Polypropylene composite material, and preparation method and application thereof

Abstract

This invention belongs to the field of polypropylene materials, specifically disclosing a polypropylene composite material, its preparation method, and its application. By adding a coupling agent to modify nano-silica and low molecular weight polyethylene glycol in the raw materials of the polypropylene composite material, this invention promotes the penetration and absorption of the melt and trapped gas during the injection molding process, while maintaining the material's high rigidity and toughness. This allows the melt to better fill the mold, significantly improving appearance defects such as flow marks in the molded product. Overall, this results in a polypropylene composite material that possesses good appearance, high rigidity, and toughness, meeting the requirements for textured parts.

Description

Technical Field

[0001] This invention belongs to the field of polypropylene materials, specifically relating to a polypropylene composite material, its preparation method, and its application. Background Technology

[0002] Polypropylene (PP) is widely used in automotive interior parts, appliance housings, and other fields requiring a high-end appearance due to its low cost and balanced performance. Typically, molten plastic is injected into a mold with an etched texture on its surface. The resulting parts have a specific texture to enhance aesthetics, conceal flow marks and scratches, and provide a comfortable feel. However, a common and challenging problem during injection molding is "poor texture replication," where the molten plastic fails to completely fill the microcavities of the mold surface, resulting in blurred and unclear textures on the finished product, exhibiting issues such as localized shine, flow marks, and obvious streaks. Existing research and practice indicate that a significant cause of this problem is "air trapping" during the injection molding process. Air trapping occurs when the molten metal advances within the mold cavity, pushing forward air. If this air cannot be expelled through the mold's venting system in time, it becomes compressed and trapped between the melt and the mold wall, especially in fine structures like textured surfaces. Existing technologies for solving the problem of poor reproduction of injection molding texture mainly involve adjusting the fluidity of the material, increasing mold venting, and treating the textured surface of the mold with micro-cracks to enhance the mold's venting capacity, or covering the abnormal appearance by spraying paint on the parts. However, none of these methods can fundamentally solve the problem of poor product appearance caused by texture reproduction. Summary of the Invention

[0003] In view of the appearance defects such as flow marks in polypropylene products after injection molding, the present invention will provide a polypropylene composite material, its preparation method and application.

[0004] To achieve the above objectives, the following technical solutions are specifically included: On one hand, the present invention provides a polypropylene composite material comprising the following raw material components in parts by weight: 49-71 parts polypropylene, 4-45.5 parts mineral filler, 0.4-5.5 parts coupling agent modified nano-silica, and 0.09-2.1 parts polyethylene glycol; wherein the number average molecular weight of the polyethylene glycol is 200-600.

[0005] In the polypropylene composite material of this invention, the nano-silica modified with a coupling agent exhibits good compatibility with the matrix. During injection molding, the coupling agent modification allows the nano-silica to be more uniformly dispersed in the melt and forms tiny, discontinuous protrusions between the melt front and the mold wall. This creates a microscopically rough interface between the melt front and the mold, disrupting the complete, smooth contact interface between the melt and the mold. These microscopic discontinuities on the rough interface provide tiny escape channels for compressed air, allowing it to be channeled to the main exhaust system instead of being completely trapped. Therefore, the presence of coupling agent-modified nano-silica creates physical channels for gas escape during injection molding from an "interface channeling" perspective, improving the "trapped gas" defect when the melt fills the mold and reducing appearance defects such as flow marks on the product.

