Low heat release flame retardant polyolefin cable material and its twin screw modification method

Abstract

The present application relates to cable material modification technical field, specifically to a kind of low heat release flame-retardant polyolefin cable material and its double-screw modification method;Including polyolefin matrix resin 100 parts, phosphorus-containing triphenylene structure intumescent flame retardant 18 to 28 parts, transition metal chelate char-forming catalyst 0.5 to 3 parts, nano synergistic flame retardant 3 to 8 parts, compatibilizer 5 to 10 parts, antioxidant 0.3 to 1 part, lubricant 0.5 to 2 parts;By introducing transition metal chelate char-forming catalyst, catalyze polyolefin to form carbon quickly when burning, inhibit the peak value of heat release rate in the initial stage of fire, solve the problem of traditional system carbonation lag.

Description

Technical Field

[0001] This invention relates to the field of cable material modification technology, and in particular to a low-heat-release flame-retardant polyolefin cable material and its twin-screw modification method. Background Technology

[0002] Flame-retardant polyolefin cable materials are crucial for ensuring the safe operation of cables in fires. In existing technologies, halogen-free flame-retardant polyolefin cable materials primarily use metal hydroxides such as magnesium hydroxide and aluminum hydroxide as flame retardants. These release water of crystallization and absorb heat upon heating to lower the material temperature and dilute flammable gases. To achieve a sufficient flame retardancy rating, the amount of metal hydroxide added typically needs to reach more than 60% of the base resin. Another commonly used flame-retardant system is the intumescent flame retardant, composed of an acid source, a carbon source, and a gas source. During combustion, it forms an expanded char layer on the material surface, providing thermal and oxygen insulation. Among these, intumescent flame retardants containing phosphorus and phenanthrene structures have attracted attention due to their high charring efficiency and good thermal stability. In terms of processing methods, a twin-screw extruder is typically used to feed all components into the main feed port for melt blending, or a side-feeding method is used to add the flame retardant to reduce its thermal shear degradation.

[0003] However, in the aforementioned existing technologies, both metal hydroxide systems and traditional intumescent flame retardant systems exhibit slow char formation rates in the early stages of a fire. A large amount of heat is generated before the char layer is formed, making it difficult to effectively suppress the peak heat release rate of the material. Metal hydroxides can only release water of crystallization at high temperatures, and the endothermic reaction lags behind the rapid temperature rise in the early stages of combustion. The esterification and cross-linking char formation reaction of traditional intumescent flame retardants requires high temperatures to proceed fully, and an effective heat-insulating char layer cannot be formed quickly in the early stages of a fire, causing the material to continuously release a large amount of heat to the surrounding area in the early stages of combustion, accelerating the spread of the fire. Therefore, there is an urgent need for a flame-retardant polyolefin cable material and its preparation method that can initiate the char formation reaction earlier in a lower temperature range and significantly suppress the heat release rate in the early stages of a fire. Summary of the Invention

[0004] The purpose of this invention is to provide a low heat release flame retardant polyolefin cable material and its twin-screw modification method, aiming to solve the technical problem that in the prior art, whether it is a metal hydroxide system or a traditional intumescent flame retardant system, the char formation rate is slow in the early stage of a fire, and a large amount of heat is generated before the char layer is formed, making it difficult to effectively suppress the peak heat release rate of the material.

[0005] To achieve the above objectives, the present invention employs a low-heat-release flame-retardant polyolefin cable material, which is composed of the following components in parts by weight:

[0006] 100 parts of polyolefin matrix resin, 18 to 28 parts of phosphorus-containing heterophenanthrene intumescent flame retardant, 0.5 to 3 parts of transition metal chelate char-forming catalyst, 3 to 8 parts of nano-synergistic flame retardant, 5 to 10 parts of compatibilizer, 0.3 to 1 part of antioxidant, and 0.5 to 2 parts of lubricant.

[0007] The polyolefin matrix resin is a blend of one or more of the following: ethylene-vinyl acetate copolymer, linear low-density polyethylene, and polyolefin elastomer.

[0008] The ethylene-vinyl acetate copolymer contains 18% to 28% vinyl acetate and has a melt index of 2 to 6 grams per ten minutes.

[0009] The phosphorus-containing phenanthrene-structured intumescent flame retardant is a derivative of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, i.e., DOPO, with a phosphorus content of not less than 12% and an initial thermal decomposition temperature of not less than 280 degrees Celsius.

[0010] The transition metal chelate carbonization catalyst is iron acetylacetonate or cobalt acetylacetonate, with an iron or cobalt mass content of not less than 15% and a thermal decomposition temperature range of 180 to 250 degrees Celsius.

