Hot-oil-resistant impact-resistant polypropylene composition as well as preparation method and application thereof

Abstract

The invention discloses a hot oil resistant and impact resistant polypropylene composition and a preparation method and application thereof, the polypropylene composition comprises the following components in parts by weight: 50-70 parts of co-polypropylene, 15-25 parts of a flexibilizer, 15-25 parts of an inorganic filler, 1-3 parts of an oil resistant auxiliary agent, 0.5-1 part of a dispersant and 0.1-0.3 part of a nucleating agent, the toughening agent is any one of an ethylene-methacrylate copolymer, an ethylene-butyl acrylate-glycidyl methacrylate copolymer or a maleic anhydride grafted polyolefin elastomer. The polypropylene composition provided by the invention has excellent hot oil resistance and high impact strength, and also has good surface smoothness and food contact safety.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a heat-resistant oil-based impact-resistant polypropylene composition, its preparation method, and its application. Background Technology

[0002] Polypropylene (PP) has become the mainstream material for disposable lunch boxes due to its advantages such as light weight, non-toxicity, chemical resistance, excellent processing performance, and low cost. Among them, homopolymer polypropylene and ordinary impact copolymer polypropylene are widely used in takeaway lunch boxes and other fields due to their good rigidity and processing fluidity. However, with the rapid development of the takeaway industry and the improvement of quality requirements, traditional polypropylene lunch boxes have exposed serious defects in three aspects: impact resistance, heat and oil resistance, and surface smoothness. Moreover, there is a significant "inverse" contradiction among these three aspects, making it difficult to meet the needs of high-end applications. In terms of heat and oil resistance, the temperature of oily foods such as fried foods and braised dishes in Chinese fast food can reach 80-120℃, while the heat distortion temperature of ordinary polypropylene is relatively low (90-100℃ for homopolymer PP and 85-95℃ for copolymer PP). When filled with hot oil, it is easy to soften, warp, or even leak. At the same time, the polypropylene molecular chain has a high affinity for oil, and long-term contact can easily cause swelling and a decrease in strength. In terms of impact resistance, thin-walled lunch boxes are easily damaged during transportation and delivery, especially in low-temperature winter environments where their toughness decreases sharply, and even slight impacts can cause them to break and leak. Regarding surface smoothness, the surface gloss after injection molding is low, and flow marks and pitting are prone to appear. When adding fillers to improve rigidity, uneven distribution of the fillers can create "white spots" or "orange peel" effects, lowering the product's quality and increasing oil adhesion. More importantly, improving heat oil resistance requires adding inorganic fillers, but this reduces impact toughness and surface smoothness; improving impact resistance requires adding elastomer toughening agents, but this weakens heat oil resistance and affects gloss; improving surface smoothness often requires reducing the amount of filler, thus sacrificing heat oil resistance.

[0003] Therefore, there is an urgent need to develop a polypropylene composition that can simultaneously achieve heat resistance to oil, impact resistance, and a smooth surface. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a heat-resistant, oil-resistant, impact-resistant polypropylene composition, its preparation method, and its applications. By carefully selecting the matrix resin, toughening agent, inorganic filler, and functional additives, and optimizing the formulation and process, this invention aims to prepare a disposable polypropylene material for lunch boxes that combines excellent heat-resistant oil properties, high impact strength, and good surface smoothness, thereby overcoming the deficiencies of existing technologies.

[0005] This invention provides a heat-resistant, oil-resistant, impact-resistant polypropylene composition, comprising, by weight, the following components: 50-70 parts of copolymer polypropylene, such as 50, 55, 60, 65, or 70 parts; 15-25 parts of toughening agent, such as 15, 18, 20, 22, or 25 parts; 15-25 parts of inorganic filler, such as 15, 18, 20, 22, or 25 parts; 1-3 parts of oil-resistant additive, such as 1, 1.5, 2, 2.5, or 3 parts; 0.5-1 part of dispersant, such as 0.5, 0.6, 0.7, 0.8, 0.9, or 1 part; and 0.1-0.3 parts of nucleating agent, such as 0.1, 0.2, or 0.3 parts. The toughening agent is any one of ethylene-methacrylate copolymer, ethylene-butyl acrylate-glycidyl methacrylate copolymer, or maleic anhydride-grafted polyolefin elastomer.

