Preparation method of special material for thermal forming of polypropylene

Abstract

The invention relates to a preparation method of a special material (polypropylene polymer) for thermal forming of polypropylene. The polypropylene polymer comprises a propylene-ethylene random copolymer, a main antioxidant, an auxiliary antioxidant, an acid acceptor and a nucleating agent, the crystallization temperature of the polypropylene polymer is 110-122 DEG C, the thermal deformation temperature is 84-96 DEG C, the tensile yield strength is 34-37 MPa, the flexural modulus is 1600-1700 MPa, the cantilever beam impact strength is 5.0-6.5 KJ / m < 2 >, and the polypropylene polymer has excellent mechanical properties. The melting point is 157-162 DEG C; and the haze is 3-16%. The invention provides a method for preparing a polypropylene polymer, which comprises the following steps: in the presence of a catalyst, an optional cocatalyst and an external electron donor, polymerizing propylene and ethylene in a liquid-phase bulk polymerization and gas-phase polymerization serial polymerization process to obtain a propylene-ethylene random copolymer, and mixing the propylene-ethylene random copolymer with the main antioxidant, the auxiliary antioxidant, the acid acceptor and the nucleating agent to obtain the special material for thermal forming of polypropylene.

Description

Technical Field

[0001] The present invention relates to a method for preparing a polypropylene thermoforming material. Specifically, the present invention relates to a method for preparing a polypropylene polymer for thermoforming processing (i.e., a polypropylene thermoforming material). The polypropylene polymer has favorable properties, including balanced rigidity and toughness and excellent haze performance. Background Art

[0002] Thermoforming is a molding method in which a thermoplastic sheet is heated to a softening temperature, and under external force such as gas pressure, liquid pressure or mechanical pressure, the heated and softened sheet is pressed against the contour of a mold to obtain a shape similar to the mold surface, and the product is obtained after cooling, shaping and trimming. Thermoformed products usually require the preparation of sheets first, and then secondary processing according to the specifications of the final product. Types of thermoformed products include cups, plates and other daily utensils, medical utensils, electronic instrument accessories, radio and TV housings, billboards, bathtubs, toys, helmets, packaging utensils, automotive parts, building components, chemical equipment, radar covers and aircraft cabin covers, etc. The types of plastics used to prepare thermoformed products include but are not limited to PS, PMMA, PVC, ABS, PE, PP, PA, PC, PET, etc.

[0003] A common application area of ​​thermoformed products is the packaging industry, which is closely related to people's lives, including cold chain transportation, fast food boxes, beverage containers, cosmetics, stationery, pharmaceutical packaging, etc. Polypropylene is non-toxic and safer than other polymers, making it a suitable material for the above applications.

[0004] Thermoforming polypropylene materials need to have a good balance of stiffness and toughness, so that they can meet the higher melt strength requirements in thermoforming processing and meet appropriate processing efficiency. In addition, thermoforming polypropylene materials with excellent haze are preferred for certain applications.

[0005] The present invention provides a method for preparing a polypropylene material for thermoforming that meets the above requirements. In the present invention, the polypropylene material for thermoforming is prepared by combining a bulk-gas phase process, using a specific catalytic system including a main catalyst and an external electron donor, and using additives. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a rigid-toughness balanced transparent polypropylene polymer for thermoforming (also called polypropylene material or polypropylene thermoforming special material).

[0007] The present invention provides a method for preparing a polypropylene polymer, the method comprising:

