A polyolefin plastic, its preparation method and application

Abstract

The application discloses a kind of polyolefin plastics and its preparation method and application, the polyolefin plastics includes first modified plastic material and second modified plastic material;The first modified plastic material includes the following mass percentage of components: polystyrene 90~96%, thermoplastic elastomer 3~9%, auxiliary 0.1~2%;The second modified plastic material includes the following mass percentage of components: polypropylene 45~60%, thermoplastic elastomer 4~10%, halogen-free flame retardant masterbatch 35~45%.The polyolefin plastics in the application has balanced physical and mechanical properties, good toughness, excellent flame retardancy, high and low temperature resistance, can be vacuum formed, excellent processing performance and other characteristics, and can be applied to larger size plastic parts.

Description

Technical Field

[0001] This invention relates to the field of materials, specifically to a polyolefin plastic, its preparation method, and its applications. Background Technology

[0002] In the electric vehicle industry, the battery pack cover, as a key component of the battery system, needs to meet multiple performance requirements simultaneously. Among these, flame retardancy and molding / processing performance have been key areas of focus in recent years. Currently, the main materials for battery pack covers on the market are metal and glass fiber reinforced resin. Metal materials have high strength and good flame retardancy, but their weight is relatively large, which is not conducive to achieving the goal of long driving range for electric vehicles. Glass fiber reinforced resin performs better in terms of strength and rigidity, but its molding and processing costs are high, and it is prone to stress cracking.

[0003] Furthermore, while traditional plastic materials such as polyolefins possess excellent molding and processing properties, their flame retardant properties are relatively poor. To improve the flame retardancy of polyolefins, large amounts of flame retardants are typically added, but this reduces the material's mechanical properties. Simultaneously, the addition of flame retardants also negatively impacts the material's processing performance, leading to problems such as melt fracture and surface defects during processing.

[0004] Therefore, in view of the problems existing in the prior art, the present invention aims to provide a polyolefin plastic to overcome the shortcomings of metal and glass fiber reinforced resins in terms of flame retardancy and molding and processing performance. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, one of the objectives of the present invention is to provide a polyolefin plastic.

[0006] The second objective of this invention is to provide a method for preparing polyolefin plastics.

[0007] The third objective of this invention is to provide a battery pack cover.

[0008] The fourth objective of this invention is to provide an application of polyolefin plastics in the field of electric vehicles.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A first aspect of the present invention provides a polyolefin plastic comprising a first modified plastic material and a second modified plastic material; the first modified plastic material comprises the following components by weight percentage: 90-96% polystyrene, 3-9% thermoplastic elastomer, and 0.1-2% additives; the second modified plastic material comprises the following components by weight percentage: 45-60% polypropylene, 4-10% thermoplastic elastomer, and 35-45% halogen-free flame retardant masterbatch.

[0011] The melt flow rate of the polypropylene measured at 230°C and 2.16 kg was (0.01~3) g / 10 min.

[0012] The melt flow rate of the polystyrene measured at 200°C and 5 kg was (3-8) g / 10 min.

[0013] The polystyrene used in this invention is high-impact polystyrene. As the main component of the first modified plastic, high-impact polystyrene imparts excellent processing characteristics and balanced physical and mechanical properties to the material. The thermoplastic elastomer in the first and second modified plastic materials of this invention primarily improves the material's impact toughness and low-temperature resistance, while also improving the compatibility between high-impact polystyrene and polypropylene, preventing delamination of multilayer sheets. The polypropylene used in this invention is high melt strength polypropylene, which, as the main component of the second modified plastic, imparts good melt strength to the material. The halogen-free flame retardant masterbatch mainly imparts good flame retardant properties to the material, enabling it to meet the safety requirements of battery pack covers. The polyolefin plastic in this invention possesses excellent mechanical properties and melt strength, allowing it to be processed into products using vacuum forming without cracking, wrinkling, or thinning of the wall during the vacuum forming process.

