A low-smoke and halogen-free flame-retardant photovoltaic cable and its preparation method

Abstract

The present invention provides a low-smoke and halogen-free flame-retardant photovoltaic cable and a preparation method thereof, which relates to the technical field of cable processing. The preparation method includes: mixing and granulating modified polyvinyl chloride, polyethylene, ethylene propylene diene monomer rubber and additives to obtain masterbatch; melting and extruding the masterbatch to coat the surface of a conductor core to obtain a photovoltaic cable; wherein, magnesium aluminum hydrotalcite is linked to the surface of the modified polyvinyl chloride through an esterification reaction. The masterbatch obtained by the present invention is melted and extruded on the surface of the conductor core as an insulating layer. Since the modified polyvinyl chloride has better flame-retardant performance and anti-aging performance, the safety and service life of the photovoltaic cable can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cable processing, and more particularly, to a low-smoke, halogen-free, flame-retardant photovoltaic cable and a preparation method thereof. Background Art

[0002] Photovoltaic cables are special cables in solar power generation systems, mainly used for power transmission between components and between components and inverters. The basic structure of a photovoltaic cable includes: a conductor core, an insulating layer, and a sheath layer. The conductor usually uses high-purity oxygen-free copper or tin-plated copper. The material of the insulating layer is usually a polymer, and the sheath layer is made of a polymer or composite material with characteristics such as heat resistance, ultraviolet resistance, acid and alkali resistance, and moisture resistance.

[0003] According to the actual use requirements and application scenarios of photovoltaic cables, there are certain differences in the structure of photovoltaic cables, but the insulating layer is always a very important and indispensable structure in photovoltaic cables, which plays the role of protecting the core and preventing electric leakage.

[0004] Since photovoltaic cables are often used in harsh outdoor environments, such cables need to have characteristics such as high temperature resistance, ultraviolet resistance, and corrosion resistance. In addition to meeting the above performances, the fire resistance and flame retardancy of photovoltaic cables are also crucial.

[0005] As mentioned above, the insulating layer of photovoltaic cables generally uses high molecular compounds or their compositions such as polyvinyl chloride (PVC), polyethylene (PE), ethylene propylene rubber (EPR), etc. The deficiencies in the related prior art are: the fire resistance and flame retardancy of the insulating layer material are not ideal enough.

[0006] Especially for photovoltaic cables, which work in a harsh outdoor environment for a long time, after long-term use and aging of the insulating layer, the fire resistance and flame retardancy are further deteriorated, resulting in the safety of photovoltaic cables not being effectively guaranteed. Summary of the Invention

[0007] One of the problems solved by the present invention is how to provide a low-smoke, halogen-free, flame-retardant photovoltaic cable with excellent fire resistance and flame retardancy, especially after long-term use, the fire resistance and flame retardancy can still be effectively guaranteed.

[0008] To solve at least one of the above problems, the present invention provides a preparation method for a low-smoke, halogen-free, flame-retardant photovoltaic cable, including:

[0009] S1. Mixing and granulating modified polyvinyl chloride, polyethylene, ethylene propylene diene monomer, and additives to obtain masterbatch;

[0010] S2. Melting and extruding the masterbatch and coating it on the surface of the conductor core to obtain a photovoltaic cable;

[0011] Wherein, magnesium aluminum hydrotalcite is linked to the surface of the modified polyvinyl chloride through an esterification reaction.

[0012] In any of the above technical solutions, the additives include a stabilizer, a plasticizer, and an antioxidant; by mass ratio, polyvinyl chloride: polyethylene: ethylene-propylene-diene monomer rubber: stabilizer: plasticizer: antioxidant = (60 - 66):(20 - 22):(8 - 12):(2 - 4):(1 - 2):(1 - 2).

[0013] In any of the above technical solutions, the stabilizer includes at least one of the following or a combination thereof: trimethyl phosphate, barium stearate, calcium zinc dimerate.

[0014] In any of the above technical solutions, the plasticizer includes at least one of the following or a combination thereof: trioctyl trimellitate, tetraester of benzene tetracarboxylic acid, dioctyl phthalate.

[0015] In any of the above technical solutions, the antioxidant includes at least one of the following or a combination thereof: pentaerythritol ester, n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, dilauryl thiodipropionate.

[0016] In any of the above technical solutions, the mixing temperature for mixing and pelletizing is 90°C to 120°C, the mixing speed is 600 r / min to 1200 r / min, and the mixing time is 15 min to 20 min.

[0017] In any of the above technical solutions, the melting temperature for melt extrusion is 185°C to 200°C, and the melting time is 20 min to 40 min.

[0018] In any of the above technical solutions, the modified polyvinyl chloride is prepared through the following steps:

[0019] A1. Treat polyvinyl chloride with glutathione to obtain carboxylated polyvinyl chloride;

[0020] A2. Treat hydrotalcite with serine to obtain hydroxylated magnesium-aluminum hydrotalcite;

[0021] A3. Mix and heat the hydroxylated magnesium-aluminum hydrotalcite and the carboxylated polyvinyl chloride under acidic conditions to obtain the modified polyvinyl chloride.

[0022] In any of the above technical solutions, the hydroxylated magnesium-aluminum hydrotalcite undergoes chemical swelling intercalation treatment with ammonium sulfate and serine as intercalating agents, as well as ultrasonic swelling intercalation treatment.

[0023] In any of the above technical solutions, the modified polyvinyl chloride is prepared through the following steps:

[0024] B1. Dissolve glutathione in water, add triethanolamine, polyvinyl alcohol, polyvinyl chloride, and ethanol, and heat under reflux for reaction to obtain carboxylated polyvinyl chloride;

[0025] B2. Mix ammonium persulfate, serine, phosphoryl chloride, and magnesium-aluminum hydrotalcite evenly, add water for chemical swelling intercalation treatment, then dropwise add an aqueous calcium chloride solution and perform alkalization treatment to obtain hydroxylated magnesium-aluminum hydrotalcite;

[0026] B3. Add concentrated sulfuric acid, hydroxylated magnesium-aluminum hydrotalcite, and carboxylated polyvinyl chloride to ethanol, heat and apply ultrasonic waves for ultrasonic swelling intercalation treatment, and then perform a reflux reaction to obtain modified polyvinyl chloride.