[0008] In the presence of a catalyst (also called a main catalyst), a cocatalyst and an external electron donor, propylene and ethylene are polymerized in a polymerization process of liquid phase bulk polymerization and gas phase polymerization in series to obtain a propylene-ethylene random copolymer, wherein the amount of ethylene comonomer in the propylene-ethylene random copolymer is 0.4-3.0 wt%, preferably 0.8-3.0 wt%, preferably 1.5-2.5 wt% and the MFR of the propylene-ethylene random copolymer is 1-10 g / 10 min, preferably 2.5-3.5 g / 10 min; wherein the liquid phase bulk polymerization is carried out in a liquid phase bulk polymerization kettle, and the gas phase polymerization is carried out in a gas phase fluidized bed, ... The temperature of the combined polymerization is 70±5°C, preferably 70±2°C, more preferably 70±1°C, the pressure is 2.0-4.0MPa, preferably 2.7-3.3MPa, the hydrogen concentration is 0.1-1.0% by volume, preferably 0.2-0.6% by volume, and the ethylene concentration is 0.6-2.5% by volume, preferably 1.0-1.8% by volume, and wherein the gas phase fluidized bed polymerization temperature is 75±5°C, the reaction pressure is 1.0-3.0MPa, preferably 1.7-2.5MPa, the hydrogen concentration is 0.1-1.0% by volume, preferably 0.2-0.6% by volume, and the ethylene concentration is 0.8-3.0% by volume, preferably 1.0-2.2% by volume; and

[0009] The propylene-ethylene random copolymer is blended with a primary antioxidant, an auxiliary antioxidant, an acid absorber and a nucleating agent to obtain the polypropylene polymer, wherein the polypropylene polymer has a crystallization temperature of 110-122° C., a heat deformation temperature of 84-96° C., a tensile yield strength of 33-37 MPa, a flexural modulus of 1600-1700 MPa, and a room temperature impact strength of 5.0-6.5 KJ / m 2 , melting point of 157-162°C and haze of 3-16%. DETAILED DESCRIPTION

[0010] The invention provides a method for preparing a rigid-toughness balanced transparent polypropylene polymer for thermoforming (also called polypropylene material or polypropylene thermoforming special material).

[0011] The rigid-tough balanced transparent polypropylene polymer for thermoforming prepared by the method of the present invention comprises a propylene-ethylene random copolymer containing an ethylene comonomer. The amount of the ethylene comonomer in the propylene-ethylene random copolymer can be 0.4-3.0 weight %, preferably 0.8-2.8 weight %, preferably 1.5-2.5 weight %. In some embodiments, the amount of the ethylene comonomer in the propylene-ethylene random copolymer can be 0.8-2.4 weight %.

[0012] The MFR of the propylene-ethylene random copolymer of the present invention may be 1-10 g / 10 min, preferably 2.5-3.5 g / 10 min (230° C., 2.16 Kg).

[0013] The rigid-toughness balanced transparent polypropylene polymer for thermoforming of the present invention further comprises a primary antioxidant, a secondary antioxidant, an acid absorber and a nucleating agent.

[0014] The propylene-ethylene random copolymer of the present invention is blended with a primary antioxidant, a secondary antioxidant, an acid absorber and a nucleator to obtain a rigid-tough balanced transparent polypropylene polymer for thermoforming of the present invention. In some embodiments, the propylene-ethylene random copolymer of the present invention is blended with a primary antioxidant, a secondary antioxidant, an acid absorber and a nucleator and extruded and granulated to obtain a rigid-tough balanced transparent polypropylene polymer for thermoforming of the present invention. The primary antioxidant, the secondary antioxidant, the acid absorber and the nucleator can be provided separately, or two or more of the primary antioxidant, the secondary antioxidant, the acid absorber and the nucleator can be provided as an auxiliary agent package. In some embodiments, the primary antioxidant, the secondary antioxidant, the acid absorber and the nucleator are provided together as an auxiliary agent package.

[0015] Antioxidants can improve the processing stability and thermal oxidative aging of materials. The antioxidant system used in the present invention includes a primary antioxidant and a secondary antioxidant. In the present invention, a phenolic antioxidant is used as the primary antioxidant, and a phosphite antioxidant is used as the secondary antioxidant. In some embodiments, the phenolic antioxidant may be selected from tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl alcohol ester; and the phosphite antioxidant may be selected from bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite, tris[2,4-di-tert-butylphenyl]phosphite. Preferably, the mass ratio between the phenolic antioxidant and the phosphite antioxidant may be 2:1-1:3, preferably 1:1-1:2.