[0014] Preferably, the melt tensile tension of the polypropylene, measured by the capillary method, is 5–25 cN.

[0015] The polypropylene used in this invention has specific melt flow rate and melt tensile tension, unlike homopolymer polypropylene and block copolymer polypropylene materials, and is a high melt strength polypropylene. Compared with homopolymer polypropylene and block copolymer polypropylene materials, the high melt strength polypropylene used in this invention has good melt strength, a wider melting range, and excellent extrusion processing and molding performance, which can greatly improve the defect of polypropylene materials being difficult to vacuum form.

[0016] Preferably, the thermoplastic elastomer is selected from at least one of styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), styrene-ethylene / propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-propylene block copolymer (SEEPS). This invention uses styrene block copolymer-based thermoplastic elastomers, which can improve the material's room temperature impact toughness and low-temperature resistance, and also act as a compatibilizer for high-impact polystyrene and polypropylene, promoting the compatibility of the two layers and preventing delamination.

[0017] Preferably, the halogen-free flame retardant masterbatch comprises a halogen-free flame retardant and a masterbatch; based on the total mass percentage of the halogen-free flame retardant masterbatch being 100%, the mass percentage of the halogen-free flame retardant is 50-80%.

[0018] Preferably, the halogen-free flame retardant is a flame retardant containing phosphorus and nitrogen elements, and based on the total molar percentage of the halogen-free flame retardant being 100%, the molar percentage of phosphorus is 15-30% and the molar percentage of nitrogen is 15-35%.

[0019] Preferably, the additive is selected from at least one of laser engraving additives, antioxidants, and lubricants.

[0020] Preferably, the laser engraving agent is a metal compound capable of absorbing laser energy; the laser engraving agent in this invention is used to give the polyolefin plastic of this invention laser-engravable properties, and any laser engraving agent in the prior art can be used, such as: iron oxide powder, aluminum powder, etc. More preferably, the laser engraving agent is LS-402 from ECARX (Germany).

[0021] Preferably, based on 100% of the total mass percentage of the polyolefin plastic, the additives comprise the following components by mass percentage: 0.1-0.5% laser engraving additive, 0.1-0.5% antioxidant, and 0.1-0.5% lubricant. The laser engraving additive in this invention imparts good laser energy absorption properties to the material, achieving excellent marking clarity; the antioxidant prevents high-temperature oxidative degradation of the material during processing and improves its resistance to oxidative degradation during use; the lubricant imparts good lubrication properties to the material, improves the dispersion of flame retardants and fillers in the material, reduces friction between the material and the equipment cylinder, and improves the material's release properties and surface gloss.

[0022] Preferably, the antioxidant is selected from pentaerythritol tetrakis[methyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid (antioxidant 3114), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (antioxidant 330), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, etc. At least one of (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione (antioxidant 1790), tris(nonylphenyl) phosphite (antioxidant TNPP), tris(2,4-di-tert-butyl) phenyl phosphite (antioxidant 168), and pentaerythritol diphosphite (2,4-di-tert-butylphenol) (antioxidant 626).

[0023] Preferably, the lubricant is selected from at least one of zinc stearate, calcium stearate, magnesium stearate, polyethylene wax, polypropylene wax, and N,N'-ethylene bis-stearamide.

[0024] Preferably, the mass ratio of the first modified plastic material to the second modified plastic material is (3-12):1; more preferably, the mass ratio of the first modified plastic material to the second modified plastic material is (3-10):1.

[0025] Preferably, the polyolefin plastic is a layered material with no less than two layers.

