Polyolefin cable material suitable for extrusion pipe moulds and process for the production thereof

Abstract

The application discloses a polyolefin cable material suitable for an extrusion pipe type mold and a preparation method thereof, and relates to the technical field of cable materials. The polyolefin cable material suitable for the extrusion pipe type mold comprises the following components in parts by weight: 80-90 parts of aluminum hydroxide, 0.5-0.8 parts of methyl silicone oil, 5-6 parts of grafting material, 2-3 parts of polyolefin elastomer, 1-2.5 parts of color masterbatch, 20-30 parts of ethylene / vinyl acetate copolymer, 5-10 parts of metallocene polyethylene, 0.5-1.5 parts of antioxidant, 5-6 parts of crust agent, 0.2-0.6 parts of red phosphorus and 0.5-1.5 parts of low-molecular-weight ethylene / 1-hexene copolymer. The low-molecular-weight ethylene / 1-hexene copolymer penetrates into the cable material and reduces the binding force between the molecular chains of the material, so that the problems of high elongation at break and poor combustion performance of the cable after aging due to high internal stress are solved.

Description

Technical Field

[0001] The present application relates to the technical field of cable materials, and in particular to a polyolefin cable material suitable for a tube extrusion die and a preparation method thereof. Background Art

[0002] During the plastic melt processing, due to factors such as the orientation of the macromolecular chain and cooling shrinkage, an internal stress will be generated. The greater the rigidity of the molecular chain (for example, with benzene rings), the higher the melt viscosity, and the easier it is to generate internal stress; the greater the polarity of the molecular chain group, the more difficult it is to eliminate the internal stress. Like stress, internal stress can cause material deformation, and long-term internal stress can cause product creep. When the internal stress is too large, it can manifest as changes in product size and warping of the product at the mildest; in severe cases, the product may crack and break after a period of use. When ordinary halogen-free, low-smoke, flame-retardant polyolefin cable sheath materials are used to make cables using an extrusion die, a large internal stress will be generated inside the cable sheath layer, which will make the material's elongation at break relatively high and will also affect the level of burning drips / particles. Therefore, in order to improve the elongation at break of the cable sheath layer after aging and the cable's combustion grade performance, the present application proposes a polyolefin cable material suitable for an extrusion die and a preparation method thereof. Summary of the Invention

[0003] The main purpose of this application is to provide a polyolefin cable material suitable for an extrusion die and a preparation method thereof, aiming to solve the technical problem that the elongation at break and the burning grade performance of the cable after aging when the polyolefin cable material is made into a cable through an extrusion die are not ideal.

[0004] To achieve the above-mentioned purpose, the present application proposes a polyolefin cable material suitable for an extrusion tube mold, which comprises the following components in parts by weight: 80-90 parts of aluminum hydroxide, 0.5-0.8 parts of methyl silicone oil, 5-6 parts of grafting material, 2-3 parts of polyolefin elastomer, 1-2.5 parts of masterbatch, 20-30 parts of ethylene / vinyl acetate copolymer, 5-10 parts of metallocene polyethylene, 0.5-1.5 parts of antioxidant, 5-6 parts of encrusting agent, 0.2-0.6 parts of red phosphorus and 0.5-1.5 parts of low molecular weight ethylene / 1-hexene copolymer.

[0005] Optionally, the synthesis step of the low molecular weight ethylene / 1-hexene copolymer comprises:

[0006] The gas in the reactor is replaced by an inert gas, and then the gas in the reactor is replaced by ethylene;

[0007] After the ethylene gas replacement, ethylene was continuously introduced into the reactor, and then toluene and 1-hexene were introduced, the temperature was adjusted to 60° C., a co-catalyst was added and stirred, and then the catalyst was added to react;

[0008] After reacting for 5 minutes, ethylene was cut off, and the reacted material was added to a mixed solution of ethanol and hydrochloric acid, stirred, filtered, and then washed alternately with water and ethanol, and dried at 75°C-85°C to obtain a low molecular weight ethylene / 1-hexene copolymer.

[0009] Optionally, before the step of replacing the gas in the reactor with nitrogen and then replacing the gas in the reactor with ethylene, the process further comprises:

[0010] Refluxing the toluene through a sodium wire to remove water, and distilling the toluene under reflux under nitrogen protection using benzophenone as an indicator in the presence of the sodium wire to obtain pretreated toluene;

[0011] Ethylene and inert gas are passed through molecular sieve, silver molecular sieve and sodium potassium alloy for purification to obtain pretreated ethylene and pretreated inert gas;

[0012] After 1-hexene was stirred with CaH2 overnight, it was distilled off under nitrogen protection to obtain pretreated 1-hexene.

