, namely modified carbon nanotubes (acid-treated).

[0089] Preparation method of polypropylene conductive composite material:

[0090] (1) The modified carbon nanotubes, conductive carbon black, micron-sized SiO2 and nano-sized SiO2 were put into a high-speed grinder according to the proportion, blended and ground at 1200 rpm for 30 min, and dried to prepare a premixed masterbatch;

[0091] (2) Put the premixed masterbatch and the remaining components into a twin-screw extruder for melt extrusion, specifically:

[0092] The twin-screw extruder has kneading elements in the front section (temperature 190°C) and the middle section (temperature 210°C) for high shear dispersion, and a low shear thread in the rear section (temperature 220°C) to protect the fibers;

[0093] Polypropylene (PP) matrix, premixed masterbatch and additives are added into the main feeding port, glass fiber is added into the side feeding port at the rear stage, and the polypropylene conductive composite material is prepared by water-cooling strands and pelletizing.

[0094] The polypropylene conductive composite material was injection molded at a temperature of 190°C for the front section, 200°C for the middle section, and 210°C for the rear section, a mold temperature of 75°C, and an injection pressure of 80 MPa to obtain a finished polypropylene conductive composite material.

[0095] Example 2

[0096] The polypropylene conductive composite material is composed of the following components in mass fractions:

[0097] 58.4% polypropylene (PP) matrix, 0.5% modified carbon nanotubes (plasma treated), 2.5% conductive carbon black, 2% micron-sized SiO2 (particle size 1-2μm, average particle size 1.5μm), 1.0% nano-sized SiO2 (particle size 50-100nm), 30% glass fiber (E glass fiber, continuous fiber) and 5.6% additives (5% maleic anhydride grafted polypropylene, 0.2% BASF antioxidant 1010, 0.2% BASF antioxidant 168, 0.2% BASF UV absorber TINUVIN 326).

[0098] Among them, the preparation method of modified carbon nanotubes (plasma treated) is: modifying carbon nanotubes by plasma treatment, and the specific plasma treatment is: power is 120W, treatment time is 80s, treatment gas is oxygen, gas flow rate is 10L / min, treatment distance is 15mm, and carbon nanotubes modified with oxygen-containing polar groups are obtained, which are modified carbon nanotubes (plasma treated).

[0099] Preparation method of polypropylene conductive composite material:

[0100] (1) In a kneader at 180°C, 300 rpm, 200°C, vacuum -0.5 bar, and 0.2 MPa, the modified carbon nanotubes, conductive carbon black, micron-sized SiO2, nano-sized SiO2, and 5% MA-g-PP (maleic anhydride grafted polypropylene) were melt-blended for 30 min to form a viscous masterbatch; after cooling, the masterbatch was crushed into granules to prepare a premixed masterbatch for subsequent extruder feeding;

[0101] (2) Put the premixed masterbatch and the remaining components into a twin-screw extruder for melt extrusion, specifically:

[0102] The front section (temperature 200°C) and middle section (temperature 210°C) of the twin-screw extruder are responsible for strong shear dispersion of the premixed masterbatch, and the back section (temperature 220°C);

[0103] Premixed masterbatch, polypropylene (PP) matrix and remaining additives are added through the main feeding port, glass fiber is added through the side feeding port, and the final discharge is underwater pelletized to prepare polypropylene conductive composite materials.

[0104] The polypropylene conductive composite material was injection molded at a temperature of 190°C for the front section, 200°C for the middle section, and 210°C for the rear section, a mold temperature of 75°C, and an injection pressure of 80 MPa to obtain a finished polypropylene conductive composite material.

[0105] Example 3

[0106] The polypropylene conductive composite material is composed of the following components in mass fractions:

[0107] 59.4% polypropylene (PP) matrix, 1.5% modified carbon nanotubes (maleic anhydride grafted polypropylene modified), 1.5% conductive carbon black, 1.2% micron-sized SiO2 (particle size 1-2μm, average particle size 1.5μm), 0.8% nano-sized SiO2 (particle size 50-200nm, average particle size 100nm), 30% glass fiber (E glass fiber, chopped 4.5mm) and 5.6% additives (5% maleic anhydride grafted polypropylene, 0.2% BASF antioxidant 1010, 0.2% BASF antioxidant 168, 0.2% BASF UV absorber TINUVIN 326).