[0027] In any of the above technical solutions, in B1, by mass ratio, triethanolamine: polyvinyl alcohol: glutathione: polyvinyl chloride: water: ethanol = (2 - 4): (4 - 6): (6 - 8): (20 - 30): (10 - 15): 100.

[0028] In any of the above technical solutions, in B2, by mass ratio, calcium chloride: ammonium sulfate: serine: phosphoryl chloride: magnesium-aluminum hydrotalcite = (6 - 10): (4 - 8): (60 - 80): (10 - 20): 100.

[0029] In any of the above technical solutions, in B3, by mass ratio, concentrated sulfuric acid: hydroxylated magnesium-aluminum hydrotalcite: carboxylated polyvinyl chloride: ethanol = (15 - 20): (4 - 6): 100: 300.

[0030] In any of the above technical solutions, in B1, the temperature of the reflux reaction is 80°C to 90°C, and the time is 8h to 12h.

[0031] In any of the above technical solutions, in B2, magnesium-aluminum hydrotalcite is prepared by a chemical method from magnesium salt and aluminum salt in an alkaline environment.

[0032] In any of the above technical solutions, in B3, the frequency of the ultrasonic swelling treatment is 80kHz to 120kHz, and the time is 2h to 3h.

[0033] In any of the above technical solutions, in B3, the temperature of the reflux reaction is 80°C to 90°C, and the time is 2h to 4h.

[0034] The present invention also provides a low-smoke and halogen-free flame-retardant photovoltaic cable, which is obtained by using the preparation method of any of the above technical solutions.

[0035] Beneficial effects

[0036] The present invention provides a method for preparing a low-smoke, halogen-free, flame-retardant photovoltaic cable. The method first involves mixing and granulating modified polyvinyl chloride, polyethylene, ethylene propylene diene monomer rubber, and additives to obtain masterbatch. Then, the masterbatch is melt-extruded and coated on the surface of the conductor core to obtain the photovoltaic cable. Among them, magnesium aluminum hydrotalcite is linked to the surface of the modified polyvinyl chloride through an esterification reaction.

[0037] In the first aspect, the present invention controls the basic components and ratios of the insulating layer material used in the photovoltaic cable. The three main polymer raw materials used in the insulating layer material are polyvinyl chloride, polyethylene, and ethylene propylene diene monomer rubber. As mentioned above, among many polymer materials, polyvinyl chloride has relatively excellent thermal stability, chemical stability, and mechanical strength. Polyethylene has a certain compatibility with polyvinyl chloride during the processing process. Adding an appropriate amount of polyethylene can improve the processing performance of polyvinyl chloride, enhance its fluidity and extrusion efficiency. A small amount of ethylene propylene diene monomer rubber has excellent weather resistance, which helps the insulating material maintain stable performance in harsh environments.

[0038] In the second aspect, the present invention improves the preparation process of the insulating layer material used in the photovoltaic cable. In the prior art, generally, polymer polymers such as polyvinyl chloride and polyethylene, as well as various inorganic or organic additives, are mixed, granulated, and melt-extruded together. For inorganic additives (generally flame retardants or toughening agents), the large difference in surface energy between their surfaces and the polymer surfaces is the reason for the poor dispersion performance of inorganic additives in polymer polymers. The prior art generally adopts methods such as preparing nano-sized inorganic materials, treating with coupling agents, and creating surface defects to promote the dispersion of inorganic additives in polymer polymers by changing the surface properties of inorganic additives. Different from the prior art, the present invention is committed to using magnesium aluminum hydrotalcite as an inorganic additive, and through a wet chemical process and an organic chemical reaction, hydroxyl groups and carboxyl groups are respectively aggregated on the surfaces of magnesium aluminum hydrotalcite and polyvinyl chloride. Then, under specific reaction conditions, the esterification reaction between hydroxyl groups and carboxyl groups is utilized to uniformly and stably disperse the magnesium aluminum hydrotalcite powder on the surface of polyvinyl chloride in a chemically linked manner. The above-mentioned pre-treatment method through chemical linkage ensures the uniform dispersion of magnesium aluminum hydrotalcite in polyvinyl chloride, makes it not easy to agglomerate during subsequent melt mixing, and enables the insulating material to have stable performance, not easy to age during long-term use, excellent flame retardant performance, as well as mechanical and mechanical properties, and can be maintained for a long time.

