A foamable polypropylene material, its preparation method and application

Abstract

This invention discloses a foamable polypropylene material, its preparation method, and its application, belonging to the field of polymer materials technology. By introducing two expandable microspheres with different foaming property parameters into the polypropylene resin matrix, the dimensional stability of the product is improved. At the same time, the introduction of low-melting-point polypropylene resin and hyperbranched polyester into the polypropylene resin matrix achieves high dispersibility and compatibility between components. The product does not exhibit shrinkage marks, has low gloss, and moderate surface roughness, making it more suitable for the use of decorative parts in automotive interiors.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a foamable polypropylene material, its preparation method, and its application. Background Technology

[0002] In the automotive manufacturing industry, the process of preparing automotive decorative parts using polypropylene materials has become relatively mature. However, due to the high crystallinity of polypropylene resin itself, the dimensional stability is not high when designed into thicker parts, resulting in large shrinkage and visible shrinkage marks. While some traditional chemically foamed polypropylene products have improved dimensional stability, the large number of pores that appear inside the product after foaming can lead to uneven surfaces and shrinkage marks. In addition, chemical foaming requires specific equipment for production, which is quite cumbersome.

[0003] On the other hand, existing polypropylene automotive trim parts generally have a high gloss level, which can easily cause light refraction in the driver's cabin, affecting the driver's driving experience. Furthermore, the smooth surface of these products has a low coefficient of friction, making it easy for objects placed on them to slip during driving, resulting in a poor driving experience. Therefore, these trim parts often require the addition of secondary components such as blankets or anti-slip films, but this in turn affects the aesthetics of the car's interior. Summary of the Invention

[0004] Based on the shortcomings of existing technologies, the purpose of this invention is to provide a foamable polypropylene material. By introducing two expandable microspheres with different foaming property parameters into the polypropylene resin matrix, the dimensional stability of the product is improved. At the same time, the introduction of low-melting-point polypropylene resin and hyperbranched polyester into the polypropylene resin matrix works together to achieve high dispersibility and compatibility between components. The surface of this product will not exhibit shrinkage marks, has low gloss, and moderate surface roughness, making it more suitable for the use of interior decorative parts in automobiles.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A foamable polypropylene material comprising the following components in parts by weight:

[0007] 100 parts of polypropylene composition, 0.1 to 8 parts of expandable microspheres and / or expandable masterbatch;

[0008] The polypropylene composition includes 90-97 parts of polypropylene resin, 2-10 parts of low-melting-point polypropylene, and 0.1-0.5 parts of hyperbranched polyester.

[0009] The expandable microspheres include expandable microsphere A and expandable microsphere B; the initial foaming temperature of expandable microsphere A is ≥190℃;

[0010] The initial foaming temperature of the expandable microspheres B is ≥125℃, and the peak foaming temperature is 195~205℃.

[0011] The initial foaming temperature of the expandable microsphere B is less than that of the expandable microsphere A.

[0012] The low-melting-point polypropylene has a melting point ≤90℃.

[0013] In some embodiments, the initial foaming temperature and peak foaming temperature of the expandable microspheres A and / or B are determined with reference to the method described in paragraph

[0047] of the specification CN108912384B.

[0014] Preferably, the expandable microspheres comprise 0.5 to 5 parts of expandable microsphere A and 0.1 to 3 parts of expandable microsphere B;

[0015] Preferably, the expandable microspheres include a shell and a core, the shell comprising a thermoplastic polymer and the core comprising an expandable material.

[0016] Preferably, the initial foaming temperature of the expandable microsphere A is 200-250°C, and the peak foaming temperature is 230-265°C; the initial foaming temperature of the expandable microsphere B is 135-145°C.

