A flexible halogen-free high-efficiency flame-retardant polyolefin cable material and its preparation method

Abstract

The present invention provides a flexible halogen-free highly flame-retardant polyolefin cable compound and a preparation method thereof. The weight parts of the cable compound are as follows: 30-70 parts of modified polyolefin, 30-70 parts of ethylene-vinyl acetate copolymer, 40-80 parts of surface-treated inorganic flame retardant, 30-50 parts of filler, and 5-15 parts of compatibilizer; wherein, the modified polyolefin is obtained by subjecting polyethylene to ultraviolet grafting reaction with an organic acid monomer and neutralizing with sodium hydroxide. The flexible halogen-free highly flame-retardant polyolefin cable compound described in the present invention has both a large tensile strength and elongation at break, as well as excellent flame retardant properties.

Description

Technical Field

[0001] The present invention relates to the technical field of cable materials, and particularly to a flexible halogen-free and highly flame-retardant polyolefin cable material and a preparation method thereof. Background Art

[0002] With the continuous development of science and technology and social economy, people have higher and higher requirements for the safety and environmental protection performance of wire and cable products. Due to the poor flame retardancy of traditional polyvinyl chloride (PVC) cable materials, fires are likely to occur, and at the same time, a large amount of toxic hydrogen chloride gas will be released during combustion, causing damage to the lives of people and building equipment, and its large-scale application has gradually been restricted. Therefore, it is of great significance to develop low-smoke and halogen-free flame-retardant cable materials. Most low-smoke and halogen-free flame-retardant cable materials are based on polyolefins, which do not have flame retardancy themselves and need to add a large amount of inorganic flame retardants to achieve high-efficiency flame retardant performance. However, since most polyolefins are non-polar materials, they have very poor compatibility with inorganic flame retardants with strong polarity, which seriously affects the processing performance and physical and mechanical properties of the cable material after adding a large amount of inorganic flame retardants. At the same time, since the inorganic flame retardant particles are in a dispersed state in the matrix, a continuous barrier layer needs to be formed to achieve the flame retardant effect during combustion, which often requires a large amount of inorganic flame retardant addition. Restricted by the above influencing factors, the flexibility of the halogen-free flame-retardant cable material prepared by the traditional method of adding inorganic flame retardants is not ideal enough, and the tensile strength and elongation at break need to be further improved.

[0003] Developing a new type of halogen-free flame-retardant cable material with both high flexibility and high flame retardant effect is a key technical problem that urgently needs to be solved in the research and development of high-performance cables. However, there are still a series of challenges in preparing a new type of halogen-free flame-retardant cable material with high flexibility and high flame retardant effect by the traditional method of adding pure inorganic flame retardants to improve the flame retardant effect. In view of the deficiencies in the prior art, the present invention patent proposes a new preparation method for a flexible halogen-free and highly flame-retardant polyolefin cable material. By grafting a new type of sodium organic salt in the matrix resin to replace part of the inorganic filler and flame retardant, the combination with the matrix and the dispersion of inorganic particles are enhanced, thereby effectively improving the flexibility of the cable; at the same time, sodium carbonate and carbon nanosheets are in-situ generated during the combustion process (J. Mater. Chem. A, 2022, 10, 9726 - 9736), which are used as an isolation layer and a filler respectively, significantly improving the flame retardant effect of the cable. The cable material prepared by this method has excellent comprehensive high flexibility and high flame retardant effect. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a flexible halogen-free highly flame-retardant polyolefin cable material and its preparation method in view of the deficiencies of the prior art, and particularly relates to a modification method for grafting sodium organic acid salt onto polyethylene by light induction, which can in-situ generate carbon nanosheets and sodium carbonate as a flame-retardant isolation layer and filler during combustion, inhibit the dripping phenomenon generated during material combustion, and have a good synergistic effect with inorganic flame retardants, reduce the usage amounts of inorganic fillers and flame retardants, improve the mechanical properties of the material, and achieve the effects of synergistic flame retardancy and toughening simultaneously.

[0005] Another object of the present invention is to provide a preparation method for a flexible halogen-free highly flame-retardant polyolefin cable material.

