A foamable flame-retardant polypropylene material, its preparation method and use

Abstract

The application provides a foamable flame-retardant polypropylene material and a preparation method and application thereof. The foamable flame-retardant polypropylene material comprises a flame-retardant core layer and a flame-retardant surface layer coated on the surface of the flame-retardant core layer; the flame-retardant core layer comprises the following components in parts by weight: binary random copolymerized polypropylene 100-120 parts, a first char forming agent 5-25 parts, a first auxiliary char forming agent 0.5-2 parts, and a halogen-free flame retardant 13-30 parts; and the flame-retardant surface layer comprises the following components in parts by weight: ternary random copolymerized polypropylene 100-120 parts, a second char forming agent 3-5 parts, and a second auxiliary char forming agent 0.2-0.5 parts. The application provides a polypropylene foaming material which is super-light and has flame-retardant properties, and has good flame-retardant properties and bonding properties under the premise of ensuring low density.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant foamed materials technology, specifically relating to a foamable flame-retardant polypropylene material, its preparation method, and its application. Background Technology

[0002] In recent years, polypropylene (PP), as one of the five major general-purpose plastics, has shown broad application prospects in production and daily life. Currently, polypropylene foam material (EPP) prepared using high-pressure carbon dioxide as a physical foaming agent is odorless and non-toxic, non-absorbent, and possesses certain strength, a wide operating temperature range, good heat resistance, and good shape recovery stability. After repeated impacts and flexural deformations, it can quickly recover to its original shape without permanent deformation. Therefore, it has become the fastest-growing compression-resistant cushioning foam plastic. Furthermore, because it is prone to β-degradation and easy to recycle, its environmental friendliness is superior to other foam materials.

[0003] However, on the one hand, polypropylene's poor toughness, low melt strength, and poor foaming properties make it difficult to use ordinary polypropylene for foaming materials, limiting its application in thermoforming and foaming materials. On the other hand, most polymer materials are highly flammable when exposed to fire, and polypropylene is no exception. Polypropylene has a low limiting oxygen index, produces smoke and molten material dripping during combustion, has a high calorific value, and its flame spreads rapidly and is difficult to extinguish, thus easily causing fires, resulting in casualties and property damage. Furthermore, polypropylene foam is more easily ignited, which greatly reduces the safety of the products and further limits the application range of foam materials.

[0004] To further expand the application scenarios of polypropylene foam materials, it is necessary to modify the polypropylene material to improve its flame retardancy and melt strength, thereby meeting the requirements for use as foam materials. Currently, the main methods for preparing polypropylene flame retardant materials in existing technologies are as follows: (1) Adding halogenated flame retardants: Halogenated flame retardants can form chloride or bromide layers on the surface of combustibles, thereby inhibiting the combustion reaction. However, they are prone to producing harmful gases such as hydrogen halides during high-temperature combustion, which limits their widespread application; (2) Using metal hydroxide flame retardants: Metal hydroxide flame retardants absorb heat and dehydrate during combustion, preventing the polymer from heating up. At the same time, they release water vapor to dilute the oxygen concentration and form a metal oxide flame retardant layer on the polymer surface. However, the above materials need to reach a high loading to achieve a good flame retardant effect; (3) Adding silicon flame retardants: Silicon flame retardants are produced by silicon elements participating in the combustion reaction of materials to generate inorganic oxides such as silicates and form a carbonized layer on the surface of the material, thereby isolating the air and playing a flame retardant role. However, silicon flame retardants are not easy to disperse, which easily leads to poor flame retardant stability. Moreover, the production cost of silicon flame retardants is high.

[0005] Existing flame-retardant polypropylene foam materials are mainly produced by blending polypropylene and flame retardants before foaming. For example, CN115403709A discloses a flame-retardant polypropylene foam and its preparation method. Specifically, polypropylene resin, fluororubber, flame-retardant monomers, and antioxidants are mixed and melt-extruded in a twin-screw extruder to obtain a composite material. The composite material is then uniformly mixed with a foaming agent and added to a foaming injection molding machine to obtain polypropylene foam. The density of the obtained polypropylene foam is 0.12-0.3 g / cm³. 3 However, the addition of flame-retardant monomers negatively impacts the mechanical properties of polypropylene foam, reducing its overall strength, toughness, and impact resistance. Furthermore, the addition of flame retardants also affects the foaming properties of polypropylene, decreasing its foaming ratio and increasing its density.

[0006] Therefore, there is an urgent need to develop an ultralight, flame-retardant, and low-energy-consumption polypropylene foam material that not only reduces the foaming density of the material while ensuring high melt strength, but also has good flame-retardant properties. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a foamable flame-retardant polypropylene material, its preparation method, and its applications. Addressing the difficulties in preparing polypropylene foam materials with both ultra-low density and high flame retardancy, as well as the high energy consumption and poor adhesion in current polypropylene foam particle steam molding processes, the present invention provides an ultra-lightweight polypropylene foam material with flame-retardant properties, exhibiting good flame retardancy and adhesion performance while maintaining low density.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a foamable flame-retardant polypropylene material, the foamable flame-retardant polypropylene material comprising a flame-retardant core layer and a flame-retardant surface layer covering the surface of the flame-retardant core layer.

[0010] The flame-retardant core layer comprises the following components in parts by weight: 100-120 parts of binary random copolymer polypropylene, 5-25 parts of first charring agent, 0.5-2 parts of first charring aid, and 13-30 parts of halogen-free flame retardant.

[0011] The flame-retardant surface layer comprises the following components in parts by weight: 100-120 parts of ternary random copolymer polypropylene, 3-5 parts of the second charring agent, and 0.2-0.5 parts of the second charring aid.

[0012] First, the flame-retardant core layer material provided by this invention selects binary random copolymer polypropylene as the foamable main material. This is primarily to provide mechanical strength and performance, as the melting point of binary random copolymer polypropylene is higher than that of ternary random copolymer polypropylene, but lower than that of homopolymer polypropylene and binary isotactic copolymer polypropylene. This allows for a balance between good foaming performance and mechanical properties. Simultaneously, a halogen-free flame retardant system is used to reduce environmental pollution while ensuring good flame retardant effects. Furthermore, the addition of a first charring agent and a first charring aid helps form a stable char film during combustion, resulting in a polypropylene foam material with both ultra-low density and high flame-retardant performance. Furthermore, this invention selects ternary random copolymer polypropylene as the main material for the flame-retardant surface layer. This not only provides high adhesion but also, due to its low melting point, reduces the vapor pressure during steam molding post-processing, thereby reducing energy consumption. Furthermore, since the flame-retardant surface layer needs to provide high adhesion, the addition of too much filler will affect its own adhesion effect. Therefore, the present invention controls the content of the second charring agent and the second charring aid in the flame-retardant surface layer to be lower than the content of the corresponding components in the flame-retardant core layer, so as to ensure good adhesion between the flame-retardant surface layer and the flame-retardant core layer, promote the stable formation of char film, and thus better protect the flame-retardant core layer.

