A self-reinforced polypropylene cable insulation material by polypropylene graft copolymer and a method for preparing the same

Abstract

This invention discloses a self-reinforced polypropylene cable insulation material and its preparation method using a polypropylene graft copolymer, relating to the field of polymer materials. The preparation method includes: firstly, preparing a polypropylene graft copolymer via melt grafting or electron beam radiation grafting; subsequently, melt-blending the copolymer with polypropylene to prepare a primary masterbatch; and finally, melt-blending the primary masterbatch with polypropylene, an antioxidant, a voltage stabilizer, and processing aids to obtain the cable insulation material. This invention induces the matrix polypropylene to produce a β-crystal form through the polypropylene graft copolymer. The β-crystal form and polar vinyl monomers together achieve elastomer-independent self-reinforcement, simultaneously improving the material's toughness, heat resistance, and DC dielectric properties. This solves the performance degradation problem caused by traditional elastomer blending and is suitable for high-voltage DC cable insulation.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and specifically relates to a high-performance polypropylene (PP)-based insulation material for cables and its preparation method, specifically a polypropylene cable insulation material that achieves self-reinforcement through polypropylene graft copolymerization. Background Technology

[0002] Polypropylene (PP), a semi-crystalline thermoplastic polymer, is considered an ideal alternative to cross-linked polyethylene (XLPE) due to its excellent electrical insulation properties, high heat resistance, low density, and recyclability. It can be used to manufacture environmentally friendly thermoplastic power cables.

[0003] However, pure polypropylene materials have inherent defects such as high hardness, poor toughness, insufficient impact resistance, and easy accumulation of space charge under high voltage DC electric field, which seriously limit their application in high voltage cables, especially DC cable insulation.

[0004] To improve the mechanical properties of polypropylene, existing technologies typically employ physical blending with low-hardness elastomers (such as SEBS), as disclosed in Chinese patents with publication numbers CN117106258A, CN120329678A, and CN119978615A. While this method can improve the toughness and impact resistance of the material to some extent, it introduces new problems: the addition of elastomers usually leads to a decrease in the heat resistance of polypropylene and deteriorates its melt processing fluidity; more importantly, the introduction of elastomers significantly reduces the breakdown strength of the composite material and degrades its dielectric properties, thus greatly limiting its application in high-voltage DC cables.

[0005] To avoid the drawbacks of physical blending, introducing polar functional groups into the polypropylene molecular chain through chemical grafting is an effective means of controlling its properties at the molecular level. For example, grafting monomers containing specific functional groups onto the polypropylene molecular chain can effectively improve the crystallization behavior of polypropylene, inducing the formation of β-crystals, thereby achieving toughening of the material at the microstructure level. However, how to simultaneously improve the toughness, heat resistance, and DC dielectric properties of polypropylene materials without relying on elastomer blending through specific graft copolymer structures and optimized processing techniques has become a pressing technical challenge in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a self-reinforced polypropylene cable insulation material through polypropylene graft copolymerization and its preparation method. This method aims to simultaneously improve the material's toughness, heat resistance, and DC dielectric properties without relying on elastomer blending.

[0007] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0008] On one hand, the present invention provides a method for preparing a self-reinforced polypropylene cable insulation material by means of a polypropylene graft copolymer, comprising the following steps:

[0009] Step (1) Preparation of polypropylene graft copolymer: Polar vinyl monomers are grafted onto polypropylene by melt grafting or electron beam radiation grafting to obtain polypropylene graft copolymer; the polypropylene graft copolymer is used to provide nucleation sites for inducing β crystallization and to introduce polar groups that suppress space charge in the polypropylene matrix.

[0010] Step (2) Preparation of primary masterbatch: Take 10-50 parts by weight of the polypropylene graft copolymer obtained in step (1) and 50-90 parts by weight of polypropylene for melt blending, so that the polypropylene graft copolymer is pre-dispersed in the matrix, and then granulated and dried to obtain primary masterbatch.

[0011] Step (3) Preparation of cable insulation material: Take 0.5-10 parts by weight of the primary masterbatch obtained in step (2), 88-98 parts of polypropylene, 0.05-0.5 parts of antioxidant, 0.05-0.5 parts of voltage stabilizer and 0.05-5.5 parts of processing aid and melt blend them to induce the matrix polypropylene to produce β crystal form through the uniformly dispersed polypropylene graft copolymer. The β crystal form and polar vinyl monomer are used as the internal reinforcing phase to achieve self-reinforcement. Then, granulation and drying are carried out to finally obtain a cable insulation material with excellent comprehensive performance.

[0012] Further, in step (1), the polar vinyl monomer is selected from one or two of 4-vinylphenol, hydroxyethyl methacrylate, hydroxypropyl methacrylate, styrene, p-methylstyrene, acrylic acid, methacrylic acid, maleic acid, itaconic anhydride, N-hydroxymethylacrylamide, glycidyl methacrylate, vinyltrimethoxysilane and γ-methacryloyloxypropyltrimethoxysilane.

[0013] Further, in step (1), the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min;

[0014] and / or;

[0015] In step (2), the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min;

[0016] and / or;

[0017] In step (3), the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min.

[0018] Further, in step (1), the melt grafting method includes: mixing 85-99 parts by weight of polypropylene, 1-15 parts by weight of polar vinyl monomer and 0-0.5 parts by weight of free radical initiator to obtain a premix; performing melt grafting of the premix at 175-220°C under inert gas protection for 5-20 minutes; dissolving the grafted product in xylene, heating at 110-140°C for 1-4 hours, and then precipitating in a precipitation solvent at 0-10°C, and obtaining the polypropylene graft copolymer after washing, filtering and drying.