[0013] Optionally, the co-catalyst is modified methylaluminoxane, and the catalyst is a salicylaldimine-type [O, N, S] tridentate titanium complex.

[0014] Optionally, the antioxidant includes pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dilauryl thiodipropionate, and 2,2′-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0015] The present application also proposes a method for preparing a polyolefin cable material suitable for an extrusion tube die, comprising the following steps:

[0016] S1, mixing all the components and performing banburying to obtain a mixture;

[0017] S2, plasticizing and extruding the mixture through a double-stage screw, hot-cutting and granulating, and cooling to obtain a semi-finished product;

[0018] S3. Repeat the process of step S2 on the semi-finished product to obtain a finished polyolefin cable material.

[0019] Optionally, the step of mixing all the components and kneading to obtain a mixture comprises:

[0020] Add all components into the internal mixer for internal mixing. Set the internal mixing pressure current to 250A. When the internal mixing temperature is 110℃-115℃, carry out the first powder sweep and continue the internal mixing. When the internal mixing temperature is 130℃-135℃, carry out the second powder sweep and continue the internal mixing. When the internal mixing temperature reaches 180℃, end the internal mixing.

[0021] Optionally, the step of plasticizing and extruding the mixed material through a double-stage screw comprises:

[0022] The mixed material is plasticized by passing through a twin-screw extruder and a single-screw extruder in sequence.

[0023] Optionally, when the mixture is plasticized by a twin-screw extruder, the temperature of the feeding zone of the twin-screw extruder is 115℃-125℃, and the nine temperature zones of the twin-screw extruder are set to 125℃-135℃, 125℃-135℃, 120℃-130℃, 120℃-130℃, 115℃-125℃, 115℃-125℃, 105℃-115℃, 105℃-115℃, and 105℃-115℃, respectively, and the current of the twin-screw extruder is set to 180A-210A.

[0024] Optionally, when the mixture is plasticized by a single-screw extruder, the temperatures of the three temperature control zones of the single-screw extruder are set to 115°C-125°C, 130°C-140°C, and 140°C-150°C, respectively, the temperature of the screen-changing zone of the single-screw extruder is 145°C-155°C, the head temperature of the single-screw extruder is 145°C-155°C, and the current of the single-screw extruder is set to 50A-90A.

[0025] The present application is based on the problem that when a polyolefin cable material is used to produce a cable sheath layer using an extrusion die, the cable sheath layer has a high rate of change in elongation at break after aging and a low combustion grade performance of the cable. It is found that when the polyolefin cable material is used to make a cable using an extrusion die, a high internal stress is formed inside the cable sheath layer in a direction parallel to the cable axis, which makes the polymer molecular chain segments inside the sheath layer arranged in the direction of the tensile force, so that the cable has a high elongation at break; and because the cable sheath melt is subjected to a large tensile force when the extrusion die is used to prepare the cable, the cable material melt is arranged in the flow direction during the flow filling process of the cable material melt, and the polyolefin cable material melt is cooled by cooling water after coming out of the die mouth, so that the directional conformation is frozen and internal stress is generated. When the cable sheath layer is heated by flame, part of the internal stress inside the cable sheath layer disappears, and the molecular chain changes from a stretched state to a relaxed state, which makes the heated cable sheath layer deform and curl, resulting in the carbon layer at the flame burning location to easily fall off, which is not conducive to the combustion performance of the cable. Therefore, in order to improve the elongation at break and the cable combustion grade performance after aging, the present application starts from reducing the internal stress of the cable sheath layer. Conventional polyolefin cable materials often use ethylene / vinyl acetate copolymers with high vinyl acetate content to improve the elongation at break of cable materials. However, ethylene / vinyl acetate copolymers have a large number of polar groups, which leads to the production of polyolefin cable materials using them as raw materials. When using extrusion molds to produce cables, internal stress will still be generated during the flow filling and cold water cooling process. The higher the melt viscosity, the easier it is to generate internal stress, and the greater the polarity of the molecular chain groups, the more It is difficult to eliminate internal stress, so this application avoids the large-scale use of ethylene / vinyl acetate copolymer and adopts low-molecular-weight ethylene / 1-hexene copolymer as a substitute. It does not contain a large number of polar groups. When using an extrusion mold to produce cables, the low-molecular-weight ethylene / 1-hexene copolymer will penetrate into the interior of the cable material and reduce the bonding force between the molecular chains of the material, so that the molecular chains of the cable material melt in a stretched state can be quickly transformed into a curled state after cooling, so as to reduce the generation of internal stress, thereby solving the problem of high elongation at break and poor combustion performance of the cable after aging due to the high internal stress of the cable sheath layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0027] Figure 1 Schematic diagram of the chemical structure of the catalyst described in the examples of this application;