[0017] To address the challenges of maintaining dimensional stability or achieving high flatness after foaming in large, thick automotive interior parts made from existing polypropylene materials, which leads to shrinkage marks, high gloss, low roughness, and a poor user experience, this invention introduces two types of expandable microspheres with gradient distributions of foaming initiation and peak temperatures into a polypropylene resin matrix. These two types of expandable microspheres achieve different foaming ratios and foaming effects within the conventional injection molding temperature range of 200–240°C during the same heating process. Expandable microsphere B, with its lower foaming temperature and peak temperature, foams... The larger size of the expandable microspheres B provides a certain degree of roughness and resistance to deformation to the product surface. However, due to the gaps between the expandable microspheres B, the surface is relatively rough after foaming, with obvious unevenness and poor flatness. Therefore, it is necessary to use expandable microspheres A, which are smaller in size after foaming, to fill the gaps between the expandable microspheres B while achieving sufficient dimensional stability, thereby improving the surface flatness of the product and avoiding shrinkage defects after foaming. On the other hand, if expandable microspheres A are used alone, the product will also show shrinkage due to insufficient dimensional stability.

[0018] Meanwhile, to ensure the dispersibility and compatibility of the two expandable microspheres in the matrix resin, the product further incorporates specific low-melting-point polypropylene and hyperbranched polyester as compounding components to form a polypropylene composition. This avoids the inability to achieve the expected dimensional stability and surface roughness due to compatibility and dispersion issues of the expandable microspheres. Furthermore, these two components can be dispersed on the surface during product injection molding, effectively controlling the surface gloss and roughness to meet the requirements of automotive interior parts. However, if the low-melting-point polypropylene or hyperbranched polyester is replaced with dispersants or compatibilizers used in conventional polypropylene products, or other common hyperbranched polymer products such as hyperbranched polyamides, the same appearance and performance may not be achieved, and the product surface may become excessively rough, resulting in a poorer user experience.

[0019] Preferably, the thermoplastic polymer is a polymer obtained by reacting at least one of nitrile monomers, acrylate monomers, amide monomers, and carboxyl-containing reactive monomers with polymerizable double bonds.

[0020] Preferably, the nitrile monomers include at least one of acrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile; the acrylate monomers include at least one of methyl acrylate, ethyl acrylate, butyl acrylate, dicyclopentenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobornyl methacrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl acrylate; the carboxyl-containing reactive monomers with polymerizable double bonds include at least one of unsaturated monocarboxylic acids and unsaturated dicarboxylic acids; and the amide monomers include at least one of acrylamide, methacrylamide, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, and N,N-dimethylacrylamide.

[0021] More preferably, the unsaturated monocarboxylic acid includes at least one of acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, and α-methylcinnamic acid; and the unsaturated dicarboxylic acid includes at least one of maleic acid, itaconic acid, fumaric acid, and citraconic acid.

[0022] Preferably, the mass ratio of the nitrile monomer, acrylate monomer, amide monomer, and carboxyl-containing reactive monomer with polymerizable double bonds is (50-100):(10-100):(1-50):(1-50).

[0023] Preferably, the expandable substance includes at least one of isobutane, isooctane, pentane, and isopentane.

[0024] More preferably, the mass content of the expandable material in the expandable microspheres is 10-45 wt%.

[0025] More preferably, the expandable microspheres can be commercially available products or can be prepared by means of methods described in, for example, CN108912384B and CN113731310B. Those skilled in the art can choose according to actual needs.

[0026] Preferably, the expandable microsphere masterbatch includes expandable microspheres A, expandable microspheres B, and a matrix resin, wherein the matrix resin includes at least one of polypropylene resin and polyethylene resin, and the total mass content of expandable microspheres A and expandable microspheres B in the expandable microspheres is 40-60%.

[0027] More preferably, the matrix resin is polypropylene resin.

[0028] More preferably, the expandable microspheres can be added in the form of masterbatch. Specifically, the expandable microsphere masterbatch is prepared according to the method for preparing polypropylene / expandable microsphere foaming masterbatch according to any one of claims 1 to 9, referring to Appendix CN117362893A, comprising the following steps:

[0029] Step S1: After dissolving polypropylene in a solvent, an initiator and a silane coupling agent are added to prepare grafted polypropylene;

[0030] Step S2: Add expandable microspheres, nucleating agent, water-producing agent, catalyst, and surfactant to the solution in step S1 above, and stir thoroughly until homogeneous;

[0031] Step S3: After the solution in step S2 is stirred, transfer the flask to water at a certain temperature for quenching and continue stirring until homogeneous. The silane self-crosslinked PP / expandable microsphere composite precipitates from the organic solution, is filtered, and then washed three times with ethanol.

