Process for the preparation of glycidyl ester and dcp dual crosslinked eaa and ldpe cable material

Abstract

The application relates to a preparation method of a glycidyl ester and DCP double-crosslinking EAA and LDPE cable material, and relates to the field of high-voltage direct-current cable materials.The preparation method of the high-voltage direct-current cable material is as follows: a certain amount of low-density polyethylene (LDPE) is mixed with small molecules of 4,4'-diphenyldicarboxylic acid diglycidyl ester, ethylene acrylic acid copolymer (EAA) and dicumyl peroxide (DCP) in a torque rheometer to obtain a mixed material; the mixed material is pressed and formed in a flat curing machine, and then crosslinked after temperature rising, so that a high-voltage direct-current cable material with significantly improved tensile strength is obtained.The application adds two crosslinking agents, namely DCP and diphenyldicarboxylic acid diglycidyl ester, in the LDPE and EAA, so that the LDPE and EAA simultaneously undergo free radical crosslinking and nucleophilic addition crosslinking, and other components are not added, the mechanical properties of the material are greatly improved, and the pressure resistance grade of the cable material is improved.

Description

Technical Field

[0001] The invention relates to a method for preparing a glycidyl ester and DCP double-crosslinked EAA and LDPE cable material, belonging to the technical field of high-voltage direct current cable material preparation. Background Art

[0002] Currently, cable materials both domestically and internationally are composed of low-density polyethylene (LDPE) and various additives such as voltage stabilizers and antioxidants. LDPE is the primary component contributing to the material's insulating properties. However, due to its poor mechanical and thermal properties, it must be enhanced by adding a free radical crosslinker (DCP) to form cross-linked low-density polyethylene (XLPE). Polyethylene itself possesses excellent electrical properties, which are further enhanced by cross-linking. However, as the withstand voltage rating of DC cable materials continues to rise, XLPE must undergo modification (doping, grafting, purity enhancement, esterification, and cross-linking) to meet application requirements.

[0003] The present invention adds two crosslinking agents, DCP and diglycidyl biphenyl dicarboxylate, to LDPE and EAA, so that LDPE and EAA undergo free radical crosslinking and nucleophilic addition crosslinking simultaneously without adding other components, thereby significantly improving the mechanical properties of the material and simultaneously improving the electrical resistance level of the cable material. Summary of the Invention

[0004] A method for preparing a high-voltage direct current cable material comprising diglycidyl biphenyl dicarboxylate and DCP double-crosslinked EAA and LDPE is characterized in that a certain amount of low-density polyethylene (LDPE), small molecule diglycidyl 4,4'-biphenyl dicarboxylate, ethylene acrylic acid copolymer (EAA) and dicumyl peroxide (DCP) are added into a torque vulcanizer for melt blending to obtain a mixed material; the mixed material is press-formed in a flat vulcanizer, then heated for cross-linking, and cooled to obtain a high-voltage direct current cable material having significantly improved tensile strength.

[0005] Furthermore, according to the weight content, the content of EAA is 5%-20% of the mass fraction of LDPE, EAA and diglycidyl 4,4'-biphenyldicarboxylate, the content of LDPE is 73%-93% of the mass fraction of LDPE, EAA and diglycidyl 4,4'-biphenyldicarboxylate, the content of DCP is 1.6% of the mass fraction of LDPE, and the content of diglycidyl 4,4'-biphenyldicarboxylate is 1.8%-7.4% of the mass fraction of LDPE, EAA and diglycidyl 4,4'-biphenyldicarboxylate.

[0006] A second object of the present invention is to provide a method for preparing the composite material, the method comprising the following steps:

[0007] S1, melt blending; blending the EAA / LDPE composite insulation material uniformly to obtain a mixed insulation material;

[0008] S2, processing and molding; pressing and molding the mixed insulating material in a flat vulcanizing machine, and then cross-linking it under pressure, cooling it, and then subjecting it to vacuum drying treatment to obtain the insulating composite material LEED.

[0009] Further defined, S1 specifically comprises: adding the mixture into a torque rheometer at 115° C. and a rotation speed of 60 rpm and uniformly mixing for 10 minutes, and then adding DCP and mixing for 2 minutes to obtain a composite material.

[0010] It is further defined that the pressing temperature in S2 is 115° C. and the pressure is 15 MPa.

[0011] It is further defined that the pressurized cross-linking temperature in S2 is 175° C. and the pressure is 15 MPa.

[0012] It is further defined that the vacuum drying treatment temperature in S2 is 80° C. and the time is 24 h.

