Polypropylene resin, process for its preparation and use thereof

Abstract

The application relates to the field of high polymer materials, and discloses a polypropylene resin, a preparation method and application of the polypropylene resin, wherein the polypropylene resin comprises a polypropylene homopolymer phase and a rubber phase dispersed in the homopolymer phase, the rubber phase is a copolymer of ethylene and an alpha-olefin; the content of the homopolymer phase is 70-80 wt% and the content of the rubber phase is 20-30 wt% based on the polypropylene resin; and the average sphericity of the rubber phase is 1-1.5. Injection-molded products made of the polypropylene resin can effectively avoid the formation of "flow marks" on the surface of the products, and the polypropylene resin has good rigidity and toughness balance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a polypropylene resin, its preparation method, and its applications. Background Technology

[0002] Polypropylene is a thermoplastic polymer with excellent comprehensive properties, characterized by low production cost, low density, high product transparency, good chemical stability and electrical insulation, and ease of processing. Due to its excellent performance-price ratio, polypropylene is the fastest-growing thermoplastic resin among the five major general-purpose resins, second only to polyethylene in production volume. It is widely used in many fields such as the automotive industry, home appliances, electronics, agriculture, packaging, building materials, furniture, and textiles.

[0003] In the automotive industry, driven by the trend towards lightweight vehicles, large-scale, thin-walled injection molded products are increasingly widely used. For these types of parts, not only excellent mechanical properties are essential, but also aesthetic appeal. However, large, thin-walled injection molded parts have a higher rate of surface defects, are prone to flow marks, and these defects become increasingly pronounced as the material ages.

[0004] In the molding process of large injection molded parts, the melt flow is relatively long, and under the action of shear force, it is prone to flow instability, resulting in periodic differences in the surface gloss of the injection molded products, macroscopically forming the phenomenon of "flow marks". Controlling the stress applied to the polymer melt can effectively reduce the occurrence of "flow marks", including using appropriate "gate" design and controlling suitable injection molding process parameters. However, current methods cannot fundamentally solve the "flow mark" defect. From the perspective of mechanical balance performance and the flexibility of large component design, it is more necessary to start with the raw materials, and on the basis of considering mechanical properties, improve the shear thinning resistance of the polymer melt through structural design. Only in this way can the "flow mark" defect be fundamentally solved, providing the parts with excellent aesthetic appearance.

[0005] CN110753726A discloses a polypropylene composition with excellent surface appearance, but requires the additional addition of peroxide and crosslinking agent to the polypropylene composition. CN112679842A discloses a polypropylene composition for efficiently improving flow marks, which includes a flow mark improver, said flow mark improver being a high molecular weight homopolymer polypropylene with a melt flow rate of <0.5g / 10min and a weight-average molecular weight Mw >1.5×106g / mol under test conditions of 230℃ and 2.16kg. The high molecular weight homopolymer polypropylene will lead to reduced fluidity of the composition and increased processing difficulty. Summary of the Invention

[0006] To overcome the problem of "flow marks" on the surface of injection molded products in the prior art, a polypropylene resin, its preparation method and application are provided. This polypropylene resin can effectively reduce the "flow marks" defect on the surface of injection molded products.

[0007] To achieve the above objectives, a first aspect of the present invention provides a polypropylene resin comprising a polypropylene homopolymer phase and a rubber phase dispersed in the homopolymer phase, wherein the rubber phase is a copolymer of ethylene and α-olefin.

[0008] Based on the polypropylene resin, the content of the homopolymer phase is 70-80 wt%, and the content of the rubber phase is 20-30 wt%.

[0009] The average sphericity of the rubber phase is 1-1.5.

[0010] A second aspect of the present invention provides a method for preparing the polypropylene resin provided in the first aspect of the present invention, comprising the following steps:

[0011] (1) In the presence of Ziegler-Natta catalyst, alkylaluminum, molecular weight regulator and external electron donor, propylene undergoes homopolymerization to obtain homopolymer polypropylene;

[0012] (2) In the presence of a molecular weight regulator, the homopolymer polypropylene is copolymerized with ethylene and α-olefin to obtain the polypropylene resin;

[0013] In step (2), the molar ratio of ethylene to α-olefin is 0.8-1.3:1, and the molar ratio of molecular weight regulator to ethylene is 0.005-0.05:1.

