High-rigidity low-warp polypropylene material for automobile structural parts and method for producing the same

Abstract

The application relates to the field of polypropylene materials, in particular to a high-rigidity low-warp polypropylene material for automobile structural parts and a preparation method thereof. The polypropylene material comprises the following components calculated in parts by mass: 50-65 parts of polypropylene resin, 10-15 parts of talcum powder, 2-5 parts of a compatilizer, 0.2-0.6 parts of an antioxidant, 0.5-1.5 parts of a lubricant, and 15-30 parts of modified glass fiber. The modified glass fiber is alkali-free chopped glass fiber grafted with a beta nucleating agent, and the beta nucleating agent comprises one or more of metal glutarate, metal pimelate, metal adipate, metal terephthalate and metal phthalate. By adding the modified glass fiber grafted with the beta nucleating agent, the warp deformation of the polypropylene material caused by the anisotropic distribution of the glass fiber is improved, the assembly precision of the automobile structural parts is met, and excellent rigidity is simultaneously achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polypropylene materials, in particular to a high-rigidity and low-warpage polypropylene material for automobile structural parts and a preparation method thereof. BACKGROUND

[0002] Polypropylene (PP) has the advantages of abundant source, low price and light weight, and is widely used in the automobile field, becoming the largest and fastest-growing variety of automobile plastics. In recent years, with the rapid development of the automobile industry, the performance requirements for automobile structural parts are becoming higher and higher. In order to improve the mechanical properties of polypropylene materials for automobile structural parts, adding glass fibers to the polypropylene matrix is an effective means. Glass fibers include long-cut glass fibers and short-cut glass fibers.

[0003] Long-cut glass fibers can significantly improve the mechanical properties of polypropylene, but long-cut glass fibers have the disadvantages of high shear sensitivity, poor flowability, high cost, poor processability, high requirement for equipment, and easy occurrence of floating fibers, which are not conducive to industrial application. Compared with long-cut glass fibers, short-cut glass fibers have the advantages of low cost, strong process adaptability and difficulty in floating fibers, and the improvement of mechanical properties can meet most demands. Therefore, short-cut glass fibers are widely used in reinforced polypropylene materials. However, due to the size characteristics of short-cut glass fibers and the molding process, short-cut glass fiber reinforced polypropylene materials are prone to warpage deformation, which affects the assembly accuracy and use of automobile structural parts.

[0004] Therefore, it has become a research hotspot in the field of polypropylene materials to develop a high-rigidity and low-warpage polypropylene material for automobile structural parts. SUMMARY

[0005] In order to solve the above problems, the present application provides a high-rigidity and low-warpage polypropylene material for automobile structural parts and a preparation method thereof. By adding modified glass fibers grafted with β nucleating agents, the polypropylene material has excellent rigidity and low warpage.

[0006] The first aspect of the present application provides a high-rigidity and low-warpage polypropylene material for automobile structural parts, which comprises the following components calculated by mass parts: 50-65 parts of polypropylene resin; 10-15 parts of talc; 2-5 parts of a compatibilizer; 0.2-0.6 parts of an antioxidant; 0.5-1.5 parts of a lubricant; and 15-30 parts of modified glass fibers; wherein the modified glass fibers are alkali-free short-cut glass fibers grafted with β nucleating agents, and the β nucleating agents include one or more of metal salts of glutaric acid, metal salts of pimelic acid, metal salts of adipic acid, metal salts of terephthalic acid and metal salts of phthalic acid.

[0007] The applicant found through research that the reason for the warpage of the glass fiber reinforced polypropylene material is that the chopped glass fiber has a certain aspect ratio, and in the process of injection molding of the polypropylene material, it is easy to rotate under the action of shearing and then orient along the flow direction. Talcum powder, which is commonly used to improve the mechanical properties of polypropylene materials, is an inorganic alpha nucleating agent that promotes the formation of spherical alpha spherulites in polypropylene materials. The molecular chains of alpha spherulites are tightly packed, and the chain segments are neatly arranged during cooling, thereby generating high volume shrinkage. However, due to the fact that the size of the glass fiber does not change significantly at high temperature / cooling and the rigid structure, the anisotropic orientation of the chopped glass fiber will lead to the inhibition of the shrinkage of the polypropylene material along the orientation direction of the glass fiber (i.e. the injection molding flow direction) during the cooling and crystallization stage, while the shrinkage of the polypropylene material perpendicular to the orientation direction is larger. This difference in shrinkage rate causes the polypropylene material to warp and deform, and the interface to participate in the tensile stress, inducing the debonding of polypropylene and filler, the shrinkage rate of the polypropylene material in the debonding area further increases, forming a larger shrinkage rate gradient with the non-debonding area, further leading to a difference in shrinkage, and thus causing a vicious cycle, resulting in more serious warpage of the material.