[0019] Furthermore, the free radical initiator is selected from at least one of dicumyl peroxide, di-tert-butyl peroxide, benzoyl peroxide, tert-butyl peroxide, tert-butyl peroxide-2-ethylhexanoate, methyl ethyl ketone peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, and azoisobutyl cyanoformamide.

[0020] Further, in step (1), the electron beam irradiation grafting method includes: dissolving 1-10 parts by weight of polar vinyl monomer in 5-30 parts of swelling agent, and placing it together with 65-75 parts of polypropylene in a container, and then removing oxygen from the container by inert gas replacement; then irradiating the container with an electron beam at an irradiation dose of 2-100 kGy and an irradiation temperature of 5-70°C; dissolving the irradiated grafted product in xylene, heating it at 110-140°C for 1-4 hours, and then precipitating it in a precipitation solvent at 0-10°C, and obtaining the polypropylene graft copolymer after washing, filtering and drying.

[0021] Furthermore, the swelling agent is selected from at least one of water, methanol, ethanol, acetone, benzene, and toluene.

[0022] Further, in step (3), the antioxidant is selected from one or two of antioxidant 697, antioxidant S-9228, antioxidant 3114, antioxidant DSTP, antioxidant DLTP, antioxidant 1010, antioxidant BHT, antioxidant 1024, antioxidant 1076 and antioxidant 1098;

[0023] and / or;

[0024] The voltage stabilizer is selected from at least one of aromatic ketone compounds, polycyclic aromatic hydrocarbon compounds, and organophosphorus compounds.

[0025] Furthermore, in step (3), the processing aids include flame retardants and / or inorganic fillers;

[0026] The flame retardant is selected from one or more of the following: ammonium polyphosphate, pentaerythritol, melamine, aluminum hydroxide, magnesium hydroxide, polysiloxane, and layered double hydroxides.

[0027] The inorganic filler is selected from one or more of barium sulfate, silicon dioxide, calcium carbonate, talc, titanium dioxide, and zinc borate.

[0028] On the other hand, the present invention provides a self-reinforced polypropylene cable insulation material prepared by the above-described method using a polypropylene graft copolymer.

[0029] The functions of each raw material in this invention are as follows:

[0030] Polypropylene graft copolymer: The core functional component in this invention, it does not act as a simple filler, but plays a triple synergistic effect in the matrix: (a) nucleating agent: induces the matrix polypropylene to produce a β crystal form that is beneficial to toughness; (b) charge trapping center: its polar functional groups can capture and bind space charge, improving the charge distribution under DC electric field; (c) compatibility improver: because it is derived from polypropylene, it has excellent compatibility with the matrix polypropylene and will not produce harmful interfaces.

[0031] Polar vinyl monomers: provide a source of polar functional groups and are the chemical basis for the functionalization of polypropylene graft copolymers.

[0032] Antioxidants: prevent materials from aging due to thermal oxidation during processing and use, thus ensuring the service life of the materials.

[0033] Voltage stabilizer: Improves the breakdown strength of materials and is one of the key additives in high-voltage cable insulation materials.

[0034] Processing aids (such as flame retardants and inorganic fillers): impart specific functions such as flame retardancy and reinforcement to materials as needed.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) This invention abandons the traditional approach of elastomer blending and instead introduces a polypropylene graft copolymer with excellent compatibility with the matrix, which serves as a nucleation point within the matrix, inducing the polypropylene to generate a toughening β-crystal form. This strengthening effect, resulting from the change in the material's own structure, fundamentally avoids the deterioration of heat resistance and electrical insulation properties caused by the introduction of heterogeneous components (such as elastomers), thus achieving self-reinforcement within the material.

[0037] (2) This invention ingeniously achieves simultaneous optimization of multiple properties through a single functional component (polypropylene graft copolymer): First, the β-crystal form induced by the polypropylene graft copolymer effectively improves the toughness of the material. At the same time, its good compatibility with the matrix and the refined grain structure ensure that the rigidity of the material is not compromised, achieving a balance between high strength and high toughness. Second, the introduction of the polypropylene graft copolymer increases the crystallization temperature of the material and refines the grains, thereby simultaneously enhancing the heat resistance of the material. Third, the polar functional groups on the grafted chains form deep-level charge traps in the insulating system, which can effectively capture and bind space charges, significantly inhibiting charge injection and migration, thereby improving the charge distribution under a DC electric field and increasing the breakdown strength.

[0038] (3) The unique “primary masterbatch” preparation step of this invention ensures that the key functional component (polypropylene graft copolymer) is highly uniformly dispersed in the final matrix. This uniform dispersion is a prerequisite for the polypropylene graft copolymer to stably and efficiently induce a large number of β crystals and avoid performance defects or fluctuations caused by local aggregation, thereby ensuring the excellent performance and consistency of the final product.

[0039] (4) The material prepared by this invention has a dense and uniform spherulitic morphology with fine grains, and the polypropylene graft copolymer has good interfacial bonding with the matrix with no obvious phase separation defects. This optimized microstructure is the fundamental reason why the material obtains excellent macroscopic properties. Attached Figure Description

[0040] Figure 1 This is a polarized light microscope image of the spherulite morphology of the cable insulation material obtained in Example 1 of the present invention.

[0041] Figure 2 This is a polarized light microscope image of the spherulite morphology of the cable insulation material obtained in Comparative Example 1 of the present invention.

