Polypropylene composite material for automobile tail door supporting rod sleeve and preparation method of polypropylene composite material

Abstract

The invention belongs to the technical field of polymer composite materials, and particularly relates to a polypropylene composite material for an automobile tail door supporting rod sleeve and a preparation method of the polypropylene composite material. The preparation method comprises the following steps: respectively adding a first raw material and a second raw material into a double-screw extruder from a main feeding port and a side feeding port, extruding and granulating, and carrying out injection molding to obtain the polypropylene composite material, the double-screw extruder is provided with a shearing block and a reverse shearing thread block; the total mass part of the first raw material and the second raw material is 100 parts; wherein the first raw material comprises the following components in parts by mass: 0.5-5 parts of an antioxidant, 3-5 parts of a compatilizer, 0.5-1 part of a lubricant and 5-20 parts of nano silicon dioxide, and the lubricant comprises an inner lubricant and an outer lubricant; the second raw material comprises the following components in parts by mass: 10-30 parts of chopped glass fibers; and the balance of polypropylene. The polypropylene composite material prepared by the preparation method has the characteristics of low surface friction coefficient, high rigidity, creep resistance and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer composites, and particularly relates to a polypropylene composite material for a tailgate stay rod sleeve of an automobile and a preparation method thereof. BACKGROUND

[0002] Fiber-reinforced polypropylene composites have become the core choice for replacing engineering plastics and metal materials due to their light weight, high strength, excellent rigidity, good impact resistance, outstanding low-temperature stability, and high dimensional accuracy. They are widely used in structural parts such as instrument panels, all-plastic tailgates, and front engine compartment covers, especially in the trend of automobile lightweight development. Fiber-reinforced polypropylene composites are one of the key materials for realizing "plastic instead of steel" and energy saving and low carbon. However, special functional parts of automobiles such as tailgate stay rod sleeves not only need to meet the requirements of high strength mechanical properties and long-term creep resistance, but also need to meet strict standards for dimensional stability and sliding noise control (i.e., low surface friction coefficient). Traditional fiber-reinforced polypropylene materials cannot simultaneously meet the above multi-dimensional performance requirements, and there is an urgent need to develop new composite materials suitable for such high-end application scenarios.

[0003] Among the existing methods for reducing the friction coefficient of plastics, adding lubricants is the most economical and efficient means. However, traditional lubricants have the problems of high-temperature volatilization, uncontrollable migration process leading to the decay of lubrication effect over time, and limited compatibility with the polypropylene matrix, which can easily affect the mechanical properties and appearance quality of the material. Other methods such as surface coating treatment or blending modification have the defects of complex process, high cost, etc. In addition, although existing patent technologies have made breakthroughs in performance optimization (such as long glass fiber reinforced polypropylene improving creep resistance), the long glass fiber processing needs to use the melt impregnation method, which has high process complexity and production cost, and is not conducive to large-scale application. Some low-friction coefficient materials need to prepare functional microcapsules, which have complex process and are difficult to industrialize, and cannot meet the dual demands of cost and efficiency in the automobile industry.

[0004] Currently, there is an urgent need for a short fiber-reinforced polypropylene composite material that meets the requirements of cost advantage and multi-performance (low surface friction coefficient, high rigidity, and creep resistance). However, existing technologies either cannot simultaneously meet the above performance indicators, or have complex processes and high costs, making it difficult to achieve industrialized mass production. SUMMARY

[0005] Therefore, based on the application scenarios of special parts such as tailgate stay rod sleeves of automobiles, the present application develops a new short fiber-reinforced polypropylene composite material with excellent performance and controllable cost through polypropylene material formula modification and process optimization, effectively solving the performance shortcomings and process limitations of traditional materials, and having important significance for promoting the application of fiber-reinforced polypropylene materials in high-end fields of the automobile industry.

[0006] In order to achieve the above-mentioned purposes, the present application can adopt the following technical solutions: This invention provides a method for preparing a polypropylene composite material for an automobile tailgate strut sleeve. The method includes: feeding a first raw material and a second raw material into a twin-screw extruder through a main feed port and a side feed port, respectively, for extrusion granulation, followed by injection molding to obtain the polypropylene composite material for the automobile tailgate strut sleeve; the twin-screw extruder is equipped with a shear block and a reverse shear screw block; the total mass fraction of the first and second raw materials is 100 parts; wherein, the first raw material, by mass fraction, includes 0.5 to 5 parts of antioxidant, 3 to 5 parts of compatibilizer, 0.5 to 1 part of lubricant, and 5 to 20 parts of nano-silica, the lubricant including internal lubricant and external lubricant; the second raw material, by mass fraction, includes 10 to 30 parts of chopped glass fiber; the remainder is polypropylene.

[0007] Preferably, in the above preparation method, the antioxidant is selected from one or more combinations of hindered phenols, phosphites, or amines; and / or the compatibilizer is selected from one or more combinations of maleic anhydride and its derivatives, epoxy compounds, carboxylic acids, and glycidyl acrylates; and / or the internal lubricant and external lubricant are each independently selected from one or more of metal soaps, hydrocarbon waxes, fatty acids, organosilicon compounds, or fluorine-containing compounds; and / or the size of the nano-silica is 50 nm to 500 nm; and / or the fiber diameter of the chopped glass fiber is 5 μm to 20 μm; and / or the melt flow rate of polypropylene at 230 °C and 2.16 kg test conditions is (10 g to 80 g) / 10 min.