[0006] A flexible halogen-free highly flame-retardant polyolefin cable material, characterized in that it is composed of the following raw materials in parts by weight: 30 - 70 parts of sodium organic acid-modified polyolefin, 30 - 70 parts of ethylene-vinyl acetate copolymer, 40 - 80 parts of surface-treated inorganic flame retardant, 30 - 50 parts of filler, and 5 - 15 parts of compatibilizer.

[0007] The polyolefin is low-density polyethylene, with a melt index of 1 - 3 g / 10 min, a molecular weight of 300,000 - 500,000, and a density of 0.918 - 0.980 g / cm 3 。

[0008] The modified polyolefin is obtained by subjecting polyethylene to an ultraviolet grafting reaction with an organic acid monomer and then neutralizing it with sodium hydroxide.

[0009] The preparation of the modified polyolefin includes the following steps: dispersing polyolefin, organic acid monomer, and photoinitiator evenly in a solvent, placing the conical flask containing the suspension on a magnetic stirrer for stirring, irradiating it under an ultraviolet lamp, adding an appropriate amount of sodium hydroxide, and after the reaction ends, subjecting the mixture to vacuum filtration, washing, and drying. The reaction equation is as follows:

[0010]

[0011] The specific preparation method of the modified polyolefin: (1) Stir low-density polyethylene powder, organic acid monomer, and photoinitiator evenly in a solvent; (2) Place the above mixed suspension under ultraviolet light irradiation to generate free radicals for polymerization reaction. The irradiation time is 1 - 3 h, the ultraviolet light intensity is 1000 W, and stirring is carried out simultaneously; (3) After the irradiation ends, add sodium hydroxide and react for 0.5 - 2 h, then carry out vacuum filtration, wash twice with water, and store it for standby after vacuum drying.

[0012] The organic acid is one of terephthalic acid, diphenic acid, quinolinic acid, indole-3-carboxylic acid, oxo-o-nicotinic acid, and L-2-pyridinecarboxylic acid.

[0013] In the modified polyolefin described above, the weight ratio of low-density polyethylene to organic acid monomer is 1:(1-5).

[0014] The photoinitiator described above is one of 2-dimethylamino-2-benzyl-1-[4-(4-morpholinyl)phenyl]-1-butanone, ethyl 2,4,6-trimethylbenzoyl phenylphosphinate, and methyl benzoylformate, and the concentration is 0.001-0.05 mol / L.

[0015] The solvent described above is water, ethanol, or acetone.

[0016] The molar ratio of the addition amount of the sodium hydroxide described above to the organic acid is 5:(5-9).

[0017] In the ethylene-vinyl acetate copolymer described above, the content of vinyl acetate is 26-35%, and the melt index is 7-10 g / 10 min.

[0018] The inorganic flame retardant described above is surface-treated magnesium hydroxide and aluminum hydroxide, and the weight ratio of the two is 1:1.

[0019] The surface treatment agent of the inorganic flame retardant described above is one or both of sodium bis(2-ethylhexyl) phosphate and sodium bis(2-ethylhexyl) sulfosuccinate.

[0020] The compatibilizer described above is one or two of maleic anhydride grafted polyethylene, maleic anhydride grafted EVA, and maleic anhydride grafted POE.

[0021] The filler described above is one or a mixture of several of nano calcium carbonate, calcined kaolin, silica lime, fumed silica, and talc powder.

[0022] The preparation method of the flexible halogen-free high-efficiency flame-retardant polyolefin cable material described in the present invention includes the following steps:

[0023] 1) Weigh the matrix resin, flame retardant, filler, and compatibilizer;

[0024] 2) Add the weighed matrix resin to a kneader, and knead at 150-170 °C for 10-20 min;

[0025] 3) Add the weighed flame retardant, filler, compatibilizer, and matrix resin to a high-speed mixer in sequence, and stir and mix at a speed of 300-500 r / min for 5-15 min to obtain a premix;

[0026] 4) Add the obtained premix to the hopper of a twin-screw extruder, and melt blend, extrude, cool, air-dry, and pelletize through a high-temperature extruder.