[0028] Figure 2 This is a combustion test diagram of a cable sheath made of a polyolefin cable material suitable for a tube extrusion die according to an embodiment of the present application;

[0029] Figure 3 This is a combustion test diagram of a cable sheath made of polyolefin cable material in the comparative example of this application. DETAILED DESCRIPTION

[0030] The following is a clear and complete description of the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0031] When ordinary halogen-free, low-smoke, flame-retardant polyolefin cable sheath materials are manufactured using an extrusion die, high internal stress is generated within the sheath parallel to the cable axis. This causes the polymer molecular segments within the sheath to align in the direction of the tensile force, resulting in a relatively high elongation at break. Furthermore, cables manufactured using an extrusion die experience high internal stress within the sheath due to the high tensile force exerted on the melt of the cable sheath. When the cable sheath is heated by flames, some of the internal stress disappears, and the molecular chains transition from a stretched state to a relaxed state. This causes the heated cable sheath to deform and curl, making it easier for the carbon layer to fall off at the point of combustion. This exposes the non-flame-retardant material within the cable to the flames, resulting in unsatisfactory combustion results and affecting the level of combustion droplets and particulates.

[0032] In response to the technical problems of polyolefin cable materials in the above-mentioned prior art, an embodiment of the present application provides a polyolefin cable material suitable for an extrusion tube mold, which includes the following components, by weight: 80-90 parts of aluminum hydroxide, 0.5-0.8 parts of methyl silicone oil, 5-6 parts of grafting material, 2-3 parts of polyolefin elastomer, 1-2.5 parts of masterbatch, 20-30 parts of ethylene / vinyl acetate copolymer, 5-10 parts of metallocene polyethylene, 0.5-1.5 parts of antioxidant, 5-6 parts of encrusting agent, 0.2-0.6 parts of red phosphorus and 0.5-1.5 parts of low molecular weight ethylene / 1-hexene copolymer.

[0033] The present application aims to improve the elongation at break and the cable combustion grade performance after aging of the cable sheath layer, starting from reducing the internal stress of the cable sheath layer. Conventional polyolefin cable materials often use ethylene / vinyl acetate copolymers with high vinyl acetate content to improve the elongation at break of the cable materials. However, ethylene / vinyl acetate copolymers have a large number of polar groups, which leads to the polyolefin cable materials produced with them as raw materials. When using extrusion molds to produce cables, internal stress will still be generated during the flow filling and cold water cooling process. The higher the melt viscosity, the easier it is to generate internal stress, and the greater the polarity of the molecular chain groups, the more difficult it is to eliminate Internal stress, so the present application avoids using a large amount of ethylene / vinyl acetate copolymer, and adopts a low molecular weight ethylene / 1-hexene copolymer as a substitute, which does not contain a large number of polar groups. When using an extrusion mold to produce cables, the low molecular weight ethylene / 1-hexene copolymer will penetrate into the interior of the cable material and reduce the bonding force between the molecular chains of the material, so that the molecular chains of the cable material melt in a stretched state can be quickly transformed into a curled state after cooling, so as to reduce the generation of internal stress, thereby solving the problem of a high rate of change in elongation at break and poor combustion performance of the cable after aging due to the high internal stress of the cable sheath layer. At the same time, aluminum hydroxide and red phosphorus are used for flame retardancy. When exposed to fire, they can char and expand, thereby playing a flame retardant role. At the same time, the masterbatch also has a flame retardant effect, and the grafted material can effectively promote the fusion of the components. Methyl silicone oil can increase the lubrication effect of each component and make the components mix evenly. Ethylene / vinyl acetate copolymer can improve the tensile strength of the cable material. Metallocene polyethylene improves the performance of the cable material during extrusion and shortens the extrusion performance, so that a highly flame retardant, low-smoke, halogen-free polyolefin cable material can be finally obtained. Moreover, when the cable is made into a tube-extrusion mold, the cable sheath layer is not prone to generate high internal stress.

[0034] In a specific application, the ethylene / vinyl acetate copolymer contains 28% vinyl acetate content and 33% vinyl acetate content, and the encrusting agent includes a physical encrusting agent and a chemical encrusting agent.

[0035] As an embodiment of the present application, the synthesis step of the low molecular weight ethylene / 1-hexene copolymer includes:

[0036] The gas in the reactor is replaced by an inert gas, and then the gas in the reactor is replaced by ethylene;

[0037] After the ethylene gas replacement, ethylene was continuously introduced into the reactor, and then toluene and 1-hexene were introduced, the temperature was adjusted to 60° C., a co-catalyst was added and stirred, and then the catalyst was added to react;

[0038] After reacting for 5 minutes, ethylene was cut off, and the reacted material was added to a mixed solution of ethanol and hydrochloric acid, stirred, filtered, and then washed alternately with water and ethanol, and dried at 75°C-85°C to obtain a low molecular weight ethylene / 1-hexene copolymer.