[0006] Meanwhile, nano-silica can serve as a potential nucleating agent for polypropylene crystallization, slightly increasing the crystallization temperature and enhancing the nucleation effect. This allows the product to solidify more quickly upon contact with the cold mold wall, locking in the texture and further reducing appearance defects such as flow marks. However, a sufficient amount of nano-silica is needed to create a large-area micro-rough interface on the surface of the melt front, and increasing its dosage will further degrade the product's appearance and toughness. The inventors of this invention discovered that introducing low molecular weight polyethylene glycol into the raw materials will form a large number of submicron-sized micropores in situ on the matrix during injection molding. This can construct venting channels inside the melt, allowing the gas it carries to be discharged. This not only promotes the discharge of its own internal gas, but also, due to its appropriate content, it will not produce large bubbles like traditional foaming agents, but will form micron-sized micropores. These micropores are mainly concentrated at the melt front. When the melt comes into contact with the cold mold surface, the surface layer cools and solidifies rapidly, "freezing" these micropores below the surface layer, forming a microscopically porous transition layer. This porous transition layer can absorb some of the trapped air like a sponge and increase gas permeability, allowing the trapped air to diffuse out more quickly through this porous layer. This promotes the penetration and absorption of the melt's own gas and the trapped air, thereby improving the appearance defects such as flow marks on the product.

[0007] Furthermore, the presence of nano-silica in the melt, combined with the porous structure created by the small-molecule gas products from the vaporization or partial decomposition of low-molecular-weight polyethylene glycol, along with the microscopic discontinuities formed by the nano-silica, creates a microscopically rough interface and microscopically porous channels that facilitate gas venting. This further enhances the permeation and absorption of gases and trapped air within the melt, improving the overall venting efficiency of the injection molding process and reducing appearance defects such as flow marks in the product. In addition, the presence of low-molecular-weight polyethylene glycol and coupling agent-modified nano-silica synergistically improves gas permeation and absorption, achieving a better reduction in appearance defects such as flow marks. Therefore, even with a low dosage of coupling agent-modified nano-silica, the product can maintain a superior appearance. This avoids sacrificing the material's mechanical properties while overcoming appearance defects, allowing the material to maintain high rigidity and toughness, resulting in a material with excellent overall performance in terms of appearance, rigidity, and toughness.

[0008] Preferably, the polypropylene composite material comprises the following components in parts by weight: 50-70 parts polypropylene, 5-45 parts mineral filler, 0.5-5 parts coupling agent modified nano-silica, and 0.1-2 parts polyethylene glycol.

[0009] More preferably, the weight parts of polypropylene in the polypropylene composite material may specifically include 50 parts, 52 parts, 54 parts, 56 parts, 58 parts, 60 parts, 62 parts, 64 parts, 66 parts, 68 parts, 70 parts, etc., as well as specific values ​​between the above-mentioned points.

[0010] More preferably, the weight parts of the mineral filler in the polypropylene composite material may specifically include 5 parts, 9 parts, 13 parts, 17 parts, 21 parts, 25 parts, 29 parts, 33 parts, 37 parts, 41 parts, 45 parts, etc., as well as specific values ​​between the above-mentioned points.

[0011] More preferably, the weight percentage of the coupling agent-modified nano-silica in the polypropylene composite material may specifically include 0.5 parts, 0.95 parts, 1.4 parts, 1.85 parts, 2.3 parts, 2.75 parts, 3.2 parts, 3.65 parts, 4.1 parts, 4.55 parts, 5.0 parts, etc., as well as specific values ​​between the above-mentioned points.

[0012] More preferably, the weight parts of polyethylene glycol in the polypropylene composite material may specifically include 0.1 parts, 0.29 parts, 0.48 parts, 0.67 parts, 0.86 parts, 1.05 parts, 1.24 parts, 1.43 parts, 1.62 parts, 1.81 parts, 2.0 parts, etc., as well as specific values ​​between the above-mentioned points.

[0013] Common polypropylene resins in the art can be used in this invention, including but not limited to at least one of homopolymer polypropylene, random copolymer polypropylene, and block copolymer polypropylene.

[0014] Preferably, the melt mass flow rate (MFR) of the polypropylene, tested according to ISO 1133-2011 at 230°C and 2.16 kg load, is 10-30 g / 10 min, specifically 10 g / 10 min, 11 g / 10 min, 12 g / 10 min, 13 g / 10 min, 14 g / 10 min, 15 g / 10 min, 16 g / 10 min, 17 g / 10 min, 18 g / 10 min, 19 g / 10 min, etc. The specific point values ​​included in the ranges are g / 10min, 20g / 10min, 21g / 10min, 22g / 10min, 23g / 10min, 24g / 10min, 25g / 10min, 26g / 10min, 27g / 10min, 28g / 10min, 29g / 10min, 30g / 10min, etc., as well as the specific point values ​​between the above-mentioned point values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the ranges.