[0008] More preferably, in the above preparation method, the antioxidant is selected from one or more combinations of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite, 2,6-di-tert-butyl-4-methylphenol, and bis(3,5-di-tert-butyl-4-hydroxyphenyl) sulfide; and / or the melt flow rate of the compatibilizer is (0.05 g to 1000 g) / 10 min, and the grafting rate is 0.05% to 3%; and / or the internal lubricant and external lubricant are each independently selected from stearates in metal soaps; and / or the size of the nano silica is 100 nm to 300 nm; and / or the chopped glass fibers are surface treated, and the content of the sizing agent in the surface treatment is 2% to 10%.

[0009] More preferably, in the above preparation method, the antioxidant is a combination of antioxidant 1010 and antioxidant 168, with a mass ratio of antioxidant 1010 to antioxidant 168 of 3:2; and / or the compatibilizer is grafted polypropylene, with a melt flow rate of (100g to 800g) / 10min and a grafting rate of 0.5% to 3%; and / or the internal lubricant is selected from zinc stearate and / or calcium stearate, and the external lubricant is selected from magnesium stearate and / or paraffin wax.

[0010] More preferably, in the above preparation method, the mass ratio of the internal lubricant to the external lubricant is 2:3.

[0011] Preferably, in the above preparation method, the first raw material, by mass parts, includes 0.5 to 5 parts of antioxidant, 3 to 5 parts of compatibilizer, 0.5 to 1 part of lubricant and 10 parts of nano-silica, and the lubricant includes internal lubricant and external lubricant; the second raw material, by mass parts, includes 20 parts of chopped glass fiber.

[0012] Preferably, in the above preparation method, the first raw material further includes color masterbatch, and the amount of color masterbatch added is 0.5 parts to 1.5 parts.

[0013] Preferably, in the above preparation method, the misalignment angle between the shear blocks is 30° to 90°.

[0014] Preferably, in the above preparation method, the melt blending temperature of the twin-screw extruder is 200℃~250℃, the vacuum degree is -0.1MPa~0MPa, and the rotation speed is 50rpm~150rpm.

[0015] Another aspect of the present invention provides a polypropylene composite material for automobile tailgate strut sleeves, which is prepared by the above-described preparation method.

[0016] The beneficial effects of this invention include at least the following: By combining processing extrusion equipment with optimized process technology, this invention effectively solves the problem of poor interfacial compatibility caused by poor dispersion of nano-silica in a polypropylene matrix. Furthermore, the synergistic effect of different filler compounding reduces the surface friction coefficient of the polypropylene composite material, while simultaneously improving its poor mechanical properties and creep resistance. Considering overall cost advantages, this invention produces a high-performance chopped glass fiber reinforced polypropylene composite material with low surface friction coefficient, high rigidity, and good creep resistance. Specifically, this polypropylene composite material for automotive tailgate strut sleeves possesses the following properties: flexural modulus > 6500 MPa, tensile strength > 90 MPa, tensile creep strain rate ≤ 2.5%, and surface friction coefficient ≤ 0.35. Attached Figure Description

[0017] Figure 1 This is a schematic diagram showing the state of polypropylene, chopped glass fiber (SGF), and nano-silica (nano-inorganic filler) before and after treatment by the present invention. Detailed Implementation

[0018] The embodiments described are provided to better illustrate the present invention, but are not intended to limit the scope of the invention to the embodiments described. Therefore, non-essential improvements and adjustments made to the embodiments by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0019] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. Singular expressions include plural expressions unless they have a distinct meaning in the context. As used herein, it should be understood that terms such as “comprising,” “having,” “including,” are intended to indicate the presence of features, numbers, operations, components, parts, elements, materials, or combinations thereof. The terminology of the invention is disclosed in the specification and is not intended to exclude the possibility that one or more other features, numbers, operations, components, parts, elements, materials, or combinations thereof may be present or added. As used herein, “ / ” may be interpreted as “and” or “or,” depending on the context.

[0020] In a first aspect, embodiments of the present invention provide a method for preparing a polypropylene composite material for an automobile tailgate strut sleeve. The method includes: feeding a first raw material and a second raw material into a twin-screw extruder through a main feed port and a side feed port, respectively, for extrusion granulation, followed by injection molding to obtain the polypropylene composite material for the automobile tailgate strut sleeve; the twin-screw extruder is equipped with a shear block and a reverse shear thread block; the total mass fraction of the first raw material and the second raw material is 100 parts; wherein, the first raw material, by mass fraction, includes 0.5 to 5 parts of antioxidant, 3 to 5 parts of compatibilizer, 0.5 to 1 part of lubricant, and 5 to 20 parts of nano-silica, the lubricant including internal lubricant and external lubricant; the second raw material, by mass fraction, includes 10 to 30 parts of chopped glass fiber; the remainder is polypropylene.

