Polypropylene grafted copolymer self-reinforced polypropylene cable insulation material and preparation method thereof

Abstract

The invention discloses a polypropylene grafted copolymer self-reinforced polypropylene cable insulation material and a preparation method thereof, and relates to the field of high polymer materials. The preparation method of the material comprises the following steps: firstly, preparing a polypropylene grafted copolymer by a melt grafting method or an electron beam radiation grafting method; carrying out melt blending on the master batch and polypropylene to prepare a primary master batch; and finally, carrying out melt blending on the primary master batch, polypropylene, an antioxidant, a voltage stabilizer and a processing aid to obtain the cable insulating material. The polypropylene grafted copolymer induces the matrix polypropylene to generate a beta crystal form, and the beta crystal form and the polar vinyl monomer jointly realize self-enhancement independent of an elastomer, so that the toughness, the heat resistance and the direct-current dielectric property of the material are synchronously improved, and the problem of performance reduction caused by blending of traditional elastomers is solved; the method is suitable for the high-voltage direct-current cable insulation field.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a high-performance polypropylene (PP) based insulation material for cables and a preparation method thereof, in particular to a polypropylene cable insulation material self-reinforced by a polypropylene graft copolymer. BACKGROUND

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

[0003] However, pure polypropylene material has inherent defects such as high hardness, poor toughness, insufficient impact resistance, and easy accumulation of space charge under high-voltage direct-current electric field, which seriously limits its application in high-voltage cable, especially in direct-current cable insulation field.

[0004] To improve the mechanical properties of polypropylene, the existing technology usually adopts a method of physical blending with a low-hardness elastomer (such as SEBS), for example, the technologies disclosed in Chinese patents with application publication numbers CN117106258A, CN120329678A and CN119978615A. Although this method can improve the toughness and impact resistance of the material to a certain extent, it introduces new problems: the addition of the elastomer usually leads to a decrease in the heat resistance of the polypropylene material and deteriorates its melt processing flowability; more importantly, the introduction of the elastomer significantly reduces the breakdown strength of the composite material and deteriorates its dielectric properties, thereby greatly limiting its application in high-voltage direct-current cables.

[0005] To avoid the drawbacks of physical blending, introducing polar functional groups on the polypropylene molecular chain through chemical grafting is an effective means to regulate its properties from the molecular level. For example, grafting monomers containing specific functional groups onto the polypropylene molecular chain can effectively improve the crystallization behavior of polypropylene and induce the formation of β crystal form, thereby achieving the toughening of the material at the microstructure level. However, how to use a specific graft copolymer structure and optimized processing technology to simultaneously improve the toughness, heat resistance and direct-current dielectric properties of polypropylene material without relying on elastomer blending has become a technical problem to be solved in the field. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and provide a polypropylene cable insulation material self-reinforced by a polypropylene graft copolymer and a preparation method thereof. The method aims to simultaneously improve the toughness, heat resistance and direct-current dielectric properties of the material without relying on elastomer blending.

[0007] To achieve the above object, the present application adopts the following specific schemes: In one aspect, the present application provides a preparation method of a self-reinforced polypropylene cable insulation material by a polypropylene graft copolymer, comprising the following steps: Step (1), preparing a polypropylene graft copolymer: grafting a polar vinyl monomer onto polypropylene by a melt grafting method or an electron beam radiation grafting method to obtain a polypropylene graft copolymer; the polypropylene graft copolymer is used to provide nucleation points for inducing β crystallization in a polypropylene matrix and introduce polar groups for inhibiting space charge; Step (2), preparing a primary master batch: taking 10-50 parts by weight of the polypropylene graft copolymer prepared in step (1) and 50-90 parts by weight of polypropylene to melt blend, so as to pre-disperse the polypropylene graft copolymer in the matrix, and then granulating and drying to obtain a primary master batch; Step (3), preparing a cable insulation material: taking 0.5-10 parts by weight of the primary master batch prepared in step (2), 88-98 parts by weight of polypropylene, 0.05-0.5 parts by weight of an antioxidant, 0.05-0.5 parts by weight of a voltage stabilizer and 0.05-5.5 parts by weight of a processing aid to melt blend, so as to induce the matrix polypropylene to generate β crystal form by the uniformly dispersed polypropylene graft copolymer, and realize self-reinforcement by taking the β crystal form and the polar vinyl monomer as internal reinforcing phases, and then granulating and drying to finally obtain a cable insulation material with excellent comprehensive performance.

[0008] 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-hydroxymethyl acrylamide, glycidyl methacrylate, vinyltrimethoxysilane and γ-methacryloyloxypropyltrimethoxysilane.

[0009] Further, 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.

[0010] Further, in step (1), the melt grafting method comprises: uniformly mixing 85-99 parts by weight of polypropylene, 1-15 parts by weight of polar vinyl monomer and 0-0.5 parts of free radical initiator to obtain a premix; carrying out melt reaction grafting of the premix at 175-220°C under protection of inert gas, and the reaction time is 5-20 minutes; dissolving the product after reaction grafting in xylene, heating at 110-140°C for 1-4 hours, then settling in a settling solvent at 0-10°C, after washing, filtering and drying, the polypropylene grafted copolymer is obtained.