[0016] In the present invention, the acid scavenger can be selected from calcium stearate and zinc stearate.

[0017] In the present invention, the nucleating agent is Milliken (Milland) nucleating agent NX8000K.

[0018] As known to those skilled in the art, the nucleating agent can improve the transparency, heat resistance, rigidity and toughness of the material, while increasing the crystallization temperature of the material, thereby increasing the molding rate of the material.

[0019] Those skilled in the art can appropriately select the amount of the primary antioxidant, the secondary antioxidant, the acid absorbing agent and the nucleating agent. In some embodiments, the weight ratio of the propylene-ethylene random copolymer, the primary antioxidant, the secondary antioxidant, the acid absorbing agent and the nucleating agent is: 100 parts of the propylene-ethylene random copolymer; 0.05-0.25 parts of the primary antioxidant; 0.05-0.5 parts of the secondary antioxidant; 0.05-0.5 parts of the acid absorbing agent; and 0.05-0.4 parts of the nucleating agent.

[0020] The rigid-toughness balanced transparent polypropylene polymer for thermoforming of the present invention has excellent material properties. The crystallization temperature of the rigid-toughness balanced transparent polypropylene polymer for thermoforming of the present invention can be 110-122°C, preferably 114-118°C, and more preferably 116-117°C; the heat deformation temperature can be 84-96°C, preferably 88-96°C, and more preferably 89-94°C; the tensile yield strength can be 34-37MPa, preferably 35-37MPa, and more preferably 35.2-37MPa; the flexural modulus can be 1600-1700MPa, preferably 1600-1680MPa, and more preferably 1610-1670MPa; the normal temperature impact strength can be 5.0-6.5KJ / m 2 , preferably 5.5-6.5KJ / m 2 ; More preferably 5.6-6.3KJ / m 2 The melting point may be 157-162°C, preferably 158-161°C, more preferably 158.5-160°C, and the haze may be 3-16%, preferably 5-15%, more preferably 6-14%.

[0021] In the present invention, the tensile properties are tested according to GB / T 1040.2-2006; the bending properties are tested according to GB / T 9341-2008; the impact resistance is tested according to GB / T 1043.1-2008; the heat deformation temperature is tested according to GB / T 1634.2-2019; the MFR is tested according to GB / T 3682.1-2018; and the haze is tested according to GB / T2410-2008.

[0022] The ethylene content in the propylene-ethylene random copolymer of the present invention is determined by 13 C-NMR determination.

[0023] The melting point and crystallization temperature were measured by DSC from 20 to 200 °C at a heating rate of 10 °C / min.

[0024] The method for preparing a rigid-tough balanced transparent polypropylene polymer for thermoforming of the present invention may include: polymerizing propylene and ethylene in a polymerization process of liquid phase bulk polymerization and gas phase polymerization in series in the presence of a catalyst, a co-catalyst and an external electron donor, wherein the liquid phase bulk polymerization is carried out in a liquid phase bulk polymerization kettle, and the gas phase polymerization is carried out in a gas phase fluidized bed, wherein the temperature of the liquid phase bulk polymerization is 70±5°C, preferably 70±2°C, more preferably 70±1°C, the pressure is 2.0-4.0MPa, preferably 2.7-3.3MPa, the hydrogen concentration is 0.1-1.0% by volume, preferably 0.2-0.6% by volume, and the ethylene concentration is 0.6 -2.5 volume %, preferably 1.0-1.8 volume %, and the gas phase fluidized bed polymerization temperature is 75±5°C, the reaction pressure is 1.0-3.0MPa, preferably 1.7-2.5MPa, the hydrogen concentration is 0.1-1.0 volume %, preferably 0.2-0.6 volume % and the ethylene concentration is 0.8-3.0 volume %, preferably 1.0-2.2 volume %, to obtain a propylene-ethylene random copolymer; and the propylene-ethylene random copolymer is mixed with a primary antioxidant, an auxiliary antioxidant, an acid absorber and a nucleating agent to obtain a rigid-tough balanced transparent polypropylene polymer for thermoforming (i.e., the polypropylene material of the present invention or a polypropylene thermoforming special material).