[0006] This invention achieves multi-layered protection against high-temperature oil media through the synergistic construction of a triple protection system. Firstly, regarding the rigid framework, the invention incorporates inorganic fillers into the formulation to form an interpenetrating three-dimensional rigid network within the polypropylene matrix. This network structure itself possesses extremely high thermal stability; when the material comes into contact with high-temperature hot oil, the rigid framework effectively resists thermal softening, providing structural support for the material. Simultaneously, the addition of a nucleating agent significantly improves the crystallinity of polypropylene, resulting in a more regular and dense molecular chain arrangement. The synergistic effect of these two factors raises the material's heat distortion temperature from 95℃ for ordinary impact-resistant copolymer polypropylene to 110-120℃, making the material sufficient to withstand boiling oil (100-120℃) environments. Furthermore, the physical binding effect of the fillers restricts the thermal movement and swelling tendency of the polypropylene molecular chains in the hot oil medium, ensuring the material maintains dimensional stability even after prolonged contact with hot oil, avoiding problems such as deformation and leakage caused by swelling. Secondly, the toughening agent specifically selected in this invention can form a chemical barrier in the system that is different from the rigid skeleton mentioned above. This invention has found that using a specific toughening agent can introduce polar functional groups into the polypropylene molecular structure and fundamentally change the surface and interface properties of the material. According to the principle of "like dissolves like", non-polar hot oil molecules lack affinity with polar surfaces and are difficult to penetrate, wet or corrode the material. These polar groups build an effective "chemical barrier" inside and on the surface of the material, delaying the adsorption, penetration and diffusion of oil, so that the material can maintain its physical properties and structural integrity when in contact with hot oil. Meanwhile, this invention, by introducing an oil-resistant additive, can further form an oleophobic surface layer in the system. During melt blending, the oil-resistant additive spontaneously migrates to the material surface and forms a dense, low-surface-energy coating after injection molding, further blocking the penetration of oil molecules into the material's interior. This creates a complementary and synergistic effect with the aforementioned rigid framework and chemical barrier. Furthermore, the addition of the oil-resistant additive fundamentally alters the interfacial tension between the material surface and the oil medium, increasing the oil contact angle from less than 10° (almost complete wetting) in ordinary polypropylene to greater than 10°, achieving a transformation from "oleophilic" to "oleophobic." Therefore, hot oil on the food container surface can bead up and roll off rather than spread and wet, significantly reducing oil adhesion and further improving heat-resistant oil properties. Since the addition of inorganic fillers often negatively impacts surface smoothness, this invention ensures this by controlling their uniformity within the system. By adding a dispersant and preferentially coating the filler surface during preparation, the agglomeration of inorganic fillers in the system can be greatly avoided, thereby reducing their impact on surface smoothness.

[0007] Furthermore, the toughening agent is an ethylene-butyl acrylate-glycidyl methacrylate copolymer. The ethylene-butyl acrylate-glycidyl methacrylate copolymer (PTW) possesses a unique "reactive toughening" mechanism and a "triple functional synergy" effect in the system of this invention. From a molecular structure perspective, PTW provides basic compatibility with the polypropylene matrix through ethylene units, polar ester units to construct an oil-resistant chemical barrier, and highly reactive epoxy groups through glycidyl methacrylate units, enabling it to form strong chemical bonds with the polypropylene matrix and the surface of inorganic fillers. Compared to ethylene-methacrylate copolymer (EMA), PTW achieves this through chemical anchoring. Instead of physical entanglement and bonding with the matrix, PTW improves impact strength with less sacrifice in rigidity and heat resistance. Furthermore, the significantly enhanced reactivity of the epoxy groups on the filler surface strengthens the filler-matrix interfacial bond, avoiding the high-temperature migration and insufficient long-term stability defects of EMA. Compared to maleic anhydride-grafted polyolefin elastomers (POE-g-MAH), PTW's functional groups are uniformly distributed throughout the molecular chain through copolymerization, rather than being introduced later through grafting. Therefore, the reaction sites are more uniformly distributed, resulting in superior thermal stability. Simultaneously, the dual polarity of the ester and epoxy groups contributes to its outstanding heat-resistant oil performance. Thus, using PTW achieves optimal rigidity-toughness balance through reactive toughening, ensures excellent long-term heat-resistant oil performance through dual polarity barriers and chemical anchoring effects, and further enhances overall performance through interfacial reactions with the filler.