[0008] The applicant further found through research that grafting a compound with beta nucleation effect on the surface of the chopped glass fiber is beneficial to improve the warpage of the polypropylene material. The reason for this may be that the beta nucleating agent on the surface of the glass fiber induces the formation of beta lamellae around the glass fiber during cooling, and the presence of the glass fiber often induces the distribution of these beta lamellae perpendicular to the orientation direction of the glass fiber. Compared to the high shrinkage of alpha spherulites, beta lamellae have lower shrinkage characteristics, and the distribution of beta lamellae perpendicular to the orientation direction of the glass fiber is beneficial to balance the high shrinkage caused by alpha spherulites in this direction, thereby making the shrinkage rate of the polypropylene material perpendicular to the fiber orientation direction approach the shrinkage rate parallel to the fiber orientation direction, and alleviating the warpage of the material; and the beta lamellae structure has excellent toughness and can absorb tensile stress through plastic deformation, making the stress uniform, reducing the risk of interface debonding, and thus avoiding further shrinkage difference caused by debonding, further improving the warpage of the polypropylene material. And the beta lamellae structure can combine with the three-dimensional network of the surrounding alpha spherulites to form a crystalline structure with a tight overall structure, and this alpha / beta coexisting structure around the glass fiber is beneficial to further improve the impact resistance of polypropylene. Compared to other methods of adding beta nucleating agent, such as physical mixing or loading beta nucleating agent on the glass fiber through crystallization, the grafting method can achieve uniform and stable distribution of beta nucleating agent on the surface of the glass fiber, and play an excellent nucleation role in forming a specific oriented beta lamellae in a specific area, thereby effectively reducing the shrinkage rate difference and improving the warpage of the chopped glass fiber reinforced polypropylene material. When the mass fraction of the modified glass fiber is in the above range, the polypropylene material has excellent bending modulus and low warpage.

[0009] In any embodiment, the method for preparing the modified glass fiber comprises the following steps: (1) dispersing the alkali-free chopped glass fiber in a mixed solvent of ethanol and deionized water, adding aminopropyl triethoxysilane, stirring and reacting at 60-80°C for 10-14 hours, and centrifuging and drying to obtain the alkali-free chopped glass fiber modified by the amino group on the surface; (2) dispersing the dicarboxylic compound in dichloromethane, adding dichlorosulfoxide and a catalyst N,N-dimethylformamide, stirring and reacting at 22-28°C for 1-3 hours, and removing the dichloromethane to obtain a first intermediate product, wherein the dicarboxylic compound comprises one or more of glutaric acid, pimelic acid, adipic acid, terephthalic acid and phthalic acid, and the molar ratio of the dicarboxylic compound to dichlorosulfoxide is 1:1; (3) dispersing the first intermediate product in dichloromethane, adding the alkali-free glass fiber modified by the amino group on the surface, stirring and reacting at 0-10°C for 10-14 hours, centrifuging to obtain a solid, and drying to obtain a second intermediate product; (3) dispersing the second intermediate product and the metal hydroxide in methanol, stirring and reacting at 22-28°C for 20-28 hours, and centrifuging and drying to obtain the modified glass fiber, wherein the metal hydroxide comprises at least one of an alkali metal hydroxide and an alkaline earth metal hydroxide.

[0010] The siloxyl group in the aminopropyl triethoxysilane molecule generates a silanol group after hydrolysis, which can undergo condensation reaction with a large number of hydroxyl groups on the surface of the glass fiber to form stable chemical bonds, so that the aminopropyl triethoxysilane molecule is firmly connected to the surface of the glass fiber, providing an amino active site for the glass fiber, and obtaining the chopped glass fiber modified by the amino group; further, by controlling the molar ratio of the dicarboxylic compound to dichlorosulfoxide to be 1:1, the single carboxylic acid of the dicarboxylic compound is acylated to obtain the first intermediate product, and the amino group of the glass fiber modified by the amino group and the acyl chloride group undergo acylation reaction under the condition of 0-10°C, which has higher reaction activity and the reaction product is easier to purify, so that the glass fiber is grafted with the dicarboxylic compound to obtain the second intermediate product; further, the free carboxyl group of the dicarboxylic compound grafted on the glass fiber reacts with the metal hydroxide to obtain the glass fiber grafted with the dicarboxylic metal salt (such as at least one of glutaric acid metal salt, pimelic acid metal salt, adipic acid metal salt, terephthalic acid metal salt and phthalic acid metal salt), and the special lattice structure formed by the fatty chain or benzene ring in the dicarboxylic compound and the metal ion (such as at least one of alkali metal ion and alkaline earth metal ion) and the carboxylate matches the hexagonal crystal system parameter of the polypropylene β lamella, and thus can induce the growth of the β lamella to improve the warpage.

