A polypropylene resin having excellent low-temperature toughness and a method for producing the same

Abstract

The application discloses a kind of polypropylene resin with excellent low-temperature toughness and a preparation method thereof.The toughness loss of the polypropylene resin at-20 DEG C compared with that at 20 DEG C is less than 10%, and the toughness loss at-30 DEG C compared with that at 20 DEG C is less than 20%.In the process of preparing the polypropylene resin, at least a step of ethylene-propylene copolymerization by periodically changing the concentration ratio of ethylene monomer and propylene monomer in the reaction environment is included.The polypropylene resin obtained by the application has excellent impact performance and can maintain high toughness in low-temperature use environment, and has potential as a thermoplastic elastomer.

Description

Invention Field

[0001] This invention relates to the field of polypropylene resin technology, and more specifically, to a polypropylene resin with excellent low-temperature toughness and its preparation method. Background Technology

[0002] Polypropylene (PP) possesses excellent mechanical properties such as heat resistance, high strength, processability, and low cost, making it one of the most widely used commercial plastics. Due to its superior properties, PP is widely used in the automotive, home appliance, engineering, and electronics industries. The demand for PP is increasing year by year, and its production is also continuously growing. However, because of the high regularity of its molecular structure, PP has relatively poor impact resistance, a disadvantage that becomes more pronounced at lower temperatures, thus significantly limiting its use in many applications.

[0003] Currently, the main industrial solution to this problem is to use two reactors in series. The first reactor is used to produce homopolymer polypropylene as the matrix, and the second reactor is used to produce ethylene-propylene copolymer. The ethylene-propylene copolymer grows in the pores of the polypropylene matrix, and the resulting in-reactor alloy is called impact-resistant polypropylene (IPC).

[0004] Besides in-situ blending in the reactor, there are many other ways to incorporate a rubber phase into polypropylene, and physical blending is also a commonly used toughening method. Physical blending can be used to add nucleating agents, rubber phases, etc., to polypropylene to improve its mechanical properties. Polyolefin thermoplastic elastomers constitute a large portion of this process, mainly including ethylene propylene diene monomer (EPM), ethylene propylene diene monomer (EPDM), nitrile butadiene rubber (NBR), ethylene octene copolymer (POE), block copolymer (OBC), and reactor-type elastomers (RTPO).

[0005] Currently, to improve the toughness of materials, existing technologies mainly rely on blending, adding elastomers and nucleating agents. This effectively improves the toughness at room temperature, but the toughness drops sharply as the temperature decreases. Patent CN 102977456 discloses a polypropylene toughening modifier and its modified polypropylene products, using polyethylene and ethylene-octene copolymers to increase the crystallinity of polypropylene, refining its crystal grains and improving its toughness. Patent CN 106349571 discloses a polypropylene toughening modified material, adding liquid rubber and thermoplastic elastomers to a polypropylene matrix to obtain the toughening modified material. Patent CN 115558195 discloses a high-impact copolymer polypropylene resin with both high fluidity and rigidity, a rubber phase content of 30%–40%, and a notched impact strength of a simply supported beam greater than 50 kJ / m at room temperature. 2However, the impact performance is significantly reduced at low temperatures; the notched impact strength of a simply supported beam at -20℃ is only 8 kJ / m. 2 . Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a polypropylene resin with excellent low-temperature toughness and its preparation method.

[0007] According to a first aspect of the present invention, the present invention provides a method for preparing a polypropylene resin with excellent low-temperature toughness, the method comprising steps 1, 2, and 3, or comprising steps 2 and 3, or comprising steps 1 and 3, or comprising step 3:

[0008] 1) Prepolymerize propylene by controlling the pressure at 1–30 bar and the temperature at 10–50 °C;

[0009] 2) The pressure is controlled at 1-100 bar and the temperature is controlled at 40-90℃ for propylene homopolymerization;

[0010] 3) The temperature is controlled at 40-90℃ and the pressure is controlled at 1-100 bar. The fractions of ethylene monomer and propylene monomer in the reaction environment are changed periodically to carry out ethylene-propylene copolymerization.

[0011] Preferably, the preparation method of the polypropylene resin with excellent low-temperature toughness includes the following steps 1, 2 and 3.

[0012] According to a preferred embodiment of the present invention, in step 3), the percentage of ethylene monomer in the reaction environment varies from 10% to 90%, and the corresponding percentage of propylene monomer varies from 90% to 10%. As a preferred embodiment of the present invention, the difference in the percentage of ethylene in the reaction environment before and after the transformation is not less than 30%.

[0013] According to a preferred embodiment of the present invention, the fractions of ethylene monomer and propylene monomer in the periodically changing reaction environment are: two reaction mixtures containing different molar ratios of ethylene and propylene are supplied to the polymerization reactor in a periodically switching manner.