[0026] Preferably, the polyolefin plastic has two layers. The inner layer of the polyolefin plastic is a flame-retardant polypropylene layer made of the second modified plastic material, and the outer layer of the polyolefin plastic is an impact-resistant polystyrene layer made of the first modified plastic material. In this invention, the polyolefin plastic is co-extruded using both the first and second modified plastic materials. The inner layer, a flame-retardant polypropylene layer, has excellent flame-retardant properties, providing protection against accidental battery fires. Simultaneously, the good electrical insulation and solvent resistance of polypropylene contribute to the safety of the battery pack. The outer layer, a high-impact polystyrene layer, imparts balanced physical and mechanical properties, good impact toughness, and the ability to laser-mark various logos and patterns onto the multi-layer sheet.

[0027] A second aspect of the present invention is to provide a method for preparing the polyolefin plastic provided in the first aspect of the present invention, comprising the following steps:

[0028] S1: The raw materials of the first modified plastic material are mixed and then extruded to obtain the first modified plastic material;

[0029] S2: The first modified plastic material is placed in extruder A, and the raw materials of the second modified plastic material are mixed and placed in extruder B. The materials extruded from extruder A and extruder B are then injected into a T-die, and then shaped, cooled, and drawn to obtain the polyolefin plastic.

[0030] The inner layer of the polyolefin plastic of this invention is made by directly melting and extruding a mixture of halogen-free flame retardant masterbatch and high melt strength polypropylene and thermoplastic elastomer. This method is convenient to operate and has low processing costs. At the same time, since this second type of modified plastic is made using a separate extruder, the feed rate can be easily adjusted, thereby adjusting the thickness of the inner layer and enabling continuous switching between different models of multi-layer composite flame retardant polyolefin sheets.

[0031] Preferably, the mixing time in step S1 is 2 to 30 minutes; more preferably, the mixing time in step S1 is 2 to 15 minutes; even more preferably, the mixing time in step S1 is 2 to 5 minutes.

[0032] Preferably, the mixing speed in step S1 is 1000-3000 rpm.

[0033] Preferably, the extruder used in step S1 is a parallel twin-screw extruder with a length-to-diameter ratio of 40:1.

[0034] Preferably, the extrusion step in step S1 is as follows: the temperatures of each section from the extruder hopper to the die are set to: 100-180℃, 130-200℃, 170-230℃, 170-230℃, 170-230℃, 170-230℃, 170-230℃, 170-230℃, 190-240℃, 190-250℃; the screw speed of the extruder main unit is set to 400-900 r / min; the frequency of the main hopper feed screw is set to 25-50 Hz; and the vacuum degree is 500-650 mmHg. Then, the material is extruded, cooled, and dried to obtain the first modified plastic material.

[0035] Preferably, the cooling step uses water for cooling.

[0036] Preferably, in step S2, the temperatures of extruder A and extruder B are 180–230°C.

[0037] Preferably, the mixing time in step S2 is 2 to 30 minutes; more preferably, the mixing time in step S2 is 2 to 15 minutes; even more preferably, the mixing time in step S2 is 2 to 5 minutes.

[0038] Preferably, the mixing speed in step S2 is 1000-3000 rpm.

[0039] Preferably, the feeding rate of the first modified plastic material is 300-400 kg / h.

[0040] Preferably, the feeding rate of the second modified plastic material is 40-100 kg / h.

[0041] A third aspect of the invention provides a battery pack cover comprising the polyolefin plastic described in the first aspect of the invention.

[0042] The fourth aspect of the present invention provides the application of the polyolefin plastics provided in the first aspect of the present invention in the field of electric vehicles.

[0043] The beneficial effects of this invention are: the polyolefin plastic in this invention has balanced physical and mechanical properties, good toughness, excellent flame retardancy, high and low temperature resistance, and excellent processing performance. It can be applied to larger-sized plastic parts. Furthermore, the polyolefin plastic in this invention can be processed into products by extrusion molding and vacuum forming. During vacuum forming, the products do not crack, wrinkle, or have thinned walls. Therefore, vacuum forming can be used to process finished products with excellent performance.

