A composite flame-retardant cable material and a method for producing the same

Abstract

The application relates to the technical field of cable materials, and particularly discloses a composite flame-retardant cable material and a preparation method thereof, which comprises the following components: base resin: ethylene-vinyl acetate copolymer 50-70 parts; composite flame-retardant system: ammonium polyphosphate / pentaerythritol 15-25 parts, Mg / Al-LDH 5-10 parts; synergistic smoke suppressant: a compound of zinc borate and silicon dioxide with a mass ratio of 1:1 1-3 parts. Through the synergistic effect of the ammonium polyphosphate / pentaerythritol intumescent flame-retardant system and the Mg / Al-LDH, a gas phase-coagulation phase dual flame-retardant mechanism is formed, the composite system can reach UL-94 V-0 level when the total addition amount of the flame retardant is less than or equal to 35%, and the limiting oxygen index (LOI) is greater than or equal to 32%, which is significantly better than that of a traditional single flame-retardant system.

Description

Technical Field

[0001] This invention relates to the field of cable material technology, and in particular to a composite flame-retardant cable material and its preparation method. Background Technology

[0002] With the rapid development of the new energy industry and the increasing safety requirements of power transmission and distribution systems, the synergistic improvement of the flame retardant properties and comprehensive mechanical properties of cable materials has become a core issue in the industry.

[0003] Traditional flame-retardant cable materials often employ single or binary synergistic mechanisms. For example, inorganic flame retardants require 40-60 wt% to achieve the UL-94 V-0 rating, but this leads to a decrease in tensile strength of the material of more than 30%. Halogenated flame retardants, while highly efficient, release toxic gases during combustion, failing to meet environmental requirements. Intumescent flame retardant systems, while environmentally friendly, suffer from poor char stability and are prone to secondary combustion at high temperatures. Biotechnological flame retardants, such as phytic acid and chitosan, can address environmental concerns, but their poor thermal stability makes them prone to decomposition and failure.

[0004] Although the industry has attempted to optimize performance through multi-component synergy, nanocompositing, and radiation crosslinking, the contradiction between material embrittlement and deteriorated processing fluidity caused by high levels of flame retardants remains unresolved. Therefore, there is an urgent need to develop a novel composite flame-retardant cable material to achieve a synergistic improvement in flame retardancy and mechanical properties, while also maintaining environmental friendliness. Summary of the Invention

[0005] In view of this, the present invention proposes a composite flame-retardant cable material and its preparation method.

[0006] The technical solution of this invention is achieved as follows: This invention provides a composite flame-retardant cable material, comprising a matrix resin, a composite flame-retardant system, and a synergistic smoke suppressant, comprising, by weight:

[0007] 50-70 parts of matrix resin

[0008] Composite flame retardant system: 15-25 parts ammonium polyphosphate / pentaerythritol, 5-10 parts Mg / Al-LDH

[0009] Synergistic smoke suppressant: 1-3 parts of a compound of zinc borate and silica in a 1:1 mass ratio.

[0010] In the above embodiments, the matrix resin is an ethylene-vinyl acetate copolymer, or a blend of ethylene-vinyl acetate copolymer and polyurethane.

[0011] In some embodiments, the composite flame retardant system further includes 3-8 parts of phosphated chitosan, wherein the degree of phosphating of the phosphated chitosan is 30-50%.

[0012] The preparation method of the above-mentioned phosphated chitosan includes:

[0013] Dissolve 100 parts of chitosan in 2% acetic acid solution to prepare a 5wt% colloidal solution, and keep it at 40℃ and stir for 2 hours.

[0014] Add 30-50 parts of 50wt% phytic acid and 10-15 parts of urea to the colloidal solution, adjust the pH to 4.5-5.0, and react at 80℃ for 6-8 hours under nitrogen protection.

[0015] The reaction solution was poured into ethanol to precipitate the precipitate, filtered, dried under vacuum at 60°C for 24 hours, pulverized, and sieved (particle size ≤ 50 μm) to obtain the final product.

[0016] In some embodiments, the method further includes 2-5 parts of organically modified montmorillonite, which has undergone hexadecyltrimethylammonium bromide intercalation treatment.

