Polypropylene-based insulating material as well as preparation method and application thereof

Abstract

The invention relates to a polypropylene-based insulating material as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, carrying out melt blending on polypropylene, polyethylene, a photoinitiator, a bridging aid and an antioxidant; and S2, carrying out chain regulation and control on the melt-blended mixture under the irradiation of ultraviolet light to prepare the insulating material. The raw material components are subjected to melt blending and then subjected to ultraviolet light irradiation, and free radicals are initiated through ultraviolet light irradiation, so that a polypropylene phase and a polyethylene phase in the insulating material are connected in a covalent bond form through the bridging auxiliary agent, the inter-phase action strength is enhanced, and the mechanical and physical properties and the direct current performance of the insulating material are improved.

Description

Technical Field

[0001] The present application relates to the technical field of composite materials, and in particular to a polypropylene-based insulating material and a preparation method and application thereof. Background Art

[0002] In recent years, thermoplastic polypropylene cable materials with recyclable characteristics have entered the promotion and application period, and are gradually replacing thermosetting cross-linked polyethylene (XLPE) to become the main insulation material for power cables. Compared with thermosetting cross-linked polyethylene, polypropylene insulated cables not only have excellent electrical properties, but also eliminate the cross-linking and degassing steps in the production process, greatly reducing energy consumption and having good recyclability. However, whether it is homopolymer polypropylene or copolymer polypropylene material with a small amount of ethylene chain segments introduced, polypropylene materials with propylene as the main structural unit have the characteristics of high chain regularity. The obtained cable insulation material has high hardness and poor low-temperature brittleness. The DC performance cannot meet the needs of high-voltage DC cables, thus limiting its application in the field of cable insulation. Summary of the invention

[0003] Based on this, it is necessary to provide a polypropylene-based insulating material and a preparation method and application thereof, wherein the insulating material has excellent mechanical properties and DC properties and meets the material requirements for high-voltage DC cables.

[0004] In one aspect of the present application, a method for preparing a polypropylene-based insulating material is provided, comprising the following steps:

[0005] S1: melt blending polypropylene, polyethylene, photoinitiator, bridging aid and antioxidant;

[0006] S2: Chain-regulating the melt-blended mixture under ultraviolet light irradiation to obtain the polypropylene-based insulating material.

[0007] The above-mentioned preparation method of the present application melt-blends polypropylene, polyethylene, photoinitiator, bridging agent and antioxidant, and then irradiates with ultraviolet light. The ultraviolet light irradiation triggers free radicals, so that the polypropylene phase and the polyethylene phase in the insulating material are connected in the form of covalent bonds through the bridging agent, and the covalent bond connection between the polypropylene and polyethylene macromolecular chains is realized, thereby enhancing the interphase interaction strength, improving the molecular weight of the insulating material, effectively suppressing the phase separation problem caused by the difference in crystallization dynamics, and then greatly improving the stress-strain characteristics and tensile properties of the insulating material, and finally improving the mechanical physical properties and DC properties of the insulating material. This application successfully introduces polyethylene to modify the polypropylene-based insulating material, which not only reduces the hardness of the insulating material, increases the toughness of the insulating material, but also solves the problem of poor compatibility between polypropylene and polyethylene. In addition, the bridging agent introduces a large number of deep traps into the insulating material, which can reduce the conductive current of the insulating material and suppress the problem of space charge accumulation under high fields, thereby further improving the DC properties of the insulating material. The above-mentioned preparation method regulates the molecular chain of the insulating material, and the obtained insulating material is still a thermoplastic material, no gel is produced, and processing and recycling are not affected. The viscosity of the insulating material obtained by the above preparation method is also greatly improved after chain reconstruction, which meets the requirements of large thickness insulation extrusion. The melting temperature of the insulating material obtained by the above preparation method is higher than 90°C, which eliminates the need for the introduction of elastomers, improves the reliability of the insulating material at long-term working temperature, and greatly reduces the cost of the insulating material.