[0008] Furthermore, the copolymer polypropylene is either impact-resistant copolymer polypropylene or random copolymer polypropylene. Impact-resistant copolymer polypropylene is preferred. To simultaneously improve heat oil resistance and impact resistance, this invention constructs a multi-stage energy dissipation mechanism through the selection and formulation of specific toughening agents. By selecting the impact-resistant copolymer polypropylene, due to its inherent "island structure," the rubber phase can induce crazing to absorb impact energy. The addition of toughening agents further optimizes this structure. Specific toughening agents form chemical bonds through reactive toughening, avoiding the "toughening but reducing stiffness" defect of traditional toughening agents, and further improving impact resistance.

[0009] Furthermore, the melt index of the copolymerized polypropylene is 15-25 g / 10min, such as 15, 16, 20, 22, 24, or 25 g / 10min, and the test standard is ASTM D1238, with test conditions of 230℃ and 2.16 kg. In this invention, controlling the melt index within the range of 15-25 g / 10min allows the composition to achieve an optimal balance between processing fluidity, mechanical properties, and product quality. Firstly, the melt has sufficient flow length to quickly fill thin-walled and complex-structured container cavities, ensuring uniform dispersion of inorganic fillers and toughening agents and preventing surface pitting. Controlling the melt index within 15-25 g / 10min also ensures sufficient basic toughness of the matrix. Through synergy with nucleating agents, the heat distortion temperature of the composition can be significantly increased, meeting the requirements for boiling oil resistance. Simultaneously, it ensures that the composition does not easily migrate or precipitate during long-term contact with high-temperature hot oil, ensuring long-term stability. If the melt flow index is too low, the high viscosity will make it difficult to fill during injection molding, easily causing short shots and flow marks, which in turn leads to poor filler dispersion and surface pitting. At the same time, it will hinder the uniform dispersion of toughening agent in the system, resulting in a decrease in toughening effect. If the melt flow index is too high, it will significantly reduce the toughness and impact strength of the matrix. It will also be easy to migrate and precipitate in high-temperature hot oil, weakening the heat-resistant oil performance and forming a hazy surface or precipitates on the surface, affecting food safety and appearance quality.

[0010] Furthermore, the mass ratio of the copolymerized polypropylene to the inorganic filler is (2.5-5):1. Controlling the mass ratio of copolymerized polypropylene to inorganic filler within this range enables deep synergy between the matrix and the filler. Firstly, the "island structure" of the polypropylene matrix and the rigid network of the filler can form an ideal interpenetrating structure: the rubber phase provides elastic buffering for the filler network, preventing it from becoming brittle under load; the filler network provides rigid support for the rubber phase, allowing it to fully shear and yield upon impact. This "rigid-flexible interlocking" mechanism achieves effective stress transfer and dissipation at the multiphase interface, significantly improving impact strength and heat distortion temperature. If the mass ratio is lower than 2.5:1, the matrix continuity is easily reduced, making the filler more prone to agglomeration and forming rapid crack propagation channels, thus reducing impact strength and surface smoothness. If the mass ratio is higher than 5:1, it is difficult to form a rigid network between the matrix and the filler, lacking crack deflection and bridging effects, resulting in a decrease in heat distortion temperature, reduced resistance to boiling oil, and a "tough but not rigid" state in the material, with insufficient heat oil resistance.

