A modified polypropylene foam material and a method for producing the same

Abstract

The application belongs to the field of high polymer materials, and particularly relates to a modified polypropylene foaming material and a preparation method thereof. The modified polypropylene foaming material is prepared from a blank through mold foaming, and the preparation raw materials of the blank include, in parts by weight, 50-90 parts of homopolymer polypropylene, 10-40 parts of polystyrene, 1-10 parts of fluorine-containing functional monomer, 0.01-0.5 parts of initiator, 0.01-1 parts of catalyst, 0.1-0.5 parts of nucleating agent, 1-10 parts of decabromodiphenyl ethane, 0.2-5 parts of antimony trioxide and 0.05-5 parts of anti-dripping agent. The homopolymer polypropylene is modified by using multiple components in cooperation, so that the comprehensive performance of the material is significantly improved. The material has the advantages of strong stability, high Shore C hardness, large compressive strength, low dielectric constant, excellent anti-aging performance, good flame-retardant effect and wide application prospect in the field of new energy vehicles.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, and particularly relates to a modified polypropylene foam material and its preparation method. Background Technology

[0002] Polypropylene is a semi-crystalline thermoplastic polymer. Polypropylene (PP) foam materials are lightweight, cost-effective, have excellent impact resistance, heat resistance and environmental adaptability, are recyclable, and have low processing costs. It is one of the fastest growing materials in the world and can be widely used in many fields such as packaging, automotive, electronic structural components, logistics and transportation, toys and sports equipment, and construction.

[0003] Molded polypropylene (PP) foam is an important member of the PP foam family. With the rapid development of new energy vehicles, the requirements for new materials are becoming increasingly stringent. As the "heart" of new energy vehicles, the power battery provides the vehicle with propulsion. Battery heat insulation panels and bottom protective plates made of PP molded foam can absorb energy and resist impact, better protecting the blade-type batteries of new energy vehicles. Due to the special nature of the application scenarios, PP molded foam materials, in addition to meeting mechanical properties, also need to meet flame retardancy, low dielectric properties, and aging resistance, placing higher demands on overall performance. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a modified polypropylene foam material and its preparation method. The modified polypropylene foam material provided by this invention has strong stability, high Shore C hardness, high compressive strength, low dielectric constant, excellent anti-aging properties, and good flame retardant effect.

[0005] This invention provides a modified polypropylene foam material, which is made by compression molding of a preform. The raw materials for preparing the preform, by weight, include:

[0006]

[0007]

[0008] Preferably, the number average molecular weight of the homopolymer polypropylene is 5 × 10⁻⁶. 4 ~20×10 4 The homopolymer polypropylene has a melt index of 2–5 g / 10 min; the polystyrene has a number-average molecular weight of 20 × 10⁻⁶. 4 ~30×10 4 The melt index of the polystyrene is 1 to 10 g / 10 min.

[0009] Preferably, the fluorinated functional monomer is one or more selected from octafluoropentyl acrylate, dodecafluoroheptyl methacrylate, hexafluorobutyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, and hexafluorobutyl methacrylate.

[0010] Preferably, the initiator is dicumyl peroxide and / or 2,4-di-tert-butyl peroxide; the catalyst is one or more of the following: zinc 2-thiol benzothiazole, N-cyclohexyl-2-benzothiazole sulfenamide, tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetrabenzylthiuram disulfide, zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc ethylphenyl dithiocarbamate, zinc dibenzyl dithiocarbamate, NN′-diphenylthiourea, zinc dialkyl dithiophosphate, thiomelamine, and NN′-m-phenylenebismaleimide.

[0011] Preferably, the nucleating agent is one or more selected from calcium carbonate, talc, kaolin, montmorillonite, silica, diatomaceous earth, and silica fume; the particle size D of the nucleating agent is... 97 ≤10μm.

[0012] Preferably, the whiteness of the antimony trioxide is ≥93; the particle size D of the antimony trioxide is... 97 ≤1μm.

[0013] Preferably, the anti-dripping agent is acrylate-coated polytetrafluoroethylene.

[0014] This invention provides a method for preparing the modified polypropylene foam material described above, comprising the following steps:

[0015] a) Homopolymer polypropylene, polystyrene, fluorinated functional monomers, initiator, catalyst, nucleating agent, decabromodiphenyl ethane, antimony trioxide and anti-dripping agent are melt-blended and shaped to obtain a preform;

[0016] b) The preform is molded and foamed to obtain a modified polypropylene foam material.

[0017] Preferably, in step a), the temperature of the melt blending is 140–190°C; and the thickness of the preform is 8–20 mm.

