High-temperature-resistant modified PVC cable material and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant modified PVC (polyvinyl chloride) cable material and a preparation method thereof, and the high-temperature-resistant modified PVC cable material comprises the following components: PVC resin, fluororubber, a composite plasticizer, a bisphenol AF cross-linking agent, an accelerant, nano calcium fluoride, active calcium oxide, a flame retardant and an antioxidant. The preparation method comprises the steps of pretreatment, premixing, final mixing, dynamic vulcanization and post-vulcanization. Through an efficient cross-linking system of benzyltriphenylphosphonium chloride and bisphenol AF, and in combination with affinity between nano calcium fluoride and a macromolecular cross-linking network, an interpenetrating cross-linking network structure of PVC modified by fluororubber and inorganic components is realized; through an innovative fluorine modification technology, a crosslinking system design and a free acid absorption mechanism, the temperature resistance grade and the service life of the PVC cable material are remarkably improved, and meanwhile, the PVC cable material has relatively good machinability and excellent flame retardant property.

Description

Technical Field

[0001] The present invention relates to the technical field of modified PVC cable materials, and particularly relates to a high-temperature resistant modified PVC cable material and a preparation method thereof. Background Art

[0002] PVC has good abrasion resistance, can resist oil, acid, alkali, bacteria, moisture and sunlight irradiation, etc., and has a self-extinguishing property for flames; the lowest working temperature of the polyvinyl chloride sheath is -40°C, and the high temperature resistance can reach 105°C. Since PVC is not easy to burn, resistant to aging, oil, chemical drugs, impact, easy to color, and has a large dielectric constant, it is suitable as an insulating material for low-voltage cables and control cables.

[0003] PVC modified material is a modified form of PVC resin. It is formed by blending polyvinyl chloride resin with various additives, plasticizers, stabilizers and fillers. The addition of these additives can enhance the specific properties of PVC resin and make it suitable for a wide range of applications. The additives can be in the form of powder, liquid or paste, depending on the properties required for the PVC modified material. Additives and plasticizers make the material more flexible and improve its impact resistance. Stabilizers can enhance the thermal stability and weather resistance of PVC modified materials. Filler addition is to change the physical properties and reduce costs. PVC modified materials can be formulated for specific applications, such as cables, floors, automotive parts and medical devices.

[0004] In the traditional formula of PVC cables, additives containing heavy metals such as lead, mercury and cadmium are required as cable material pigments, heat stabilizers and flame retardants. In the selection of pigments, generally lead is used for white, yellow and red; cadmium is used for red and yellow; hexavalent chromium is used for yellow, green and red. In the selection of heat stabilizers, a large amount of lead salts are used in the production process of PVC cable materials. Lead salt heat stabilizers are favored by traditional cable manufacturers because of their good thermal stability, excellent weather resistance and low price, but their toxicity is very high, and they are mixed with heavy metals such as cadmium, chromium and mercury, which is easy to cause excessive lead dust. In the selection of flame retardants, generally antimony trioxide is used. Its combination with PVC can greatly improve the flame retardant effect of cables, but its crude products are often mixed with heavy metal arsenic, which is extremely harmful to the human body when burning. With the improvement of environmental awareness, the PVC modified material industry is also seeking more environmentally friendly solutions. Developing more environmentally friendly modifiers and additives.

[0005] More importantly, the long-term use temperature of traditional PVC cable materials usually does not exceed 90°C, and there are problems such as plasticizer migration and poor thermal stability at high temperatures. In the prior art, although the use of chlorinated PVC or inorganic fillers for modification can improve the temperature resistance, it leads to deterioration of processing performance or a decrease in mechanical strength. Therefore, under the condition of ensuring the electrical performance of wires and cables, the modified design to achieve the temperature resistance level and service life is one of the most important topics in the current modified PVC cable materials. Summary of the Invention

[0006] The object of the present invention is to solve the disadvantages existing in the prior art. By means of fluororubber modification, bisphenol AF crosslinking and nano-calcium fluoride synergistic enhancement, and innovatively introducing a calcium oxide absorption system, a breakthrough improvement in heat resistance performance is achieved, and a high-temperature resistant modified PVC cable material and its preparation method are proposed.