[0011] The nano-synergistic flame retardant is surface-hydroxylated nano-attapulgite or nano-hydrotalcite with an average particle size of no more than 100 nanometers.

[0012] The compatibilizer is maleic anhydride-grafted polyethylene or maleic anhydride-grafted ethylene-octene copolymer, with a grafting rate of 0.8% to 1.5%.

[0013] The antioxidant is a compound of hindered phenolic antioxidants and phosphite antioxidants, with a weight ratio of 1:1 to 2:1.

[0014] The lubricant is one or more of polyethylene wax, calcium stearate, or ethylene bis-stearamide.

[0015] This invention also provides a twin-screw modification method for low-heat-release flame-retardant polyolefin cable materials, comprising the following steps:

[0016] A transition metal chelate char-forming catalyst and a phosphorus-containing phenanthrene-structured intumescent flame retardant were pretreated and mixed in a high-speed mixer to obtain a catalytic flame retardant premix.

[0017] The polyolefin matrix resin is premixed with compatibilizer, antioxidant and lubricant in another high-speed mixer to obtain matrix premix;

[0018] The matrix premix is ​​added from the main feed port of the twin-screw extruder, and the catalytic flame retardant premix and the nano-synergistic flame retardant are added from the side feed port of the twin-screw extruder for melt blending and extrusion.

[0019] The extrudate is water-cooled, air-dried, and pelletized to obtain low-heat-release flame-retardant polyolefin cable material.

[0020] In the step of adding the matrix premix from the main feed port of the twin-screw extruder and adding the catalytic flame retardant premix and the nano-synergistic flame retardant from the side feed port of the twin-screw extruder for melt blending extrusion:

[0021] The twin-screw extruder has a screw length-to-diameter ratio of 40 to 48 and a screw speed of 200 to 350 revolutions per minute;

[0022] The twin-screw extruder is set with ten temperature zones in sequence along the material flow direction. The temperature of each zone is set as follows: Zone 1: 130 to 150 degrees Celsius; Zone 2: 150 to 170 degrees Celsius; Zone 3: 170 to 190 degrees Celsius; Zones 4 to 9: 180 to 195 degrees Celsius; Zone 10: 175 to 185 degrees Celsius.

[0023] In the step of adding the matrix premix from the main feed port of the twin-screw extruder and adding the catalytic flame retardant premix and the nano-synergistic flame retardant from the side feed port of the twin-screw extruder for melt blending extrusion:

[0024] The side feed port is located at the corresponding position in the fourth temperature zone of the twin-screw extruder;

[0025] The catalytic flame retardant premix and the nano-synergistic flame retardant are fed separately using independent loss-in-weight metering feeders, with the feeding accuracy controlled within ±0.5%.

[0026] In the step of adding the matrix premix from the main feed port of the twin-screw extruder and adding the catalytic flame retardant premix and the nano-synergistic flame retardant from the side feed port of the twin-screw extruder for melt blending extrusion:

[0027] The screw assembly of a twin-screw extruder, along the material flow direction, includes, in sequence, a forward conveying element, a forward kneading block, a reverse threading element, a forward conveying element, a toothed disc element, a forward kneading block, a reverse threading element, and a forward conveying element;

[0028] The total length of the kneading block accounts for 20% to 25% of the total length of the screw;

[0029] The total length of the toothed disc element accounts for 8% to 12% of the total length of the screw.

[0030] In the step of pretreating and mixing the transition metal chelate char-forming catalyst with the phosphorus-containing phenanthrene-structured intumescent flame retardant in a high-speed mixer to obtain the catalytic flame retardant premix:

[0031] The pretreatment mixing temperature is 40 to 60 degrees Celsius, and the mixing time is 5 to 10 minutes;

[0032] In the step of premixing the polyolefin matrix resin with compatibilizer, antioxidant and lubricant in another high-speed mixer to obtain matrix premix, the premixing time is 3 to 5 minutes and the premixing temperature is room temperature.

[0033] After the extrudate is water-cooled, air-dried, and pelletized to obtain low-heat-release flame-retardant polyolefin cable material:

[0034] After pelleting, the particles are dried at 80 to 90 degrees Celsius for 2 to 4 hours. Then, particles that do not meet the size requirements are separated by a vibrating screen, and qualified particles are vacuum-packed and stored.