[0017] In the above embodiments, the preparation method of the organically modified montmorillonite includes:

[0018] 100 parts of sodium-based montmorillonite were mixed with water and sonicated at 40 kHz and 60 °C for 1 h to prepare a 5 wt% suspension. An ethanol solution containing 30 parts of hexadecyltrimethylammonium bromide (hexadecyltrimethylammonium bromide: ethanol = 1:10) was added dropwise, and the mixture was stirred at 80 °C for 6 h. After centrifugation and washing until no Br- was detected, the mixture was vacuum dried at 60 °C, ground, sieved (particle size ≤ 20 μm), and activated at 120 °C for 2 h to obtain organo-modified montmorillonite.

[0019] In some embodiments, the organically modified montmorillonite is distributed radially in the material matrix, with a surface concentration that is 150-200% higher than that in the core.

[0020] A second aspect of the present invention also provides a method for preparing the above-mentioned cable material, comprising the following steps:

[0021] Step 1: Disperse Mg / Al-LDH with silane coupling agent KH-550 in an ethanol solution by ultrasonication, filter and dry to obtain surface-modified Mg / Al-LDH;

[0022] Step 2: Mix the base resin with ammonium polyphosphate / pentaerythritol at 160-170℃ for 5-10 minutes;

[0023] Step 3: Add the surface-modified Mg / Al-LDH from Step 1 to the mixture obtained in Step 2, and continue mixing at 140-150℃ for 8-12 minutes.

[0024] Step 4: Add a synergistic smoke suppressant to the mixture obtained in Step 3, and granulate it by extrusion using a twin-screw extruder at a temperature range of 150-170℃.

[0025] In some embodiments, the ultrasonic dispersion conditions in step one are: treatment at 40 kHz and 60 °C for 30-60 min, with a mass ratio of Mg / Al-LDH to silane coupling agent KH-550 of 10:1.

[0026] In some embodiments, in step four, the temperature zones of the twin-screw extruder are: 150-155°C at the feed end, 165-170°C in the compression section, 160-165°C in the homogenization section, and the screw speed is 200-400 rpm.

[0027] In some implementations, step three involves two stages of mixing: the first stage is mixing at 140°C and 40 rpm for 5 minutes; the second stage is mixing at 150°C and 60 rpm for 5 minutes.

[0028] In some embodiments, when the raw materials also include phosphated chitosan, step one is: ultrasonically disperse Mg / Al-LDH, phosphated chitosan and silane coupling agent KH-550 in an ethanol solution, filter and dry to obtain surface-modified Mg / Al-LDH.

[0029] In some embodiments, when the raw materials also include organically modified montmorillonite, step four is: adding organically modified montmorillonite and a synergistic smoke suppressant to the mixture obtained in step three, and granulating it by extrusion using a twin-screw extruder at a temperature range of 150-170°C.

[0030] When the ammonium phosphate / pentaerythritol (APP / PER) intumescent flame retardant system decomposes upon heating, it releases a large amount of inert gases (NH3, H2O) to dilute the oxygen concentration (gas-phase flame retardancy). Simultaneously, it generates PO·-containing free radicals, which capture reactive free radicals (such as H·, OH·) during combustion through a chain reaction, inhibiting flame propagation. At the same time, Mg / Al-LDH undergoes endothermic decomposition at high temperatures to form MgO / Al2O3 metal oxides, creating a dense char layer (condensed-phase flame retardancy). This char layer possesses the following characteristics:

[0031] Physical barrier: The carbon layer has a low thermal conductivity, effectively preventing heat transfer to the substrate;

[0032] Chemical stability: The metal oxide reacts with the polyphosphate generated by the decomposition of APP to form stable pyrophosphate, which enhances the carbon layer's resistance to high-temperature oxidation.

[0033] Phosphated chitosan undergoes the following reaction during combustion:

[0034] Free radical quenching: Phosphated chitosan releases PO· and NH3 upon thermal decomposition, where PO· interrupts the chain reaction by capturing H· / OH· free radicals, and NH3 further dilutes oxygen;

[0035] Catalytic carbonization: Phosphorus elements form a POC cross-linking structure with the carbon chains in the EVA matrix, promoting the formation of a dense carbon layer.

[0036] In the staged temperature-controlled mixing process (140℃→120℃), montmorillonite particles are driven by the thermophoretic force generated by the temperature gradient to migrate from the high-temperature zone (core) to the low-temperature zone (surface).