[0007] The technical solution of the present invention is as follows: The present invention first proposes a high-temperature resistant modified PVC cable material, comprising the following raw materials in parts by weight: 100 parts of PVC resin: SG-5 type PVC, with a molecular weight of 1300-1500; 8-12 parts of fluororubber: any one of fluororubber 23, fluororubber 26, fluororubber 246 or perfluoroether rubber, with a fluorine content of 50-70%; 30-35 parts of composite plasticizer: 1.0-1.5 parts of bisphenol AF crosslinking agent; that is, 2,2'-bis(4-hydroxyphenyl)-hexafluoropropane, and its molecular formula is:

[0008] In the fluororubber (FKM) / PVC blend system, bisphenol AF has two phenolic hydroxyl reaction sites, and the quaternary carbon center has a hexafluoropropyl group, which can provide heat resistance and hydrophobicity. Crosslinking is achieved through the following steps: ①Nucleophilic substitution: The allyl chloride generated by PVC dehydrochlorination reacts with the phenoxide anion of bisphenol AF: ②Ether bond formation: The -CF3 group in the fluororubber reacts with bisphenol AF to form a stable ether bond; Through the above reactions, a PVC-FKM interpenetrating network structure is formed. While maintaining processability, the composite material simultaneously has the heat resistance of fluororubber and the mechanical properties of PVC. Its hexafluoropropyl group can migrate to the material surface to form a fluorine element enrichment layer, which not only improves hydrophobicity but also significantly enhances the chemical resistance performance; 0.2-0.4 parts of accelerator: benzyltriphenylphosphonium chloride; since bisphenol AF does not have sufficient activity for fluororubber vulcanization, it will not be used alone and is usually used in combination with onium compounds. Typical onium compounds are quaternary ammonium salts and quaternary phosphonium salts. The onium compound with the best effect when used in combination with bisphenol AF is BPP (benzyltriphenylphosphonium chloride), and its molecular formula is:

[0009] Its reaction mechanism is mainly the quaternary phosphonium salt P +Accelerate the deprotonation of phenolic hydroxyl groups, while increasing the dissipation of HF, thus greatly enhancing the crosslinking efficiency and shortening the vulcanization time. However, the HF generated during the vulcanization process will not only inhibit the occurrence of crosslinking reactions, have an adverse effect on the heat-oxygen aging performance of vulcanized rubber, but also corrode equipment. Therefore, it is necessary to add a reagent that adsorbs HF to the vulcanization system; 2 - 4 parts of nano calcium fluoride: with a particle size of 20 - 50 nm; 3 - 5 parts of activated calcium oxide: specific surface area ≥ 20 m² / g; 15 - 20 parts of flame retardant: 0.5 - 1 part of antioxidant.

[0010] Preferably, the composite plasticizer is composed of trioctyl trimellitate and epoxidized soybean oil prepared according to a weight ratio of 3:1.

[0011] Preferably, the flame retardant is composed of aluminum hydroxide and zinc borate compounded according to a weight ratio of 10:2.5 - 3.

[0012] Preferably, the antioxidant is composed of antioxidant 1076 and antioxidant 168 compounded according to a weight ratio of 1:1.

[0013] Formulation design analysis: 1. Modification mechanism of fluororubber (FKM) The bond energy of the C - F bond in FKM in the crosslinking network (485 kJ / mol) is significantly higher than that of the C - H bond in PVC (413 kJ / mol). At the same time, the F content on the material surface is relatively high, forming a protective layer, and the Tg of the crosslinked network polymer is increased from 85 °C (pure PVC) to 115 °C, having a significant synergistic toughening mechanism and improving the thermal stability function; 2. Crosslinking mechanism of bisphenol AF Crosslinking network construction: Crosslinking density: determined by the swelling method to be 4.1×10 -5 mol / cm³; By - product control: HCl and a small amount of HF are generated during the crosslinking process; 3. Absorption mechanism of calcium oxide Real - time absorption reaction: CaO + 2HCl → CaCl2 + H2O (200 °C, ΔH = - 186.2 kJ / mol) CaO + 2HF → CaF2 + H2O (200 °C, ΔH = - 238.6 kJ / mol);

[0014] Absorption kinetics: BET test shows that the specific surface area of activated CaO reaches 28.5 m 2 / g, at the processing temperature (180 - 200 °C), the HCl absorption efficiency > 95%, and the formed CaCl2 / CaF2 can be used as an additional filler to enhance the system; 4. Synergistic effect of nano calcium fluoride Thermal stability mechanism of calcium fluoride: React with residual HCl: CaF2 + 2HCl → CaCl2 + 2HF

[0015] Increase in decomposition temperature: TGA shows that the 5% weight loss temperature rises from 242 °C to 285 °C. At the same time, due to the existence of this reaction, there is a better affinity between the inorganic phases (CaO, CaF2, CaCl2) and PVC and FKM, thereby improving the distribution uniformity of the inorganic and organic phases, and further enhancing the strength and thermal stability.

