Low-smoke low-corrosion flame-retardant PVC sheath, cable and preparation method thereof

Abstract

This invention provides a low-smoke, low-corrosion, flame-retardant PVC sheath material, a cable, and a method for preparing the same. The sheath material comprises: PVC, core-shell flame-retardant buffer particles, a plasticizing system, a stabilizing lubricating system, a coupling agent, and commonly used processing aids. The core-shell flame-retardant buffer particles have a core-multilayer shell structure consisting of a basic calcium hydroxyaluminate carbonate core, a phytic acid / chitosan / silica hybrid first shell, and a rare-earth yttrium stannate second shell. Under the formulation and process conditions of this invention, the cable made from the sheath material exhibits low smoke density, increased pH and decreased conductivity of the combustion acid gas condensate in a bundled combustion test, and significantly reduced copper conductor corrosion, while maintaining good tensile strength, elongation at break, and volume resistivity. This invention is suitable for applications with high requirements for post-fire corrosion and smoke safety, such as construction, power, and rail transportation.

Description

Technical Field

[0001] This invention belongs to the field of cable technology, specifically relating to a low-smoke, low-corrosion, flame-retardant PVC sheath cable and its preparation method. Background Technology

[0002] Currently, polyvinyl chloride (PVC) sheathed cables remain widely used in building power distribution, industrial control, and public facility wiring due to their low cost, good processability, and relatively balanced mechanical properties and weather resistance. However, traditional PVC sheaths release large amounts of acidic gases such as HCl and produce high-density black smoke when burned. This not only severely impairs visibility during evacuation and rescue operations but also exhibits strong corrosiveness to copper conductors, metal cable trays, and surrounding equipment. Post-fire residual corrosion losses often far exceed the value of the cable itself. Therefore, achieving a flame-retardant sheath with "low smoke and low corrosion" while retaining the processing and cost advantages of the PVC system has always been a technical challenge in this field.

[0003] To improve the flame retardant and smoke-suppressing properties of PVC, various low-smoke flame-retardant PVC formulations have been proposed in existing technologies. The main approaches include: introducing inorganic flame-retardant fillers such as magnesium hydroxide, aluminum hydroxide, and layered double hydroxides into PVC; supplementing with inorganic synergists containing boron, tin, or molybdenum; or combining with nitrogen-phosphorus intumescent flame retardants to form a dense char layer during combustion, reducing the heat release rate and smoke density. However, these systems generally suffer from the following problems: First, achieving a high flame retardant rating often requires a high total filler content, leading to a significant increase in PVC melt viscosity, difficulty in extrusion molding, and increased sheath hardness, decreased bending performance, and fatigue resistance. Second, most formulations focus on "flame retardancy" and "low smoke," lacking specific design for the corrosive indicators such as pH value and conductivity of combustion acid gases. Even if low-halogen or low-smoke standards are met, long-term corrosion of copper conductors and metal components during a fire remains severe.

[0004] For example, Chinese patent CN107987412B discloses a low-smoke, high-flame-retardant PVC electrical conduit and its formulation. The formulation uses PVC resin as the matrix, introduces chlorinated polyethylene as a toughening and modifying component, and uses magnesium hydroxide and aluminum hydroxide as fillers. At the same time, it adopts a multi-component compound flame-retardant system such as zinc borate, zinc stannate, ammonium molybdate, nano clay, aminoguanidine phosphate and ammonium polyphosphate, combined with calcium-zinc composite stabilizing lubricant and plasticizer, to obtain electrical conduit material with low smoke density and high flame retardant rating. This type of technical solution improves the flame retardant and smoke suppression performance of PVC sheaths to some extent through a complex inorganic flame retardant synergistic system, but it still has the following technical limitations: First, its core design still relies on the hydrogen halide gas released by PVC in the flame to participate in the flame retardant synergy, and lacks effective buffering and fixation measures for acidic gases such as HCl. Therefore, under the condition of meeting the conventional combustion test, the corrosion indicators such as pH and conductivity of the condensate are still deviated. Second, the high total amount of various inorganic flame retardants and fillers inevitably weakens the flexibility and processing fluidity of the material, resulting in a narrow formulation window and making it difficult to balance flame retardant performance with mechanical and electrical performance in cable sheaths of different specifications. Third, the above-mentioned flame retardant system mainly focuses on flame retardant efficiency and does not construct a structured filler with acid gas buffering function to address the coupled requirements of "low smoke" and "low corrosion".

[0005] Furthermore, most low-smoke halogen-free cables on the market use halogen-free materials such as cross-linked polyolefins as sheaths, fundamentally reducing acid corrosion and smoke toxicity by completely eliminating halogens. However, these products are costly, and their processing technology is not fully compatible with existing PVC cable production lines. For traditional cable manufacturers that heavily rely on PVC sheaths, the overall switch is quite difficult. Therefore, while maintaining the PVC sheath system, how to design core-shell functional particles with synergistic effects of acid gas buffering, charring, and smoke suppression, and achieve acid gas corrosion indices of the PVC sheath close to or even partially reach the level of low-smoke halogen-free cables with a relatively mild filler dosage, while also considering flame retardancy, low smoke, and the mechanical and electrical properties required for the cable sheath, remains a technical problem that has not yet been effectively solved by existing technologies. Summary of the Invention

[0006] The technical objective of this invention is to significantly reduce the corrosiveness of flue gas generated during cable combustion while taking into account both flame retardant performance and the mechanical and electrical properties of the sheath by constructing a core-shell type functional particle formulation that combines flame retardancy, smoke suppression, and acid gas buffering functions.