[0037] The silane coupling agent (KH-550) grafts amino functional groups onto the surface of montmorillonite through a hydrolysis-condensation reaction, which significantly reduces the interfacial tension between the filler and the matrix and promotes the directional migration of particles in the melt.

[0038] During twin-screw extrusion, the shear force field generated by the screw rotation causes the sheet-like montmorillonite to align along the flow direction, forming a "brick-mud" barrier structure.

[0039] After CTAB intercalation treatment, the interlayer spacing of organic montmorillonite is expanded, making it easier to exfoliate into nanosheets during melt blending. The uniformly dispersed nanosheets enhance the toughness of the material through the crack pinning effect.

[0040] The present invention has the following advantages over the prior art:

[0041] The cable material of this invention forms a dual gas-phase-condensed-phase flame-retardant mechanism through the synergistic effect of the ammonium polyphosphate / pentaerythritol intumescent flame-retardant system and Mg / Al-LDH. The ammonium polyphosphate / pentaerythritol system decomposes upon heating to generate inert gas, thereby diluting oxygen, and simultaneously generates PO free radicals to capture active free radicals in the combustion chain reaction. Mg / Al-LDH undergoes endothermic decomposition at high temperatures, releasing water of crystallization to lower the system temperature and forming a metal oxide char layer, effectively isolating heat and oxygen transfer. This composite system achieves UL-94 V-0 rating and a limiting oxygen index (LOI) ≥32% when the total flame retardant content is ≤35%, significantly superior to traditional single flame-retardant systems. The vinyl acetate segments of EVA provide molecular chain flexibility, balancing the stress concentration effect of rigid flame retardant particles. The layered structure of Mg / Al-LDH is uniformly dispersed after surface modification, avoiding mechanical defects caused by agglomeration. Detailed Implementation

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 scope of protection of the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this invention pertain. If any definition stated in this section is contrary to or otherwise inconsistent with a definition stated in a patent, patent application, published patent application, or other publication incorporated herein by reference, the definitions listed here shall prevail over those incorporated herein by reference.

[0044] Unless otherwise specified, the methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials, reagents, and instruments used are conventional materials, reagents, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0045] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all subranges contained therein.

[0046] Example 1

[0047] This embodiment provides a basic improvement scheme.

[0048] The raw material composition by weight is as follows:

[0049] 60 EVA

[0050] APP / PER (2:1) 20 servings

[0051] 8 parts of Mg / Al-LDH (interlayer spacing 2.8 nm)

[0052] Two parts of zinc borate / silicon dioxide (1:1).

[0053] Preparation method:

[0054] Step 1: Disperse Mg / Al-LDH with silane coupling agent KH-550 in ethanol solution by ultrasonication at 40 kHz and 60 °C for 30-60 min, filter and dry to obtain surface-modified Mg / Al-LDH.

[0055] Step 2: Mix EVA and APP / PER at 165℃ for 8 minutes;

[0056] Step 3: Add the surface-modified Mg / Al-LDH obtained in Step 1 to the mixture obtained in Step 2, and mix at 140℃ and 40 rpm for 5 min, and then mix at 150℃ and 60 rpm for 5 min.

[0057] Step 4: Add zinc borate / silica to the mixture obtained in Step 3, and extrude and granulate it through a twin-screw extruder at 155°C at the feed end, 170°C at the compression section, 165°C at the homogenization section, and a screw speed of 300 rpm.

[0058] Example 2

[0059] Based on Example 1, this embodiment adds 5 parts of phosphated chitosan (phosphating degree 40%).

[0060] Preparation method: Step 1: Disperse Mg / Al-LDH, phosphated chitosan and silane coupling agent KH-550 in ethanol solution by ultrasonication, filter and dry to obtain surface-modified Mg / Al-LDH; other steps are the same as in Example 1.

[0061] Example 3

[0062] Based on Example 2, this embodiment also adds 3 parts of organically modified montmorillonite (CTAB intercalation).

[0063] Preparation method: Step 4: Add organically modified montmorillonite and zinc borate / silica to the mixture obtained in Step 3, and granulate by extrusion using a twin-screw extruder. The feed temperature is 155°C, the compression temperature is 170°C, the homogenization temperature is 165°C, and the screw speed is 300 rpm. Other steps are the same as in Example 2.

[0064] Example 4

[0065] This embodiment is based on Example 2, but uses phosphated chitosan with a phosphating degree of 30%, while keeping other conditions the same.