[0039] Thirdly, in order to chemically link magnesium aluminum hydrotalcite with polyvinyl chloride through an esterification reaction, the present invention needs to hydroxylate magnesium aluminum hydrotalcite and carboxylate polyvinyl chloride. Among various treatment agents capable of achieving hydroxylation or carboxylation, the present invention selects glutathione to carboxylate polyvinyl chloride and serine salt to hydroxylate hydrotalcite. Glutathione is formed by the condensation of three amino acids, namely glutamic acid, cysteine, and glycine, through peptide bonds, and it has two carboxyl groups and one mercapto group. Through a nucleophilic substitution reaction between the mercapto group and the chlorine atom of polyvinyl chloride, the carboxyl group of glutathione is introduced into the macromolecular chain of polyvinyl chloride, thereby obtaining polyvinyl chloride linked with more carboxyl groups. Serine contains an amino group, a hydroxyl group, and a carboxyl group. Among them, the hydroxyl group can be used to chemically link with carboxylated polyvinyl chloride through an esterification reaction. The carboxyl group helps serine enter the interlayer of magnesium aluminum hydrotalcite. In order to make serine combine with magnesium aluminum hydrotalcite, it is necessary to make serine enter the interlayer of magnesium aluminum hydrotalcite for intercalation. The van der Waals diameter of serine is relatively large, and the difference between the interlayer spacing of magnesium aluminum hydrotalcite and the van der Waals diameter of serine is relatively small. In order to make more serine enter the interlayer of magnesium aluminum hydrotalcite, it is necessary to further expand the interlayer spacing of magnesium aluminum hydrotalcite. The present invention grinds and mixes ammonium sulfate, serine, pyrophosphoryl chloride, and magnesium aluminum hydrotalcite evenly in acetone, and then adds a small amount of water and stands for reaction. During this process, ammonium sulfate decomposes and releases gas in an aqueous environment, and the pressure brought by the gas release drives the hydrotalcite to expand evenly, increasing the interlayer spacing. In addition, ammonium sulfate produces hydrogen ions due to the hydrolysis of ammonium ions in water, thereby creating an acidic environment. Under acidic conditions, a proton in the carboxyl group of serine will transfer to the amino group to form an ammonium ion. The further increased number of ammonium ions can exchange more with the cations in the interlayer of hydrotalcite, helping to open the interlayer spacing of hydrotalcite and promoting the intercalation of serine into hydrotalcite. In addition, by dropping calcium chloride aqueous solution and creating an alkaline environment, the interlayer cations of magnesium aluminum hydrotalcite can undergo an ion exchange reaction with calcium ions, introducing calcium ions into the interlayer. The phosphate ions generated by the hydrolysis of pyrophosphoryl chloride can increase the interlayer spacing of magnesium aluminum hydrotalcite by itself, and can also combine with calcium ions through electrostatic interaction, effectively adsorbing and capturing calcium ions into the interlayer of magnesium aluminum hydrotalcite. Therefore, the mutual cooperation of ammonium sulfate, calcium salt, and serine and the chemical intercalation treatment help to make more serine enter the interlayer of magnesium aluminum hydrotalcite. Thus, the expansion of the interlayer spacing and the combination with serine improve the dispersibility of the magnesium aluminum hydrotalcite of the present invention and make it easier to link with carboxylated polyvinyl chloride.

[0040] Fourthly, before the esterification reaction, the present invention heats up and ultrasonically expands the mixture of hydroxylated magnesium-aluminum hydrotalcite and carboxylated polyvinyl chloride. Concentrated sulfuric acid can be used as a catalyst to drive the esterification reaction under heating conditions of 80°C to 90°C, achieving the purpose of linking magnesium-aluminum hydrotalcite to the surface of modified polyvinyl chloride through the esterification reaction. The above method ensures the uniform dispersion of magnesium-aluminum hydrotalcite and avoids its agglomeration in the melting process. In addition, for polyvinyl chloride materials, hydrogen chloride is slowly released during long-term use, and hydrogen chloride can capture active free radicals, leading to the degradation of polyvinyl chloride. The uniform distribution of magnesium-aluminum hydrotalcite in polyvinyl chloride helps magnesium-aluminum hydrotalcite fully capture the hydrogen chloride generated by the degradation of polyvinyl chloride, interrupt the degradation chain reaction, thereby stabilizing polyvinyl chloride and preventing its aging. Detailed implementation manners

[0041] To make the above objects, features and advantages of the present invention more obvious and understandable, the following will be described in detail in combination with specific embodiments of the present invention.

[0042] Unless otherwise specified, the reagents and raw materials used in the present invention can be purchased through commercial channels. The experimental methods without specific conditions described in the following examples are carried out according to conventional methods and conditions, or selected according to the product instructions.

[0043] The present invention provides a method for preparing a low-smoke and halogen-free flame-retardant photovoltaic cable, and the photovoltaic cable at least includes a core and an insulating layer. For photovoltaic cables, their cores generally use high-purity oxygen-free copper or tin-plated copper, and their insulating layers are generally prepared from high-molecular compounds such as polyvinyl chloride, polyethylene, ethylene-propylene rubber or their combinations.

[0044] As an insulating material, the reason why polyvinyl chloride can be widely used in the wire and cable industry is that in addition to having sufficient electrical insulation performance, polyvinyl chloride also has relatively high strength and hardness, and can withstand a certain amount of mechanical stress, achieving the purpose of protecting the cable core.

[0045] One of the important criteria for measuring the performance of polyvinyl chloride insulating materials is the flame-retardant performance. In order to improve the fire and heat resistance of such insulating layer materials, a flame retardant can be selected and added thereto. Flame retardants generally include two types: inorganic flame retardants and organic flame retardants. Inorganic flame retardants mainly include inorganic compounds such as magnesium hydroxide, aluminum hydroxide, montmorillonite, and diatomaceous earth. Organic flame retardants mainly include halogen-based flame retardants (such as decabromodiphenyl ether, tetrabromobisphenol A, hexabromocyclododecane, etc.), phosphorus-based flame retardants (such as phosphates, phosphaphenanthrene, phosphonitrile compounds, etc.), nitrogen-based flame retardants (such as melamine, melamine cyanurate), etc.

[0046] Some flame retardant materials release smoke when burning. Since its diffusion speed is much greater than the flame spread speed, it is easy to prevent personnel from evacuating quickly and hinder fire extinguishing work. Therefore, some inorganic flame retardants with smokeless and smoke suppression effects have gradually become the focus and hot spot of research for those skilled in the art.