[0008] In some embodiments, in S2, the ultraviolet light irradiation time is 0.5s~10s.

[0009] In some embodiments, in parts by mass, the polypropylene is 40 to 90 parts, the polyethylene is 10 to 60 parts, the photoinitiator is 0.1 to 0.6 parts, the bridging aid is 0.1 to 1.0 parts, the antioxidant is 0.3 to 1.5 parts, and the total parts by mass of the polypropylene and the polyethylene is 100 parts.

[0010] In some embodiments, in parts by mass, the polypropylene is 50 parts to 60 parts, the polyethylene is 40 parts to 50 parts, the photoinitiator is 0.3 parts to 0.6 parts, the bridging aid is 0.2 parts to 0.6 parts, the antioxidant is 0.3 parts to 0.5 parts, and the total parts by mass of the polypropylene and the polyethylene is 100 parts.

[0011] In some embodiments, the method for preparing the polypropylene-based insulating material satisfies at least one of the following conditions:

[0012] (1) The bridging aid comprises at least one of trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate and triallyl isocyanurate;

[0013] (2) The photoinitiator comprises at least one of benzophenone, 2,4-dihydroxybenzophenone and Michler's ketone;

[0014] (3) The polypropylene comprises at least one of homopolymer polypropylene and copolymer polypropylene, and the melt index of the polypropylene at a temperature of 230° C. and a load of 2.16 kg is 1.8 g / 10 min to 2.4 g / 10 min;

[0015] (4) The polyethylene comprises at least one of a low-density polyethylene and a linear low-density polyethylene, and the polyethylene has a melt index of 1.6 g / 10 min to 2.2 g / 10 min at a temperature of 190° C. and a load of 2.16 kg.

[0016] In some embodiments, after the melt blending and before the ultraviolet light irradiation, the following steps are further included:

[0017] The melt-blended mixture is subjected to hot pressing molding, the temperature of the hot pressing molding is 190° C. to 220° C., and the pressure of the hot pressing molding is 5 MPa to 20 MPa.

[0018] In some embodiments, the melt blending satisfies at least one of the following conditions:

[0019] (1) The temperature of the melt blending is 180°C to 200°C;

[0020] (2) The speed of the blending equipment for melt blending is 40 r / min to 60 r / min;

[0021] (3) The melt blending time is 10 min to 20 min.

[0022] A second aspect of the present application provides a polypropylene-based insulating material, wherein the polypropylene-based insulating material is prepared by the method for preparing the polypropylene-based insulating material described in the first aspect.

[0023] The third aspect of the present application provides an insulating product, comprising a polypropylene-based insulating material prepared by the preparation method described in the first aspect, or comprising a polypropylene-based insulating material described in the second aspect.

[0024] The fourth aspect of the present application provides a cable, comprising a polypropylene-based insulating material prepared by the preparation method described in the first aspect, or comprising a polypropylene-based insulating material described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1The stress-strain test results of the insulating materials prepared in Examples 1-3 and Comparative Examples 1-2 are shown.

[0026] Figure 2 The figure is a hardness test result diagram of the insulating materials prepared in Examples 1-3 and Comparative Examples 1-2.

[0027] Figure 3 This is a graph showing the melt index test results of the insulating materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2.

[0028] Figure 4 The conductive current test results of the insulating materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 are shown in FIG.

[0029] Figure 5 This is a graph showing the spatial charge distribution test results of the insulating material prepared in Example 1.

[0030] Figure 6 This is a graph showing the spatial charge distribution test results of the insulating material prepared in Example 2.

[0031] Figure 7 This is a graph showing the spatial charge distribution test results of the insulating material prepared in Example 3.

[0032] Figure 8 This is a graph showing the spatial charge distribution test results of the insulating material prepared in Comparative Example 2.