[0039] The present application first replaces the gas in the reactor with an inert gas, and then replaces the gas with ethylene to ensure that the remaining impurity gas in the reactor is not released. Then, ethylene is continuously and stably introduced, and toluene and 1-hexene are introduced. After adjusting the temperature, a co-catalyst is added and stirred until the reaction system is stable. Then, the catalyst is added to start the synthesis reaction. After the reaction is completed, impurities are removed by a mixed solution of ethanol and hydrochloric acid, and impurities such as hydrochloric acid remaining on the surface of the copolymer are removed by alternating washing with water and ethanol multiple times. After drying the water, a low molecular weight ethylene / 1-hexene copolymer is obtained.

[0040] As an embodiment of the present application, before the steps of replacing the gas in the reactor with nitrogen and then replacing the gas in the reactor with ethylene, the method further includes:

[0041] Refluxing the toluene through a sodium wire to remove water, and distilling the toluene under reflux under nitrogen protection using benzophenone as an indicator in the presence of the sodium wire to obtain pretreated toluene;

[0042] Ethylene and inert gas are passed through molecular sieve, silver molecular sieve and sodium potassium alloy for purification to obtain pretreated ethylene and pretreated inert gas;

[0043] After 1-hexene was stirred with CaH2 overnight, it was distilled off under nitrogen protection to obtain pretreated 1-hexene.

[0044] In order to improve the purity of the synthesized low molecular weight ethylene / 1-hexene copolymer, the gas to be used in the synthesis process is first pretreated, and the water in the toluene can be removed by refluxing with a sodium wire. Benzophenone is used as an indicator. If a blue substance is generated during the reflux and does not fade for 30 seconds, it can be considered that the water has been completely removed. Ethylene and inert gas are respectively Molecular sieve, silver molecular sieve and sodium potassium alloy purification treatment can remove moisture and oxygen from ethylene and inert gas; 1-hexene is stirred with CaH2 overnight and then distilled under nitrogen protection to improve the purity of 1-hexene.

[0045] As an embodiment of the present application, the cocatalyst is modified methylaluminoxane, and the catalyst is a salicylaldimine-type [O, N, S] tridentate titanium complex. The chemical structure diagram of the salicylaldimine-type [O, N, S] tridentate titanium complex is as shown in FIG. Figure 1As shown in the figure (where R is methyl), the modified methylaluminoxane itself has very low activity, but the salicylaldimine-type [O,N,S] tridentate titanium complex can catalyze ethylene polymerization with extremely high activity under the action of modified methylaluminoxane, and can make 1-hexene more easily enriched, coordinated and inserted, so that ethylene and 1-hexene can be rapidly polymerized, thereby promoting the synthesis of low molecular weight ethylene / 1-hexene copolymers.

[0046] As an embodiment of the present application, the antioxidant includes pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dilauryl thiodipropionate and 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0047] This application uses pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dilauryl thiodipropionate, and 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as antioxidants to enhance the weather resistance of cable materials and extend the service life of the cable sheath. Specifically, the weight ratio of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, dilauryl thiodipropionate, and 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 4:3:5.

[0048] The embodiments of the present application also provide a method for preparing a polyolefin cable material suitable for an extrusion tube die, comprising the following steps:

[0049] S1, mixing all the components and performing banburying to obtain a mixture;

[0050] S2, plasticizing and extruding the mixture through a double-stage screw, hot-cutting and granulating, and cooling to obtain a semi-finished product;

[0051] S3. Repeat the process of step S2 on the semi-finished product to obtain a finished polyolefin cable material.

[0052] The preparation method of the present application first performs banburying of all components to increase the stirring, mixing and friction between the components, then performs double-stage screw plasticizing extrusion to ensure the plasticizing performance of the material in the subsequent hot-cut granulation process, then performs hot-cut granulation, cuts the plasticized material into granules to obtain a semi-finished product, and repeats the double-stage screw plasticizing extrusion and hot-cut granulation to ensure that the polyolefin cable material is fully plasticized and its performance is more stable.

[0053] As an embodiment of the present application, the step of mixing all components and kneading to obtain a mixture includes:

[0054] Add all components into the internal mixer for internal mixing. Set the internal mixing pressure current to 250A. When the internal mixing temperature is 110℃-115℃, carry out the first powder sweep and continue the internal mixing. When the internal mixing temperature is 130℃-135℃, carry out the second powder sweep and continue the internal mixing. When the internal mixing temperature reaches 180℃, end the internal mixing.