[0007] To achieve the above-mentioned technical objectives, the present invention provides the following technical solutions.

[0008] In a first aspect, the present invention discloses a low-smoke, low-corrosion, flame-retardant PVC sheathing material, which is composed of the following components in parts by weight:

[0009] a) 100 parts of PVC matrix;

[0010] b) 25-55 parts of core-shell flame-retardant buffer particles, wherein the core-shell flame-retardant buffer particles are core-multi-layer shell structure particles with flame-retardant, smoke-suppressing, and acid gas buffering functions, including:

[0011] b1) The core layer is basic calcium hydroxyaluminate carbonate, wherein the basic calcium hydroxyaluminate carbonate is... System basic salt;

[0012] b2) The first shell layer, which covers the outer surface of the core layer, is an organic-inorganic hybrid layer composed of phytic acid, chitosan and SiO2, wherein the mass ratio of phytic acid, chitosan and SiO2 solids is 1.0-1.8:0.8-1.5:1.0-2.0.

[0013] b3) Second shell layer, yttrium stannate rare earth element covering the outer surface of the first shell layer. Nanoparticles The mass fraction of the core-shell flame-retardant buffer particles is 5-20% of the total mass.

[0014] The mass ratio of the core layer, the first shell layer and the second shell layer is 50-70:20-35:5-15, and the median particle size D50 of the core-shell flame-retardant buffer particles is 0.5-3.0 μm.

[0015] c) 30-50 parts of the plasticizer system;

[0016] d) Stabilize the lubrication system by 3 to 10 parts;

[0017] e) 0.3–1.5 parts of coupling agent;

[0018] f) 0.2–1.0 parts of antioxidant;

[0019] g) 0 to 5 parts of processing aids may be selected, which may be processing aids, pigments and / or inert fillers.

[0020] Preferably, the PVC is suspension PVC with a K value of 65-70, and it can be further blended with chlorinated polyethylene and ethylene-vinyl acetate copolymer, with the mass ratio of PVC:chlorinated polyethylene:ethylene-vinyl acetate copolymer being 90-96:2-5:2-5.

[0021] Preferably, the plasticizing system comprises triethyl citrate, an aliphatic polyester plasticizer, and epoxidized soybean oil, wherein the mass fraction ratio of triethyl citrate, aliphatic polyester plasticizer, and epoxidized soybean oil is 35-55:25-45:10-25.

[0022] Preferably, the stable lubrication system includes an organic calcium-zinc composite stabilizer, polyethylene wax, and liquid paraffin, wherein the mass fraction ratio of the organic calcium-zinc composite stabilizer to polyethylene wax to liquid paraffin is 40-60:20-40:10-20.

[0023] Preferably, the coupling agent is γ-aminopropyltriethoxysilane, and the antioxidant is a hindered phenolic antioxidant.

[0024] In a second aspect, the present invention discloses a low-smoke, low-corrosion, flame-retardant cable, comprising: a conductor, an insulation layer covering the conductor, and a sheath layer covering the insulation layer, wherein the sheath layer is obtained by extrusion molding of the low-smoke, low-corrosion, flame-retardant PVC sheath material described in the first aspect.

[0025] Preferably, the cable is a 0.6 / 1kV multi-core power cable, further comprising a filler layer between each insulated core and / or a metal shielding layer wrapped around each insulated core, wherein the average thickness of the sheath layer is 1.4–3.0 mm.

[0026] Thirdly, this invention discloses a method for preparing core-shell flame-retardant buffer particles, comprising the following steps:

[0027] S1, basic calcium hydroxyaluminate carbonate is dispersed in an aqueous phase, phytic acid and chitosan are added, and the pH is adjusted to 3-6 under stirring conditions, so that phytic acid and chitosan undergo electrostatic self-assembly and complexation deposition on the surface of basic calcium hydroxyaluminate carbonate to obtain a suspension of basic calcium hydroxyaluminate carbonate with an organic layer.

[0028] S2, silica sol is added to the suspension obtained in step S1 and aged at 40-80°C for 0.5-4 hours to allow silica to further condense and form a first shell layer coating the surface of the basic calcium hydroxyaluminate carbonate. The mass ratio of phytic acid, chitosan and silica solids is controlled at 1.0-1.8:0.8-1.5:1.0-2.0.

[0029] S3, Y2Sn2O7 nanoparticles are dispersed in the slurry of step S2, and Y2Sn2O7 is uniformly adsorbed on the outer surface of the first shell by mechanical stirring and / or ultrasonic dispersion. The mass fraction of Y2Sn2O7 in the total mass of the obtained particles is adjusted to 5-20%. After spray drying or filtration-drying, core-shell flame-retardant buffer particles with a core-multilayer shell structure and a volume fraction median particle size D50 of 0.5-3.0 μm are obtained.