[0015] The polypropylene resin of the present invention has a mass percentage content of not less than 40% in the polypropylene composite material, more preferably not less than 50%, and even more preferably not less than 70%.

[0016] In this invention, the number-average molecular weight of polyethylene glycol was obtained by gel permeation chromatography.

[0017] Preferably, the mass ratio of the coupling agent-modified nano-silica to polyethylene glycol is 1.5-10:1, specifically 1.5:1, 1.75:1, 2:1, 2.25:1, 2.5:1, 2.75:1, 3:1, 3.25:1, 3.5:1, 3.75:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, etc., as well as the specific ratios between the above ratios. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific values ​​included in the range.

[0018] Preferably, the coupling agent in the coupling agent-modified nano-silica includes at least one of silane coupling agents and titanate coupling agents.

[0019] More preferably, the silane coupling agent includes at least one of aminosilane, epoxysilane, and vinylsilane, such as at least one of KH-550 (γ-aminopropyltriethoxysilane), KH-792 (N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane), KH-602 (N-phenyl-γ-aminopropyltrimethoxysilane), KH-560 (γ-(2,3-epoxypropoxy)propyltrimethoxysilane), A-151 (vinyltriethoxysilane), and VTMO (vinyltrimethoxysilane).

[0020] More preferably, the titanate coupling agent includes at least one of isopropyltriisostearoyl titanate, monoalkoxy pyrophosphate type, and isopropyltris(dioctylphosphoyloxy) titanate.

[0021] Preferably, the D50 of the nano-silica modified by the coupling agent is 30-300 nm, specifically 30 nm, 50 nm, 70 nm, 90 nm, 110 nm, 130 nm, 150 nm, 170 nm, 190 nm, 210 nm, 230 nm, 250 nm, 270 nm, 290 nm, 300 nm, etc., as well as specific values ​​between the above ranges. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific values ​​included in the range. The D50 of the nano-silica is tested using laser particle size analysis.

[0022] Preferably, the mineral filler includes at least one of talc powder, mica powder, and wollastonite.

[0023] Preferably, the mesh size of the mineral filler is 200-3000 mesh, specifically 200 mesh, 250 mesh, 300 mesh, 325 mesh, 400 mesh, 500 mesh, 600 mesh, 800 mesh, 1000 mesh, 1250 mesh, 1500 mesh, 1800 mesh, 2000 mesh, 2500 mesh, 3000 mesh, etc., as well as specific values ​​between the above ranges. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific values ​​included in the range. The mesh size of the mineral filler is tested using a sieving method.

[0024] Preferably, it further includes 0.1-2 parts by weight of processing aids, said processing aids including at least one of antioxidants, weathering agents, and lubricants.

[0025] More preferably, the antioxidant is present in a weight fraction of 0.01-1 parts.

[0026] More preferably, the weathering agent is present in a weight ratio of 0.01-1 parts.

[0027] More preferably, the lubricant is present in a weight fraction of 0.01-1 parts.

[0028] More preferably, the lubricant includes at least one of amide lubricants and stearic acid lubricants.

[0029] More preferably, the antioxidant includes at least one of hindered phenolic antioxidants, phosphite antioxidants, thioesters, and other antioxidants.

[0030] More preferably, the antioxidant includes at least one of antioxidant 1010, antioxidant 168, antioxidant 1076, and antioxidant DLTDP.

[0031] More preferably, the weathering agent includes at least one of benzophenones, benzotriazoles, salicylates, triazines, substituted acrylonitriles, and hindered amine light stabilizers.

[0032] In this invention, other (functional) additives may be added as needed, such as, but not limited to, antioxidants, weather-resistant agents, and lubricants. Conventional antioxidants, weather-resistant agents, and lubricants in the art can be used in this invention to increase the functionality of polypropylene composites and improve their overall performance.