[0018] Preferably, in step b), the specific process of compression molding foaming includes:

[0019] The preform is placed in the mold cavity of the molding foaming equipment, then supercritical gas is introduced and kept at temperature and pressure for a period of time. After that, the pressure is released and the material is shaped to obtain the modified polypropylene foam material.

[0020] The supercritical gas is carbon dioxide; the pressure for heat preservation and pressure holding is 8-20 MPa, the temperature is 140-170℃, and the time is 1-5 h; the pressure release time is ≤2 s.

[0021] Compared with existing technologies, this invention provides a modified polypropylene foam material and its preparation method. The modified polypropylene foam material provided by this invention is made from a preform through molding and foaming. By weight, the raw materials for preparing the preform include: 50-90 parts homopolymer polypropylene, 10-40 parts polystyrene, 1-10 parts fluorinated functional monomers, 0.01-0.5 parts initiator, 0.01-1 parts catalyst, 0.1-0.5 parts nucleating agent, 1-10 parts decabromodiphenyl ethane, 0.2-5 parts antimony trioxide, and 0.05-5 parts anti-dripping agent. This invention significantly improves the comprehensive performance of the material by synergistically modifying homopolymer polypropylene with multiple components. The material exhibits strong stability, high Shore C hardness, high compressive strength, low dielectric constant, excellent anti-aging properties, and good flame retardant effect, showing broad application prospects in the field of new energy vehicles. More specifically, the technical solution of this invention includes at least the following advantages:

[0022] (1) Under the action of initiator and catalyst, fluorine-containing functional monomers are used to melt graft polypropylene and polystyrene polymers, which reduces the crystallinity of polypropylene and widens the foaming window of homopolymer polypropylene, realizing the feasibility of homopolymer polypropylene molding foaming; homopolymer polypropylene, polystyrene and fluorine-containing functional monomers intertwine with each other in the form of chemical bonds to form a spatial network structure, and the synergistic effect makes the foamed material have good mechanical properties.

[0023] (2) Fluorine-containing functional monomers are incorporated into the molecular chain segments of homopolymer polypropylene. The fluorine-carbon bond energy is relatively high, and fluorine atoms have a strong attraction to electrons. Under a small applied electric field, this reduces polarization, thereby lowering the dielectric properties of the material. Fluorine atoms not only bond firmly to carbon atoms but also are densely packed on the outer layer of the carbon skeleton, effectively preventing the exposure of carbon atoms and carbon chains and improving the anti-aging properties of the foamed material. Therefore, the anti-aging properties of the foamed material are superior. Simultaneously, the introduction of fluorine-containing functional monomers can regulate the melt strength of the polypropylene foamed material, thereby controlling the cell structure during the polypropylene foaming process, promoting uniform cell distribution, reducing cell merging and rupture, and ensuring uniform cell size.

[0024] (3) Replacing styrene comonomer with catalyst not only has high catalytic efficiency and good grafting effect, but also protects operators and the environment.

[0025] (4) Decabromodiphenyl ethane, antimony trioxide and anti-dripping agent are used to provide good flame retardant properties for polypropylene foam material. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 This is a scanning electron microscope image of the modified polypropylene foam material of Example 1 provided by the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention provides a modified polypropylene foam material, which is made by compression molding of a preform, wherein the preform is made by melt blending of raw materials; by weight, the raw materials for preparing the preform include:

[0030]

[0031] In the modified polypropylene foam material provided by this invention, the number-average molecular weight of the homopolymer polypropylene is preferably 5 × 10⁻⁶. 4 ~20×10 4 Specifically, it can be 5×10 4 6×10 4 7×10 4 8×10 4 9×10 4 10×10 4 11×10 4 12×10 4 13×10 4 14×10 4 15×10 4 16×10 4 17×10 4 18×10 4 19×10 4 Or 20×10 4The melt index of the homopolymer polypropylene is preferably 2 to 5 g / 10 min, specifically 2 g / 10 min, 2.3 g / 10 min, 2.5 g / 10 min, 2.7 g / 10 min, 2.8 g / 10 min, 3 g / 10 min, 3.2 g / 10 min, 3.5 g / 10 min, 3.7 g / 10 min, 4 g / 10 min, 4.2 g / 10 min, 4.5 g / 10 min, 4.7 g / 10 min, or 5 g / 10 min.