[0047] Among various inorganic flame retardants, magnesium-aluminum hydrotalcite is a relatively commonly used and effective one. Magnesium-aluminum hydrotalcite belongs to layered double hydroxides (LDH), which is a compound with a special layered structure. Magnesium-aluminum hydrotalcite combines the advantages of magnesium hydroxide and aluminum hydroxide flame retardants. When decomposed at high temperature, it will absorb a large amount of heat and release a large amount of water and carbon dioxide, having excellent flame retardancy and smoke suppression properties. In addition, the magnesium-aluminum oxides generated after the decomposition of hydrotalcite combine with the carbides formed during the combustion of polymer materials, and can form a protective film on the material surface to block the intrusion of oxygen, thereby enhancing the flame retardant effect.

[0048] Despite the above advantages, when magnesium-aluminum hydrotalcite is used as a flame retardant for polyvinyl chloride materials, there are also certain deficiencies.

[0049] Since hydrotalcite particles are prone to uneven dispersion in the polymer matrix, resulting in agglomeration of hydrotalcite in materials such as polyvinyl chloride and polyethylene. This not only makes it difficult to fully exert its flame retardant effect, but may also lead to a decrease in the mechanical and mechanical properties (such as tensile strength, etc.) of polymer materials and accelerate the aging rate during long-term use. Therefore, if the dispersion uniformity of magnesium-aluminum hydrotalcite in polyvinyl chloride materials can be improved, it will be helpful for improving the mechanical and mechanical properties, as well as the flame retardant properties of polyvinyl chloride insulating materials.

[0050] For the above reasons, the present invention modifies the prior art through the following technical solutions, in order to improve the flame retardant properties (especially the flame retardant properties after long-term use) of the photovoltaic cable insulating layer, and at the same time improve its mechanical and mechanical properties, thereby providing a photovoltaic cable more suitable for long-term use in harsh outdoor natural environments.

[0051] The present invention provides a method for preparing a low-smoke and halogen-free flame retardant photovoltaic cable, and the method includes:

[0052] S1. Mixing and granulating modified polyvinyl chloride, polyethylene, ethylene propylene diene monomer rubber and additives to obtain masterbatch;

[0053] S2. Melting and extruding the masterbatch and coating it on the surface of the conductor core to obtain a photovoltaic cable;

[0054] Wherein, magnesium-aluminum hydrotalcite is linked to the surface of the modified polyvinyl chloride through an esterification reaction.

[0055] The present invention preferably uses polyvinyl chloride with an average molecular weight of 50,000 - 100,000. The additives used in the present invention include stabilizers, plasticizers, and antioxidants. Among them, the functions of the above additives belong to the prior art, and the present invention will not elaborate herein.

[0056] Regarding the component ratio, preferably, by mass ratio, polyvinyl chloride: polyethylene: ethylene-propylene-diene rubber: stabilizer: plasticizer: antioxidant = (60 - 66): (20 - 22): (8 - 12): (2 - 4): (1 - 2): (1 - 2).

[0057] It can be understood that in the insulating material of the present invention, the main raw material is polyvinyl chloride. Appropriate polyethylene can improve the processing performance of polyvinyl chloride, enhance its fluidity and extrusion efficiency, and a small amount of ethylene-propylene-diene rubber is used to improve the weather resistance of the insulating material. The above ratio enables the insulating material of the present invention to remain relatively stable under extreme outdoor climate conditions, so it is more suitable for application in photovoltaic cables; and it is easy to process and form, with a relatively wide process window for melting and extrusion.

[0058] In the present invention, the modified polyvinyl chloride is prepared through the following steps:

[0059] A1. Treat polyvinyl chloride with glutathione to obtain carboxylated polyvinyl chloride;

[0060] A2. Treat hydrotalcite with serine to obtain hydroxylated magnesium-aluminum hydrotalcite;

[0061] A3. Mix and heat the hydroxylated magnesium-aluminum hydrotalcite and carboxylated polyvinyl chloride under acidic conditions to obtain modified polyvinyl chloride.

[0062] Specifically, in A1, the method of treating polyvinyl chloride with glutathione is as follows: Dissolve glutathione in water, add triethanolamine, polyvinyl alcohol, polyvinyl chloride, and ethanol, and heat under reflux for reaction to obtain carboxylated polyvinyl chloride. After obtaining carboxylated polyvinyl chloride, the solvent can be removed under negative pressure, and the solvent and acid-binding agent can be recycled. Preferably, by mass ratio, triethanolamine: polyvinyl alcohol: glutathione: polyvinyl chloride: water: ethanol = (2 - 4): (4 - 6): (6 - 8): (20 - 30): (10 - 15): 100. The temperature of the heating reflux reaction is preferably 80°C to 90°C, and the time is 8h to 12h.

[0063] Glutathione is formed by the condensation of three amino acids, namely glutamic acid, cysteine, and glycine, through peptide bonds, and it has two carboxyl groups and one mercapto group. In the above steps, triethanolamine and polyvinyl alcohol are used as acid-binding agents, and ethanol is mainly used as the reaction medium. Through heating under reflux, the mercapto group of glutathione undergoes a nucleophilic substitution reaction with the chlorine atom of polyvinyl chloride, thereby introducing the carboxyl group of glutathione into the macromolecular chain of polyvinyl chloride to obtain polyvinyl chloride linked with carboxyl groups.

[0064] In A2, the preparation method of the hydrotalcite used is as follows: using magnesium salt and aluminum salt as raw materials, it is prepared by a chemical method in an alkaline environment. The specific steps are as follows. According to the mass ratio of magnesium chloride: aluminum nitrate: water = (10 - 15): (20 - 25): 100, magnesium chloride and aluminum nitrate are dispersed evenly in water to obtain a magnesium-aluminum salt solution; an aqueous solution of alkali metal hydroxide with a concentration of 6wt% to 12wt% is added dropwise to the magnesium-aluminum salt solution and stirred until the pH value reaches 10 to 12. After standing and aging for 2h to 4h, the solid matter is filtered, washed, and dried to obtain magnesium-aluminum hydrotalcite; among them, the aqueous solution of alkali metal hydroxide is an aqueous solution of sodium hydroxide or potassium hydroxide.

