A low melt index, high modulus, high impact resistance polypropylene resin and its preparation method and application

Abstract

The present invention discloses a low melt index, high modulus, high impact resistance polypropylene resin and its preparation method and application, belonging to the technical field of polymer material synthesis. The preparation method provided by the present invention comprises the following steps: adding an external electron donor, a main catalyst, a cocatalyst and refined propylene into a polymerization kettle, introducing hydrogen gas and then carrying out a polymerization reaction to obtain polypropylene powder; mixing the polypropylene powder with a main antioxidant, an auxiliary antioxidant, calcium stearate, a β-crystal nucleating agent and a copolymerized polypropylene resin containing an ethylene phase, and extruding and pelletizing through a twin-screw extruder to obtain the product. By adding appropriate additives, the polypropylene resin prepared by the present invention has both high rigidity and high toughness, the flexural modulus can reach more than 1600 MPa, the impact strength at room temperature can reach more than 110 kJ / m 2 above, and the low temperature impact strength (-20 °C) can reach 5 kJ / m 2 above, and the melt index is below 0.3 g / 10 min, which is suitable as a special material for polypropylene winding sewage pipes and meets the A-level index of melt mass flow rate in the GB T 35451.2-2018 standard.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material synthesis, and in particular to a polypropylene resin with low melt index, high modulus and high impact resistance, and a preparation method and application thereof. Background Art

[0002] The information disclosed in the background art of the present invention is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an indication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Polypropylene with low melt index, high modulus and high impact resistance is the main raw material for making winding drainage pipes. Compared with traditional drainage polyethylene double-wall corrugated pipes, fiberglass pipes, cement pipes, etc., this kind of pipe has significant advantages in terms of chemical resistance, anti-aging performance, etc., and is very suitable for municipal, construction, farmland and highway rain and sewage discharge projects. In the face of situations such as extraordinary rainfall or large-scale drainage, large-diameter high-modulus polypropylene winding pipes have obvious advantages. Polypropylene winding drainage pipes have the following advantages compared with traditional PE and PVC pipes: high modulus results in high ring stiffness and better ability to resist external force loads; low density, light weight, and material saving; good shaping, small pipe shrinkage, and higher flow rate; high tensile strength, better anti-bending deformation ability and tensile ability, and anti-geological settlement ability.

[0004] At present, the polypropylene with low melt index, high modulus and high impact resistance is produced by the loop process method. However, this method is a continuous production, and it is not flexible to switch grades, and a large amount of transitional materials are generated; at the same time, it is very difficult for the polypropylene material prepared by this method to simultaneously have good rigidity and toughness. Therefore, how to provide a polypropylene resin with low melt index, high modulus and high impact resistance based on the batch process method and make it suitable for the production of winding pipes is an urgent problem to be solved. Summary of the Invention

[0005] In view of this, the present invention provides a polypropylene resin with low melt index, high modulus and high impact resistance, and a preparation method and application thereof, which solve the problems of inflexible grade switching and difficulty in simultaneously meeting high rigidity and high toughness when producing polypropylene resin by the loop process method.

[0006] In the first aspect, the present invention provides a preparation method of a polypropylene resin with low melt index, high modulus and high impact resistance, comprising the following steps:

[0007] Adding an external electron donor, a main catalyst, a cocatalyst and refined propylene into a polymerization kettle, introducing hydrogen gas and then carrying out a polymerization reaction to obtain polypropylene powder;

[0008] Mix the polypropylene powder with a primary antioxidant, a secondary antioxidant, calcium stearate, a β-crystal nucleating agent, and a copolymerized polypropylene resin containing an ethylene phase, and extrude and pelletize them through a twin-screw extruder to obtain the product.

[0009] Preferably, the external electron donor is selected from dicyclopentyl dimethoxysilane.

[0010] Preferably, the main catalyst is a TiC14 / MgC12 catalyst, and the mass fraction of Ti in the main catalyst is 2-4 wt%; for every ton of propylene, the addition amount of the main catalyst is 12-60 g.

[0011] Preferably, the cocatalyst is triethylaluminum; the molar ratio of Al in the triethylaluminum to Ti in the main catalyst is (200-240):1.

[0012] Preferably, for every ton of propylene, the addition amount of the external electron donor is 15-55 mL.

[0013] Preferably, the pressure of the polymerization reaction is 3-3.8 MPa, the temperature of the polymerization reaction is 65-82 °C, and the time of the polymerization reaction is 2-3 h.

[0014] Preferably, the concentration of hydrogen is 200-300 ppm.

[0015] Preferably, the mass ratio of the polypropylene powder, the primary antioxidant, the secondary antioxidant, calcium stearate, the β-crystal nucleating agent, and the copolymerized polypropylene resin containing an ethylene phase is 100:(0.1-0.3):(0.05-0.2):(0.02-0.1):(0.02-0.15):(3-10).