[0011] Furthermore, the inorganic filler is any one or more of needle-shaped wollastonite, flake-shaped talc powder, or silica microspheres. Traditional spherical fillers such as alumina, due to their isotropic morphology, weak interfacial bonding, and lack of synergistic mechanisms, are difficult to achieve synergistic improvements in multiple properties, including rigidity-toughness balance, surface quality, and heat-resistant oil performance. However, the specific inorganic filler used in this invention can form a multi-dimensional synergistic effect with the polypropylene matrix, toughening agent, nucleating agent, and dispersant.

[0012] Furthermore, the inorganic filler is flake-shaped talc. In the system of this invention, flake-shaped talc can simultaneously improve the surface smoothness, oil barrier effect, and processability of the composition, while also reducing production costs. Regarding surface smoothness, its two-dimensional flakes are oriented parallel to the surface of the product during injection molding, forming a smooth and flat microstructure, with high process robustness and low susceptibility to orientation lines. Furthermore, because its flake surface is easily and uniformly coated by dispersants, it can stably control the agglomerate size at an extremely low level, eliminating pitting defects from the source. Regarding oil barrier effect, the stacking of talc flakes can form a highly efficient "maze effect," greatly extending the penetration path of oil molecules and significantly increasing the barrier efficiency. Simultaneously, its flake structure can form a three-dimensional synergistic effect with surface oil-resistant additives.

[0013] Furthermore, the flake diameter of the talc powder is 2-5 μm. Controlling the flake diameter of the talc powder within the range of 2-5 μm is key to achieving synergistic optimization of surface smoothness, heat oil resistance, and impact strength. Regarding surface smoothness, 2-5 μm is just below the human eye's resolution threshold, allowing for parallel orientation to form a continuous smooth layer during injection molding. If the flake diameter is too large, visible pitting will form on the surface; if the flake diameter is too small, discontinuous orientation layers will lead to a decrease in gloss. Regarding oil barrier properties, controlling the flake diameter within this range allows the flakes to form a dense "brick wall structure," maximizing the labyrinth effect and significantly increasing the heat distortion temperature. If the flake diameter is too large, the increased gaps between the flakes can easily form penetration channels; if the flake diameter is too small, insufficient flake area makes effective stacking difficult, both of which reduce barrier efficiency. Regarding impact strength, since the flake diameter of 2-5 μm falls within the optimal window for toughening rigid particles, it can significantly improve impact strength by inducing local plastic deformation and crack deflection. When the flake diameter is too large, the particles are prone to becoming crack initiators, thus reducing impact strength. When the flake diameter is too small, brittle fracture is easily induced due to stress field superposition, resulting in a weak toughening effect. In terms of processing and dispersibility, a flake diameter of 2-5 μm has a moderate specific surface area, allowing for effective coating of the dispersant and good melt flowability. When the flake diameter is too small, the specific surface area increases dramatically, leading to agglomeration. When the flake diameter is too large, the movement resistance is high, leading to sedimentation. Both of these result in uneven dispersion and processing difficulties.

[0014] Furthermore, it also includes 0.1-0.3 parts by weight of antioxidant.