[0065] In A2, the method of treating the hydrotalcite with serine is as follows: ammonium persulfate, serine, pyrophosphoryl chloride, and magnesium-aluminum hydrotalcite are mixed evenly, then water is added for chemical swelling intercalation treatment, and then an aqueous solution of calcium chloride is added dropwise and alkalization treatment is carried out to obtain hydroxylated magnesium-aluminum hydrotalcite. Preferably, by mass ratio, calcium chloride: ammonium sulfate: serine: pyrophosphoryl chloride: magnesium-aluminum hydrotalcite = (6 - 10): (4 - 8): (60 - 80): (10 - 20): 100

[0066] The purpose of the above steps is to intercalate serine into the interlayer of magnesium-aluminum hydrotalcite. Considering that the interlayer distance of magnesium-aluminum hydrotalcite is about 0.77nm and the van der Waals diameter of serine is more than 0.56nm, and the size difference between the two is small. In order to make more serine enter the interlayer of magnesium-aluminum hydrotalcite, it is necessary to further open the interlayer distance of magnesium-aluminum hydrotalcite. For this reason, in the present invention, ammonium sulfate, serine, pyrophosphoryl chloride, and magnesium-aluminum hydrotalcite are mixed in a certain proportion, ground and mixed evenly in a sufficient amount of acetone and then taken out. After taking out, it can be directly added with a small amount of water and left standing for reaction without washing. During this process, ammonium sulfate chemically intercalates magnesium-aluminum hydrotalcite, promoting the entry of ammonium ions and serine into the interlayer of magnesium-aluminum hydrotalcite. Serine will also further release intercalatable ammonium ions in the acidic environment of ammonium sulfate. The addition of calcium chloride enables ammonium sulfate, calcium salt, and serine to cooperate with each other, and through chemical intercalation treatment, calcium ions also help more serine enter the interlayer of magnesium-aluminum hydrotalcite.

[0067] In A3, the method of mixing and heating magnesium aluminum hydroxylated hydrotalcite and carboxylated polyvinyl chloride under acidic conditions for an esterification reaction is as follows: concentrated sulfuric acid, magnesium aluminum hydroxylated hydrotalcite, and carboxylated polyvinyl chloride are added to ethanol, heated, and ultrasonic waves are applied for ultrasonic swelling and intercalation treatment, and then heated under reflux for reaction to obtain modified polyvinyl chloride. Preferably, by mass ratio, concentrated sulfuric acid: magnesium aluminum hydroxylated hydrotalcite: carboxylated polyvinyl chloride: ethanol = (15 - 20): (4 - 6): 100: 300. Preferably, the frequency of the ultrasonic swelling treatment is 80 kHz to 120 kHz, and the time is 2 h to 3 h. The temperature of the heating under reflux reaction is 80 °C to 90 °C, and the time is 2 h to 4 h.

[0068] The low-temperature heating and ultrasonic swelling before esterification are to further optimize the intercalation effect. Driving the occurrence of the esterification reaction under the heating condition of 80 °C to 90 °C can achieve the purpose of connecting magnesium aluminum hydrotalcite to the surface of the modified polyvinyl chloride through the esterification reaction. Preferably, in the esterification reaction, a water-carrying agent can be used to dehydrate in a timely manner. The water-carrying agent can be molecular sieve or an organic water-carrying agent such as cyclohexane.

[0069] After obtaining the modified polyvinyl chloride, the granulation and melting processes can be carried out using existing technologies. The specifications and models of the stabilizer, plasticizer, and antioxidant can be selected and adjusted by those skilled in the art. Exemplarily, the stabilizer includes at least one of the following or a combination thereof: trimethyl phosphate, barium stearate, calcium zinc dimer acid. The plasticizer includes at least one of the following or a combination thereof: trioctyl trimellitate, tetraester of benzene tetracarboxylic acid, dioctyl phthalate. The antioxidant includes at least one of the following or a combination thereof: pentaerythritol ester, n-octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, dilauryl thiodipropionate.

[0070] The mixing and granulation of the modified polyvinyl chloride, polyethylene, ethylene propylene diene monomer, and additives can be carried out using a mixer and granulation equipment. The size of the granulation is preferably 0.5 mm to 2 mm. The melt extrusion is carried out using a melting equipment and a screw extrusion equipment. The temperature range of the melting equipment and the rotation speed of the screw extrusion equipment can be selected and adjusted by those skilled in the art.

[0071] Preferably, the mixing temperature for mixing and granulation is 90 °C to 120 °C, the mixing speed is 600 r / min to 1200 r / min, and the mixing time is 15 min to 20 min. The melting temperature for melt extrusion is 185 °C to 200 °C, and the melting time is 20 min to 40 min.

[0072] In the process of melt extruding the masterbatch to coat the surface of the conductor wire core, the conductor wire core used can be obtained through the following steps:

[0073] B1. Screening the conductive metal blank;

[0074] B2. Draw the screened conductive metal blank into a bare wire;

[0075] B3. Strands the bare wires to form a wire core;

[0076] Among them, the conductive metal blank is preferably industrial pure copper. The screening criteria for B1 are as follows: through image detection combined with manual screening, obtain a conductive metal blank without defects such as oxidation, burrs, and cracks on the surface. The wire drawing step of B2 includes: using a wire drawing machine to stretch the conductive metal blank in stages to a metal wire with a target diameter (preferably 0.1 mm to 0.4 mm); after stretching, send the metal wire into a steam chamber, and the temperature in the steam chamber is controlled at 78 °C to 80 °C, and keep it warm in the steam chamber for 2 h to 3 h; then use an annealing furnace to anneal the metal wire at a temperature of 550 °C to 650 °C for 2 h to 4 h; finally, clean the oil stains and dust to obtain a bare wire. In B3, the number of bare wires required to strand and form a wire core can be determined by those skilled in the art according to actual needs.