[0033] Fig. 9 This is a graph showing the spatial charge distribution test results of the insulating material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0036] In the field of cable insulation materials, compared with thermosetting cross-linked polyethylene insulation materials, polypropylene insulation materials not only have excellent electrical properties, but also eliminate the cross-linking and degassing steps in the production process, greatly reducing energy consumption and having good recyclability. However, whether it is homopolymer polypropylene or copolymer polypropylene insulation materials with a small amount of ethylene chain segments, polypropylene insulation materials with propylene as the main structural unit have the problem of high chain regularity, and the obtained insulation materials have the disadvantages of high hardness and poor low-temperature brittleness, which limits the application of polypropylene materials in the field of cable insulation.

[0037] At present, the commonly used toughening modification method for polypropylene insulation materials is to introduce low-modulus elastomers into polypropylene insulation materials through blending modification, thereby reducing the hardness of the material and making it more flexible. However, as common polypropylene toughening modification materials, such as ethylene-propylene copolymer and ethylene-octene copolymer, they face the following problems in the modification of polypropylene DC cable materials: First, the crystallization melting temperature of these materials is generally lower than 90°C, which causes the elastomer to be in a molten state when the cable is running for a long time, and its electrical insulation reliability deteriorates, and its long-term working stability is worrying; second, the price of elastomer is very high, resulting in high cost of polypropylene cables, which greatly restricts the promotion and application of this product; third, there are a lot of catalyst residues inside the elastomer material during synthesis, resulting in poor space charge and conductivity characteristics, and the DC performance is not ideal.

[0038] Because the melting temperature of low-density polyethylene and linear low-density polyethylene is higher than 90°C, the cost is low, and very high purity can be achieved during synthesis, researchers have proposed to use polyethylene and polypropylene blends to solve the above problems. However, in actual applications, it is found that the compatibility of polyethylene and polypropylene is very poor. During the cooling process of the blended material, the difference in the crystallization kinetics of the two phases makes the interface between the phases obvious, resulting in significant deterioration of the mechanical and physical properties of the blended material. At the same time, a large number of interfaces in the material lead to the accumulation of carrier transport and space charge, making the DC performance of the obtained blended material unable to meet the needs of high-voltage DC cables.

[0039] Based on this, one embodiment of the present application provides a method for preparing a polypropylene-based insulating material, comprising the following steps:

[0040] S1: melt blending polypropylene, polyethylene, photoinitiator, bridging aid and antioxidant;

[0041] S2: Chain-regulating the melt-blended mixture under ultraviolet light irradiation to obtain the polypropylene-based insulating material.

[0042] In this application, polypropylene, polyethylene, photoinitiator, bridging agent and antioxidant are melt-blended, and then irradiated with ultraviolet light. The ultraviolet light irradiation triggers free radicals, so that the polypropylene phase and the polyethylene phase in the insulating material are connected in the form of covalent bonds through the bridging agent, and the covalent bond connection between the polypropylene and polyethylene macromolecular chains is realized, thereby enhancing the interphase interaction strength, improving the molecular weight of the insulating material, effectively suppressing the phase separation problem caused by the difference in crystallization dynamics, and then greatly improving the stress-strain characteristics and tensile properties of the insulating material, and finally improving the mechanical physical properties and DC properties of the insulating material. This application successfully introduces polyethylene to modify the polypropylene-based insulating material, which not only reduces the hardness of the insulating material, increases the toughness of the insulating material, but also solves the problem of poor compatibility between polypropylene and polyethylene. In addition, the bridging agent introduces a large number of deep traps into the insulating material, which can reduce the electrical conduction current of the insulating material and suppress the problem of space charge accumulation under high fields, thereby further improving the DC properties of the insulating material. The preparation method of this application regulates the molecular chain of the insulating material, and the obtained insulating material is still a thermoplastic material, without gel production, and does not affect processing and recycling. The viscosity of the insulating material of the present application is also greatly improved after chain reconstruction, which meets the requirements of large thickness insulation extrusion. The melting temperature of the insulating material of the present application is higher than 90°C, which eliminates the need for the introduction of elastomers, improves the reliability of the insulating material at long-term working temperatures, and greatly reduces the cost of the insulating material.