[0027] The present invention discloses the following technical effects: A flexible halogen-free and highly efficient flame-retardant polyolefin cable material provided by the present invention has excellent flame-retardant performance, flexibility, low smoke and non-toxicity, environmental friendliness, etc., and good processing performance.

[0028] A flexible halogen-free and highly efficient flame-retardant polyolefin cable material provided by the present invention uses modified low-density polyethylene and ethylene-vinyl acetate copolymer as matrix resins, and additives such as modified inorganic flame retardants and compatibilizers are added to this matrix resin. The unique formula realizes high-efficiency flame retardancy with a low dosage of flame retardant. Polyethylene grafted with sodium organic acid salt (special sodium organic acid salt) can synergistically improve the flexibility and flame-retardant effect of the cable material. The principle is as follows: 1) During the preparation of the cable material, the sodium organic acid salt grafted on polyethylene can act as a filler and a synergistic flame retardant, significantly reducing the dosage of the filler and the flame retardant. Compared with traditional inorganic fillers and flame retardants, the special functional groups (such as COO-) on its organic acid salt are easy to contact with the matrix resin, improving the dispersion effect, and thus significantly enhancing the flexibility of the cable material; 2) During the combustion process, the sodium organic acid salt has a special synergistic flame-retardant function. On the one hand, sodium carbonate will be in-situ generated by the sodium organic acid salt and uniformly distributed in the matrix. Sodium carbonate has stable physical properties and can play a good heat insulation effect. At the same time, the in-situ generated sodium carbonate has high reactivity and has a catalytic effect on the subsequent carbonization process, inducing the formation of carbon nanosheets; on the other hand, the grafted sodium organic acid salt and the flame retardant are uniformly distributed throughout the cable material. Combustion will form a special structure in which a flame-retardant barrier layer (Al2O3, MgO), sodium carbonate, and a carbon nanosheet isolation layer are uniformly compounded. The barrier layer and sodium carbonate have good oxygen isolation effects, while the carbon nanosheet layer has excellent heat insulation effects in a low-oxygen environment. The three work together to improve the oxygen isolation and heat insulation effects, significantly improving the flame-retardant performance of the cable material.

[0029] Polyethylene grafted with sodium organic acid salt is not only beneficial to increasing the flexibility of the matrix resin, but also can in-situ form flaky carbon and sodium carbonate during combustion, cooperate with metal hydroxides to form a dense protective layer to block the transmission of oxygen, thereby inhibiting combustion, enhancing the flame-retardant performance, and reducing the addition amount of the flame retardant. This product has the characteristics of excellent flame-retardant performance and flexibility, low smoke and non-toxicity, environmental friendliness, and good processing performance. The limiting oxygen index ≥ 35, and the elongation at break ≥ 200%, which is suitable for the production of flexible and highly efficient flame-retardant building cables. Specific Embodiments

[0030] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0031] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the description of the present invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of the present invention are obvious to those skilled in the art. The description and examples of the present invention are merely exemplary.

[0032] For the embodiment of the present invention, the raw material formula is shown in Table 1.

[0033] Table 1 Formula of Flexible Halogen-Free High-Efficiency Flame-Retardant Polyolefin Cable Compound

[0034]

[0035] Wherein:

[0036] Example 1

[0037] The flexible halogen-free high-efficiency flame-retardant polyolefin cable compound is prepared from the following raw materials in parts by weight: 30 parts of modified low-density polyethylene (the specific gravity of polyethylene / organic acid is 1:2), 70 parts of ethylene-vinyl acetate copolymer, 20 parts of modified magnesium hydroxide and 20 parts of aluminum hydroxide are used as inorganic flame retardants, 25 parts of talc powder and 25 parts of white carbon black are used as fillers, and 5 parts of maleic anhydride grafted EVA is used as a compatibilizer.

[0038] The steps of its preparation method include:

[0039] 1) Add low-density polyethylene powder to water and stir, while adding the photoinitiator diphenylacetone with a concentration of 0.02 mol / L, and then add the organic acid monomer L-2-pyridinecarboxylic acid, and the weight ratio of polyethylene to it is 1:2; place the above mixed suspension under ultraviolet light irradiation to generate free radicals for polymerization reaction, the irradiation time is 1.5 h, the ultraviolet light intensity is 1000 W, and stir at the same time; after the irradiation ends, add sodium hydroxide (the addition amount of sodium hydroxide and the molar ratio of organic acid is 5:10), react for 1 h, then carry out vacuum filtration, wash with water 2 times, and store after vacuum drying for later use.