[0042] Figure 3 This is a SEM image of the cable insulation material obtained in Embodiment 1 of the present invention. Detailed Implementation

[0043] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0044] This invention provides a self-reinforced polypropylene cable insulation material made of polypropylene graft copolymer and its preparation method. The method involves introducing specific functional groups onto the polypropylene molecular chain via melt grafting or electron beam radiation grafting to obtain a polypropylene graft copolymer. This graft copolymer itself induces the matrix polypropylene to form a β-crystal structure, thereby toughening the matrix polypropylene material. Simultaneously, the introduced polar groups effectively suppress space charge and improve the material's heat resistance, ultimately resulting in a cable insulation material with excellent overall performance. The preparation method is described in detail below.

[0045] Step (1), Preparation of polypropylene graft copolymer

[0046] Polypropylene graft copolymers are obtained by introducing specific functional groups into the polypropylene molecular chain through melt grafting or electron beam irradiation grafting. This step is a key chemical modification and functionalization step to achieve "self-reinforcement". Through the grafting reaction, polar functional groups with specific functions are introduced into the polypropylene molecular chain: these functional groups can act as efficient nucleation sites, inducing the matrix polypropylene to produce β-crystals; on the other hand, their polarity can form deep-level charge traps in the insulating system, suppressing space charge.

[0047] The method for preparing polypropylene graft copolymers using melt grafting (hereinafter referred to as "Method A") includes: mixing polypropylene, polar vinyl monomers, and free radical initiators in a high-speed mixer at room temperature and a rotation speed of 120 rpm for 5-30 min to ensure uniform dispersion and obtain a premix; feeding the premix into a torque rheometer or a twin-screw extruder and performing melt reaction grafting under inert gas protection; adding the grafted product to xylene, heating and reacting for a period of time, then pouring it into a sedimentation solvent for sedimentation, followed by washing and filtering the sedimented product; finally, vacuum drying the solid product at 60-80℃ to constant weight to obtain the polypropylene graft copolymer.

[0048] A method for preparing polypropylene graft copolymers using electron beam irradiation grafting (hereinafter referred to as "Method B") includes: firstly, dissolving a polar vinyl monomer in a swelling agent, then placing it and polypropylene in a container, and completely removing oxygen from the container by inert gas replacement; placing the container containing the materials under an electron beam irradiation device for irradiation; adding the irradiated grafted product to xylene, heating and reacting for a period of time, then pouring it into a sedimentation solvent for sedimentation, followed by washing and filtering the sedimented product; finally, vacuum drying the solid product at 60-80℃ to constant weight to obtain the polypropylene graft copolymer.

[0049] Furthermore, in methods A and B, the polar vinyl monomer is selected from one or two of the following substances: 4-vinylphenol, hydroxyethyl methacrylate, hydroxypropyl methacrylate, styrene, p-methylstyrene, acrylic acid, methacrylic acid, maleic acid, itaconic anhydride, N-hydroxymethylacrylamide, glycidyl methacrylate, vinyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

[0050] Furthermore, in methods A and B, the polar vinyl monomers need to be subjected to vacuum distillation before use to remove the polymerization inhibitors.

[0051] Furthermore, in methods A and B, the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min. Furthermore, in method A, the polypropylene is preferably isotactic polypropylene granules or powder; in method B, the polypropylene is preferably isotactic polypropylene powder or film.

[0052] Furthermore, in method A, the free radical initiator is an organic peroxide or an azo compound, specifically selected from at least one of dicumyl peroxide, di-tert-butyl peroxide, benzoyl peroxide, tert-butyl peroxide, tert-butyl peroxide-2-ethylhexanoate, methyl ethyl ketone peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, and azoisobutyl cyanoformamide.

[0053] Furthermore, in Method A, the composition of the polypropylene, polar vinyl monomer, and free radical initiator, by weight, is: 85-99 parts polypropylene, 1-15 parts polar vinyl monomer, and 0-0.5 parts free radical initiator.

[0054] Furthermore, in methods A and B, the inert gas is nitrogen or argon.

[0055] Furthermore, in method A, the reaction temperature of the melt reaction grafting is 175-220℃, the reaction time is 5-20 min, and the rotation speed of the torque rheometer or twin-screw extruder is 40-250 rpm.

[0056] Furthermore, in methods A and B, the heating temperature of the xylene is 110-140℃, and the reaction time is 1-4h.

[0057] Furthermore, in methods A and B, the settling solvent is acetone or methanol, and the settling temperature is 0-10°C.

[0058] Furthermore, in methods A and B, the dissolution, sedimentation, filtration and washing processes are repeated at least twice to thoroughly remove homopolymers and unreacted monomers.

[0059] Furthermore, in method B, the swelling agent is at least one of water, methanol, ethanol, acetone, benzene, and toluene, and its function is to dilute the polar vinyl monomer and promote the swelling and diffusion of the monomer into the polypropylene.

[0060] Furthermore, in method B, the composition of the polypropylene, polar vinyl monomer and swelling agent, by weight parts, is: 65-75 parts polypropylene, 1-10 parts polar vinyl monomer and 5-30 parts swelling agent, and it is necessary to ensure that the polypropylene is completely immersed in the swelling agent.

[0061] Furthermore, in method B, the irradiation dose of the radiation graft is 2-100 kGy, and the irradiation temperature is 5-70℃.

[0062] Step (2) Preparation of primary masterbatch

[0063] The polypropylene graft copolymer obtained in step (1) is melt-blended with polypropylene in a Banbury mixer or twin-screw extruder, followed by granulation and drying to produce a primary masterbatch with a high graft copolymer content. This step is the core process to ensure the uniform and stable performance of the final product. By preparing a high-concentration primary masterbatch, it is possible to ensure that the polypropylene graft copolymer is highly uniformly dispersed in the final matrix, laying the foundation for the stable and uniform induction of β-crystal form in all polypropylene matrices and avoiding performance fluctuations caused by uneven dispersion.