[0013] A third object of the present invention is to provide an application of the composite material, specifically, the composite material is used to manufacture a high-voltage DC cable.

[0014] The present invention has the following beneficial effects:

[0015] (1) The present invention introduces two epoxy groups into the aromatic ring, which can be cross-linked with the polymer containing carboxyl groups. The formed ester polymerization points can effectively capture charges, and the cross-linking in situ introduces deep traps.

[0016] (2) The aromatic compound in the present invention can effectively "capture" electrons, provide strong electron-withdrawing induction and electron-withdrawing conjugation effects, and can more effectively exert its ability to "capture" electrons, significantly enhancing the DC breakdown performance of the high-voltage DC cable material.

[0017] (3) The LEED composite insulation material prepared by the present invention has a simple preparation process, low cost, and easy-to-obtain materials, and has prospects for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Infrared spectrum test charts of LEED high-voltage DC cable materials provided by different embodiments;

[0019] Figure 2 Thermal elongation diagram of LEED high-voltage DC cable materials provided by different embodiments;

[0020] Figure 3 Tensile test result curves of LEED high-voltage DC cable materials provided by different embodiments;

[0021] Figure 4 Weibull distribution diagrams of DC breakdown field strength of LEED high-voltage DC cable materials provided in different embodiments, where (a) is after modification and (b) is before modification;

[0022] Figure 5 Conductivity and current characteristic curves of high-voltage DC cable materials provided in different embodiments; (a) is after modification, and (b) is before modification;

[0023] Figure 6 DC breakdown current characteristic curves of LEED high-voltage DC cable materials provided in different embodiments; (a) is after modification, and (b) is before modification. DETAILED DESCRIPTION

[0024] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0025] Embodiment 1:

[0026] The process of preparing LEED modified composite materials in this example is as follows:

[0027] (1) Melt blending: 37.26 g of LDPE, 2 g of EAA and 0.74 g of the epoxy compound 4,4'-diglycidyl biphenyl dicarboxylate were added to a torque rheometer, melted at 115 °C, with a rotation speed of 60 r / min, and mixed for 10 min. Then, 0.59 g of DCP was added and mixed for 2 min to obtain an LDPE / EAA blend composite material, in which the content of EAA was 5% of the mass fraction of LDPE, EAA and 4,4'-diglycidyl biphenyl dicarboxylate.

[0028] (2) Processing and molding: The LDPE / EAA blended composite material was pressed in a flat vulcanizer at a temperature of 115°C and a pressure of 15 MPa, and then pressed for 30 minutes at a temperature of 175°C and a pressure of 15 MPa to complete cross-linking, thereby obtaining a biphenyl-type small molecule epoxy compound with an EAA content of 5% and DCP double-crosslinked XLPE high-voltage DC cable material LE5ED. 1.6 .

[0029] Example 2:

[0030] (1) Melt blending: 34.53 g of LDPE, 4 g of EAA and 1.47 g of the epoxy compound 4,4'-diglycidyl biphenyl dicarboxylate were added to a torque rheometer and melted at 115 °C at a speed of 60 r / min. After mixing for 10 min, 0.55 g of DCP was added and mixed for 2 min to obtain an LDPE / EAA blend composite material, in which the content of EAA was 10% of the mass fraction of LDPE, EAA and 4,4'-diglycidyl biphenyl dicarboxylate.

[0031] (2) Processing and molding: The LDPE / EAA blended composite material was pressed in a flat vulcanizer at a temperature of 115°C and a pressure of 15 MPa, and then pressed for 30 minutes at a temperature of 175°C and a pressure of 15 MPa to complete cross-linking, thereby obtaining a biphenyl-type small molecule epoxy compound with an EAA content of 10% and a DCP double-crosslinked XLPE high-voltage DC cable material LE. 10 ED 1.6 .

[0032] Example 3

[0033] (1) Melt blending: 31.79 g of LDPE, 6 g of EAA and 2.21 g of the epoxy compound 4,4'-diglycidyl biphenyl dicarboxylate were added to a torque rheometer, melted at 115 °C, with a rotation speed of 60 r / min, and mixed for 10 min. Then, 0.51 g of DCP was added and mixed for 2 min to obtain an LDPE / EAA blend composite material, in which the content of EAA was 15% of the mass fraction of LDPE, EAA and 4,4'-diglycidyl biphenyl dicarboxylate.