[0011] Further, the free radical initiator is at least one selected from the group consisting of dicumyl peroxide, di-tert-butyl peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, methyl ethyl ketone peroxide, azobis isobutyronitrile, azobis isohexylnitrile, azoisobutyryl cyanamide.

[0012] Further, in step (1), the electron beam radiation grafting method comprises: dissolving 1-10 parts of polar vinyl monomer in 5-30 parts of swelling agent, and placing it together with 65-75 parts of polypropylene in a container, then replacing the oxygen in the container with inert gas; then carrying out electron beam irradiation of the container at an irradiation dose of 2-100 kGy and an irradiation temperature of 5-70°C; dissolving the product after irradiation grafting in xylene, heating at 110-140°C for 1-4 hours, then settling in a settling solvent at 0-10°C, after washing, filtering and drying, the polypropylene grafted copolymer is obtained.

[0013] Further, the swelling agent is at least one selected from the group consisting of water, methanol, ethanol, acetone, benzene, toluene.

[0014] Further, in step (3), the antioxidant is one or two selected from the group consisting 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 at least one selected from the group consisting of aromatic ketone compounds, condensed ring aromatic hydrocarbon compounds and organic phosphorus compounds.

[0015] Further, in step (3), the processing aid comprises a flame retardant and / or an inorganic filler. The flame retardant is one or more selected from the group consisting of ammonium polyphosphate, pentaerythritol, melamine, aluminum hydroxide, magnesium hydroxide, polysiloxane, layered double hydroxide. The inorganic filler is one or more selected from the group consisting of barium sulfate, silicon dioxide, calcium carbonate, talc, titanium dioxide, zinc borate.

[0016] In another aspect, the present application provides a self-reinforced polypropylene cable insulation material prepared by the above method.

[0017] The roles of the raw materials in the present application are as follows: Polypropylene graft copolymer: the core functional component in the present application, which is not a simple filler, but plays a triple synergistic effect in the matrix: (a) nucleating agent: inducing the matrix polypropylene to generate β crystal form beneficial to toughness; (b) charge trapping center: its polar functional groups can capture and bind space charges, improving the charge distribution under direct current electric field; (c) compatibility improver: being derived from polypropylene itself, it has excellent compatibility with the matrix polypropylene and will not produce harmful interfaces.

[0018] Polar vinyl monomer: a source of polar functional groups, which is the chemical basis for functionalizing the polypropylene graft copolymer.

[0019] Antioxidant: prevents the material from aging due to thermal oxidation during processing and use, ensuring the service life of the material.

[0020] Voltage stabilizer: improves the breakdown strength of the material, and is one of the key additives for high-voltage cable insulation materials.

[0021] Processing aids (such as flame retardants, inorganic fillers): impart specific functions such as flame retardation and reinforcement to the material as needed.

[0022] Compared with the prior art, the present application has the following beneficial effects: (1) The present application discards the traditional elastomer blending approach, and by introducing a polypropylene graft copolymer with excellent compatibility with the matrix, it acts as a nucleation point in the matrix, inducing the polypropylene itself to generate β crystal form with toughening effect. This strengthening effect resulting from the change in the material's own structure fundamentally avoids the deterioration of heat resistance and electrical insulation performance caused by the introduction of heterogeneous components (such as elastomers), achieving self-strengthening within the material.

[0023] (2) The present application ingeniously realizes the 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, while its excellent compatibility with the matrix and refined grain structure ensure that the rigidity of the material is not compromised, achieving the unity of high strength and high toughness. Second, the introduction of the polypropylene graft copolymer increases the crystallization temperature of the material and refines the crystal grains, thereby simultaneously enhancing the heat resistance of the material. Third, the polar functional groups on the grafting chains form deep-level charge traps in the insulation system, which can effectively capture and bind space charges, significantly inhibiting charge injection and migration, thereby improving the charge distribution under direct current electric field and increasing the breakdown strength.

[0024] (3) The unique "primary masterbatch" preparation step of the present application ensures that the key functional component (polypropylene graft copolymer) is highly homogeneously dispersed in the final matrix. This homogeneous dispersion is the prerequisite for the polypropylene graft copolymer to stably and efficiently induce a large amount of β crystal form and avoid performance defects or fluctuations due to local aggregation, thereby ensuring the excellent and consistent performance of the final product.

[0025] (4) The material prepared by the present application has a dense and uniform spherulitic morphology with fine crystal grains, and the interface between the polypropylene graft copolymer and the matrix is well bonded without obvious phase separation defects. This optimized microstructure is the fundamental reason for the material to obtain excellent macroscopic properties. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a polarizing microscope image of the spherulitic morphology of the cable insulation material obtained in Example 1 of the present application.