[0016] Preferably, the primary antioxidant is antioxidant 1010, and the secondary antioxidant is antioxidant 168.

[0017] Preferably, in the copolymerized polypropylene resin containing an ethylene phase, the ethylene phase content is 1-5 wt%.

[0018] In a second aspect, the present invention provides a low melt index, high modulus, and high impact resistance polypropylene resin prepared by the above preparation method.

[0019] In a third aspect, the present invention provides the application of the above low melt index, high modulus, and high impact resistance polypropylene resin in the preparation of polypropylene wound sewage pipes.

[0020] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0021] (1) The present invention uses an intermittent bulk process to prepare a low melt index, high modulus, and high impact resistance polypropylene resin, which can facilitate grade switching and has less transition material;

[0022] (2) In the production process of polypropylene resin, by adding appropriate additives, a polypropylene resin with low melt index, high modulus, and high impact resistance is prepared, which has both high rigidity and high toughness. The flexural modulus can reach above 1600 MPa, and the impact strength at room temperature can reach 110 kJ / m 2 or above, and the impact strength at low temperature (-20 °C) can reach 5 kJ / m 2 or above, and the melt index is below 0.3 g / 10 min, which is suitable as a special material for polypropylene wound sewage pipes and meets the A-level index of melt mass flow rate in GB T 35451.2-2018 standard. Detailed implementation manners

[0023] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0024] The present invention provides a method for preparing a polypropylene resin with low melt index, high modulus, and high impact resistance, which includes the following steps:

[0025] Add an external electron donor, a main catalyst, a co-catalyst, and refined propylene into a polymerization kettle, introduce hydrogen, and then carry out a polymerization reaction to obtain polypropylene powder;

[0026] Mix the polypropylene powder with a main antioxidant, an auxiliary antioxidant, calcium stearate, a β-crystal nucleating agent, and a copolymer polypropylene resin containing an ethylene phase, and extrude and pelletize through a twin-screw extruder to obtain the product.

[0027] The present invention does not impose special restrictions on the refining process of propylene, and a commonly used refining method in the art can be adopted. Preferably, the raw material propylene is passed through a solid caustic tower, a hydrolysis tower, a desulfurization tower, a drying tower, a deoxygenation tower, a molecular sieve dryer, and a desulfurization, phosphorus, and arsenic tower in sequence for the refining of polypropylene raw materials to obtain propylene raw materials for polymerization reaction. The present invention does not impose special restrictions on the specific process conditions of the solid caustic tower, the hydrolysis tower, the desulfurization tower, the drying tower, the deoxygenation tower, the molecular sieve dryer, and the desulfurization, phosphorus, and arsenic tower, and commonly used refining parameters by those skilled in the art can be adopted.

[0028] In the present invention, the external electron donor is selected from dicyclopentyl dimethoxysilane. In the present invention, the main catalyst is selected from a TiC14 / MgC12 catalyst, and the mass fraction of Ti in the main catalyst is 2-4 wt%; for each ton of propylene, the addition amount of the main catalyst is 12-60 g. The selection of appropriate external electron donor and main catalyst can improve the isotacticity and flexural strength of the polypropylene resin.

[0029] In the present invention, the cocatalyst is triethylaluminum; the molar ratio of Al in the triethylaluminum to Ti in the main catalyst is (200 - 240):1. The main function of the cocatalyst is to remove trace impurities in propylene and improve the reaction activity.

[0030] In the present invention, the addition amount of the external electron donor per ton of propylene is 15 - 55 mL.

[0031] In the present invention, the pressure of the polymerization reaction is 3 - 3.8 MPa, the temperature of the polymerization reaction is 65 - 82 °C, and the time of the polymerization reaction is 2 - 3 h.

[0032] In the present invention, the concentration of hydrogen per ton of propylene is 200 - 300 ppm. The melt index of the polypropylene resin is regulated by controlling the addition amount of hydrogen.

[0033] In the present invention, the mass ratio of the polypropylene powder, the main antioxidant, the auxiliary antioxidant, calcium stearate, the β-crystal nucleating agent, and the ethylene-containing phase copolymerized polypropylene resin is 100:(0.1 - 0.3):(0.05 - 0.2):(0.02 - 0.1):(0.02 - 0.15):(3 - 10). The addition of calcium stearate can play a certain strengthening role, improve the processing performance of polypropylene, and at the same time improve the impact resistance and thermal stability of polypropylene.