[0066] Example 5

[0067] This embodiment is based on Example 2, but uses phosphated chitosan with a phosphating degree of 50%, while keeping other conditions the same.

[0068] Example 6

[0069] This embodiment is based on Example 3, but uses 2 parts of boron nitride nanosheets (h-BN, thickness ≤5nm) to replace the organo-modified montmorillonite, and other conditions are the same as in Example 3.

[0070] Example 7

[0071] This embodiment is based on Example 3, but uses 3 parts of titanium dioxide nanotubes (TiO2NT, diameter 20-30nm) to replace the organo-modified montmorillonite, and other conditions are the same as in Example 3.

[0072] Example 8

[0073] This embodiment is based on Example 3, except that the matrix resin is replaced with an equal mass of EVA / TPU blend, with an EVA:TPU mass ratio of 7:3, and other conditions are the same as in Example 3.

[0074] Example 9

[0075] This embodiment is based on Example 3, except that the matrix resin is replaced with an equal mass of EVA / TPU blend, with an EVA:TPU mass ratio of 5:5, and other conditions are the same as in Example 3.

[0076] Example 10

[0077] This embodiment is based on Example 3, except that the matrix resin is replaced with an equal mass of EVA / TPU blend, with an EVA:TPU mass ratio of 3:7, and other conditions are the same as in Example 3.

[0078] Comparative Example 1

[0079] This comparative example provides a traditional APP / PER cable material system.

[0080] The raw material composition by weight is as follows:

[0081] 60 EVA

[0082] APP / PER (2:1) 35 servings

[0083] Preparation method:

[0084] EVA and APP / PER were mixed at 165°C for 8 minutes, and then mixed at 145°C for another 10 minutes. The mixture was then extruded and granulated using a twin-screw extruder with the feed end at 155°C, the compression section at 170°C, the homogenization section at 165°C, and the screw speed at 300 rpm.

[0085] Comparative Example 2

[0086] This comparative example is based on Example 2, except that Mg / Al-LDH is removed, while the other steps are the same as in Example 2.

[0087] Comparative Example 3

[0088] Based on Example 3, this comparative example eliminates gradient temperature control and adopts homogeneous mixing. That is, step three is: add the surface-modified Mg / Al-LDH treated in step one to the mixture obtained in step two, and continue mixing at 145°C and 50 rpm for 10 min.

[0089] Comparative Example 4

[0090] This comparative example is based on Example 2, except that the phosphated chitosan is replaced with an equal amount of unmodified chitosan, and the other steps are the same as in Example 2.

[0091] Comparative Example 5

[0092] This comparative example is based on Example 3, but with APP / PER replaced by 25 parts of decabromodiphenyl ethane (DBDPE) + Sb2O3 (3:1), and Mg / Al-LDH and zinc borate / silica removed.

[0093] Comparative Example 6

[0094] Based on Comparative Example 3, step four of this comparative example is as follows: organic modified montmorillonite and zinc borate / silica are added to the mixture obtained in step three, and the mixture is extruded and granulated using a twin-screw extruder. The temperature of the feed end, compression section, and homogenization section are all 160°C, and the screw speed is 300 rpm. Other steps are the same as in Comparative Example 3.

[0095] Comparative Example 7

[0096] This comparative example is based on Example 3, except that the silane coupling agent KH-550 in Example 3 is replaced with titanate NDZ-201, while other conditions remain the same.

[0097] The cable materials prepared according to the different embodiments and comparative examples were subjected to performance tests, including:

[0098] Limiting Oxygen Index (LOI): GB / T2406.0-2009

[0099] Vertical burning (UL-94): GB / T 2408-2021 (1.6mm thickness)

[0100] Cone calorimetry (CONE): ISO 5660-1, Peak heat release rate (pHRR), Total heat release (THR)

[0101] Tensile strength and elongation at break: GB / T 1040.1-2018, tensile rate 50 mm / min

[0102] Impact strength: GB / T 1843-2008 (Cantilever beam notched impact)

[0103] Smoke density (SDR): GB / T 8323.2-2008

[0104] Toxic gas release: GC-MS detection of CO, HCN, and halogen gas content in combustion products

[0105] Damp heat aging: GB / T 2951.12-2008, 85℃ / 85%RH, performance retention rate after 1000h

[0106] Low-temperature toughness: Bending test after freezing at -40℃ for 24 hours (visual inspection for cracks).