[0043] In some embodiments, in S2, the ultraviolet irradiation time is 0.5s to 10s. The molecular chain complexity can be controlled by the irradiation time. When the ultraviolet irradiation time is 0.5s to 10s, the insulating material obtained not only has low hardness, good low-temperature brittleness, excellent mechanical properties and DC properties, but also avoids the generation of gel. The insulating material is still thermoplastic, has the advantages of thermoplastic materials, and does not affect processing and recycling.

[0044] As an example, the time of ultraviolet light irradiation can be 0.5s, 0.6s, 0.7s, 0.8s, 0.9s, 1.0s, 1.5s, 2s, 2.5s, 3s, 3.5s, 4s, 4.5s, 5s, 5.5s, 6s, 6.5s, 7s, 7.5s, 8s, 8.5s, 9s, 9.5s and 10s, or it can be within the range formed by any two of the above point values ​​as end values.

[0045] Furthermore, in S2, the ultraviolet light irradiation time is 3s to 7s. When the ultraviolet light irradiation time is 3s to 7s, the insulating material has excellent stress-strain characteristics, thereby improving the mechanical properties of the insulating material.

[0046] Furthermore, in S2, the ultraviolet light irradiation time is 5s to 7s. When the ultraviolet light irradiation time is 5s to 7s, the stress-strain characteristics are optimal, and the obtained insulating material has better comprehensive properties such as heat resistance, toughness and direct current performance.

[0047] In some embodiments, in S2, the wavelength of the ultraviolet light source is 365nm, and the light power is 1641mW / cm 2 Under the irradiation of ultraviolet light of this wavelength and optical power, more free radicals can be initiated, making the polypropylene phase and the polyethylene phase in the insulating material more tightly connected by covalent bonds.

[0048] In some embodiments, the polypropylene is 40 to 90 parts, the polyethylene is 10 to 60 parts, the photoinitiator is 0.1 to 0.6 parts, the bridging aid is 0.1 to 1.0 parts, the antioxidant is 0.3 to 1.5 parts, and the total weight of the polypropylene and the polyethylene is 100 parts. Within this raw material ratio range, the compatibility of polypropylene and polyethylene is better, and the obtained insulating material has better heat resistance, toughness and DC performance.

[0049] As an example, the polypropylene may be 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts, 70 parts, 71 parts, 72 parts, 73 parts, 74 parts, 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, 80 parts, 81 parts, 82 parts, 83 parts, 84 parts, 85 parts, 86 parts, 87 parts, 88 parts The amount of the mixture may be 0.1-0.2 parts, 0.89 parts and 0.90 parts, and may be within the range consisting of any two of the above values ​​as end values, preferably 50-60 parts.

[0050] As an example, the polyethylene can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts The amount of the mixture may be 40 to 50 parts, 59 to 60 parts, or may be within the range consisting of any two of the above values ​​as end values, preferably 40 to 50 parts.

[0051] As an example, the photoinitiator may be 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part and 0.6 part, or may be within a range consisting of any two of the above point values ​​as end values, preferably 0.3 part to 0.6 part.

[0052] As an example, the bridging aid can be 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part and 1.0 part, or it can be within the range consisting of any two of the above point values ​​as end values, preferably 0.2 part to 0.6 part.

[0053] As an example, the antioxidant can be 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts and 1.5 parts, or it can be within the range consisting of any two of the above point values ​​as end values, preferably 0.3 parts to 0.5 parts.

[0054] In some embodiments, the polypropylene is 50 to 60 parts, the polyethylene is 40 to 50 parts, the photoinitiator is 0.3 to 0.6 parts, the bridging agent is 0.2 to 0.6 parts, the antioxidant is 0.3 to 0.5 parts, and the total weight of the polypropylene and the polyethylene is 100 parts. Within this raw material ratio range, the mechanical properties and DC properties of the insulating material are further improved.