[0025] In some embodiments, the liquid phase bulk polymerization is carried out in one or two liquid phase bulk polymerization reactors, and the gas phase polymerization is carried out in two gas phase fluidized beds.

[0026] In the method of the present invention, when two liquid phase bulk polymerization reactors are used, the two polymerization reactors can use the same or similar conditions, including temperature, pressure, hydrogen concentration and ethylene concentration. In the method of the present invention, when two gas phase fluidized beds are used, the two gas phase fluidized beds can use the same or similar conditions, including temperature, pressure, hydrogen concentration and ethylene concentration.

[0027] In the method of the present invention, the operation of the liquid phase bulk polymerization reactor is controlled by the material level in the reactor. In some embodiments, 50% volume level is used as the control standard to enable the device to operate continuously and stably.

[0028] In the method of the present invention, the gas phase fluidized bed is operated by controlling the material level. In some embodiments, the 50% volume material level is used as the control standard to enable the device to operate continuously and stably.

[0029] In some embodiments, the polymerization process of liquid phase bulk polymerization and gas phase polymerization in series of the present invention is a Hypol process. For the Hypol process used in the present invention, it can be two liquid phase bulk reactors and two gas phase fluidized beds in series, or it can be one liquid phase bulk reactor and two gas phase fluidized beds in series.

[0030] In some embodiments, the methods of the present invention do not utilize a loop reactor, apparatus, or device.

[0031] The catalyst used in the method of the present invention is a ZN (Ziegler-Natta) catalyst, preferably a catalyst with Ti as the active center containing a diether component as an internal electron donor. In some embodiments, the catalyst used in the method of the present invention can be supported by magnesium chloride or alkyl magnesium or silicon dioxide. In some embodiments, the catalyst is preferably BCZ-208 of Sinopec Catalyst Co., Ltd.

[0032] The external electron donor used in the method of the present invention can be selected from cyclohexyl-methyl-dimethoxysilane (Donor-C), dicyclopentyl-dimethoxysilane (Donor-D), diisopropyldimethoxysilane, diisobutyldimethoxysilane or a mixture thereof.

[0033] The method of the present invention uses a co-catalyst. The co-catalyst can be selected from triethylaluminum, trimethylaluminum, triisobutylaluminum, preferably triethylaluminum.

[0034] The method of the present invention may also include a pre-contacting step. As known to those skilled in the art, the pre-contacting step includes adding propylene, ethylene, a catalyst system (including a main catalyst and a co-catalyst) and an external electron donor into a pre-contacting tank for pre-contacting. The pre-contacting temperature may be 0 to 25° C. and the pressure may be 2.7 to 3.3 MPa. The pre-contacting step may be controlled at a material level of 50 to 100 volume %.

[0035] Those skilled in the art can appropriately select the amount of the main catalyst, the co-catalyst and the external electron donor. In some embodiments, the molar ratio (Al / Si / Ti) of the co-catalyst, the external electron donor and the main catalyst used can be (65-100): (6-13): 1; for example, it can be 80: 9: 1, etc. The molar ratio Al / Si / Ti is calculated based on the Al in the co-catalyst, the Si in the external electron donor and the Ti in the main catalyst.

[0036] The transparent polypropylene polymer with balanced rigidity and toughness for thermoforming of the present invention has particularly favorable comprehensive properties, including crystallization temperature, heat deformation temperature, tensile yield strength, flexural modulus, room temperature impact strength and haze; these favorable properties make it particularly suitable for preparing transparent thermoformed products, such as beverage cups, tableware, etc. The polypropylene polymer of the present invention has suitable fluidity, good transparency, no yellowing, no odor, high heat resistance, good rigidity and toughness balance and can be quickly molded.