[0064] Furthermore, the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min.

[0065] Furthermore, by weight, the composition of the polypropylene graft copolymer and polypropylene is: 10-50 parts polypropylene graft copolymer and 50-90 parts polypropylene.

[0066] Furthermore, the melt blending temperature is 185-205℃, the rotation speed is 50-150rpm, and the time is 5-15min.

[0067] Furthermore, the granulation process is water-cooled pelletizing, and the main unit speed of the pelletizer is 750-1000 rpm.

[0068] Furthermore, the drying process is vacuum drying, with a drying temperature of 70-90℃ and a drying time of 12-24 hours.

[0069] Step (3) Preparation of cable insulation material

[0070] The primary masterbatch obtained in step (2), polypropylene, antioxidant, voltage stabilizer, and processing aids are melt-blended in a twin-screw extruder, and then granulated and dried to obtain the cable insulation material. This step is the final product molding and performance realization step. The uniformly dispersed primary masterbatch acts as a "seed" in the final polypropylene matrix, inducing the formation of a large number of fine β crystals; at the same time, the addition of antioxidants, voltage stabilizers, and other additives further ensures the long service life and electrical performance of the material.

[0071] Furthermore, the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min.

[0072] Furthermore, the antioxidant is selected from one or two of antioxidant 697, antioxidant S-9228, antioxidant 3114, antioxidant DSTP, antioxidant DLTP, antioxidant 1010, antioxidant BHT, antioxidant 1024, antioxidant 1076, and antioxidant 1098.

[0073] Furthermore, the voltage stabilizer is at least one of aromatic ketone compounds, polycyclic aromatic hydrocarbon compounds, and organophosphorus compounds.

[0074] Furthermore, the processing aids include flame retardants and / or inorganic fillers; the flame retardants are selected from one or more of ammonium polyphosphate, pentaerythritol, melamine, aluminum hydroxide, magnesium hydroxide, polysiloxane, and layered double hydroxides; the inorganic fillers are selected from one or more of barium sulfate, silicon dioxide, calcium carbonate, talc, titanium dioxide, and zinc borate.

[0075] Furthermore, by weight, the primary masterbatch, polypropylene, antioxidant, voltage stabilizer, and processing aid are composed of: 0.5-10 parts primary masterbatch, 88-98 parts polypropylene, 0.05-0.5 parts antioxidant, 0.05-0.5 parts voltage stabilizer, and 0.05-5.5 parts processing aid.

[0076] Furthermore, the melt blending temperature is 180-210℃, the rotation speed is 50-150rpm, and the time is 5-15min.

[0077] Furthermore, the granulation process is water-cooled pelletizing, and the main unit speed of the pelletizer is 750-1000 rpm.

[0078] Furthermore, the drying process is vacuum drying, with a drying temperature of 70-90℃ and a drying time of 12-24 hours.

[0079] Furthermore, the cable insulation material obtained in step (3) is granular, and its subsequent processing can be carried out according to the actual shape and specifications of the cable insulation material.

[0080] The present invention will be further illustrated below with specific embodiments, but these embodiments are only used to explain the present invention in detail and are not intended to limit the scope of protection of the claims of this application.

[0081] In this invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the field; the methods in the following embodiments are conventional methods in the field unless otherwise specified.

[0082] Example 1

[0083] This embodiment provides a method for preparing a self-reinforced polypropylene cable insulation material using polypropylene graft copolymers, including the following steps:

[0084] (1) Preparation of polypropylene graft copolymer (melt grafting method)

[0085] By mass, 90 parts of isotactic polypropylene granules with a melt index of 2.4 g / 10 min, 4.8 parts of methacrylic acid, 5 parts of styrene, and 0.2 parts of dicumyl peroxide were mixed in a high-speed mixer at room temperature and a rotation speed of 120 rpm for 30 min to ensure uniform dispersion, resulting in a premix. The premix was then fed into a twin-screw extruder and subjected to melt grafting under nitrogen protection at a screw speed of 250 rpm, a reaction temperature of 180 °C, and a reaction time of 15 min. The grafted product was added to xylene and heated to 140 °C for 3 h. The solution was then poured into methanol at 5 °C for precipitation, followed by washing and filtration. This process of dissolution, precipitation, and filtration was repeated twice to thoroughly remove homopolymers and unreacted monomers. Finally, the solid product was vacuum dried at 80 °C to constant weight to obtain the polypropylene graft copolymer.

[0086] (2) Preparation of primary masterbatch

[0087] By mass, 30 parts of the polypropylene graft copolymer obtained in step (1) and 70 parts of isotactic polypropylene with a melt index of 2.8 g / 10 min were melt-blended in a twin-screw extruder at a melt temperature of 200°C, a screw speed of 75 rpm, and a blending time of 10 min. Then, the mixture was granulated by water-cooled pelletizing at a speed of 800 rpm. Finally, the pellets were vacuum-dried at 80°C for 12 h to obtain the primary masterbatch.

[0088] (3) Preparation of cable insulation materials

[0089] By mass, 5 parts of the primary masterbatch obtained in step (2), 90 parts of isotactic polypropylene with a melt index of 2.8 g / 10 min, 0.4 parts of antioxidant DLTP, 0.4 parts of Miescherichia cochinchinensis (voltage stabilizer), 0.2 parts of magnesium hydroxide and 4 parts of calcium carbonate were melt-blended in a twin-screw extruder at a melt temperature of 190°C, a screw speed of 50 rpm and a blending time of 15 min. Then, the material was granulated by water-cooled pelletizing at a speed of 1000 rpm. Finally, the pellets were vacuum-dried at 80°C for 24 h to obtain the cable insulation material.