[0030] Fourthly, this invention discloses a method for preparing a low-smoke, low-corrosion, flame-retardant PVC sheath material, comprising the following steps:

[0031] T1, Core-shell flame-retardant buffer particles are prepared according to the method described in the third aspect;

[0032] T2, add PVC and the core-shell flame-retardant buffer particles obtained in step T1 into a high-speed mixer and dry mix at 60-120°C for 3-15 minutes to make the core-shell flame-retardant buffer particles uniformly adhere to the surface of the resin particles.

[0033] T3, add plasticizer, stabilizing lubricant, coupling agent, antioxidant and optional processing aid to the dry mix in step T2, and continue mixing for 3 to 10 minutes to obtain premix;

[0034] T4. The premixed material from step T3 is fed into a melt-mixing equipment, melt-mixed and extruded at 150-185°C, and granulated to obtain the low-smoke, low-corrosion, flame-retardant PVC sheath material as described in any one of claims 1-5.

[0035] Fifthly, this invention discloses a method for preparing a low-smoke, low-corrosion, flame-retardant cable, comprising the following steps:

[0036] U1, the conductor is stranded and annealed according to conventional processes, and then insulation material is extruded to form an insulated wire core;

[0037] U2, using the low-smoke, low-corrosion, flame-retardant PVC sheath material obtained by the preparation method described in the fourth aspect as the sheath extrusion material, the insulated wire core is extruded into a sheath layer using an extruder at a barrel temperature of 150-185°C, and after cooling and shaping, the wire is wound up to obtain the low-smoke, low-corrosion, flame-retardant cable as described in claim 6 or 7.

[0038] This invention achieves overall control over the pyrolysis path and flue gas composition during combustion by introducing core-shell flame-retardant buffer particles with an "alkaline core-bio-based char-forming layer-rare earth smoke-suppressing shell" into the PVC sheath system: using basic calcium aluminum hydroxyl carbonate as the core, it preferentially reacts with acidic gases such as HCl under high temperature and acidic environments, providing strong alkaline absorption and pH buffering; an organic-inorganic hybrid first shell composed of phytic acid, chitosan, and silica is constructed on its outer surface, which on the one hand utilizes the phosphorus- and nitrogen-rich char-forming characteristics of phytic acid and chitosan to promote the formation of a dense char layer with a rich inorganic framework, and on the other hand enhances the thermal stability and physical shielding effect of the char layer through SiO2; then rare earth yttrium stannate (Y2Sn2O7) nanoparticles are loaded on the outermost layer, concentrating the rare earth catalytic carbonization, smoke suppression, and toxic smoke reduction capabilities at the flame-smoke interface. Through this functionally layered and gradient-coordinated core-shell structure, acid gas absorption, char formation and smoke suppression are orderly coupled on the same particle, and work in synergy with the PVC matrix and plasticizing and stabilizing system to achieve deep regulation of the release of combustion acid gases and the generation of flue gas.

[0039] Thanks to the aforementioned core-shell flame-retardant buffer particles and their synergistic design with the PVC sheath formulation, this invention, while maintaining the processing technology and cost advantages of conventional PVC sheaths, can significantly reduce the corrosiveness and opacity of combustion flue gas with a moderate filler dosage. On the one hand, the basic calcium hydroxyaluminate carbonate core and the phytic acid / chitosan / SiO2 hybrid layer synergistically absorb and solidify acidic decomposition products such as HCl, resulting in a significant increase in the pH of the condensate and a significant decrease in conductivity. Some indicators can approach the level of low-smoke halogen-free cables, thereby effectively mitigating corrosion damage to copper conductors and metal components after a fire. On the other hand, the outer Y2Sn2O7 nanoparticles and the bio-based char layer work together to reduce smoke density and the amount of toxic smoke generated, ensuring that the flame does not spread to the top of the sample during bundled combustion tests and that the maximum specific optical density is controlled at a low level. At the same time, with the reasonable plasticizing and stabilizing system, the sheath material can still maintain good tensile strength, elongation at break, and volume resistivity, achieving a comprehensive performance balance of "flame retardancy, low smoke, low corrosion, and processability". Detailed Implementation

[0040] 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, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0041] I. Terminology Explanation

[0042] Unless otherwise specified, the following terms shall have the following meanings in this invention:

[0043] Core-shell flame-retardant buffer particles: These are particles with a core-multi-shell structure consisting of a "basic calcium hydroxyaluminate core / phytic acid-chitosan-silica hybrid first shell / rare earth yttrium stannate second shell". During the combustion of PVC, these particles simultaneously play the roles of absorbing and buffering acidic gases, promoting char formation and blocking, and suppressing smoke and reducing toxicity.

[0044] Basic calcium aluminum carbonate: refers to the basic salts of the Ca-Al-CO3-OH series, which can be calcium aluminum double salts with a hydrotalcite-like structure or a basic carbonate-like structure. In this invention, they are usually provided in the form of wet precipitation or commercial slurry.

[0045] Phytic acid (PA): refers to inositol hexaphosphate, which can be derived from plant raw materials such as corn and rice. It has high phosphorus content and polyhydroxy properties, and is used as a bio-based phosphorus flame retardant / charring agent in this invention.

[0046] Chitosan (CS): refers to a linear polysaccharide obtained by deacetylation of chitin. It is generally acid-soluble and has good char-forming ability and interfacial film-forming ability.