[0044] The polyolefin plastic in this invention is co-extruded using a first modified plastic material and a second modified plastic material, resulting in a plastic material with advantages such as good compatibility, excellent mechanical properties, good toughness, resistance to high and low temperatures, good processability, laser marking capability, and thermoforming capability. Compared to currently widely used injection-molded thermoplastics, the polyolefin plastic material in this invention is easy to extrude and thermoform, offering convenient molding, high cost-effectiveness, and applicability to larger-sized plastic parts such as battery pack covers and automotive trunks. Detailed Implementation

[0045] The following examples provide a more detailed description of the specific implementation of the present invention, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described below are methods that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0046] Information on the raw materials used in the embodiments and comparative examples of this invention is as follows:

[0047] High-impact polystyrene 1: trade name HIPS 8265, melt flow rate of 3.5 g / 10 min (test conditions: 200℃, 5.0 KG), purchased from Total, France;

[0048] High-impact polystyrene 2: Trade name HIPS PH-88SF, melt flow rate of 4.0 g / 10 min (test conditions: 200℃, 5.0 KG), purchased from Zhenjiang Chimei Chemical Co., Ltd.;

[0049] Thermoplastic elastomer 1: Trade name SEBS 7551, purchased from Lee Chang Yung Chemical Co., Ltd., Taiwan, China;

[0050] Thermoplastic elastomer 2: Trade name SEPS2063, melt flow rate of 7 g / 10 min (test conditions: 230℃, 2.16 KG), purchased from Kuraray Corporation, Japan;

[0051] Laser engraving additive: Trade name LS-402, purchased from Aika Special Effects Pigments (Zhuhai) Co., Ltd.;

[0052] Lubricant: N,N'-ethylene bis-stearamide (EBS), commercially available;

[0053] High melt strength polypropylene 1: trade name PPE02ES, purchased from Zhenhai Refining & Chemical Branch of China Petroleum & Chemical Corporation;

[0054] High melt strength polypropylene 2: trade name HMSPP H-001, purchased from China Petrochemical Corporation Beijing Yanshan Petrochemical Co., Ltd.;

[0055] Halogen-free flame retardant masterbatch 1: Trade name lydorflam5001M, purchased from Guangdong Shunde Tongcheng New Material Technology Co., Ltd.;

[0056] Halogen-free flame retardant masterbatch 2: Trade name HF-800M7N, purchased from Zhongshan Kangnuode New Materials Co., Ltd.

[0057] Example 1

[0058] The formulation of the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example is shown in Table 1, Example 1.

[0059] The multilayer composite flame-retardant polyolefin sheet used for battery pack covers in this example was prepared using the following method, with the specific steps as follows:

[0060] (1) After weighing the materials of the first type of modified plastic in Table 1 according to the proportion, add them to a high-speed mixer (speed of 1500 rpm) and stir for 3 minutes. Add the uniformly stirred materials to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. Set the temperatures of each section of the extruder from the hopper to the die (10 zones in total): 150℃, 180℃, 200℃, 230℃, 230℃, 230℃, 220℃, 220℃, 240℃. The screw speed of the main extruder is 450 r / min, the frequency of the main hopper feed screw is 28 Hz, and the vacuum degree is 500 mmHg. Then, the materials are blended, melted, and extruded. The pellets that come out of the extruder die are cooled by a water tank, dried by a fan, and then entered a pelletizer for pelletizing to obtain the first type of modified plastic with a length of 3-5 mm.

[0061] (2) After weighing the materials of the second type of modified plastic in Table 1 according to the proportion, add them to a high-speed mixer (speed of 1500 rpm) and stir for 3 minutes to obtain the second type of modified plastic.

[0062] (3) The first modified plastic and the second modified plastic were placed in the hoppers of two single-screw extruders respectively. The length-to-diameter ratio of the screws was 28:1. The processing temperature of the extruders from the hopper to the die was set to 180℃, 200℃, 200℃, 200℃, 220℃, 220℃, and 230℃ respectively. The feeding rates of the two materials were controlled to be 400KG / h and 40KG / h (10:1) respectively. The two materials were melt-co-extruded into the T-die, shaped by the cooling roller, cooled, and drawn to obtain the multi-layer composite flame-retardant polyolefin sheet that can be used as a battery pack cover in this example.