[0035] This invention discloses a low-heat-release flame-retardant polyolefin cable material and its twin-screw modification method. A catalytic flame-retardant premix is ​​formed by pre-mixing a transition metal chelate char-forming catalyst with a phosphorus-containing phenanthrene-structured intumescent flame retardant. This premix is ​​then added from the side feed port of the twin-screw extruder. This avoids premature contact and pre-reaction between the catalyst and the flame retardant during processing, ensuring that the catalyst fully releases metal ions during the combustion stage. This catalyzes the dehydrogenation and cyclization of the polyolefin molecular chains and accelerates the formation of a graphitized carbon layer, allowing the char-forming reaction to begin earlier at a lower temperature range. This results in the rapid formation of a dense, heat-insulating carbon layer in the early stages of a fire, effectively suppressing the peak heat release rate. Simultaneously, the nano-synergistic flame retardant acts as a skeletal support in the carbon layer, enhancing its density and thermal stability, further reducing the total heat release during combustion. Furthermore, this side-feeding method avoids the flame retardant undergoing high shear stress throughout the screw extruder, reducing its thermal degradation and maintaining good mechanical properties and extrusion processability. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of the steps in the twin-screw modification method for low-heat-release flame-retardant polyolefin cable material according to the present invention.

[0038] Figure 2 This is a flowchart of the steps in Embodiment 1 of the present invention.

[0039] Figure 3 This is a flowchart of the steps in Embodiment 2 of the present invention.

[0040] Figure 4 This is a flowchart of the steps in Embodiment 3 of the present invention. Detailed Implementation

[0041] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0042] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0043] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0044] Please see Figures 1-4 This invention provides a twin-screw modification method for low-heat-release flame-retardant polyolefin cable materials, comprising the following steps:

[0045] S1: The transition metal chelate carbonization catalyst and the phosphorus-containing phenanthrene structure intumescent flame retardant are pretreated and mixed in a high-speed mixer to obtain a catalytic flame retardant premix.

[0046] S2: Premix the polyolefin matrix resin with compatibilizer, antioxidant and lubricant in another high-speed mixer to obtain matrix premix;

[0047] S3: The matrix premix is ​​added from the main feed port of the twin-screw extruder, and the catalytic flame retardant premix and the nano-synergistic flame retardant are added from the side feed port of the twin-screw extruder for melt blending and extrusion.

[0048] S4: The extrudate is water-cooled, air-dried, and pelletized to obtain low-heat-release flame-retardant polyolefin cable material.

[0049] In this process, the transition metal chelate char-forming catalyst and the phosphorus-containing phenanthrene-structured intumescent flame retardant are pre-treated and mixed in a high-speed mixer. This pre-treatment aims to ensure the catalyst is uniformly adhered to the surface of the flame retardant particles, forming a stable catalytic flame retardant premix. This prevents premature thermal decomposition or pre-reaction of both materials during subsequent twin-screw extrusion due to screw shear heating, ensuring that metal ions are fully released during combustion to exert their catalytic char-forming effect. The polyolefin matrix resin is then pre-mixed separately with compatibilizers, antioxidants, and lubricants to ensure uniform coating of the resin particles with these additives. This improves the uniformity of the matrix during plasticization and reduces uneven flame retardant dispersion caused by local viscosity differences in the subsequent melting stage. The feeding method, which involves adding the matrix premix at the main feed port and the catalytic flame retardant premix and nano-synergistic flame retardant at the side feed ports, ensures that the matrix resin is fully melted and plasticized in the first few temperature zones before the flame retardant and catalyst enter the screw at the corresponding position in the fourth temperature zone. This avoids thermal degradation of the flame retardant due to prolonged high-temperature shearing throughout the screw, and also reduces the risk of decomposition of transition metal chelates due to premature contact with the melt during processing. The side feed position is chosen in the fourth temperature zone, corresponding to the stage where the matrix resin has essentially melted but the viscosity has not yet decreased significantly. This facilitates rapid wetting and dispersion of the flame retardant and nano-synergistic flame retardant in the melt, preventing insufficient mixing shear force due to excessively low melt viscosity. The catalytic flame retardant premix and nano-synergistic flame retardant are fed separately using independent loss-in-weight metering feeders to precisely control their ratio and avoid feeding fluctuations caused by differences in their bulk densities, thereby ensuring stable content of catalyst and synergistic flame retardant in each batch of product. After extrusion, the melt is cooled and solidified by water to prevent the flame retardant from decomposing or migrating at high temperatures. After air drying to remove surface moisture, it is granulated to obtain finished particles.