[0055] The present application first performs internal mixing of all components in an internal mixer and controls the internal mixing temperature. Under severe frictional heat generation and closed conditions, the heat that is difficult to dissipate will cause the colloid to be violently oxidized at high temperature and undergo cracking and destruction, thereby achieving the purpose of mechanical plasticizing and making the mixture have both plastic flow and appropriately high elastic deformation.

[0056] As an embodiment of the present application, the step of plasticizing and extruding the mixture through a double-stage screw includes:

[0057] The mixed material is plasticized by passing through a twin-screw extruder and a single-screw extruder in sequence.

[0058] As an implementable embodiment of the present application, when the mixture is plasticized by a twin-screw extruder, the temperature of the feeding zone of the twin-screw extruder is 115°C-125°C, and the nine temperature zones of the twin-screw extruder are set to 125°C-135°C, 125°C-135°C, 120°C-130°C, 120°C-130°C, 115°C-125°C, 115°C-125°C, 105°C-115°C, 105°C-115°C, and 105°C-115°C, respectively. The current of the twin-screw extruder is set to 180A-210A.

[0059] The present application extrude the mixed material through a twin-screw extruder and limit the temperature of the extrusion process. The mixed material is heated in nine temperature zones of the twin-screw extruder and then extruded, which can make the material have a better compression effect, and improve the plasticity and fluidity of the material, ensuring that the material still has good plasticizing properties after subsequent granulation.

[0060] As an implementable embodiment of the present application, when the mixture is plasticized by a single-screw extruder, the temperatures of the three temperature control zones of the single-screw extruder are set to 115°C-125°C, 130°C-140°C, and 140°C-150°C, respectively, the temperature of the screen changing zone of the single-screw extruder is 145°C-155°C, the head temperature of the single-screw extruder is 145°C-155°C, and the current of the single-screw extruder is set to 50A-90A.

[0061] After passing through the twin-screw extruder, the material is heated and plasticized and extruded through the three temperature control zones of the single-screw extruder, so that the material can be fully plasticized and the plasticizing performance is improved.

[0062] The above technical solutions of the present application are described in detail below with reference to specific embodiments.

[0063] Example 1

[0064] The preparation of low molecular weight ethylene / 1-hexene copolymer comprises the following steps:

[0065] Refluxing the toluene through a sodium wire to remove water, and distilling the toluene under reflux under nitrogen protection using benzophenone as an indicator in the presence of the sodium wire to obtain pretreated toluene;

[0066] Ethylene and inert gas are passed through molecular sieve, silver molecular sieve and sodium potassium alloy for purification to obtain pretreated ethylene and pretreated inert gas;

[0067] After 1-hexene was stirred with CaH2 overnight, it was distilled out under nitrogen protection to obtain pretreated 1-hexene;

[0068] The gas in the reactor is replaced twice by the pretreated inert gas, and then the gas in the reactor is replaced twice by the pretreated ethylene;

[0069] Then, the pretreated ethylene was continuously introduced into the reactor, followed by 10 L of pretreated toluene and 50 mL of pretreated 1-hexene. The temperature was adjusted to 60° C., 10 mL of modified methylaluminoxane as a co-catalyst was added and stirred for 5 minutes, and then 18.6 mg of a salicylaldimine-type (O, N, S) tridentate titanium complex as a catalyst was added to react.

[0070] After 5 minutes of reaction, ethylene was immediately cut off, and the reacted material was added to a mixed solution of ethanol and hydrochloric acid, wherein the mass ratio of ethanol to hydrochloric acid was 9:1, and stirred. The mixture was filtered and then washed alternately with water and ethanol three times, and then dried at 80°C to obtain a low molecular weight ethylene / 1-hexene copolymer.

[0071] Example 2

[0072] A polyolefin cable material suitable for a tube extrusion die is prepared by the following steps:

[0073] Aluminum hydroxide 84 kg, methyl silicone oil 0.64 kg, grafting material 5.6 kg, polyolefin elastomer 2.4 kg, color masterbatch 1.8 kg, ethylene / vinyl acetate copolymer 23 kg, metallocene polyethylene 8 kg, tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester 0.32 kg, dilauryl thiodipropionate 0.24 kg, 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] 0.4 kg, physical coagulation agent 3.2 kg, chemical coagulation agent 2.4 kg, red phosphorus 0.4 kg, and low molecular weight ethylene / 1-hexene copolymer 1 kg are added to a Banbury mixer for mixing, the mixing pressure current is set to 250 A, the mixing temperature is 110°C, the first powdering is performed, the mixing is continued, the second powdering is performed when the mixing temperature is 130°C, the mixing is continued, and the mixing is ended when the mixing temperature is up to 180°C, to obtain a mixture;