[0027] Figure 2 is a polarizing microscope image of the spherulitic morphology of the cable insulation material obtained in Comparative Example 1 of the present application.

[0028] Figure 3 is a SEM image of the cable insulation material obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0029] The technical solutions of the present application will be described in detail below with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0030] The present application provides a polypropylene graft copolymer self-reinforced polypropylene cable insulation material and a preparation method thereof. The method introduces specific functional groups on the polypropylene molecular chain by melt grafting method or electron beam radiation grafting method to obtain a polypropylene graft copolymer, which itself induces the matrix polypropylene to produce β crystal form, thereby achieving the toughening of the matrix polypropylene material. At the same time, the introduced polar groups can effectively suppress space charge and improve the heat resistance of the material, and finally obtain a cable insulation material with excellent comprehensive performance. The preparation method is described in detail below.

[0031] Step (1), preparation of polypropylene graft copolymer Polypropylene grafted copolymer is prepared by introducing specific functional groups on the polypropylene molecular chain through melt grafting method or electron beam radiation grafting method. This step is the key chemical modification and functionalization step to achieve "self-reinforcement". Through grafting reaction, polar functional groups with specific functions are introduced on the polypropylene molecular chain: on the one hand, these functional groups can act as efficient nucleation points to induce the polypropylene matrix to produce β crystal form; on the other hand, their polarity can form deep level charge traps in the insulating system to inhibit space charge.

[0032] In the method A for preparing polypropylene grafted copolymer by melt grafting method, the polypropylene, polar vinyl monomer and free radical initiator are mixed in a high-speed mixer at room temperature at a speed of 120 rpm for 5-30 min to ensure uniform dispersion, to obtain a premix; the premix is put into a torque rheometer or a twin-screw extruder for melt reaction grafting under the protection of inert gas; the product after reaction grafting is added to xylene, heated for a period of time, then poured into a settling solvent for settling, and then the settled product is washed and filtered; finally, the solid product is vacuum dried at 60-80°C to constant weight to obtain the polypropylene grafted copolymer.

[0033] In the method B for preparing polypropylene grafted copolymer by electron beam radiation grafting method, the polar vinyl monomer is first dissolved in a swelling agent, then the polypropylene is placed in a container, and the oxygen in the container is completely removed by inert gas replacement; the container with the material is placed under an electron beam irradiation device for irradiation; the product after irradiation grafting is added to xylene, heated for a period of time, then poured into a settling solvent for settling, and then the settled product is washed and filtered; finally, the solid product is vacuum dried at 60-80°C to constant weight to obtain the polypropylene grafted copolymer.

[0034] Further, in the method A and the method B, the polar vinyl monomer is selected from one or two of the following substances: 4-vinyl phenol, hydroxyethyl methacrylate, hydroxypropyl methacrylate, styrene, p-methyl styrene, acrylic acid, methacrylic acid, maleic acid, itaconic anhydride, N-hydroxymethyl acrylamide, glycidyl methacrylate, vinyl trimethoxysilane, γ-methacryloyloxypropyl trimethoxysilane.

[0035] Further, in the method A and the method B, the polar vinyl monomer needs to be distilled under reduced pressure before use to remove the polymerization inhibitor therein.

[0036] Further, in the method A and the method B, the polypropylene is isotactic polypropylene, and the melt index is 1.6-3.5 g / 10 min. Further, in the method A, the polypropylene is preferably isotactic polypropylene in the form of granules or powder; and in the method B, the polypropylene is preferably isotactic polypropylene in the form of powder or film.

[0037] Further, in the method A, the free radical initiator is at least one selected from the group consisting of organic peroxide and azo compound, and is specifically selected from the group consisting of dicumyl peroxide, di-tert-butyl peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, methyl ethyl ketone peroxide, azobis isobutyronitrile, azobis isohexylnitrile, and azoisobutyrylformamide.

[0038] Further, in the method A, the polypropylene, the polar vinyl monomer and the free radical initiator are composed of 85-99 parts of polypropylene, 1-15 parts of polar vinyl monomer and 0-0.5 parts of free radical initiator.

[0039] Further, in the method A and the method B, the inert gas is nitrogen or argon.

[0040] Further, in the 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 the twin-screw extruder is 40-250 rpm.

[0041] Further, in the method A and the method B, the heating temperature of the xylene is 110-140 ℃, and the reaction time is 1-4 h.

[0042] Further, in the method A and the method B, the sedimentation solvent is acetone or methanol, and the sedimentation temperature is 0-10 ℃.

[0043] Further, in the method A and the method B, the dissolving, sedimentation, filtering and washing process is repeated at least twice to completely remove the homopolymer and unreacted monomer.

[0044] Further, in the method B, the swelling agent is at least one selected from the group consisting of water, methanol, ethanol, acetone, benzene and toluene, and functions to dilute the polar vinyl monomer and promote the swelling and diffusion of the monomer into the polypropylene.