[0050] Polyolefin matrix resin provides the material's basic mechanical and electrical insulation properties. ethylene-vinyl acetate copolymer is blended with linear low-density polyethylene and polyolefin elastomers, balancing polar compatibility, rigidity, and flexibility. A phosphorus-containing phenanthrene-structured intumescent flame retardant decomposes upon heating to produce phosphoric acid, promoting dehydration and char formation in the matrix. Simultaneously, it releases phosphorus-containing free radicals to inhibit gas-phase combustion. Its thermal decomposition temperature is higher than the processing temperature, ensuring processing safety. A transition metal chelate char-forming catalyst releases iron or cobalt ions during combustion, catalyzing the dehydrogenation and cyclization of the polyolefin molecular chains, enabling the char formation reaction to begin at a lower temperature, rapidly forming a dense char layer in the early stages of a fire. Nano-synergistic flame retardants are embedded in the char layer, providing skeletal support, enhancing the char layer's density and erosion resistance, and preventing char layer peeling and failure. The maleic anhydride groups of the compatibilizer react with the hydroxyl groups on the flame retardant surface, improving the uniformity of the flame retardant's dispersion in the matrix. Antioxidants prevent thermo-oxidative degradation during processing, and lubricants reduce melt viscosity and improve extrusion smoothness. These three elements work together to ensure the material's processing stability and long-term performance.

[0051] Example 1

[0052] S101: 1.5 parts of acetylacetone iron and 22 parts of DOPO-based intumescent flame retardant are pre-mixed in a high-speed mixer. The mixing temperature is set at 50 degrees Celsius, the mixing time is 8 minutes, and the speed is 800 rpm to obtain a catalytic flame retardant premix.

[0053] S102: 70 parts of ethylene-vinyl acetate copolymer, 30 parts of linear low-density polyethylene, 8 parts of maleic anhydride-grafted polyethylene, 0.3 parts of hindered phenolic antioxidant, 0.3 parts of phosphite antioxidant, 1.0 part of polyethylene wax, and 0.5 parts of calcium stearate are premixed in another high-speed mixer for 4 minutes at room temperature and 600 rpm to obtain the matrix premix. The ethylene-vinyl acetate copolymer contains 22% vinyl acetate and has a melt index of 4 g / 10 min. The grafting rate of the maleic anhydride-grafted polyethylene is 1.0%. The DOPO-based intumescent flame retardant contains 14% phosphorus and has an initial thermal decomposition temperature of 295°C. The acetylacetone iron contains 16% iron by mass and has a thermal decomposition temperature range of 190 to 240°C.

[0054] S103: Add the matrix premix from the main feed port of the twin-screw extruder;

[0055] S104: Add 5 parts of the catalytic flame retardant premix and 5 parts of surface hydroxylated nano-attapulgite from the side feed port of the twin-screw extruder. The side feed port is located at the corresponding position of the fourth temperature zone of the twin-screw extruder. The catalytic flame retardant premix and the nano-attapulgite are each fed by an independent loss-in-weight metering feeder. The feeding accuracy is controlled within ±0.5%. The average particle size of the nano-attapulgite is 80 nanometers.

[0056] S105: Set the twin-screw extruder screw length-to-diameter ratio to 44, screw speed to 280 rpm, and set the temperatures of each zone as follows: Zone 1 140 degrees Celsius, Zone 2 160 degrees Celsius, Zone 3 180 degrees Celsius, Zone 4 185 degrees Celsius, Zone 5 188 degrees Celsius, Zone 6 190 degrees Celsius, Zone 7 192 degrees Celsius, Zone 8 190 degrees Celsius, Zone 9 188 degrees Celsius, Zone 10 180 degrees Celsius;

[0057] S106: The screw assembly of the twin-screw extruder is set to be, along the material flow direction, a forward conveying element, a forward kneading block, a reverse threading element, a forward conveying element, a toothed disc element, a forward kneading block, a reverse threading element, and a forward conveying element. The total length of the kneading block accounts for 22% of the total screw length, and the total length of the toothed disc element accounts for 10% of the total screw length, for melt blending extrusion.

[0058] S107: The extrudate is water-cooled, air-dried, and pelletized. The pellets are dried at 85 degrees Celsius for 3 hours. Particles that do not meet the size requirements are separated by a vibrating screen. The qualified particles are vacuum-packed and stored to obtain low heat release flame retardant polyolefin cable material.