[0013] Secondly, the flame-retardant polypropylene foam material prepared by this invention has a low density and super-fine pores. Under the same density, the pores are small and fine, which is conducive to enhancing the mechanical properties of the material. This is because the number of pore walls increases under the same unit volume, which increases the specific surface area. When the foam material is under stress, it can be transmitted to the entire foam material through the pore walls, thereby playing a buffering role.

[0014] Finally, by controlling the structure and composition of each layer of the foamable flame-retardant polypropylene material, the present invention enables the prepared flame-retardant polypropylene foam material to have the advantages of low density, high flame retardancy, good mechanical properties and low energy consumption, thus having good application prospects in the fields of sound insulation materials, cushioning materials and electrical and electronic products.

[0015] In this invention, the weight parts of the binary random copolymer polypropylene are 100-120 parts, for example, 100 parts, 102 parts, 108 parts, 110 parts, 112 parts, 115 parts, 118 parts, 120 parts, etc.

[0016] In this invention, the weight of the first charring agent is 5-25 parts, for example, it can be 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, 22 parts, 25 parts, etc.

[0017] In this invention, the weight of the first char-forming agent is 0.5-2 parts, for example, it can be 0.5 parts, 0.8 parts, 1 part, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, etc.

[0018] In this invention, the halogen-free flame retardant is in the form of 13-30 parts by weight, for example, 13 parts, 15 parts, 18 parts, 20 parts, 22 parts, 25 parts, 28 parts, 30 parts, etc.

[0019] In this invention, the ternary random copolymer polypropylene is 100-120 parts by weight, for example, 100 parts, 102 parts, 108 parts, 110 parts, 112 parts, 115 parts, 118 parts, 120 parts, etc.

[0020] In this invention, the second charring agent is 3-5 parts by weight, for example, 3 parts, 3.2 parts, 3.5 parts, 3.8 parts, 4 parts, 4.2 parts, 4.5 parts, 4.8 parts, 5 parts, etc.

[0021] In this invention, the second char-forming agent is 0.2-0.5 parts by weight, for example, 0.2 parts, 0.22 parts, 0.25 parts, 0.28 parts, 0.3 parts, 0.32 parts, 0.35 parts, 0.4 parts, 0.42 parts, 0.45 parts, 0.48 parts, 0.5 parts, etc.

[0022] Preferably, the flame-retardant core layer comprises the following components in parts by weight: 100 parts of binary random copolymer polypropylene, 5-25 parts of first charring agent, 0.5-2 parts of first charring aid, and 13-30 parts of flame retardant.

[0023] In this invention, by further optimizing the weight proportions of each component in the flame-retardant core layer, the flame-retardant core layer has better flame-retardant effect, foaming performance and comprehensive mechanical properties.

[0024] Preferably, the flame-retardant surface layer comprises the following components in parts by weight: 100 parts of ternary random copolymer polypropylene, 3-5 parts of the second charring agent, and 0.2-0.5 parts of the second charring aid.

[0025] In this invention, by further optimizing the weight proportions of each component in the flame-retardant surface layer, the flame-retardant surface layer material and the flame-retardant core layer material achieve good adhesion, and the adhesion between particles during steam molding is also ensured, resulting in a final product with excellent mechanical properties.

[0026] Preferably, the binary random copolymer polypropylene includes ethylene-propylene random copolymer polypropylene and / or propylene-butadiene random copolymer polypropylene, and more preferably ethylene-propylene random copolymer polypropylene.

[0027] Preferably, the melting point of the binary random copolymer polypropylene is 140-155℃, more preferably 140-150℃, for example, it can be 140℃, 142℃, 145℃, 148℃, 150℃, 152℃, 155℃, etc.

[0028] In this invention, by controlling the melting point of binary random copolymer polypropylene, the material can achieve both good foaming performance and comprehensive mechanical properties. If the melting point is too low, the foam material will have poor mechanical properties, while if it is too high, the material will need to be foamed under higher pressure and temperature, which will increase the energy consumption of foaming.

[0029] Preferably, the melt index of the binary random copolymer polypropylene at 230°C and 2.16 kg is 5-20 g / 10 min, more preferably 5-15 g / 10 min, for example, it can be 5 g / 10 min, 8 g / 10 min, 10 g / 10 min, 12 g / 10 min, 15 g / 10 min, 18 g / 10 min, 20 g / 10 min, etc.

[0030] In this invention, by adjusting the melt index of binary random copolymer polypropylene, the material can have a better extrusion effect and a better wetting and dispersion effect on flame retardants. If the melt index is too low, it will lead to extrusion difficulties and reduced dispersion performance of flame retardants. Conversely, it will lead to problems such as easy breakage during extrusion and poor flame retardant performance.

[0031] Preferably, the ternary random copolymer polypropylene includes ethylene propylene butyl random copolymer polypropylene and / or ethylene propylene octyl random copolymer polypropylene, and more preferably ethylene propylene butyl random copolymer polypropylene.

[0032] Preferably, the melting point of the ternary random copolymer polypropylene is 120-135℃, more preferably 120-130℃, for example, it can be 120℃, 122℃, 125℃, 128℃, 130℃, 132℃, 135℃, etc.

[0033] In this invention, by controlling the melting point of ternary random copolymer polypropylene, it is made to have lower steam molding energy consumption and better heat resistance of the product. Too low a melting point will result in poor heat resistance of the product, while too high a melting point will result in increased steam molding energy consumption of the foamed material.

[0034] Preferably, the melt index of the ternary random copolymer polypropylene at 230℃ and 2.16kg is 5-10g / 10min, more preferably 5-8g / 10min, for example, it can be 5g / 10min, 6g / 10min, 7g / 10min, 8g / 10min, 9g / 10min, 10g / 10min, etc.

[0035] In this invention, by adjusting the melt index of ternary random copolymer polypropylene, it can achieve better extrusion effect and coating performance for flame-retardant core material. Too low a melt index will lead to extrusion difficulties, while too high a melt index will result in poor coating effect for flame-retardant core material.

