90°c thermoplastic halogen-free low-smoke flame-retardant polyolefin sheath material and preparation method therefor

Abstract

Disclosed in the present invention are a 90°C thermoplastic halogen-free low-smoke flame-retardant polyolefin sheath material and a preparation method therefor. The sheath material is prepared from raw materials comprising the following components in parts by mass: 20-40 parts of an ethylene-vinyl acetate copolymer, 20-40 parts of a linear low-density polyethylene, 2-10 parts of a high-density polyethylene, 20-40 parts of a metallocene ethylene-octylene copolymer, 10-15 parts of a maleic-anhydride-grafted metallocene linear low-density polyethylene copolymer, 58-73 parts of aluminum hydroxide, 20-25 parts of modified magnesium hydroxide, 64-84 parts of a synergistic flame retardant, 2-3 parts of a coupling agent, 1-4 parts of a lubricant, 1-3 parts of an antioxidant, and 2-7 parts of a coloring agent, wherein the synergistic flame retardant comprises lithium oxide. A matrix resin has low-temperature performance, mechanical properties and cracking resistance. With regard to flame retardance, a large amount of the synergistic flame retardant, i.e., lithium oxide, is added to a traditional magnesium-aluminum compound flame-retardant system, and therefore an off-white hard shell can be formed during a combustion process while low heat release is ensured, thereby ensuring no dripping during the combustion process.

Description

A 90°C thermoplastic halogen-free low-smoke flame-retardant polyolefin sheath material and its preparation method Technical Field

[0001] The present invention relates to a cable sheath, in particular to a 90°C thermoplastic halogen-free low-smoke flame-retardant polyolefin sheath material and a preparation method thereof. Background Art

[0002] As people's requirements for environmental protection and safety become increasingly higher, in order to simultaneously meet the requirements of low heat release and no dripping, and to improve the strength of the jacket after combustion, there are currently two common technical routes:

[0003] 1) Using clay minerals such as montmorillonite, kaolin, and sepiolite as shelling agents:

[0004] This technology can form a ceramic shell after combustion, but its disadvantage is that the extrusion process is relatively difficult, and the production efficiency is significantly lower than that of ordinary low-smoke halogen-free materials. Specifically, the current and head pressure of the single-screw extruder are increased, the extrusion speed is increased, and the surface is shark skin and is very easy to absorb moisture. It needs to be vacuumed and sealed, and needs to be dried again after a period of storage, otherwise the extrusion will easily cause air holes and other phenomena.

[0005] 2) Use nitrogen-phosphorus synergistic expansion shell forming agents:

[0006] Cable materials using this technology form a dense, porous carbon shell after combustion. However, the drawback is that smoke generation is relatively high, failing to meet smoke generation requirements. This results in a low addition amount, insufficient carbon shell strength, and the tendency for occasional dripping. Furthermore, existing smoke suppressants are primarily designed to control smoke generation from the base resin and are unable to reduce smoke generation from intumescent shell-forming agents.

[0007] Therefore, it is urgent to find a new technical route that can take into account flame retardancy, smoke emission and extrusion processing performance while meeting the requirements of low heat release and no dripping.

[0008] Summary of the Invention

[0009] In view of the problem that the above-mentioned cable sheath materials cannot take into account low heat release, drip-free flame retardancy, smoke emission and extrusion processing performance at the same time, the present invention provides a 90°C thermoplastic halogen-free low-smoke flame-retardant polyolefin sheath material and a preparation method thereof. The sheath material has good flame retardant effect, no dripping during combustion, low smoke emission and excellent extrusion processing performance.