[0034] (2) Processing and molding: The LDPE / EAA blended composite material was pressed in a flat vulcanizer at a temperature of 115°C and a pressure of 15 MPa, and then pressed for 30 minutes at a temperature of 175°C and a pressure of 15 MPa to complete cross-linking, thereby obtaining a biphenyl-type small molecule epoxy compound with an EAA content of 15% and a DCP double-crosslinked XLPE high-voltage DC cable material LE. 15 ED 1.6 .

[0035] Embodiment 4:

[0036] (1) Melt blending: 29.05 g of LDPE, 8 g of EAA and 2.95 g of the epoxy compound 4,4'-diphenyldicarboxylic acid diglycidyl ester were added to a torque rheometer, melted at 115 ° C, with a rotation speed of 60 r / min, and mixed for 10 min. Then, 0.46 g of DCP was added and mixed for 2 min to obtain an LDPE / EAA blend composite material, in which the content of EAA was 20% of the mass fraction of LDPE, EAA and 4,4'-diphenyldicarboxylic acid diglycidyl ester.

[0037] (2) Processing and molding: The LDPE / EAA blended composite material was pressed in a flat vulcanizer at a temperature of 115°C and a pressure of 15 MPa, and then pressed for 30 minutes at a temperature of 175°C and a pressure of 15 MPa to complete cross-linking, thereby obtaining a biphenyl-type small molecule epoxy compound with an EAA content of 20% and a DCP double-crosslinked XLPE high-voltage DC cable material LE. 20 ED 1.6 .

[0038] The performance tests were conducted on the biphenyl-type small molecule epoxy compounds and DCP double-crosslinked XLPE high-voltage DC cable materials prepared in Examples 1 to 4 above. The specific test results are as follows:

[0039] (1) The molecular structures of the above eight materials were tested, analyzed and characterized by Fourier transform infrared spectrometer (FT / IR 6100) to verify whether they successfully participated in the cross-linking reaction. The thickness of the sample selected in the experiment was 100 μm thin slice, the test spectrum wave number range was 500-4000 cm-1, the scanning accuracy was 2 cm-1, and the number of scans was 30. The results are as follows: Figure 1 shown.

[0040] Depend on Figure 1 It can be seen that compared with the EAA / LDPE blend material, the modified high-voltage DC cable material has a new absorption peak near 3487 cm-1, which corresponds to the absorption peak of the hydroxyl group in the composite material, and the sharp peak at 1700 cm-1 red-shifts to 1725 cm-1 and becomes a broad peak, which corresponds to the characteristic peak of the ester group in the composite material, indicating that the cross-linking is successful.

[0041] (2) Prepare dumbbell specimens and measure cross-sectional area according to the test method specified in GB / T2951.11-2008. Cut the prepared modified high-voltage DC cable material sample into a dumbbell-shaped specimen with a thickness of 1 mm using a cutter. Its total length is 75 mm and the effective test portion width is 4 ± 0.2 mm. Its surface is smooth and free of defects visible to the naked eye. Marking lines with a spacing of 20 mm are marked on the narrow section with a marker pen. The test is carried out in a 200℃ natural ventilation oven. The specimen is suspended from the upper chuck and clamped with the lower chuck. A weight is added to the lower chuck. The weight = 20.4 × specimen thickness × specimen width (including clamps, support rods and weights). After the specimen is kept in the oven at 200℃ for 15 minutes, the distance between the marking lines is measured and the elongation is calculated.

[0042] Depend on Figure 2 It can be seen that the elongation decreases significantly with the increase of EAA, and the elongation reaches 28.4% when the EAA content is 20% of the mass fraction of LDPE, EAA and 4,4'-diglycidyl biphenyldicarboxylate.

[0043] (3) The above four materials were tested using a WDW-10C universal testing machine in accordance with the national standard GB / T528-2009. According to the test method required by the standard, the prepared modified EAA / LDPE composite material sample was cut into a dumbbell-shaped specimen with a thickness of 1 mm using a cutter. Its total length was 75 mm, the effective test portion width was 4 ± 0.2 mm, and its surface was smooth without visible defects. Marking lines with a spacing of 20 mm were marked on the narrow section with a marker pen. The clamp spacing was set to 20 mm, the tensile rate was set to 250 mm / min, and each material was tested 5 times.

[0044] Depend on Figure 3 It can be seen that under the same experimental conditions, the mechanical properties of the modified high-voltage DC cable material are significantly improved, with its elongation at break reaching 1109.46% and its tensile strength reaching 31.19 MPa.