[0047] Y2Sn2O7: refers to rare earth yttrium stannate, which can be obtained as nano or submicron-sized powders through solid-phase synthesis. In this invention, it is mainly used for smoke suppression, catalytic carbonization, and reduction of toxic fumes.

[0048] Parts by weight: Unless otherwise specified, the amount of each component in the formula is based on 100 parts by weight of PVC.

[0049] II. Raw Material Description

[0050] The present invention can use the following raw materials (those skilled in the art can substitute similar products according to the availability of procurement):

[0051] PVC: Suspension PVC with a K value of 67.

[0052] Chlorinated polyethylene (CPE): 35wt% chlorine content, used to improve flexibility and low-temperature performance.

[0053] Ethylene-vinyl acetate copolymer (EVA): VA content 18wt%.

[0054] Basic calcium hydroxyaluminate slurry: solid content 40wt%.

[0055] Phytic acid: Industrial grade, 70wt% aqueous solution.

[0056] Chitosan: Viscosity (1wt% acetic acid solution).

[0057] Silica sol: SiO2 solid content 30wt%.

[0058] Y2Sn2O7 powder: Median particle size D 50 Approximately 80-150nm.

[0059] Triethyl citrate (TEC), aliphatic polyester plasticizer (polyester diol ester), epoxidized soybean oil (ESBO).

[0060] Organic calcium-zinc stabilizer, polyethylene wax, liquid paraffin.

[0061] γ-aminopropyltriethoxysilane (KH-550).

[0062] Hindered phenolic antioxidants (such as 1010).

[0063] Processing aids: acrylate processing aids, fluoropolymer processing aids, etc.

[0064] III. General Preparation Methods for Core-Shell Flame-Retardant Buffer Particles

[0065] The preparation process of core-shell flame-retardant buffer particles is described below using a general process, which is applicable to the subsequent embodiments.

[0066] 3.1 Preprocessing of the core layer

[0067] (1) Take a certain amount of basic calcium hydroxyl aluminum slurry, add deionized water to dilute to a solid content of 10-20 wt%, and mechanically stir at 300-600 r / min to obtain a uniform suspension.

[0068] (2) If it is necessary to adjust the particle size, it can be sheared and dispersed for 5 to 10 minutes at 5000 to 8000 r / min to improve the uniformity of subsequent shell coating.

[0069] 3.2 Construction of the first shell (phytic acid / chitosan / SiO2 hybrid layer)

[0070] (3) Add an acidic chitosan solution to the above suspension and adjust the pH to 3-4 by diluting the acetic acid solution to dissolve the chitosan and make it positively charged.

[0071] (4) Slowly add phytic acid aqueous solution, and maintain the pH in the range of 3 to 6 while stirring, so that phytic acid and chitosan can undergo electrostatic self-assembly and complexation deposition on the surface of basic calcium hydroxyaluminate carbonate to form an organic layer containing P / N elements. The amount of phytic acid and chitosan added should be controlled in the range of "phytic acid: chitosan (based on solids) = 1.0 to 1.8: 0.8 to 1.5".

[0072] (5) After stirring for 30-60 min, add silica sol and adjust the system temperature to 40-80℃. At this temperature, age for 0.5-4 h to allow SiO2 to undergo condensation in the formed phytic acid / chitosan layer and crosslink with the surface hydroxyl and amino groups, thereby forming the first organic-inorganic hybrid shell. The mass ratio of phytic acid, chitosan and SiO2 solids is controlled within the range of 1.0-1.8:0.8-1.5:1.0-2.0.

[0073] 3.3 Construction of the second shell (Y2Sn2O7 outer shell)

[0074] (6) Disperse Y2Sn2O7 powder in a small amount of deionized water, and add 0.1 to 0.5 wt% dispersant. Use ultrasound or high-speed shearing to form a stable suspension.

[0075] (7) Slowly add the Y2Sn2O7 suspension to the slurry in step (5) and stir at 300-600 r / min for 30-60 min to allow the Y2Sn2O7 nanoparticles to be uniformly adsorbed on the surface of the first shell layer and fixed to the outer layer of the particles through hydrogen bonding, electrostatics and physical embedding. Adjust the amount of Y2Sn2O7 to 5-20 wt% of the total mass of the dried particles.

[0076] 3.4 Drying and Particle Size Control

[0077] (8) The obtained slurry is separated into solid and liquid phases by spray drying or filtration-drying process. Spray drying is preferred to control the degree of particle agglomeration and volume distribution. During spray drying, the inlet temperature can be 150-200℃ and the outlet temperature can be 80-100℃ to obtain dried powder.

[0078] (9) If necessary, the dried powder can be lightly air-classified or sieved to ensure the volume fractional median particle size D of the core-shell flame-retardant buffer particles. 50 The particle size should be controlled within the range of 0.5 to 3.0 μm to balance acid gas absorption efficiency, dispersibility, and impact on the mechanical properties of PVC.

[0079] IV. General Preparation Method of Low-Smoke, Low-Corrosion, Flame-Retardant PVC Sheath Material

[0080] 4.1 Dry Mixing and Premixing

[0081] (1) Add PVC (and optional CPE, EVA and other blended resins) to a high-speed mixer and heat it to 60-90℃;

[0082] (2) Add the pre-made core-shell flame-retardant buffer particles and dry mix for 3 to 10 minutes to make them evenly adhere to the surface of the resin particles.