[0014] The third aspect of the present invention provides an application of the polypropylene resin provided in the first aspect of the present invention in automotive interior and exterior trim parts.

[0015] The technical aspects provided by this invention have the following beneficial effects:

[0016] (1) The polypropylene resin provided by the present invention has a good balance of rigidity and toughness;

[0017] (2) Injection molded products made with the polypropylene resin provided by the present invention, especially large thin-walled products, can effectively avoid the formation of "flow marks" on the surface of the products. Attached Figure Description

[0018] Figure 1 and Figure 2 Scanning electron microscope (SEM) image of a cross-section of a polypropylene resin A5 injection molded section;

[0019] Figure 3 and Figure 4 This is a scanning electron microscope (SEM) image of a cross-section of a D2 injection-molded polypropylene resin slice. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The first aspect of the present invention provides a polypropylene resin, the polypropylene resin comprising a polypropylene homopolymer phase and a rubber phase dispersed in the homopolymer phase, wherein the rubber phase is a copolymer of ethylene and α-olefin;

[0022] Based on the polypropylene resin, the content of the homopolymer phase is 70-80 wt%, and the content of the rubber phase is 20-30 wt%.

[0023] The average sphericity of the rubber phase is 1-1.5.

[0024] When the content of the homopolymer phase and the rubber phase and the average sphericity of the polypropylene resin provided by the present invention are within the above range, the polypropylene resin has good rigidity and toughness balance, and the rubber phase is not prone to microscopic deformation during the product molding process, which can effectively avoid the formation of "flow marks" on the surface of the injection molded product.

[0025] Typically, the location of the first flow mark is used to describe the surface quality of injection molded parts. The first flow mark represents the distance between the gate of the injection molded part and the location of the first flow mark. The larger this distance, the more difficult it is for the "flow mark" to form, and the better the surface quality of the injection molded part. Conversely, the smaller the distance, the worse the surface quality.

[0026] In this invention, the method for testing the average sphericity of the rubber phase is as follows:

[0027] Polypropylene resin was heated to 210℃ to melt it, and injected into a mold at 45℃ under a pressure of 75MPa. The pressure was held at 60MPa for 2 seconds, followed by a holding time of 60 seconds and a cooling time of 20 seconds. The material was then demolded and injection molded into a sheet measuring 250×40×2.5mm. The sheet was sliced ​​along the injection flow direction and immersed in 50℃ xylene liquid for 240 minutes to etch away the rubber phase from the polypropylene resin. The cross-section of the slice was observed using a scanning electron microscope at a magnification of 1000 / 5000. The aspect ratio of all remaining pores in the etched rubber phase within the field of view was determined using ImageJ image analysis software, and their arithmetic mean was calculated to obtain the average sphericity of the polypropylene resin rubber phase.

[0028] According to a preferred embodiment of the present invention, based on the polypropylene resin, the content of the homopolymer phase is 73-77 wt%, and the content of the rubber phase is 23-27 wt%.

[0029] In this invention, when the content of homopolymer phase and rubber phase in the polypropylene resin is within the above-mentioned range, the rigidity-toughness balance of the polypropylene resin can be further improved.

[0030] In the polypropylene resin, the contents of the homopolymer phase and the rubber phase are calculated by the amount of feed for the copolymerization reaction.

[0031] Homopolymer phase mass content = mass of homopolymer polypropylene / mass of polypropylene resin × 100%;

[0032] Rubber phase mass content = (mass of reacted ethylene + mass of reacted α-olefin) / mass of polypropylene resin × 100%.

[0033] According to the present invention, preferably, the average sphericity of the rubber phase is 1.1-1.3.

[0034] In this invention, when the average sphericity of the rubber phase is within the above-mentioned range, the generation of "flow marks" can be further avoided.

[0035] According to a preferred embodiment of the present invention, the polypropylene resin contains 5-15 wt% structural units derived from ethylene.

[0036] More preferably, the polypropylene resin contains 8-12 wt% structural units derived from ethylene.

[0037] According to a preferred embodiment of the present invention, the molecular weight distribution index of the polypropylene resin is 8-14.