[0040] 2) Weigh the matrix resin, flame retardant, filler, and compatibilizer according to the formula;

[0041] 3) Add the weighed matrix resin to a kneader and knead at 160 °C for 15 min;

[0042] 4) Add the weighed flame retardant, filler, compatibilizer, and matrix resin to a high-speed mixer in sequence, and stir and mix at a speed of 500 r / min for 10 min to obtain a premix;

[0043] 5) Add the obtained premix into the hopper of a twin-screw extruder, and melt, blend, extrude, cool, air-dry, and pelletize it through a high-temperature extruder to obtain a flexible halogen-free high-efficiency flame-retardant polyolefin cable material.

[0044] Example 2

[0045] The flexible halogen-free high-efficiency flame-retardant polyolefin cable material is prepared from the following raw materials in parts by weight: 50 parts of modified low-density polyethylene (the ratio of polyethylene to organic acid is 1:2), 50 parts of ethylene-vinyl acetate copolymer, 30 parts of modified magnesium hydroxide and 30 parts of aluminum hydroxide are used as inorganic flame retardants, 20 parts of talc powder and 20 parts of silica are used as fillers, and 10 parts of maleic anhydride-grafted EVA is used as a compatibilizer.

[0046] Its preparation method is the same as that of Example 1.

[0047] Example 3

[0048] The flexible halogen-free high-efficiency flame-retardant polyolefin cable material is prepared from the following raw materials in parts by weight: 70 parts of modified low-density polyethylene (the ratio of polyethylene to organic acid is 1:2), 30 parts of ethylene-vinyl acetate copolymer, 40 parts of modified magnesium hydroxide and 40 parts of aluminum hydroxide are used as inorganic flame retardants, 15 parts of talc powder and 15 parts of silica are used as fillers, and 15 parts of maleic anhydride-grafted EVA is used as a compatibilizer.

[0049] Its preparation method is the same as that of Example 1.

[0050] Example 4

[0051] The flexible halogen-free high-efficiency flame-retardant polyolefin cable material is prepared from the following raw materials in parts by weight: 30 parts of modified low-density polyethylene (the ratio of polyethylene to organic acid is 1:3), 70 parts of ethylene-vinyl acetate copolymer, 30 parts of modified magnesium hydroxide and 30 parts of aluminum hydroxide are used as inorganic flame retardants, 20 parts of talc powder and 20 parts of silica are used as fillers, and 5 parts of maleic anhydride-grafted EVA is used as a compatibilizer.

[0052] Its preparation method is the same as that of Example 1.

[0053] Example 5

[0054] The flexible halogen-free high-efficiency flame-retardant polyolefin cable material is prepared from the following raw materials in parts by weight: 50 parts of modified low-density polyethylene (the ratio of polyethylene to organic acid is 1:3), 50 parts of ethylene-vinyl acetate copolymer, 40 parts of modified magnesium hydroxide and 40 parts of aluminum hydroxide are used as inorganic flame retardants, 15 parts of talc powder and 15 parts of silica are used as fillers, and 10 parts of maleic anhydride-grafted EVA is used as a compatibilizer.

[0055] Its preparation method is the same as that of Example 1.

[0056] Example 6

[0057] The flexible halogen-free high-efficiency flame-retardant polyolefin cable compound is prepared from the following raw materials in parts by weight: 70 parts of modified low-density polyethylene (the ratio of polyethylene to organic acid is 1:3), 30 parts of ethylene-vinyl acetate copolymer, 20 parts of modified magnesium hydroxide and 20 parts of aluminum hydroxide as inorganic flame retardants, 25 parts of talc and 25 parts of silica as fillers, and 15 parts of maleic anhydride grafted EVA as a compatibilizer.

[0058] Its preparation method is the same as that of Example 1.