[0090] Example 2

[0091] This embodiment provides a method for preparing a self-reinforced polypropylene cable insulation material using polypropylene graft copolymers, including the following steps:

[0092] (1) Preparation of polypropylene graft copolymer (radiation grafting method)

[0093] First, 5 parts by mass of p-methylstyrene were dissolved in 25 parts by toluene. Then, this solution was placed in a container with 70 parts by melt index of isotactic polypropylene powder (1.8 g / 10 min). The oxygen in the container was completely removed by nitrogen purging. The container containing the material was then irradiated under an electron beam irradiation device at a dose of 50 kGy and a temperature of 65 °C. The irradiated grafted product was added to xylene and heated to 110 °C for 4 h. The solution was then poured into methanol at 0 °C to settle, followed by washing and filtration. The purification process was repeated twice. Finally, the solid product was vacuum dried at 60 °C to constant weight to obtain the polypropylene graft copolymer.

[0094] (2) Preparation of primary masterbatch

[0095] By mass, 10 parts of the polypropylene graft copolymer obtained in step (1) and 90 parts of isotactic polypropylene with a melt index of 3.5 g / 10 min were melt-blended in a twin-screw extruder at a melt temperature of 190°C, a screw speed of 150 rpm, and a blending time of 5 min. Then, the mixture was granulated by water-cooled pelletizing at a speed of 900 rpm. Finally, the pellets were vacuum-dried at 70°C for 12 h to obtain the primary masterbatch.

[0096] (3) Preparation of cable insulation materials

[0097] By mass, 2 parts of the primary masterbatch obtained in step (2), 95.5 parts of isotactic polypropylene with a melt index of 3.5 g / 10 min, 0.05 parts of antioxidant 1010, 0.5 parts of triphenyl phosphate (voltage stabilizer), 0.5 parts of ammonium polyphosphate, 0.3 parts of pentaerythritol and 0.15 parts of melamine were melt-blended in a twin-screw extruder at a melt temperature of 210°C, a screw speed of 150 rpm and a blending time of 5 min. Then, the material was granulated by water-cooled pelletizing at a pelletizer speed of 800 rpm. Finally, the pellets were vacuum-dried at 80°C for 12 h to obtain the cable insulation material.

[0098] Example 3

[0099] This embodiment provides a method for preparing a self-reinforced polypropylene cable insulation material using polypropylene graft copolymers, including the following steps:

[0100] (1) Preparation of polypropylene graft copolymer (radiation grafting method)

[0101] By mass, 10 parts of N-hydroxymethylacrylamide were first dissolved in 25 parts of methanol. Then, this solution was placed in a container with 65 parts of isotactic polypropylene film with a melt index of 2.0 g / 10 min. The oxygen in the container was completely removed by argon purging. The container was then irradiated with an electron beam at a dose of 10 kGy and a temperature of 70 °C. The irradiated grafted product was added to xylene and heated to 120 °C for 1 h. The solution was then poured into acetone at 10 °C to settle, followed by washing and filtration. This purification process was repeated twice. Finally, the solid product was vacuum dried at 70 °C to constant weight to obtain the polypropylene graft copolymer.

[0102] (2) Preparation of primary masterbatch

[0103] By mass, 50 parts of the polypropylene graft copolymer obtained in step (1) and 50 parts of isotactic polypropylene with a melt index of 2.4 g / 10 min were melt-blended in a twin-screw extruder at a melt temperature of 185°C, a screw speed of 100 rpm, and a blending time of 8 min. Then, the mixture was granulated by water-cooled pelletizing at a speed of 750 rpm. Finally, the pellets were vacuum-dried at 70°C for 20 h to obtain the primary masterbatch.

[0104] (3) Preparation of cable insulation materials

[0105] By mass, 1 part of the primary masterbatch obtained in step (2), 94 parts of isotactic polypropylene with a melt index of 2.4 g / 10 min, 0.1 parts of antioxidant S-9228, 0.1 parts of acenaphthene (voltage stabilizer), 0.3 parts of polysiloxane and 4.5 parts of barium sulfate were melt-blended in a twin-screw extruder at a melting temperature of 200°C, a screw speed of 100 rpm and a blending time of 8 min. Then, the material was granulated by water-cooled pelletizing at a speed of 950 rpm. Finally, the pellets were vacuum-dried at 60°C for 24 h to obtain the cable insulation material.

[0106] Example 4

[0107] This embodiment provides a method for preparing a self-reinforced polypropylene cable insulation material using polypropylene graft copolymers, including the following steps:

[0108] (1) Preparation of polypropylene graft copolymer (melt grafting method)

[0109] By mass, 85 parts of isotactic polypropylene powder with a melt index of 3.5 g / 10 min, 11 parts of glycidyl methacrylate, 3.5 parts of hydroxyethyl methacrylate, and 0.5 parts of azobisisobutyronitrile were mixed in a high-speed mixer at room temperature and a rotation speed of 120 rpm for 25 min to ensure uniform dispersion, resulting in a premix. The premix was then placed in a rheometer and subjected to melt grafting under argon protection at a rotation speed of 200 rpm, a reaction temperature of 220 °C, and a reaction time of 5 min. The grafted product was added to xylene and heated to 125 °C for 2 h. The solution was then poured into methanol at 10 °C to settle, followed by washing and filtration. This purification process was repeated twice. Finally, the solid product was vacuum dried at 75 °C to constant weight to obtain the polypropylene graft copolymer.