[0045] Further, in the method B, the polypropylene, the polar vinyl monomer and the swelling agent are composed of 65-75 parts of polypropylene, 1-10 parts of polar vinyl monomer and 5-30 parts of swelling agent, and the polypropylene is completely immersed in the swelling agent.

[0046] Further, in the method B, the radiation dose of the radiation grafting is 2-100 kGy, and the radiation temperature is 5-70 ℃.

[0047] Step (2), preparation of primary masterbatch The polypropylene graft copolymer prepared in step (1) is melt blended with polypropylene in a banbury mixer or a twin-screw extruder, followed by granulation and drying to prepare a primary masterbatch with high graft copolymer content. This step is the core process step to ensure uniform and stable performance of the final product. By preparing a high-concentration primary masterbatch, it can be ensured that the polypropylene graft copolymer is highly uniformly dispersed in the final matrix, laying the foundation for subsequent stable and uniform induction of the β crystal phase in all polypropylene matrices, and avoiding performance fluctuations due to uneven dispersion.

[0048] Further, the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min.

[0049] Further, the composition of the polypropylene graft copolymer and polypropylene is 10-50 parts of polypropylene graft copolymer and 50-90 parts of polypropylene by weight.

[0050] Further, the melt blending temperature is 185-205°C, the rotation speed is 50-150 rpm, and the time is 5-15 min.

[0051] Further, the granulation process is water-cooled cutting, and the main machine rotation speed of the cutter is 750-1000 rpm.

[0052] Further, the drying process is vacuum drying, the drying temperature is 70-90°C, and the drying time is 12-24 h.

[0053] Step (3), preparation of cable insulation material The primary masterbatch prepared in step (2), polypropylene, antioxidant, voltage stabilizer, and processing aid are melt blended in a twin-screw extruder, and then granulated and dried to obtain the cable insulation material. This step is the molding and performance realization step of the final product. The uniformly dispersed primary masterbatch acts as a "seed" in the final polypropylene matrix to induce the formation of a large number of fine β crystals; at the same time, the addition of antioxidants, voltage stabilizers, and other aids further ensures the long service life and electrical properties of the material.

[0054] Further, the polypropylene is isotactic polypropylene with a melt index of 1.6-3.5 g / 10 min.

[0055] Further, 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.

[0056] Further, the voltage stabilizer is at least one of aromatic ketone compound, condensed ring aromatic hydrocarbon compound, and organic phosphorus compound.

[0057] Further, the processing aid comprises flame retardant and / or inorganic filler; the flame retardant is selected from one or more of ammonium polyphosphate, pentaerythritol, melamine, aluminum hydroxide, magnesium hydroxide, polysiloxane, and layered double hydroxide; the inorganic filler is selected from one or more of barium sulfate, silicon dioxide, calcium carbonate, talc, titanium dioxide, and zinc borate.

[0058] Further, the composition of the primary masterbatch, polypropylene, antioxidant, voltage stabilizer, and processing aid is 0.5-10 parts of primary masterbatch, 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.

[0059] Further, the melt blending temperature is 180-210℃, the rotation speed is 50-150rpm, and the time is 5-15min.

[0060] Further, the granulation process is water-cooling cutting, and the main machine rotation speed of the cutting machine is 750-1000rpm.

[0061] Further, the drying process is vacuum drying, the drying temperature is 70-90℃, and the drying time is 12-24h.

[0062] Further, the cable insulation material obtained in step (3) is in the form of granules, and the subsequent treatment can be performed according to the actual shape and specification of the cable insulation material.

[0063] The application will be further described in the following specific examples, but the examples are only used to explain the application in detail, and are not used to limit the protection scope of the claims.

[0064] In the application, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art; the methods in the following examples are conventional methods in the art, unless otherwise specified.

[0065] Example 1 The present embodiment provides a preparation method of a self-reinforced polypropylene cable insulation material by polypropylene graft copolymer, comprising the following steps: (1) Preparation of polypropylene graft copolymer (melt grafting method) A premix was prepared by mixing 90 parts of isotactic polypropylene pellets 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 in a high-speed mixer at room temperature at a speed of 120 rpm for 30 min to ensure uniform dispersion; the premix was then fed into a twin-screw extruder for melt reaction grafting under nitrogen protection, with a screw speed of 250 rpm and a reaction temperature of 180 °C for 15 min; the product after reaction grafting was added to xylene and heated to 140 °C for 3 h, then the solution was poured into methanol at 5 °C for sedimentation, followed by washing, filtering, and repeating the above dissolution, sedimentation and filtering process twice to completely remove the homopolymer and unreacted monomer; finally, the solid product was vacuum dried at 80 °C to constant weight to obtain a polypropylene graft copolymer; (2) Preparation of primary masterbatch A primary masterbatch was prepared by melt blending 30 parts of the polypropylene graft copolymer prepared in step (1) with 70 parts of isotactic polypropylene with a melt index of 2.8 g / 10 min 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; followed by granulation by water cooling and granulating at a main machine speed of 800 rpm; and finally, the granules were vacuum dried at 80 °C for 12 h to obtain the primary masterbatch. (3) Preparation of cable insulation material A cable insulation material was prepared by melt blending 5 parts of the primary masterbatch prepared 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 Michler's ketone (voltage stabilizer), 0.2 parts of magnesium hydroxide and 4 parts of calcium carbonate 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; followed by granulation by water cooling and granulating at a main machine speed of 1000 rpm; and finally, the granules were vacuum dried at 80 °C for 24 h to obtain the cable insulation material.