[0074] The mixture is then sequentially subjected to a double-screw extruder and a single-screw extruder for plasticization, wherein the feeding zone temperature of the double-screw extruder is 120°C, the nine temperature zones of the double-screw extruder are set to 130°C, 130°C, 125°C, 125°C, 120°C, 120°C, 110°C, 110°C, and 110°C respectively, the current of the double-screw extruder is set to 195 A, the three temperature control zones of the single-screw extruder are set to 120°C, 135°C, and 145°C respectively, the screen changer zone temperature of the single-screw extruder is 150°C, the die temperature of the single-screw extruder is 150°C, and the current of the single-screw extruder is set to 70 A, and then the mixture is hot cut and granulated by a granulator, and cooled by a fan, to obtain a semi-finished product.

[0075] The semi-finished product is then sequentially subjected to a double-screw extruder and a single-screw extruder for plasticization, and then hot cut and granulated by a granulator, and cooled by a fan, to obtain a finished polyolefin cable material.

[0076] Example 3

[0077] A polyolefin cable material suitable for an extrusion tube mold is prepared by the following steps:

[0078] 80 kg of aluminum hydroxide, 0.5 kg of methyl silicone oil, 5 kg of grafting material, 2 kg of polyolefin elastomer, 1 kg of masterbatch, 20 kg of ethylene / vinyl acetate copolymer, 5 kg of metallocene polyethylene, 0.3 kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.22 kg of dilauryl thiodipropionate, 0.4 kg of 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 3 kg of physical encrusting agent, 2 kg of chemical encrusting agent, 0.2 kg of red phosphorus, and 0.5 kg of low molecular weight ethylene / 1-hexene copolymer were added into a banbury mixer for banburying. The banburying pressure current was set to 250 A. When the banburying temperature was 112° C., a first powder sweep was performed, and banburying was continued. When the banburying temperature was 132° C., a second powder sweep was performed, and banburying was continued. After the banburying temperature reached 180° C., banburying was terminated to obtain a mixture.

[0079] The mixed material is then plasticized by a twin-screw extruder and a single-screw extruder in sequence, wherein the temperature of the feeding zone of the twin-screw extruder is 115° C., the nine temperature zones of the twin-screw extruder are respectively set to 125° C., 125° C., 120° C., 120° C., 115° C., 115° C., 105° C., 105° C., 105° C., the current of the twin-screw extruder is set to 180A, the temperatures of the three temperature control zones of the single-screw extruder are respectively set to 115° C., 130° C., and 140° C., the temperature of the screen changing zone of the single-screw extruder is 145° C., the head temperature of the single-screw extruder is 145° C., the current of the single-screw extruder is set to 50A, and then the mixed material is hot-cut and granulated by a pelletizer and cooled by a fan to obtain a semi-finished product;

[0080] The semi-finished product is then plasticized by a twin-screw extruder and a single-screw extruder in sequence, and then hot-cut and granulated by a pelletizer. After cooling by a fan, a finished polyolefin cable material is obtained.

[0081] Example 4

[0082] A polyolefin cable material suitable for a tube extrusion die is prepared by the following steps:

[0083] 90kg of aluminum hydroxide, 0.8kg of methyl silicone oil, 6kg of grafting material, 3kg of polyolefin elastomer, 2.5kg of masterbatch, 30kg of ethylene / vinyl acetate copolymer, 10kg of metallocene polyethylene, 0.35kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 0.25kg of dilauryl thiodipropionate, 0.25kg of 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] ] 0.5 kg, 3.5 kg of physical crusting agent, 2.5 kg of chemical crusting agent, 0.6 kg of red phosphorus and 1.5 kg of low molecular weight ethylene / 1-hexene copolymer were added into a banbury mixer for banburying, the banburying pressure current was set to 250 A, and when the banburying temperature was 115° C., a first powder sweep was carried out, and banburying was continued. When the banburying temperature was 135° C., a second powder sweep was carried out, and banburying was continued. After the banburying temperature reached 180° C., the banburying was terminated to obtain a mixture;

[0084] The mixed material is then plasticized by a twin-screw extruder and a single-screw extruder in sequence, wherein the temperature of the feeding zone of the twin-screw extruder is 125° C., the nine temperature zones of the twin-screw extruder are respectively set to 135° C., 135° C., 130° C., 130° C., 125° C., 125° C., 115° C., 115° C., 115° C., the current of the twin-screw extruder is set to 210 A, the temperatures of the three temperature control zones of the single-screw extruder are respectively set to 125° C., 140° C., and 150° C., the temperature of the screen changing zone of the single-screw extruder is 155° C., the head temperature of the single-screw extruder is 155° C., the current of the single-screw extruder is set to 90 A, and then the mixed material is hot-cut and granulated by a pelletizer and cooled by a fan to obtain a semi-finished product;

[0085] The semi-finished product is then plasticized by a twin-screw extruder and a single-screw extruder in sequence, and then hot-cut and granulated by a pelletizer. After cooling by a fan, a finished polyolefin cable material is obtained.