[0045] (4) The eight materials were subjected to DC breakdown field strength testing at 30°C using cylindrical electrodes, with a voltage ramp rate of 1 kV / s and a sample thickness of 100 μm. The samples and electrodes were immersed in transformer oil throughout the entire process. Ten groups of samples were selected for repeated testing under each experimental condition.

[0046] The two-parameter Weibull distribution is used to perform statistics on the DC breakdown strength experimental data, which is described as follows:

[0047] P(E)=1-exp(-(E / Eb)β)

[0048] Where: P(E) is the cumulative failure probability, E is the measured breakdown field strength, Eb is the characteristic breakdown field strength when the breakdown probability is 63.2%, and β is the shape parameter.

[0049] The Weibull distribution of DC breakdown strength of the above four materials is as follows: Figure 4 shown.

[0050] Depend on Figure 4 It can be seen that the DC breakdown strength of the four modified HVDC cable materials has been improved to varying degrees compared to the unmodified materials. Similar to the conductivity test results, the addition of epoxy compounds significantly increased the breakdown strength of each content. Compared to the unmodified low-density polyethylene (LDPE) DC breakdown strength of 309.3 kV / mm, the modified HVDC cable material reached a maximum of 423 kV / mm when the EAA content was 15% by weight of LDPE, EAA, and 4,4'-diglycidyl biphenyldicarboxylate. This content demonstrates excellent stability of the HVDC cable material.

[0051] The Weibull distribution of the AC breakdown strength of the above four materials is as follows: Figure 6 shown.

[0052] Depend on Figure 6 The AC breakdown strength of the four modified HVDC cable materials was found to be improved to varying degrees compared to their unmodified counterparts. The addition of epoxy compounds significantly enhanced the breakdown strength of each component. Compared to the unmodified low-density polyethylene (LDPE) with an AC breakdown strength of 98.25 kV / mm, the modified HVDC cable material reached a maximum of 116 kV / mm when the EAA content reached 15% by weight of LDPE, EAA, and diglycidyl 4,4'-biphenyldicarboxylate.

[0053] (5) According to the electric field strength and temperature of the insulation layer of the high-voltage DC cable during operation, the above four materials are tested for conductivity and current of 200 μm samples at a field strength of 5 kV to 40 kV within the cable operating temperature range of 30 ° C to obtain their EJ curves, as shown in Figure 2. Figure 5 As shown, the polarization time was set to 1 h.

[0054] Depend on Figure 5 It can be seen that Figure 3 It can be seen that the conductivity of the modified high-voltage DC cable material is not only significantly lower than that of the unmodified composite material, but also has the lowest conductivity when the EAA content is 15%. In addition, the conductivity of the high-voltage DC cable material composite material at 20kV / mm when the EAA content of the unmodified composite material is 15% of the mass fraction of LDPE, EAA and 4,4'-diphenyldicarboxylic acid diglycidyl ester is reduced from 2.53×10-11S / m to 1.15×10- 11 S / m, which indicates that the introduced traps suppress the free movement of charges, which improves the electrical insulation of the HVDC cable material.

[0055] The above description is merely a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above. Some modifications and changes to the present invention should also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a glycidyl ester and DCP double crosslinked EAA and LDPE cable material, characterized in that: Low-density polyethylene (LDPE), diglycidyl 4,4'-biphenyldicarboxylate, ethylene acrylic acid copolymer (EAA), and dicumyl peroxide (DCP) are melt-blended in a torque vulcanizer to obtain a mixed material. The mixed material is then pressed and formed in a flat-plate vulcanizer, heated and cross-linked, and cooled to obtain a cable material with significantly improved tensile strength. The mass of EAA is 5%-20% of the mass of LDPE, EAA and 4,4'-diglycidyl biphenyldicarboxylate; The mass of LDPE is 73%-93% of the mass of LDPE, EAA and 4,4'-diglycidyl biphenyldicarboxylate; The mass of diglycidyl 4,4'-biphenyldicarboxylate is 1.8%-7.4% of the mass of LDPE, EAA and diglycidyl 4,4'-biphenyldicarboxylate; The mass of DCP is 1.6% of the mass of LDPE.

2. Application of the glycidyl ester and DCP double cross-linked EAA and LDPE cable material prepared by the method of claim 1, characterized in that: Used to prepare high-voltage DC cable materials.

3. The use according to claim 2, characterized in that: The tensile strength of the high-voltage DC cable material can reach 26.7 MPa-31.2 MPa, and the elongation at break can reach 526.8%-1109.5%.

Images