[0038] In this invention, when the molecular weight distribution index of the polypropylene resin is within the above-mentioned range, the polymer has good processing fluidity and can improve the shear deformation resistance of the polymer melt, effectively avoiding the generation of flow marks.

[0039] More preferably, the molecular weight distribution index of the polypropylene resin is 10-12.

[0040] According to the present invention, preferably, the molecular weight distribution index of the homopolymer phase is 3-5.

[0041] In this invention, when the molecular weight distribution index of the homopolymer phase is within the above-mentioned range, the macromolecular content of the homopolymer phase is relatively low, which can reduce the shear orientation of the polymer melt during the mold filling process and avoid the generation of flow marks.

[0042] More preferably, the molecular weight distribution index of the homopolymer phase is 3-4.

[0043] According to a preferred embodiment of the present invention, the melt index of the polypropylene resin measured at 230°C and 2.16 kg load is 10-30 g / 10 min.

[0044] In this invention, when the melt index of the polypropylene resin is within the above-mentioned range, the polypropylene resin has good flowability.

[0045] More preferably, the melt index of the polypropylene resin measured at 230°C and 2.16 kg load is 22-28 g / 10 min.

[0046] According to the present invention, preferably, the isotactic index of the homopolymer phase is not less than 93.5%.

[0047] In this invention, when the isotactic index of the homopolymer phase is within the above-mentioned range, the polypropylene resin provided by this invention has better rigidity-toughness balance.

[0048] More preferably, the isotactic index of the homopolymer phase is not less than 94.5%.

[0049] According to a preferred embodiment of the present invention, the content of xylene-soluble substances in the polypropylene resin is 15-28 wt%.

[0050] In this invention, when the content of xylene-soluble substances in the polypropylene resin is within the above-mentioned range, the polypropylene resin provided by this invention has good toughness and surface quality.

[0051] More preferably, the content of xylene-soluble substances in the polypropylene resin is 18-25 wt%.

[0052] According to the present invention, preferably, the ethylene content in the xylene soluble is 40-65 wt%.

[0053] In this invention, when the ethylene content in the xylene-soluble material is within the above-mentioned range, it can further improve the toughness of the polypropylene resin and has an ideal intrinsic viscosity of xylene-soluble material, which helps to improve the shear thinning resistance of the rubber phase, improve the flow stability of the rubber phase during injection molding, and help to reduce the generation of flow marks.

[0054] More preferably, the ethylene content in the xylene-soluble substance is 45-55 wt%.

[0055] According to a preferred embodiment of the present invention, the xylene-soluble intrinsic viscosity of the polypropylene resin is 3-7 dL / g, and the xylene-insoluble intrinsic viscosity is 0.5-1.8 dL / g.

[0056] In this invention, xylene-soluble substances refer to substances that can dissolve in xylene at 40°C, and xylene-insoluble substances refer to substances that are insoluble in xylene at 40°C. The intrinsic viscosity of xylene-soluble substances is determined using xylene as a solvent at 40°C; the intrinsic viscosity of xylene-insoluble substances is determined using xylene as a solvent at 160°C.

[0057] More preferably, in the polypropylene resin, the intrinsic viscosity of xylene-soluble matter is 4-6 dL / g, and the intrinsic viscosity of xylene-insoluble matter is 1.4-1.6 dL / g.

[0058] When the intrinsic viscosity of xylene-soluble and xylene-insoluble components in the polypropylene resin is within the above range, the rubber phase melt has high elasticity and short relaxation time. The flow of the homopolymer phase will not have a significant impact on the morphology of the rubber phase. Therefore, the rubber phase is not easily deformed, has high sphericity, and the surface quality of the product is good.

[0059] According to the present invention, preferably, the intrinsic viscosity ratio of the xylene soluble component to the xylene insoluble component is 2-8:1.

[0060] More preferably, the intrinsic viscosity ratio of the xylene-soluble component to the xylene-insoluble component is 3-7:1.