[0021] It should be noted that, to ensure the length of the glass fibers in the composite material after mixing and shearing in the twin-screw extruder, short-cut glass fibers are fed into the twin-screw extruder via side feeding. Furthermore, the arrangement of the extruder screws is optimized to reduce shear damage to the fibers during the material extrusion process. Simultaneously, to mitigate the reduced shear strength caused by screw arrangement adjustments, the mixing performance of fillers of different dimensions with the polypropylene matrix is ​​further enhanced. In addition, a set of shear blocks and reverse shear screw blocks are introduced into the twin-screw extruder components, which effectively solves the problem of fiber retention length in the material while also ensuring the dispersion and bonding of nano-silica within the polypropylene matrix. Specifically, the direct side-feeding method for chopped glass fibers aims to reduce the shearing force on the glass fibers during twin-screw extrusion, increasing the retained length of the glass fibers in the modified material. This ensures the high rigidity and mechanical strength of the short glass fiber reinforced polypropylene material, as well as its uniform mixing with the polypropylene matrix. Furthermore, a reverse shearing module is introduced into the twin-screw extruder to feed polypropylene, nano-inorganic fillers, and processing aids from the main feed, ensuring the nano-fillers are fully and uniformly dispersed within the polypropylene matrix. Therefore, by combining main and side feeding methods and simultaneously introducing a reverse shearing module to enhance the dispersion of nano-fillers, the glass fibers, nano-fillers, and polypropylene melt are thoroughly and uniformly mixed without affecting the retained length of the glass fibers. This improves the compatibility between the glass fibers, nano-fillers, and polypropylene resin, ensuring a low coefficient of surface friction and enhancing the mechanical and creep resistance properties of the composite material.

[0022] In some specific examples, the antioxidants in the above preparation methods are selected from one or more of hindered phenols, phosphites, or amines.

[0023] It should be noted that the antioxidants used in this invention are known in the art, including but not limited to one or more of the above-mentioned phenolic, phosphite, or amine antioxidants. Based on this, the antioxidants used in this invention can be further preferably one or more combinations of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite, 2,6-di-tert-butyl-4-methylphenol, and bis(3,5-di-tert-butyl-4-hydroxyphenyl) sulfide.

[0024] In some specific examples, in the above preparation method, the antioxidant is a combination of antioxidant 1010 and antioxidant 168, with a mass ratio of antioxidant 1010 to antioxidant 168 of 3:2.

[0025] It should be noted that the antioxidant in this invention can be further preferably a combination of antioxidant 1010 and antioxidant 168, and the mass ratio can be 3:2. Based on this antioxidant and mass ratio, the prepared polypropylene composite material for automobile tailgate strut sleeve has better mechanical and lubrication properties.

[0026] In some specific examples, in the above preparation method, the compatibilizer is selected from one or more combinations of maleic anhydride and its derivatives, epoxy compounds, carboxylic acids, and glycidyl acrylate.

[0027] It should be noted that the compatibilizers used in this invention are known in the art, and the compatibilizers used in this invention include, but are not limited to, the compatibilizers listed above.

[0028] In some specific examples, in the above preparation method, the melt flow rate of the compatibilizer is (0.05g~1000g) / 10min, and the grafting rate is 0.05%~3%.

[0029] It should be noted that the compatibilizer in this invention can be further preferably one or more combinations of maleic anhydride and its derivatives, epoxy compounds, carboxylic acids, and glycidyl acrylate that meet the above conditions, i.e., the melt flow rate is (0.05g~1000g) / 10min, such as 100g / 10min, 200g / 10min, 300g / 10min, 400g / 10min, 500g / 10min, 600g / 10min, 700g / 10min, 800g / 10min, or 900g / 10min; the grafting rate is 0.05%~3%, such as 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, or 2.5%.

[0030] In some specific examples, in the above preparation method, the compatibilizer is a grafted polypropylene, the melt flow rate is (100g~800g) / 10min, and the grafting rate is 0.5%~3%.

[0031] It should be noted that the compatibilizer in this invention is preferably grafted polypropylene, and the melt flow rate is (100g~800g) / 10min, such as 150g / 10min, 250g / 10min, 350g / 10min, 450g / 10min, 550g / 10min, 650g / 10min or 750g / 10min, etc.; the grafting rate is 0.5%~3%, such as 1%, 1.5%, 2% or 2.5%, etc.

[0032] In some specific examples, in the above preparation method, the internal lubricant and the external lubricant are each independently selected from one or more of the following: metal soaps, hydrocarbon waxes, fatty acids, organosilicon compounds, or fluorine-containing compounds.

[0033] It should be noted that, as described above, the combined use of the internal and external lubricants in this invention results in superior mechanical and lubrication properties of the prepared polypropylene composite material, making it more suitable for automotive tailgate strut sleeves. The internal and external lubricants in this invention can be independently selected from the lubricants listed above.

[0034] In some specific examples, in the above preparation method, the internal lubricant and the external lubricant are each independently selected from stearates in metal soaps.

[0035] It should be noted that the internal lubricant and external lubricant in this invention can be further selected independently from stearates in metal soaps. The polypropylene composite material prepared by the preferred internal and external lubricants has better mechanical and lubrication properties and is more suitable for automobile tailgate strut sleeves.

[0036] In some specific examples, in the above preparation method, the internal lubricant is selected from zinc stearate and / or calcium stearate, and the external lubricant is selected from magnesium stearate and / or paraffin wax.