[0034] The present invention finds that the β-crystal nucleating agent and the ethylene-containing phase copolymerized polypropylene resin can have a great influence on the toughness of the polypropylene resin. The appropriate addition thereof can improve the low-temperature toughness and room-temperature toughness of the polypropylene resin. However, excessive addition of the β-crystal nucleating agent and the ethylene-containing phase copolymerized polypropylene resin will both cause a significant reduction in rigidity.

[0035] In the present invention, the main antioxidant is antioxidant 1010, and the auxiliary antioxidant is antioxidant 168. The main antioxidant and the auxiliary antioxidant can play a synergistic role and together play a role in preventing the oxidative decomposition of polypropylene.

[0036] In the present invention, in the ethylene-containing phase copolymerized polypropylene resin, the ethylene phase content is 1 - 5 wt%. The introduction of the ethylene phase can improve the low-temperature impact performance of the final polypropylene resin.

[0037] The present invention also provides a low melt index, high modulus, and high impact polypropylene resin prepared by the above preparation method. The low melt index, high modulus, and high impact polypropylene resin obtained by the present invention has both rigidity and toughness, the flexural modulus can reach more than 1600 MPa, the room-temperature impact strength can reach 110 kJ / m 2 above, and the low-temperature impact strength (-20 °C) can reach 5 kJ / m 2Above, and the melt index is below 0.3 g / 10 min, which is suitable as a special material for polypropylene wound sewage pipes and meets the A-level index of melt mass flow rate in the GB T 35451.2-2018 standard.

[0038] The present invention also provides the application of the above-mentioned low melt index, high modulus and high impact resistance polypropylene resin in the preparation of polypropylene wound sewage pipes.

[0039] The technical solution of the present invention will be further described below with specific embodiments.

[0040] Example 1

[0041] This example provides a preparation method of a low melt index, high modulus and high impact resistance polypropylene resin.

[0042] The raw material propylene enters the refining unit of the device. The raw material propylene first enters the solid caustic soda tower to remove trace acidic substances, inorganic sulfur and most of the micro water, then enters the hydrolysis tower and the desulfurization tower to remove organic sulfur, then enters the alumina drying tower to remove trace water, enters the deoxidation tower to remove trace oxygen, water is generated in this process, and then enters the molecular sieve drying tower to remove trace impurities and trace water, and finally enters the desulfurization and dephosphorization tower. After analysis and testing, when water, oxygen, sulfur, etc. are qualified, it is used for polymerization. The propylene is sent to the polymerization unit by a propylene pump.

[0043] The cocatalyst triethylaluminum is pressed into the cocatalyst metering tank through nitrogen.

[0044] Under the protection of nitrogen, the external electron donor dicyclopentyl dimethoxysilane is then flushed into the polymerization kettle.

[0045] Open the catalyst hopper. Under the protection of nitrogen, pour the main catalyst TiC14 / MgC12 (Ti content is 3 wt%, catalyst model is S-copo) into the catalyst feeding port, and flush the main catalyst into the polymerization kettle with propylene.

[0046] Open the hydrogen valve on the polymerization kettle and add hydrogen to the polymerization kettle.

[0047] Continue to add propylene. When the propylene reaches the set value, close the propylene feed valve.

[0048] Start the heating system and raise the temperature slowly, then enter the constant temperature stage. React at a constant temperature for 2.5 hours. Open the propylene recovery valve to recover the unreacted propylene monomer. The recovered propylene is condensed and then enters the propylene recovery tank as a recovered material and is used as a raw material for standby.

[0049] Replace the flash tank with nitrogen until it is qualified, and press the polypropylene powder in the polymerization kettle to the flash tank. Replace it with nitrogen multiple times until the volume content of propylene in the tail gas is less than 0.8%. The polypropylene powder enters the granulator.

[0050] Adjust the extrusion granulation processing conditions of the twin-screw extruder, and add 2 kg of antioxidant 1010, 1 kg of antioxidant 168, 0.5 kg of calcium stearate, 0.3 kg of β-crystal nucleating agent NA-328, and 50 kg of ethylene-containing copolymer polypropylene resin EP200R (ethylene phase content is 3 wt%) to each ton of polypropylene powder. The final product, a special material for polypropylene winding sewage pipes, is obtained through extrusion granulation.

[0051] In this example, the polymerization reaction conditions are shown in Table 1, and the extrusion granulation processing conditions of the twin-screw extruder are shown in Table 2.

[0052] Table 1 Polymerization reaction conditions of Example 1

[0053]

[0054] Example 2

[0055] Compared with Example 1, the difference in this example is that the addition amount of the ethylene-containing copolymer polypropylene resin EP200R (ethylene phase content is 3 wt%) is 80 kg (per ton of polypropylene powder).