[0014] According to a preferred embodiment of the present invention, in step 3), the transition time required for the fractions of ethylene monomer and propylene monomer to switch from one set ratio to another is 0.1 to 10 minutes. Taking the periodic switching between two different reaction environments (two different concentration ratios of ethylene monomer and propylene monomer) during polymerization as an example, the present invention reduces the transition time required for switching the reaction environment from a larger (smaller) concentration ratio of ethylene monomer and propylene monomer to a smaller (larger) concentration ratio to 0.1 to 10 minutes.

[0015] According to a preferred embodiment of the present invention, the frequency of the concentration ratio of ethylene monomer and propylene monomer in the periodic change reaction environment is 20-90 times / hour, preferably 24-60 times / hour.

[0016] According to a preferred embodiment of the present invention, the reaction time in step 3) is 5-30 min, preferably 5-20 min, more preferably 10-20 min, the reaction temperature is preferably 50-70°C, and the stirring speed is 350-650 r / min.

[0017] In step 3), before changing the reaction environment, it is preferable to purge and evacuate the remaining raw material gas in the reactor from the previous polymerization step.

[0018] According to a preferred embodiment of the present invention, after step 2), the solvent in the reactor is dried using a vacuum pump for 10 to 20 minutes.

[0019] According to a preferred embodiment of the present invention, the reaction temperature of propylene prepolymerization in step 1) is 10-30°C, the partial pressure of propylene is 0.1-0.2 MPa, and the partial pressure of hydrogen is 0.01-0.1 MPa.

[0020] According to a preferred embodiment of the present invention, in step 2), the polymerization reaction temperature is 60-70°C, the propylene pressure is 0.5-0.6 MPa, the reaction time is 10-50 min, and the stirring speed is 450-600 r / min.

[0021] According to a second aspect of the present invention, the present invention provides a polypropylene resin with excellent low-temperature toughness, wherein the toughness loss at -20°C compared to 20°C is less than 10%, and the toughness loss at -30°C compared to 20°C is less than 20%.

[0022] The polypropylene resin with excellent low-temperature toughness described above is preferably prepared using the above preparation method.

[0023] According to a preferred embodiment of the present invention, the polypropylene comprises 10-100% by mass of an ethylene-propylene copolymer, wherein the xylene-soluble component in the ethylene-propylene copolymer accounts for 40-90 wt% by mass.

[0024] According to a preferred embodiment of the present invention, the glass transition temperature of the copolymer in the polypropylene resin is -40°C to -60°C.

[0025] According to a preferred embodiment of the present invention, the content of the fraction obtained by heating and rinsing the polypropylene resin below 50°C is in the range of 5 to 40 wt%, the content of the fraction at 80°C is in the range of 1 to 10 wt%, and the content of the fraction at 100°C is in the range of 5 to 25 wt%.

[0026] According to a preferred embodiment of the present invention, the melt index of the polypropylene resin is 0.3 g / 10 min to 200 g / 10 min, preferably 0.3 g / 10 min to 60 g / 10 min; and the isotacticity is 95 to 99.9%.

[0027] A prominent feature of the polypropylene resin provided by this invention is that its xylene-soluble content is lower than that of commercial impact-resistant materials, yet its toughness at both room temperature and low temperatures is significantly higher than that of commercial products. It is known that the higher the content of the room-temperature soluble xylene fraction, i.e., the rubber phase content, the better the impact resistance of the product. However, the applicant unexpectedly discovered that the high-impact material provided by this invention still exhibits excellent low-temperature toughness even with a constant rubber phase content. Furthermore, it was found that the high-impact material provided by this invention possesses this characteristic because of the special segmental composition of the rubber phase; the good compatibility between the multiphase components significantly enhances the polymer's toughening effect. The polypropylene resin provided by this invention also has a relatively high content of the 100°C fraction, which plays a crucial role in improving the compatibility of the multiphase polypropylene, acting as a binder. Attached Figure Description

[0028] The present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the drawings are provided only for a better understanding of the invention and should not be construed as limiting the invention.