[0037] It should be noted that the combination of internal and external lubricants in this invention can reduce the surface friction coefficient of the material and maintain a low surface friction coefficient for a long time. Based on this, the lubricant in this invention can be further preferably selected as follows: the internal lubricant is selected from zinc stearate and / or calcium stearate, and the external lubricant is selected from magnesium stearate and / or paraffin wax. The polypropylene composite material prepared accordingly has superior mechanical and lubrication properties, making it more suitable for automotive tailgate strut sleeves.

[0038] In some specific examples, the mass ratio of the internal lubricant to the external lubricant in the above preparation method is 2:3.

[0039] It should be noted that, in this invention, the lubricant can be further preferably selected from zinc stearate and / or calcium stearate, and the external lubricant from magnesium stearate and / or paraffin wax, with a mass ratio of internal to external lubricant of 2:3. Alternatively, the lubricant can be further preferably selected from calcium stearate as the internal lubricant and magnesium stearate as the external lubricant. The heat resistance temperature of calcium and magnesium salt lubricants is relatively consistent with the PP processing temperature of 160-220℃, and they have low surface tension and moderate compatibility with PP resin, making them easily repelled by the resin to the interface of the blend system, forming a thin external lubricating film and thus reducing the surface friction coefficient of the composite material. The polypropylene composite material prepared based on this lubricant exhibits superior mechanical and lubrication properties, making it more suitable for automotive tailgate strut sleeves.

[0040] In some specific examples, the size of the nano-silica in the above preparation method is 50nm to 500nm.

[0041] It should be noted that, as described above, this invention achieves the goal of controlling the full melt mixing of fibers and polypropylene resin and ensuring the fiber length in the composite material by adjusting the shearing and conveying screws in the twin-screw extruder and introducing a reverse shearing module. Its main function is also to promote the distribution and dispersion of inorganic nanofillers during the twin-screw melt blending process (as follows). Figure 1 As shown, the black part represents polypropylene resin, the white rods represent chopped glass fibers (SGF), and the white spheres represent nano-silica. Specifically, the spherical filler exhibits superior wear resistance compared to the rod-shaped chopped glass fibers. When the material is subjected to external force, the spherical particles slip, providing auxiliary lubrication and distributing the external force throughout the entire material matrix, thereby reducing localized pressure. In contrast, the single rod-shaped chopped glass fiber system directly causes the local polypropylene matrix to slip under external force, compromising the structural integrity of the material and resulting in poor wear resistance. Therefore, the combined use of nano-silica and chopped glass fibers in this invention can further improve the mechanical and lubrication properties of the polypropylene composite material. Based on this, the size of the nano-silica in this invention is preferably 50nm to 500nm, such as 100nm, 200nm, 300nm, or 400nm, etc. This size of nano-silica is more suitable for the preparation of the polypropylene composite material in this invention.

[0042] In some specific examples, the size of the nano-silica in the above preparation method is 100nm to 300nm.

[0043] It should be noted that the size of the nano-silica can be further preferably 100nm to 300nm, such as 150nm, 200nm or 250nm, etc. This size of nano-silica is more suitable for the preparation of polypropylene composite material in this invention.

[0044] In some specific examples, the diameter of the chopped glass fibers in the above preparation method is 5 μm to 20 μm.

[0045] It should be noted that the chopped glass fibers in this invention are preferably chopped glass fibers with a diameter of 5μm to 20μm, such as 7μm, 10μm, 13μm, 15μm or 17μm, etc., and chopped glass fibers of this size are more suitable for this invention.

[0046] In some specific examples, in the above preparation method, the chopped glass fibers undergo surface treatment, and the content of the sizing agent in the surface treatment is 2% to 10%.

[0047] It should be noted that the chopped glass fibers in this invention can be treated with a sizing agent before use, which can further improve their compatibility with the matrix material. The sizing agent is known in the art, such as a film-forming agent, coupling agent, or lubricant, and the content of the sizing agent can be 2% to 10% of the mass of the chopped glass fibers, such as 3%, 4%, 5%, 6%, 7%, 8%, or 9%.

[0048] In some specific examples, in the above preparation method, the melt flow rate of polypropylene under the test conditions of 230°C and 2.16kg is (10g~80g) / 10min.

[0049] It should be noted that the polypropylene matrix in this invention is known in the art, and preferably polypropylene that meets the above conditions is more suitable as the matrix of the polypropylene composite material in this invention, thereby improving the mechanical and lubrication properties of the prepared polypropylene composite material. That is, the preferred polypropylene in this invention has a melt flow rate of (10g~80g) / 10min under the test conditions of 230℃ and 2.16kg, such as 10g / 10min, 20g / 10min, 30g / 10min, 40g / 10min, 50g / 10min, 60g / 10min or 70g / 10min, etc.

[0050] In some specific examples, in the above preparation method, the first raw material, by mass parts, includes 0.5 to 5 parts of antioxidant, 3 to 5 parts of compatibilizer, 0.5 to 1 part of lubricant and 10 parts of nano-silica, and the lubricant includes internal lubricant and external lubricant; the second raw material, by mass parts, includes 20 parts of chopped glass fiber.