[0059] Example 7

[0060] The flexible halogen-free high-efficiency flame-retardant polyolefin cable compound is prepared from the following raw materials in parts by weight: 30 parts of modified low-density polyethylene (the ratio of polyethylene to organic acid is 1:4), 70 parts of ethylene-vinyl acetate copolymer, 40 parts of modified magnesium hydroxide and 40 parts of aluminum hydroxide as inorganic flame retardants, 15 parts of talc and 15 parts of silica as fillers, and 5 parts of maleic anhydride grafted EVA as a compatibilizer.

[0061] Its preparation method is the same as that of Example 1.

[0062] Example 8

[0063] The flexible halogen-free high-efficiency flame-retardant polyolefin cable compound is prepared from the following raw materials in parts by weight: 50 parts of modified low-density polyethylene (the ratio of polyethylene to organic acid is 1:4), 50 parts of ethylene-vinyl acetate copolymer, 20 parts of modified magnesium hydroxide and 20 parts of aluminum hydroxide as inorganic flame retardants, 25 parts of talc and 25 parts of silica as fillers, and 10 parts of maleic anhydride grafted EVA as a compatibilizer.

[0064] Its preparation method is the same as that of Example 1.

[0065] Example 9

[0066] The flexible halogen-free high-efficiency flame-retardant polyolefin cable compound is prepared from the following raw materials in parts by weight: 70 parts of modified low-density polyethylene (the ratio of polyethylene to organic acid is 1:4), 30 parts of ethylene-vinyl acetate copolymer, 30 parts of modified magnesium hydroxide and 30 parts of aluminum hydroxide as inorganic flame retardants, 20 parts of talc and 20 parts of silica as fillers, and 15 parts of maleic anhydride grafted EVA as a compatibilizer.

[0067] Its preparation method is the same as that of Example 1.

[0068] Comparative Example 1

[0069] Flexible halogen-free highly efficient flame-retardant polyolefin cable material is prepared from the following raw materials in parts by weight: 50 parts of unmodified low-density polyethylene, 50 parts of ethylene-vinyl acetate copolymer, 50 parts of modified magnesium hydroxide and 50 parts of aluminum hydroxide are used as inorganic flame retardants, 15 parts of talc powder and 15 parts of white carbon black are used as fillers, and 15 parts of maleic anhydride grafted EVA is used as a compatibilizer.

[0070] Its preparation method is the same as that of Example 1.

[0071] Comparative Example 2

[0072] Flexible halogen-free highly efficient flame-retardant polyolefin cable material is prepared from the following raw materials in parts by weight: 70 parts of unmodified low-density polyethylene, 30 parts of ethylene-vinyl acetate copolymer, 40 parts of modified magnesium hydroxide and 40 parts of aluminum hydroxide are used as inorganic flame retardants, 25 parts of talc powder and 25 parts of white carbon black are used as fillers, and 15 parts of maleic anhydride grafted EVA is used as a compatibilizer.

[0073] Its preparation method is the same as that of Example 1.

[0074] Referring to the national standard of the People's Republic of China GB / T 32129-2015 "Halogen-free Flame-retardant Cable Materials for Electric Wires and Cables", the toughness, flame-retardant performance and electrical properties of Examples 1-9 and Comparative Examples 1-2 are tested, and the performance of the cable materials prepared in each example is shown in Table 2.

[0075] Table 2 Performance of Cable Materials in Different Examples

[0076]

[0077]

[0078] Analyzing the data in Table 2, the following conclusions can be drawn:

[0079] By grafting sodium organic acid onto polyethylene, the usage amount of inorganic flame retardant can be significantly reduced, achieving a more excellent flame-retardant effect, and at the same time improving the tensile strength and elongation at break of the material, indicating that the grafting method of the present invention can significantly improve the mechanical properties and flame-retardant performance of the cable material. The speculated mechanism is as follows: The grafted sodium organic acid salt can form a dense carbon layer and sodium carbonate on the melt surface during combustion, producing a synergistic effect with the inorganic flame retardant, playing a role in heat insulation and oxygen isolation, and preventing the further combustion of polyolefin. In addition, the introduction of sodium organic acid salt can also expand the distance between polyolefin molecular chains, thereby improving the dispersion of inorganic nanoparticles in the resin and further improving the tensile strength and flame-retardant performance of polyolefin materials.