[0061] A second aspect of the present invention provides a method for preparing the polypropylene resin provided in the first aspect of the present invention, comprising the following steps:

[0062] (1) In the presence of Ziegler-Natta catalyst, alkylaluminum, molecular weight regulator and external electron donor, propylene undergoes homopolymerization to obtain homopolymer polypropylene;

[0063] (2) In the presence of a molecular weight regulator, the homopolymer polypropylene is copolymerized with ethylene and α-olefin to obtain the polypropylene resin;

[0064] In step (2), the molar ratio of ethylene to α-olefin is 0.8-1.3:1, and the molar ratio of molecular weight regulator to ethylene is 0.005-0.05:1.

[0065] In this invention, when the molar ratio of ethylene to α-olefin is within the above range, the intrinsic viscosity of the rubber phase can be effectively increased, and the interaction between the rubber phase and the homopolymer phase is low. During the melt flow process, the rubber phase is not easily affected by the homopolymer phase, thereby reducing the generation of flow marks.

[0066] According to a preferred embodiment of the present invention, the mass ratio of ethylene to α-olefin in step (2) is 0.9-1.1:1.

[0067] According to the present invention, preferably, the mass ratio of the molecular weight regulator to ethylene in step (2) is 0.008-0.02:1.

[0068] In this invention, when the mass ratio of the molecular weight regulator to ethylene in step (2) is within the above range, it can further improve the intrinsic viscosity of the rubber phase, improve the shear thinning resistance of the rubber phase, enhance the flow stability of the rubber phase during injection molding, and make the injection molded products less prone to flow marks.

[0069] According to the present invention, preferably, the α-olefin comprises propylene and optionally C4-C 12 α-Alkenes, such as 1-butene, 1-pentene, and 1-hexene.

[0070] According to a preferred embodiment of the present invention, in step (1), the mass ratio of the alkyl aluminum to the external electron donor is ≥40.

[0071] In this invention, when the mass ratio of the alkylaluminum to the external electron donor is within the above-mentioned range, it is beneficial to reduce the amount of hydrogen added. At the same time, in synergy with the preferred catalyst, it can ensure that the homopolymer still has a high isotactic index and ensure the rigidity of the polypropylene resin.

[0072] More preferably, the mass ratio of the alkylaluminum to the external electron donor is 40-50:1.

[0073] According to the present invention, preferably, the mass ratio of the catalyst to propylene in step (1) is 1:10000-30000.

[0074] In this invention, the mass ratio of catalyst to propylene can affect the molecular weight and molecular weight distribution of the polypropylene homopolymer phase, and thus affect the melt index of the polypropylene homopolymer phase. In this invention, when the mass ratio of catalyst to propylene in step (1) is within the above-mentioned range, a polypropylene homopolymer phase with a melt index of 10-30 g / 10 min measured at 230°C and 2.16 kg load can be obtained.

[0075] More preferably, the mass ratio of the catalyst to propylene in step (1) is 1:15000-25000.

[0076] According to a preferred embodiment of the present invention, in step (1), the molar ratio of the molecular weight regulator to propylene is 0.003-0.01:1.

[0077] In this invention, the amount of molecular weight regulator is the main factor affecting the molecular weight of polypropylene resin. When the mass ratio of molecular weight regulator to propylene in step (1) is within the above range, a polypropylene resin with a melt index of 10-30 g / 10 min can be obtained.

[0078] More preferably, the mass ratio of the molecular weight regulator to propylene is 0.05-0.08:1.

[0079] According to the present invention, preferably, the mass ratio of the Ziegler-Natta catalyst to alkylaluminum in step (1) is 1:1-8.

[0080] More preferably, the mass ratio of the Ziegler-Natta catalyst to alkylaluminum is 1:2-5.

[0081] According to the present invention, preferably, the mass ratio of homopolymer polypropylene to added ethylene in step (2) is 1:0.05-0.5.

[0082] More preferably, the mass ratio of homopolymer polypropylene to added ethylene in step (2) is 1:0.1-0.4.

[0083] In this invention, the Ziegler-Natta catalyst may be selected from at least one of Basell ZN101-1, Basell ZN118, Basell ZN121, Sinopec HR and Sinopec DQC catalysts.

[0084] In a specific embodiment of the present invention, the Ziegler-Natta catalyst is a Sinopec HR catalyst, the main component of which is TiCl4.

[0085] The present invention allows for a wide range of specific types of alkyl aluminum, such as trimethylaluminum, triethylaluminum, and triisobutylaluminum. In some embodiments of the present invention, the alkyl aluminum is triethylaluminum.