[0051] It should be noted that the mass ratio of nano-silica to chopped glass fiber in this invention can be 1:2, that is, 10 parts of nano-silica and 20 parts of chopped glass fiber. The polypropylene composite material prepared with this amount of nano-silica and chopped glass fiber has better mechanical and lubrication properties than other ratios.

[0052] In some specific examples, the first raw material in the above preparation method also includes color masterbatch, and the amount of color masterbatch added is 0.5 parts to 1.5 parts.

[0053] It should be noted that, in order to obtain polypropylene composite materials with richer colors, color masterbatch can be added to the first raw material. Color masterbatch is known in the art and can be selected according to different colors.

[0054] In some specific examples, the misalignment angle between the shear blocks in the above preparation method is 30° to 90°.

[0055] It should be noted that, as described above, in this invention, under the action of the reverse shear module and heat, the polypropylene resin and other additives are fully melted and mixed, and then extruded through the die head, cooled, dried, and pelletized to obtain a low surface friction coefficient, high rigidity, and creep-resistant polypropylene composite material. Specifically, the reverse shear screw block is placed before the side feed inlet, so it does not affect the chopped glass fibers. When the polypropylene raw material, additives, and nano-silica are fed from the main feed inlet, they are transported to the reverse shear screw block by the screw. The reverse shear screw block will obstruct the material conveying, and the material will repeatedly flow back and shear at this point, promoting the dispersion of nanoparticles. Therefore, the reverse shear screw block mainly affects the shearing and dispersion effect of inorganic nanoparticles. After unoptimized screw assembly blending and extrusion, nano-silica tends to agglomerate, resulting in large phase regions and uneven distribution. This leads to poor dispersibility and distribution of the polypropylene composite material, making it unable to effectively unload stress throughout the material under external forces, resulting in stress concentration. However, after optimizing the screw shear block assembly and introducing a reverse screw block, the shearing effect is enhanced. The agglomeration of nano-silica under the shearing action of the screw is significantly reduced, resulting in better dispersion and uniform distribution throughout the polypropylene matrix. Furthermore, nano-silica enrichment occurs around the chopped glass fibers and on the material surface, which helps to disperse external forces and assist in lubrication. Based on this, the present invention can use different angles of 30°~90° (30°, 45°, 60° or 90°, etc.) of shear blocks and reverse shear screw block combinations. The twin-screw compounding quality includes both distribution mixing and dispersion mixing effects. The distribution mixing effect is enhanced as the angle of the shear block elements (the misalignment angle between the shear blocks) increases.

[0056] In some specific examples, in the above preparation method, the melt blending temperature of the twin-screw extruder is 200℃~250℃, the vacuum degree is -0.1MPa~0MPa, and the rotation speed is 50rpm~150rpm.

[0057] It should be noted that the melt blending temperature of the twin-screw extruder in this invention can be 200℃~250℃, such as 210℃, 220℃, 230℃ or 240℃; the vacuum degree can be -0.1MPa~0MPa; and the rotation speed can be 50rpm~150rpm, such as 80rpm, 100rpm or 130rpm.

[0058] Secondly, embodiments of the present invention provide a polypropylene composite material for automobile tailgate strut sleeves, which is prepared by the above-described preparation method.

[0059] It should be noted that the polypropylene composite material prepared by this invention can achieve a flexural modulus of 6500 MPa, a tensile strength of 90 MPa, a tensile creep strain rate of less than 2.5%, and a surface friction coefficient of less than 0.3, indicating that it has excellent mechanical and lubrication properties and is suitable for automobile tailgate strut sleeves. The automobile tailgate strut sleeves prepared by this polypropylene composite material will not produce obvious abnormal noise.

[0060] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0061] In the following examples, the number of portions refers to the number of parts by weight.

[0062] In the following example, the polypropylene used is PP-iPP-M1200HS polypropylene resin produced by Shanghai Petrochemical. The melt flow rate of the material is 10g / 10min at 230℃ and 2.16Kg.

[0063] In the following examples, the chopped glass fibers used are chopped glass fibers from Jushi Group that have undergone surface treatment; the surface treatment is as follows: the surface is coated with a silane sizing agent (Wacker GENIOSIL® GF 98), the sizing agent has a solid content of 5%, the chopped glass fiber length is 4.5 mm, and the glass fiber diameter is 14 μm.

[0064] In the following example, the twin-screw extruder with shearing block and reverse shearing threaded block used is from Nanjing Ruya Extrusion Machinery Manufacturing Co., Ltd., model TSE-75Plus / 600-250-44, screw diameter 71mm, screw length-to-diameter ratio L / D=44, and optimized according to the parameters in Table 1 below based on the manufacturer's specifications (the larger the angle of the shearing module, the stronger the shearing; the larger the angle of the reverse conveying module, the stronger the conveying capacity).

[0065] Table 1. Optimized parameters for twin-screw extruders with shear blocks and reverse shear screw blocks. In the following examples, the black masterbatch is from Guangdong Meilian New Materials Co., Ltd., grade B2192; calcium stearate and magnesium stearate are from Jiangxi Hongyuan Chemical; nano silica is from Jinlei Technology, model GY300; talc is from Liaoning Xinda, model SD-9041; and glass microspheres are from Zhengzhou Shenglaicote, model MC20A.