[0066] Example 2 The present embodiment provides a method for preparing a polypropylene cable insulation material self-reinforced by a polypropylene graft copolymer, comprising the following steps: (1) Preparation of polypropylene graft copolymer (radiation grafting method) Firstly, 5 parts of p-methylstyrene was dissolved in 25 parts of toluene, then the solution was mixed with 70 parts of isotactic polypropylene powder having a melt index of 1.8 g / 10 min in a container, and the container was thoroughly purged of oxygen by nitrogen replacement; the container with the mixture was placed under an electron beam irradiation device for irradiation at a dose of 50 kGy and a temperature of 65 °C; the product after radiation grafting was added to xylene, heated to 110 °C for 4 h, then the solution was poured into methanol at 0 °C for precipitation, followed by washing, filtration, and the above purification process was repeated twice; finally, the solid product was dried at 60 °C under vacuum to constant weight to obtain a polypropylene graft copolymer; (2) Preparation of primary masterbatch The polypropylene graft copolymer prepared in step (1) was melt blended with 90 parts of isotactic polypropylene having a melt index of 3.5 g / 10 min in a twin-screw extruder at a melt temperature of 190 °C, a screw rotation speed of 150 rpm, and a blending time of 5 min; then the pellets were prepared by water cooling and granulation at a main machine rotation speed of 900 rpm; finally, the pellets were vacuum dried at 70 °C for 12 h to obtain a primary masterbatch. (3) Preparation of cable insulation material The primary masterbatch prepared in step (2) was melt blended with 95.5 parts of isotactic polypropylene having 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 in a twin-screw extruder at a melt temperature of 210 °C, a screw rotation speed of 150 rpm, and a blending time of 5 min; then the pellets were prepared by water cooling and granulation at a main machine rotation speed of 800 rpm; finally, the pellets were vacuum dried at 80 °C for 12 h to obtain the cable insulation material.

[0067] Example 3 The present embodiment provides a method for preparing a polypropylene cable insulation material self-reinforced by a polypropylene graft copolymer, comprising the following steps: (1) Preparation of polypropylene graft copolymer (radiation grafting method) First, 10 parts of N-hydroxymethyl acrylamide was dissolved in 25 parts of methanol, and then mixed with 65 parts of isotactic polypropylene film having a melt index of 2.0 g / 10 min in a container, and the container was thoroughly purged of oxygen by argon replacement; the container was placed under an electron beam irradiation device for irradiation at a dose of 10 kGy and an irradiation temperature of 70°C; the product after radiation grafting was added to xylene, heated to 120°C for 1 h, and then poured into acetone at 10°C for sedimentation, followed by washing, filtration, and repeating the above purification process twice; finally, the solid product was vacuum dried at 70°C to a constant weight to obtain a polypropylene graft copolymer; (2) Preparation of primary masterbatch The polypropylene graft copolymer prepared in step (1) was melt blended with 50 parts of isotactic polypropylene having a melt index of 2.4 g / 10 min in a twin-screw extruder at a melt temperature of 185°C, a screw rotation speed of 100 rpm, and a blending time of 8 min; followed by water-cooling and pelletizing at a main machine rotation speed of 750 rpm; and finally, the pellets were vacuum dried at 70°C for 20 h to obtain a primary masterbatch. (3) Preparation of cable insulation material The primary masterbatch prepared in step (2) was melt blended with 94 parts of isotactic polypropylene having a melt index of 2.4 g / 10 min, 0.1 part of antioxidant S-9228, 0.1 part of acenaphthene (voltage stabilizer), 0.3 part of polysiloxane, and 4.5 parts of barium sulfate in a twin-screw extruder at a melt temperature of 200°C, a screw rotation speed of 100 rpm, and a blending time of 8 min; followed by water-cooling and pelletizing at a main machine rotation speed of 950 rpm; and finally, the pellets were vacuum dried at 60°C for 24 h to obtain the cable insulation material.