[0032] In the modified polypropylene foam material provided by this invention, the number-average molecular weight of the polypropylene reflects the degree of polymerization and molecular chain length of the polypropylene monomers, and the number-average molecular weight is 5 × 10⁻⁶. 4 ~20×10 4 Polypropylene has strong rigidity, and after modification, it exhibits good mechanical properties in compression molding foam. The melt strength of polypropylene is related to its melt index; a lower melt index results in higher melt strength. In the compression molding foaming process, high pressure of 8–20 MPa is used. During the instantaneous depressurization process, the driving force of the cells is relatively large. If the melt strength of the substrate is low, phenomena such as cell rupture and collapse may occur. Therefore, a melt index of 2–5 g / 10 min for polypropylene raw materials is more suitable for compression molding foaming.

[0033] In the modified polypropylene foam material provided by the present invention, the content of homopolymer polypropylene in the raw materials can specifically be 50 parts by weight, 52 parts by weight, 55 parts by weight, 57 parts by weight, 60 parts by weight, 62 parts by weight, 65 parts by weight, 67 parts by weight, 70 parts by weight, 72 parts by weight, 75 parts by weight, 78 parts by weight, 80 parts by weight, 82 parts by weight, 85 parts by weight, 87 parts by weight, or 90 parts by weight.

[0034] In the modified polypropylene foam material provided by this invention, the number-average molecular weight of the polystyrene is preferably 20 × 10⁻⁶. 4 ~30×10 4 Specifically, it can be 20×10 4 21×10 4 22×10 4 23×10 4 24×10 4 25×10 4 26×10 4 27×10 4 28×10 4 29×10 4 Or 30×10 4The melt index of the polystyrene is preferably 1 to 10 g / 10 min, specifically 1 g / 10 min, 1.5 g / 10 min, 2 g / 10 min, 2.3 g / 10 min, 2.5 g / 10 min, 3 g / 10 min, 3.5 g / 10 min, 4 g / 10 min, 4.5 g / 10 min, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, or 10 g / 10 min.

[0035] In the modified polypropylene foam material provided by this invention, polypropylene suffers from drawbacks such as large molding shrinkage and low surface hardness. Compared with polypropylene, polystyrene has smaller molding shrinkage and higher surface hardness due to the presence of benzene ring structure. The addition of the polystyrene component not only solves the problems of large molding shrinkage and low surface hardness of polypropylene, but also, since polystyrene is a non-crystalline polymer, it contributes significantly to reducing the crystallinity of the material. Furthermore, its melt strength is not sensitive to the foaming temperature, which to some extent broadens the polypropylene foaming window and improves the effect of polypropylene molding foaming. The resulting polypropylene foam material has a smooth, flat, and uniform surface.

[0036] In the modified polypropylene foam material provided by the present invention, the content of polystyrene in the raw materials can be specifically 10 parts by weight, 12 parts by weight, 15 parts by weight, 17 parts by weight, 20 parts by weight, 23 parts by weight, 25 parts by weight, 27 parts by weight, 30 parts by weight, 32 parts by weight, 35 parts by weight, 37 parts by weight, or 40 parts by weight.

[0037] In the modified polypropylene foam material provided by the present invention, the fluorinated functional monomer is preferably one or more of octafluoropentyl acrylate, dodecafluoroheptyl methacrylate, hexafluorobutyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, and hexafluorobutyl methacrylate.

[0038] In the modified polypropylene foam material provided by this invention, the fluorinated functional monomer reacts with polypropylene and polystyrene macromolecular free radicals under the action of an initiator and a catalyst, and is chemically bonded to the polypropylene and polystyrene molecular chain segments, forming a network structure through mutual entanglement. Fluorine atoms have a strong attraction to electrons, resulting in a higher electron density and a smaller atomic radius. When an external electric field is applied to the material, electrons are tightly adsorbed, making it difficult for the atomic nucleus and electron center of gravity to shift, reducing polarization and thus lowering the dielectric properties of the material. The carbon-fluorine bond energy in fluorocarbon compounds is relatively high, and fluorine atoms are not only firmly bonded to carbon atoms but also arranged very tightly on the outer layer of the carbon skeleton, effectively preventing the exposure of carbon atoms and carbon chains, thus resulting in better anti-aging properties of the foam material. At the same time, the introduction of the fluorinated functional monomer can regulate the melt strength of the polypropylene foam material, thereby controlling the cell structure during the polypropylene foaming process, promoting uniform cell distribution, reducing cell merging and rupture, and ensuring uniform cell size.

[0039] In the modified polypropylene foam material provided by the present invention, the content of the fluorinated functional monomer in the raw materials can specifically be 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, 5 parts by weight, 5.5 parts by weight, 6 parts by weight, 6.5 parts by weight, 7 parts by weight, 7.5 parts by weight, 8 parts by weight, 8.5 parts by weight, 9 parts by weight, 9.5 parts by weight, or 10 parts by weight.