[0083] (3) Add the plasticizing system, organic calcium-zinc stabilizer, lubricant, antioxidant, coupling agent and optional processing aid in sequence, continue mixing for 3 to 10 minutes, and control the discharge temperature at 100 to 120°C to obtain a uniform premix.

[0084] 4.2 Melt Mixing and Granulation

[0085] (4) The above premixed material is fed into a twin-screw extruder and melt-mixed at a barrel temperature of 150-185°C and an appropriate screw speed. The screw structure can adopt a combination section that strengthens dispersion and distribution mixing.

[0086] (5) The extruded strip is cooled with water and then cut into pellets to obtain the low-smoke, low-corrosion, flame-retardant PVC sheath material of the present invention.

[0087] V. Cable sheath extrusion into cabling

[0088] 5.1 Sheath Extrusion

[0089] (1) Select multi-strand copper conductors, which are stranded and annealed, and then combined with wire cores with extruded insulation layers to form a cable;

[0090] (2) Add the sheath material of the present invention to the cable extruder, control the barrel temperature at 150-185°C, and adjust the extrusion pressure and linear speed according to the cable specifications so that the sheath is extruded outside the insulated wire core to obtain a uniform and dense sheath layer.

[0091] (3) After the sheath is extruded, it is water-cooled and shaped and then wound up to obtain the low-smoke, low-corrosion, flame-retardant cable of the present invention.

[0092] VI. Performance Testing Methods

[0093] Unless otherwise stated, the performance tests in this embodiment are performed according to the following criteria:

[0094] Combustion acid gas test: Determine the pH value and conductivity of the condensate according to GB / T17650.2.

[0095] Smoke density test: The maximum specific optical density Ds,max shall be determined in accordance with GB / T17651.2.

[0096] Bundled cable combustion test: Flame spread height shall be assessed in accordance with GB / T18380.3.

[0097] Mechanical properties: tensile strength and elongation at break were determined according to GB / T2951.14; retention rate after heat aging was performed according to GB / T2951.12.

[0098] Volume resistivity: determined according to GB / T2951.21.

[0099] Corrosion depth of copper conductors: After a simulated flame-water spray test, the sheath was removed and the maximum corrosion depth of the copper surface was measured using metallographic measurement or optical profilometry.

[0100] VII. Examples and Comparative Examples

[0101] The sheath materials of Examples 1-4 and Comparative Examples 1-4 were all prepared according to "IV. General Preparation Method of Low Smoke Low Corrosion Flame Retardant PVC Sheath Material" in this specification. The only differences were in the formulation components and whether or not core-shell flame retardant buffer particles were used. The sheaths were extruded on the same multi-core cable structure.

[0102] 7.1 Example of Core-Shell Flame-Retardant Cushioning Particle Formulation

[0103] Table 1 shows the typical composition (on a dry powder basis) of the core-shell flame-retardant buffer particles used in the embodiments.

[0104] Table 1. Composition of core-shell flame-retardant buffer particles (mass percentage)

[0105]

[0106] K-1 is mainly used in Examples 1 and 2, K-2 is used in Example 3 to enhance smoke suppression performance, and K-3 is used to compare the effect of the core / shell ratio on performance in the core-shell structure.

[0107] 7.2 Example: Sheath Material Formulation and Preparation

[0108] Example 1 (E1) uses K-1 particles, with 35 parts of core-shell flame-retardant buffer particles and a medium level of plasticization.

[0109] PVC (K67): 100 parts;

[0110] CPE: 5 parts; EVA: 3 parts;

[0111] Core-shell flame-retardant buffer particles K-1: 35 parts;

[0112] Triethyl citrate (TEC): 22 parts;

[0113] Aliphatic polyester plasticizer: 13 parts;

[0114] Epoxidized soybean oil (ESBO): 7 parts;

[0115] Organic calcium and zinc stabilizer: 4 parts;

[0116] PE wax: 2 parts;

[0117] Liquid paraffin: 1 part;

[0118] γ-aminopropyltriethoxysilane: 0.8 parts;

[0119] Antioxidant 1010: 0.5 parts;

[0120] Processing aids: 2 parts.

[0121] Example 2 (E2)

[0122] K-1 particles were used, with a slightly lower core-shell particle content (28 parts), to verify the performance under lower filler conditions.

[0123] PVC (K67): 100 parts;

[0124] CPE: 4 parts;

[0125] EVA: 2 portions;

[0126] Core-shell flame-retardant buffer particles K-1: 28 parts;

[0127] TEC: 20 servings;

[0128] Aliphatic polyester plasticizer: 15 parts;

[0129] ESBO: 8 servings;

[0130] Organic calcium and zinc stabilizer: 4 parts;

[0131] PE wax: 2 parts;

[0132] Liquid paraffin: 1 part;

[0133] γ-aminopropyltriethoxysilane: 0.8 parts;

[0134] Antioxidant 1010: 0.5 parts;

[0135] Processing aids: 1.5 parts.

[0136] Example 3 (E3)

[0137] K-2 particles were used, with a relatively high amount of core-shell particles (45 parts). K-2 was used to enhance smoke suppression and acid gas buffering.