[0077] It can be understood that after coating the insulating material on the surface of the conductor wire core, a cable coated with an insulating layer is obtained. Those skilled in the art can continue to apply or fill other materials outside the cable according to actual needs. For example, in order to protect the cable, a sheath layer needs to be wrapped outside the insulating layer. In addition, the photovoltaic cable may further include a shielding layer located between the insulating layer and the sheath layer. The shielding layer is mainly used to reduce electromagnetic interference, and the shielding material can be copper wire, aluminum wire, steel wire, etc. A filling layer can also be filled inside the sheath layer. The filling layer is mainly used to make the cable round and stable in structure. Some fillers also have water-blocking and flame-retardant functions. Commonly used materials include polypropylene ropes, fiberglass ropes, asbestos ropes, etc. In addition, other structures such as a puncture-resistant layer, an armor layer, and a waterproof layer can be provided between the insulating layer and the sheath layer. The sheath layer can be one layer or two layers including an inner sheath layer and an outer sheath layer.

[0078] Example 1

[0079] In this example, a magnesium-aluminum hydrotalcite sample was prepared, and the preparation steps are as follows:

[0080] 1. Disperse magnesium chloride and aluminum nitrate in distilled water according to the mass ratio of magnesium chloride: aluminum nitrate: water = 10:20:100, and stir evenly with magnetic force to obtain a magnesium-aluminum salt solution;

[0081] 2. Drop an 8 wt% aqueous sodium hydroxide solution into the magnesium-aluminum salt solution and stir until the pH value reaches 11. Let it stand for 2 h, then filter the solid matter, wash it once with ethanol and twice with water, and dry it by infrared at 110 °C to obtain magnesium-aluminum hydrotalcite sample 1.

[0082] Example 2

[0083] In this example, a magnesium-aluminum hydrotalcite sample was prepared, and the preparation steps are as follows:

[0084] 1. Magnesium chloride and aluminum nitrate were dispersed in distilled water according to the mass ratio of magnesium chloride: aluminum nitrate: water = 15:25:100, and magnetically stirred evenly to obtain a magnesium-aluminum salt solution;

[0085] 2. A 6wt% aqueous sodium hydroxide solution was added dropwise to the magnesium-aluminum salt solution and stirred until the pH value reached 11. After standing and aging for 4 h, the solid was filtered, washed once with ethanol and twice with water, and dried by infrared at 110 °C to obtain magnesium-aluminum hydrotalcite sample 2.

[0086] Example 3

[0087] In this example, a carboxylated polyvinyl chloride sample was prepared, and the preparation steps are as follows:

[0088] 1. Glutathione was dissolved in water according to the mass ratio of triethanolamine: polyvinyl alcohol: glutathione: polyvinyl chloride: water: ethanol = 2:6:6:20:10:100, and then triethanolamine, polyvinyl alcohol, polyvinyl chloride and ethanol were added and mixed evenly to obtain a first mixture;

[0089] 2. The first mixture was heated under reflux at 85 °C for 10 h to remove the solvent. The reaction product was washed once with ethanol, twice with water, and dried by hot air at 80 °C to obtain carboxylated polyvinyl chloride sample 1.

[0090] Example 4

[0091] In this example, a carboxylated polyvinyl chloride sample was prepared, and the preparation steps are as follows:

[0092] 1. Glutathione was dissolved in water according to the mass ratio of triethanolamine: polyvinyl alcohol: glutathione: polyvinyl chloride: water: ethanol = 4:4:8:30:15:100, and then triethanolamine, polyvinyl alcohol, polyvinyl chloride and ethanol were added and mixed evenly to obtain a first mixture;

[0093] 2. The same as step 2 of Example 3 to obtain carboxylated polyvinyl chloride sample 2.

[0094] Example 5

[0095] In this example, a hydroxylated magnesium-aluminum hydrotalcite sample was prepared, and the preparation steps are as follows:

[0096] 1. Mix ammonium persulfate, serine, phosphoryl chloride, and the magnesium-aluminum hydrotalcite sample 1 prepared in Example 1 in a mass ratio of ammonium persulfate:serine:phosphoryl chloride:magnesium-aluminum hydrotalcite = 4:60:15:100. Use sufficient acetone and zirconia balls as the medium, and conduct wet grinding for 2 h through a planetary ball mill. After grinding, separate the solid matter to obtain a second mixture.

[0097] 2. First, mix the ground second mixture with water in a mass ratio of water:second mixture = 10:100, and let it stand for 2 h. Then, prepare a 55 wt% calcium chloride aqueous solution with calcium chloride in a mass ratio of calcium chloride:magnesium-aluminum hydrotalcite = 6:100. According to the addition amount of magnesium-aluminum hydrotalcite in the second mixture, dropwise add the calcium chloride aqueous solution to the second mixture and stir well. After dropping, adjust the pH to 10, let it stand for 2 h, then separate the solid matter, wash it twice with water, and conduct infrared drying below 100 °C to obtain the hydroxylated magnesium-aluminum hydrotalcite sample 1.

[0098] Example Six

[0099] In this example, a hydroxylated magnesium-aluminum hydrotalcite sample was prepared, and the preparation steps are as follows:

[0100] 1. Mix ammonium persulfate, serine, phosphoryl chloride, and the magnesium-aluminum hydrotalcite sample 2 prepared in Example 2 in a mass ratio of ammonium persulfate:serine:phosphoryl chloride:magnesium-aluminum hydrotalcite = 8:80:15:100. Use sufficient acetone and zirconia balls as the medium, and conduct wet grinding for 2 h through a planetary ball mill. After grinding, separate the solid matter to obtain a second mixture.