[0011] In any embodiment, the dicarboxylic compound in step (2) comprises glutaric acid and phthalic acid, and the molar ratio of glutaric acid to phthalic acid is 1:1-3:1.

[0012] The present application finds through experimental research that the dicarboxylic acid compound includes glutaric acid and phthalic acid and the molar ratio of glutaric acid and phthalic acid is 1:1-3:1, so that when the dicarboxylic acid metal salt grafted on the glass fiber includes glutaric acid metal salt and phthalic acid metal salt in a suitable ratio, the warpage of the polypropylene material is further improved, and at the same time, it has more excellent rigidity, and through analysis, this may be due to the fact that the glutaric acid metal salt is mainly flexible aliphatic chain, the main body of the phthalic acid metal salt is rigid benzene ring, the temperature of the two β nucleating agents induced nucleation and the size of the finally formed β spherulite are different, and under the synergistic effect of the suitable ratio, the temperature range of the β lamellar crystal generated during cooling is wider, the content of the β lamellar crystal generated perpendicular to the orientation direction of the glass fiber is higher, and finally, it includes larger β spherulites with better toughness and smaller β spherulites with better strength, so as to further improve the warpage, and at the same time, it has more excellent strength.

[0013] In any embodiment, the metal hydroxide in step (4) includes at least one of barium hydroxide and potassium hydroxide.

[0014] The present application finds through experimental research that the metal hydroxide includes at least one of barium hydroxide and potassium hydroxide, and the modified glass fiber has an excellent improvement effect on the warpage of the polypropylene material. The present application further finds through experimental research that the metal hydroxide is barium hydroxide, and the divalent metal ion makes the β nucleating agent formed on the glass fiber have a chelated carboxylate structure and a strong polarization ability of barium ion, both of which make the efficiency of the β nucleating agent in inducing the polypropylene matrix to form β lamellar crystals more efficient, which is beneficial to further improving the content of the β lamellar crystal generated perpendicular to the orientation direction of the glass fiber, and further improving the warpage of the polypropylene material, while having excellent strength.

[0015] In any embodiment, the mass ratio of the alkali-free short-cut glass fiber to the aminopropyl triethoxysilane in step (1) is 4:1-10:1.

[0016] The present application further finds through experimental research that controlling the mass ratio of the glass fiber to the aminopropyl triethoxysilane in step (1) in the above range makes the glass fiber have a suitable amino grafting rate, and then has a suitable β nucleating agent grafting rate, so that the prepared polypropylene material has excellent warpage and rigidity.

[0017] In any embodiment, the length of the alkali-free short-cut glass fiber in step (1) is 3mm-5mm, and the diameter is 12μm-15μm.

[0018] The length and diameter of the short-cut glass fiber in the above range have excellent processing ability and mechanical property enhancement effect.

[0019] In any embodiment, the polypropylene resin comprises a high impact polypropylene resin having a melt index of 0.5 g / 10 min-20 g / 10 min at 230℃, 2.16 kg and a high flow polypropylene resin having a melt index of 25 g / 10 min-30 g / 10 min at 230℃, 2.16 kg.

[0020] The high impact polypropylene resin can provide excellent rigidity but poor flowability, making injection molding difficult; the high flow polypropylene resin has good flowability and can meet the structural requirements of automobile structural parts such as bumper materials when injection molding, and is also conducive to reducing the shear-induced anisotropic orientation of glass fibers, but has poor rigidity; the combination of the high impact polypropylene resin and the high flow polypropylene resin can meet the dual requirements of mechanical properties and processing performance.

[0021] In any embodiment, the antioxidant comprises a hindered phenol primary antioxidant 1010 and a phosphite auxiliary antioxidant 168.