[0063] Table 1 shows the formulations of multilayer composite flame-retardant polyolefin sheets for use in battery pack covers in Examples 1-6.

[0064]

[0065] Example 2

[0066] The formulation of the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example is shown in Table 1, Example 2.

[0067] The method for preparing the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example differs from that in Example 1 in that the feeding rates of the two single-screw extruders are controlled at 360KG / h and 40KG / h (9:1), respectively.

[0068] Example 3

[0069] The formulation of the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example is shown in Table 1, Example 3.

[0070] The method for preparing the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example differs from that in Example 1 in that the feeding rates of the two single-screw extruders are controlled at 320KG / h and 40KG / h (8:1), respectively.

[0071] Example 4

[0072] The formulation of the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example is shown in Table 1, Example 4.

[0073] The method for preparing the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example differs from that in Example 1 in that the feeding rates of the two single-screw extruders are controlled at 360KG / h and 60KG / h (6:1), respectively.

[0074] Example 5

[0075] The formulation of the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example is shown in Table 1, Example 5.

[0076] The method for preparing the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example differs from that in Example 1 in that the feeding rates of the two single-screw extruders are controlled at 360KG / h and 90KG / h (4:1), respectively.

[0077] Example 6

[0078] The formulation of the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example is shown in Table 1, Example 6.

[0079] The method for preparing the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example differs from that in Example 1 in that the feeding rates of the two single-screw extruders are controlled at 300 KG / h and 100 KG / h (3:1), respectively.

[0080] Example 7

[0081] The difference between the multilayer composite flame-retardant polyolefin sheet used for battery pack covers in this example and Example 6 is that the thermoplastic elastomer 2 in the second modified plastic is replaced with an equal amount of polyolefin elastomer (brand name: POELC565, LG Chem, South Korea).

[0082] The preparation method of the multilayer composite flame-retardant polyolefin sheet that can be used as a battery pack cover in this example is the same as that in Example 6.

[0083] Example 8

[0084] The multilayer composite flame-retardant polyolefin sheet used for the battery pack cover in this example has the same formulation as in Example 1.

[0085] The preparation method of the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example differs from that in Example 1 in that the feeding rates of the two modified plastics are controlled at 360KG / h and 30KG / h (12:1), respectively.

[0086] Comparative Example 1

[0087] The difference between the multi-layer composite flame-retardant polyolefin sheet used for battery pack covers in this example and Example 1 is that general-purpose polystyrene (GPPS525, China Petroleum & Chemical Corporation Guangzhou Branch) is used instead of the high-impact polystyrene 1 in Example 1.

[0088] The preparation method of the multilayer composite flame-retardant polyolefin sheet that can be used as a battery pack cover in this example is the same as in Example 1.

[0089] Comparative Example 2

[0090] The difference between the multilayer composite flame-retardant polyolefin sheet used for battery pack covers in this example and Example 1 is that the thermoplastic elastomer 1 in the first modified plastic in Example 1 is replaced with an equal amount of high-impact polystyrene 1; and the thermoplastic elastomer 1 in the second modified plastic is replaced with an equal amount of high melt strength polypropylene 1.

[0091] The preparation method of the multilayer composite flame-retardant polyolefin sheet that can be used as a battery pack cover in this example is the same as in Example 1.

[0092] Comparative Example 3

[0093] The difference between the multi-layer composite flame-retardant polyolefin sheet used for battery pack covers in this example and Example 1 is that the high melt strength polypropylene 1 is replaced with an equal amount of ordinary homopolymer polypropylene (grade: PPH-T03, China Petroleum & Chemical Corporation Maoming Branch).

[0094] The preparation method of the multilayer composite flame-retardant polyolefin sheet that can be used as a battery pack cover in this example is the same as in Example 1.