[0040] In the modified polypropylene foam material provided by this invention, the initiator is preferably dicumyl peroxide and / or 2,4-di-tert-butyl peroxide. In this invention, homopolymer polypropylene and polystyrene undergo chain segment breakage under the action of the initiator, forming macromolecular free radicals, which further react with the grafted monomers under the action of a catalyst.

[0041] In the modified polypropylene foam material provided by the present invention, the content of the initiator in the raw materials can specifically be 0.01 parts by weight, 0.03 parts by weight, 0.05 parts by weight, 0.07 parts by weight, 0.1 parts by weight, 0.12 parts by weight, 0.15 parts by weight, 0.17 parts by weight, 0.2 parts by weight, 0.23 parts by weight, 0.25 parts by weight, 0.27 parts by weight, 0.3 parts by weight, 0.32 parts by weight, 0.35 parts by weight, 0.37 parts by weight, 0.4 parts by weight, 0.42 parts by weight, 0.45 parts by weight, 0.47 parts by weight, or 0.5 parts by weight.

[0042] In the modified polypropylene foam material provided by the present invention, the catalyst is preferably one or more of 2-thiol-benzothiazole zinc salt, N-cyclohexyl-2-benzothiazole sulfenamide, tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetrabenzylthiuram disulfide, zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc ethylphenyl dithiocarbamate, zinc dibenzyl dithiocarbamate, NN′-diphenylthiourea, zinc dialkyl dithiophosphate, thiomelamine, and NN′-m-phenylenebismaleimide, more preferably one or more of 2-thiol-benzothiazole zinc salt, tetramethylthiuram disulfide, zinc dimethyl dithiocarbamate, and zinc dialkyl dithiophosphate.

[0043] In the modified polypropylene foam material provided by this invention, the low reactivity of fluorinated monomers leads to numerous side reactions and degradation reactions, resulting in a low grafting rate of fluorinated monomers. The catalyst, containing electron-donating groups, inhibits the chain-breaking reaction between polypropylene and polystyrene while simultaneously promoting the activity of excited-state monomer molecules, thereby increasing the grafting rate. Furthermore, polypropylene melt grafting modification typically involves a dual-monomer approach, with the first monomer serving as the main grafting monomer and styrene as a co-monomer due to its high reactivity. However, styrene poses significant health risks and environmental hazards. Using a catalyst instead of the styrene co-monomer not only ensures high catalytic efficiency but also avoids the use of styrene, protecting operators and the environment.

[0044] In the modified polypropylene foam material provided by the present invention, the content of the catalyst in the raw materials can specifically be 0.01 parts by weight, 0.05 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.35 parts by weight, 0.4 parts by weight, 0.45 parts by weight, 0.5 parts by weight, 0.55 parts by weight, 0.6 parts by weight, 0.65 parts by weight, 0.7 parts by weight, 0.75 parts by weight, 0.8 parts by weight, 0.85 parts by weight, 0.9 parts by weight, 0.95 parts by weight, or 1 part by weight.

[0045] In the modified polypropylene foam material provided by this invention, the nucleating agent is preferably one or more selected from calcium carbonate, talc, kaolin, montmorillonite, silica, diatomaceous earth, and silica fume; the particle size D of the nucleating agent is... 97 Preferably, it should be ≤10μm.

[0046] In the modified polypropylene foam material provided by this invention, the nucleating agent provides nucleation sites for the formation of polypropylene cells. The particle size of the nucleating agent determines its dispersion in the polymer, thereby affecting the morphology of the cell structure; particle size D 97Preferably, the nucleating agent is ≤10μm, specifically 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm or 10μm, which can ensure the uniform dispersion of the nucleating agent in the polymer.

[0047] In the modified polypropylene foam material provided by the present invention, the nucleating agent in the raw materials can specifically be 0.1 parts by weight, 0.12 parts by weight, 0.15 parts by weight, 0.17 parts by weight, 0.2 parts by weight, 0.23 parts by weight, 0.25 parts by weight, 0.27 parts by weight, 0.3 parts by weight, 0.32 parts by weight, 0.35 parts by weight, 0.37 parts by weight, 0.4 parts by weight, 0.42 parts by weight, 0.45 parts by weight, 0.47 parts by weight, or 0.5 parts by weight.

[0048] In the modified polypropylene foam material provided by this invention, the decabromodiphenyl ethane is a halogenated flame retardant with high flame retardant efficiency and good flame retardant effect. Its carbon-bromine bond energy is not high, making it relatively easy to break. When combustion occurs, decabromodiphenyl ethane begins to decompose before the polypropylene decomposes. After decomposition, the Br· free radicals generated can capture the active free radicals generated by the polymer combustion reaction, thereby terminating the combustion reaction. At the same time, HBr itself is non-flammable and has a density greater than air, which will encapsulate the material, preventing it from further contacting the air and preventing the combustion reaction from proceeding further.