[0032] Step S4: Filter and wash the insoluble matter from step S3 above, and dry it in a forced-air drying oven at 60℃~80℃ for 2-4 hours to obtain polypropylene / expandable microsphere foaming masterbatch.

[0033] Those skilled in the art can also prepare expandable microsphere masterbatches using other common masterbatch preparation methods, as long as the basic properties of the expandable microspheres in the masterbatch are not affected, and are not limited by the description in this invention.

[0034] Preferably, the average particle size of the expandable microsphere A is 7–15 μm, and the average particle size of the expandable microsphere B is 10–25 μm.

[0035] More preferably, the average particle size of the expandable microsphere A is a value within the range of one or any two of 7μm, 9μm, 10μm, 12μm, 13μm, and 15μm, and the average particle size of the expandable microsphere B is a value within the range of one or any two of 10μm, 12μm, 14μm, 15μm, 18μm, 20μm, 22μm, and 25μm.

[0036] More preferably, the average particle size of the expandable microspheres A and B is directly confirmed by a two-dimensional microscope. At a magnification of 50 to 500 times, the expandable microspheres A and B are distinguished by particle size under a microscope. Then, according to the positioning, the magnification is increased to 300 to 800 times. At a fixed magnification, at least 100 expandable microspheres A and 100 expandable microspheres B in the same plane are screened using mapping software for particle size testing, and the average value is finally calculated, which is the average particle size of the two expandable microspheres.

[0037] Preferably, the expandable microspheres A in the polypropylene composition are in the range of one or any two of the following weight values: 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, and 5 parts; and the expandable microspheres B in the polypropylene composition are in the range of one or any two of the following weight values: 0.1 parts, 0.5 parts, 0.8 parts, 1 part, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.2 parts, 2.5 parts, 2.8 parts, and 3 parts.

[0038] More preferably, the mass ratio of the expandable microsphere A to the expandable microsphere B is (1-5):1.

[0039] Through experiments conducted by the inventors, it was discovered that when the two expandable microspheres are compounded in the above ratio, they can achieve better dispersion and filling after foaming and expansion. The product has moderate surface roughness and lower gloss without shrinkage.

[0040] Preferably, the polypropylene resin has a melting point of 150–170°C and a melt flow rate of 10–35 g / 10 min at 230°C and 2.16 kg load, according to ISO 1133-2011.

[0041] More preferably, the melt flow rate of the polypropylene resin at 230°C and 2.16 kg load is one or any two of the following values: 10 g / 10 min, 12 g / 10 min, 15 g / 10 min, 18 g / 10 min, 20 g / 10 min, 25 g / 10 min, 30 g / 10 min, 32 g / 10 min, and 35 g / 10 min.

[0042] Preferably, the low-melting-point polypropylene has a melting point of 70–90°C and a melt flow rate of 300–3000 g / 10 min at 230°C and 2.16 kg load, according to ISO 1133-2011.

[0043] More preferably, the melt flow rate of the low-melting-point polypropylene at 230°C and 2.16 kg load is one or any two of the following values: 300 g / 10 min, 320 g / 10 min, 350 g / 10 min, 400 g / 10 min, 800 g / 10 min, 1000 g / 10 min, 1200 g / 10 min, 1500 g / 10 min, 1800 g / 10 min, 2000 g / 10 min, 2200 g / 10 min, 2400 g / 10 min, 2600 g / 10 min, 2800 g / 10 min, and 3000 g / 10 min.

[0044] More preferably, the melt flow rate of the low-melting-point polypropylene at 230°C and 2.16 kg load is 340–2800 g / 10 min.