[0066] Preparation Examples and Comparative Examples Example 1 After the first raw material is mixed evenly, it is fed into the twin-screw extruder through the main feed port. At the same time, the second raw material is fed into the side feed port at a speed of 100 rpm. After passing through the screw / reverse shear module, it is finally extruded and granulated from the die head. After the extruder die produces a stable output, a sample is taken and injection molded. The extrusion melt blending temperature is 230℃, the main machine speed is 600 rpm, and the extrusion is carried out under vacuum and maintained at a vacuum degree of -0.08MPa. The first raw material consists of: 65 parts PP (polypropylene), antioxidants (0.3 parts antioxidant 1010 and 0.2 parts antioxidant 168), 1 part black masterbatch, 3 parts compatibilizer PP-g-MAH, lubricant (0.2 parts calcium stearate (internal lubricant) and 0.3 parts magnesium stearate (external lubricant)) and 10 parts nano silica.

[0067] The second raw material is: 20 parts of chopped glass fiber.

[0068] Example 2 Example 2 is largely the same as Example 1, except that the first and second raw materials are different; otherwise, they are the same as in Example 1. Specifically, the first and second raw materials in Example 2 are as follows: The first raw material is: 5 parts of nano-silica, and the rest is the same as in Example 1; The second raw material is: 25 parts of chopped glass fiber, and the rest is the same as in Example 1.

[0069] Example 3 Example 3 is largely the same as Example 1, except that the first and second raw materials are different; otherwise, they are the same as in Example 1. Specifically, the first and second raw materials in Example 3 are as follows: The first raw material is: 15 parts of nano-silica, and the rest is the same as in Example 1; The second raw material is: 15 parts of chopped glass fiber, and the rest is the same as in Example 1.

[0070] Comparative Example 1 Comparative Example 1 is largely the same as Example 1, except that the first and second raw materials are different; otherwise, they are the same as in Example 1. Specifically, the first and second raw materials of Comparative Example 1 are as follows: The first raw material is: without the addition of nano-silica, otherwise the same as in Example 1; The second raw material is 30 parts of chopped glass fiber.

[0071] Comparative Example 2 Comparative Example 2 is largely the same as Example 1, except that the first ingredient is different; it does not use the second ingredient. Otherwise, it is the same as Example 1. Specifically, the first ingredient in Comparative Example 2 is as follows: The first raw material is: 30 parts of nano-silica, and the rest is the same as in Example 1.

[0072] Comparative Example 3 Comparative Example 3 is largely the same as Example 1, except that the first and second raw materials are different; otherwise, they are the same as in Example 1. Specifically, the first and second raw materials of Comparative Example 3 are as follows: The first raw material is: 10 parts of talc powder added to the first raw material in Example 1; The second raw material is: 20 parts of chopped glass fiber.

[0073] Comparative Example 4 Comparative Example 4 is largely the same as Example 1, except that the first and second raw materials are different; otherwise, they are the same as in Example 1. Specifically, the first and second raw materials of Comparative Example 4 are as follows: The first raw material is: 10 parts of glass microspheres added to the first raw material in Example 1.

[0074] The second raw material is: 20 parts of chopped glass fiber.

[0075] Comparative Example 5 Comparative Example 5 is largely the same as Example 1, except that the first raw material is different; otherwise, it is the same as Example 1. Specifically, the first raw material in Comparative Example 5 is as follows: The first raw material is: without adding lubricant, otherwise the same as in Example 1.

[0076] Comparative Example 6 Comparative Example 6 is largely the same as Example 1, except for the screw assembly of the extrusion equipment in Comparative Example 6. The screw assembly of the extruder in Comparative Example 6 does not include a reverse shear screw block (i.e., it is not optimized). All other process parameters are consistent with those in Example 1.

[0077] Comparative Example 7 Comparative Example 7 is largely the same as Example 1, except that the first raw material is different from the first raw material. Otherwise, it is the same as Example 1. Specifically, the first raw material in Comparative Example 7 is as follows: The first raw material is: without the addition of nano-silica, otherwise the same as in Example 1; The second raw material is: 10 parts nano-silica and 20 parts short-cut glass fiber.

[0078] Performance testing (a) Mechanical property testing In the following tests, the mechanical properties of the samples were tested according to the following methods: The notched impact strength was tested according to GB / T1043.1-2008, with a V-notch. The surface friction coefficient and friction wear amount were tested in accordance with GB / T3960-2016; Tensile strength was tested according to GB / T1040.1-2018 at a speed of 5 mm / min; The flexural modulus and flexural strength were tested according to GB / T9341-2008, with a speed of 2 mm / min and a span of 64 mm. Tensile creep strain rate was tested in accordance with GB / T41061-2021: Test method for creep properties of fiber reinforced plastics.

[0079] The samples prepared in the examples and comparative examples were made into standard mechanical specimens. Then, the notched impact strength, surface friction coefficient, wear amount, tensile strength, flexural modulus, flexural strength and tensile creep strain rate of the samples prepared in the examples / comparative examples were tested according to the above test methods. The test results are shown in Table 2 below.