[0037] Example

[0038] The present invention is further described in detail below using examples, but the present invention is not limited to these examples.

[0039] The embodiments are carried out using a Hypol four- (two liquids + two gases) or three- (one liquid + two gases) series process.

[0040] In the embodiment, the main catalyst is BCZ-208, the co-catalyst is triethylaluminum, and the external electron donor is Donor-C or Donor-D. The amount of the co-catalyst, the external electron donor and the main catalyst is controlled by the molar ratio of Al / Si / Ti.

[0041] In the embodiment, the material level of 50 volume % is used as the control parameter to achieve stable operation of the device.

[0042] In the embodiment, the primary antioxidant is 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, the secondary antioxidant is bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite, the acid absorber is zinc stearate, and the nucleating agent is Milliken nucleating agent NX8000K.

[0043] Embodiment 1

[0044] Two liquid phase bulk reactors and two gas phase fluidized beds are arranged in series. Propylene, ethylene, catalytic system and external electron donor are added to the pre-contact tank, wherein the temperature is 0-25°C, the pressure is 2.7-3.2MPa, and the molar ratio of the co-catalyst, Donor-D and main catalyst is Al / Si / Ti of 80:9:1. During the polymerization reaction, the reaction temperature of the first and second liquid phase bulk reactors is 70±1° C., the reaction pressure is 2.7-3.2 MPa, the hydrogen dosage of the two reactors is controlled to be 0.3-0.6% by volume, and the ethylene concentration is 1.0-1.8% by volume; the reaction temperature of the third and fourth gas phase fluidized beds is 75±5° C., the reaction pressure is 1.7-2.5 MPa, the hydrogen dosage of the two beds is controlled to be 0.3-0.6% by volume, and the ethylene concentration is 1.0-1.8% by volume, and a random copolymer polypropylene powder with an MFR of 2.8 g / 10 min is obtained by polymerization; then, a premix of four auxiliary agents, including 0.05% of a primary antioxidant, 0.1% of an auxiliary antioxidant, 0.05% of an acid absorber, and 0.1% of a nucleating agent, is added and extruded and granulated, the granulation temperature is 195-230° C., and the cooling water temperature is 54-60° C., to obtain a rigid-toughness balanced transparent thermoforming polypropylene material, and its properties are shown in Table 1.

[0045] Embodiment 2

[0046] Two liquid phase bulk reactors and two gas phase fluidized beds are arranged in series. Propylene, ethylene, catalytic system and external electron donor are added to the pre-contact tank, wherein the temperature is 0-25°C, the pressure is 2.7-3.2MPa, and the molar ratio of the amount of the co-catalyst, Donor-D and the main catalyst is Al / Si / Ti is 70:10:1. During the polymerization reaction, the reaction temperature of the first and second liquid phase bulk reactors is 70±1°C, the reaction pressure is 2.7-3.2MPa, the hydrogen dosage of the two reactors is controlled to be 0.3-0.6% by volume, and the ethylene concentration is 1.0-1.8% by volume. The reaction temperature of the third and fourth gas phase fluidized beds is 75±5°C, the reaction pressure is 1.7-2.5MPa, the hydrogen dosage of the two beds is controlled to be 0.3-0.6% by volume, and the ethylene concentration is 1.2-1.8% by volume. A random copolymer polypropylene powder with an MFR of 2.9g / 10min is obtained by polymerization, and then a premix of four additives, including 0.05% of a primary antioxidant, 0.1% of an auxiliary antioxidant, 0.05% of an acid absorber, and 0.2% of a nucleating agent, is added and extruded and granulated. The granulation temperature is 195-230°C, and the cooling water temperature is 54-60°C to obtain a rigid-toughness balanced transparent thermoforming polypropylene material, and its properties are shown in Table 1.