[0029] Figure 1 A schematic diagram of the polymerization process for preparing high and low temperature toughness polypropylene resin is shown. Detailed Implementation

[0030] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0031] Polymer preparation

[0032] The polymerization process is divided into two parts: slurry polymerization and gas-phase polymerization. First, propylene slurry polymerization is carried out, with the dissolved propylene content in the slurry ranging from 2% to 10% molar. The advantage of a high propylene concentration is increased catalyst activity per unit time, with polymerization temperatures ranging from 65 to 85°C and pressures from 1 to 40 bar. Slurry polymerization can be carried out in any reactor known for slurry polymerization, including continuously stirred batch reactors and circulating reactors. The slurry can be continuously or intermittently removed from the reactor. Hydrogen is introduced into the polymerization stage to control the melt index of polypropylene. The amount of hydrogen required to achieve the desired melt index depends on the catalyst used and the polymerization conditions. Desired polymer properties have been obtained in slurry polymerization in a circulating reactor, where the hydrogen / ethylene molar ratio is 0.02 to 0.08. The average residence time in the slurry polymerization stage is 30 to 80 min. After the polypropylene homopolymerization stage, the water bath temperature is adjusted to 80°C, and simultaneously, a vacuum pump is used to extract the n-heptane solvent from the reactor until the pressure inside the reactor reaches -0.9, at which point the extraction is stopped.

[0033] The ethylene and propylene gas-phase polymerization is then carried out, with the gas-phase polymerization stage involving alternating switching of two ethylene-propylene mixtures in different proportions. The polymerization atmosphere is switched at a predetermined frequency. The desired polymer properties have been obtained in the gas-phase polymerization in the fluidized bed reactor, and hydrogen can be introduced simultaneously to control the molecular weight. The process is conducted in a gas-phase fluidized bed reactor. The fluidized bed polymerization reactor operates at a temperature ranging from 65 to 90°C. The pressure is 1 to 30 bar. The average residence time in the ethylene copolymerization stage is 10 to 100 minutes.

[0034] Example 1

[0035] The initial temperature was 30°C. The catalyst, co-catalyst, and electron donor were added to a 1.5L stirred tank R1. The catalyst, co-catalyst, and electron donor were flushed into the tank from the catalyst tube using n-heptane solvent. The stir bar was turned on and the speed was set to 500 rpm. 0.4 bar of hydrogen was added through the hydrogen line, and propylene monomer was added through the propylene line, maintaining a system pressure of 1.5 bar. Prepolymerization began for 15 minutes, with the tank temperature controlled between 15 and 30°C. After prepolymerization, the tank temperature was raised to 60°C, and propylene monomer was added through the propylene line, pressurizing the tank to 6 bar. The temperature was maintained at 70°C, and the reaction was allowed to proceed for 30 minutes. After the polypropylene homopolymerization stage, the water bath temperature was adjusted to 80°C. Simultaneously, a vacuum pump was used to remove the n-heptane solvent from the tank until the pressure inside the tank reached -0.9 bar, at which point the vacuuming process was stopped.

[0036] Then, the gas-phase homopolymerization stage begins. In the first stage, the polypropylene matrix is ​​separated by a separator and enters reactor R2. Simultaneously, two pre-mixed ethylene / propylene gases are added to the bottom of the reactor. The gas-phase polymerization stage involves alternating between two ethylene / propylene gas mixtures with different E / P ratios of 3:1 and 1:3, respectively. The switching frequency is set to 24 times / h (i.e., a gas switching operation is performed every 2.5 minutes, and every two switching operations constitute a complete switching cycle, where one switching cycle refers to the cycle of switching from the first gas mixture to the second gas mixture and then back to the first gas mixture), with a total reaction residence time of 20 minutes. Before the gas switching, a vacuum pump is used to remove residual gas from the reactor before the next stage of gas introduction. The gas-phase reaction temperature is 70℃, and the pressure is 5 bar. After the second polymerization stage, the product is obtained by cyclone separation.

[0037] Example 2

[0038] The initial temperature was 30°C. The catalyst, co-catalyst, and electron donor were added to a 1.5L stirred tank R1. The catalyst, co-catalyst, and electron donor were flushed into the tank from the catalyst tube using n-heptane solvent. The stir bar was turned on and the speed was set to 500 rpm. 0.4 bar of hydrogen was added through the hydrogen line, and propylene monomer was added through the propylene line, maintaining a system pressure of 1.5 bar. Prepolymerization began for 15 minutes, with the tank temperature controlled between 15 and 30°C. After prepolymerization, the tank temperature was raised to 60°C, and propylene monomer was added through the propylene line, pressurizing the tank to 6 bar. The temperature was maintained at 70°C, and the reaction was allowed to proceed for 30 minutes. After the polypropylene homopolymerization stage, the water bath temperature was adjusted to 80°C. Simultaneously, a vacuum pump was used to remove the n-heptane solvent from the tank until the pressure inside the tank reached -0.9 bar, at which point the vacuuming process was stopped.