[0036] Preferably, the first charring agent and the second charring agent each independently comprise triazine and / or carbon black.

[0037] Preferably, the first char-forming agent and the second char-forming agent each independently comprise any one or a combination of at least two of magnesium oxide, silicon dioxide, or zinc oxide.

[0038] Preferably, the halogen-free flame retardant comprises a combination of phosphorus-based and nitrogen-based flame retardants.

[0039] Preferably, the phosphorus-based flame retardant includes ammonium polyphosphate and / or melamine polyphosphate, and more preferably ammonium polyphosphate.

[0040] Preferably, the phosphorus-based flame retardant is 10-20 parts by weight, for example, 10 parts, 12 parts, 13 parts, 15 parts, 18 parts, 20 parts, etc.

[0041] Preferably, the nitrogen-based flame retardant includes melamine cyanurate and / or dicyandiamide, with melamine cyanurate being the most preferred.

[0042] Preferably, the nitrogen-based flame retardant is 3-10 parts by weight, for example, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc.

[0043] Preferably, the flame-retardant core layer and the flame-retardant surface layer each independently include a first additive.

[0044] Preferably, the first additive includes a dispersant and / or an anti-drip agent.

[0045] Preferably, the dispersant comprises PEG4000.

[0046] Preferably, the anti-drip agent comprises any one or a combination of at least two of polytetrafluoroethylene, polyvinylidene fluoride, or polychlorotrifluoroethylene.

[0047] Preferably, the first auxiliary agent is 3.2-5.5 parts by weight, for example, 3.2 parts, 3.5 parts, 3.8 parts, 4 parts, 4.2 parts, 4.5 parts, 4.8 parts, 5 parts, 5.2 parts, 5.5 parts, etc.

[0048] Preferably, the dispersant is 3-5 parts by weight, for example, 3 parts, 3.2 parts, 3.5 parts, 3.8 parts, 4 parts, 4.2 parts, 4.5 parts, 4.8 parts, 5 parts, etc.

[0049] Preferably, the anti-drip agent is present in 0.2-0.5 parts by weight, for example, 0.2 parts, 0.22 parts, 0.25 parts, 0.28 parts, 0.3 parts, 0.32 parts, 0.35 parts, 0.4 parts, 0.42 parts, 0.45 parts, 0.48 parts, 0.5 parts, etc.

[0050] In a second aspect, the present invention provides a method for preparing a foamable flame-retardant polypropylene material according to the first aspect, the method comprising the following steps:

[0051] According to the formula, the binary random copolymer polypropylene, the first charring agent, the first charring aid and the halogen-free flame retardant are mixed once, and the flame retardant core layer particles are obtained after one extrusion and blending.

[0052] According to the formula, the ternary random copolymer polypropylene, the second charring agent and the second charring aid are mixed twice, and the flame-retardant surface particles are obtained after two extrusions and blending.

[0053] The flame-retardant core particles and the flame-retardant surface particles are melt-plasticized and then co-extruded to obtain a foamable flame-retardant polypropylene material.

[0054] Preferably, the flow channel structure shape of the die head in the co-extrusion process includes a circle or a rectangle.

[0055] In this invention, foamable flame-retardant polypropylene granules and foamable flame-retardant polypropylene sheets are prepared by changing the die head of the co-extrusion equipment.

[0056] Preferably, the diameter of the filament exiting the circular flow channel structure is 1-1.5 mm, for example, it can be 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, etc.

[0057] Thirdly, the present invention provides a flame-retardant polypropylene foam material, which is foamed from the foamable flame-retardant polypropylene material according to the first aspect.

[0058] Fourthly, the present invention provides a method for preparing the flame-retardant polypropylene foam material according to the third aspect, the method comprising the following steps:

[0059] The flame-retardant polypropylene material described in the first aspect is foamed to obtain the flame-retardant polypropylene foam material.

[0060] Preferably, the foaming method includes supercritical fluid foaming.

[0061] Preferably, the supercritical fluid used for foaming includes carbon dioxide.

[0062] Preferably, the supercritical fluid foaming temperature is 115-145℃, for example, 115℃, 118℃, 120℃, 122℃, 125℃, 128℃, 130℃, 132℃, 135℃, 138℃, 140℃, 142℃, 145℃, etc.; the pressure is 7-30 MPa, for example, 7 MPa, 9 MPa, 10 MPa, 12 MPa, 15 MPa, 18 MPa, 20 MPa, 22 MPa, 25 MPa, 28 MPa, 30 MPa, etc.

[0063] In this invention, the specific process of supercritical fluid foaming of flame-retardant polypropylene particles is as follows: flame-retardant polypropylene particles are placed in a supercritical fluid foaming vessel, the temperature in the vessel is set to 70-100℃, medium water is added to the vessel, CO2 gas is introduced at 7-20MPa under stirring conditions, and then the temperature is raised to 115-140℃. The valve is opened from the lower end of the vessel to release pressure and gas, and foamed particles are obtained. Flame-retardant polypropylene foamed particles with an outer layer of macroporous foamed layer and an inner layer of microporous foamed body have a foaming ratio of 25-40 times.

[0064] The specific process of supercritical fluid foaming of flame-retardant polypropylene sheets is as follows: the flame-retardant polypropylene sheets are placed in a supercritical fluid foaming kettle, the temperature is set to 135-145℃, CO2 gas is introduced at 12-30MPa, saturated for 1-3 hours, and then the pressure is quickly released to obtain foamed sheets. The outer layer of the sheets is a macroporous foamed layer, the inner layer is a microporous foamed body, the foaming ratio is 15-30 times, and the flame retardant rating is V-0.

[0065] Preferably, the supercritical fluid foaming process further includes steam molding.

[0066] In this invention, the specific process of steam molding includes: vacuum-inhaling flame-retardant polypropylene granules into a mold, and after being pressurized by air, steam molding is performed to obtain foamed granule products with different shapes and flame retardant rating of V-0; polypropylene foam boards can be steam-molded to obtain multi-layer foam boards, or they can be cut and then molded to obtain products of other shapes.