[0055] In some embodiments, the bridging aid includes at least one of trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, and triallyl isocyanurate.

[0056] In some embodiments, the bridging aid includes trimethylolpropane trimethacrylate and ethoxylated trimethylolpropane triacrylate. The carbonyl groups in trimethylolpropane trimethacrylate and ethoxylated trimethylolpropane triacrylate introduce a large number of deep traps into the insulating material, thereby improving the DC performance of the insulating material.

[0057] In some embodiments, the bridging auxiliary agent is trimethylolpropane trimethacrylate.

[0058] In some embodiments, the photoinitiator includes at least one of benzophenone, 2,4-dihydroxybenzophenone and Michler's ketone.

[0059] In some embodiments, the polypropylene includes at least one of homopolypropylene and copolymer polypropylene, and the melt index of the polypropylene at 230° C. and 2.16 kg load is 1.8 g / 10 min to 2.4 g / 10 min.

[0060] In some embodiments, the polyethylene includes at least one of a low-density polyethylene and a linear low-density polyethylene, and the polyethylene has a melt index of 1.6 g / 10 min to 2.2 g / 10 min at a temperature of 190° C. and a load of 2.16 kg.

[0061] In some embodiments, the antioxidant includes at least one of antioxidant 1010 , antioxidant 1035 , antioxidant 1024 , and antioxidant 300 .

[0062] In some embodiments, after the melt blending and before the ultraviolet light irradiation, the following steps are further included:

[0063] The melt-blended mixture is subjected to hot pressing molding, the temperature of the hot pressing molding is 190° C. to 220° C., and the pressure of the hot pressing molding is 5 MPa to 20 MPa.

[0064] Furthermore, the melt-blended mixture is heat-pressed in a flat-plate vulcanizer to obtain a PP blend sheet in a molten state.

[0065] In some embodiments, the melt blending temperature is 180°C to 200°C.

[0066] In some embodiments, the rotation speed of the blending equipment for melt blending is 40 r / min to 60 r / min.

[0067] In some embodiments, the melt blending time is 10 min to 20 min.

[0068] A second aspect of the present application provides a polypropylene-based insulating material, which is prepared by the method for preparing the polypropylene-based insulating material described in the first aspect.

[0069] The third aspect of the present application provides an insulating product, comprising a polypropylene-based insulating material prepared by the preparation method described in the first aspect, or comprising a polypropylene-based insulating material described in the second aspect.

[0070] The fourth aspect of the present application provides a cable, which includes a polypropylene-based insulating material prepared by the preparation method described in the first aspect, or includes a polypropylene-based insulating material described in the second aspect.

[0071] Furthermore, a high-voltage cable is provided, which includes the polypropylene-based insulating material prepared by the preparation method described in the first aspect, or includes the polypropylene-based insulating material described in the second aspect.

[0072] A fifth aspect of the present application provides an electrical device comprising the high-voltage cable as described in the fourth aspect.

[0073] The following are specific embodiments.

[0074] Example 1

[0075] This embodiment provides a polypropylene-based insulating material, and the raw materials for preparation include the following components in parts by mass: 60 parts of copolymerized polypropylene (K8003), 40 parts of linear low-density polyethylene (7042), 0.5 parts of photoinitiator, 0.4 parts of bridging aid, and 0.3 parts of antioxidant 1010. The melting index of copolymerized polypropylene (K8003) at a temperature of 230°C and a load of 2.16Kg is 2.1g / 10min. The melting index of linear low-density polyethylene (7042) at a temperature of 190°C and a load of 2.16Kg is 1.9 g / 10min.