[0033] On the other hand, the present invention provides a method for preparing the polypropylene composite material, comprising the following steps: S1. The nano-silica is immersed in a solution containing a coupling agent, filtered, and dried to obtain coupling agent modified nano-silica. S2. The coupling agent-modified nano-silica is mixed evenly with the remaining raw materials, and then melt-extruded and granulated in sequence to obtain the polypropylene composite material.

[0034] Preferably, in step S1, the concentration of the coupling agent in the solution containing the coupling agent is 10wt%-20wt%.

[0035] Preferably, in step S1, the mass ratio of coupling agent to nano-silica in the solution containing coupling agent is (0.1-0.6):1.

[0036] Preferably, in step S1, the soaking time is 1-6 hours.

[0037] Preferably, in step S2, the temperature of the melt extrusion is 180-230°C.

[0038] Furthermore, the present invention also provides an automotive part prepared according to the aforementioned polypropylene composite material.

[0039] Preferably, the automotive parts include at least one of the following: a door panel, pillar, instrument panel, side skirt, and wheel arch with a leather-like texture.

[0040] Compared with the prior art, the present invention has the following beneficial effects: By adding coupling agent to modify nano-silica and low molecular weight polyethylene glycol in the raw materials of polypropylene composite material, the present invention promotes the penetration and absorption of the melt and trapped gas inside the mold during the injection molding process while maintaining the high rigidity and toughness of the material. This allows the melt to fill the mold better, which can significantly improve the appearance defects such as flow marks of the product obtained after injection molding. In summary, the polypropylene composite material has good appearance, high rigidity and toughness, which meets the requirements of textured parts. Detailed Implementation

[0041] To better illustrate the purpose, technical solution, and advantages of the present invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, all raw materials used in the embodiments and comparative examples of the present invention are commercially available, and the same raw materials were used in all parallel experiments.

[0042] (1) Polypropylene: PP-1: Grade PP K9930, melt flow rate 30g / 10min, manufacturer: Guangzhou Petrochemical. PP-2: Grade PP K9017, melt flow rate 17g / 10min, manufacturer: Formosa Chemicals & Fibre. PP-3: Grade PP SP179, melt flow rate 10g / 10min, manufacturer Lanzhou Petrochemical; (2) Mineral fillers The raw materials purchased for the mineral packing are of the required size, or the raw materials for the mineral packing are obtained by screening.

[0043] Talc powder: TYT-777A, 3000 mesh, Haicheng Tianyuan; Mica powder: YM-SW500, 500 mesh, Suzhou Shenwei Nonmetallic Materials Co., Ltd.; Wollastonite: WFB-10, 200 mesh, Hubei Fengjiashan Silicon Fiber Co., Ltd.; (3) Coupling agent: Coupling agent 1: Silane coupling agent, KH-560, Nanjing Shuguang Silane Chemical Co., Ltd.; Coupling agent 2: Titanate coupling agent, NXH-401, Nanjing Xuanhao New Material Technology Co., Ltd.

[0044] (4) Nano-silica: Nano silica 1: SP30, with an average particle size (D50) of 30nm after sieving, from Xuancheng Jingrui New Materials; Nano silica 2: SP50, with an average particle size (D50) of 50nm after sieving, Hangzhou Jiupeng New Materials; Nano silica 3:300N, with an average particle size (D50) of 300nm after sieving, from Ningbo Beigaer New Materials; Nano titanium dioxide, ZH-Ti-10NR, Anhui Zhonghang Nanotechnology Development Co., Ltd.; (5) Polyethylene glycol-1: PEG 200, number average molecular weight 200, Jiangsu Haian Petrochemical; Polyethylene glycol-2: PEG 300, number average molecular weight 300, Jiangsu Haian Petrochemical; Polyethylene glycol-3: PEG 600, number average molecular weight 600, Jiangsu Haian Petrochemical; Polyethylene glycol-4: PEG 800, number average molecular weight 800, Jiangsu Haian Petrochemical; Ethylene glycol: Suzhou Jiujia Chemical Co., Ltd.; (6) Antioxidants: Antioxidants: The antioxidants are SONOX 1010 and SONOX 168 in a 1:1 mass ratio, both of which are commercially available; (7) Lubricant: Ethylene bis-stearamide, commercially available; (8) Weathering agent: hindered amine light stabilizer T-81, commercially available.