[0108] The preparation method of the modified carbon nanotubes (maleic anhydride grafted polypropylene modified) is: modifying carbon nanotubes by grafting maleic anhydride onto polypropylene, specifically:

[0109] Prepare the impregnation solution by dissolving 20 parts by weight of PP-g-MAH (Eastman G-3015, maleic anhydride grafting rate of 1 wt%, melt index of 5 g / 10 min) in 80 parts by weight of benzene. Stir at 300 rpm at 80°C for 30 minutes to fully dissolve the PP-g-MAH.

[0110] The carbon nanotubes were impregnated with the impregnation solution at 80° C., and then dried at 110° C. for 2 hours to a water content of ≤0.1 wt %, to prepare modified carbon nanotubes (maleic anhydride grafted polypropylene modified).

[0111] Preparation method of polypropylene conductive composite material:

[0112] (1) The modified carbon nanotubes, conductive carbon black, micron-sized SiO2 and nano-sized SiO2 were rolled in a ball mill for 60 min at a speed of 50 rpm; isopropyl alcohol solvent was added to form a slurry, which was ultrasonically dispersed and then dried to prepare a premixed masterbatch;

[0113] (2) Put the premixed masterbatch and other components into a twin-screw extruder for melt extrusion, specifically:

[0114] Twin-screw extruder front section (temperature 190°C), middle section (temperature 220°C) and back section (temperature 220°C),

[0115] Polypropylene (PP) matrix, premixed masterbatch and additives are added to the main feeding port, residual agglomerates are broken up in the kneading section, glass fiber is added to the low shear zone at the rear of the side feeding port, and the material is water-cooled and pelletized after discharge to prepare polypropylene conductive composite materials.

[0116] The polypropylene conductive composite material was injection molded at a temperature of 190°C for the front section, 200°C for the middle section, and 210°C for the rear section, a mold temperature of 80°C, and an injection pressure of 80 MPa to obtain a finished polypropylene conductive composite material.

[0117] Example 4

[0118] The difference between Example 4 and Example 1 is that the modified carbon nanotubes (acid-treated) in the components are replaced with unmodified carbon nanotubes (ie, carbon nanotubes) of equal mass.

[0119] A polypropylene conductive composite material and a polypropylene conductive composite material finished product were prepared according to the method of Example 1.

[0120] Comparative Example 1

[0121] The difference between Comparative Example 1 and Example 1 is that the nano-scale SiO2 in the component is replaced with micron-scale SiO2 of equal mass.

[0122] A polypropylene conductive composite material and a polypropylene conductive composite material finished product were prepared according to the method of Example 1.

[0123] Comparative Example 2

[0124] The difference between Comparative Example 2 and Example 1 is that the micron-sized SiO2 in the component is replaced by nano-sized SiO2 of the same mass.

[0125] A polypropylene conductive composite material and a polypropylene conductive composite material finished product were prepared according to the method of Example 1.

[0126] Comparative Example 3

[0127] The difference between Comparative Example 3 and Example 1 is that the micron-sized SiO2 and nano-sized SiO2 in the components are replaced by a polypropylene matrix of equal mass.

[0128] A polypropylene conductive composite material and a polypropylene conductive composite material finished product were prepared according to the method of Example 1.

[0129] Comparative Example 4

[0130] The difference between Comparative Example 4 and Example 1 is that the composition and mass fraction of each component are different:

[0131] The polypropylene conductive composite material in Comparative Example 4 is composed of the following components in mass fractions:

[0132] 49.4% polypropylene (PP) matrix, 15% conductive carbon black, 30% glass fiber (E glass fiber, chopped 4.5mm) and 5.6% additives (5% maleic anhydride grafted polypropylene, 0.2% BASF antioxidant 1010, 0.2% BASF antioxidant 168, 0.2% BASF UV absorber TINUVIN 326).

[0133] A polypropylene conductive composite material and a polypropylene conductive composite material finished product were prepared according to the method of Example 1.

[0134] Test example

[0135] The finished polypropylene conductive composite materials of Examples 1-4 and Comparative Examples 1-4 were tested for their flexural strength, volume resistivity, and weather resistance.

[0136] Bending strength test method: Refer to GB / T 9341-2008 standard for testing, and the number of samples tested is 10.

[0137] Volume resistivity test method: Refer to GB / T 1410-2006 standard for testing, and the number of samples tested is 10.