[0086] Comparative Example 1

[0087] Compared to Example 2, no low molecular weight ethylene / 1-hexene copolymer was added.

[0088] Experimental Example 1

[0089] The polyolefin cable material prepared in Example 2 of the present application is used as sample No. 1, and the polyolefin cable material prepared in Comparative Example 1 is used as sample No. 2. Both sample No. 1 and sample No. 2 are made into cable sheaths using a tube extrusion mold. The cable specifications are WDZB1-YJY-5×6mm 2 , and then the cable sheath layers made of sample No. 1 and sample No. 2 were made into dumbbell specimens according to GB / T12706.2-2020 standard, marked as sample No. 1 and sample No. 2, respectively. The tensile strength change rate and elongation at break of sample No. 1 and sample No. 2 before and after aging were measured respectively. The test results are shown in Table 1 below.

[0090] Table 1

[0091]

[0092] According to GB / T12706.2-2020, the tensile strength of the cable sheath layer of the halogen-free low-smoke flame-retardant polyolefin sheath material before aging is ≥9.0 MPa, and the elongation at break is ≥125%; after aging at 100℃ in an oven for 168h, the tensile strength is ≥9.0 MPa, and the change rate of the tensile strength after aging is within ±40%, the elongation at break after aging is ≥100%, and the change rate of the elongation at break is within ±40%. When the cable sheath is cut into dumbbell pieces with a standard dumbbell knife for aging test, the dumbbell pieces will be aged in a 100℃ oven for 168h, which is equivalent to annealing treatment of the plastic pieces. The polyolefin molecular chain segments in the dumbbell pieces rearrange, and part of the internal stress disappears. The molecular chain changes from the stretched state to the relaxed random arrangement state. At this time, the elongation at break of the dumbbell piece after aging is relatively low. Before aging, the polyolefin molecular chain in the dumbbell piece is in a stretched state, has high internal stress, and the molecular chain segments are arranged along the stretching force direction. The elongation at break obtained by the tensile test is relatively high. This makes the difference between the elongation at break of the dumbbell piece before and after aging larger. Therefore, the change rate of the elongation at break after aging may exceed the range of ±40%, resulting in unqualified product test. As shown in Table 1, the change rates of the elongation at break of the No. 1 sample and the No. 2 sample after aging are both within the range of ±40%, and the change rate of the elongation at break of the No. 1 sample after aging is obviously lower than that of the No. 2 sample. This indicates that the polyolefin cable material prepared by the application example can obviously improve the elongation at break of the cable sheath after aging.

[0093] Experimental Example 2

[0094] The polyolefin cable material prepared by the application example 2 is used as the No. 1 sample, and the polyolefin cable material prepared by the comparative example 1 is used as the No. 2 sample. The No. 1 sample and the No. 2 sample are both made into cable sheaths by using an extrusion pipe mold. The specification of the cable is WDZB1-YJY-5×6mm 2 . The cable sheaths made of the No. 1 sample and the No. 2 sample are respectively subjected to B1 level combustion test according to GB / T31247-2014. The combustion test diagram of the cable sheath made of the No. 1 sample is shown in Figure 2 , and the combustion test diagram of the cable sheath made of the No. 2 sample is shown in Figure 3 .

[0095] The results show that when the cable is subjected to a B1-level combustion test, the cable sheath is heated by the flame, the internal stress of the cable sheath disappears, and the molecular chains change from a stretched state to a relaxed state, which causes the heated cable sheath to deform and curl, resulting in the carbon layer at the flame burning location to easily fall off. In addition, the position of the blowtorch during the combustion process also makes the carbon layer easily washed away by the impact force of the blowtorch flame, exposing the non-flame retardant material inside the cable to the flame. At the same time, if the fallen carbon layer is small, non-combustible fragments that are completely carbonized, the burning droplets / particles level can be judged as d0. If the fallen carbon layer is small, combustible fragments that are incompletely carbonized, the burning droplets / particles level can be judged as d1 or d2.

[0096] contrast Figure 2 and Figure 3 It can be seen that Figure 2 The sheath layer of the cable is carbonized at the position where it contacts the flame. The carbonized layer is complete and there is no shedding of the carbon layer. The flame retardant effect is good and the burning droplets / particles can be judged as d1 or d2. Figure 3 The carbonized layer at the position where the cable contacts the flame falls off severely, and the cable sheath layer is curled and deformed, with poor flame retardant effect. The burning droplets / particles level can be judged as d0, indicating that the cable sheath prepared by the polyolefin cable material prepared in the embodiment of the present application can significantly improve the cable combustion grade performance.