[0045] Examples 1-18 and Comparative Examples 1-7 A polypropylene composite material, the preparation method of which includes the following steps: S1. The following method is used to prepare the coupling agent modified nano-inorganic particles: the inorganic particles are immersed in an aqueous solution containing 15wt% coupling agent (silane coupling agent or titanate coupling agent) for 2 hours according to the mass ratio of coupling agent to nano-inorganic particles (nano-silica or nano-titanium dioxide) of 0.3:1, and then filtered and dried to obtain nano-inorganic particles with coupling agent surface graft modification.

[0046] S2. Weigh each raw material according to the formula in Table 1-2. Add all raw materials except mineral fillers to a high-speed mixer and mix thoroughly. Then, add the mixed material to the extruder through the main feed port. Add the mineral fillers through the side feed port. The length-to-diameter ratio of the extrusion screw is 36-48:1. After mixing, melting, and homogenizing, extrude and granulate. Set the extruder temperature as follows: Zone 1 80-120℃, Zones 2-5 180-200℃, and other zones 200-230℃. After granulation, obtain the polypropylene composite material.

[0047] To verify the performance of the polypropylene composite material described in this invention, the polypropylene composite materials prepared in the examples and comparative examples were subjected to performance tests. The specific test methods and acceptance criteria are as follows: (1) Impact strength: The notched impact strength of the polypropylene composites of the above examples and comparative examples was tested according to ISO 180-2019; the impact performance was ≥12KJ / m 2 Considered qualified; (2) Flexural strength: The flexural strength of the polypropylene composites of the above examples and comparative examples was tested according to ISO 178-2019; a flexural strength ≥25MPa was considered qualified; (3) Appearance performance: The leather-textured sheet was injection molded according to the injection molding process of the above embodiments and comparative examples. The injection molding size was 200mm×200mm×3mm. The flow marks on the appearance of the leather-textured sheet were compared. The larger the area of ​​the flow marks, the worse the leather texture replication effect. The following evaluation criteria were used for rating: A: No flow marks; B: Flow mark area is within 1cm² 2 up to 4cm 2 between; C: Flow mark area is 4cm² 2 up to 9cm 2 between; D: Flow mark area greater than 9cm² 2 .

[0048] The test results are shown in Table 1-2.

[0049] Table 1 Table 2 In Examples 1-3, as the melt flow rate of PP decreased, the flexural strength and impact strength of the material increased slightly, while the appearance properties decreased.

[0050] In Examples 1 and 4-5, the mineral fillers are talc powder, mica powder, and wollastonite, respectively. Mica powder has a slight effect on flow marks. The flexural strength from high to low is mica powder, wollastonite, and talc powder, respectively. The impact strength from high to low is talc powder, mica powder, and wollastonite, respectively.

[0051] In Examples 1 and 6, the silane coupling agent in Example 1 was replaced with an equal amount of titanate coupling agent to modify the surface of nano-silica. This slightly improved the flexural strength and impact strength, while maintaining comparable appearance. It can be seen that both silane coupling agent and titanate coupling agent have a modifying effect on the surface of nano-silica and can improve its dispersibility in the system.

[0052] In Examples 1 and 7-8, as the particle size of the coupling agent-modified nano-silica gradually increases, the appearance properties remain basically unchanged, but the bending strength and impact strength of the material first increase and then decrease. Therefore, when the particle size is 50-800μm, it can maintain good rigidity, toughness and appearance properties.

[0053] In Examples 10, 1, and 9, with the same total weight of coupling agent-modified nano-silica and low molecular weight polyethylene glycol, the mass ratio of the two was 1.7:1, 3:1, and 7:1, respectively. As the amount of coupling agent-modified nano-silica gradually increased and the amount of low molecular weight polyethylene glycol gradually decreased, the flexural strength gradually increased, and the appearance performance improved. Therefore, when the mass ratio of the two is between 1.7 and 7:1, the rigidity, toughness, and appearance performance are all superior.