[0107] The test results are shown in the table below:

[0108]

[0109] In the above test results:

[0110] Comparing Example 2 with Comparative Example 1, it can be seen that the LOI increased from 28.5% to 35.8% (+25.6%), and the pHRR decreased by 61.5% (480→185 kW / m²), indicating that the ternary system played a good synergistic role.

[0111] A comparison of Example 3 and Comparative Example 3 shows that the LOI increased from 33.2% to 37.5% (+12.9%), indicating that the gradient structure brought about an optimization effect.

[0112] Comparing Example 2 with Comparative Example 4, it can be seen that the tensile strength increased from 13.8 MPa to 15.8 MPa (+14.5%), and the elongation at break increased from 250% to 310%. This indicates that phosphating chitosan modification significantly improves mechanical properties.

[0113] A comparison of Example 8 and Example 3 shows that the tensile strength increased from 16.5 MPa to 18.0 MPa (+9.1%), and the low-temperature toughness was significantly improved (no cracks at -40℃), indicating that the EVA and TPU blend system has better mechanical properties in the technical solution of this invention.

[0114] A comparison of Example 3 and Comparative Example 5 shows that the smoke density (SDR) decreased from 48 to 15 (a decrease of 68.8%), and the CO emission decreased from 0.32 g / g to 0.08 g / g (a decrease of 75%), demonstrating the environmental advantages of the halogen-free system of this application.

[0115] A comparison of Example 2 and Comparative Example 4 shows that the toxic gas HCN was not detected (GC-MS verification), while the unmodified chitosan system released trace amounts of NH3, demonstrating the environmental friendliness of the bio-based synergist.

[0116] In Example 3, compared to Comparative Example 3, the LOI retention rate increased from 89.5% to 97.3%, demonstrating that the gradient structure inhibits flame retardant migration. In Example 3, compared to Comparative Example 7, the silane coupling agent (KH-550) increased the tensile strength retention rate from 82.1% to 97.3%.

[0117] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite flame-retardant cable material, characterized in that, The composite flame-retardant cable material comprises a base resin, a composite flame-retardant system and a synergistic smoke suppressant, and comprises, by weight fraction: 50-70 parts of the base resin, which is ethylene-vinyl acetate copolymer or a blend of ethylene-vinyl acetate copolymer and polyurethane, wherein when it is a blend, the mass ratio of ethylene-vinyl acetate copolymer to polyurethane is 7:3 or 5:5; The composite flame-retardant system: 15-25 parts of ammonium polyphosphate / pentaerythritol, 5-10 parts of Mg / Al-LDH, and 3-8 parts of phosphonated chitosan with a degree of phosphonation of 30-50%; The synergistic smoke suppressant: 1-3 parts of a composite of zinc borate and silicon dioxide at a mass ratio of 1:1; 2-5 parts of organically modified montmorillonite, which is treated by intercalation with cetyltrimethylammonium bromide; The organically modified montmorillonite is radially gradiently distributed in the material matrix, and the concentration of the surface layer is 150-200% higher than that of the core; The preparation method of the composite flame-retardant cable material comprises the following steps: Step one: ultrasonic dispersion of Mg / Al-LDH, phosphonated chitosan and silane coupling agent KH-550 in an ethanol solution, filtration and drying to obtain surface-modified Mg / Al-LDH, the ultrasonic dispersion conditions are: 40 kHz, 60℃ for 30-60 min, and the mass ratio of Mg / Al-LDH to silane coupling agent KH-550 is 10:1; Step two: mastication of the base resin and ammonium polyphosphate / pentaerythritol at 160-170℃ for 5-10 min; Step three: addition of the surface-modified Mg / Al-LDH treated in step one to the mixture obtained in step two for further mixing, which is divided into two stages, the first stage: mixing at 140℃ and a rotation speed of 40 rpm for 5 min; the second stage: mixing at 150℃ and a rotation speed of 60 rpm for 5 min; Step four: addition of organically modified montmorillonite and synergistic smoke suppressant to the mixture obtained in step three, and extrusion granulation through a twin-screw extruder at a temperature range of 150-170℃, the temperature zoning of the twin-screw extruder is: 150-155℃ at the feeding end, 165-170℃ at the compression section, 160-165℃ at the homogenization section, and the screw rotation speed is 200-400 rpm.

Images