[0076] The specific preparation steps are as follows:

[0077] Copolymer polypropylene (K8003), linear low-density polyethylene (7042), photoinitiator (benzophenone), bridging aid (trimethylolpropane trimethacrylate) and antioxidant 1010 are uniformly mixed in the above proportions, the resulting mixture is melt-blended at 190°C and 60r / min for 10min, and press-molded in a flat-plate vulcanizer at 180°C and 15MPa to obtain a molten PP blend specimen, which is irradiated under an ultraviolet light source for 3s to achieve a chain regulation reaction of the material.

[0078] Polypropylene-based insulating material samples (PP / LLDPE-3s) were prepared.

[0079] Example 2

[0080] Example 2 is basically the same as Example 1, except that the irradiation time under the ultraviolet light source is 5s.

[0081] Polypropylene-based insulating material samples (PP / LLDPE-5s) were prepared.

[0082] Example 3

[0083] Example 3 is basically the same as Example 1, except that the irradiation time under the ultraviolet light source is 7s.

[0084] Polypropylene-based insulating material samples (PP / LLDPE-7s) were prepared.

[0085] Example 4

[0086] Example 4 is basically the same as Example 1, except that the copolymerized polypropylene (K8003) is 90 parts and the linear low-density polyethylene (7042) is 10 parts.

[0087] Example 5

[0088] Example 5 is basically the same as Example 1, except that the copolymerized polypropylene (K8003) is 40 parts and the linear low-density polyethylene (7042) is 60 parts.

[0089] Example 6

[0090] Example 6 is basically the same as Example 1, except that the amount of the bridging auxiliary agent is 1 part.

[0091] Comparative Example 1

[0092] Comparative Example 1 is basically the same as Example 1, except that the photoinitiator and the bridging agent are omitted, and the reaction mixture is cooled for 10 min. -4 Drying treatment at 80°C for 24 h under Pa vacuum replaces UV irradiation.

[0093] Polypropylene insulation specimens (PP / LLDPE) were prepared.

[0094] Comparative Example 2

[0095] Comparative Example 2 is substantially the same as Example 1, except that the raw materials used in the preparation are 100 parts of copolymerized polypropylene (K8003) and 0.3 parts of antioxidant, and the cooling and vacuum drying at 80° C. for 24 h are used instead of ultraviolet irradiation.

[0096] Polypropylene insulation specimens (PP) were prepared.

[0097] Comparative Example 3

[0098] Comparative Example 3 is substantially the same as Example 1, except that the photoinitiator is omitted in the preparation of raw materials, and the ultraviolet light irradiation step is omitted.

[0099] Comparative Example 4

[0100] Comparative Example 4 is substantially the same as Example 1, except that the bridging auxiliary agent is omitted.

[0101] The insulating materials prepared in Examples 1 to 6 and Comparative Examples 1 to 4 were tested for hardness, melt index, gel mass content, conduction current and average space charge density. The test results are shown in Table 1 below.

[0102] Table 1

[0103]

[0104] Combined with Table 1 above Figure 1 , Figure 2 It can be seen that the samples prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were punched into standard dumbbell-shaped samples and subjected to stress-strain tests according to the standard of GB / T1040.2-2006, with a tensile speed of 50 mm / min. In order to eliminate the error of the test, each group of materials was tested 5 times and the average value was taken. Figure 1 It can be seen that the PP material of comparative example 2 has good tensile properties, but its yield strength is relatively high, about 17.5MPa, which indicates that its hardness is relatively high, while the PP / LLDPE material of comparative example 1, which is simply blended, has a weak interphase force due to the difference in crystallization dynamics, which seriously deteriorates its tensile properties, and the tensile strength and elongation at break are reduced to 11.28MPa and 169.02%. The yield strength of the three insulating materials PP / LLDPE-3s, PP / LLDPE-55s and PP / LLDPE-7s of Examples 1 to 3, after the insulating material chains are regulated by ultraviolet irradiation, decreases, and their tensile strength and elongation at break are significantly improved compared with PP / LLDPE, among which the materials irradiated for 5s and 7s have the most excellent stress-strain properties.