[0086] This invention allows for a wide range of specific types of molecular weight regulators. The molecular weight regulators in steps (1) and (2) can be independently selected from hydrogen and small molecule alkanes such as ethane and propane. In some embodiments of this invention, the molecular weight regulator in steps (1) and (2) is hydrogen.

[0087] In this invention, those skilled in the art can conventionally select appropriate reaction temperatures and pressures.

[0088] According to some specific embodiments of the present invention, the reaction temperature in step (1) is 65-75°C and the pressure is 3.2-3.8 MPa. The reaction temperature in step (2) is 70-78°C and the pressure is 1.2-1.6 MPa.

[0089] According to the present invention, additives may be added when preparing polypropylene resin, and the specific type, amount and timing of the additives can be conventionally selected by those skilled in the art.

[0090] In some embodiments of the present invention, the method for preparing the polypropylene resin further includes extruding and granulating the resulting resin after the copolymerization reaction is completed.

[0091] This invention does not impose any particular limitations on the specific conditions for extrusion granulation, and those skilled in the art can choose conventionally. In some embodiments of this invention, the extruder temperature is 200-230°C, and the pelletizing water temperature is 55-65°C.

[0092] In some embodiments of the present invention, in the extrusion granulation process, based on the polypropylene resin, 0.1-0.2 wt% of antioxidant and 0.03-0.1 wt% of halogen absorbent are added.

[0093] Furthermore, the antioxidant comprises phenolic antioxidants and phosphite antioxidants, wherein the mass ratio of the phenolic antioxidants to the phosphite antioxidants is 1:1-3, preferably 1:1.5-2.5.

[0094] The phenolic antioxidant may be selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], catechol, resorcinol, 3,9-bis[1,1-dimethyl-2-[(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane and triethylene glycol bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylonitrile, preferably pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0095] The phosphite antioxidant is selected from tris(2,4-di-tert-butylphenyl) phosphite and / or pentaerythritol diisodecyl diphosphite, preferably tris(2,4-di-tert-butylphenyl) phosphite.

[0096] The halogen absorbent may be calcium stearate and / or hydrotalcite, preferably calcium stearate.

[0097] In some specific embodiments of the present invention, in step (1):

[0098] The feed rate for the Ziegler-Natta catalyst is 1-1.5 kg / h;

[0099] The feed rate for alkylaluminum is 2-8 kg / h;

[0100] The propylene feed rate is 20,000-45,000 kg / h;

[0101] In some specific embodiments of the present invention, in step (2):

[0102] The feed rate for homopolymer polypropylene is 20,000-40,000 kg / h;

[0103] The ethylene feed rate is 3000-5000 kg / h;

[0104] The feed rate for α-olefins is 500-2000 kg / h;

[0105] The third aspect of the present invention provides an application of the polypropylene resin provided in the first aspect of the present invention in automotive interior and exterior trim parts.

[0106] In this invention, the method for preparing injection molded specimens refers to GB / T 17037.1-2019;

[0107] The ethylene content in polypropylene resin was determined by infrared spectroscopy.

[0108] The content of homopolymer phase and rubber phase is calculated based on the amount of feed used in the copolymerization reaction;

[0109] The melt flow index (MFR) was determined according to GB / T 3682-2000 at 230℃ and 2.16kg load.

[0110] The method for determining tensile strength shall refer to GB / T 1040.2-2022;

[0111] The method for determining the flexural modulus is in accordance with GB / T 9341-2008;

[0112] The method for determining the impact strength of simply supported beams shall refer to GB / T 1043.1-2008;

[0113] The method for determining heat distortion temperature (HDT) shall refer to GB / T 1634.2-2004;

[0114] The molecular weight distribution index (PDI) is the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn); the weight-average molecular weight and number-average molecular weight were determined using a gel permeation chromatograph from PolymerChar.

[0115] The method for determining the isotactic index of homopolymer is as follows: GB / T 2412-2008;

[0116] The ethylene content, intrinsic viscosity of xylene solubles, and intrinsic viscosity of xylene insolubles were determined using a Polymer CharCrystal CRYSTEX instrument.