[0138] PVC (K67): 100 parts;

[0139] CPE: 6 parts;

[0140] EVA: 3 parts;

[0141] Core-shell flame-retardant buffer particles K-2: 45 parts;

[0142] TEC: 18 servings;

[0143] Aliphatic polyester plasticizer: 14 parts;

[0144] ESBO: 8 servings;

[0145] Organic calcium-zinc stabilizer: 4.5 parts;

[0146] PE wax: 2.5 parts;

[0147] Liquid paraffin: 1 part;

[0148] γ-aminopropyltriethoxysilane: 1.0 part;

[0149] Antioxidant 1010: 0.5 parts;

[0150] Processing aids: 2 parts.

[0151] Example 4 (E4)

[0152] K-3 particles were used, which have a higher proportion of Ca-Al cores in the core-shell structure, to verify their impact on acid gas performance and mechanical properties.

[0153] PVC (K67): 100 parts;

[0154] CPE: 5 parts;

[0155] EVA: 3 parts;

[0156] Core-shell flame-retardant buffer particles K-3: 40 parts;

[0157] TEC: 21 copies;

[0158] Aliphatic polyester plasticizer: 13 parts;

[0159] ESBO: 7 servings;

[0160] Organic calcium and zinc stabilizer: 4 parts;

[0161] PE wax: 2 parts;

[0162] Liquid paraffin: 1 part;

[0163] γ-aminopropyltriethoxysilane: 0.8 parts;

[0164] Antioxidant 1010: 0.5 parts;

[0165] Processing aids: 2 parts.

[0166] 7.3 Comparative Example

[0167] Comparative Example 1 (C1): Conventional Sb2O3 Filler Type Low Smoke Flame Retardant PVC Sheath

[0168] PVC (K67): 100 parts;

[0169] CPE: 5 parts;

[0170] EVA: 3 parts;

[0171] Aluminum hydroxide (ATH): 25 parts;

[0172] Magnesium hydroxide (MDH): 15 parts;

[0173] Zinc borate: 6 parts;

[0174] Antimony trioxide (Sb₂O₃): 5 parts;

[0175] CaCO3: 10 parts;

[0176] DOP: 30 servings;

[0177] ESBO: 6 servings;

[0178] Organic lead stabilizer: 4 parts;

[0179] Paraffin wax: 2 parts;

[0180] Antioxidant: 0.5 parts;

[0181] Processing aids: 2 parts.

[0182] Comparative Example 2 (C2): Only Ca-Al core, no shell

[0183] It is basically the same as E1, but K-1 particles are replaced with uncoated basic calcium aluminum hydroxyl carbonate 35phr, and phytic acid, chitosan, SiO2 and Y2Sn2O7 are not added.

[0184] Comparative Example 3 (C3): A physical mixture of PA, CS, SiO2, and Y2Sn2O7, without a core-shell structure.

[0185] The formulation is the same as that in E1, including PVC, CPE, EVA, plasticizer system, and stabilizer system. However, phytic acid, chitosan, SiO2 and Y2Sn2O7 are added directly to the sheath formulation in powder form at a mass ratio of K-1. The core-shell structure is not pre-constructed, and only a small amount of conventional CaCO3 is retained as filler.

[0186] Comparative Example 4 (C4): Conventional Ca-Zn / ATH / LDH type low-smoke, low-corrosion PVC sheath

[0187] PVC (K67): 100 parts;

[0188] CPE: 5 parts;

[0189] EVA: 3 parts;

[0190] ATH: 25 copies;

[0191] Hydrotalcite (LDH): 10 parts;

[0192] Zinc borate: 6 parts;

[0193] CaCO3: 10 parts;

[0194] TEC: 22 copies;

[0195] DOA: 13 copies;

[0196] ESBO: 7 servings;

[0197] Organic Ca–Zn stabilizer: 4 parts;

[0198] PE wax: 2 parts;

[0199] Liquid paraffin: 1 part;

[0200] Antioxidant: 0.5 parts;

[0201] Processing aids: 2 parts.

[0202] VIII. Performance Test Results and Analysis

[0203] 8.1 Comparison of Flame Retardant, Low Smoke and Acid Corrosion Indicators

[0204] Table 2 shows the test results of the embodiments and comparative examples of the present invention in terms of flame retardancy, low smoke and acid corrosion.

[0205] Table 2 Comparison of Flame Retardancy, Smoke Density, and Corrosivity to Acid Gases

[0206]

[0207] As shown in Table 2, traditional Cl containing Sb and Pb exhibits significant corrosiveness with a high smoke density (Ds,max≈1.65), a condensate pH of approximately 3.1, and a conductivity as high as 22.5 μS / mm, resulting in a maximum corrosion depth of approximately 45 μm for copper conductors.

[0208] Although C2 using only Ca–Al cores and C3 using a physical mixture of PA / CS / SiO2 / Y2Sn2O7 are improvements over C1, their pH values ​​are mostly between 4.0 and 4.3, and their conductivity is between 11 and 14 μS / mm, which are still significantly higher than those of the embodiments of the present invention.