[0059] First, 1.5 parts of acetylacetone iron and 22 parts of DOPO-based intumescent flame retardant were pre-mixed in a high-speed mixer at 50 degrees Celsius and 800 rpm for 8 minutes to obtain a catalytic flame retardant premix. Simultaneously, 70 parts of ethylene-vinyl acetate copolymer, 30 parts of linear low-density polyethylene, 8 parts of maleic anhydride-grafted polyethylene, 0.3 parts of hindered phenolic antioxidant, 0.3 parts of phosphite antioxidant, 1.0 part of polyethylene wax, and 0.5 parts of calcium stearate were mixed in another high-speed mixer. The matrix premix was obtained by premixing for 4 minutes at a speed of 600 rpm. The matrix premix was then added through the main feed port of the twin-screw extruder. Five parts of the catalytic flame-retardant premix and five parts of surface-hydroxylated nano-attapulgite were added through the side feed ports corresponding to the fourth temperature zone using independent loss-in-weight metering feeders. The twin-screw extruder had an aspect ratio of 44, a screw speed of 280 rpm, and the ten zone temperatures were set sequentially to 140°C, 160°C, 180°C, 185°C, 188°C, and 188°C. The screw assembly, consisting of a forward conveying element, a forward kneading block, a reverse threaded element, a forward conveying element, a toothed disc element, a forward kneading block, a reverse threaded element, and a forward conveying element, operates at temperatures of 180°C, 190°C, 192°C, 190°C, 188°C, and 180°C. The kneading block comprises 22% of the total screw length, and the toothed disc element comprises 10%. Melt-blending extrusion is performed. The extrudate is water-cooled, air-dried, pelletized, and then dried at 85°C for 3 hours before being screened by a vibrating sieve. After removing particles that do not meet the particle size requirements, the material is vacuum-packed and stored to obtain low heat release flame retardant polyolefin cable material. The low heat release specifically refers to the material being tested according to the cone calorimeter method of GB / T16172-2007 at a radiation power of 50kW / m², with a peak heat release rate of 215kW / m² and a total heat release of 62MJ / m², which is 43% lower than the peak heat release rate of traditional intumescent flame retardant polyolefin cable material without catalyst of the same formula.

[0060] Example 2

[0061] S201: 2.0 parts of cobalt acetylacetone and 25 parts of DOPO-based intumescent flame retardant are pre-mixed in a high-speed mixer. The mixing temperature is set at 45 degrees Celsius, the mixing time is 10 minutes, and the speed is 900 rpm to obtain a catalytic flame retardant premix.

[0062] S202: 60 parts of ethylene-vinyl acetate copolymer, 25 parts of linear low-density polyethylene, 15 parts of polyolefin elastomer, 8 parts of maleic anhydride-grafted ethylene-octene copolymer, 0.4 parts of hindered phenolic antioxidant, 0.2 parts of phosphite antioxidant, 1.0 part of ethylene bis-stearamide, and 0.5 parts of polyethylene wax are premixed in another high-speed mixer for 5 minutes at room temperature and 700 rpm to obtain the matrix premix. The ethylene-vinyl acetate copolymer contains 25% vinyl acetate and has a melt index of 5 g / 10 min. The grafting rate of the maleic anhydride-grafted ethylene-octene copolymer is 1.2%. The DOPO-based intumescent flame retardant contains 13% phosphorus and has an initial thermal decomposition temperature of 290°C. The cobalt acetylacetone contains 16% cobalt by mass and has a thermal decomposition temperature range of 185 to 235°C.

[0063] S203: Add the matrix premix from the main feed port of the twin-screw extruder;

[0064] S204: Six parts of the catalytic flame retardant premix and the surface hydroxylated nano-attapulgite were added separately from the side feed port of the twin-screw extruder. The side feed port was located at the corresponding position of the fourth temperature zone of the twin-screw extruder. The catalytic flame retardant premix and the nano-attapulgite were each fed by an independent loss-in-weight metering feeder, and the feeding accuracy was controlled within ±0.5%. The average particle size of the nano-attapulgite was 70 nanometers.

[0065] S205: The twin-screw extruder is set with a screw length-to-diameter ratio of 46, a screw speed of 300 rpm, and the temperature settings for each zone are as follows: Zone 1 135 degrees Celsius, Zone 2 155 degrees Celsius, Zone 3 175 degrees Celsius, Zone 4 183 degrees Celsius, Zone 5 186 degrees Celsius, Zone 6 190 degrees Celsius, Zone 7 193 degrees Celsius, Zone 8 192 degrees Celsius, Zone 9 185 degrees Celsius, and Zone 10 178 degrees Celsius.

[0066] S206: The screw assembly of the twin-screw extruder is set to be, along the material flow direction, a forward conveying element, a forward kneading block, a reverse threading element, a forward conveying element, a toothed disc element, a forward kneading block, a reverse threading element, and a forward conveying element. The total length of the kneading block accounts for 23% of the total screw length, and the total length of the toothed disc element accounts for 11% of the total screw length. Melt blending extrusion is performed.

[0067] S207: The extrudate is water-cooled, air-dried, and pelletized. The pellets are dried at 82 degrees Celsius for 4 hours. Particles that do not meet the size requirements are separated by a vibrating screen. The qualified particles are vacuum-packed and stored to obtain low heat release flame retardant polyolefin cable material.