[0022] The combination of the antioxidants 1010 and 168 can improve the thermal stability and antioxidant properties of the polypropylene material.

[0023] In any embodiment, the compatibilizer comprises a maleic anhydride grafted polypropylene.

[0024] The maleic anhydride groups in the molecular structure of the maleic anhydride grafted polypropylene can form covalent bonds with the surface hydroxyl groups of fillers such as glass fibers and talc, achieving compatibility between the fillers and the polypropylene matrix, which is conducive to reducing interfacial debonding and alleviating the deterioration of the warpage of the polypropylene material and further improving the mechanical properties.

[0025] In any embodiment, the lubricant comprises one or more of polyethylene wax, ethylene bis fatty acid amide, silicone masterbatch, and pentaerythritol stearate.

[0026] The lubricant can help reduce internal friction between polypropylene molecular chains, improve melt flow rate, reduce the friction coefficient between the melt and the mold, make the injection molding, extrusion and other processes smoother, and reduce the anisotropic orientation of glass fibers, thereby further improving the warpage of the polypropylene material.

[0027] The application also provides a preparation method of a high-rigidity low-warpage polypropylene material for automobile structural parts, comprising the following steps: mixing polypropylene resin, talc, compatibilizer, antioxidant, and lubricant according to the mass ratio, and then adding them to the main feeding port of a twin-screw extruder; adding modified glass fibers to the side feeding port of the twin-screw extruder; the temperature of each zone of the twin-screw extruder is 180℃-220℃; and extruding and drying to obtain a high-rigidity low-warpage polypropylene material for automobile structural parts.

[0028] The modified glass fiber is added through the side feeding port, which helps to retain the grafted β nucleating agent on the glass fiber, and is conducive to further improving the warpage of the polypropylene material.

[0029] In summary, the present application has the following beneficial effects:

[0030] By using the glass fiber grafted with the β nucleating agent, it is conducive to inducing the generation of the β lamellar structure perpendicular to the orientation of the glass fiber near the glass fiber. The low shrinkage rate characteristics of the β lamellar structure make the shrinkage rate of the polypropylene material along the orientation direction of the glass fiber and the shrinkage rate perpendicular to the orientation direction of the glass fiber smaller, thereby improving the warpage of the polypropylene material.

[0031] By selecting a suitable preparation process and selecting the grafting rate and the type of grafted β nucleating agent, the warpage of the polypropylene material is further improved, and at the same time, the rigidity is more excellent.

[0032] By adding the modified glass fiber through the side feeding port, it is conducive to retaining the grafted β nucleating agent, thereby further improving the warpage of the polypropylene material. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below. In the following description, a large number of specific details are set forth in order to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application, so the present application is not limited by the specific examples disclosed below. Unless otherwise specified, the raw materials used in the examples of the present application are commercially available raw materials. The present application is further described in detail below in combination with examples and comparative examples.

[0034] Preparation Example 1

[0035] (1) Take 8 g of chopped glass fiber (alkali-free chopped glass fiber ECS13-4.5-T538D, Taishan Glass Fiber, length 4.5 mm, diameter 13 μm) and disperse it in 300 mL of an ethanol aqueous solution (obtained by mixing deionized water and anhydrous ethanol at a volume ratio of 3:1), add 1 g of aminopropyl triethoxysilane, and place the mixed system in a 70°C water bath and stir at a speed of 100 rpm for 12 hours. After the reaction is completed, centrifuge the mixed solution 3 times, and vacuum dry the obtained solid at a drying temperature of 100°C for 4 hours to obtain a glass fiber modified with aminosilane on the surface;

[0036] (2) Take 1 mol of dicarboxylic acid compound phthalic acid and disperse it in 200 mL of dichloromethane, add 1 mol of dichloro sulfoxide and 1 mL of N,N-dimethylformamide, stir at 25°C at a rotation speed of 200 rpm for 2 hours, after the reaction is completed, remove the dichloromethane using a rotary evaporator to obtain a first intermediate product.

[0037] (3) Take 1 g of the first intermediate product prepared in step (2) and disperse it in 100 mL of dichloromethane, ultrasonically disperse it uniformly to obtain a dispersion liquid of the first intermediate product. Take 4 g of the surface amino-modified glass fiber prepared in step (1), drop it into the above-prepared dispersion liquid at 0°C, stir at a rotation speed of 100 rpm for 12 hours, centrifuge the reaction mixture 3 times to obtain a solid, wash it with anhydrous ethanol 3 times to obtain a second intermediate product.