[0054] In Examples 11, 1, and 12, the amount of coupling agent-modified nano-silica gradually increased, the flexural strength gradually increased, the impact strength first increased and then decreased, and the appearance performance improved. Therefore, when the amount is 0.5-5 parts, the material has better rigidity, toughness, and appearance performance.

[0055] In Examples 13, 1, and 14, the amount of low molecular weight polyethylene glycol gradually increased, resulting in a slight decrease in flexural strength and impact strength, and an initial increase followed by a decrease in appearance performance. When the amount of low molecular weight polyethylene glycol was between 0.1 and 2 parts, the material exhibited superior rigidity, toughness, and appearance performance.

[0056] In Examples 1 and 15-16, the low molecular weight polyethylene glycols used were PEG 300, PEG 200, and PEG 600, respectively. All of these materials could give the material superior rigidity, toughness, and appearance properties. Among them, PEG 300 had the best overall performance.

[0057] Compared to Example 1, Comparative Example 1, which did not use coupling agent-modified nano-silica, had unsatisfactory appearance performance, and its rigidity and toughness decreased compared to Example 1. Comparative Example 2, which did not contain coupling agent-modified nano-silica and used only a single, equal amount of low molecular weight polyethylene glycol, had extremely poor toughness and appearance performance. Comparative Example 3, which did not contain low molecular weight polyethylene glycol and used only a single, equal amount of coupling agent-modified nano-silica, also had poor appearance performance. It is evident that the presence of coupling agent-modified nano-silica and low molecular weight polyethylene glycol can synergistically improve the material's appearance performance while achieving good rigidity and toughness. Furthermore, considering Comparative Example 4, which used coupling agent-modified nano-titanium dioxide, it is clear that replacing silica with titanium dioxide cannot achieve a similar effect. Comparative Examples 5 and 6 used excessively high molecular weight polyethylene glycol and ethylene glycol, respectively. The former could not achieve melting or partial vaporization, while the latter had an excessively fast vaporization rate, failing to effectively improve the material's appearance performance, and its compatibility issues degraded the material's toughness.

[0058] 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 polypropylene composite material, characterized in that, The raw material components include the following parts by weight: 49-71 parts polypropylene, 4-45.5 parts mineral filler, 0.4-5.5 parts coupling agent modified nano-silica, and 0.09-2.1 parts polyethylene glycol; wherein the number average molecular weight of the polyethylene glycol is 200-600.

2. The polypropylene composite material as described in claim 1, characterized in that, The mass ratio of the coupling agent-modified nano-silica to polyethylene glycol is 1.5-10:

1.

3. The polypropylene composite material as described in claim 1, characterized in that, The coupling agent in the modified nano-silica includes at least one of silane coupling agents and titanate coupling agents.

4. The polypropylene composite material as described in claim 1, characterized in that, The D50 of the nano-silica modified by the coupling agent is 50nm-800nm.

5. The polypropylene composite material as described in claim 1, characterized in that, The mineral filler includes at least one of talc powder, mica powder, and wollastonite.

6. The polypropylene composite material as described in claim 1, characterized in that, The melt flow rate of the polypropylene tested according to ISO 1133-2011 at 230°C and 2.16 kg load was 10-30 g / 10 min.

7. The polypropylene composite material as described in claim 1, characterized in that, It also includes 0.1-2 parts by weight of processing aids, which include at least one of antioxidants, weathering agents, and lubricants.

8. A method for preparing the polypropylene composite material according to any one of claims 1-7, characterized in that, Includes the following steps: S1. The nano-silica is immersed in a solution containing a coupling agent, filtered, and dried to obtain coupling agent modified nano-silica. S2. The coupling agent-modified nano-silica is mixed evenly with the remaining raw materials, and then melt-extruded and granulated in sequence to obtain the polypropylene composite material.

9. An automotive part made of polypropylene composite material according to any one of claims 1-7.

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