[0045] Preferably, the melting points of the polypropylene resin and the low-melting-point polypropylene are tested using the differential scanning calorimeter (DSC) method according to GB / T 19466.3—2004 Plastics Differential Scanning Calorimetry (DSC) Part 3. The heating rate is typically 10℃ / min, the cooling rate is 10℃ / min, the temperature range is 30~250℃, the atmosphere is N2, the flow rate is 50mL / min, and the data from the second heating is taken.

[0046] The purpose of using low-melting-point polypropylene is not only to improve the dispersibility of expandable microspheres in polypropylene resin, thereby avoiding surface unevenness in the product, but also to enhance the compatibility between the overall resin and the expandable microspheres. Furthermore, this component will be distributed on the product surface after injection molding, effectively controlling the surface gloss and roughness of the product. Without this component, the product will not only have poor surface performance, but may even have surface unevenness issues, resulting in shrinkage marks.

[0047] More preferably, in the foamable polypropylene material, the total mass content of polypropylene resin and low-melting-point polypropylene is ≥80wt%.

[0048] Preferably, the hyperbranched polyester includes at least one of terminal carboxyl hyperbranched polyester and terminal hydroxyl hyperbranched polyester, with a number average molecular weight of 800-6500 g / mol.

[0049] Preferably, the number-average molecular weight of the hyperbranched polyester is one or any two of the following values: 800 g / mol, 1200 g / mol, 1500 g / mol, 2000 g / mol, 2500 g / mol, 3000 g / mol, 3500 g / mol, 4000 g / mol, 4500 g / mol, 5000 g / mol, 5500 g / mol, 6000 g / mol, and 6500 g / mol.

[0050] Preferably, the hyperbranched polyester has 5 to 25 molar carboxyl groups and / or hydroxyl groups per unit molar.

[0051] More preferably, the number of carboxyl groups and / or hydroxyl groups per molar of the hyperbranched polyester is a range of one or both of the following: 5, 8, 10, 12, 15, 18, 20, 22, 25.

[0052] More preferably, the hyperbranched polyester is a hydroxyl-terminated hyperbranched polyester.

[0053] Hyperbranched polyesters with different functional groups have a certain impact on the foaming effect of expandable microspheres, and also have a certain impact on the compatibility of the foamed expandable microspheres in the resin system. When the hyperbranched polyester is preferably of the above-mentioned type, the overall performance of the product is better.

[0054] Preferably, the polypropylene composition further includes 0.1 to 0.3 parts of coupling agent.

[0055] More preferably, the coupling agent includes at least one of vinyl silane coupling agents, amino silane coupling agents, methacryloxy silane coupling agents, titanate coupling agents, and aluminum-titanium composite silane coupling agents.

[0056] The expandable polypropylene material of this invention uses expandable microspheres as solid fillers, which can effectively improve the dimensional stability of the product. Based on this, those skilled in the art can further add a certain amount of coupling agent to the polypropylene composition to improve the relative stability of the expandable microspheres and further suppress the shrinkage and creep of the polypropylene resin.

[0057] Preferably, in addition to the coupling agent described above, the polypropylene composition may also include 0.1 to 1 part of other processing aids, including but not limited to at least one of antioxidants, antistatic agents, and release agents.

[0058] Based on the needs of the actual product, those skilled in the art may appropriately introduce some components commonly used in polypropylene products without affecting the product performance, such as antioxidants to improve the product's conventional oxidation resistance, and release agents to improve the product's release performance, etc.

[0059] More preferably, the polypropylene composition includes 0.1 to 0.2 parts of antioxidant.

[0060] More preferably, the antioxidant includes at least one of hindered phenolic antioxidants, phosphite antioxidants, and hindered amine antioxidants.

[0061] More preferably, the antioxidant is a mixture of hindered phenolic antioxidants and phosphite antioxidants, with a mass ratio of 1:(0.8 to 1.2).