[0049] In the modified polypropylene foam material provided by the present invention, the content of decabromodiphenyl ethane in the raw materials can specifically be 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, 5 parts by weight, 5.5 parts by weight, 6 parts by weight, 6.5 parts by weight, 7 parts by weight, 7.5 parts by weight, 8 parts by weight, 8.5 parts by weight, 9 parts by weight, 9.5 parts by weight, or 10 parts by weight.

[0050] In the modified polypropylene foam material provided by this invention, the whiteness of the antimony trioxide is preferably ≥93; the particle size D of the antimony trioxide is... 97 Preferably, the thickness is ≤1μm. In this invention, when antimony trioxide is used in combination with the halogenated flame retardant decabromodiphenyl ethane, the efficiency of the halogenated flame retardant can be greatly improved. In the initial stage of combustion, the melting process first forms a protective film on the material surface to isolate air, and the combustion temperature is reduced through internal endothermic reaction. At high temperature, antimony trioxide is vaporized, diluting the oxygen concentration in the air, thereby playing a flame-retardant role.

[0051] In the modified polypropylene foam material provided by the present invention, the content of antimony trioxide in the raw materials can specifically be 0.2 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 1 part by weight, 1.2 parts by weight, 1.5 parts by weight, 1.7 parts by weight, 2 parts by weight, 2.3 parts by weight, 2.5 parts by weight, 2.7 parts by weight, 3 parts by weight, 3.2 parts by weight, 3.5 parts by weight, 3.7 parts by weight, 4 parts by weight, 4.2 parts by weight, 4.5 parts by weight, 4.7 parts by weight, or 5 parts by weight.

[0052] In the modified polypropylene foam material provided by this invention, the anti-dripping agent is preferably acrylate-coated polytetrafluoroethylene (PTFE). Polymer combustion dripping refers to the phenomenon of molten polymer falling during combustion. This phenomenon is absolutely prohibited in polymer flame retardancy because dripping can ignite objects below the burning object, which is a major factor in the spread of fire. In this invention, acrylate-coated PTFE is less prone to agglomeration, has good compatibility with resin, and can significantly increase the polymer melt strength and elastic modulus. Even if the melt is stretched, it will not drip due to its high strength, thus playing an anti-dripping role and reducing the spread of flame.

[0053] In the modified polypropylene foam material provided by the present invention, the content of the anti-dripping agent in the raw materials can specifically be 0.05 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.7 parts by weight, 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, or 5 parts by weight.

[0054] The present invention also provides a method for preparing the modified polypropylene foam material described in the above technical solution, comprising the following steps:

[0055] a) Homopolymer polypropylene, polystyrene, fluorinated functional monomers, initiator, catalyst, nucleating agent, decabromodiphenyl ethane, antimony trioxide and anti-dripping agent are melt-blended and shaped to obtain a preform;

[0056] b) The preform is molded and foamed to obtain a modified polypropylene foam material.

[0057] In the preparation method proposed in this invention, in step a), the raw materials are preferably premixed uniformly before melt blending; the melt blending temperature is preferably 140-190℃, specifically 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃ or 190℃.

[0058] In the preparation method proposed in this invention, in step a), the melt blending is preferably carried out in an extruder; wherein, the length-to-diameter ratio of the extruder is preferably 20 to 50, specifically 20, 25, 30, 35, 40, 44, 45, or 50; the main engine speed of the extruder is preferably 200 to 400 r / min, specifically 200 r / min, 230 r / min, 250 r / min, 270 r / min, 300 r / min, 320 r / min, or 350 r / min. The extruder's speed is preferably 10-25 r / min, specifically 10 r / min, 12 r / min, 15 r / min, 17 r / min, 20 r / min, 23 r / min, or 25 r / min. The extruder's temperature range is preferably set to 150℃, 170℃, 180℃, 185℃, 185℃, 185℃, 185℃, 180℃, and 180℃. In this invention, during melt blending, polypropylene undergoes grafting modification. The extruder's aspect ratio, main unit and feeder speeds, processing temperature, and the decomposition of polypropylene segments, monomer grafting rate, and product performance are closely related. Excessively high processing temperatures or prolonged material residence time in the screw may lead to the formation of bubbles and severe degradation of polypropylene. Insufficient processing temperatures prevent material melting, while insufficient material residence time in the screw cannot guarantee complete grafting reaction, resulting in a low grafting rate.