[0067] Fifthly, the present invention provides a flame-retardant foam product comprising the flame-retardant polypropylene foam material according to the third aspect.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] This invention provides a foamable flame-retardant polypropylene material. Firstly, the flame-retardant core layer material is selected as the main foamable material of binary random copolymer polypropylene, primarily to provide mechanical strength and performance. Simultaneously, a halogen-free flame retardant system is employed to reduce environmental pollution while ensuring good flame-retardant effects. Furthermore, a first charring agent and a first char-forming aid are added to form a stable char film during combustion, resulting in a polypropylene foam material with both ultra-low density and high flame-retardant properties. Simultaneously, this invention selects ternary random copolymer polypropylene as the main material of the flame-retardant surface layer. This not only provides high adhesion but also, due to its low melting point, reduces the vapor pressure during steam molding post-processing, thereby reducing energy consumption. Furthermore, since the flame-retardant surface layer needs to provide high adhesion, the addition of too much filler will affect its own adhesion effect. Therefore, the present invention controls the content of the second charring agent and the second charring aid in the flame-retardant surface layer to be lower than the content of the corresponding components in the flame-retardant core layer, so as to ensure good adhesion between the flame-retardant surface layer and the flame-retardant core layer, promote the stable formation of char film, and thus better protect the flame-retardant core layer.

[0070] Secondly, the flame-retardant polypropylene foam material prepared by this invention has a low density and super-fine pores. Under the same density, the pores are small and fine, which is conducive to enhancing the mechanical properties of the material. This is because the number of pore walls increases under the same unit volume, which increases the specific surface area. When the foam material is under stress, it can be transmitted to the entire foam material through the pore walls, thereby playing a buffering role.

[0071] Finally, by controlling the structure and composition of each layer of the foamable flame-retardant polypropylene material, the present invention enables the obtained flame-retardant polypropylene foam material to have the advantages of low density, high flame retardancy, good mechanical properties and low energy consumption. Therefore, it has good application prospects in the fields of sound insulation materials, cushioning materials and electrical and electronic products. Attached Figure Description

[0072] Figure 1These are photos of the foamable flame-retardant polypropylene material in Example 1 before and after foaming;

[0073] Figure 2 The image shows the morphology and cell structure of the flame-retardant polypropylene foam material in Example 1.

[0074] Figure 3 These are photos of the foamable flame-retardant polypropylene material in Example 2 before and after foaming;

[0075] Figure 4 This is a morphology diagram of the flame-retardant polypropylene foam material in Example 2;

[0076] Figure 5 This is a photograph of the flame-retardant polypropylene foam balls in Example 3;

[0077] Figure 6 The image shows the cell structure of the flame-retardant polypropylene foam board in Example 4.

[0078] Figure 7 This is a photograph of the flame-retardant polypropylene foam board in Example 4 during combustion;

[0079] Figure 8 This is a photograph of the flame-retardant polypropylene multilayer composite foam material in Example 5;

[0080] Figure 9 This is a photograph of the polypropylene foam material in Comparative Example 1 during combustion.

[0081] Figure 10 The image shows a photograph and cell structure diagram of the foamable flame-retardant polypropylene material in Comparative Example 3 after foaming. Detailed Implementation

[0082] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0083] Example 1

[0084] This embodiment provides a foamable flame-retardant polypropylene material, such as... Figure 1-2 As shown, the foamable flame-retardant polypropylene material includes a flame-retardant core layer and a flame-retardant surface layer covering the surface of the flame-retardant core layer.

[0085] The flame-retardant core layer comprises the following components in parts by weight: 100 parts of ethylene-propylene random copolymer polypropylene (melting point 150℃, melt index 15g / 10min at 230℃ and 2.16kg, grade RP344P-K), 5 parts of PEG4000, 15 parts of triazine as the first charring agent, 0.75 parts of zinc oxide as the first charring aid, 15 parts of ammonium polyphosphate, 6 parts of melamine cyanurate, and 0.3 parts of PTFE; the flame-retardant surface layer comprises the following components in parts by weight: 100 parts of ethylene-propylene-butadiene random copolymer polypropylene (melting point 130℃, melt index 7g / 10min at 230℃ and 2.16kg, grade FL7632L), 3 parts of PEG4000, 3 parts of carbon black as the second charring agent, 0.5 parts of zinc oxide as the second charring aid, and 0.2 parts of PTFE.

[0086] This embodiment also provides a method for preparing the above-mentioned foamable flame-retardant polypropylene material and the flame-retardant polypropylene foam material thereof, which includes the following steps:

[0087] The flame-retardant core layer formulation is mixed evenly according to the formula, and then extruded and granulated using a twin-screw extruder to obtain flame-retardant core layer granules. The flame-retardant surface layer formulation is also mixed evenly according to the formula, and then extruded and granulated using a twin-screw extruder to obtain flame-retardant surface layer granules. The flame-retardant core layer granules are then fed into extruder I, melted and plasticized, and then introduced into co-extrusion die III. Extruder II melts and plasticizes the flame-retardant surface layer granules and then introduces them into co-extrusion die III. Through the circular co-extrusion die III, the surface molten material coats the surface of the core molten material, and the filaments are extruded through a 1.5mm diameter circular die. After traction and cooling, the fine filaments are cut by a pelletizer to obtain flame-retardant polypropylene granules with a diameter of 1mm ± 0.05mm and a length of 1.0-2.0mm. The extruded and granulated flame-retardant polypropylene granules are placed in a foaming reactor, the temperature of which is set to 70℃. Water is added to the reactor, and CO2 gas is introduced at 8MPa under stirring conditions. The temperature is then raised to 115℃, and the valve at the bottom of the reactor is opened to release pressure and gas, resulting in foamed granules. The outer layer of the granules is a macroporous foam layer, and the inner layer is a microporous foam body. The overall density of the granules is 0.033g / cm³. 3 The foaming ratio is 31.2, the outer layer thickness after foaming is 150μm, and the inner layer pore size is 1-2μm.

[0088] The above-mentioned foamed granules were steam-formed at a pressure of 1.2 bar. The tensile strength of the granule sheet was 1.19 MPa, the yield strength was 1.186 MPa, the limiting oxygen index was 31%, and the flame retardant rating was V-0.

[0089] Example 2

[0090] This embodiment provides a foamable flame-retardant polypropylene material, which includes a flame-retardant core layer and a flame-retardant surface layer covering the surface of the flame-retardant core layer.

[0091] The flame-retardant core layer comprises the following components in parts by weight: 100 parts of ethylene-propylene random copolymer polypropylene (melting point 150℃, melt index 15g / 10min at 230℃ and 2.16kg, grade RP344P-K), 5 parts of PEG4000, 20 parts of triazine as the first charring agent, 1.25 parts of zinc oxide as the first charring aid, 15 parts of ammonium polyphosphate, 5 parts of melamine cyanurate, and 0.4 parts of PTFE; the flame-retardant surface layer comprises the following components in parts by weight: 100 parts of ethylene-propylene-butadiene random copolymer polypropylene (melting point 130℃, melt index 7g / 10min at 230℃ and 2.16kg, grade FL7632L), 3 parts of PEG4000, 5 parts of triazine as the second charring agent, 0.5 parts of zinc oxide as the second charring aid, and 0.25 parts of PTFE.