[0038] (4) Add 4 g of the second intermediate product prepared in step (3) and 2 g of barium hydroxide to 200 mL of methanol, stir to mix thoroughly, stir at 25°C at a rotation speed of 200 rpm for 24 hours, centrifuge the reaction mixture 3 times, vacuum dry the obtained solid at a drying temperature of 100°C for 4 hours to obtain a glass fiber grafted with barium phthalate.

[0039] Preparation Example 2-7

[0040] Preparation Example 2-7 is basically the same as the preparation method of Preparation Example 1, the difference is that the dicarboxylic acid compound added in step (2) of Preparation Example 2-7 is different, and the others are the same as Preparation Example 1, which is as follows:

[0041] Preparation Example 2: Use equimolar amount of terephthalic acid to replace phthalic acid.

[0042] Preparation Example 3: Use equimolar amount of heptanedioic acid to replace phthalic acid.

[0043] Preparation Example 4: Use equimolar amount of pentanedioic acid to replace phthalic acid.

[0044] Preparation Example 5: Use pentanedioic acid and phthalic acid to replace phthalic acid, the total amount of moles of pentanedioic acid and phthalic acid is the same as the amount of moles of phthalic acid, and the mole ratio of pentanedioic acid and phthalic acid is 1:1.

[0045] Preparation Example 6: Use pentanedioic acid and phthalic acid to replace phthalic acid, the total amount of moles of pentanedioic acid and phthalic acid is the same as the amount of moles of phthalic acid, and the mole ratio of pentanedioic acid and phthalic acid is 2:1.

[0046] Preparation Example 7: Substituting phthalic acid with glutaric acid and phthalic acid, the total molar amount of glutaric acid and phthalic acid is the same as the molar amount of phthalic acid, and the molar ratio of glutaric acid and phthalic acid is 3:1.

[0047] Preparation Example 8

[0048] The preparation method of Preparation Example 8 is basically the same as that of Preparation Example 6, except that equal mass of potassium hydroxide is used to replace barium hydroxide in step (4) of Preparation Example 8, and the others are the same as those of Preparation Example 6.

[0049] Preparation Examples 9-10

[0050] The preparation method of Preparation Examples 9-10 is basically the same as that of Preparation Example 6, except that the mass ratio of chopped glass fibers and aminopropyl triethoxysilane is different in step (1) of Preparation Examples 9-10, and the others are the same as those of Preparation Example 6, which are as follows:

[0051] Preparation Example 9: The mass of chopped glass fibers is 7.2 g, the mass of aminopropyl triethoxysilane is 1.8 g, and the mass ratio of chopped glass fibers to aminopropyl triethoxysilane is 4:1.

[0052] Preparation Example 10: The mass of chopped glass fibers is 8.2 g, the mass of aminopropyl triethoxysilane is 0.8 g, and the mass ratio of chopped glass fibers to aminopropyl triethoxysilane is 10.25:1.

[0053] Preparation Example 11

[0054] The preparation method of the modified glass fiber of Preparation Example 11 is as follows:

[0055] Dissolve 1 g of barium phthalate in dimethylbenzene at 80°C, add 4 g of chopped glass fiber (alkali-free chopped glass fiber ECS13-4.5-T538D, Taishan Glass Fiber, length 4.5 mm, diameter 13 μm), reflux at 100°C for 1 hour, cool to room temperature (25°C), and make barium phthalate crystallize on the surface of the glass fiber. Centrifuge and dry at 100°C for 4 hours to obtain the modified glass fiber.

[0056] Preparation Example 12

[0057] The preparation method of Preparation Example 12 is basically the same as that of Preparation Example 1, except that equal molar amount of benzoic acid is used to replace phthalic acid in step (2), and the others are the same as those of Preparation Example 1. Example 1