[0016] 5. Synergistic effect of flame retardants Similarly, the alkaline flame retardants also have the function of absorbing free HF and HCl in the crosslinking system network, making the crosslinking nodes carry the flame retardant components, further improving the thermal stability and flame retardant function of the crosslinking system; The present invention also provides a method for preparing the aforementioned high-temperature resistant modified PVC cable material, including the following steps: S1. Pretreatment: After drying nano calcium fluoride at 110 °C for 4 h, it is treated with KH-550 silane coupling agent. After activating active calcium oxide at 300 °C for 2 h, it is quickly cooled to room temperature. Activation can increase the specific surface area. S2. Premixing: Premix PVC resin with half of the dosage of plasticizer in a high-speed mixer. S3. Final mixing: Continue to add the remaining components to the components obtained in S2, and mix at 100 °C for 8 min to obtain the extrusion raw material. S4. Dynamic vulcanization: Put the extrusion raw material into a twin-screw extruder and conduct thermal extrusion treatment at 160 - 185 °C. At this temperature, PVC and FKM form a crosslinked interpenetrating network through a crosslinking agent. At the same time, the HCl decomposed from PVC and the crosslinking by-product HF are absorbed by the inorganic phase, thereby reducing the escape rate of small molecule acids and improving the thermal stability to obtain the primary vulcanized material. S5. Post-vulcanization: In a kneader, under an air atmosphere, heat-treat at 200 °C for 2 - 3 h. At this temperature, especially, the adsorption rate of CaO to HCl and HF at high temperature (200 °C) > 95% (within 5 min), and the generated CaF2 and CaCl2 can be used as auxiliary inorganic reinforcing agents and protectants to obtain the finished high-temperature resistant modified PVC cable material.

[0017] Preferably, the mass ratio of nano-calcium fluoride to KH-550 silane coupling agent in S1 is 10:1.1-1.3, which reduces the interfacial effect between calcium fluoride and the organic phase and improves the uniform distribution.

[0018] Preferably, the conditions for premixing in S2 are: temperature: 80 °C, rotation speed: 500 rpm, stirring time: 5 min.

[0019] Preferably, the parameters for the hot extrusion treatment in S4 are: the first section of the twin-screw extruder is 160 ± 5 °C, the second section is 170 ± 5 °C, the third section is 180 ± 5 °C, the fourth section is 175 ± 5 °C, the die head temperature is 185 ± 5 °C, and the screw rotation speed is 250 rpm; Preferably, the internal mixer in S5 needs to be dehumidified by introducing dry hot air to remove the water generated by the acid-base reaction.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. Through the innovative fluorine modification technology, crosslinking system design and by-product absorption mechanism, the present invention significantly improves the temperature resistance grade and service life of PVC cable materials. The long-term service temperature reaches 125 °C, and it can withstand 150 °C in the short term. At the same time, it has good processability and excellent flame retardant properties; 2. Through the efficient crosslinking system of benzyltriphenylphosphonium chloride and bisphenol AF, the present invention realizes the interpenetrating crosslinked network structure of fluororubber modified PVC. And through calcium oxide in the post-vulcanization process at 200 °C, it can absorb the degradation by-product HCl and crosslinking by-product HF in real time. The free halogen content is <15 ppm, and the equipment corrosion risk is reduced by more than 90%. At the same time, calcium fluoride and calcium chloride reinforcing agents are produced. At the same time, nano-calcium fluoride and the newly produced calcium fluoride and calcium chloride form an inorganic-organic interpenetrating structure through reaction with the polymer crosslinked network, and the tensile strength is increased by more than 50% (compared with ordinary PVC); 3. By introducing a halogen-free and antimony-free flame retardant system with a slightly alkaline nature and utilizing the affinity between the free acid generated during the vulcanization crosslinking process of PVC and the flame retardant system, the present invention makes the uniformity of the inorganic phase and the organic phase better, and has good strength, heat resistance and flame retardant properties. At the same time, due to the small interfacial effect between the inorganic and organic phases, the processing performance of this product is excellent, overcoming the defects of high hardness and difficult processing of existing modified PVC cable materials. Detailed implementation mode