[0110] (2) Preparation of primary masterbatch

[0111] By mass, 10 parts of the polypropylene graft copolymer obtained in step (1) and 90 parts of isotactic polypropylene with a melt index of 2.1 g / 10 min were melt-blended in a twin-screw extruder at a melt temperature of 195°C, a screw speed of 120 rpm, and a blending time of 12 min. Then, the mixture was granulated by water-cooled pelletizing at a speed of 750 rpm. Finally, the pellets were vacuum-dried at 90°C for 12 h to obtain the primary masterbatch.

[0112] (3) Preparation of cable insulation materials

[0113] By mass, 10 parts of the primary masterbatch obtained in step (2), 88 parts of isotactic polypropylene with a melt index of 2.1 g / 10 min, 0.05 parts of antioxidant 1098, 0.05 parts of benzophenone (voltage stabilizer) and 0.1 parts of talc were melt-blended in a twin-screw extruder at a melting temperature of 200°C, a screw speed of 80 rpm and a blending time of 10 min. Then, the material was granulated by water-cooled pelletizing at a speed of 850 rpm. Finally, the pellets were vacuum-dried at 80°C for 12 h to obtain the cable insulation material.

[0114] Example 5

[0115] This embodiment provides a method for preparing a self-reinforced polypropylene cable insulation material using polypropylene graft copolymers, including the following steps:

[0116] (1) Preparation of polypropylene graft copolymer (melt grafting method)

[0117] By mass, 92 parts of isotactic polypropylene granules with a melt index of 1.8 g / 10 min, 3.4 parts of maleic acid, 4.5 parts of styrene, and 0.1 parts of tert-butyl peroxide-2-ethylhexanoate were mixed in a high-speed mixer at room temperature and a rotation speed of 120 rpm for 25 min to ensure uniform dispersion, resulting in a premix. The premix was then fed into a twin-screw extruder and subjected to melt grafting under nitrogen protection at a screw speed of 150 rpm, a reaction temperature of 210 °C, and a reaction time of 10 min. The grafted product was added to xylene and heated to 130 °C for 2 h. The solution was then poured into acetone at 5 °C for precipitation, followed by washing and filtration. This purification process was repeated twice. Finally, the solid product was vacuum dried at 60 °C to constant weight to obtain the polypropylene graft copolymer.

[0118] (2) Preparation of primary masterbatch

[0119] By mass, 15 parts of the polypropylene graft copolymer obtained in step (1) and 85 parts of isotactic polypropylene with a melt index of 3.0 g / 10 min were melt-blended in a twin-screw extruder at a melt temperature of 195°C, a screw speed of 100 rpm, and a blending time of 7 min. Then, the mixture was granulated by water-cooled pelletizing at a speed of 800 rpm. Finally, the pellets were vacuum-dried at 80°C for 15 h to obtain the primary masterbatch.

[0120] (3) Preparation of cable insulation materials

[0121] By mass, 3.5 parts of the primary masterbatch obtained in step (2), 90 parts of isotactic polypropylene with a melt index of 3.0 g / 10 min, 0.5 parts of antioxidant BHT, 0.5 parts of phosphite (voltage stabilizer), 0.5 parts of layered double hydroxide and 5 parts of titanium dioxide were melt-blended in a twin-screw extruder at a melt temperature of 180°C, a screw speed of 150 rpm and a blending time of 12 min; then granulation was carried out by water-cooled pelletizing at a pelletizer speed of 800 rpm; finally, the pellets were vacuum dried at 70°C for 24 h to obtain the cable insulation material.

[0122] Example 6

[0123] This embodiment provides a method for preparing a self-reinforced polypropylene cable insulation material using polypropylene graft copolymers, including the following steps:

[0124] (1) Preparation of polypropylene graft copolymer (radiation grafting method)

[0125] By mass, 8 parts styrene were first dissolved in 22 parts benzene, and then this solution was placed in a container with 70 parts isotactic polypropylene powder with a melt index of 2.4 g / 10 min. The oxygen in the container was completely removed by argon purging. The container was then irradiated under an electron beam irradiation device with an irradiation dose of 90 kGy and an irradiation temperature of 10 °C. The irradiated grafted product was added to xylene and heated to 140 °C for 1 h. The solution was then poured into methanol at 10 °C to precipitate, followed by washing and filtration. The purification process was repeated twice. Finally, the solid product was vacuum dried at 80 °C to constant weight to obtain the polypropylene graft copolymer.

[0126] (2) Preparation of primary masterbatch

[0127] By mass, 40 parts of the polypropylene graft copolymer obtained in step (1) and 60 parts of isotactic polypropylene with a melt index of 2.4 g / 10 min were melt-blended in a twin-screw extruder at a melt temperature of 190°C, a screw speed of 90 rpm, and a blending time of 10 min. Then, the mixture was granulated by water-cooled pelletizing at a speed of 750 rpm. Finally, the pellets were vacuum-dried at 80°C for 12 h to obtain the primary masterbatch.

[0128] (3) Preparation of cable insulation materials

[0129] By mass, 5 parts of the primary masterbatch obtained in step (2), 92 parts of isotactic polypropylene with a melt index of 2.4 g / 10 min, 0.5 parts of antioxidant 1024, 0.2 parts of acetophenone (voltage stabilizer), 0.3 parts of ammonium polyphosphate and 2 parts of zinc borate were melt-blended in a twin-screw extruder at a melt temperature of 210°C, a screw speed of 100 rpm and a blending time of 10 min; then granulation was carried out by water-cooled pelletizing at a main speed of 950 rpm; finally, the pellets were vacuum dried at 60°C for 24 h to obtain the self-reinforced polypropylene cable insulation material.