[0068] Example 4 The present embodiment provides a method for preparing a polypropylene cable insulation material self-reinforced by a polypropylene graft copolymer, comprising the following steps: (1) Preparation of polypropylene graft copolymer (melt grafting method) A mixture of 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 part of azobisisobutyronitrile was mixed in a high-speed mixer at room temperature for 25 min at a speed of 120 rpm to ensure uniform dispersion, to obtain a premix; the premix was put into a rheometer, and a melt reaction grafting was carried out under the protection of argon, the speed of the rheometer was 200 rpm, the reaction temperature was 220°C, and the reaction time was 5 min; the product after reaction and grafting was added to xylene, heated to 125°C and reacted for 2 h, then the solution was poured into methanol at 10°C for sedimentation, followed by washing, filtering, and repeating the above purification process twice; finally, the solid product was dried at 75°C under vacuum to constant weight to obtain a polypropylene graft copolymer; (2) Preparation of primary masterbatch A polypropylene graft copolymer prepared in step (1) was melt blended with 90 parts of isotactic polypropylene with a melt index of 2.1 g / 10 min in a twin-screw extruder, the melt temperature was 195°C, the screw speed was 120 rpm, and the blending time was 12 min; then granulation was carried out by water cooling and granulating, the main machine speed of the granulator was 750 rpm; finally, the granules were vacuum dried at 90°C for 12 h to obtain a primary masterbatch. (3) Preparation of cable insulation material A primary masterbatch prepared in step (2) was melt blended with 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 in a twin-screw extruder, the melt temperature was 200°C, the screw speed was 80 rpm, and the blending time was 10 min; then granulation was carried out by water cooling and granulating, the main machine speed of the granulator was 850 rpm; finally, the granules were vacuum dried at 80°C for 12 h to obtain the cable insulation material.

[0069] Example 5 The present embodiment provides a method for preparing a polypropylene cable insulation material self-reinforced by a polypropylene graft copolymer, comprising the following steps: (1) Preparation of polypropylene graft copolymer (melt grafting method) A mixture of 92 parts of isotactic polypropylene pellets with a melt index of 1.8 g / 10 min, 3.4 parts of maleic acid, 4.5 parts of styrene and 0.1 part of tert-butyl peroxy-2-ethylhexanoate was mixed in a high-speed mixer at room temperature at a speed of 120 rpm for 25 min to ensure uniform dispersion, to obtain a premix; the premix was put into a twin-screw extruder to carry out melt reaction grafting under the protection of nitrogen, the screw speed was 150 rpm, the reaction temperature was 210°C, and the reaction time was 10 min; the product after reaction grafting was added to xylene, heated to 130°C and reacted for 2 h, then the solution was poured into acetone at 5°C for sedimentation, followed by washing, filtering, and repeating the above purification process twice; finally, the solid product was dried at 60°C under vacuum to constant weight to obtain a polypropylene graft copolymer; (2) Preparation of primary masterbatch A mixture of 15 parts of the polypropylene graft copolymer prepared in step (1) and 85 parts of isotactic polypropylene with a melt index of 3.0 g / 10 min was 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 granulation was carried out by water cooling and granulating at a main machine speed of 800 rpm; finally, the granules were vacuum dried at 80°C for 15 h to obtain a primary masterbatch. (3) Preparation of cable insulation material A mixture of 3.5 parts of the primary masterbatch prepared 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 was 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 cooling and granulating at a main machine speed of 800 rpm; finally, the granules were vacuum dried at 70°C for 24 h to obtain the cable insulation material.

[0070] Example 6 The present embodiment provides a method for preparing a polypropylene cable insulation material self-reinforced by a polypropylene graft copolymer, comprising the following steps: (1) Preparation of polypropylene graft copolymer (radiation grafting method) First, 8 parts of styrene was dissolved in 22 parts of benzene, then it was mixed with 70 parts of isotactic polypropylene powder having a melt index of 2.4 g / 10 min in a container, and the container was thoroughly purged of oxygen by argon replacement; the container was placed under an electron beam irradiation device for irradiation, the irradiation dose was 90 kGy, and the irradiation temperature was 10°C; the product after radiation grafting was added to xylene, heated to 140°C for 1 h, then the solution was poured into 10°C methanol for sedimentation, followed by washing, filtering, and repeating the above purification process twice; finally, the solid product was vacuum dried at 80°C to constant weight to obtain a polypropylene graft copolymer; (2) Preparation of primary masterbatch In parts by mass, 40 parts of the polypropylene graft copolymer prepared in step (1) was melt blended with 60 parts of isotactic polypropylene having a melt index of 2.4 g / 10 min in a twin-screw extruder, the melt temperature was 190°C, the screw rotation speed was 90 rpm, and the blending time was 10 min; then granulation was performed by water cooling and pelletizing, the main machine rotation speed of the pelletizer was 750 rpm; finally, the granules were vacuum dried at 80°C for 12 h to obtain a primary masterbatch. (3) Preparation of cable insulation material In parts by mass, 5 parts of the primary masterbatch prepared in step (2), 92 parts of isotactic polypropylene having 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, the melt temperature was 210°C, the screw rotation speed was 100 rpm, and the blending time was 10 min; then granulation was performed by water cooling and pelletizing, the main machine rotation speed of the pelletizer was 950 rpm; finally, the granules were vacuum dried at 60°C for 24 h to obtain the self-reinforced polypropylene cable insulation material.