[0101] 2. First, mix the ground second mixture with water in a mass ratio of water:second mixture = 20:100, and let it stand for 2 h. Then, prepare a 55 wt% calcium chloride aqueous solution with calcium chloride in a mass ratio of calcium chloride:magnesium-aluminum hydrotalcite = 10:100. According to the addition amount of magnesium-aluminum hydrotalcite in the second mixture, dropwise add the calcium chloride aqueous solution to the second mixture and stir well. After dropping, adjust the pH to 10, let it stand for 2 h, then separate the solid matter, wash it twice with water, and conduct infrared drying below 100 °C to obtain the hydroxylated magnesium-aluminum hydrotalcite sample 2.

[0102] Example Seven

[0103] In this example, a modified polyvinyl chloride sample was prepared, and the preparation steps are as follows:

[0104] According to the mass ratio of concentrated sulfuric acid: magnesium aluminum hydroxylated hydrotalcite: carboxylated polyvinyl chloride: ethanol = 15:5:100:300, concentrated sulfuric acid, the magnesium aluminum hydroxylated hydrotalcite sample 1 of Example 5, and the carboxylated polyvinyl chloride sample 1 of Example 3 were added to ethanol. First, the temperature was raised to 50 °C and stirred for 1 h, then ultrasonic expansion treatment was carried out at a frequency of 100 kHz for 2 h, and finally, heating reflux reaction was carried out at 80 °C for 3 h. After the reaction, the solid was separated, washed twice with acetone, washed twice with water, and dried by infrared drying below 100 °C to obtain the modified polyvinyl chloride sample 1.

[0105] Example 8

[0106] In this example, a modified polyvinyl chloride sample was prepared. The preparation steps were the same as those in Example 7, except that the magnesium aluminum hydroxylated hydrotalcite used was the magnesium aluminum hydroxylated hydrotalcite sample 2 of Example 6, and the carboxylated polyvinyl chloride used was the modified polyvinyl chloride sample 2 of Example 4.

[0107] Example 9

[0108] In this example, a polyvinyl chloride insulating material was prepared, and its preparation steps were as follows:

[0109] 1. According to the mass ratio of polyvinyl chloride: polyethylene: ethylene propylene diene monomer: trimethyl phosphate: dioctyl phthalate: dilauryl thiodipropionate = 65:20:10:2:2:1, using the modified polyvinyl chloride sample 1 obtained in Example 7, the above raw materials were fed into a mixer and kneaded at 100 °C at a speed of 600 r / min for 20 min, and then extruded and granulated to obtain masterbatch between 0.5 mm and 1 mm;

[0110] 2. The masterbatch was fed into a melting device, melted in the temperature range of 185 °C to 200 °C for 20 min, and extruded by a single-screw device to obtain the polyvinyl chloride insulating material sample 1.

[0111] It can be understood that if the extruded material is coated on the surface of an industrial pure copper conductor core in the above step 2, a photovoltaic cable can be obtained. In this example, in order to test the performance of the polyvinyl chloride insulating material, it was directly extruded and then cooled and formed.

[0112] Example 10

[0113] In this example, a polyvinyl chloride insulating material was prepared. The preparation steps were the same as those in Example 9, except that the modified polyvinyl chloride sample 2 obtained in Example 8 was used to obtain the polyvinyl chloride insulating material sample 2.

[0114] Comparative Example 1

[0115] In this comparative example, a polyvinyl chloride insulating material sample 3 was prepared, and its preparation process was as follows:

[0116] 1. According to the mass ratio of magnesium aluminum hydrotalcite: polyvinyl chloride: polyethylene: ethylene propylene diene monomer: trimethyl phosphate: dioctyl phthalate: dilauryl thiodipropionate = 3:65:20:10:2:2:1, use the magnesium aluminum hydrotalcite sample 1 of Example 1 and other commercially purchased raw materials and feed them into a mixer. At 100 °C, mix them at a rotation speed of 600 r / min for 20 min, and extrude and pelletize to obtain masterbatch between 0.5 mm and 1 mm.

[0117] 2. Feed the masterbatch into a melting device, melt it in the temperature range of 185 °C to 200 °C for 20 min, and extrude it with a single-screw device to obtain polyvinyl chloride insulating material sample 3.

[0118] Comparative Example 2

[0119] This comparative example prepared a polyvinyl chloride insulating material sample 4, and its preparation process is as follows:

[0120] 1. According to the mass ratio of serine: magnesium aluminum hydrotalcite = 60:100, mix serine and the magnesium aluminum hydrotalcite sample 1 prepared in Example 1, use sufficient acetone, use zirconia balls as the medium, and carry out wet grinding for 2 h through a planetary ball mill. After the grinding is completed, separate the solid matter to obtain a second mixture.

[0121] 2. According to the mass ratio of calcium chloride: magnesium aluminum hydrotalcite = 6:100, prepare a 55 wt% calcium chloride aqueous solution with calcium chloride, and according to the addition amount of magnesium aluminum hydrotalcite in the second mixture, drop the calcium chloride aqueous solution into the second mixture and stir well. After the dropping is completed, adjust the pH to 10, let it stand for 2 h, then separate the solid matter, wash it twice with water, and dry it by infrared drying below 100 °C to obtain the magnesium aluminum hydrotalcite for use in the following steps.

[0122] 3. According to the mass ratio of concentrated sulfuric acid: magnesium aluminum hydrotalcite: carboxylated polyvinyl chloride: ethanol = 15:5:100:300, add concentrated sulfuric acid, the magnesium aluminum hydrotalcite obtained in step 2 of this comparative example, and the carboxylated polyvinyl chloride sample 1 of Example 3 into ethanol, heat and reflux at 80 °C for 3 h. After the reaction is completed, separate the solid matter, wash it twice with acetone, wash it twice with water, and dry it by infrared drying below 100 °C to obtain the polyvinyl chloride for use in the following steps.