[0092] This embodiment also provides a method for preparing the above-mentioned foamable flame-retardant polypropylene material and the flame-retardant polypropylene foam material thereof, which includes the following steps:

[0093] The flame-retardant core layer formulation is mixed evenly according to the formula, and then extruded and granulated using a twin-screw extruder to obtain flame-retardant core layer granules. The flame-retardant surface layer formulation is also mixed evenly according to the formula, and then extruded and granulated using a twin-screw extruder to obtain flame-retardant surface layer granules. The flame-retardant core layer granules are then fed into extruder I, melted and plasticized, and then introduced into co-extrusion die III. Extruder II melts and plasticizes the flame-retardant surface layer granules and then introduces them into co-extrusion die III. Through the circular co-extrusion die III, the molten surface material coats the surface of the molten core layer material. The filaments are extruded through a 1.5mm diameter circular die, and after traction and cooling, the filaments are cut by a pelletizer to obtain flame-retardant polypropylene granules with a diameter of 1mm ± 0.05mm and a length of 1.0-2.0mm. The extruded and granulated flame-retardant polypropylene granules are placed in a foaming reactor, the temperature of which is set to 80℃. Water is added to the reactor, and CO2 gas is introduced at 8MPa under stirring conditions. The temperature is then raised to 116℃, and the pressure is released by opening the valve at the bottom of the reactor to obtain foamed granules. Figure 3-4 As shown, the outer layer of the particles is a macroporous foam layer, and the inner layer is a microporous foam body. The overall density of the particles is 0.029 g / cm³. 3 The foaming ratio is 36.27, the outer layer thickness after foaming is 150μm, and the inner layer cell size is 1-2μm.

[0094] The above-mentioned foamed granules were steam-formed at a pressure of 1.2 bar. The tensile strength of the granule plate was 1.05 MPa, the yield strength was 1.049 MPa, the limiting oxygen index was 30%, and the flame retardant rating was V-0.

[0095] Example 3

[0096] The difference between this embodiment and Embodiment 2 is that a spherical mold is used in the steam forming process to obtain the desired result. Figure 5 The flame-retardant polypropylene foam balls shown are otherwise identical to those in Example 2.

[0097] Example 4

[0098] This embodiment provides a foamable flame-retardant polypropylene sheet, which includes a flame-retardant core layer and a flame-retardant surface layer covering the surface of the flame-retardant core layer.

[0099] The flame-retardant core layer comprises the following components in parts by weight: 100 parts of ethylene-propylene random copolymer polypropylene (melting point 150℃, melt index 15g / 10min at 230℃ and 2.16kg, grade RP344P-K), 5 parts of PEG4000, 22 parts of triazine (first charring agent), 1.25 parts of zinc oxide (first charring aid), 15 parts of ammonium polyphosphate, 5 parts of melamine cyanurate, and 0.4 parts of PTFE; the flame-retardant surface layer comprises the following components in parts by weight: 100 parts of ethylene-propylene-butadiene random copolymer polypropylene (melting point 130℃, melt index 7g / 10min at 230℃ and 2.16kg, grade FL7632L), 3 parts of PEG4000, 5 parts of triazine (second charring agent), 0.5 parts of zinc oxide (second charring aid), and 0.25 parts of PTFE.

[0100] This embodiment also provides a method for preparing the above-mentioned foamable flame-retardant polypropylene sheet and the flame-retardant foamed polypropylene sheet material, which includes the following steps:

[0101] The flame-retardant core layer formulation is mixed according to the formula, and then extruded and granulated using a twin-screw extruder to obtain flame-retardant core layer granules. The flame-retardant surface layer formulation is also mixed according to the formula and extruded and granulated using a twin-screw extruder to obtain flame-retardant surface layer granules. These flame-retardant core layer granules are then fed into extruder I, melted and plasticized, and then introduced into co-extrusion die III. Extruder II melts and plasticizes the flame-retardant surface layer granules and then introduces them into co-extrusion die III. Through the circular co-extrusion die III, the surface melt material coats the surface of the core melt material. The material exits through a square die, and after traction and cooling, the sheet is cut into pieces to obtain flame-retardant polypropylene sheets with dimensions of 15cm × 20cm × 1.0cm (length × width × height). The sheets are then placed in a mold in a flatbed foaming equipment, with the mold temperature set to 138℃. CO2 gas is introduced at 20MPa and saturated for 2 hours. Afterward, the valve is quickly opened to release pressure and gas, resulting in foamed sheets. Figure 6-7 As shown, the density of the board is 0.046 g / cm³. 3 It has a foaming ratio of 22.8, a core layer cell size of 200μm, a limiting oxygen index of 31%, and a flame retardant rating of V-0.

[0102] Example 5

[0103] This embodiment provides a method such as Figure 8 The foamable flame-retardant polypropylene multilayer composite board material shown is shown.

[0104] The flame-retardant core layer of the first foamable flame-retardant polypropylene sheet comprises the following components in parts by weight: 100 parts of ethylene-propylene random copolymer polypropylene (melting point 150℃, melt index 15g / 10min at 230℃ and 2.16kg, grade RP344P-K), 5 parts of PEG4000, 15 parts of triazine (first charring agent), 5 parts of carbon black (first charring agent), 1.25 parts of zinc oxide (first charring aid), 15 parts of ammonium polyphosphate, 5 parts of melamine cyanurate, and 0.4 parts of PTFE; the flame-retardant surface layer comprises the following components in parts by weight: 100 parts of ternary random copolymer polypropylene (melting point 130℃, melt index 7g / 10min at 230℃ and 2.16kg, grade FL7632L), 3 parts of PEG4000, 5 parts of triazine (second charring agent), 0.5 parts of zinc oxide (second charring aid), and PTFE. 0.25 copies.