[0068] The process involves first pre-mixing 2.0 parts of cobalt acetylacetone and 25 parts of DOPO-based intumescent flame retardant in a high-speed mixer at 45°C and 900 rpm for 10 minutes to obtain a catalytic flame retardant premix; simultaneously, 60 parts of ethylene-vinyl acetate copolymer, 25 parts of linear low-density polyethylene, 15 parts of polyolefin elastomer, 8 parts of maleic anhydride-grafted ethylene-octene copolymer, 0.4 parts of hindered phenolic antioxidant, 0.2 parts of phosphite antioxidant, 1.0 part of ethylene bis-stearamide, and polyethylene wax are added. 0.5 parts were premixed at room temperature for 5 minutes at 700 rpm in another high-speed mixer to obtain the matrix premix. The matrix premix was then added through the main feed port of a twin-screw extruder. Six parts of the catalytic flame-retardant premix and surface-hydroxylated nano-attapulgite were added separately through the side feed ports corresponding to the fourth temperature zone using independent loss-in-weight metering feeders. The twin-screw extruder had a length-to-diameter ratio of 46, a screw speed of 300 rpm, and the ten zone temperatures were set sequentially to 135°C, 155°C, 175°C, and 1... The screw assembly, consisting of a forward conveying element, a forward kneading block, a reverse threaded element, a forward conveying element, a toothed disc element, a forward kneading block, a reverse threaded element, and a forward conveying element, was applied at temperatures of 83°C, 186°C, 190°C, 193°C, 192°C, 185°C, and 178°C. The kneading block comprised 23% of the total screw length, and the toothed disc element comprised 11%. Melt-blending extrusion was performed. The extrudate was then water-cooled, air-dried, pelletized, and dried at 82°C for 4 hours. After separating unqualified particles by vibrating screen, the material is vacuum-packed and stored to obtain low heat release flame retardant polyolefin cable material. The low heat release specifically refers to the peak heat release rate of the material being 198 kW / m² and the total heat release being 58 MJ / m², as tested according to the cone calorimeter method in GB / T16172-2007 at a radiation power of 50 kW / m². Compared with the traditional intumescent flame retardant polyolefin cable material without catalyst of the same formula, the peak heat release rate is reduced by 47%.

[0069] Example 3

[0070] S301: 1.0 part of acetylacetone iron and 20 parts of DOPO-based intumescent flame retardant are pre-mixed in a high-speed mixer. The mixing temperature is set at 55 degrees Celsius, the mixing time is 6 minutes, and the speed is 850 rpm to obtain a catalytic flame retardant premix.

[0071] S302: 50 parts of linear low-density polyethylene, 40 parts of ethylene-vinyl acetate copolymer, 10 parts of polyolefin elastomer, 6 parts of maleic anhydride-grafted polyethylene, 0.5 parts of hindered phenolic antioxidant, 0.3 parts of phosphite antioxidant, and 1.2 parts of calcium stearate are premixed in another high-speed mixer for 3 minutes at room temperature and 550 rpm to obtain the matrix premix. The ethylene-vinyl acetate copolymer contains 20% vinyl acetate and has a melt index of 3 g / 10 min. The grafting rate of the maleic anhydride-grafted polyethylene is 0.9%. The DOPO-based intumescent flame retardant contains 15% phosphorus and has an initial thermal decomposition temperature of 300°C. The acetylacetone iron contains 17% iron by mass and has a thermal decomposition temperature range of 195 to 245°C.

[0072] S303: Add the matrix premix from the main feed port of the twin-screw extruder;

[0073] S304: Add 7 parts of the catalytic flame retardant premix and nano-hydrotalcite separately from the side feed port of the twin-screw extruder. The side feed port is located at the corresponding position of the fourth temperature zone of the twin-screw extruder. The catalytic flame retardant premix and nano-hydrotalcite each use an independent loss-in-weight metering feeder, and the feeding accuracy is controlled within ±0.5%. The average particle size of the nano-hydrotalcite is 90 nanometers.

[0074] S305: The twin-screw extruder is set with a screw length-to-diameter ratio of 42, a screw speed of 250 rpm, and the temperature settings for each zone are as follows: Zone 1 145 degrees Celsius, Zone 2 165 degrees Celsius, Zone 3 183 degrees Celsius, Zone 4 187 degrees Celsius, Zone 5 190 degrees Celsius, Zone 6 192 degrees Celsius, Zone 7 194 degrees Celsius, Zone 8 192 degrees Celsius, Zone 9 186 degrees Celsius, and Zone 10 182 degrees Celsius.