[0058] 42 parts of high impact polypropylene resin (copolymerized polypropylene resin K8303, purchased from Yanshan Petrochemical, melt index at 230℃, 2.16 kg is 2 g / 10 min), 18 parts of high flow polypropylene resin (copolymerized polypropylene resin EP548R, purchased from China CNOOC Shell, melt index at 230℃, 2.16 kg is 28 g / 10 min), 14 parts of talc (purchased from Tianyuan Company, model TYT-8875B, mesh number is 2000), 3 parts of maleic anhydride grafted polypropylene (brand CA100, grafting rate of maleic anhydride is 1%, Arkema), 0.25 parts of antioxidant 1010 (Tianjin LIANLONG RIANOX), 0.25 parts of antioxidant 168 (Tianjin LIANLONG RIANOX), 1 part of ethylene bis fatty acid amide are weighed by mass parts and uniformly mixed in a high-speed mixer. The mixture is added to a twin-screw extruder through the main feeding port, and 22 parts of the modified glass fiber prepared in Preparation Example 1 is added to the twin-screw extruder through the side feeding port. The temperature of each section of the barrel from the feeding port to the die head is controlled in turn as 180℃, 210℃, 210℃, 220℃, 220℃, 210℃, 210℃, 210℃, 205℃, 205℃. The high-rigidity low-warpage polypropylene material for automobile structural parts is obtained by melt extrusion granulation at a twin-screw speed of 500 rpm.

[0059] Example 2-3

[0060] The preparation method of Example 2-3 is basically similar to that of Example 1, except that the mass fraction of the modified glass fiber is different, and the total mass fraction of the raw materials changes accordingly, and the others remain the same as Example 1.

[0061] Example 2: The mass fraction of the modified glass fiber is 15 parts.

[0062] Example 3: The mass fraction of the modified glass fiber is 30 parts. Example 4

[0063] The preparation method of Example 4 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 2 is used in Example 4 instead of the modified glass fiber prepared in Preparation Example 1, and the others remain the same as Example 1. Example 5

[0064] The preparation method of Example 5 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 3 is used in Example 5 instead of the modified glass fiber prepared in Preparation Example 1, and the others remain the same as Example 1. Example 6

[0065] The preparation method of Example 6 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 4 is used to replace the modified glass fiber prepared in Preparation Example 1 in Example 6, and the other conditions are the same as those in Example 1. Example 7

[0066] The preparation method of Example 7 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 5 is used to replace the modified glass fiber prepared in Preparation Example 1 in Example 7, and the other conditions are the same as those in Example 1. Example 8

[0067] The preparation method of Example 8 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 6 is used to replace the modified glass fiber prepared in Preparation Example 1 in Example 8, and the other conditions are the same as those in Example 1. Example 9

[0068] The preparation method of Example 9 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 7 is used to replace the modified glass fiber prepared in Preparation Example 1 in Example 9, and the other conditions are the same as those in Example 1. Example 10

[0069] The preparation method of Example 10 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 8 is used to replace the modified glass fiber prepared in Preparation Example 1 in Example 10, and the other conditions are the same as those in Example 1. Example 11

[0070] The preparation method of Example 11 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 9 is used to replace the modified glass fiber prepared in Preparation Example 1 in Example 11, and the other conditions are the same as those in Example 1. Example 12

[0071] The preparation method of Example 12 is basically similar to that of Example 1, except that the modified glass fiber prepared in Preparation Example 10 is used to replace the modified glass fiber prepared in Preparation Example 1 in Example 12, and the other conditions are the same as those in Example 1.

[0072] Comparative Example 1

[0073] The preparation method of Comparative Example 1 is basically similar to that of Example 1, except that the chopped glass fiber (alkali-free chopped glass fiber ECS13-4.5-T538D, Taishan Glass Fiber, length 4.5 mm, diameter 13 μm) is used to replace the modified glass fiber prepared in Preparation Example 1.

[0074] Comparative Example 2

[0075] Comparative Example 2 was prepared in a manner similar to Example 1, except that 18 parts by mass of chopped glass fibers (alkali-free chopped glass fiber ECS13-4.5-T538D, Taishan Fiberglass, 4.5 mm in length, 13 μm in diameter) and 4 parts by mass of barium phthalate (purchased from Alpha Company) were used instead of the modified glass fiber prepared in Preparation Example 1.

[0076] Comparative Example 3

[0077] Comparative Example 3 was prepared in a manner similar to Example 1, except that the modified glass fiber prepared in Preparation Example 11 was used instead of the modified glass fiber prepared in Preparation Example 1, and other conditions were the same as those in Example 1.

[0078] Comparative Example 4

[0079] Comparative Example 4 was prepared in a manner similar to Example 1, except that the modified glass fiber prepared in Preparation Example 12 was used instead of the modified glass fiber prepared in Preparation Example 1, and other conditions were the same as those in Example 1.