[0062] Another object of the present invention is to provide a method for preparing the foamable polypropylene material, comprising the following steps:

[0063] The raw material components of the polypropylene composition are added to a screw extruder for melt extrusion granulation to obtain the polypropylene composition. Subsequently, the polypropylene composition is mixed with expandable microspheres and / or expandable microsphere masterbatch to obtain the foamable polypropylene material.

[0064] It should be noted that in the technical solution of the present invention, the polypropylene composition is mixed with expandable microspheres and / or expandable microsphere masterbatch by physical mixing, such as mixing with a mixer, mixing with a homogenizer, etc., as long as the mixing effect is expected under normal conditions, and the specific mixing method is not limited.

[0065] Preferably, the heating temperature of the screw extruder is 100-220°C, and the screw speed is 350-450 rpm.

[0066] The preparation method of the foamable polypropylene mixture described in this invention is simple, requires little equipment, and can achieve industrial-scale production.

[0067] Another object of the present invention is to provide the application of the foamable polypropylene material in the preparation of automotive interior parts.

[0068] More preferably, the automotive interior components include an instrument panel and a sub-instrument panel.

[0069] Another object of the present invention is to provide a polypropylene article obtained by injection molding from a material comprising the foamable polypropylene material described herein.

[0070] Preferably, the injection molding is performed using a single-screw extruder, and the temperature zones of the single-screw extruder are set as follows: feeding zone 40-60℃, zone 1 200-210℃, zone 2 200-210℃, zone 3 230-240℃, zone 4 230-240℃, and zone 5 235-240℃.

[0071] The expandable polypropylene material described in this invention is based on the synergistic combination of three key components: expandable microspheres, low-melting-point polypropylene, and hyperbranched polyester. It not only exhibits ideal dimensional stability after injection molding but also boasts a good appearance without shrinkage marks. Furthermore, it has moderate surface roughness and low gloss. Automotive interior parts made from this material not only provide a superior user experience without requiring additional accessories and without affecting the driver's normal driving, but also offer excellent aesthetics, refinement, and high overall cost-effectiveness.

[0072] It should be noted that the expandable polypropylene material described in this invention can be packaged as a single component or as multiple components, such as two-component or three-component packages. When it is packaged as multiple components, the polypropylene composition is packaged as a single component, and expandable microspheres A and B are packaged as one or two components. There are no absolute limitations on the form and order of packaging and use.

[0073] The beneficial effects of this invention are that it provides a foamable polypropylene material. By introducing two expandable microspheres with different foaming property parameters into the polypropylene resin matrix, the dimensional stability of the product is improved. At the same time, the introduction of low-melting-point polypropylene resin and hyperbranched polyester into the polypropylene matrix resin works together to achieve high dispersibility and compatibility between components. This product does not exhibit shrinkage marks, has low gloss, and moderate surface roughness, making it more suitable for the use of interior decorative parts in automobiles. Detailed Implementation

[0074] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this invention are commonly used reagents and instruments.

[0075] Examples 1-14

[0076] Examples of the foamable polypropylene material, its preparation method, and its application according to the present invention are shown in Table 2.

[0077] The method for preparing the foamable polypropylene material includes the following steps:

[0078] The raw material components of the polypropylene composition are added to the main feeding system of a screw extruder according to the formulation in Table 1 for melt extrusion granulation to obtain the polypropylene composition. During melt extrusion, the temperature zones of the screw extruder are set as follows: Zone 1 120℃, Zone 2 220℃, Zone 3 220℃, Zone 4 210℃, Zone 5 210℃, Zone 6 210℃, Zone 7 210℃, Zone 8 210℃, Zone 9 210℃, Zone 10 210℃. The screw speed is 400 rpm and the screw length-to-diameter ratio is 40:1.

[0079] The polypropylene composition and expandable microspheres were then mixed evenly using a mixer to obtain the foamable polypropylene material.

[0080] Comparative Examples 1-12

[0081] The differences between the comparative examples and the embodiments are only in the types and proportions of components, as shown in Tables 3-4.