[0105] The flame-retardant core layer of the second foamable flame-retardant polypropylene sheet comprises the following components in parts by weight: 100 parts of ethylene-propylene random copolymer polypropylene (melting point 150℃, melt index 15g / 10min at 230℃ and 2.16kg, grade RP344P-K), 5 parts of PEG4000, 13 parts of triazine (first charring agent), 2 parts of carbon black (first charring agent), 1.25 parts of zinc oxide (first charring aid), 15 parts of ammonium polyphosphate, 5 parts of melamine cyanurate, and 0.4 parts of PTFE; the flame-retardant surface layer comprises the following components in parts by weight: 100 parts of ethylene-propylene-butadiene random copolymer polypropylene (melting point 130℃, melt index 7g / 10min at 230℃ and 2.16kg, grade FL7632L), PEG4000, and triazine (first charring agent), 2 parts of carbon black (first charring agent), 1.25 parts of zinc oxide (first charring aid), 15 parts of ammonium polyphosphate, 5 parts of melamine cyanurate, and 0.4 parts of PTFE; 3 parts, 5 parts of triazine as the second charring agent, 0.5 parts of zinc oxide as the second charring aid, and 0.25 parts of PTFE.

[0106] This embodiment also provides a method for preparing the above-mentioned foamable flame-retardant polypropylene multilayer composite board material and the flame-retardant polypropylene multilayer foamed composite board material, which includes the following steps:

[0107] The flame-retardant core layer formulation is mixed according to the formula, and then extruded and granulated using a twin-screw extruder to obtain flame-retardant core layer granules. The flame-retardant surface layer formulation is also mixed according to the formula and extruded and granulated using a twin-screw extruder to obtain flame-retardant surface layer granules. These flame-retardant core layer granules are then fed into extruder I, melted and plasticized, and then introduced into co-extrusion die III. Extruder II melts and plasticizes the flame-retardant surface layer granules and then introduces them into co-extrusion die III. Through the circular co-extrusion die III, the surface melt material coats the surface of the core melt material. The material exits through a square die, and after traction and cooling, the sheet is cut into pieces to obtain flame-retardant polypropylene sheets with dimensions of 20cm × 30cm × 1.0cm (length × width × height). The sheets are then placed in a mold in a flat-plate foaming equipment. The mold temperature is set to 138℃, and CO2 gas is introduced at 20MPa for 2 hours until saturation. Afterward, the valve is quickly opened to release pressure and gas, yielding the first foamed sheet with a density of 0.048g / cm³. 3 The foaming ratio is 21.85.

[0108] The flame-retardant core layer formulation is mixed according to the formula, and then extruded and granulated using a twin-screw extruder to obtain flame-retardant core layer granules. The flame-retardant surface layer formulation is also mixed according to the formula and extruded and granulated using a twin-screw extruder to obtain flame-retardant surface layer granules. These flame-retardant core layer granules are then fed into extruder I, melted and plasticized, and then introduced into co-extrusion die III. Extruder II melts and plasticizes the flame-retardant surface layer granules and then introduces them into co-extrusion die III. Through the circular co-extrusion die III, the surface melt material coats the surface of the core melt material. The material exits through a square die, and after traction and cooling, the sheet is cut into pieces to obtain flame-retardant polypropylene sheets with dimensions of 20cm × 30cm × 1.0cm (length × width × height). These sheets are then placed in a mold in a flat-plate foaming equipment. The mold temperature is set to 138℃, and CO2 gas is introduced at 23MPa for 2 hours until saturation. Afterward, the valve is quickly opened to release pressure and gas, resulting in a second foamed sheet with a density of 0.036g / cm³. 3 The foaming ratio is 29.13.

[0109] Two layers of second foamed board and three layers of first foamed board are alternately stacked and placed into a molding machine to obtain flame-retardant polypropylene multilayer composite foamed material.

[0110] Example 6

[0111] The difference between this embodiment and Embodiment 1 is that the melting point of the ethylene-propylene random copolymer polypropylene in the flame-retardant core layer is 140°C, while all other aspects are the same as in Embodiment 1.

[0112] Example 7

[0113] The difference between this embodiment and Embodiment 1 is that the melting point of the ethylene-propylene random copolymer polypropylene in the flame-retardant core layer is 155°C, while all other aspects are the same as in Embodiment 1.

[0114] Example 8

[0115] The difference between this embodiment and Embodiment 1 is that the melt index of the random copolymer polypropylene in the flame-retardant core layer is 5 g / 10 min, while all other aspects are the same as in Embodiment 1.

[0116] Example 9

[0117] The difference between this embodiment and Embodiment 1 is that the melt index of the random copolymer polypropylene in the flame-retardant core layer is 20 g / 10 min, while all other aspects are the same as in Embodiment 1.

[0118] Example 10

[0119] The difference between this embodiment and Embodiment 1 is that the melting point of the ethylene-propylene-butyl random copolymer polypropylene in the flame-retardant surface layer is 120°C, while all other aspects are the same as in Embodiment 1.

[0120] Example 11

[0121] The difference between this embodiment and Embodiment 1 is that the melting point of the ethylene-propylene-butadiene random copolymer polypropylene in the flame-retardant surface layer is 135°C, while all other aspects are the same as in Embodiment 1.

[0122] Example 12

[0123] The difference between this embodiment and Example 1 is that the melt index of the random copolymer polypropylene (EPR) in the flame-retardant surface layer is 5 g / 10 min, while all other aspects are the same as in Example 1.

[0124] Example 13

[0125] The difference between this embodiment and Example 1 is that the melt index of the random copolymer polypropylene (EPR) in the flame-retardant surface layer is 10 g / 10 min, while all other aspects are the same as in Example 1.

[0126] Example 14

[0127] The difference between this embodiment and Embodiment 1 is that the melt index of the ethylene-propylene-butadiene random copolymer polypropylene in the flame-retardant surface layer is 2 g / 10 min, and the melt index of the ethylene-propylene-butadiene random copolymer polypropylene in the flame-retardant core layer is 2 g / 10 min. All other aspects are the same as in Embodiment 1.

[0128] Example 15

[0129] The difference between this embodiment and Embodiment 1 is that the melt index of the ethylene-propylene-butadiene random copolymer polypropylene in the flame-retardant surface layer is 15 g / 10 min, and the melt index of the ethylene-propylene-butadiene random copolymer polypropylene in the flame-retardant core layer is 25 g / 10 min. All other aspects are the same as in Embodiment 1.

[0130] Comparative Example 1

[0131] This comparative example provides a pure polypropylene foam material, prepared by the following method:

[0132] 100 parts of pure polypropylene material were placed in a foaming reactor, and the temperature inside the reactor was set to 70℃. Water was added to the reactor, and CO2 gas was introduced at 10MPa under stirring. The temperature was then raised to 115℃, and the pressure was released by opening the valve at the bottom of the reactor to obtain foamed granules with a particle density of 0.035g / cm³. 3 The foaming ratio is 25.71. These granules are steam-molded at a pressure of 1.5 bar, with a limiting oxygen index of 17%. Figure 9 As shown, its flame retardant rating is V-2.