[0095] Comparative Example 4

[0096] The multilayer composite flame-retardant polyolefin sheet used for battery pack covers in this example was prepared using the following method, with the specific steps as follows:

[0097] (1) After weighing the materials of the first type of modified plastic in Example 6 of Table 1 according to the proportion, add them to a high-speed mixer (speed of 1500 rpm) and stir for 3 minutes. Add the uniformly stirred materials to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. Set the temperatures of each section of the extruder from the hopper to the die (10 zones in total): 150℃, 180℃, 200℃, 230℃, 230℃, 230℃, 220℃, 220℃, 240℃. The screw speed of the main extruder is 450 r / min, the frequency of the main hopper feed screw is 28 Hz, and the vacuum degree is 500 mmHg. Then, the materials are blended, melted, and extruded. The pellets that come out of the extruder die are cooled by a water tank, dried by a fan, and then entered a pelletizer for pelletizing to obtain the first type of modified plastic with a length of 3-5 mm.

[0098] (2) The following components are formulated in the following mass percentages: 58.5% high melt strength polypropylene (brand name: HMSPP H-001, China Petrochemical Corporation Beijing Yanshan Petrochemical Co., Ltd.), 10% thermoplastic elastomer (brand name: SEPS2063, Kuraray Corporation, Japan), and 31.5% halogen-free flame retardant (brand name: HF-800AZ, Zhongshan Connor New Materials Co., Ltd.).

[0099] After weighing the above materials according to the specified ratio, add them to a high-speed mixer (1500 rpm) and mix for 3 minutes. Add the uniformly mixed material to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. Set the temperatures of each section of the extruder from the hopper to the die (10 zones in total): 150℃, 180℃, 180℃, 180℃, 170℃, 170℃, 170℃, 190℃, 200℃. Set the screw speed of the main extruder to 400 rpm, the frequency of the main hopper feed screw to 25 Hz, and the vacuum degree to 500 mmHg. Then, the materials are blended, melted, and extruded. The pellets exiting the extruder die are cooled in a water tank, dried by a fan, and then pelletized in a pelletizer to obtain a second type of modified plastic with a length of 3–5 mm.

[0100] (3) The first modified plastic and the second modified plastic were placed in the hoppers of two single-screw extruders respectively. The screw length-to-diameter ratio was 28:1. The processing temperature of the extruders was set to 180-230℃. The feeding rates of the two materials were controlled to be 300KG / h and 100KG / h respectively. The two materials were melt-co-extruded into the T-die, shaped by the cooling roller, cooled and drawn to obtain the multi-layer composite flame-retardant polyolefin sheet that can be used as the top cover of the battery pack in this example.

[0101] Comparative Example 5

[0102] The composite flame-retardant polyolefin sheet used in this example for battery pack covers is formulated with the following mass percentages: high-impact polystyrene 1:48%, thermoplastic elastomer 1:4.25%, high melt strength polypropylene 1:30%, halogen-free flame retardant masterbatch 1:17.5%, laser engraving additive 0.05%, antioxidant 1010 0.05%, antioxidant 168 0.05%, and lubricant 0.1%.

[0103] The composite flame-retardant polyolefin sheet used for battery pack covers in this example was prepared using the following method, with the specific steps as follows:

[0104] After weighing the above materials according to the specified ratio, add them to a high-speed mixer (1500 rpm) and mix for 3 minutes. Add the uniformly mixed material to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. Set the temperatures of each section of the extruder from the hopper to the die (10 zones in total): 150℃, 180℃, 200℃, 230℃, 230℃, 230℃, 220℃, 220℃, 240℃. Set the main screw speed to 450 rpm, the main hopper feed screw frequency to 28 Hz, and the vacuum degree to 500 mmHg. Then, the materials are blended, melted, and extruded. The extruded pellets are cooled in a water tank, dried by a fan, and then pelletized in a pelletizer to obtain flame-retardant polyolefin materials with a length of 3–5 mm.