[0059] In the preparation method proposed in this invention, in step a), the shape of the molding is preferably a plate; after molding, it is preferably calendered, cooled and shaped, and cut to finally obtain a blank plate that meets the size specifications; the thickness of the blank plate is preferably 8-20mm, specifically 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm. In this invention, when the blank is subsequently subjected to compression molding and foaming, supercritical carbon dioxide will permeate and diffuse within the blank. The thicker the blank, the longer the heat preservation and pressure holding time is required. The heat preservation and pressure holding time is proportional to the square of the blank thickness. Compression molding and foaming is an intermittent production process. If the blank is too thick, the heat preservation and pressure holding time is long and the efficiency is low. If the blank is too thin, the foamed product is prone to warping. Therefore, the above requirements are made for the thickness of the blank.

[0060] In the preparation method proposed in this invention, step b) preferably includes the following specific process: placing the preform into the mold cavity of a molding foaming device, then introducing supercritical gas and maintaining the temperature and pressure for a period of time, followed by rapid depressurization and shaping to obtain modified polypropylene foam material. The supercritical gas is carbon dioxide; the pressure of the heat preservation and pressure maintenance is preferably 8–20 MPa, specifically 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, or 20 MPa; the temperature of the heat preservation and pressure maintenance is preferably 140–170°C, specifically 140°C, 142°C, 145°C, 147°C, 150°C, 152°C, 15 ... The temperatures are 7℃, 160℃, 162℃, 165℃, 167℃, or 170℃; the preferred heat preservation and pressure holding time is 1–5 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours; the preferred pressure release time is ≤2 seconds, specifically 0.5 seconds, 0.6 seconds, 0.7 seconds, 0.8 seconds, 0.9 seconds, 1 second, 1.1 seconds, 1.2 seconds, 1.3 seconds, 1.4 seconds, 1.5 seconds, 1.6 seconds, 1.7 seconds, 1.8 seconds, 1.9 seconds, or 2 seconds. In this invention, a pressure holding pressure of 8–20 MPa is beneficial for the penetration and diffusion of carbon dioxide within the board, providing a suitable driving force during the instantaneous pressure release process. The polypropylene foam material obtained under a pressure of 8–20 MPa has a cell density of 10-1. 8 pcs / cm 3 The above refers to cells with a pore size of less than 100μm.

[0061] In this invention, the modified polypropylene foam material prepared by the above-mentioned raw material composition and process preferably has a Shore C hardness of ≥82, a 10% compressive strength of ≥700KPa, a dielectric constant of ≤1.30, and an anti-aging performance of level 5.

[0062] For clarity, the following examples and comparative models will be used to provide a detailed description.

[0063] In the following embodiments and comparative examples of the present invention, a twin-screw extruder was used for melt blending and extrusion of sheets, wherein the length-to-diameter ratio (L / D) of the extruder was 44, and the speeds of the main extruder and the feeder were 300 r / min and 16 r / min, respectively; the extruder temperature ranges were set as follows: 150°C, 170°C, 180°C, 185°C, 185°C, 185°C, 185°C, 185°C, 180°C, 180°C.

[0064] Example 1

[0065] A modified polypropylene foam material and its preparation method are described below:

[0066] (1) 80 parts by weight of homopolymer polypropylene (number average molecular weight of 10×10) 4 10 parts by weight of polystyrene (number average molecular weight 25×10⁻⁶) with a melt index of 2.8 g / 10 min. 4 The following ingredients are mixed evenly: 8 parts by weight of octafluoropentyl acrylate (melt index 2.5 g / 10 min), 0.1 parts by weight of dicumyl peroxide, 0.3 parts by weight of 2-thiol benzothiazole zinc salt, 0.2 parts by weight of calcium carbonate with D97 of 8 μm, 2 parts by weight of decabromodiphenyl ethane, 1 part by weight of antimony trioxide, and 0.1 parts by weight of acrylate-coated polytetrafluoroethylene (A-3800, Mitsubishi Corporation, Japan, the same below). The mixture is then melt-extruded through a twin-screw extruder to form a slab, which is then calendered, cooled and shaped, and cut into 10 mm thick sheets.

[0067] (2) Place the 10mm sheet obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and maintain the temperature and pressure for a period of time. The temperature is 160℃, the pressure is 16MPa, and the holding time is 2h. After that, the pressure is quickly released within 2s. After shaping, the modified polypropylene foam material is obtained (scanning electron microscopy observation results are as follows). Figure 1 (As shown).