[0133] Comparative Example 2

[0134] The difference between this comparative example and Example 2 is that only the flame-retardant core layer particles were placed in the foaming reactor, the temperature in the reactor was set to 80°C, water was added to the reactor, CO2 gas was introduced at 8MPa under stirring, and then the temperature was raised to 116°C. The valve at the bottom of the reactor was opened to release pressure and gas, resulting in foamed particles with a particle density of 0.036 g / cm³. 3 The foaming ratio was 31.87. The particles were steam molded at a pressure of 1.8 bar, with a limiting oxygen index of 30% and a flame retardant rating of V-0. All other parameters were the same as in Example 2.

[0135] Comparative Example 3

[0136] This comparative example provides a commercially available flame-retardant polypropylene foam material, prepared by the following method:

[0137] Commercially available flame-retardant PP granules (purchased from Wancom Chemical Co., Ltd., brand name Wancom PPM4506R) were placed in a foaming reactor. The reactor temperature was set to 70℃. Water and PEG4000 surfactant were added to the reactor. CO2 gas was introduced at 7MPa under stirring. Then, the temperature was raised to 115℃, and the pressure was released by opening the valve at the bottom of the reactor to obtain foamed granules with a density of 0.291 g / cm³. 3 ,like Figure 10 As shown, it has a flat, wrinkled appearance with ruptured cells, a foaming ratio of 3.43 times, a limiting oxygen index of 29%, and a flame retardant rating of V-0.

[0138] Comparative Example 4

[0139] The difference between this comparative example and Example 1 is that the content of ammonium polyphosphate in the flame-retardant core layer is 9 parts, the content of melamine cyanurate is 3 parts, and the rest are the same as in Example 1.

[0140] Comparative Example 5

[0141] The difference between this comparative example and Example 1 is that the content of carbon black as a charring agent in the flame-retardant surface layer is 1 part, and the content of zinc oxide as a second charring agent is 0.2 parts, while the rest are the same as in Example 1.

[0142] Comparative Example 6

[0143] The difference between this comparative example and Example 1 is that the ethylene-propylene random copolymer polypropylene in the flame-retardant core layer is replaced with an equal weight proportion of ternary random copolymer polypropylene; all other aspects are the same as in Example 1.

[0144] Comparative Example 7

[0145] The difference between this comparative example and Example 1 is that the ternary random copolymer polypropylene in the flame-retardant surface layer is replaced with an equal weight of ethylene propylene random copolymer polypropylene; all other aspects are the same as in Example 1.

[0146] Test conditions

[0147] The flame-retardant polypropylene foam materials provided in Examples 1 to 15 and Comparative Examples 1 to 7 were tested using the following methods:

[0148] (1) Density test: The density of the foamed sample was determined according to the standard GB / T 1033-2008.

[0149] (2) Limiting oxygen index test: The limiting oxygen index of the sample was measured using a critical oxygen index analyzer in accordance with the standard of GB / T 2406-2019.

[0150] (3) Mechanical property testing: The tensile strength and yield strength of the sample were measured according to the standard GB / T 4744-1997;

[0151] (4) Scanning electron microscopy test: The morphology of the bubbles was observed using a JSM-7500F electron microscope;

[0152] (5) Flame retardant performance test: The vertical burning performance of the sample is tested according to the UL-94 standard.

[0153] The test results are shown in Table 1:

[0154] Table 1

[0155]

[0156]

[0157] As can be seen from Table 1, the flame-retardant polypropylene foam materials prepared in Examples 1-13 have excellent low density, flame-retardant properties and good mechanical properties, and can be prepared with excellent comprehensive performance under low molding pressure.

[0158] Compared with Example 1, the melt index of the copolymer polypropylene resin in the flame-retardant core layer and flame-retardant surface layer in Example 14 is lower, resulting in poorer fluidity and poorer dispersion of the flame retardant. This leads to increased molding energy consumption and poorer flame retardant performance of the material after foaming. In Example 15, the melt index of the polypropylene resin in the flame-retardant core layer and flame-retardant surface layer is higher, and the molecular weight is lower. Therefore, it is prone to dripping during the flame retardant test, resulting in poor flame retardant performance of the material.

[0159] Compared to Example 1, Comparative Example 1 used ordinary polypropylene resin without a flame retardant system, resulting in a foam material requiring high steam molding pressure and exhibiting poor flame retardant performance. Comparative Example 2 used only flame-retardant core layer resin, leading to high steam molding pressure and low tensile strength in the prepared foam material. Comparative Example 3 used commercially available flame-retardant polypropylene, resulting in a foam material with high density and high steam molding pressure, failing to achieve lightweight and low energy consumption. Comparative Example 4 reduced the flame retardant content in the core layer, preventing the prepared foam material from achieving V-0 flame retardant performance. Comparative Example 5 reduced the charring agent content in the surface layer, preventing the prepared foam material from achieving V-0 flame retardant performance. Comparative Example 6 replaced the ethylene-propylene random copolymer polypropylene in the flame-retardant core layer with an equal weight proportion of ternary random copolymer polypropylene, resulting in a foam material with lower mechanical properties. Comparative Example 7 replaced the ternary random copolymer polypropylene in the flame-retardant surface layer with an equal weight proportion of ethylene-propylene random copolymer polypropylene, resulting in high steam molding pressure and failing to achieve low energy consumption.

[0160] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A foamable, flame-retardant polypropylene material, characterized in that, The foamable flame-retardant polypropylene material comprises a flame-retardant core layer and a flame-retardant skin layer covering the surface of the flame-retardant core layer. The flame-retardant core layer comprises the following components in parts by weight: binary random copolymerized polypropylene 100-120 parts, first char-forming agent 8-25 parts, first char-forming aid 0.75-2 parts, and halogen-free flame retardant 13-30 parts. The flame-retardant skin layer comprises the following components in parts by weight: ternary random copolymerized polypropylene 100-120 parts, second char-forming agent 3-5 parts, and second char-forming aid 0.2-0.5 parts. The binary random copolymerized polypropylene has a melt index of 5-20 g / 10 min at 230 ℃ and 2.16 kg. The ternary random copolymerized polypropylene has a melt index of 5-10 g / 10 min at 230 ℃ and 2.16 kg.

2. Foamable flame-retardant polypropylene material according to claim 1, characterized in that The flame-retardant core layer comprises the following components in parts by weight: binary random copolymerized polypropylene 100 parts, first char-forming agent 8-25 parts, first char-forming aid 0.75-2 parts, and halogen-free flame retardant 13-30 parts.