[0071] Comparative Example 1 The difference between this comparative example and Example 1 is that no polypropylene graft copolymer was prepared, and only the polypropylene system was blended, the specific steps are as follows: in parts by mass, 95 parts of isotactic polypropylene having a melt index of 2.8 g / 10 min, 0.4 parts of antioxidant DLTP, 0.4 parts of Michler's ketone (voltage stabilizer), 0.2 parts of magnesium hydroxide, and 4 parts of calcium carbonate were melt blended in a twin-screw extruder, the melt temperature was 190°C, the screw rotation speed was 50 rpm, and the blending time was 15 min; then granulation was performed by water cooling and pelletizing, the main machine rotation speed of the pelletizer was 1000 rpm; finally, the granules were vacuum dried at 80°C for 24 h to obtain a polypropylene blend material.

[0072] Comparative Example 2 The difference between this comparative example and Example 1 is that no primary masterbatch was prepared, the specific steps are as follows: (1) Preparation of polypropylene graft copolymer (melt grafting method) The formulation and operation steps are the same as step (1) of Example 1. (2) Preparation of cable insulation material The polypropylene graft copolymer prepared 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 Michler's ketone (voltage stabilizer), 0.2 parts of magnesium hydroxide, and 4 parts of calcium carbonate were melt blended in a twin-screw extruder, with a melt temperature of 190°C, a screw rotation speed of 50 rpm, and a blending time of 15 min. Subsequently, the pellets were prepared by water cooling and cutting, with a cutting machine main speed of 1000 rpm. Finally, the pellets were vacuum dried at 80°C for 24 h to obtain the cable insulation material.

[0073] Comparative Example 3 In this comparative example, instead of using the prepared polypropylene graft copolymer for self-reinforcement of the insulation material, a traditional elastomer (SEBS thermoplastic elastomer) was used to modify the polypropylene system. The specific steps are as follows: 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 Michler's ketone (voltage stabilizer), 0.2 parts of magnesium hydroxide, and 4 parts of calcium carbonate were melt blended in a twin-screw extruder, with a melt temperature of 190°C, a screw rotation speed of 50 rpm, and a blending time of 15 min. Subsequently, the pellets were prepared by water cooling and cutting, with a cutting machine main speed of 1000 rpm. Finally, the pellets were vacuum dried at 80°C for 24 h to obtain the polypropylene blend material.

[0074] The cable insulation materials in each example and comparative example were tested for performance. The cable insulation materials were prepared into appropriate forms for testing according to the test methods, and then the tensile strength and elongation at break of the samples were tested according to GB / T 1040-2006 standard; the bending 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°C / h; the breakdown strength of the samples was tested according to IEC 60243-1 standard using the continuous voltage rise method, with a voltage rise rate of 1 kV / s; the β crystal content in the cable insulation material was calculated by wide-angle X-ray diffraction and peak separation; the spherulite morphology of the cable insulation material after isothermal crystallization at 140°C for 10 min was observed by polarizing microscope; the microstructure of the samples was tested by scanning electron microscope. The test results of the cable insulation materials are shown in Table 1.

[0075] Table 1 Test results of each experimental example and comparative example From the experimental data shown in Table 1, it can be seen that the tensile strength, elongation at break and bending modulus of the cable insulation material prepared by the preparation method of the present application (Example 1) are as high as 35.1 MPa, 224% and 485 MPa, respectively, and the heat distortion temperature is increased to 144℃, and the breakdown strength is as high as 385 kV / mm. These data show that the material not only maintains excellent rigidity and heat resistance, but also achieves significant toughening effect, and has excellent insulation performance.

[0076] Through the system comparison of examples and comparative examples, it can be seen that the technical scheme of the present application shows overall performance advantage compared with the traditional method. Compared with Comparative Example 1 which does not carry out graft modification, the tensile strength of Example 1 is increased by nearly 13%, and the breakdown strength is increased by more than 220%, proving that the polypropylene graft copolymer successfully induces the toughened crystal structure of the polypropylene matrix, and the polar functional groups introduced effectively inhibit the accumulation of space charge. It is particularly worth noting that after Comparative Example 2 uses the same components but omits the primary master batch preparation process, its tensile strength and breakdown strength decrease by about 8% and 57% respectively, and the performance data fluctuation increases significantly, which reveals that the primary master batch process plays a key role in realizing the uniform dispersion of the polypropylene graft copolymer and the stable formation of the β crystal form. After Comparative Example 3 is toughened by the traditional SEBS elastomer, although a similar elongation at break is obtained, its tensile strength, bending modulus, heat distortion temperature and breakdown strength are all significantly decreased, fully exposing the inherent defects of the elastomer toughening technology that cannot overcome the mutual restriction of rigidity, toughness and insulation performance.