[0068] Example 2

[0069] A modified foaming material and its preparation method are described below:

[0070] (1) 70 parts by weight of homopolymer polypropylene (number average molecular weight of 12×10⁻⁶) 4 15 parts by weight of polystyrene (number average molecular weight 30×10⁻⁶) with a melt index of 2.5 g / 10 min. 4 The following ingredients were uniformly mixed: 10 parts by weight of dodecafluoroheptyl methacrylate (melt index 1.5 g / 10 min), 0.2 parts by weight of 2,4-di-tert-butyldiisopropylbenzene peroxide, 0.15 parts by weight of tetramethylthiuram disulfide, 0.15 parts by weight of talc with a D97 of 9 μm, 1.5 parts by weight of decabromodiphenyl ethane, 0.5 parts by weight of antimony trioxide, and 0.2 parts by weight of acrylate-coated polytetrafluoroethylene. The mixture was then melt-extruded using a twin-screw extruder to form a slab. After calendering, cooling and shaping, the slab was cut into sheets with a thickness of 12 mm.

[0071] (2) Place the 12mm board obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and keep it warm and pressurized for a period of time. The heat preservation temperature is 155℃, the pressure is 20MPa, and the heat preservation and pressure preservation time is 2.5h. After that, the pressure is quickly released within 1.5s, and the modified polypropylene foam material is obtained after shaping.

[0072] Example 3

[0073] A modified polypropylene foam material and its preparation method are described below:

[0074] (1) 70 parts by weight of homopolymer polypropylene (number average molecular weight of 8×10⁻⁶) 4 20 parts by weight of polystyrene (number average molecular weight 20×10⁻⁶) with a melt index of 3.5 g / 10 min. 4 The following ingredients are mixed evenly: 5 parts by weight of hexafluorobutyl acrylate (melt index 3.5 g / 10 min), 0.3 parts by weight of dicumyl peroxide, 0.5 parts by weight of zinc dimethyl dithiocarbamate, 0.5 parts by weight of kaolin with a D97 of 7 μm, 2.5 parts by weight of decabromodiphenyl ethane, 0.8 parts by weight of antimony trioxide, and 0.15 parts by weight of acrylate-coated polytetrafluoroethylene. The mixture is then melt-extruded using a twin-screw extruder to form a slab. After calendering, cooling and shaping, the slab is cut into sheets with a thickness of 15 mm.

[0075] (2) Place the 15mm board obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and keep it warm and pressurized for a period of time. The heat preservation temperature is 165℃, the pressure is 10MPa, and the heat preservation and pressure preservation time is 4h. After that, the pressure is quickly released within 1.2s, and the modified polypropylene foam material is obtained after shaping.

[0076] Example 4

[0077] A modified polypropylene foam material and its preparation method are described below:

[0078] (1) 65 parts by weight of homopolymer polypropylene (number average molecular weight of 15×10⁻⁶) 4 25 parts by weight of polystyrene (number average molecular weight 26 × 10⁻⁶) with a melt index of 2.0 g / 10 min. 4 The following ingredients are mixed evenly: 10 parts by weight of hexafluorobutyl methacrylate (melt index 2.3 g / 10 min), 0.25 parts by weight of 2,4-di-tert-butyl peroxide, 0.6 parts by weight of zinc dialkyl dithiophosphate, 0.1 parts by weight of silica with a D97 of 10 μm, 3 parts by weight of decabromodiphenyl ethane, 0.6 parts by weight of antimony trioxide, and 0.15 parts by weight of acrylate-coated polytetrafluoroethylene. The mixture is then melt-extruded using a twin-screw extruder to form a slab. After calendering, cooling and shaping, the slab is cut into sheets with a thickness of 20 mm.

[0079] (2) Place the 20mm board obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and keep it warm and pressurized for a period of time. The heat preservation temperature is 150℃, the pressure is 12MPa, and the heat preservation and pressure preservation time is 5h. After that, the pressure is quickly released within 1s, and after shaping, a low dielectric constant polypropylene foam material is obtained.

[0080] Comparative Example 1

[0081] Comparative Example 1 uses copolymer polypropylene Zhenhai Refining & Chemical E02ES as the raw material for compression molding foam. The preparation process steps are as follows:

[0082] (1) 100 parts by weight of copolymer polypropylene E02ES and 0.2 parts by weight of calcium carbonate with D97 of 8μm are uniformly mixed and then melt-extruded by a twin-screw extruder to form a slab. After calendering, cooling and shaping, the slab is cut into a 12mm thick sheet.

[0083] (2) Place the 12mm board obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and keep it warm and pressurized for a period of time. The heat preservation temperature is 140℃, the pressure is 12MPa, the heat preservation and pressure preservation time is 2h, and then the pressure is quickly released within 2s. After shaping, polypropylene foam material is obtained.