[0056] Example 3

[0057] Compared with Example 1, the difference in this example is that the addition amount of the β-crystal nucleating agent NA-328 is 0.5 kg (per ton of polypropylene powder).

[0058] Comparative Example 1

[0059] Compared with Example 1, the difference in this comparative example is that the β-crystal nucleating agent NA-328 and the ethylene-containing copolymer polypropylene resin EP200R are not added.

[0060] Comparative Example 2

[0061] Compared with Example 1, the difference in this comparative example is that the ethylene-containing copolymer polypropylene resin EP200R is not added.

[0062] Comparative Example 3

[0063] Compared with Example 1, the difference in this comparative example is that the addition amount of the ethylene-containing copolymer polypropylene resin EP200R (ethylene phase content is 3 wt%) is 150 kg (per ton of polypropylene powder).

[0064] Comparative Example 4

[0065] Compared with Example 1, the difference in this comparative example is that the addition amount of the β-crystal nucleating agent NA-328 is 2 kg.

[0066] Comparative Example 5

[0067] This comparative example is different from Example 1 in that the external electron donor in this comparative example is cyclohexylmethyl dimethoxysilane.

[0068] Test Example

[0069] The properties of the polypropylene resins of Examples 1 to 3 and Comparative Examples 1 to 5 were measured, and the test results are shown in Table 2.

[0070] Table 2 Performance Measurement of Polypropylene Resins of Examples 1 to 3 and Comparative Examples 1 to 5

[0071]

[0072] Note: The test standard for flexural modulus is GB / T 9341-2008; the room temperature impact strength is measured at 23°C, and the low temperature impact strength is measured at -20°C. The test standard is GB / T 1043.1-2008; the test standard for melt index is GB / T 3682.1-2018.

[0073] As can be seen from Table 2, in Comparative Example 1, due to the absence of a nucleating agent and copolymerized PP, the room temperature and low temperature impacts were significantly reduced, and the flexural modulus and tensile strength increased; compared with Comparative Example 1, Comparative Example 2 added a nucleating agent, and the room temperature impact resistance was significantly improved, but the flexural modulus decreased; in Comparative Example 3, the addition amount of the ethylene-containing copolymerized polypropylene resin was too much, resulting in a significant decrease in the flexural modulus and tensile strength, and the low temperature and room temperature impact properties also decreased; in Comparative Example 4, the addition amount of the nucleating agent was too much, which also caused a significant decrease in the flexural modulus and tensile strength, and the low temperature and room temperature impact properties decreased slightly; in Comparative Example 5, the external electron donor was replaced with cyclohexylmethyl dimethoxysilane, and it can be seen that the values related to rigidity and toughness were all slightly lower than those in Example 1.

[0074] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a low melt index, high modulus, high impact polypropylene resin, characterized in that: The steps include: Adding an external electron donor, a main catalyst, a co-catalyst and purified propylene into a polymerization kettle, introducing hydrogen to carry out polymerization reaction, and obtaining polypropylene powder; The polypropylene powder is mixed with a primary antioxidant, an auxiliary antioxidant, calcium stearate, a β-crystal nucleating agent and a copolymerized polypropylene resin containing an ethylene phase, and the mixture is extruded and granulated by a twin-screw extruder to obtain a product; The external electron donor is selected from dicyclopentyldimethoxysilane; the amount of the external electron donor added is 15 to 55 mL per ton of propylene; The main catalyst is a TiC14 / MgC12 catalyst, the mass fraction of Ti in the main catalyst is 2-4wt%; the addition amount of the main catalyst is 12-60g per ton of propylene; The co-catalyst is triethylaluminum; the molar ratio of Al in the triethylaluminum to Ti in the main catalyst is (200-240):1; The mass ratio of the polypropylene powder, the primary antioxidant, the auxiliary antioxidant, calcium stearate, the β-crystal nucleating agent and the copolymerized polypropylene resin containing the ethylene phase is 100: (0.1-0.3): (0.05-0.2): (0.02-0.1): (0.02-0.15): (3-10); In the copolymerized polypropylene resin containing an ethylene phase, the content of the ethylene phase is 1 to 5 wt%.

2. The preparation method according to claim 1, characterized in that The polymerization reaction pressure is 3-3.8 MPa, the polymerization reaction temperature is 65-82° C., and the polymerization reaction time is 2-3 hours.

3. The preparation method according to claim 1, characterized in that: The concentration of the hydrogen is 200-300 ppm.

4. The preparation method according to claim 1, characterized in that: The main antioxidant is antioxidant 1010, and the auxiliary antioxidant is antioxidant 168.

5. The low melt index, high modulus, high impact polypropylene resin prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the low melt index, high modulus, high impact polypropylene resin as claimed in claim 5 in the preparation of polypropylene wound sewage pipes.

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