[0117] The distance of the first flow mark is the distance between the gate of the injection molded sample and the location where the first flow mark appears.

[0118] The test method for the average sphericity of the rubber phase is as follows:

[0119] Polypropylene resin was heated to 210℃ to melt it, and injected into a mold at 45℃ under a pressure of 75MPa. The pressure was held at 60MPa for 2 seconds, followed by a holding time of 60 seconds and a cooling time of 20 seconds. The material was then demolded and injection molded into a sheet measuring 250×40×2.5mm. The sheet was sliced ​​along the injection flow direction and immersed in 50℃ xylene liquid for 240 minutes to etch away the rubber phase from the polypropylene resin. The cross-section of the slice was observed using a scanning electron microscope at a magnification of 1000 / 5000. The aspect ratio of all remaining pores in the etched rubber phase within the field of view was determined using ImageJ image analysis software, and their arithmetic mean was calculated to obtain the average sphericity of the polypropylene resin rubber phase.

[0120] The present invention will be described in detail below through embodiments.

[0121] In the following examples, the Ziegler-Natta catalyst HR was purchased from Sinopec;

[0122] Ziegler-Natta catalysts ZN121 and ZN168 were purchased from Basell;

[0123] Unless otherwise specified, all other reagents and raw materials are commercially purchased.

[0124] All tests were performed in 5 parallel sets, and the average value was taken.

[0125] Example 1

[0126] Prepare polypropylene resin according to the following steps:

[0127] (1) In a Spherizone multi-zone circulating reactor, propylene was polymerized in the presence of Ziegler-Natta catalyst ZN121, co-catalyst triethylaluminum (TEA), and external electron donor cyclohexyl-methyl-dimethoxysilane. The reaction temperature was 70℃ and the pressure was 3.0 MPa. The feed rate of Ziegler-Natta catalyst was 1.4 kg / h, the feed rate of triethylaluminum was 5.6 kg / h, and the mass ratio (T / D) of triethylaluminum to external electron donor was 50:1. The propylene feed rate was 35,500 kg / h. Hydrogen was used as a molecular weight regulator, and the hydrogen feed rate was 15 kg / h.

[0128] That is, the mass ratio of catalyst to propylene is 1:25357, the mass ratio of catalyst to triethylaluminum is 1:4, and the molar ratio of hydrogen to propylene is 0.0088:1.

[0129] The product was subjected to gas-solid separation through a bag filter to obtain homopolymer polypropylene powder and carrier gas. The melt index of the polypropylene powder was 180 g / 10 min at 230℃ and 2.16 kg load. The carrier gas was compressed and recycled.

[0130] (2) The above-mentioned polypropylene powder is fed into a gas-phase copolymerization reactor, where ethylene, propylene, and hydrogen are introduced for gas-phase copolymerization. The reaction temperature is 80℃ and the pressure is 1.4MPa. The feed rate of the homopolymer polypropylene powder is 33000kg / h, the feed rate of ethylene is 4500kg / h, the mass ratio of homopolymer polypropylene to added ethylene is 1:0.14, the molar ratio of ethylene to propylene is 1:1, and the molar ratio of the molecular weight regulator hydrogen to ethylene is 0.012:1. The product undergoes gas-solid separation through a bag filter to obtain impact-resistant polypropylene powder and carrier gas. The carrier gas is compressed and recycled.

[0131] (3) The impact-resistant polypropylene powder was mixed with composite antioxidant B215 and calcium stearate, and then melt-extruded using an extruder. The amount of composite antioxidant B215 added was 0.15 wt% of the impact-resistant polypropylene powder, and the amount of calcium stearate added was 0.05 wt% of the impact-resistant polypropylene powder. The extruder screw speed was 280 rpm, and the barrel temperature was 230℃. After extrusion, the mixture was pelletized at a pelletizing water temperature of 60℃ to obtain polypropylene resin A1.

[0132] Example 2

[0133] Polypropylene resin was prepared using the method described in Example 1, except that in step (2), the ethylene feed rate was 4300 kg / h, the mass ratio of homopolymer polypropylene to added ethylene was 1:0.14, and the molar ratio of ethylene to propylene was 1.22:1, resulting in polypropylene resin A2.