[0097] The above description is merely an optional embodiment of the present application and does not limit the patent scope of the present application. All equivalent structural transformations made using the contents of the present application specification under the inventive concept of the present application, or direct / indirect application in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A polyolefin cable material suitable for an extrusion tube die, characterized in that: The invention comprises the following components in parts by weight: 80-90 parts of aluminum hydroxide, 0.5-0.8 parts of methyl silicone oil, 5-6 parts of grafting material, 2-3 parts of polyolefin elastomer, 1-2.5 parts of masterbatch, 20-30 parts of ethylene / vinyl acetate copolymer, 5-10 parts of metallocene polyethylene, 0.5-1.5 parts of antioxidant, 5-6 parts of encrusting agent, 0.2-0.6 parts of red phosphorus and 0.5-1.5 parts of low molecular weight ethylene / 1-hexene copolymer; The synthesis steps of the low molecular weight ethylene / 1-hexene copolymer include: Refluxing the toluene through a sodium wire to remove water, and distilling the toluene under reflux under nitrogen protection using benzophenone as an indicator in the presence of the sodium wire to obtain pretreated toluene; Ethylene and inert gas are passed through molecular sieve, silver molecular sieve and sodium potassium alloy for purification to obtain pretreated ethylene and pretreated inert gas; After 1-hexene was stirred with CaH2 overnight, it was distilled out under nitrogen protection to obtain pretreated 1-hexene; The gas in the reactor is replaced by an inert gas, and then the gas in the reactor is replaced by ethylene; After gas replacement with ethylene, ethylene is continuously introduced into the reactor, followed by introduction of toluene and 1-hexene, the temperature is adjusted to 60° C., a co-catalyst is added and stirred, and then a catalyst is added to carry out the reaction; wherein the co-catalyst is modified methylaluminoxane, and the catalyst is a salicylaldimine-type (O, N, S) tridentate titanium complex; After reacting for 5 minutes, ethylene was cut off, and the reacted material was added to a mixed solution of ethanol and hydrochloric acid, stirred, filtered, and then washed alternately with water and ethanol, and dried at 75°C-85°C to obtain a low molecular weight ethylene / 1-hexene copolymer.

2. The polyolefin cable material suitable for tube extrusion die according to claim 1, characterized in that: The antioxidants include pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dilaurylthiodipropionate, and 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

3. A method for preparing a polyolefin cable material suitable for a tube extrusion die according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1, mixing all the components and performing banburying to obtain a mixture; S2, plasticizing and extruding the mixture through a double-stage screw, hot-cutting and granulating, and cooling to obtain a semi-finished product; S3. Repeat the process of step S2 on the semi-finished product to obtain a finished polyolefin cable material.

4. The method for preparing a polyolefin cable material suitable for an extrusion tube die according to claim 3, wherein: The step of mixing all the components and kneading them to obtain a mixture comprises: Add all components into the internal mixer for internal mixing. Set the internal mixing pressure current to 250A. When the internal mixing temperature is 110℃-115℃, carry out the first powder sweep and continue the internal mixing. When the internal mixing temperature is 130℃-135℃, carry out the second powder sweep and continue the internal mixing. When the internal mixing temperature reaches 180℃, end the internal mixing.

5. The method for preparing a polyolefin cable material suitable for an extrusion tube die according to claim 3, wherein: The step of plasticizing and extruding the mixed material through a double-stage screw comprises: The mixed material is plasticized by passing through a twin-screw extruder and a single-screw extruder in sequence.

6. The method for preparing a polyolefin cable material suitable for an extrusion tube die according to claim 5, characterized in that: When the mixed material is plasticized by a twin-screw extruder, the temperature of the feeding zone of the twin-screw extruder is 115°C-125°C, and the nine temperature zones of the twin-screw extruder are set to 125°C-135°C, 125°C-135°C, 120°C-130°C, 120°C-130°C, 115°C-125°C, 115°C-125°C, 105°C-115°C, 105°C-115°C, and 105°C-115°C, respectively. The current of the twin-screw extruder is set to 180A-210A.

7. The method for preparing a polyolefin cable material suitable for an extrusion tube die according to claim 5, characterized in that: When the mixed material is plasticized by the single-screw extruder, the temperatures of the three temperature control zones of the single-screw extruder are set to 115°C-125°C, 130°C-140°C, and 140°C-150°C, respectively, the temperature of the screen changing zone of the single-screw extruder is 145°C-155°C, the head temperature of the single-screw extruder is 145°C-155°C, and the current of the single-screw extruder is set to 50A-90A.

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