[0082] In the components described in each embodiment and comparative example,

[0083] Polypropylene resin 1 is PP HP500N produced by PetroChina Daqing Refining & Chemical Co., Ltd., with a melting point of 167.2℃ and a melt flow rate of 12g / 10min at 230℃ and 2.16kg load.

[0084] Polypropylene resin 2 is Shell's PP EP548R, with a melting point of 165.3℃ and a melt flow rate of 25g / 10min at 230℃ and a load of 2.16kg.

[0085] The expandable microspheres B1 are DU608M produced by Xineng Chemical, with an average particle size of 22μm, an initial foaming temperature of 135~145℃, and a peak foaming temperature of 195~205℃.

[0086] The expandable microspheres B2 are produced by Xineng Chemical as DU608S, with an average particle size of 12μm, an initial foaming temperature of 135~145℃, and a peak foaming temperature of 195~205℃.

[0087] The expandable microspheres A1 are DU240 produced by Xineng Chemical, with an average particle size of 13μm, an initial foaming temperature of 205~215℃, and a peak foaming temperature of 230~240℃.

[0088] The expandable microspheres A2 are DU260 produced by Xineng Chemical, with an average particle size of 8μm, an initial foaming temperature of 200-250℃, and a peak foaming temperature of 255-265℃.

[0089] The expandable microspheres A3 are WU152-M produced by Xineng Chemical, with an average particle size of 18μm, an initial foaming temperature of 92-97℃, and a peak foaming temperature of 148-155℃.

[0090] The expandable microspheres B3 are DU180 produced by Xineng Chemical, with an average particle size of 32μm, an initial foaming temperature of 135~145℃, and a peak foaming temperature of 185~195℃.

[0091] The expandable microspheres B4 are produced by Xineng Chemical as DU175-M, with an average particle size of 22μm, an initial foaming temperature of 132~142℃, and a peak foaming temperature of 180~190℃.

[0092] The low-melting-point polypropylene 1 is Idemitsu S400 produced in Japan, with a melting point of 80℃ and a melt flow rate of 2600g / 10min at 230℃ and a load of 2.16kg.

[0093] Low-melting-point polypropylene 2 is Idemitsu S600 produced in Japan, with a melting point of 80℃ and a melt flow rate of 390g / 10min at 230℃ and a load of 2.16kg.

[0094] Compatibilizer 1 is PC-1 produced by Foshan Baichen, which is maleic anhydride grafted polypropylene with a grafting rate of 0.85%.

[0095] Compatibilizer 2 is MA8510 produced by Mitsui Chemicals, which is maleic anhydride grafted with POE, with a grafting rate of 1%.

[0096] The lubricant is erucamide produced by Croda Chemical.

[0097] Hyperbranched polyester 1 is HyPer H2O2 produced by Wuhan Hyperbranching, a hydroxyl-terminated hyperbranched polyester with a number-average molecular weight of 1200 g / mol and a molar number of hydroxyl groups of 11 / mol.

[0098] The hyperbranched polyester 2 is HyPer H302 produced by Wuhan Hyperbranching, a hydroxyl-terminated hyperbranched polyester with a number average molecular weight of 2500 g / mol.

[0099] The hyperbranched polyester 3 is HyPer C302 produced by Wuhan Hyperbranching, a carboxyl-terminated hyperbranched polyester with a number-average molecular weight of 2800 g / mol;

[0100] The hyperbranched polyester 4 is HyPer C102 produced by Wuhan Hyperbranching, a carboxyl-terminated hyperbranched polyester with a number average molecular weight of 2600 g / mol.

[0101] The hyperbranched polyamide is HPN202 produced by Wuhan Hyperbranching, a hydroxyl-terminated hyperbranched polyamide with a number-average molecular weight of 2700 g / mol.

[0102] Coupling agent 1 is JH-A110, an aminosilane coupling agent produced by Hubei Jianghan New Materials.

[0103] Coupling agent 2 is SG-SI 172, a vinyl silane coupling agent produced by Nanjing Shuguang Silane Chemical Co., Ltd.