[0047] Embodiment 3

[0048] Two liquid phase bulk reactors and two gas phase fluidized beds are arranged in series. Propylene, ethylene, catalytic system and external electron donor are added to the pre-contact tank, wherein the temperature is 0-25°C, the pressure is 2.7-3.2MPa, and the molar ratio of the co-catalyst, Donor-D and main catalyst is Al / Si / Ti of 70:12:1. During the polymerization reaction, the reaction temperature of the first and second liquid phase bulk reactors is 70±1°C, the reaction pressure is 2.7-3.2MPa, the hydrogen dosage of the two reactors is controlled to be 0.3-0.6% by volume, and the ethylene concentration is 1.0-1.8% by volume. The reaction temperature of the third and fourth gas phase fluidized beds is 75±5°C, the reaction pressure is 1.7-2.5MPa, the hydrogen dosage of the two beds is controlled to be 0.3-0.6% by volume, and the ethylene concentration is 1.3-1.9% by volume. A random copolymer polypropylene powder with an MFR of 3.0g / 10min is obtained by polymerization, and then a premix of four additives, including 0.05% of a primary antioxidant, 0.1% of an auxiliary antioxidant, 0.05% of an acid absorber, and 0.3% of a nucleating agent, is added and extruded and granulated. The granulation temperature is 195-230°C, and the cooling water temperature is 54-60°C to obtain a rigid-toughness balanced transparent thermoforming polypropylene material, and its properties are shown in Table 1.

[0049] Embodiment 4

[0050] A liquid phase bulk reactor and two gas phase fluidized beds are arranged in series. Propylene, ethylene, catalytic system and external electron donor are added to the pre-contact tank, wherein the temperature is 0-25°C, the pressure is 2.7-3.2MPa, and the molar ratio of the co-catalyst, Donor-D and main catalyst is Al / Si / Ti of 70:10:1. In the polymerization reaction, the reaction temperature of the first liquid phase bulk reactor is 70±1°C, the reaction pressure is 2.7-3.2MPa, the hydrogen dosage of the two reactors is controlled to be 0.2-0.4% by volume, and the ethylene concentration is 1.0-1.8% by volume. The reaction temperature of the second and third gas phase fluidized beds is 75±5°C, the reaction pressure is 1.7-2.5MPa, the hydrogen dosage of the two beds is controlled to be 0.2-0.4% by volume, and the ethylene concentration is 1.6-2.2% by volume. A random copolymer polypropylene powder with an MFR of 3.1g / 10min is obtained by polymerization, and then a premix of four additives including 0.05% of a primary antioxidant, 0.1% of an auxiliary antioxidant, 0.05% of an acid absorber, and 0.2% of a nucleating agent is added for extrusion granulation. The granulation temperature is 195-230°C, and the cooling water temperature is 54-60°C to obtain a rigid-toughness balanced transparent thermoforming polypropylene material, and its properties are shown in Table 1.

[0051] Comparative Example 1

[0052] Two liquid phase bulk reactors and two gas phase fluidized beds are arranged in series. Propylene, ethylene, catalytic system and external electron donor are added to the pre-contact tank, wherein the temperature is 0-25°C, the pressure is 2.7-3.2MPa, and the molar ratio of the co-catalyst, Donor-C and main catalyst is Al / Si / Ti of 70:10:1. During the polymerization reaction, the reaction temperature of the first and second liquid phase bulk reactors is 70±1° C., the reaction pressure is 2.7-3.2 MPa, the hydrogen dosage of the two reactors is controlled to be 0.3-0.6% by volume, and the ethylene concentration is 1.0-1.8% by volume. The reaction temperature of the third and fourth gas phase fluidized beds is 75±5° C., the reaction pressure is 1.7-2.5 MPa, the hydrogen dosage of the two beds is controlled to be 0.3-0.6% by volume, and the ethylene concentration is 1.2-2.0% by volume. A random copolymer polypropylene powder with an MFR of 3.0 g / 10 min is obtained by polymerization, and then a premix of three auxiliary agents, 0.05% of a primary antioxidant, 0.1% of an auxiliary antioxidant, and 0.05% of an acid absorber, is added and extruded and granulated. The granulation temperature is 195-230° C., and the cooling water temperature is 54-60° C. to obtain a polypropylene material, and its properties are shown in Table 1.