[0015] The present invention also provides a method for preparing the polypropylene composition, comprising the following steps: S1. Raw material pretreatment and premixing: Inorganic filler and dispersant are weighed according to weight and added to a high-speed mixer. Mixing is carried out at 800-1200 rpm for 3-5 minutes at room temperature to form pre-activated filler. The pre-activated filler is then mixed evenly with the other components weighed according to weight to obtain a mixture. In this invention, the dispersant preferentially coats the filler surface, eliminating agglomeration and reducing interfacial tension, laying the foundation for subsequent uniform compounding with the polypropylene matrix. Without pre-dispersion, the filler will agglomerate in the system, with agglomerate sizes exceeding 5 mm. μm, which leads to visible pitting and white spots on the surface of the product, severely deteriorating the surface quality. Filler agglomerates also easily increase melt flow resistance, reducing processing stability and aggravating equipment wear, ultimately resulting in large performance fluctuations between product batches, making it difficult to control stably. At the same time, the co-mixing of components can cause the dispersant to be captured by the toughening agent or matrix, making it difficult to effectively coat the filler. This leads to a weakening of the interfacial bond between the filler and the matrix, a decrease in impact strength, and failure of the rigid particle toughening mechanism. More importantly, uneven distribution of fillers in the system will prevent the formation of an effective three-dimensional rigid network or labyrinth effect, which will significantly reduce the heat distortion temperature and heat-resistant oil performance. S2. The mixed material is added to a twin-screw extruder for melt blending and extrusion granulation, and then dried to obtain the polypropylene composition.

[0016] Furthermore, the length-to-diameter ratio of the extrusion screw is (40-48):1, the extruder temperature is 80-120℃ in zone 1, 210-240℃ in zones 2-5, and 220-245℃ in zones 6-8, and the screw speed of the twin-screw extruder is 300-400 r / min.

[0017] The present invention also provides the use of the polypropylene composition in the preparation of food containers, particularly in the preparation of disposable containers resistant to heat oil.

[0018] In summary, compared with the prior art, the present invention achieves the following technical effects: (1) The polypropylene composition provided by the present invention improves the heat resistance of oil by means of a triple protection system, which enhances the rigidity of the body, chemical polarity barrier and surface oleophobic modification, and complements each other to ensure that the food container maintains shape stability, structural integrity and surface cleanliness when holding hot oily food.

[0019] (2) The polypropylene composition provided by the present invention achieves synergistic effect of function through formulation. By controlling the entire scale from molecular polarity, microstructure to surface morphology, a polypropylene composition system with excellent heat oil resistance, high impact strength and good surface smoothness is successfully constructed.

[0020] (3) The polypropylene composition provided by the present invention has a simple process and is suitable for large-scale production. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0022] Example The present invention will be further illustrated below with reference to specific embodiments and comparative embodiments. The following specific embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the following embodiments, and are not in particular limited to the types of raw materials used in the following specific embodiments.

[0023] I. The sources of raw materials for the examples and comparative examples are as follows: Copolymer polypropylene #1: PP, grade RD208CF, melt index 8 g / 10min, Borouge; Copolymer polypropylene #2: PP, grade EP18-1, melt index 18 g / 10min, LyondellBasell; Copolymer polypropylene #3: PP, grade PP 310MK10, melt index 25 g / 10min, SABIC; Copolymer polypropylene #4: PP, grade C700-35N, melt index 35 g / 10min, Dow Chemical, USA; Toughening agent #1: PTW, ethylene-butyl acrylate-glycidyl methacrylate terpolymer, brand name Elvaloy PTW, DuPont, USA; Toughening agent #2: POE-g-MAH, maleic anhydride grafted polyolefin elastomer, grade MD715, Mitsui Chemicals, Japan; Toughening agent #3: EMA, ethylene-methyl acrylate copolymer, grade 1224 AC, DuPont; Toughening agent #4: EPR, ethylene-propylene copolymer, grade EPR EP57F, JSR Japan; Inorganic filler #1: Flaky talc powder, brand name U-TALC B-4, flask diameter 4 μm, Jiangsu Youtuoke; Inorganic filler #2: Flaky talc powder, grade JS06-A3, flaky diameter 6 μm, Changxing Huayu; Inorganic filler #3: needle-shaped wollastonite, ultrafine needle-shaped wollastonite series, with an equivalent particle size of 4 μm, Hubei Fengjiashan silicon fiber; Inorganic filler #4: Silica microparticles, silica powder, with a particle size of 4 μm, manufactured by Saint Ans Technology (Dongguan). Oil-resistant additive: Fluorosilicone-modified polysiloxane, commercially available; the same substance was used in parallel experiments. Dispersant: Calcium stearate, commercially available; the same substance was used in parallel experiments. Nucleating agent: α-crystal nucleating agent, commercially available; the same substance was used in parallel experiments.