[0123] 4. According to the mass ratio of polyvinyl chloride: polyethylene: ethylene propylene diene monomer: trimethyl phosphate: dioctyl phthalate: dilauryl thiodipropionate = 65:20:10:2:2:1, feed the above raw materials into a mixer, mix them at 100 °C at a rotation speed of 600 r / min for 20 min, and extrude and pelletize to obtain masterbatch between 0.5 mm and 1 mm.

[0124] 5. Feed the mother into the melting equipment, melt it in the temperature range of 185°C to 200°C for 20 minutes, and extrude it with a single-screw equipment to obtain sample 4 of polyvinyl chloride insulating material.

[0125] Performance testing

[0126] The present invention tests the performance of samples 1 to 4 of vinyl chloride insulating materials. The detection standards for tensile strength and elongation at break refer to GB / T 1701-2001. The detection standard for limiting oxygen index refers to GB / T 2406.1-2008. The detection standard for thermal conductivity refers to GB / T 6344-2008. The conditions for the accelerated aging test are to treat the samples under the temperature condition of 110°C, the humidity condition of 80%RH, and the ultraviolet irradiation of 365nm with 600W for 144h. The results of the above performance tests are shown in Table 1.

[0127] Table 1

[0128]

[0129] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A method for preparing a low-smoke halogen-free flame-retardant photovoltaic cable, characterized in that: include: S1, mixing and granulating modified polyvinyl chloride, polyethylene, EPDM rubber and additives to obtain masterbatch; S2, melt-extrude the masterbatch and coat it on the surface of the conductor core to obtain the photovoltaic cable; Wherein, the surface of the modified polyvinyl chloride is linked with magnesium aluminum hydrotalcite through an esterification reaction; The modified polyvinyl chloride is prepared by the following steps: A1. Treating polyvinyl chloride with glutathione to obtain carboxylated polyvinyl chloride; A2. Treating hydrotalcite with serine to obtain hydroxylated magnesium aluminum hydrotalcite; the hydroxylated magnesium aluminum hydrotalcite is subjected to chemical expansion intercalation treatment using ammonium persulfate and the serine as intercalation agents, and ultrasonic expansion intercalation treatment; A3. Mixing and heating the hydroxylated magnesium aluminum hydrotalcite and the carboxylated polyvinyl chloride under acidic conditions to obtain the modified polyvinyl chloride.

2. The preparation method according to claim 1, characterized in that: The auxiliary agents include stabilizers, plasticizers and antioxidants; in terms of mass ratio, polyvinyl chloride: polyethylene: EPDM rubber: stabilizer: plasticizer: antioxidant = (60-66): (20-22): (8-12): (2-4): (1-2): (1-2).

3. The preparation method according to claim 2, characterized in that: The stabilizer comprises at least one of the following or a combination thereof: trimethyl phosphate, barium stearate, calcium zinc dimer acid; and / or The plasticizer comprises at least one of the following or a combination thereof: trioctyl trimellitate, tetramethyl pyromellitate, dioctyl phthalate; and / or The antioxidant comprises at least one of the following or a combination thereof: pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and dilauryl thiodipropionate.

4. The preparation method according to claim 1, characterized in that: The mixing temperature of the mixing and granulation is 90° C. to 120° C., the mixing speed is 600 r / min to 1200 r / min, and the mixing time is 15 min to 20 min; and / or The melt extrusion has a melting temperature of 185° C. to 200° C. and a melting time of 20 min to 40 min.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The modified polyvinyl chloride is prepared by the following steps: B1. Dissolve glutathione in water, add triethanolamine, polyvinyl alcohol, polyvinyl chloride and ethanol, heat and reflux to obtain carboxylated polyvinyl chloride; B2, after ammonium persulfate, serine, pyrophosphoryl chloride and magnesium aluminum hydrotalcite are uniformly mixed, water is added for chemical expansion and intercalation treatment, and then calcium chloride aqueous solution is added dropwise and alkalization treatment is performed to obtain hydroxylated magnesium aluminum hydrotalcite; B3, adding concentrated sulfuric acid, the hydroxylated magnesium aluminum hydrotalcite and the carboxylated polyvinyl chloride into ethanol, heating and applying ultrasound to perform ultrasonic expansion and intercalation treatment, and then heating and refluxing to obtain the modified polyvinyl chloride.

6. The preparation method according to claim 5, characterized in that: In B1, by mass ratio, triethanolamine:polyvinyl alcohol:glutathione:polyvinyl chloride:water:ethanol=(2-4):(4-6):(6-8):(20-30):(10-15):100; and / or In B2, by mass ratio, calcium chloride: ammonium persulfate: serine: pyrophosphoryl chloride: magnesium aluminum hydrotalcite = (6-10): (4-8): (60-80): (10-20): 100; and / or In B3, the mass ratio is: concentrated sulfuric acid: hydroxylated magnesium aluminum hydrotalcite: carboxylated polyvinyl chloride: ethanol = (15-20): (4-6): 100:

300.

7. The preparation method according to claim 6, characterized in that: In B1, the heating reflux reaction temperature is 80° C. to 90° C., and the time is 8 h to 12 h; and / or In B2, the magnesium aluminum hydrotalcite is prepared by a chemical method in an alkaline environment using magnesium salt and aluminum salt as raw materials; and / or In B3, the frequency of the ultrasonic expansion treatment is 80kHz to 120kHz, and the time is 2h to 3h; and / or In B3, the heating reflux reaction temperature is 80° C. to 90° C., and the time is 2 h to 4 h.

8. A low-smoke, halogen-free, flame-retardant photovoltaic cable, characterized in that: The low-smoke halogen-free flame-retardant photovoltaic cable is obtained by the preparation method according to any one of claims 1 to 7.

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