[0080] Performance Test

[0081] 1. Warpage

[0082] The polypropylene composition was injection molded into a sample with a size of 100 mm x 100 mm x 2 mm, and one corner of the sample was fixed to the horizontal table surface. The sample was allowed to stand for 72 h at room temperature to achieve sufficient shrinkage. The height of the corner was measured using a vernier caliper, and the warpage was recorded. To ensure the reliability of the test results, 5 samples were randomly selected for each test, and the average value was taken as the test result of the warpage.

[0083] 2. Flexural modulus

[0084] Flexural modulus: tested according to ISO 178-2019, with a sample size of 80 mm x 10 mm x 4 mm, a span of 64 mm, and a speed of 2 mm / min.

[0085] The polypropylene samples prepared in Examples 1-12 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1.

[0086] Table 1 Performance test table of polypropylene of Examples 1-12 and Comparative Examples 1-4

[0087] Experimental group Warpage (mm) Flexural modulus (MPa) Example 1 0.52 1750 Example 2 0.44 1590 Example 3 0.73 1800 Example 4 0.66 1770 Example 5 0.50 1680 Example 6 0.46 1620 Example 7 0.41 1690 Example 8 0.36 1670 Example 9 0.39 1680 Example 10 0.45 1710 Example 11 0.29 1580 Example 12 0.49 1720 Comparative Example 1 2.83 1890 Comparative Example 2 2.77 1760 Comparative Example 3 2.64 1570 Comparative Example 4 3.35 1640

[0088] Compared with the test results of the comparative examples 1-4 and the above table 1, it can be seen that, compared with the comparative example 1 adding unmodified glass fiber, the comparative example 2 adding a physical mixture of glass fiber and β nucleating agent, the comparative example 3 adding glass fiber loaded with β nucleating agent by crystallization, and the comparative example 4 adding glass fiber grafted with α nucleating agent, the modified glass fiber grafted with β nucleating agent in the application can effectively promote the formation of β lamellae perpendicular to the orientation direction of the glass fiber around the glass fiber in the process of cooling crystallization of the polypropylene material. The low shrinkage characteristics of the β lamellae can compensate for the high shrinkage of the α spherulites perpendicular to the orientation direction of the glass fiber, reduce the difference in shrinkage rate along the orientation direction of the glass fiber, and thus reduce the warpage of the polypropylene material, while maintaining excellent flexural modulus. The polypropylene material has excellent flexural modulus when the unmodified glass fiber is added in the comparative example 1, but the warpage is large, which is not conducive to its application in automobile structural parts. In the comparative example 2, a physical mixture of glass fiber and β nucleating agent is added, and the β nucleating agent is uniformly dispersed in the polypropylene during the preparation of the polypropylene, so that the β lamellae are isotropically distributed, and the improvement of the warpage of the material is not obvious, and the introduced β crystal reduces the flexural modulus of the polypropylene material. In the comparative example 3, the β nucleating agent is loaded on the glass fiber by crystallization, and due to the difference in fiber surface characteristics and the limitation of crystallization kinetics, the β nucleating agent on the glass fiber is non-uniformly or accumulatedly distributed, which is not conducive to the nucleation of the β nucleating agent, and the content and distribution of the generated β lamellae are small, which has little effect on the improvement of the warpage of the polypropylene material, and the flexural modulus of the material is seriously deteriorated. In the comparative example 4, benzoic acid is grafted on the glass fiber, and benzoic acid has α nucleation effect, which has no benefit for reducing the shrinkage of the polypropylene material perpendicular to the orientation direction of the glass fiber, and the formation of the transcrystalline layer further deteriorates the warpage and the flexural modulus of the polypropylene material.

[0089] As can be seen from examples 1-3, when the amount of modified glass fiber added is 15 to 30 parts, the polypropylene material has low warpage and excellent flexural modulus.

[0090] As can be seen from the comparison of examples 1, 4-6 and examples 7-9, the dicarboxylic acid compound includes glutaric acid and phthalic acid, and the molar ratio of glutaric acid to phthalic acid is 1:1-3:1, so that the glass fiber is grafted with a certain proportion of phthalic acid metal salt and glutaric acid metal salt, which is conducive to further reducing the warpage while maintaining excellent flexural modulus.

[0091] As can be seen from Examples 8 and 10, the metal hydroxide is at least one of barium hydroxide and potassium hydroxide, and the modified glass fiber prepared makes the polypropylene material have low warpage. As can be seen from the comparison between Example 8 and Example 10, the metal hydroxide is barium hydroxide, and the polypropylene material has further reduced warpage and excellent flexural modulus.