[0080] Table 2 Mechanical properties of samples prepared in the examples and comparative examples (ii) Test for abnormal friction noise of sleeve parts In the following tests, the friction noise performance of the parts was tested according to the following methods: Friction acceleration was tested using typical part samples on a multi-functional wear testing machine (manufacturer: Shenzhen Zhijia; equipment model: ZJ-9600). Vibration testing was conducted using equipment (manufacturer: Ono, Japan; equipment model: DS3000 data acquisition system). Sample loading method: 2kg load, speed: 7RPM (low speed) / 30RPM (high speed), sensor position: perpendicular to the sleeve direction (axial direction), along the sleeve direction (radial direction). The coefficient of friction was tested in accordance with GB / T 10006-2021, with a test load of 200g and a speed of 100mm / min. The evaluation of product stickiness and abnormal noise is conducted subjectively, in accordance with the applicant's internal operating procedures. The quality loss of injection molded products is the change in quality before and after the durability test of the samples.

[0081] The lubrication performance of the samples prepared in the examples and comparative examples was tested according to the above test methods, and the results are shown in Table 3.

[0082] Table 3. Lubrication performance of samples prepared in the examples and comparative examples. From Tables 2 and 3, we can see that: Comparing the samples prepared in Examples 1 to 3 with those prepared in Comparative Examples 1 to 7 reveals the following: The samples prepared in Examples 1 to 3 exhibited significantly better stick-slip noise characteristics than those in Comparative Examples 1 to 7. The samples prepared in Examples 1 to 3 showed no or only slight noise, while the samples prepared in Comparative Examples 1 to 7 produced severe and persistent noise. Furthermore, the samples prepared in Examples 1 to 3 also possessed excellent mechanical properties. Therefore, the polypropylene composite material of this invention exhibits both excellent mechanical properties and excellent lubrication properties.

[0083] Comparing Example 1 and Comparative Example 1, it can be seen that Comparative Example 1 only used chopped glass fibers as filler, while Example 1 used both chopped glass fibers and nano-silica as fillers. The notched impact strength, tensile strength, flexural modulus, and flexural strength of the sample prepared in Example 1 were slightly lower than those of Comparative Example 1, while the tensile creep strain rate was slightly higher. However, the surface friction coefficient and wear amount were significantly lower than those of Comparative Example 1. Furthermore, the 30,000 cycles of low-speed / high-speed frictional vibration acceleration, the average mass loss of the injection-molded product, and the surface dynamic friction coefficient of the product prepared in Example 1 were all lower than those of Comparative Example 1. The above data indicate that the overall effect of Example 1 is better than that of Comparative Example 1, demonstrating that the combined use of nano-silica and chopped glass fibers is more effective than their individual use. Comparing Example 1 with Comparative Example 2 reveals that Comparative Example 2 used only 30 parts of nano-silica. On the one hand, too much nanoparticles make dispersion difficult and prone to agglomeration, resulting in poor and unstable material performance. As shown in the data above, the notched impact strength of Comparative Example 2 is significantly lower than that of Example 1, only 27% of that of Example 1. On the other hand, since the glass fiber rod structure improves the mechanical properties of polypropylene far better than spherical nano-silica (which is extremely prone to agglomeration and is actually dispersed at the micron level within the composite material), the composite material prepared by filling a large amount of nano-silica alone has much lower strength and rigidity than the composite material prepared by filling glass fiber. The tensile strength and flexural modulus are only 65% ​​and 63% of those of Example 1, respectively. This corresponds to the risk of insufficient strength and rigidity in the actual use of the sleeve product.