[0209] C4 (ATH / LDH standard scheme) can achieve a pH of ≈4.4 and a conductivity of ≈10.5μS / mm in acid gas testing, with a copper corrosion depth of about 24μm, which represents the approximate level of existing low-smoke and low-corrosion PVC sheaths.

[0210] In embodiments E1-E4 of this invention, under the premise of ensuring non-spreading of bundled combustion and low smoke density (Ds,max≤1.20), the pH of the condensate is increased to above 5.0, and the conductivity is controlled within the range of approximately 3.7-4.8 μS / mm, which is significantly better than C2-C4. The maximum corrosion depth of the copper conductor is significantly reduced to only 9-14 μm, which is approximately half that of C4 and one-third to one-fifth that of C1. This indicates that the synergistic effect of the basic Ca-Al core + PA / CS / SiO2 hybrid layer / Y2Sn2O7 outer shell in the core-shell flame-retardant buffer particles significantly improves the acid gas buffering and corrosion resistance of the PVC sheath.

[0211] 8.2 Comparison of Mechanical and Electrical Properties

[0212] Table 3 lists the room temperature mechanical properties and volume resistivity of each sample.

[0213] Table 3 Comparison of Mechanical and Electrical Properties at Room Temperature

[0214]

[0215] As can be seen from Table 3:

[0216] The tensile strength of embodiments E1 to E4 of the present invention is maintained at 11.0 to 11.6 MPa, which is equal to or slightly better than that of the comparative example, indicating that good strength can still be maintained even with a high level of inorganic functional particle filling.

[0217] The elongation at break is in the range of 175-195%, which is significantly higher than that of C1, indicating that the formulation of this invention can take into account both flexibility and flame retardancy, and is suitable as a cable sheath.

[0218] The volume resistivity is higher than 1.2 × 10⁻⁶. 12 Ω.cm, higher than the common 10 in conventional halogenated PVC sheaths. 11~10 12 The Ω.cm level meets the insulation requirements of power cable sheaths.

[0219] 8.3 Thermal aging performance

[0220] Table 4 shows the mechanical retention rate after aging in hot air at 180℃ for 168 hours.

[0221] Table 4. Mechanical property retention rate before and after thermal aging

[0222]

[0223] As can be seen from Table 4, the strength retention rate of the embodiments of the present invention is ≥83%, and the elongation retention rate is about 77-78%, which is significantly better than C1-C3 and slightly better than C4. This indicates that the core-shell flame-retardant buffer particles, combined with the Ca-Zn stabilizing system and the citrate / polyester / epoxy plasticizing system, give the sheath material good thermo-oxidative stability.

[0224] In summary: In the existing ATH / LDH type or Based on the synergistic flame-retardant PVC sheath, simply increasing the alkaline filler or physically mixing PA / CS / SiO2 and Y2Sn2O7 can only improve acid gas corrosivity and smoke density to a limited extent, and it is difficult to break through the target of pH≥5.0 and conductivity≤5μS / mm.

[0225] This invention designs core-shell flame-retardant buffer particles with a "basic Ca-Al core-PA / CS / SiO2 hybrid first shell-Y2Sn2O7 second shell" and controls their dosage within the range of 25-55 phr. In synergy with the PVC matrix and specific plasticizing and stabilizing systems, it achieves the following: while maintaining good mechanical, electrical properties and processability, it increases the pH of the combustion acid gas condensate to above 5.0, reduces the electrical conductivity to about 4 μS / mm, and reduces the copper conductor corrosion depth by more than 50% compared to conventional low-smoke flame-retardant PVC sheaths. At the same time, the smoke density and bundled combustion performance reach or even exceed the level of existing low-smoke PVC sheaths.

[0226] This invention introduces core-shell flame-retardant buffer particles with acid gas buffering, char formation blocking, and smoke suppression functions into the PVC sheath system. This significantly increases the pH of the condensate produced by the cable under combustion conditions, significantly reduces the conductivity, and greatly reduces the corrosion depth of copper conductors and metal components. At the same time, it also takes into account the non-spread of bundled combustion, low smoke density, and good mechanical, electrical, and processing properties. It is suitable for application scenarios with strict requirements for post-fire corrosion damage and personnel evacuation safety, such as building power distribution, power engineering, rail transit, and data centers.

[0227] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A low-smoke, low-corrosion, flame-retardant PVC sheath material, characterized in that, Composed of the following components in parts by mass: a) 100 parts of PVC matrix; b) 25-55 parts of core-shell flame-retardant buffer particles, wherein the core-shell flame-retardant buffer particles are core-multi-layer shell structure particles with flame-retardant, smoke-suppressing, and acid gas buffering functions, including: b1) The core layer is basic calcium hydroxyaluminate carbonate, wherein the basic calcium hydroxyaluminate carbonate is... System basic salt; b2) The first shell layer, which covers the outer surface of the core layer, is an organic-inorganic hybrid layer composed of phytic acid, chitosan and SiO2, wherein the mass ratio of phytic acid, chitosan and SiO2 solids is 1.0-1.8:0.8-1.5:1.0-2.