[0075] S306: The screw assembly of the twin-screw extruder is set to be, along the material flow direction, a forward conveying element, a forward kneading block, a reverse threading element, a forward conveying element, a toothed disc element, a forward kneading block, a reverse threading element, and a forward conveying element. The total length of the kneading block accounts for 21% of the total screw length, and the total length of the toothed disc element accounts for 9% of the total screw length. Melt blending extrusion is performed.

[0076] S307: The extrudate is water-cooled, air-dried, and pelletized. The pellets are dried at 88 degrees Celsius for 2.5 hours. Particles that do not meet the size requirements are separated by a vibrating screen. The qualified particles are vacuum-packed and stored to obtain low heat release flame retardant polyolefin cable material.

[0077] First, 1.0 part of acetylacetone iron and 20 parts of DOPO-based intumescent flame retardant were pre-mixed in a high-speed mixer at 55 degrees Celsius and 850 rpm for 6 minutes to obtain a catalytic flame retardant premix. Simultaneously, 50 parts of linear low-density polyethylene, 40 parts of ethylene-vinyl acetate copolymer, 10 parts of polyolefin elastomer, 6 parts of maleic anhydride-grafted polyethylene, 0.5 parts of hindered phenolic antioxidant, 0.3 parts of phosphite antioxidant, and 1.2 parts of calcium stearate were mixed in another high-speed mixer. The matrix premix was obtained by premixing at room temperature for 3 minutes at a speed of 550 rpm. Then, the matrix premix was added through the main feed port of a twin-screw extruder. Seven parts of the catalytic flame-retardant premix and nano-hydrotalcite were added separately through the side feed ports corresponding to the fourth temperature zone using independent loss-in-weight metering feeders. The twin-screw extruder had a length-to-diameter ratio of 42, a screw speed of 250 rpm, and the ten zone temperatures were set sequentially to 145°C, 165°C, 183°C, 187°C, and 190°C. The screw assembly, consisting of a forward conveying element, a forward kneading block, a reverse threaded element, a forward conveying element, a toothed disc element, a forward kneading block, a reverse threaded element, and a forward conveying element, operates at temperatures of 192°C, 194°C, 192°C, 186°C, and 182°C. The kneading block comprises 21% of the total screw length, and the toothed disc element comprises 9%. Melt-blending extrusion is performed. The extrudate is water-cooled, air-dried, pelletized, and then dried at 88°C for 2.5 hours before being separated by a vibrating screen. Particles with unqualified particle size are vacuum-packed and stored to obtain low-heat-release flame-retardant polyolefin cable material; the low-heat-release specifically refers to the material being tested according to the cone calorimeter method of GB / T16172-2007 at a radiation power of 50kW / m², with a peak heat release rate of 232kW / m² and a total heat release of 65MJ / m², which is 39% lower than the peak heat release rate of traditional intumescent flame-retardant polyolefin cable material without catalyst of the same formula.

[0078] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0079] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A low-heat-release flame-retardant polyolefin cable material, characterized in that, It consists of the following components in parts by weight: 100 parts of polyolefin matrix resin, 18 to 28 parts of phosphorus-containing heterophenanthrene intumescent flame retardant, 0.5 to 3 parts of transition metal chelate char-forming catalyst, 3 to 8 parts of nano-synergistic flame retardant, 5 to 10 parts of compatibilizer, 0.3 to 1 part of antioxidant, and 0.5 to 2 parts of lubricant.

2. The low heat release flame-retardant polyolefin cable material as described in claim 1, characterized in that: The polyolefin matrix resin is a blend of one or more of the following: ethylene-vinyl acetate copolymer, linear low-density polyethylene, and polyolefin elastomer. The ethylene-vinyl acetate copolymer contains 18% to 28% vinyl acetate and has a melt index of 2 to 6 grams per ten minutes.

3. The low heat release flame-retardant polyolefin cable material as described in claim 1, characterized in that: The phosphorus-containing phenanthrene-structured intumescent flame retardant is a derivative of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, i.e., DOPO, with a phosphorus content of not less than 12% and an initial thermal decomposition temperature of not less than 280 degrees Celsius. The transition metal chelate carbonization catalyst is iron acetylacetonate or cobalt acetylacetonate, with an iron or cobalt mass content of not less than 15% and a thermal decomposition temperature range of 180 to 250 degrees Celsius. The nano-synergistic flame retardant is surface-hydroxylated nano-attapulgite or nano-hydrotalcite with an average particle size of no more than 100 nanometers.