[0105] The hardness test was performed on the samples of Examples 1 to 3 and Comparative Examples 1 to 2 with a thickness of 4 mm. The hardness value was read after the indenter was pressed into the sample for 15 seconds. The test results are as follows: Figure 2 As shown, from Figure 2 It can be seen that the hardness of PP is effectively reduced by blending with LLDPE, and the hardness of the three materials after UV irradiation is slightly higher than that of PP / LLDPE. This is related to the improvement of the overall consistency of the material due to the fusion of the phase interface. The hardness of the three materials PP / LLDPE-3s, PP / LLDPE-55s, and PP / LLDPE-7s is about 55HD.

[0106] Combined with Table 1 above Figure 3 It can be seen that the melt index test refers to the ASTM1238 standard, the test conditions are 230℃, 2.16kg, and the mass of the standard aperture extruded material is recorded for 10 minutes. The test results are as follows: Figure 3 As shown, from Figure 3 It can be seen that with the increase of irradiation time, the melt index of the material decreases. Under the bridging effect of the bridging agent, LLDPE and PP form branches with each other, which enhances the entanglement between molecular chains in the molten state and realizes the viscosity-increasing effect of the material.

[0107] To further investigate the cross-linking of the insulating material, the JB / T 10437-2004 standard was used to test Examples 1 to 3. The tested material was sealed in a 200-mesh filter and placed in a slightly boiling xylene solution for extraction for 12 hours. The filter was then vacuumed and dried for 24 hours to remove the xylene solution. Finally, the sample weight was weighed and the mass ratio to the original sample was taken as the gel content. To ensure the accuracy of the test results, each material was tested 5 times. The test results show that the gel content of the three materials PP / LLDPE-3s, PP / LLDPE-55s, and PP / LLDPE-7s is zero, confirming that no gel is generated in the material during the chain regulation process of the material initiated by ultraviolet irradiation, further confirming the controllability of the ultraviolet irradiation process.

[0108] Combined with Table 1 above Figure 4 It can be seen that the samples prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to DC resistivity and dielectric strength tests. The DC resistivity test was conducted at room temperature, using a three-electrode system, polarizing the sample for 15 minutes in a step-up voltage of 5 kV / mm, and then reading the conductance current flowing through the sample. Figure 4 It can be seen that the blended modified PP / LLDPE introduces a large number of interfaces, providing a large number of channels for carrier transport, so its conductance current is increased by about 1 times compared with PP materials. The conductance currents of the three insulating materials PP / LLDPE-3s, PP / LLDPE-55s, and PP / LLDPE-7s after chain regulation all decreased to varying degrees, which is related to the improved dispersion of the materials and the reduced phase spacing. The carbonyl groups in the additives are grafted into the material during ultraviolet irradiation, introducing deep trap energy levels, greatly reducing the carrier mobility, and effectively reducing the conductance current of the material. The conductance current of the PP / LLDPE-7s material under irradiation for 7s is higher than that of PP / LLDPE-5s under high field, which may be due to the degradation of the PP material due to the increase in irradiation dosage, resulting in an increase in conductance current.

[0109] Combined with Table 1 above Figure 5~Figure 9It can be seen that the samples prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to a spatial charge distribution test. The test was conducted using the electroacoustic pulse method (PEA) principle. The temperature was 30°C. The samples were polarized for 30 minutes under a 40 kV / mm DC electric field. The spatial charge distribution of each test sample at the final moment of polarization was as follows: Figures 5 to 9 As shown. Fig. 9 It can be seen that the introduction of LLDPE into PP causes more serious space charge accumulation in the material, and the maximum charge accumulation of the PP sample is about 1.37C / m 3 , while PP / LLDPE samples showed a large amount of charge injection on the cathode side, and the injection depth gradually increased with the extension of the pressurization time. At the end of the pressurization, the middle of the sample accumulated about 2.18C / m 3 The PP / LLDPE-3s sample irradiated for 3s showed obvious cathode injection characteristics, and the charge accumulation and injection phenomenon was still serious. When the irradiation time was further increased to 5s, the spatial charge distribution characteristics of the material were significantly improved due to the improvement of the phase interface and dispersion. Under the 30-min high-voltage test, the spatial charge accumulation in the sample was less than 1C / m 3 When the irradiation time was increased to 7s, the PP / LLDPE-7s sample deteriorated slightly compared with the PP / LLDPE-5s sample. The same polarity charge injection was obvious on both the cathode and anode sides, and the maximum charge accumulation in the sample was about 1.86C / m 3 .