[0084] Performance Evaluation

[0085] The properties of the polypropylene foam materials prepared in the examples and comparative examples were tested, and the test results are shown in Table 1 below:

[0086] Table 1. Performance test data of polypropylene foam materials prepared in the examples and comparative examples.

[0087]

[0088] As can be seen from the test data in the table, the crystallinity of the modified polypropylene material obtained in the embodiments of the present invention is significantly lower than that of homopolymer polypropylene. Lower crystallinity improves the diffusion and dissolution capacity of supercritical carbon dioxide within the polymer, resulting in a wider melting range and a larger foaming window. Even under fluctuating foaming process conditions, the polypropylene foam material can still maintain good quality. The modified polypropylene foam material obtained in the embodiments of the present invention exhibits high Shore C hardness, strong compressive strength, low dielectric constant, and high anti-aging grade, demonstrating excellent overall performance. Furthermore, the modified polypropylene foam product obtained in the embodiments has a regular cell structure and uniform cell distribution; this good cell structure is the foundation for the excellent overall performance of the polypropylene foam product.

[0089] The modified polypropylene foam product obtained by this invention can be used in heat insulation panels for new energy vehicle batteries and battery bottom protective panels, as well as in other industrial, construction, and daily life fields.

[0090] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A modified polypropylene foam material, characterized in that, Made from preform through molding and foaming, the raw materials for preparing the preform, by weight, include: 50-90 parts of homopolymer polypropylene; 10-40 parts of polystyrene; 1-10 parts of fluorinated functional monomers; Initiator 0.01~0.5 parts; Catalyst 0.01~1 part; Nucleating agent 0.1~0.5 parts; 1-10 parts of decabromodiphenyl ethane; 0.2-5 parts of antimony trioxide; Anti-dripping agent 0.05~5 parts; The catalyst is one or more of the following: 2-thiol-benzothiazole zinc salt, N-cyclohexyl-2-benzothiazole sulfenamide, tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetrabenzylthiuram disulfide, zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc ethylphenyl dithiocarbamate, zinc dibenzyl dithiocarbamate, NN'-diphenylthiourea, zinc dialkyl dithiophosphate, thiomelamine, and NN'-m-phenylenebismaleimide.

2. The modified polypropylene foam material according to claim 1, characterized in that, The homopolymer polypropylene has a number average molecular weight of 5 × 10⁻⁶. 4 ~20×10 4 The melt flow index of the homopolymer polypropylene is 2~5 g / 10 min. The polystyrene has a number-average molecular weight of 20 × 10⁻⁶. 4 ~30×10 4 The melt flow index of the polystyrene is 1~10 g / 10 min.

3. The modified polypropylene foam material according to claim 1, characterized in that, The fluorinated functional monomer is one or more of the following: octafluoropentyl acrylate, dodecafluoroheptyl methacrylate, hexafluorobutyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, and hexafluorobutyl methacrylate.

4. The modified polypropylene foam material according to claim 1, characterized in that, The initiator is dicumyl peroxide and / or 2,4-di-tert-butyl peroxide.

5. The modified polypropylene foam material according to claim 1, characterized in that, The nucleating agent is one or more selected from calcium carbonate, talc, kaolin, montmorillonite, silica, diatomaceous earth, and silica fume; the particle size D of the nucleating agent is... 97 ≤10μm.

6. The modified polypropylene foam material according to claim 1, characterized in that, The whiteness of the antimony trioxide is ≥93; the particle size D of the antimony trioxide is... 97 ≤1μm.

7. The modified polypropylene foam material according to claim 1, characterized in that, The anti-dripping agent is polytetrafluoroethylene coated with polyacrylate.

8. A method for preparing the modified polypropylene foam material according to any one of claims 1 to 7, characterized in that, Includes the following steps: a) Homopolymer polypropylene, polystyrene, fluorinated functional monomers, initiator, catalyst, nucleating agent, decabromodiphenyl ethane, antimony trioxide and anti-dripping agent are melt-blended and shaped to obtain a preform; b) The preform is molded and foamed to obtain a modified polypropylene foam material.

9. The preparation method according to claim 8, characterized in that, In step a), the temperature of the melt blending is 140~190℃; the thickness of the blank is 8~20mm.

10. The preparation method according to claim 8, characterized in that, In step b), the specific process of compression molding foaming includes: The preform is placed in the mold cavity of the molding foaming equipment, then supercritical gas is introduced and kept at temperature and pressure for a period of time. After that, the pressure is released and the material is shaped to obtain the modified polypropylene foam material. The supercritical gas is carbon dioxide; the pressure for heat preservation and pressure holding is 8~20MPa, the temperature is 140~170℃, and the time is 1~5h; the pressure release time is ≤2s.

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