[0138] Weathering resistance test method: The finished polypropylene conductive composite material is aged at 85°C / 85%RH (relative humidity) for 1000h.

[0139] The results are shown in Table 1.

[0140] The results in Table 1 show that, by comparing Example 1 with Comparative Examples 1-3, it can be seen that, compared with the polypropylene conductive composite material using only one of nano-SiO2 and micron-SiO2 or no SiO2, Example 1 uses a combination of nano-SiO2 and micron-SiO2, and its volume resistivity is reduced by more than 98%. After aging for 1000 hours at 85°C / 85%RH, the attenuation rate of the flexural strength is reduced from 18-26% to 15%. This indicates that the present application uses nano-SiO2 and micron-SiO2 to prepare a polypropylene conductive composite material, which can significantly improve its conductive properties and weather resistance.

[0141] Compared with Comparative Examples 1-4, the volume resistivity and the attenuation rate of the flexural strength of the polypropylene composite materials of Examples 1-4 after aging at 85°C / 85%RH for 1000h are significantly reduced, and the electrical conductivity and weather resistance of the polypropylene composite materials are stronger.

[0142] Compared with Comparative Example 4, Example 1 of the present application adds carbon nanotubes, micron-sized SiO2 and nano-sized SiO2, and the volume resistivity of the finished polypropylene conductive composite material is reduced by 99%, the bending strength is increased by 36.84%, and the attenuation of the bending strength after aging for 1000 hours at 85°C / 85%RH is reduced by 55.9%. This shows that the polypropylene conductive composite material of the present application is compounded with carbon nanotubes, micron-sized SiO2 and nano-sized SiO2, which can significantly improve its toughness, conductivity and weather resistance.

[0143] Table 1 Bending strength, volume resistance and weather resistance of the finished polypropylene conductive composite materials of Examples 1-4 and Comparative Examples 1-4

[0144]

[0145] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0146] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A polypropylene conductive composite material, characterized in that: The following components are included in the mass fraction: 40-86.4% polypropylene matrix, 0.5-3% modified or unmodified carbon nanotubes, 1-10% conductive carbon black, 1-5% micron-sized SiO2, 0.1-5% nano-sized SiO2, 10-50% reinforcing fiber materials and 1-10% additives.

2. The polypropylene conductive composite material according to claim 1, characterized in that: The modified carbon nanotubes include one or more of acid-treated carbon nanotubes, plasma-treated carbon nanotubes and maleic anhydride-grafted polypropylene-modified carbon nanotubes.

3. The polypropylene conductive composite material according to claim 1, characterized in that: The reinforcing fiber material includes one or more of carbon fiber, basalt fiber and glass fiber.

4. The polypropylene conductive composite material according to claim 1, characterized in that: The auxiliary agent includes one or more of a dispersing auxiliary agent, an antioxidant, an ultraviolet stabilizer, an ultraviolet absorber, a flame retardant, a coupling agent and an anti-aging additive.

5. The polypropylene conductive composite material according to claim 4, characterized in that: The coupling agent includes a silane coupling agent; The dispersing aid includes one or more of a dispersant and a compatibilizer.

6. The polypropylene conductive composite material according to claim 5, characterized in that: Compatibilizers include maleic anhydride grafted polypropylene.

7. The method for preparing the polypropylene conductive composite material according to any one of claims 1 to 6, characterized in that: The steps include: Premixing modified or unmodified carbon nanotubes, conductive carbon black, micron-sized SiO2, nano-sized SiO2 and part or all of the additives to prepare a premixed masterbatch; The premixed masterbatch and the remaining components are melt-extruded to prepare a polypropylene conductive composite material.

8. The preparation method according to claim 7, characterized in that Premixing includes grinding premixing or hot melt blending; The step of melt-extruding the premixed masterbatch and the remaining components comprises: feeding the premixed masterbatch and the remaining components into an extruder for melt-extrusion; the parameter settings of the extruder include: the front section temperature is 190-200°C, the middle section temperature is 210-220°C, and the rear section temperature is 210-220°C.

9. Use of the polypropylene conductive composite material according to any one of claims 1 to 6 or the polypropylene conductive composite material prepared by the preparation method according to any one of claims 7 to 8 in preparing a cable bracket.

10. A cable bracket, characterized in that: The raw materials include the polypropylene conductive composite material according to any one of claims 1 to 6 or the polypropylene conductive composite material prepared by the preparation method according to any one of claims 7 to 8.

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