[0053] Comparative Example 2

[0054] The production is carried out using a loop tube device. Propylene, ethylene, a catalytic system and an external electron donor are added to a prepolymerization loop tube, and the molar ratio of the amount of the co-catalyst, the external electron donor Donor-D and the main catalyst is 70:10:1. During the polymerization reaction, the loop tube controls the reaction temperature to 75±5°C, the reaction pressure to 2.9-3.6MPa, the amount of hydrogen to 0.5-0.9%, and the amount of ethylene polymerization to 1.9%. Through polymerization, a random polypropylene powder with an MFR of 3.1g / 10min is obtained, and then a premix of four auxiliary agents, 0.05% of a primary antioxidant, 0.1% of an auxiliary antioxidant, 0.05% of an acid absorber, and 0.2% of a nucleating agent, is added and extruded into granules. The granulation temperature is 195-230°C, and the cooling water temperature is 54-60°C to obtain a polypropylene material, and its properties are shown in Table 1.

[0055] The polypropylene materials obtained in the above examples and comparative examples were tested, and the results are shown in Table 1 below.

[0056] Table 1 Test performance of embodiments and comparative examples

[0057]

[0058]

[0059] As can be seen from the above table, compared with Comparative Examples 1 and 2, the transparency (haze), heat resistance (melting point), rigidity (flexural modulus), toughness (room temperature impact strength) and crystallization temperature of the polypropylene material of the present invention are improved to varying degrees in Examples 1 to 4.

[0060] The polypropylene material prepared by the method of the invention has excellent transparency, heat resistance, balanced rigidity and toughness and rapid prototyping, and is an excellent heat-resistant, rigidity-toughness balanced transparent thermoforming polypropylene material.

[0061] Although the specific implementations of the present invention have been described in detail above in conjunction with the embodiments, it should be pointed out that the protection scope of the present invention is not limited by these specific implementations, but is determined by the claims. Those skilled in the art may make appropriate changes to these implementations without departing from the technical ideas and purport of the present invention, and these changed implementations are obviously also included in the protection scope of the present invention.

Claims

1. A method for preparing a polypropylene polymer, the method comprising: In the presence of a catalyst, a cocatalyst and an external electron donor, propylene and ethylene are polymerized in a polymerization process of liquid phase bulk polymerization and gas phase polymerization in series to obtain a propylene-ethylene random copolymer, wherein the amount of ethylene comonomer in the propylene-ethylene random copolymer is 0.4-3.0 wt%, preferably 0.8-3.0 wt%, more preferably 1.5-2.5 wt% and the MFR of the propylene-ethylene random copolymer is 1-10 g / 10 min, preferably 2.5-3.5 g / 10 min; wherein the liquid phase bulk polymerization is carried out in a liquid phase bulk polymerization kettle, and the gas phase polymerization is carried out in a gas phase fluidized bed, wherein the temperature of the liquid phase bulk polymerization is 70±5°C, preferably 70±2°C, more preferably 70±1°C, the pressure is 2.0-4.0MPa, preferably 2.7-3.3MPa, the hydrogen concentration is 0.1-1.0% by volume, preferably 0.2-0.6% by volume, and the ethylene concentration is 0.6-2.5% by volume, preferably 1.0-1.8% by volume, and wherein the gas phase fluidized bed polymerization temperature is 75±5°C, the reaction pressure is 1.0-3.0MPa, preferably 1.7-2.5MPa, the hydrogen concentration is 0.1-1.0% by volume, preferably 0.2-0.6% by volume, and the ethylene concentration is 0.8-3.0% by volume, preferably 1.0-2.2% by volume; and The propylene-ethylene random copolymer is blended with a primary antioxidant, an auxiliary antioxidant, an acid absorber and a nucleating agent to obtain the polypropylene polymer, wherein the polypropylene polymer has a crystallization temperature of 110-122°C, preferably 114-118°C, and more preferably 116-117°C; a heat deformation temperature of 84-96°C, preferably 88-96°C, and more preferably 89-94°C; a tensile yield strength of 33-37MPa, preferably 34-37MPa, preferably 35-37MPa, and more preferably 35.2-37MPa; a flexural modulus of 1600-1700MPa, preferably 1600-1680MPa, and more preferably 1610-1670MPa; and a room temperature impact strength of 5.0-6.5KJ / m 2 , preferably 5.5-6.5KJ / m 2 ; More preferably 5.6-6.3KJ / m 2 ; a melting point of 157-162°C, preferably 158-161°C, more preferably 158.5-160°C; and a haze of 3-16%, preferably 5-15%, more preferably 6-14%.