[0134] Example 3

[0135] Polypropylene resin was prepared using the method described in Example 1, except that the Ziegler-Natta catalyst was Sinopec HR catalyst, resulting in polypropylene resin A3.

[0136] Example 4

[0137] Polypropylene resin was prepared using the method described in Example 1, except that in step (2), the ethylene feed rate was 3800 kg / h, the mass ratio of homopolymer polypropylene to added ethylene was 1:0.12, the molar ratio of ethylene to propylene was 0.82:1, and the molar ratio of molecular weight regulator hydrogen to ethylene was 0.03:1, resulting in polypropylene resin A4.

[0138] Example 5

[0139] Polypropylene resin was prepared using the method described in Example 1, except that in step (2), the ethylene feed rate was 3800 kg / h, the mass ratio of homopolymer polypropylene to added ethylene was 1:0.12, the molar ratio of ethylene to propylene was 0.82:1, and the molar ratio of molecular weight regulator hydrogen to ethylene was 0.005:1, resulting in polypropylene resin A5.

[0140] Figure 1 and Figure 2 The image shows a scanning electron microscope (SEM) image of a cross-section of a polypropylene resin A5 injection molded section. It can be seen that the cross-section of the pores formed by etching away the rubber phase is nearly circular, with an average sphericity closer to 1.

[0141] Example 6

[0142] Polypropylene resin was prepared using the method described in Example 1, except that in step (2), the ethylene feed rate was 5100 kg / h, the mass ratio of homopolymer polypropylene to added ethylene was 1:0.15, the molar ratio of ethylene to propylene was 1.22:1, and the molar ratio of the molecular weight regulator hydrogen to ethylene was 0.05:1. ， Polypropylene resin A6 was obtained.

[0143] Example 7

[0144] Polypropylene resin was prepared using the method described in Example 1, except that in step (2), the ethylene feed rate was 4500 kg / h, the mass ratio of homopolymer polypropylene to added ethylene was 1:0.14, the molar ratio of ethylene to propylene was 0.92:1, and the molar ratio of molecular weight regulator hydrogen to ethylene was 0.012:1, resulting in polypropylene resin A7.

[0145] Example 8

[0146] Polypropylene resin was prepared using the method described in Example 1, except that in step (2), the ethylene feed rate was 4500 kg / h, the mass ratio of homopolymer polypropylene to added ethylene was 1:0.14, the molar ratio of ethylene to propylene was 1.08:1, and the molar ratio of molecular weight regulator hydrogen to ethylene was 0.012:1, resulting in polypropylene resin A8.

[0147] Example 9

[0148] Polypropylene resin was prepared using the method described in Example 1, except that the mass ratio (T / D) of triethylaluminum to external electron donor was 40, resulting in polypropylene resin A9.

[0149] Example 10

[0150] Polypropylene resin was prepared using the method described in Example 1, except that the mass ratio (T / D) of triethylaluminum to external electron donor was 80, resulting in polypropylene resin A10.

[0151] Example 11

[0152] Polypropylene resin was prepared using the method described in Example 1, except that the mass ratio (T / D) of triethylaluminum to external electron donor was 30, resulting in polypropylene resin A11.

[0153] Comparative Example 1

[0154] Polypropylene resin was prepared using the method described in Example 1, except that in step (2), the ethylene feed rate was 4800 kg / h, the mass ratio of homopolymer polypropylene to added ethylene was 1:0.15, the molar ratio of ethylene to propylene was 0.43:1, and the molar ratio of molecular weight regulator hydrogen to ethylene was 0.012:1, resulting in polypropylene resin D1.

[0155] Comparative Example 2

[0156] Polypropylene resin was prepared using the method described in Example 1, except that the molar ratio of hydrogen to ethylene in step (2) was 0.1:1, resulting in polypropylene resin D2.

[0157] Figure 3 and Figure 4 The image shows a scanning electron microscope (SEM) image of a cross-section of a polypropylene resin D2 injection molded section. It can be seen that the cross-section of the pores formed by etching away the rubber phase is more flat and elongated.

[0158] Test case

[0159] According to the method described in the specific embodiments of this invention, polypropylene resin is injection molded, the average sphericity of the rubber phase is measured, and the distance between the first flow mark and the melt injection point during the injection process is measured.