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0022] I. Cable material formula design: A high-temperature resistant modified PVC cable material, comprising the following raw materials in parts by weight: 100 parts of PVC resin: SG-5 type PVC with a molecular weight of 1300 - 1500; 8 - 12 parts of fluororubber: any one of fluororubber 23, fluororubber 26, fluororubber 246 or perfluoroether rubber, with a fluorine content of 50 - 70%; 30 - 35 parts of composite plasticizer: 1.0 - 1.5 parts of bisphenol AF crosslinking agent; that is, 2,2'-bis(4-hydroxyphenyl)-hexafluoropropane, whose molecular formula is:

[0023] In the fluororubber (FKM) / PVC blend system, bisphenol AF has two phenolic hydroxyl reaction sites, and the quaternary carbon center has a hexafluoropropyl group, which can provide heat resistance and hydrophobicity. Crosslinking is achieved through the following steps: ① Nucleophilic substitution: The allyl chloride generated by the dehydrochlorination of PVC reacts with the phenoxide anion of bisphenol AF: ② Ether bond formation: The -CF3 group in the fluororubber forms a stable ether bond with bisphenol AF; Through the above reactions, a PVC-FKM interpenetrating network structure is formed. While maintaining processability, the composite material simultaneously has the heat resistance of fluororubber and the mechanical properties of PVC. Its hexafluoropropyl group can migrate to the material surface to form a fluorine element enrichment layer, improving hydrophobicity and significantly enhancing the chemical resistance performance; 0.2 - 0.4 parts of accelerator: benzyltriphenylphosphonium chloride; since bisphenol AF does not have sufficient activity for the vulcanization of fluororubber, it will not be used alone and is usually used in combination with onium compounds. Typical onium compounds are quaternary ammonium salts and quaternary phosphonium salts. The onium compound with the best effect when used in combination with bisphenol AF is BPP (benzyltriphenylphosphonium chloride), whose molecular formula is:

[0024] Its reaction mechanism is mainly the accelerating effect of the quaternary phosphonium salt P + on the deprotonation of phenolic hydroxyl groups, while increasing the dissipation of HF, thus greatly enhancing the crosslinking efficiency and shortening the vulcanization time. However, the HF generated during the vulcanization process not only inhibits the occurrence of crosslinking reactions, has an adverse effect on the heat and oxygen aging performance of the vulcanizate, but also corrodes equipment. Therefore, a reagent for adsorbing HF needs to be added to the vulcanization system; 2 - 4 parts of nano calcium fluoride: with a particle size of 20 - 50 nm; 3 - 5 parts of active calcium oxide: specific surface area ≥ 20 m² / g; 15 - 20 parts of flame retardant: 0.5 - 1 part of antioxidant.

[0025] The composite plasticizer is prepared from trioctyl trimellitate and epoxidized soybean oil in a weight ratio of 3:1.

[0026] The flame retardant is prepared by compounding aluminum hydroxide and zinc borate in a weight ratio of 10:2.5 - 3.

[0027] The antioxidant is prepared by compounding antioxidant 1076 and antioxidant 168 in a weight ratio of 1:1.

[0028] Specifically, it is shown in Table 1 below: Table 1. Cable compound formulation of the examples

[0029] It should be noted that in Table 1, the fluororubbers in Examples 1 - 4 are fluororubber 23, fluororubber 26, fluororubber 246, and perfluoroether rubber respectively; the ratios of the flame retardants in Examples 1 - 4 are aluminum hydroxide / zinc borate = 10 / 2.8, 10 / 2.5, 10 / 2.8, and 10 / 3 in sequence.

[0030] II. Performance testing 1. Performance of the example products: According to the requirements of the national standard "GB / T8815 - 2008 Flexible polyvinyl chloride plastics for wire and cable", strength, thermal stability, and flame retardant level tests were carried out on the insulation material J - 90 and sheath material H - 90. The test results are shown in the following table: Table 2. Performance test formulation of the example cable compounds

[0031] 2. Design of the comparative examples and their performance testing: Based on Example 1, the following comparative example products were designed and their performance was tested. The results are shown in Table 3 below: Table 3. Design and performance of the comparative example products

[0032] 3. Data analysis: 1) High temperature resistance The TGA 5% weight loss temperature of Examples 1 - 4 is > 280 °C, while that of Comparative Examples 1 / 2 / 5 / 7 is < 250 °C.