[0130] Comparative Example 1

[0131] The difference between this comparative example and Example 1 is that no polypropylene graft copolymer was prepared; only the polypropylene system was blended. The specific steps are as follows: 95 parts by mass of isotactic polypropylene with a melt index of 2.8 g / 10 min, 0.4 parts of antioxidant DLTP, 0.4 parts of Miescherichia cochinchinensis (voltage stabilizer), 0.2 parts of magnesium hydroxide, and 4 parts of calcium carbonate were melt-blended in a twin-screw extruder at a melt temperature of 190°C, a screw speed of 50 rpm, and a blending time of 15 min. Subsequently, the mixture was granulated by water-cooled pelletizing at a pelletizer speed of 1000 rpm. Finally, the pellets were vacuum-dried at 80°C for 24 h to obtain the polypropylene blend material.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 1 is that no primary masterbatch was prepared. The specific steps are as follows:

[0134] (1) Preparation of polypropylene graft copolymer (melt grafting method)

[0135] Its formula and operation steps are the same as step (1) of Example 1;

[0136] (2) Preparation of cable insulation materials

[0137] By mass, 1.5 parts of the polypropylene graft copolymer obtained in step (1), 93.5 parts of isotactic polypropylene with a melt index of 2.8 g / 10 min, 0.4 parts of antioxidant DLTP, 0.4 parts of Miescherichia coke (voltage stabilizer), 0.2 parts of magnesium hydroxide and 4 parts of calcium carbonate were melt-blended in a twin-screw extruder at a melt temperature of 190°C, a screw speed of 50 rpm and a blending time of 15 min. Then, the mixture was granulated by water-cooled pelletizing at a speed of 1000 rpm. Finally, the pellets were vacuum-dried at 80°C for 24 h to obtain cable insulation material.

[0138] Comparative Example 3

[0139] This comparative example does not utilize the prepared polypropylene graft copolymer for self-reinforcement of the insulation material. Instead, it employs a traditional elastomer (SEBS thermoplastic elastomer) to modify the polypropylene system through blending. The specific steps are as follows: By mass, 5 parts of SEBS thermoplastic elastomer, 90 parts of isotactic polypropylene with a melt index of 2.8 g / 10 min, 0.4 parts of antioxidant DLTP, 0.4 parts of Miescherichia coli (voltage stabilizer), 0.2 parts of magnesium hydroxide, and 4 parts of calcium carbonate were melt-blended in a twin-screw extruder at a melt temperature of 190°C, a screw speed of 50 rpm, and a blending time of 15 min. Subsequently, the mixture was granulated by water-cooled pelletizing at a pelletizer speed of 1000 rpm. Finally, the pellets were vacuum-dried at 80°C for 24 h to obtain the polypropylene blend material.

[0140] Performance tests were conducted on the cable insulation materials in each embodiment and comparative example. The cable insulation materials were prepared into suitable test morphologies according to the test methods. Subsequently, the tensile strength and elongation at break of the samples were tested according to GB / T 1040-2006 standard; the flexural modulus of the samples was tested according to GB / T 9341-2008 standard; the heat distortion temperature of the samples was tested according to GB / T 1634.2-2019 standard, with a load of 1.80 MPa and a heating rate of 120℃ / h; the breakdown strength of the samples was tested using the continuous voltage ramp method according to IEC 60243-1 standard, with a voltage ramp rate of 1 kV / s; the β-crystal content in the cable insulation materials was calculated using wide-angle X-ray diffraction and peak division; the spherulite morphology of the cable insulation materials after isothermal crystallization at 140℃ for 10 min was observed using a polarizing microscope; and the microstructure of the samples was tested using a scanning electron microscope. The test results of the cable insulation materials are shown in Table 1.

[0141] Table 1. Test results for each experimental example and comparative example.

[0142]

[0143] As shown in Table 1, the experimental data reveals that the cable insulation material prepared using the method of this invention (Example 1) exhibits tensile strength, elongation at break, and flexural modulus reaching 35.1 MPa, 224%, and 485 MPa, respectively. Simultaneously, its heat distortion temperature is increased to 144°C, and its breakdown strength reaches 385 kV / mm. These data demonstrate that the material achieves significant toughening while maintaining excellent rigidity and heat resistance, and possesses outstanding insulation properties.

[0144] A systematic comparison of the embodiments and comparative examples reveals that the technical solution of the present invention exhibits comprehensive performance advantages compared to traditional methods. Compared with Comparative Example 1 without graft modification, the tensile strength of Example 1 increased by nearly 13%, and the breakdown strength increased by more than 220%, proving that the polypropylene graft copolymer successfully induced a toughened crystal structure in the matrix polypropylene, while the introduced polar functional groups effectively suppressed the accumulation of space charge. Of particular note is that Comparative Example 2, using the same components but omitting the primary masterbatch preparation process, showed a decrease in tensile strength and breakdown strength of approximately 8% and 57%, respectively, and a significant increase in performance data fluctuations. This reveals the crucial role of the primary masterbatch process in achieving uniform dispersion and stable formation of the β-crystal form of the polypropylene graft copolymer. While Comparative Example 3, after toughening with traditional SEBS elastomer, achieved a similar elongation at break, its tensile strength, flexural modulus, heat distortion temperature, and breakdown strength all decreased significantly, fully exposing the inherent defect of the mutual constraint between rigidity, toughness, and insulation properties that is difficult to overcome in elastomer toughening technology.