3. The foamable, flame retardant polypropylene material of claim 1, wherein, The flame-retardant skin layer comprises the following components in parts by weight: ternary random copolymerized polypropylene 100 parts, second char-forming agent 3-5 parts, and second char-forming aid 0.2-0.5 parts.

4. The foamable, flame retardant polypropylene material of claim 1, wherein, The binary random copolymerized polypropylene comprises ethylene-propylene random copolymerized polypropylene and / or propylene-butylene random copolymerized polypropylene.

5. Foamable flame-retardant polypropylene material according to claim 4, characterized in that The binary random copolymerized polypropylene is ethylene-propylene random copolymerized polypropylene.

6. The foamable, flame retardant polypropylene material of claim 1, wherein, The binary random copolymerized polypropylene has a melting point of 140-155 ℃.

7. Foamable flame-retardant polypropylene material according to claim 6, characterized in that The binary random copolymerized polypropylene has a melting point of 140-150 ℃.

8. The foamable, flame retardant polypropylene material of claim 1, wherein, The binary random copolymerized polypropylene has a melt index of 5-15 g / 10 min at 230 ℃ and 2.16 kg.

9. The foamable, flame retardant polypropylene material of claim 1, wherein, The ternary random copolymerized polypropylene comprises ethylene-propylene-butylene random copolymerized polypropylene and / or ethylene-propylene-octene random copolymerized polypropylene.

10. Foamable flame-retardant polypropylene material according to claim 9, characterized in that The ternary random copolymerized polypropylene is ethylene-propylene-butylene random copolymerized polypropylene.

11. The foamable, flame retardant polypropylene material of claim 1, wherein, The ternary random copolymerized polypropylene has a melting point of 120-135 ℃.

12. Foamable flame-retardant polypropylene material according to claim 11, characterized in that The ternary random copolymerized polypropylene has a melting point of 120-130 ℃.

13. The foamable, flame retardant polypropylene material of claim 1, wherein, The ternary random copolymerized polypropylene has a melt index of 5-8 g / 10 min at 230 ℃ and 2.16 kg.

14. The foamable, flame retardant polypropylene material of claim 1, wherein, The first char-forming agent and the second char-forming agent each independently comprise triazine and / or carbon black.

15. The foamable, flame retardant polypropylene material of claim 1, wherein, The first char-forming aid and the second char-forming aid each independently comprise any one or a combination of at least two of magnesium oxide, silicon dioxide, or zinc oxide.

16. The foamable, flame retardant polypropylene material of claim 1, wherein, The halogen-free flame retardant comprises a combination of phosphorus-based flame retardant and nitrogen-based flame retardant.

17. The foamable, flame retardant polypropylene material of claim 16, wherein, The phosphorus-based flame retardant comprises ammonium polyphosphate and / or melamine polyphosphate.

18. The foamable, flame retardant polypropylene material of claim 17, wherein, The phosphorus-based flame retardant is ammonium polyphosphate.

19. The foamable, flame retardant polypropylene material of claim 16, wherein, The phosphorus-based flame retardant has a weight fraction of 10-20 parts by weight.

20. The foamable, flame retardant polypropylene material of claim 16, wherein, The nitrogen-based flame retardant comprises melamine cyanurate and / or dicyandiamide.

21. The foamable, flame retardant polypropylene material of claim 20, wherein, The nitrogen-based flame retardant is melamine cyanurate.

22. The foamable, flame retardant polypropylene material of claim 16, wherein, The nitrogen-based flame retardant has a weight fraction of 3-10 parts by weight.

23. The foamable, flame retardant polypropylene material of claim 1, wherein, The flame-retardant core layer and the flame-retardant skin layer each independently further comprise a first aid.

24. The foamable, flame retardant polypropylene material of claim 23, wherein, The first aid comprises a dispersant and / or an anti-dripping agent.

25. The foamable, flame retardant polypropylene material of claim 24, wherein, The dispersant comprises PEG4000.

26. The foamable, flame retardant polypropylene material of claim 24, wherein, The anti-dripping agent includes any one or a combination of at least two of polytetrafluoroethylene, polyvinylidene fluoride or polytrifluorochloroethylene.

27. The foamable, flame retardant polypropylene material of claim 23, wherein, The weight fraction of the first auxiliary agent is 3.2-5.5 parts by weight.

28. The foamable, flame retardant polypropylene material of claim 24, wherein, The weight fraction of the dispersing agent is 3-5 parts by weight.

29. The foamable, flame retardant polypropylene material of claim 24, wherein, The weight fraction of the anti-dripping agent is 0.2-0.5 parts by weight.

30. A method of making a foamable flame retardant polypropylene material according to any one of claims 1-29, characterized in that, The method includes the following steps: The binary random copolymerized polypropylene, the first char forming agent, the first auxiliary char forming agent and the halogen-free flame retardant are mixed according to the formula amount, and the flame retardant core layer particles are obtained after one-time extrusion blending; The ternary random copolymerized polypropylene, the second char forming agent and the second auxiliary char forming agent are mixed according to the formula amount, and the flame retardant surface layer particles are obtained after two-time extrusion blending; The flame retardant core layer particles and the flame retardant surface layer particles are respectively melted and plasticized, and then the flame retardant polypropylene material is obtained after co-extrusion.

31. The method of claim 30, wherein, The flow channel structure shape of the equipment die head in the co-extrusion includes a circular shape or a rectangular shape.

32. The method of claim 31, wherein, The wire diameter of the circular flow channel structure is 1-1.5 mm.

33. A flame retarded polypropylene foam material, characterized in that, The flame retardant polypropylene foam material is foamed from the flame retardant polypropylene material according to any one of claims 1-29.

34. A method of making the flame retarded polypropylene foam according to claim 33, characterized in that, The method includes the following steps: The flame retardant polypropylene foam material is foamed from the flame retardant polypropylene material according to any one of claims 1-29.

35. The method of claim 34, wherein, The foaming method includes supercritical fluid foaming.

36. The method of claim 35, wherein, The supercritical fluid foaming fluid includes carbon dioxide.

37. The method of claim 35, wherein, The supercritical fluid foaming temperature is 115-145℃, and the pressure is 7-30 Mpa.

38. The method of claim 35, wherein, The supercritical fluid foaming further includes a water vapor molding forming treatment.

39. A fire-retardant foam article, characterized by, The flame retardant foam product includes the flame retardant polypropylene foam material according to claim 33.

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