[0104] The antioxidant is a complex of commercially available hindered phenolic antioxidants and commercially available phosphite antioxidants: antioxidant 168 and antioxidant 1010 are mixed in a 1:1 mass ratio.

[0105] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0106] Table 1

[0107]

[0108] Table 2

[0109]

[0110]

[0111] Table 3

[0112]

[0113] Table 4

[0114]

[0115] To verify the performance of the polypropylene composition described in this invention, the products prepared in each embodiment and comparative example were subjected to the following performance tests, with the specific steps as follows:

[0116] (1) Gloss test: The foamable polypropylene material was injection molded into a square plate with a size of 60*100*2mm using a single screw extruder for testing. Then, according to the standard GB / T 8807-1988, the test data at 60° angle were collected.

[0117] (2) Surface roughness: The foamable polypropylene material was injection molded into a square plate with a size of 60*100*2mm using a single screw extruder for testing. The profile was tested using a profiler, and the average arithmetic deviation Ra of the profile was calculated.

[0118] (3) Appearance test: The foamable polypropylene material was injection molded into a square plate of 12.7×3.2×6mm using a single screw extruder. Then, the two-dimensional observation method was used to observe whether there were shrinkage marks on the surface of the square plate. If there were, the maximum length of the shrinkage mark was measured and recorded.

[0119] The injection temperatures of the above single-screw extruder are set as follows: feeding zone: 50℃, zone 1: 200℃, zone 2: 210℃, zone 3: 230℃, zone 4: 240℃, zone 5: 240℃.

[0120] The test results are shown in Tables 5 and 6.

[0121] Table 5

[0122]

[0123] Table 6

[0124]

[0125] As can be seen from Tables 3 and 4, the foamable polypropylene material of the present invention has good performance and decorative effect after injection molding. The gloss of the product can be maintained below 72%, and the roughness can be maintained above 0.55μm and below 1μm. At the same time, no shrinkage marks were observed in any of the products. Compared with the unmodified Comparative Example 9, its gloss is significantly reduced, and its roughness is improved to a moderate range, resulting in a significant improvement in performance.

[0126] The reason why the product can achieve the above-mentioned ideal technical effect is mainly due to the combination of two expandable microspheres. If only one type of expandable microsphere is used, as shown in Comparative Examples 1 and 2, although the overall component dispersion is higher than in the examples due to the properties of a single microsphere, resulting in higher surface roughness and lower gloss, the dimensional stability and surface smoothness of the foamed product cannot be simultaneously achieved without the combination of the two expandable microspheres, thus shrinkage marks appear in all products. Furthermore, the expandable microspheres in the product of this solution have a special foaming ratio and foaming effect based on a gradient distribution within a specific range of foaming initiation and peak temperatures. If the foaming initiation and peak temperatures are arbitrarily adjusted, as shown in Comparative Examples 3 and 4 and Comparative Example 12, and the expandable microspheres introduced in either case do not meet the requirements, regardless of whether the sizes are similar, although the product also has a gradient effect during foaming, similar to Comparative Examples 1 and 2, the product still exhibits obvious shrinkage marks, indicating that not any arbitrary combination of expandable microspheres can achieve the effect of the product in the examples. Besides expandable microspheres, the compatibility and dispersion of the compounded low-melting-point polypropylene and hyperbranched polyester are equally important. As shown in Comparative Examples 5 and 6 and Comparative Example 10, if low-melting-point polypropylene is not introduced, or if conventional compatibilizers are used instead, the compatibility and dispersion of the components in the product cannot reach the expected state, and the product will still exhibit shrinkage. In Comparative Examples 7 and 8 and Comparative Example 11, if hyperbranched polyester is not introduced or conventional lubricants or hyperbranched polyamides with similar hyperbranched structures are used as substitutes, the resulting products do not show shrinkage on the surface, but the surface roughness of the products reaches more than 1 μm. At this point, the surface roughness of the products increases sharply, and the driver's experience will be greatly reduced when used as automotive interior trim.