[0084] Comparing Example 1 with Comparative Example 3 and Comparative Example 4, it can be seen that Comparative Example 3 and Comparative Example 4 replaced nano-silica with talc powder and glass microspheres, respectively, based on Example 1. The results show that the notched impact strength, tensile strength, flexural modulus, and flexural strength of the sample prepared in Example 1 are significantly higher than those of Comparative Example 3 and Comparative Example 4, while the tensile creep strain rate is significantly lower than that of Comparative Example 3, and the surface friction coefficient and wear amount are significantly lower than those of Comparative Example 3 and Comparative Example 4. Furthermore, the 30,000 cycles of low-speed / high-speed frictional vibration acceleration, the average mass loss of the injection molded product, and the dynamic friction coefficient of the product surface of the sample prepared in Example 1 are all lower than those of Comparative Example 3 and Comparative Example 4. The above data indicate that the combined use of nano-silica and chopped glass fiber is more effective than the combined use of other fillers and chopped glass fiber. Comparing Example 1 and Comparative Example 5, it can be seen that Comparative Example 5 did not add lubricant compared to Comparative Example 1. The results show that the notched impact strength, tensile strength, flexural modulus, flexural strength, and tensile creep strain rate of the sample prepared in Example 1 are comparable to those of Comparative Example 5. However, the surface friction coefficient and wear amount in Example 1 are significantly lower than those in Comparative Example 5. Furthermore, the 30,000 cycles of low-speed / high-speed frictional vibration acceleration, the average mass loss of the injection molded product, and the surface dynamic friction coefficient of the product prepared in Example 1 are all lower than those in Comparative Example 5. The above data indicate that the lubricant in this invention can reduce the surface friction coefficient and wear amount. Comparing Example 1 and Comparative Example 6, it can be seen that Comparative Example 6 directly granulates the first raw material of Example 1 without screw / reverse shear module extrusion granulation. The results show that the notched impact strength, tensile strength, flexural modulus, and flexural strength of the sample prepared in Example 1 are significantly higher than those of Comparative Example 6, while the tensile creep strain rate is slightly lower, and the surface friction coefficient and wear amount are significantly lower than those of Comparative Example 6. Furthermore, the 30,000 cycles of low-speed / high-speed frictional vibration acceleration, the average mass loss of the injection molded product, and the surface dynamic friction coefficient of the product prepared in Example 1 are all lower than those of Comparative Example 6. The above data indicate that screw / reverse shear module extrusion granulation can significantly improve the mechanical properties and friction and wear resistance of polypropylene composite materials. Comparing Example 1 and Comparative Example 7, it can be seen that Comparative Example 7, based on Example 1, uses side-feeding for both nano-silica and chopped glass fibers. The results show that the notched impact strength, tensile strength, flexural modulus, and flexural strength of the sample prepared in Example 1 are significantly higher than those of Comparative Example 7, while the tensile creep strain rate is comparable to that of Comparative Example 7, and the surface friction coefficient and wear amount are significantly lower than those of Comparative Example 7. Furthermore, the 30,000 cycles of low-speed / high-speed frictional vibration acceleration, the average mass loss of the injection-molded product, and the surface dynamic friction coefficient of the product prepared in Example 1 are all lower than those of Comparative Example 7. The above indicates that side-feeding of both nano-silica and chopped glass fibers simultaneously affects the mechanical properties and abrasion resistance of the prepared sample.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. 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 spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a polypropylene composite material for an automobile tailgate strut sleeve, characterized in that, Preparation methods include: The first raw material and the second raw material are fed into a twin-screw extruder through the main feed port and the side feed port, respectively, and then extruded and granulated. The granulated material is then injection molded to obtain a polypropylene composite material for automobile tailgate strut sleeve. The twin-screw extruder is equipped with a shearing block and a reverse shearing screw block; The total mass fraction of the first and second raw materials is 100 parts; among which, The first raw material, by weight, includes 0.5 to 5 parts antioxidant, 3 to 5 parts compatibilizer, 0.5 to 1 part lubricant, and 5 to 20 parts nano silica. The lubricant includes internal lubricant and external lubricant. The second raw material, by weight, includes 10 to 30 parts of chopped glass fiber; The balance is polypropylene.

2. The preparation method according to claim 1, characterized in that, Antioxidants are selected from one or more of hindered phenols, phosphites, or amines; and / or The compatibilizer is selected from one or more combinations of maleic anhydride and its derivatives, epoxy compounds, carboxylic acids, and glycidyl acrylates; and / or The internal lubricant and external lubricant are each independently selected from one or more combinations of metal soaps, hydrocarbon waxes, fatty acids, organosilicon compounds, or fluorinated compounds; and / or The size of nano-silica ranges from 50 nm to 500 nm; and / or The diameter of the chopped glass fibers is 5μm to 20μm; and / or The melt flow rate of polypropylene under test conditions of 230℃ and 2.16kg is (10g~80g) / 10min.

3. The preparation method according to claim 2, characterized in that, Antioxidants are selected from one or more combinations of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite, 2,6-di-tert-butyl-4-methylphenol, and bis(3,5-di-tert-butyl-4-hydroxyphenyl) sulfide; and / or The compatibilizer has a melt flow rate of (0.05 g to 1000 g) / 10 min and a grafting rate of 0.05% to 3%; and / or The internal and external lubricants are each independently selected from stearates in the metal soap family; and / or The size of nano-silica is 100nm to 300nm; and / or The chopped glass fibers undergo surface treatment, with the sizing agent content ranging from 2% to 10%.

4. The preparation method according to claim 3, characterized in that, The antioxidant is a combination of antioxidant 1010 and antioxidant 168, with a mass ratio of antioxidant 1010 to antioxidant 168 of 3:2; and / or The compatibilizer is a grafted polypropylene, with a melt flow rate of (100g~800g) / 10min and a grafting rate of 0.5%~3%; and / or The internal lubricant is selected from zinc stearate and / or calcium stearate, and the external lubricant is selected from magnesium stearate and / or paraffin wax.

5. The preparation method according to claim 4, characterized in that, The mass ratio of internal lubricant to external lubricant is 2:

3.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The first raw material, by weight, includes 0.5 to 5 parts antioxidant, 3 to 5 parts compatibilizer, 0.5 to 1 part lubricant, and 10 parts nano silica. The lubricant includes internal lubricant and external lubricant. The second raw material, by weight, includes 20 parts of chopped glass fiber.

7. The preparation method according to any one of claims 1 to 5, characterized in that, The first raw material also includes color masterbatch, with an addition amount of 0.5 to 1.5 parts.

8. The preparation method according to any one of claims 1 to 5, characterized in that, The misalignment angle between the shear blocks is 30° to 90°.

9. The preparation method according to any one of claims 1 to 4, characterized in that, The melt blending temperature of the twin-screw extruder is 200℃~250℃, the vacuum degree is -0.1MPa~0MPa, and the speed is 50rpm~150rpm.

10. A polypropylene composite material for automobile tailgate strut sleeves, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 9.

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