4. The low heat release flame-retardant polyolefin cable material as described in claim 1, characterized in that: The compatibilizer is maleic anhydride-grafted polyethylene or maleic anhydride-grafted ethylene-octene copolymer, with a grafting rate of 0.8% to 1.5%. The antioxidant is a compound of hindered phenolic antioxidants and phosphite antioxidants, with a weight ratio of 1:1 to 2:

1. The lubricant is one or more of polyethylene wax, calcium stearate, or ethylene bis-stearamide.

5. A twin-screw modification method for low-heat-release flame-retardant polyolefin cable material, using the low-heat-release flame-retardant polyolefin cable material as described in claim 1, characterized in that, Includes the following steps: A transition metal chelate char-forming catalyst and a phosphorus-containing phenanthrene-structured intumescent flame retardant were pretreated and mixed in a high-speed mixer to obtain a catalytic flame retardant premix. The polyolefin matrix resin is premixed with compatibilizer, antioxidant and lubricant in another high-speed mixer to obtain matrix premix; The matrix premix is ​​added from the main feed port of the twin-screw extruder, and the catalytic flame retardant premix and the nano-synergistic flame retardant are added from the side feed port of the twin-screw extruder for melt blending and extrusion. The extrudate is water-cooled, air-dried, and pelletized to obtain low-heat-release flame-retardant polyolefin cable material.

6. The twin-screw modification method for low-heat-release flame-retardant polyolefin cable material as described in claim 5, characterized in that, In the step of melt-blending extrusion, the matrix premix is ​​fed from the main feed port of the twin-screw extruder, and the catalytic flame retardant premix and the nano-synergistic flame retardant are fed from the side feed port of the twin-screw extruder: The twin-screw extruder has a screw length-to-diameter ratio of 40 to 48 and a screw speed of 200 to 350 revolutions per minute; The twin-screw extruder is set with ten temperature zones in sequence along the material flow direction. The temperature of each zone is set as follows: Zone 1: 130 to 150 degrees Celsius; Zone 2: 150 to 170 degrees Celsius; Zone 3: 170 to 190 degrees Celsius; Zones 4 to 9: 180 to 195 degrees Celsius; Zone 10: 175 to 185 degrees Celsius.

7. The twin-screw modification method for low-heat-release flame-retardant polyolefin cable material as described in claim 5, characterized in that, In the step of melt-blending extrusion, the matrix premix is ​​fed from the main feed port of the twin-screw extruder, and the catalytic flame retardant premix and the nano-synergistic flame retardant are fed from the side feed port of the twin-screw extruder: The side feed port is located at the corresponding position in the fourth temperature zone of the twin-screw extruder; The catalytic flame retardant premix and the nano-synergistic flame retardant are fed separately using independent loss-in-weight metering feeders, with the feeding accuracy controlled within ±0.5%.

8. The twin-screw modification method for low-heat-release flame-retardant polyolefin cable material as described in claim 5, characterized in that, In the step of melt-blending extrusion, the matrix premix is ​​fed from the main feed port of the twin-screw extruder, and the catalytic flame retardant premix and the nano-synergistic flame retardant are fed from the side feed port of the twin-screw extruder: The screw assembly of a twin-screw extruder, along the material flow direction, includes, in sequence, a forward conveying element, a forward kneading block, a reverse threading element, a forward conveying element, a toothed disc element, a forward kneading block, a reverse threading element, and a forward conveying element; The total length of the kneading block accounts for 20% to 25% of the total length of the screw; The total length of the toothed disc element accounts for 8% to 12% of the total length of the screw.

9. The twin-screw modification method for low-heat-release flame-retardant polyolefin cable material as described in claim 5, characterized in that, In the step of pretreating and mixing a transition metal chelate char-forming catalyst with a phosphorus-containing phenanthrene-structured expandable flame retardant in a high-speed mixer to obtain a catalytic flame retardant premix: The pretreatment mixing temperature is 40 to 60 degrees Celsius, and the mixing time is 5 to 10 minutes; In the step of premixing the polyolefin matrix resin with compatibilizer, antioxidant and lubricant in another high-speed mixer to obtain matrix premix, the premixing time is 3 to 5 minutes and the premixing temperature is room temperature.

10. The twin-screw modification method for low-heat-release flame-retardant polyolefin cable material as described in claim 5, characterized in that, After the extrudate is water-cooled, air-dried, and pelletized to obtain low-heat-release flame-retardant polyolefin cable material: After pelleting, the particles are dried at 80 to 90 degrees Celsius for 2 to 4 hours. Then, particles that do not meet the size requirements are separated by a vibrating screen, and qualified particles are vacuum-packed and stored.

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