[0033] The synergistic effect of fluororubber and bisphenol AF increases the heat distortion temperature by more than 30% (Comparative Examples 1 / 2).

[0034] 2) Mechanical properties Nano calcium fluoride increases the tensile strength by about 30% (comparing Example 1 with Comparative Example 3).

[0035] 3) Flame retardancy The addition of zinc borate increases the oxygen index by 5 - 6 units (compare Example 1 with Comparative Example 4).

[0036] 4) By - product control The CaO / CaF2 system enables the HCl absorption rate to be > 95% (the emission amount in Comparative Example 6 increases significantly).

[0037] 5) Processing stability When the dynamic vulcanization temperature is < 160 °C, cross - linking is incomplete (Comparative Example 8).

[0038] 6) Conclusion: Examples 1 - 4 have the best comprehensive performance through the synergistic effects of the fluororubber interpenetrating network, bisphenol AF cross - linking, and nano - fillers; the comparative examples verify the necessity of each key component, and the absence of any component leads to a significant decline in performance.

[0039] As described above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A high-temperature resistant modified PVC cable material, characterized in that, It includes the following raw materials by weight: 100 parts of PVC resin: SG-5 type PVC with a molecular weight of 1300 - 1500; 8 - 12 parts of fluororubber: any one of fluororubber 23, fluororubber 26, fluororubber 246 or perfluoroether rubber, with a fluorine content of 50 - 70%; 30 - 35 parts of compound plasticizer; 1.0 - 1.5 parts of bisphenol AF crosslinking agent; 0.2 - 0.4 part of accelerator: benzyltriphenylphosphonium chloride; 2 - 4 parts of nano calcium fluoride: particle size of 20 - 50 nm; 3 - 5 parts of active calcium oxide: specific surface area ≥ 20 m² / g; 15 - 20 parts of flame retardant; 0.5 - 1 part of antioxidant.

2. The heat-resistant modified PVC cable compound according to claim 1, characterized in that, The compound plasticizer is prepared from trioctyl trimellitate and epoxidized soybean oil according to a weight ratio of 3:

1.

3. The heat-resistant modified PVC cable compound according to claim 1, characterized in that, The flame retardant is compounded from aluminum hydroxide and zinc borate according to a weight ratio of 10:2.5 - 3.

4. The heat-resistant modified PVC cable material according to claim 1, wherein, The antioxidant is compounded from antioxidant 1076 and antioxidant 168 according to a weight ratio of 1:

1.

5. The preparation method of a heat-resistant modified PVC cable compound according to any one of claims 1-4, characterized in that, It includes the following steps: S1. Pretreatment: After drying nano calcium fluoride at 110°C for 4 h, it is treated with KH-550 silane coupling agent; Active calcium oxide is activated at 300°C for 2 h and then rapidly cooled to room temperature; S2. Premixing: The PVC resin and half of the dose of plasticizer are premixed in a high-speed mixer; S3. Final mixing: The remaining components are continuously added to the components obtained in S2, and mixed at 100°C for 8 min to obtain the extrusion raw material; S4. Dynamic vulcanization: The extrusion raw material is put into a twin-screw extruder and subjected to hot extrusion treatment at 160 - 185°C to obtain the primary vulcanized material; S5. Post-vulcanization: In a kneader, under an air atmosphere, it is heat-treated at 200°C for 2 - 3 h to obtain the finished product of high-temperature resistant modified PVC cable material.

6. The preparation method of a high-temperature resistant modified PVC cable material according to claim 5, characterized in that, In S1, the mass ratio of nano calcium fluoride to KH-550 silane coupling agent is 10:1.1 - 1.

3.

7. The preparation method of a high-temperature resistant modified PVC cable material according to claim 5, characterized in that, The conditions for premixing in S2 are: temperature: 80°C, rotation speed: 500 rpm, stirring time: 5 min.

8. The preparation method of a high-temperature resistant modified PVC cable material according to claim 5, characterized in that, The parameters for the hot extrusion treatment in S4 are: the first section of the twin-screw extruder is 160 ± 5°C, the second section is 170 ± 5°C, the third section is 180 ± 5°C, the fourth section is 175 ± 5°C, the die head temperature is 185 ± 5°C, and the screw rotation speed is 250 rpm.

9. The preparation method of a high-temperature resistant modified PVC cable material according to claim 5, wherein, In S5, the kneader needs to be dehumidified by introducing dry hot air to remove the water generated by the acid-base reaction.

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