2. The method according to claim 1, wherein the liquid phase bulk polymerization is carried out in one or two liquid phase bulk polymerization kettles, and the gas phase polymerization is carried out in two gas phase fluidized beds; when two liquid phase bulk polymerization kettles are used, the two liquid phase bulk polymerization kettles use the same or similar conditions, and / or when two gas phase fluidized beds are used, the two gas phase fluidized beds use the same or similar conditions.

3. The method according to claim 1 or 2, wherein the polymerization process of liquid phase bulk polymerization and gas phase polymerization in series is a Hypol process; preferably, the Hypol process is two liquid phase bulk reactors and two gas phase fluidized beds in series or one liquid phase bulk reactor and two gas phase fluidized beds in series.

4. The method according to any one of claims 1 to 3, wherein the catalyst is a ZN catalyst, preferably a catalyst containing a diether component as an internal electron donor and having Ti as an active center; more preferably, the catalyst is BCZ-208 of Sinopec Catalyst Co., Ltd.; and / or The external electron donor is selected from cyclohexyl-methyl-dimethoxysilane (Donor-C), dicyclopentyl-dimethoxysilane (Donor-D), diisopropyldimethoxysilane, diisobutyldimethoxysilane, or a mixture thereof; and / or The co-catalyst is selected from triethylaluminum, trimethylaluminum, triisobutylaluminum, preferably triethylaluminum.

5. The method according to any one of claims 1 to 4, wherein the method further comprises a pre-contact step, wherein the pre-contact step comprises adding propylene, ethylene, a catalyst system and an external electron donor into a pre-contact tank for pre-contact; preferably, the molar ratio of the amount of the co-catalyst, the external electron donor and the catalyst is Al / Si / Ti (65-100): (6-13):

1.

6. The method according to any one of claims 1 to 5, wherein a phenolic antioxidant is used as a primary antioxidant and a phosphite antioxidant is used as a secondary antioxidant; preferably, the mass ratio between the phenolic antioxidant and the phosphite antioxidant is 2:1-1:3, preferably 1:1-1:2; more preferably, the phenolic antioxidant is selected from pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; and the phosphite antioxidant is selected from bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite and tris[2,4-di-tert-butylphenyl]phosphite.

7. The method according to any one of claims 1 to 6, wherein the acid absorber is selected from calcium stearate and zinc stearate, and / or the nucleating agent is Milliken nucleating agent NX8000K.

8. The method according to any one of claims 1 to 7, wherein the weight ratio of the propylene-ethylene random copolymer, the primary antioxidant, the auxiliary antioxidant, the acid absorber and the nucleating agent is: 100 parts of the propylene-ethylene random copolymer; 0.05-0.25 parts of the primary antioxidant; 0.05-0.5 parts of the auxiliary antioxidant; 0.05-0.5 parts of the acid absorber; and 0.05-0.4 parts of the nucleating agent.

9. The method according to any one of claims 1 to 8, wherein the polypropylene polymer is used in a thermoforming process.

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