[0010] In order to achieve the above-mentioned purpose, the present invention provides a 90°C thermoplastic halogen-free low-smoke flame-retardant polyolefin sheathing material. The sheathing material is made from the following raw materials in parts by mass: 20-40 parts of ethylene-vinyl acetate copolymer, 20-40 parts of linear low-density polyethylene, 2-10 parts of high-density polyethylene, 20-40 parts of metallocene ethylene-octene copolymer, 10-15 parts of maleic anhydride grafted metallocene linear low-density polyethylene copolymer, 58-73 parts of aluminum hydroxide, 20-25 parts of modified magnesium hydroxide, 64-84 parts of synergistic flame retardant, 2-3 parts of coupling agent, 1-4 parts of lubricant, 1-3 parts of antioxidant, and 2-7 parts of colorant; wherein the synergistic flame retardant includes lithium oxide. The density of linear low-density polyethylene ranges from 0.91 to 0.94 g / cm 3 , high-density polyethylene density range 0.941-0.965g / cm 3 .

[0011] In the above technical solution, the matrix resin is composed of ethylene-vinyl acetate copolymer, linear low-density polyethylene, high-density polyethylene, metallocene ethylene-octene copolymer, and maleic anhydride grafted metallocene linear low-density polyethylene copolymer, taking into account low temperature, mechanical properties and crack resistance.

[0012] In terms of flame retardancy, a large amount of synergistic flame retardant lithium oxide is added to the traditional magnesium-aluminum composite flame retardant system. While ensuring low heat release, it will form a gray-white hard shell during the combustion process to ensure that there is no dripping during the combustion process.

[0013] Due to the polarity of metal oxides, the extrusion processing performance is far superior to that of ordinary halogen-free materials. At the same time, due to the reduction in the proportion of hydroxides, the moisture absorption problem that is common in halogen-free materials is also improved.

[0014] Coupling agents are used to improve the interfacial compatibility between resin and powder, enhance the dispersion of powder, and improve mechanical and electrical properties; lubricants are used to improve the friction between the relative movement of the melt during extrusion flow and the friction between the melt and the contact surface of the equipment; antioxidants are used to improve the aging phenomenon of polymer products during production and use.

[0015] Furthermore, the synergistic flame retardant further comprises antimony oxide, wherein the content of lithium oxide accounts for 1 / 2 to 2 / 3 of the synergistic flame retardant.

[0016] In the above technical solution, antimony oxide is used as a traditional synergistic flame retardant to play a synergistic flame retardant role.

[0017] Preferably, the particle size of the synergistic flame retardant is 1 to 3 μm, which is conducive to more uniform dispersion in the blend and reduces the negative impact of the powder on the overall mechanical properties.

[0018] Preferably, the vinyl acetate content in the ethylene-vinyl acetate copolymer is greater than 35%; and / or

[0019] The linear low-density polyethylene has a tensile strength greater than 16 MPa and an elongation at break greater than 500%; and / or

[0020] The elongation at break of the metallocene ethylene-octene copolymer is greater than 900%; and / or

[0021] The tensile strength of the high-density polyethylene should be greater than 23 MPa.

[0022] The maleic anhydride grafted metallocene linear low-density polyethylene copolymer is composed of one or more metallocene linear low-density polyethylenes and a maleic anhydride copolymer.

[0023] Preferably, the aluminum hydroxide is in the form of hexagonal flakes, which has better dispersibility and can improve the tensile strength and elongation at break of the sheath at room temperature.

[0024] Preferably, the modified magnesium hydroxide is magnesium hydroxide modified with stearic acid. The advantages of stearic acid-modified magnesium hydroxide are: improving elongation at break and enhancing external lubrication (improving flow friction between the melt and the equipment).

[0025] Preferably, the coupling agent is one or a mixture of KH560, A172, KR-7, 11-100.

[0026] Preferably, the lubricant is one or a mixture of low molecular weight polyethylene wax (molecular weight of 1500-1700), zinc stearate, methyl vinyl silicone rubber, and OPE wax.

[0027] Preferably, the antioxidant is one or a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1010) and dilauryl thiodipropionate (antioxidant DLTP).