[0024] The preparation method of the polypropylene compositions of the present invention and Comparative Examples 1-4 includes the following steps: S1. Raw material pretreatment and premixing: Weigh the inorganic filler and dispersant according to the weight parts and put them into a high-speed mixer. Mix them at room temperature at a speed of 800-1200 rpm for 3-5 minutes to form a pre-activated filler. Mix the pre-activated filler with the other components weighed according to the weight parts evenly to obtain a mixture. S2. The mixed material is added to a twin-screw extruder for melt blending and extrusion granulation, and then dried to obtain the polypropylene composition; The length-to-diameter ratio of the extrusion screw is (40-48):1, the extruder temperature is 80-120℃ in zone 1, 210-240℃ in zones 2-5, and 220-245℃ in zones 6-8, and the screw speed of the twin-screw extruder is 300-400 r / min. The method for preparing the polypropylene composition of Comparative Example 5 of the present invention includes the following steps: S1. Raw material premixing: Weigh each component according to the weight parts and mix them evenly to obtain a mixture; S2. The mixed material is added to a twin-screw extruder for melt blending and extrusion granulation, and then dried to obtain the polypropylene composition; The length-to-diameter ratio of the extrusion screw is (40-48):1, the extruder temperature is 80-120℃ in zone 1, 210-240℃ in zones 2-5, and 220-245℃ in zones 6-8, and the screw speed of the twin-screw extruder is 300-400 r / min.

[0025] II. Performance Testing Methods (1) Heat distortion temperature test: Tested in accordance with GB / T 1634.2-2019.

[0026] (2) Heat resistance oil performance test: The test was conducted in accordance with the ISO 1817 standard. The test conditions were immersion in edible oil at 120°C for 2 hours and the dimensional change rate was tested.

[0027] (3) Impact resistance test: The test shall be conducted in accordance with the ASTM D256 standard.

[0028] (4) Surface smoothness performance test: The test shall be conducted in accordance with the standard of ISO 15796 and visually inspected under the D65 standard light source.

[0029] Table 1. Technical solutions and effects of the embodiments and comparative examples (unit: parts by weight)

[0030] Table 1 (Continued) Examples and Comparative Examples: Technical Solutions and Effects (Unit: Parts by Weight)

[0031] Examples 1-13 simultaneously introduce specific formulations of this invention, including copolymerized polypropylene, specific toughening agents, inorganic fillers, oil-resistant additives, dispersants, and nucleating agents. All polypropylene compositions prepared in Examples 1-13 can simultaneously ensure excellent heat-oil resistance, high impact strength, and good surface smoothness, and achieve a balance between heat-oil resistance and impact resistance. Through a multi-level synergistic molecular design of "rigid skeleton-chemical barrier-oleophobic layer," this invention, for the first time, simultaneously achieves high heat-oil resistance, high impact resistance, and excellent surface smoothness in a polypropylene matrix, which are difficult to achieve simultaneously in existing technologies. Furthermore, by constructing a three-dimensional rigid network with inorganic fillers preferentially coated with dispersants, building a chemical oil-resistant barrier with the polar functional groups of toughening agents, forming a low surface energy oleophobic coating on the surface with oil-resistant additives, and refining spherulites with nucleating agents to improve crystallinity, the components function in a functional zone and work synergistically at the microscopic level, thereby producing a polypropylene composition with excellent comprehensive performance indicators, which can perfectly meet the demanding requirements of high-end disposable lunch boxes, heat-resistant tableware and food packaging.