[0077] Combining the micro-morphology analysis with the drawings, it can be seen that the polypropylene spherulite morphology in Example 1 ( Figure 1 ) is dense and uniform, and the grain size is small, without obvious phase separation defects, indicating that the polypropylene graft copolymer acts as a nucleating agent in the matrix to effectively promote the crystallization of polypropylene. In contrast, the spherulite morphology of Comparative Example 1 ( Figure 2 ) is significantly different, further confirming the positive effect of graft modification. In addition, the SEM image of Example 1 ( Figure 3 ) shows that the polypropylene graft copolymer has good compatibility and interface combination with the polypropylene matrix, which indicates that the introduction of the polypropylene graft copolymer not only does not damage the structural integrity of the material, but also realizes the synchronous improvement of toughness and rigidity through the "self-reinforcing" effect, which explains the reason for the excellent macroscopic performance from the micro level.

[0078] In summary, the self-reinforced polypropylene cable insulation material prepared by the present application proposes a new method for realizing the synergistic improvement of polypropylene material performance through molecular design, solves the technical problem that it is difficult to simultaneously consider high toughness, high heat resistance and excellent insulation performance in the prior art, and has broad application prospects in the fields of high-voltage direct-current cable insulation, new energy cable and special electrical materials.

[0079] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application in any form. Any equivalent changes or modifications made according to the spirit of the present application should be covered within the scope of the present application.

Claims

1. A process for the preparation of a self-reinforced polypropylene cable insulation material by means of a polypropylene graft copolymer, characterized in that, The method comprises the following steps: Step (1), preparing polypropylene graft copolymer: grafting polar vinyl monomer onto polypropylene by melt grafting method or electron beam radiation grafting method to obtain polypropylene graft copolymer; the polypropylene graft copolymer is used to provide nucleation point inducing β crystallization in polypropylene matrix and introduce polar group inhibiting space charge; Step (2), preparing primary master batch: taking 10-50 parts of polypropylene graft copolymer prepared in step (1) and 50-90 parts of polypropylene by weight fraction, melt blending to pre-disperse the polypropylene graft copolymer in matrix, then granulating and drying to obtain primary master batch; Step (3), preparing cable insulation material: taking 0.5-10 parts of the primary master batch prepared 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 by weight fraction, melt blending to induce β crystal form of polypropylene matrix by the uniformly dispersed polypropylene graft copolymer, and realize self-reinforcement by the β crystal form and polar vinyl monomer as internal reinforcing phase, then granulating and drying to finally obtain cable insulation material with excellent comprehensive performance.

2. The method of claim 1, wherein, In step (1), the polar vinyl monomer is selected from one or two of 4-vinyl phenol, hydroxyethyl methacrylate, hydroxypropyl methacrylate, styrene, p-methyl styrene, acrylic acid, methacrylic acid, maleic acid, itaconic anhydride, N-hydroxymethyl acrylamide, glycidyl methacrylate, vinyl trimethoxysilane and γ-methacryloyloxypropyl trimethoxysilane.

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

4. The method of claim 1, wherein, In step (1), the melt grafting method comprises: uniformly mixing 85-99 parts of polypropylene, 1-15 parts of polar vinyl monomer and 0-0.5 parts of free radical initiator by weight fraction to obtain premix; melt reaction grafting the premix at 175-220 ℃ under inert gas protection, and the reaction time is 5-20 minutes; dissolving the product after reaction grafting in xylene, heating at 110-140 ℃ for 1-4 hours, then settling in settling solvent at 0-10 ℃, and after washing, filtering and drying, the polypropylene graft copolymer is obtained.

5. The method of claim 4, wherein, The free radical initiator is selected from at least one of dicumyl peroxide, di-tert-butyl peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, methyl ethyl ketone peroxide, azobis isobutyronitrile, azobis isohexyl nitrile and azoisobutyryl cyanamide.

6. The method of claim 1, wherein, In step (1), the electron beam radiation grafting method comprises: dissolving 1-10 parts of polar vinyl monomer in 5-30 parts of swelling agent by weight, and placing it together with 65-75 parts of polypropylene in a container, and then replacing the oxygen in the container with inert gas; then the container is subjected to electron beam irradiation at an irradiation dose of 2-100 kGy and an irradiation temperature of 5-70℃; the product after irradiation grafting is dissolved in dimethylbenzene, heated at 110-140℃ for 1-4 hours, then precipitated in a precipitating solvent at 0-10℃, washed, filtered and dried to obtain the polypropylene grafted copolymer.

7. The method of claim 6, wherein, The swelling agent is selected from at least one of water, methanol, ethanol, acetone, benzene, toluene.

8. The method of claim 1, wherein, 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, condensed ring aromatic hydrocarbon compounds and organic phosphorus compounds.

9. The method of claim 1, wherein, In step (3), the processing aid includes a flame retardant and / or an inorganic filler; The flame retardant is selected from one or more of ammonium polyphosphate, pentaerythritol, melamine, aluminum hydroxide, magnesium hydroxide, polysiloxane, layered double hydroxide; The inorganic filler is selected from one or more of barium sulfate, silicon dioxide, calcium carbonate, talc, titanium dioxide, zinc borate.

10. A self-reinforced polypropylene cable insulation material prepared by grafting a copolymer of polypropylene using the method of any one of claims 1-9.

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