[0028] The second aspect of the present invention provides a method for preparing the above-mentioned 90°C thermoplastic halogen-free, low-smoke, flame-retardant polyolefin sheathing material, which comprises the following steps: mixing the raw materials at a low speed of 50-60°C for 2-3 minutes, and at a high speed for 5-8 minutes, then kneading the mixture in an internal mixer for 20-25 minutes, placing the kneaded product in a screw extruder for extrusion, with the upper barrel temperature ranging from 120-130°C and the lower barrel temperature ranging from 135-150°C, placing the twin-screw product in a single-screw extruder for extrusion, with the barrel temperature being 130-145°C, and granulating and packaging. After passing through three sections of a high-speed mixer at different speeds, all raw materials are mixed uniformly before kneading, and liquid additives such as coupling agents are better distributed on the powder surface to achieve better performance.

[0029] Through the above technical solution, the present invention achieves the following beneficial effects:

[0030] The matrix resin of the present invention is composed of ethylene-vinyl acetate copolymer, linear low-density polyethylene, high-density polyethylene, metallocene ethylene-octene copolymer, and maleic anhydride-grafted metallocene linear low-density polyethylene copolymer, taking into account low-temperature, mechanical properties, and crack resistance. In terms of flame retardancy, a large amount of synergistic flame retardant lithium oxide is added to the traditional magnesium-aluminum composite flame retardant system. While ensuring low heat release, it forms an off-white hard shell during the combustion process, ensuring that there is no dripping during the combustion process. Due to the polarity of the metal oxide, the extrusion processing performance is far superior to that of ordinary halogen-free materials. At the same time, due to the reduced proportion of hydroxide, the moisture absorption problem commonly found in halogen-free materials is also improved. DETAILED DESCRIPTION

[0031] The following is a detailed description of the specific embodiments of the present invention in conjunction with the examples. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0032] In the following examples,

[0033] The manufacturer of ethylene-vinyl acetate copolymer is Atofena Chemical, and the model is Evatane 42-60;

[0034] The manufacturer of linear low-density polyethylene is Dow Chemical, model number is DFDA-7510NT;

[0035] The manufacturer of high-density polyethylene is Saudi Basic Industries, model number C5070D;

[0036] The manufacturer of metallocene ethylene-octene copolymer is Borealis, model number is HHM TR-457;

[0037] The manufacturer of maleic anhydride grafted metallocene linear low-density polyethylene copolymer is Nengzhiguang, model MC226;

[0038] The manufacturer of stearic acid modified magnesium hydroxide is Magnesium Shield, model number is MDL-13A.

[0039] The component contents of the sheath materials of various embodiments and comparative examples are shown in Table 1.

[0040] Table 1: Formulas of Examples and Comparative Examples

[0041] The above-mentioned base resin, flame retardant, coupling agent, lubricant, antioxidant, and colorant were mixed in a high-speed mixer at 60°C for 3 minutes at low speed and 5 minutes at high speed. The mixture was then mixed in an internal mixer for 25 minutes. The mixed product was extruded in a screw extruder with an upper barrel temperature range of 120-130°C and a lower barrel temperature range of 135-150°C. The twin-screw product was extruded in a single-screw extruder with a barrel temperature of 130-145°C, and pelletized and packaged.

[0042] The key properties of the processed sheath material were tested, and the test items, test methods and results are shown in Table 2.

[0043] Table 2 Sheath material performance table

[0044] As can be seen from Table 2, the tensile strength and elongation at break of the sheath material of the embodiment are higher than those of the comparative example, indicating that the sheath material of the present invention has good mechanical properties; the smoke density with and without flame is relatively small, achieving the purpose of low smoke, because the metal oxide forms a dense and solid shell with the matrix and other fillers after combustion, rather than being dispersed in the air in the form of small particles; and the oxygen index is relatively high, achieving good flame retardant properties, because the lithium oxide and its auxiliary flame retardant produce a solid shell while achieving efficient flame retardancy, thereby preventing oxygen from coming into contact with the internal combustibles.

[0045] The sheath material is extruded on the cable core through a 120 extruder as a sheath layer. The cable specification is 3×50mm. 2 The structure is conductor + insulation (cross-linked polyethylene) + cabling (inorganic paper rope filler + two layers of high-resistance tape) + sheath. Halogen-free screws are used during extrusion. The extrusion process details are shown in Table 3.