[0032] Comparative Examples 1-5 were all compared with Example 1. In Comparative Example 1, the mass ratio of copolymer polypropylene to inorganic filler was too low, i.e., the amount of inorganic filler added was too high. This caused the continuity of the polypropylene matrix to be disrupted. Excessive filler particles came into contact with each other and even agglomerated, forming continuous rigid agglomerates. This prevented the matrix from forming an effective stress transfer network. Under impact, these agglomerates became channels for rapid crack propagation, and the material exhibited brittle fracture characteristics. The notched impact strength of the cantilever beam decreased significantly. At the same time, the excessive filler made it difficult for the dispersant to completely coat all the filler surfaces, and the filler agglomerate size exceeded 5 mm. The human eye's resolution threshold of μm results in noticeable pitting and white spots on the injection-molded part surface, significantly reducing surface gloss. Furthermore, while excessive filler improves rigidity to some extent, the disruption of matrix continuity limits the increase in heat distortion temperature. The material is also more prone to cracking due to interface defects after hot oil immersion, and its heat resistance does not improve with increased filler content but rather declines. In Comparative Example 2, the mass ratio of copolymer polypropylene to inorganic filler is too high, indicating insufficient inorganic filler. This makes it difficult to form a continuous and effective three-dimensional rigid network within the polypropylene matrix, resulting in isolated and dispersed filler particles. Lacking a rigid framework, the material's heat distortion temperature increase is limited, typically reaching only 100-105℃, making it unable to withstand boiling oil environments. After hot oil immersion, the dimensional change rate increases significantly, and its heat resistance fails to meet standards. Additionally, the short penetration path of oil molecules in the filler weakens the barrier effect. Furthermore, insufficient filler prevents the rigid particle toughening mechanism from functioning effectively. Although the material exhibits good impact toughness due to elastomer toughening, its rigidity is insufficient, making the food container prone to bending after being filled with food. The material exhibits good surface quality but suffers from reduced heat resistance, a key performance indicator, making it unsuitable for the practical use of disposable lunch boxes. Comparative Example 3 uses a common toughening agent, EPR, instead of the specific PTW toughening agent of this invention. Ethylene-propylene copolymers are non-polar elastomers, lacking polar functional groups such as ester, epoxy, or anhydride groups in their molecular structure. According to the principle of "like dissolves like," non-polar hot oil molecules have a high affinity for non-polar EPR, easily penetrating and swelling the EPR phase, leading to a significant decrease in the material's heat resistance. Furthermore, EPR cannot form an effective interfacial bond with the specific inorganic filler of this invention, resulting in low stress transfer efficiency between the filler and the matrix. The rigid particle toughening mechanism cannot be fully utilized. Although EPR significantly improves impact strength, this comes at the cost of sacrificing rigidity and heat distortion temperature. The addition of EPR also significantly reduces the heat distortion temperature. Therefore, while Comparative Example 3 has high impact strength, its heat resistance is severely insufficient, and its surface quality is also affected, failing to achieve a balance among the three factors.In Comparative Example 4, the absence of a dispersant resulted in the inorganic filler failing to be effectively coated and dispersed in the system. The filler existed in the form of agglomerates within the polypropylene matrix, with agglomerate sizes typically exceeding 10 μm, far exceeding the human visual resolution threshold of 5 μm. This led to the formation of noticeable pitting and white spots on the surface of the injection-molded parts, severely deteriorating surface quality. Furthermore, these filler agglomerates became stress concentration points, serving as pathways for preferential crack initiation and propagation upon impact, significantly reducing the notched impact strength of the cantilever beam. Simultaneously, the lack of a dispersant in the system of this invention also weakened the interfacial bonding between the filler and the polypropylene matrix, resulting in numerous voids at the interface that could not effectively transfer stress. The rigid particle toughening mechanism failed. Regarding heat-resistant oil performance, uneven filler dispersion prevented the formation of an effective three-dimensional rigid network and labyrinth effect, leading to a decrease in heat distortion temperature and allowing oil molecules to... As the heat-resistant oil penetrates along the interfacial voids between the filler agglomerates and the matrix, its dimensional change rate increases. As a result, Comparative Example 4 shows significant deterioration in surface quality, impact strength, and heat-resistant oil performance. Although a dispersant was added in Comparative Example 5, no pre-dispersion treatment was performed. Instead, all components were mixed at once. During this process, the dispersant simultaneously contacts the filler, toughening agent, and polypropylene matrix. Some of the dispersant is captured by the toughening agent or the matrix and cannot preferentially coat the filler surface, resulting in insufficient coating of the filler surface. The filler remains in the form of agglomerates. The consequences of this process defect are similar to those of Comparative Example 4, but to a slightly lesser degree. This leads to filler agglomerates exceeding 5 μm in size, forming pits and white spots on the surface, weakening the bond between the filler and matrix, reducing impact strength, incomplete rigid network, and deteriorating heat oil resistance. Therefore, the pre-dispersion process in this invention is a crucial technical means to ensure the dispersant preferentially coats the filler surface and achieves uniform filler dispersion, and is as important as the addition of the dispersant. Without a pre-dispersion step, even if the formulation contains a dispersant, it is difficult to fully exert its effect and achieve a synergistic improvement in heat oil resistance, impact resistance, and surface smoothness. Therefore, the above comparative examples cannot guarantee a balance among the various properties of the polypropylene composition, and cannot simultaneously achieve heat oil resistance, impact resistance, and surface smoothness.