[0080] In summary, it shows that the flexible halogen-free highly efficient flame-retardant polyolefin cable material prepared by the present invention has excellent flexibility and flame-retardant performance.

[0081] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A flexible halogen-free high-efficiency flame-retardant polyolefin cable compound, characterized in that, It comprises raw materials in the following weight fractions: 30 - 70 parts of modified polyolefin, 30 - 70 parts of ethylene-vinyl acetate copolymer, 40 - 80 parts of surface-treated inorganic flame retardant, 30 - 50 parts of filler, 5 - 15 parts of compatibilizer. The modified polyolefin is obtained by subjecting polyethylene and an organic acid monomer to ultraviolet grafting reaction and neutralizing with sodium hydroxide.

2. The flexible halogen-free highly flame-retardant polyolefin cable compound according to claim 1, characterized in that, The preparation of the modified polyolefin comprises the following steps: Disperse polyethylene, organic acid monomer and photoinitiator evenly in a solvent. Place the conical flask containing the suspension on a magnetic stirrer and stir, and irradiate under an ultraviolet lamp. Add an appropriate amount of sodium hydroxide. After the reaction ends, carry out vacuum filtration, washing and drying of the mixture. The reaction equation is as follows: 。 3. The flexible halogen-free highly flame-retardant polyolefin cable compound according to claim 2, characterized in that, The polyethylene is low-density polyethylene, with a melt index of 1-3 g / 10min, a molecular weight of 300,000-500,000, and a density of 0.918-0.980 g / cm 3 , the organic acid is one of terephthalic acid, biphenyl dicarboxylic acid, quinolinic acid, indole-3-carboxylic acid, oxo-o-nicotinic acid, L-2-pyridinecarboxylic acid, the photoinitiator is one of 2-dimethylamino-2-benzyl-1-[4-(4-morpholinyl)phenyl]-1-butanone, ethyl 2,4,6-trimethylbenzoyl phenylphosphinate, methyl benzoylformate, with a concentration of 0.001-0.05 mol / L, and the solvent is water, ethanol or acetone.

4. The flexible halogen-free highly flame-retardant polyolefin cable compound according to claim 3, characterized in that, The preparation steps of the modified polyolefin are as follows: (1) Stir the powder of low-density polyethylene, organic acid monomer and photoinitiator evenly in a solvent; (2) Place the above mixed suspension under ultraviolet light irradiation to generate free radicals for polymerization reaction. The irradiation time is 1 - 3 h, the ultraviolet light intensity is 1000 - 2000 W, and stir simultaneously; (3) After the irradiation ends, add sodium hydroxide and react for 0.5 - 2 h, then carry out vacuum filtration, wash with water and dry under vacuum for storage for later use.

5. The flexible halogen-free highly flame-retardant polyolefin cable compound according to claim 4, wherein The weight ratio of low-density polyethylene to organic acid monomer is 1:(1 - 5), and the molar ratio of the added amount of sodium hydroxide to organic acid is 5:(5 - 9).

6. The flexible halogen-free high-efficiency flame-retardant polyolefin cable material according to claim 1, characterized in that: The content of vinyl acetate in the ethylene-vinyl acetate copolymer is 26 - 35%, and the melt index is 7 - 10 g / 10min.

7. A flexible halogen-free high-efficiency flame-retardant polyolefin cable compound according to claim 1, characterized in that: The inorganic flame retardant is surface-treated magnesium hydroxide and aluminum hydroxide; the surface treatment agent of the inorganic flame retardant is one or two of sodium bis(2-ethylhexyl) phosphate and sodium bis(2-ethylhexyl) sulfosuccinate.

8. A flexible halogen-free high-efficiency flame-retardant polyolefin cable compound according to claim 1, characterized in that: The compatibilizer is one or two of maleic anhydride grafted polyethylene, ethylene-butyl acrylate copolymer and maleic anhydride grafted POE; the filler is one or a mixture of several of nano calcium carbonate, calcined kaolin, silica lime, fumed silica and talcum powder.

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