[0046] Table 3 Extrusion processing status

[0047] The cables were subjected to a combustion performance test according to the method specified in GB / T 31248 and a smoke density test according to GB / T17651.2. The test results are shown in Table 4.

[0048] Table 4 Cable combustion performance

[0049] As shown in Table 4, the sheathing materials of both the Example and the Comparative Example achieved excellent combustion performance and smoke toxicity ratings, achieving B1 flame retardancy, d0 combustion droplets / particles, and t0 smoke toxicity. However, the vertical flame spread distance of the cable using the Example sheathing material was much smaller than that of the Comparative Example, and the cable also had excellent light transmission, demonstrating that its use in cables produces a low-smoke effect.

[0050] The preferred embodiments of the present invention are described in detail above in conjunction with the embodiments. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0051] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0052] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A 90°C thermoplastic halogen-free low-smoke flame-retardant polyolefin sheath material, characterized in that: The invention is prepared from the following raw materials in parts by mass: 20-40 parts of ethylene-vinyl acetate copolymer, 20-40 parts of linear low-density polyethylene, 2-10 parts of high-density polyethylene, 20-40 parts of metallocene ethylene-octene copolymer, 10-15 parts of maleic anhydride grafted metallocene linear low-density polyethylene copolymer, 58-73 parts of aluminum hydroxide, 20-25 parts of modified magnesium hydroxide, 64-84 parts of synergistic flame retardant, 2-3 parts of coupling agent, 1-4 parts of lubricant, 1-3 parts of antioxidant and 2-7 parts of colorant; wherein the synergistic flame retardant comprises lithium oxide.

2. The polyolefin sheath material according to claim 1, characterized in that: The synergistic flame retardant further comprises antimony oxide, wherein the content of lithium oxide accounts for 1 / 2 to 2 / 3 of the synergistic flame retardant.

3. The polyolefin sheath material according to claim 1 or 2, characterized in that: The particle size of the synergistic flame retardant is 1 to 3 μm.

4. The polyolefin sheath material according to claim 1, characterized in that: The vinyl acetate content of the ethylene-vinyl acetate copolymer is greater than 35%; and / or The linear low-density polyethylene has a tensile strength greater than 16 MPa and an elongation at break greater than 500%; and / or The elongation at break of the metallocene ethylene-octene copolymer is greater than 900%; and / or The tensile strength of the high-density polyethylene should be greater than 23 MPa.

5. The polyolefin sheath material according to claim 1, characterized in that: The aluminum hydroxide is in the shape of hexagonal flakes.

6. The polyolefin sheath material according to claim 1, characterized in that: The modified magnesium hydroxide is magnesium hydroxide modified with stearic acid.

7. The polyolefin sheathing material according to any one of claims 1 to 2 or 4 to 6, characterized in that The coupling agent is one of KH560, A172, KR-7, and 11-100, or a mixture of several thereof.

8. The polyolefin sheathing material according to any one of claims 1 to 2 or 4 to 6, characterized in that: The lubricant is one or a mixture of low molecular polyethylene wax, zinc stearate, methyl vinyl silicone rubber, and OPE wax.

9. The polyolefin sheath material according to any one of claims 1 to 2 or 4 to 6, characterized in that: The antioxidant is one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and dilauryl thiodipropionate, or a mixture of both.

10. The method for preparing the 90°C thermoplastic halogen-free low-smoke flame-retardant polyolefin sheathing material according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: mixing the raw materials at a low speed of 50-60°C for 2-3 minutes and at a high speed for 5-8 minutes, then kneading the mixture in an internal mixer for 20-25 minutes, placing the kneaded product on a screw extruder for extrusion, with the upper barrel temperature ranging from 120-130°C and the lower barrel temperature ranging from 135-150°C, placing the twin-screw product on a single-screw extruder for extrusion, with the barrel temperature being 130-145°C, and granulating and packaging.

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