[0092] As can be seen from Examples 8, 11 and 12, the mass ratio of the glass fiber to the silane coupling agent is 2:1-10:1, and the modified glass fiber prepared finally makes the polypropylene material have low warpage and excellent flexural modulus.

[0093] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, and the modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A high-rigidity low-warpage polypropylene material for an automotive structural member, characterized by, The polypropylene material comprises the following components calculated by mass parts: Polypropylene resin 50-65 parts; Talc 10-15 parts; Compatibilizer 2-5 parts; Antioxidant 0.2-0.6 parts; Lubricant 0.5-1.5 parts; Modified glass fiber 15-30 parts; The modified glass fiber is alkali-free short-cut glass fiber grafted with a beta nucleating agent, and the beta nucleating agent comprises one or more of metal salts of glutaric acid, pimelic acid, adipic acid, terephthalic acid and phthalic acid. The preparation method of the modified glass fiber comprises the following steps: (1) disperse alkali-free short-cut glass fiber in a mixed solvent of ethanol and deionized water, add aminopropyl triethoxysilane, stir and react at 60-80°C for 10-14 hours, centrifugal dry to obtain alkali-free short-cut glass fiber modified with surface amino groups; (2) disperse dicarboxylic acid compound in dichloromethane, add dichlorosulfoxide and catalyst N,N-dimethylformamide, stir and react at 22-28°C for 1-3 hours, remove dichloromethane to obtain a first intermediate product, wherein the dicarboxylic acid compound comprises one or more of glutaric acid, pimelic acid, adipic acid, terephthalic acid and phthalic acid, and the molar ratio of the dicarboxylic acid compound to the dichlorosulfoxide is 1:1; (3) disperse the first intermediate product in dichloromethane, add the alkali-free short-cut glass fiber modified with surface amino groups, stir and react at 0-10°C for 10-14 hours, centrifugal to obtain solid, dry to obtain a second intermediate product; (4) disperse the second intermediate product and metal hydroxide in methanol, stir and react at 22-28°C for 20-28 hours, centrifugal dry to obtain the modified glass fiber, wherein the metal hydroxide comprises at least one of alkali metal hydroxide and alkaline earth metal hydroxide; In step (2), the dicarboxylic acid compound comprises glutaric acid and phthalic acid, and the molar ratio of the glutaric acid to the phthalic acid is 1:1-3:

1.

2. The high rigidity low warpage polypropylene material for automotive structural parts according to claim 1, characterized in that, In step (4), the metal hydroxide comprises at least one of barium hydroxide and potassium hydroxide.

3. The high rigidity low warpage polypropylene material for automotive structural parts according to claim 1, wherein, In step (1), the mass ratio of the alkali-free short-cut glass fiber to the aminopropyl triethoxysilane is 4:1-10:

1.

4. The high rigidity low warpage polypropylene material for automotive structural parts according to claim 1, wherein, In step (1), the length of the alkali-free short-cut glass fiber is 3-5 mm, and the diameter is 12-15 μm.

5. The high rigidity low warpage polypropylene material for automotive structural parts according to claim 1, wherein, The polypropylene resin comprises high-impact polypropylene resin and high-flow polypropylene resin, the melt index of the high-impact polypropylene resin under the condition of 230°C and 2.16 kg is 0.5-20 g / 10 min, and the melt index of the high-flow polypropylene resin under the condition of 230°C and 2.16 kg is 25-30 g / 10 min.

6. The high rigidity low warpage polypropylene material for automotive structural parts according to claim 1, wherein, The antioxidant comprises hindered phenol primary antioxidant 1010 and phosphite auxiliary antioxidant 168; and / or, The compatibilizer comprises maleic anhydride grafted polypropylene.

7. The high rigidity low warpage polypropylene material for automotive structural parts according to claim 1, wherein, The lubricant includes one or more of polyethylene wax, ethylene bis fatty acid amide, silicone master granule, and pentaerythritol stearate.

8. A process for the production of a high-rigid low-warpage polypropylene material for automotive structural parts according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: According to the mass fraction, polypropylene resin, talcum powder, compatibilizer, antioxidant and lubricant are mixed and then added into the main feeding port of the double-screw extruder, and the modified glass fiber is added into the side feeding port of the double-screw extruder, the temperature of each zone of the double-screw extruder is 180-220 DEG C, and the high-rigidity low-warp polypropylene material for automobile structural parts is prepared after extrusion and drying.