[0160] According to the method described in the specific embodiments section of this invention, the contents of the homopolymer phase and the rubber phase are calculated, and the physicochemical parameters and mechanical properties of the polypropylene resin are determined.

[0161] The results are shown in Table 1.

[0162] Table 1

[0163]

[0164]

[0165] Table 1 (continued)

[0166]

[0167] Table 1 (continued)

[0168]

[0169]

[0170] As can be seen from the results in Table 1, the polypropylene resin rubber phase provided by the present invention has an average sphericity of 1-1.5, which results in a greater distance between the first flow mark and the melt injection point during the injection molding process, and higher surface quality of the injection molded product. At the same time, the polypropylene resin rubber phase provided by the present invention has good mechanical properties and load deformation temperature.

[0171] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polypropylene resin, characterized in that, The polypropylene resin comprises a polypropylene homopolymer phase and a rubber phase dispersed in the homopolymer phase, wherein the rubber phase is a copolymer of ethylene and α-olefin; Based on the polypropylene resin, the content of the homopolymer phase is 70-80 wt%, and the content of the rubber phase is 20-30 wt%. The average sphericity of the rubber phase is 1-1.

5.

2. The polypropylene resin according to claim 1, characterized in that, Based on the polypropylene resin, the content of the homopolymer phase is 73-77 wt%, and the content of the rubber phase is 23-27 wt%. Preferably, the average sphericity of the rubber phase is 1.1-1.

3.

3. The polypropylene resin according to claim 1 or 2, characterized in that, The polypropylene resin contains 5-15 wt% structural units derived from ethylene. Preferably, the molecular weight distribution index of the polypropylene resin is 8-14; Preferably, the molecular weight distribution index of the homopolymer phase is 3-5.

4. The polypropylene resin according to any one of claims 1-3, characterized in that, The melt flow index of the polypropylene resin measured at 230℃ and 2.16kg load was 10-30g / 10min; Preferably, the isotactic index of the homopolymer phase is not less than 93.5%.

5. The polypropylene resin according to any one of claims 1-4, characterized in that, The content of xylene-soluble substances in the polypropylene resin is 15-28 wt%. Preferably, the ethylene content in the xylene-soluble substance is 40-65 wt%.

6. The polypropylene resin according to any one of claims 1-5, characterized in that, In the polypropylene resin, the intrinsic viscosity of xylene-soluble matter is 3-7 dL / g, and the intrinsic viscosity of xylene-insoluble matter is 0.5-1.8 dL / g. Preferably, the intrinsic viscosity ratio of xylene solubles to xylene insolubles is 2-8:

1.

7. A method for preparing the polypropylene resin according to any one of claims 1-6, characterized in that, Includes the following steps: (1) In the presence of Ziegler-Natta catalyst, alkylaluminum, molecular weight regulator and external electron donor, propylene undergoes homopolymerization to obtain homopolymer polypropylene; (2) In the presence of a molecular weight regulator, the homopolymer polypropylene is copolymerized with ethylene and α-olefin to obtain the polypropylene resin; In step (2), the molar ratio of ethylene to α-olefin is 0.8-1.3:1, and the molar ratio of molecular weight regulator to ethylene is 0.005-0.05:

1.

8. The method according to claim 7, characterized in that, The molar ratio of ethylene to α-olefin in step (2) is 0.9-1.1:1; Preferably, the molar ratio of the molecular weight regulator to ethylene in step (2) is 0.008-0.02:1; Preferably, in step (2), the mass ratio of homopolymer polypropylene to added ethylene is 1:0.05-0.5; Preferably, the α-olefin comprises propylene and optionally C4-C. 12 α-olefins.

9. The method according to claim 7 or 8, characterized in that, In step (1), the mass ratio of the alkylaluminum to the external electron donor is ≥40; Preferably, in step (1), the mass ratio of the catalyst to propylene is 1:10000-30000; Preferably, in step (1), the mass ratio of the Ziegler-Natta catalyst to alkylaluminum is 1:1-8; Preferably, in step (1), the molar ratio of the molecular weight regulator to propylene is 0.003-0.01:

1.

10. The use of the polypropylene resin according to any one of claims 1-7 in automotive interior and exterior trim parts.

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