[0127] A comparison of the performance of the products obtained in Examples 1 and 8-10 shows that when hydroxyl-terminated hyperbranched polyester is selected as the compounding component, the resulting product exhibits superior performance in use. However, the ratios of the two expandable microspheres in Examples 1 and 11-14 are not identical, resulting in variations in product performance. When the preferred mass ratio of the two is within the range of (1-5):1, the surface roughness of the resulting product is further improved within a moderate range, while the gloss is lower. It should be noted, however, that in the technical solution of this application, the performance of the products obtained in Examples 11-14 is still significantly superior to the comparative examples and existing products.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A foamable polypropylene material, characterized in that, Includes the following components in parts by weight: 100 parts of polypropylene composition, 0.1-8 parts of expandable microspheres and / or expandable microsphere masterbatch; The polypropylene composition includes 90-97 parts of polypropylene resin, 2-10 parts of low-melting-point polypropylene, and 0.1-0.5 parts of hyperbranched polyester. The hyperbranched polyester is a hydroxyl-terminated hyperbranched polyester; The expandable microspheres and / or expandable microsphere masterbatch include expandable microspheres A and expandable microspheres B; The mass ratio of expandable microsphere A to expandable microsphere B is (1~5):1; The initial foaming temperature of the expandable microsphere A is 200~250℃, and the peak foaming temperature is 230~265℃. The initial foaming temperature of the expandable microspheres B is 135~145℃, and the peak foaming temperature is 195~205℃. The expandable microspheres A have an average particle size of 7~15μm, and the expandable microspheres B have an average particle size of 10~22μm; the low-melting-point polypropylene has a melting point ≤90℃.

2. The foamable polypropylene material as described in claim 1, characterized in that, The expandable microsphere masterbatch includes expandable microspheres A, expandable microspheres B, and a matrix resin, wherein the matrix resin includes at least one of polypropylene resin and polyethylene resin.

3. The foamable polypropylene material as described in claim 1, characterized in that, The expandable microspheres include a shell and a core, the shell comprising a thermoplastic polymer and the core comprising an expandable material.

4. The foamable polypropylene material as described in claim 3, characterized in that, The thermoplastic polymer is a polymer obtained by reacting at least one of nitrile monomers, acrylate monomers, amide monomers, and carboxyl-containing reactive monomers with polymerizable double bonds.

5. The foamable polypropylene material as described in claim 1, characterized in that, The polypropylene resin has a melting point of 150~170℃ and a melt flow rate of 10~35g / 10min at 230℃ and 2.16kg load, and / or the low-melting-point polypropylene has a melting point of 70~90℃ and a melt flow rate of 300~3000g / 10min at 230℃ and 2.16kg load.

6. The foamable polypropylene material as described in claim 1, characterized in that, The hyperbranched polyester has a number-average molecular weight of 800~6500 g / mol.

7. The foamable polypropylene material as described in claim 1, characterized in that, The polypropylene composition further includes 0.1 to 0.3 parts of coupling agent.

8. The foamable polypropylene material as described in claim 7, characterized in that, The coupling agent includes at least one of vinyl silane coupling agents, amino silane coupling agents, methacryloxysilane coupling agents, titanate coupling agents, and aluminum-titanium composite silane coupling agents.

9. The method for preparing the foamable polypropylene material according to any one of claims 1 to 8, characterized in that, Includes the following steps: The raw material components of the polypropylene composition are added to a screw extruder for melt extrusion granulation to obtain the polypropylene composition. Subsequently, the polypropylene composition is mixed with expandable microspheres and / or expandable microsphere masterbatch to obtain a foamable polypropylene material.

10. The use of the expandable polypropylene material as described in any one of claims 1 to 8 in the preparation of automotive interior parts.

11. The application as described in claim 10, characterized in that, The automotive interior components include the instrument panel and the sub-instrument panel.

12. A polypropylene product, characterized in that, It is obtained by injection molding of a material comprising the foamable polypropylene material according to any one of claims 1 to 8.

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