0. b3) The second shell consists of rare earth yttrium stannate (Y2Sn2O7) nanoparticles coating the outer surface of the first shell. The mass fraction of the core-shell flame-retardant buffer particles is 5-20% of the total mass. The mass ratio of the core layer, the first shell layer, and the second shell layer is 50–70:20–35:5–15, and the median particle size D of the core-shell flame-retardant buffer particles is... 50 The range is 0.5–3.0 μm; c) 30-50 parts of the plasticizer system; d) Stabilize the lubrication system by 3 to 10 parts; e) 0.3–1.5 parts of coupling agent; f) 0.2–1.0 parts of antioxidant; g) 0 to 5 parts of processing aids may be selected, which may be processing aids, pigments and / or inert fillers.

2. The low-smoke, low-corrosion, flame-retardant PVC sheath material according to claim 1, characterized in that, The PVC resin is a suspension PVC resin with a K value of 65-70, and can be further blended with chlorinated polyethylene and ethylene-vinyl acetate copolymer, with a mass ratio of PVC:chlorinated polyethylene:ethylene-vinyl acetate copolymer of 90-96:2-5:2-5.

3. The low-smoke, low-corrosion, flame-retardant PVC sheath material according to claim 1, characterized in that, The plasticizing system comprises triethyl citrate, an aliphatic polyester plasticizer, and epoxidized soybean oil, wherein the mass fraction ratio of triethyl citrate, aliphatic polyester plasticizer, and epoxidized soybean oil is 35-55:25-45:10-25.

4. The low-smoke, low-corrosion, flame-retardant PVC sheath material according to claim 1, characterized in that, The stabilized lubrication system includes an organic calcium-zinc composite stabilizer, polyethylene wax, and liquid paraffin, with a mass fraction ratio of organic calcium-zinc composite stabilizer: polyethylene wax: liquid paraffin of 40-60: 20-40: 10-20.

5. The low-smoke, low-corrosion, flame-retardant PVC sheath material according to claim 1, characterized in that, The coupling agent is γ-aminopropyltriethoxysilane, and the antioxidant is a hindered phenolic antioxidant.

6. A low-smoke, low-corrosion, flame-retardant cable, characterized in that, include: The conductor, the insulating layer covering the conductor, and the sheath layer covering the insulating layer, wherein the sheath layer is obtained by extrusion molding of the low-smoke, low-corrosion, flame-retardant PVC sheath material according to any one of claims 1 to 5.

7. The low-smoke, low-corrosion, flame-retardant cable according to claim 6, characterized in that, The cable is a 0.6 / 1kV multi-core power cable, and also includes a filler layer between each insulated core and / or a metal shielding layer wrapped around each insulated core, wherein the average thickness of the sheath layer is 1.4 to 3.0 mm.

8. A method for preparing core-shell flame-retardant buffer particles, characterized in that, Includes the following steps: S1, basic calcium hydroxyaluminate carbonate is dispersed in an aqueous phase, phytic acid and chitosan are added, and the pH is adjusted to 3-6 under stirring conditions, so that phytic acid and chitosan undergo electrostatic self-assembly and complexation deposition on the surface of basic calcium hydroxyaluminate carbonate to obtain a suspension of basic calcium hydroxyaluminate carbonate with an organic layer. S2, silica sol is added to the suspension obtained in step S1 and aged at 40-80°C for 0.5-4 hours to allow silica to further condense and form a first shell layer coating the surface of the basic calcium hydroxyaluminate carbonate. The mass ratio of phytic acid, chitosan and silica solids is controlled at 1.0-1.8:0.8-1.5:1.0-2.

0. S3, will The nanoparticles are dispersed in the slurry of step S2 by mechanical stirring and / or ultrasonic dispersion. Uniformly adsorbed on the outer surface of the first shell, adjusted The mass fraction of the obtained particles is 5-20%, and the median particle size D is obtained by spray drying or filtration-drying. 50 Core-shell flame-retardant buffer particles with a core-multilayer shell structure, ranging from 0.5 to 3.0 μm in size.

9. A method for preparing a low-smoke, low-corrosion, flame-retardant PVC sheath material, characterized in that, Includes the following steps: T1, core-shell flame-retardant buffer particles prepared according to the method described in claim 8; T2, add PVC resin and the core-shell flame-retardant buffer particles obtained in step T1 into a high-speed mixer and dry mix at 60-120°C for 3-15 minutes to make the core-shell flame-retardant buffer particles uniformly adhere to the surface of the resin particles. T3, add plasticizer, stabilizing lubricant, coupling agent, antioxidant and optional processing aid to the dry mix in step T2, and continue mixing for 3 to 10 minutes to obtain premix; T4. The premixed material from step T3 is fed into a melt-mixing equipment, melt-mixed and extruded at 150-185°C, and granulated to obtain the low-smoke, low-corrosion, flame-retardant PVC sheath material as described in any one of claims 1-5.

10. A method for preparing a low-smoke, low-corrosion, flame-retardant cable, characterized in that, Includes the following steps: U1, the conductor is stranded and annealed according to conventional processes, and then insulation material is extruded to form an insulated wire core; U2 uses the low-smoke, low-corrosion, flame-retardant PVC sheath material obtained by the preparation method described in claim 9 as the sheath extrusion material. The insulated wire core is extruded into a sheath layer using an extruder at a barrel temperature of 150-185°C. After cooling and shaping, the wire is wound up to obtain the low-smoke, low-corrosion, flame-retardant cable described in claim 6 or 7.

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