[0105] The above-mentioned flame-retardant polyolefin material is placed in the hopper of a single-screw extruder with a screw length-to-diameter ratio of 28:1. The extruder processing temperature is set to 180-230℃, and the feed rate is controlled at 440KG / h. The material is melted and enters the T-die, and is shaped, cooled, and drawn by the cooling roller to obtain the composite flame-retardant polyolefin sheet that can be used as a battery pack cover in this example.

[0106] Comparative Example 6

[0107] The multilayer composite flame-retardant polyolefin sheet used for the battery pack cover in this example has the same formulation as in Example 6.

[0108] The preparation method of the multilayer composite flame-retardant polyolefin sheet that can be used for battery pack covers in this example differs from that in Example 6 in that the feeding rates of the two modified plastics are controlled at 200KG / h and 200KG / h (1:1), respectively.

[0109] Performance testing

[0110] The flame-retardant polyolefin sheets obtained in Examples 1-6 and Comparative Examples 1-6 were cut and subjected to various performance tests. Tensile strength, cantilever beam notched impact strength, flexural strength, and flexural modulus were tested according to relevant national standards. Fire resistance was assessed using a Bunsen burner; the flame-retardant layer of the polyolefin sheet was placed under a flame at 800-850℃, and the time it took for the sample to burn through was recorded; a longer burn time indicated better fire resistance. The evaluation criteria for processability were: Excellent: Smooth production process, stable quality, and no significant fluctuations in process parameters; Medium: Generally smooth production process, relatively stable quality, but process parameters need appropriate adjustment; Poor: Unstable production process, with significant fluctuations in process parameters. The test results obtained according to the above testing methods are shown in Table 2 below.

[0111]

[0112]

[0113] As shown in Table 2, compared with Example 1, in Comparative Example 1, replacing high-impact polystyrene with general-purpose polystyrene significantly improved the material's strength and modulus, but significantly reduced its impact toughness and molding performance, failing to meet the toughness requirements for the battery pack cover. Compared with Example 1, in Comparative Example 2, without the addition of thermoplastic elastomer, the material's impact strength decreased. Furthermore, due to the significant polarity difference between high-impact polystyrene and polypropylene, they are thermodynamically incompatible, resulting in delamination of the flame-retardant polyolefin sheet during molding. Compared with Example 1, in Comparative Example 3, replacing high melt strength polypropylene with an equal amount of ordinary homopolymer polypropylene resulted in reduced melt strength, leading to thinning of the material's wall thickness during vacuum forming, and porosity in the second layer, thus reducing its processability. Compared with Example 6, in Example 7, replacing the thermoplastic elastomer in the second modified plastic with an equal amount of polyolefin elastomer resulted in a decrease in impact toughness due to the lack of compatibilizing effect between high-impact polystyrene and polypropylene. Compared to Example 6, Comparative Example 4 replaced the halogen-free flame retardant masterbatch in the second modified plastic with halogen-free flame retardant powder and processed it using twin-screw melt extrusion granulation. The overall physical and mechanical properties of the material were not significantly different; however, the low bulk density of the halogen-free flame retardant made molding and processing difficult. Compared to Example 1, Comparative Example 5 prepared flame-retardant polyolefin material using single-layer extrusion. Due to the increased contact interface between high-impact polystyrene and polypropylene, the thermodynamic incompatibility of the two-phase interface increased, resulting in a significant decrease in the material's impact strength. Compared to Example 1, Example 8 increased the feed ratio of the first and second modified plastics, i.e., reduced the thickness of the flame-retardant layer, leading to a decrease in the material's fire resistance. Compared to Example 6, Comparative Example 6 increased the feed ratio of the second and first modified plastics, i.e., increased the thickness of the flame-retardant layer, resulting in a significant improvement in the material's fire resistance.