[0033] Based on the test data in Table 1 regarding heat distortion temperature, heat-resistant oil dimensional change rate, cantilever beam notched impact strength, and surface defects, the polypropylene compositions prepared through Examples 1-13 have significant advantages over the comparative examples and can effectively meet the high standards required by customers and the market for disposable lunch boxes.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat-resistant, oil-resistant, impact-resistant polypropylene composition, characterized in that, By weight, it includes the following components: 50-70 parts of copolymerized polypropylene; 15-25 parts toughening agent; 15-25 parts of inorganic filler; 1-3 parts of oil-resistant additive; Dispersant 0.5-1 part; Nucleating agent 0.1-0.3 parts; The toughening agent is any one of ethylene-methacrylate copolymer, ethylene-butyl acrylate-glycidyl methacrylate copolymer, or maleic anhydride-grafted polyolefin elastomer.

2. The polypropylene composition according to claim 1, characterized in that, The copolymer polypropylene is either impact copolymer polypropylene or random copolymer polypropylene.

3. The polypropylene composition according to claim 1, characterized in that, The melt index of the copolymerized polypropylene is 15-25 g / 10min.

4. The polypropylene composition according to claim 1, characterized in that, The mass ratio of the copolymerized polypropylene to the inorganic filler is (2.5-5):

1.

5. The polypropylene composition according to claim 1, characterized in that, The inorganic filler is any one or more of acicular wollastonite, flaky talc powder, or silica microspheres.

6. The polypropylene composition according to claim 5, characterized in that, The flaky talc powder has a flake diameter of 2-5 μm.

7. The polypropylene composition according to claim 1, characterized in that, It also includes 0.1-0.3 parts by weight of antioxidants.

8. A method for preparing the polypropylene composition according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Raw material pretreatment and premixing: Weigh the inorganic filler and dispersant according to the weight parts and put them into a high-speed mixer. Mix them at room temperature at a speed of 800-1200 rpm for 3-5 minutes to form a pre-activated filler. Mix the pre-activated filler with the other components weighed according to the weight parts evenly to obtain a mixture. S2. The mixed material is added to a twin-screw extruder for melt blending and extrusion granulation, and then dried to obtain the polypropylene composition.

9. The method for preparing the polypropylene composition according to claim 8, characterized in that, The length-to-diameter ratio of the extrusion screw is (40-48):1, the extruder temperature is 80-120℃ in zone 1, 210-240℃ in zones 2-5, and 220-245℃ in zones 6-8, and the screw speed of the twin-screw extruder is 300-400 r / min.

10. The use of the polypropylene composition according to any one of claims 1-7 in the preparation of food containers.

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