[0145] Microscopic morphology analysis based on the attached figures shows that Example 1 ( Figure 1 The polypropylene spherulites in Comparative Example 1 were dense and uniform with small grain size and no obvious phase separation defects, indicating that the polypropylene graft copolymer acted as a nucleating agent in the matrix, effectively promoting the crystallization of polypropylene. In contrast, Comparative Example 1 ( Figure 2 The spherulite morphology of the samples showed significant differences, further confirming the positive effect of grafting modification from a structural perspective. Furthermore, the SEM images of Example 1 (…) Figure 3 The results show that the polypropylene graft copolymer has good compatibility and interfacial bonding with the polypropylene matrix. This indicates that the introduction of the polypropylene graft copolymer not only did not damage the structural integrity of the material, but also achieved a simultaneous improvement in toughness and rigidity through the "self-reinforcing" effect, which explains the reason for the excellent macroscopic performance from a microscopic level.

[0146] In summary, the self-reinforced polypropylene cable insulation material prepared by this invention proposes a new method to achieve synergistic improvement of polypropylene material performance through molecular design, solving the technical problem of simultaneously achieving high toughness, high heat resistance, and excellent insulation performance in the prior art. It has broad application prospects in the fields of high voltage DC cable insulation, new energy cables, and special electrical materials.

[0147] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a self-reinforced polypropylene cable insulation material using polypropylene graft copolymers, characterized in that, Includes the following steps: Step (1) Preparation of polypropylene graft copolymer: Polar vinyl monomers are grafted onto polypropylene by melt grafting or electron beam radiation grafting to obtain polypropylene graft copolymer; the polypropylene graft copolymer is used to provide nucleation sites for inducing β crystallization and to introduce polar groups that suppress space charge in the polypropylene matrix. Step (2) Preparation of primary masterbatch: Take 10-50 parts by weight of the polypropylene graft copolymer obtained in step (1) and 50-90 parts by weight of polypropylene for melt blending, so that the polypropylene graft copolymer is pre-dispersed in the matrix, and then granulated and dried to obtain primary masterbatch. Step (3) Preparation of cable insulation material: Take 0.5-10 parts by weight of the primary masterbatch obtained in step (2), 88-98 parts of polypropylene, 0.05-0.5 parts of antioxidant, 0.05-0.5 parts of voltage stabilizer and 0.05-5.5 parts of processing aid and melt blend them to induce the matrix polypropylene to produce β crystal form through the uniformly dispersed polypropylene graft copolymer, and use the β crystal form and polar vinyl monomer as the internal reinforcing phase to achieve self-reinforcement. Then, granulation and drying are carried out to finally obtain a cable insulation material with excellent comprehensive performance. In step (1), the polar vinyl monomer is selected from one or two of 4-vinylphenol, hydroxyethyl methacrylate, hydroxypropyl methacrylate, styrene, p-methylstyrene, acrylic acid, methacrylic acid, itaconic anhydride, N-hydroxymethylacrylamide, glycidyl methacrylate, vinyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

2. The method according to claim 1, characterized in that, In step (1), the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min; and / or; In step (2), the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min; and / or; In step (3), the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min.

3. The method according to claim 1, characterized in that, In step (1), the melt grafting method includes: mixing 85-99 parts by weight of polypropylene, 1-15 parts by weight of polar vinyl monomer and 0-0.5 parts by weight of free radical initiator to obtain a premix; performing melt grafting on the premix at 175-220°C under inert gas protection for 5-20 minutes; dissolving the grafted product in xylene and heating it at 110-140°C for 1-4 hours, followed by precipitation in a precipitation solvent at 0-10°C, and obtaining the polypropylene graft copolymer after washing, filtration and drying.

4. The method according to claim 3, characterized in that, The free radical initiator is selected from at least one of dicumyl peroxide, di-tert-butyl peroxide, benzoyl peroxide, tert-butyl peroxide, tert-butyl peroxide-2-ethylhexanoate, methyl ethyl ketone peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, and azoisobutylcyanoformamide.

5. The method according to claim 1, characterized in that, In step (1), the electron beam irradiation grafting method includes: dissolving 1-10 parts by weight of polar vinyl monomer in 5-30 parts of swelling agent, and placing it together with 65-75 parts of polypropylene in a container, and then removing oxygen from the container by inert gas replacement; then irradiating the container with an electron beam at an irradiation dose of 2-100 kGy and an irradiation temperature of 5-70°C; dissolving the irradiated grafted product in xylene, heating it at 110-140°C for 1-4 hours, and then precipitating it in a precipitation solvent at 0-10°C, and obtaining the polypropylene graft copolymer after washing, filtering and drying.

6. The method according to claim 5, characterized in that, The swelling agent is selected from at least one of water, methanol, ethanol, acetone, benzene, and toluene.

7. The method according to claim 1, characterized in that, In step (3), the antioxidant is selected from one or two of antioxidant 697, antioxidant S-9228, antioxidant 3114, antioxidant DSTP, antioxidant DLTP, antioxidant 1010, antioxidant BHT, antioxidant 1024, antioxidant 1076 and antioxidant 1098; and / or; The voltage stabilizer is selected from at least one of aromatic ketone compounds, polycyclic aromatic hydrocarbon compounds, and organophosphorus compounds.

8. The method according to claim 1, characterized in that, In step (3), the processing aids include flame retardants and / or inorganic fillers; The flame retardant is selected from one or more of ammonium polyphosphate, melamine, aluminum hydroxide, magnesium hydroxide, polysiloxane, and layered double hydroxides; or, the flame retardant is ammonium polyphosphate, pentaerythritol, and melamine. The inorganic filler is selected from one or more of barium sulfate, silicon dioxide, calcium carbonate, talc, titanium dioxide, and zinc borate.

9. A self-reinforced polypropylene cable insulation material prepared by means of a polypropylene graft copolymer according to any one of claims 1-8.

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