[0114] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A polyolefin plastic, characterized in that: Including a first modified plastic material and a second modified plastic material; The first modified plastic material comprises the following components by weight percentage: 90-96% polystyrene, 3-9% thermoplastic elastomer, and 0.1-2% additives; the second modified plastic material comprises the following components by weight percentage: 45-60% polypropylene, 4-10% thermoplastic elastomer, and 35-45% halogen-free flame retardant masterbatch. The melt flow rate of the polypropylene measured at 230°C and 2.16 kg was (0.01~3) g / 10 min. The melt flow rate of the polystyrene measured at 200°C and 5 kg was (3~8) g / 10 min. The polystyrene is high-impact polystyrene; The mass ratio of the first modified plastic material to the second modified plastic material is (3~12):1; The polyolefin plastic has two layers: the inner layer is a flame-retardant polypropylene layer made of the second modified plastic material, and the outer layer is an impact-resistant polystyrene layer made of the first modified plastic material.

2. The polyolefin plastic according to claim 1, characterized in that: The thermoplastic elastomer is selected from at least one of styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, styrene-ethylene / propylene-styrene block copolymer, styrene-ethylene-ethylene-propylene block copolymer, and polyolefin elastomer; And / or, the halogen-free flame retardant masterbatch includes a halogen-free flame retardant and a masterbatch; based on the total mass percentage of the halogen-free flame retardant masterbatch being 100%, the mass percentage of the halogen-free flame retardant is 50-80%.

3. The polyolefin plastic according to claim 2, characterized in that: The halogen-free flame retardant is a flame retardant containing phosphorus and nitrogen elements. Based on the total molar percentage of the halogen-free flame retardant being 100%, the molar percentage of phosphorus is 15-30% and the molar percentage of nitrogen is 15-35%.

4. The polyolefin plastic according to claim 1, characterized in that: The additive is selected from at least one of laser engraving additives, antioxidants, and lubricants.

5. The polyolefin plastic according to claim 4, characterized in that: Based on the total mass percentage of the polyolefin plastic being 100%, the additives include the following components by mass percentage: laser engraving additive 0.1~0.5%, antioxidant 0.1~0.5%, and lubricant 0.1~0.5%.

6. The polyolefin plastic according to claim 4, characterized in that: The antioxidant is selected from at least one of the following: pentaerythritol tetrakis[methyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, tris(nonylphenyl) phosphite, tris(2,4-di-tert-butyl)phosphite, and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite. And / or, the lubricant is selected from at least one of zinc stearate, calcium stearate, magnesium stearate, polyethylene wax, polypropylene wax, and N,N'-ethylene bis-stearamide.

7. The method for preparing the polyolefin plastic according to any one of claims 1 to 6, characterized in that: Includes the following steps: S1: The raw materials of the first modified plastic material are mixed and then extruded to obtain the first modified plastic material; S2: The first modified plastic material is placed in extruder A, and the raw materials of the second modified plastic material are mixed and placed in extruder B. The materials extruded from extruder A and extruder B are then injected into a T-die, and then shaped, cooled, and drawn to obtain the polyolefin plastic.

8. The method for preparing polyolefin plastic according to claim 7, characterized in that: The extrusion step in step S1 is as follows: the temperatures of each section from the extruder hopper to the die are set to: 100-180℃, 130-200℃, 170-230℃, 170-230℃, 170-230℃, 170-230℃, 170-230℃, 170-230℃, 190-240℃, 190-250℃; the screw speed of the extruder main unit is set to 400-900 r / min; the frequency of the main hopper feed screw is set to 25-50 Hz; and the vacuum degree is 500-650 mmHg. Then, the material is extruded, cooled, and dried to obtain the first modified plastic material. And / or, in step S2, the temperatures of extruder A and extruder B are 180–230°C.

9. A battery pack cover, characterized in that: Includes the polyolefin plastics described in any one of claims 1 to 6.

10. The application of the polyolefin plastic according to any one of claims 1 to 6 in the field of electric vehicles.

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