[0110] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a polypropylene-based insulating material, characterized in that: The steps include: S1: melt blending polypropylene, polyethylene, photoinitiator, bridging aid and antioxidant; S2: Chain-regulating the melt-blended mixture under ultraviolet light irradiation to obtain the polypropylene-based insulating material.

2. The method for preparing a polypropylene-based insulating material according to claim 1, characterized in that: In S2, the ultraviolet light irradiation time is 0.5s~10s.

3. The method for preparing a polypropylene-based insulating material according to claim 1, characterized in that: In terms of weight percentage, the polypropylene is 40 to 90 parts, the polyethylene is 10 to 60 parts, the photoinitiator is 0.1 to 0.6 parts, the bridging aid is 0.1 to 1.0 parts, the antioxidant is 0.3 to 1.5 parts, and the total weight percentage of the polypropylene and the polyethylene is 100 parts.

4. The method for preparing a polypropylene-based insulating material according to claim 3, characterized in that: In terms of weight parts, the polypropylene is 50 to 60 parts, the polyethylene is 40 to 50 parts, the photoinitiator is 0.3 to 0.6 parts, the bridging aid is 0.2 to 0.6 parts, the antioxidant is 0.3 to 0.5 parts, and the total weight parts of the polypropylene and the polyethylene is 100 parts.

5. The method for preparing a polypropylene-based insulating material according to claim 1, characterized in that: At least one of the following conditions is met: (1) The bridging aid comprises at least one of trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate and triallyl isocyanurate; (2) The photoinitiator comprises at least one of benzophenone, 2,4-dihydroxybenzophenone and Michler's ketone; (3) The polypropylene comprises at least one of homopolymer polypropylene and copolymer polypropylene, and the melt index of the polypropylene at a temperature of 230° C. and a load of 2.16 kg is 1.8 g / 10 min to 2.4 g / 10 min; (4) The polyethylene comprises at least one of a low-density polyethylene and a linear low-density polyethylene, and the polyethylene has a melt index of 1.6 g / 10 min to 2.2 g / 10 min at a temperature of 190° C. and a load of 2.16 kg.

6. The method for preparing a polypropylene-based insulating material according to any one of claims 1 to 5, characterized in that: After the melt blending and before the ultraviolet light irradiation, the following steps are also included: The melt-blended mixture is subjected to hot pressing molding, the temperature of the hot pressing molding is 190° C. to 220° C., and the pressure of the hot pressing molding is 5 MPa to 20 MPa.

7. The method for preparing a polypropylene-based insulating material according to any one of claims 1 to 5, characterized in that: The melt blending satisfies at least one of the following conditions: (1) The temperature of the melt blending is 180°C to 200°C; (2) The speed of the blending equipment for melt blending is 40 r / min to 60 r / min; (3) The melt blending time is 10 min to 20 min.

8. A polypropylene-based insulating material, characterized in that: The polypropylene-based insulating material is prepared by the method for preparing a polypropylene-based insulating material according to any one of claims 1 to 7.

9. An insulation product, characterized in that: It includes a polypropylene-based insulating material obtained by the preparation method according to any one of claims 1 to 7, or includes a polypropylene-based insulating material according to claim 8.

10. A cable, characterized in that: It includes a polypropylene-based insulating material obtained by the preparation method according to any one of claims 1 to 7, or includes a polypropylene-based insulating material according to claim 8.

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