[0039] Then, the gas-phase homopolymerization stage begins. In the first stage, the polypropylene matrix is ​​separated by a separator and enters reactor R2. Simultaneously, two pre-mixed ethylene / propylene gases are added to the bottom of the reactor. The gas-phase polymerization stage involves alternating between the two ethylene / propylene gas mixtures with different E / P ratios of 3:1 and 1:3, respectively. The switching frequency is set to 36 times / hour, i.e., a gas switching operation is performed every 1 minute and 40 seconds, with a total reaction residence time of 20 minutes. Before switching gases, a vacuum pump is used to remove residual gas from the reactor before introducing gas for the next stage. The gas-phase reaction temperature is 70°C, and the pressure is 5 bar. After the second polymerization stage, the product is obtained through cyclone separation.

[0040] Example 3

[0041] The initial temperature was 30°C. The catalyst, co-catalyst, and electron donor were added to a 1.5L stirred tank R1. The catalyst, co-catalyst, and electron donor were flushed into the tank from the catalyst tube using n-heptane solvent. The stir bar was turned on and the speed was set to 500 rpm. 0.4 bar of hydrogen was added through the hydrogen line, and propylene monomer was added through the propylene line, maintaining a system pressure of 1.5 bar. Prepolymerization began for 15 minutes, with the tank temperature controlled between 15 and 30°C. After prepolymerization, the tank temperature was raised to 60°C, and propylene monomer was added through the propylene line, pressurizing the tank to 6 bar. The temperature was maintained at 70°C, and the reaction was allowed to proceed for 30 minutes. After the polypropylene homopolymerization stage, the water bath temperature was adjusted to 80°C. Simultaneously, a vacuum pump was used to remove the n-heptane solvent from the tank until the pressure inside the tank reached -0.9 bar, at which point the vacuuming process was stopped.

[0042] Then, the gas-phase homopolymerization stage begins. In the first stage, the polypropylene matrix is ​​separated by a separator and enters reactor R2. Simultaneously, two pre-mixed ethylene / propylene gases are added to the bottom of the reactor. The gas-phase polymerization stage involves alternating between the two ethylene / propylene gas mixtures with different E / P ratios of 3:1 and 1:3, respectively. The switching frequency is set to 48 times / h, i.e., a gas switching operation is performed every 1 minute and 15 seconds, with a total reaction residence time of 20 minutes. Before switching gases, a vacuum pump is used to remove residual gas from the reactor before introducing gas for the next stage. The gas-phase reaction temperature is 70°C, and the pressure is 5 bar. After the second polymerization stage, the product is obtained through cyclone separation.

[0043] Example 4

[0044] The initial temperature was 30°C. The catalyst, co-catalyst, and electron donor were added to a 1.5L stirred tank R1. The catalyst, co-catalyst, and electron donor were flushed into the tank from the catalyst tube using n-heptane solvent. The stir bar was turned on and the speed was set to 500 rpm. 0.4 bar of hydrogen was added through the hydrogen line, and propylene monomer was added through the propylene line, maintaining a system pressure of 1.5 bar. Prepolymerization began for 15 minutes, with the tank temperature controlled between 15 and 30°C. After prepolymerization, the tank temperature was raised to 60°C, and propylene monomer was added through the propylene line, pressurizing the tank to 6 bar. The temperature was maintained at 70°C, and the reaction was allowed to proceed for 30 minutes. After the polypropylene homopolymerization stage, the water bath temperature was adjusted to 80°C. Simultaneously, a vacuum pump was used to remove the n-heptane solvent from the tank until the pressure inside the tank reached -0.9 bar, at which point the vacuuming process was stopped.

[0045] Then, the gas-phase homopolymerization stage begins. In the first stage, the polypropylene matrix is ​​separated by a separator and enters reactor R2. Simultaneously, two pre-mixed ethylene / propylene gases are added to the bottom of the reactor. The gas-phase polymerization stage involves alternating between the two ethylene / propylene gas mixtures with different E / P ratios of 3:1 and 1:3, respectively. The switching frequency is set to 60 times / hour, i.e., a gas switching operation is performed every 1 minute, with a total reaction residence time of 20 minutes. Before switching gases, a vacuum pump is used to remove residual gas from the reactor before introducing gas for the next stage. The gas-phase reaction temperature is 70℃, and the pressure is 5 bar. After the second polymerization stage, the product is obtained through cyclone separation.

[0046] Comparative Example 1

[0047] The initial temperature was 30°C. The catalyst, co-catalyst, and electron donor were added to a 1.5L stirred tank R1. The catalyst, co-catalyst, and electron donor were flushed into the tank from the catalyst tube using n-heptane solvent. The stir bar was turned on and the speed was set to 500 rpm. 0.4 bar of hydrogen was added through the hydrogen line, and propylene monomer was added through the propylene line, maintaining a system pressure of 1.5 bar. Prepolymerization began for 15 minutes, with the tank temperature controlled between 15 and 30°C. After prepolymerization, the tank temperature was raised to 60°C, and propylene monomer was added through the propylene line, pressurizing the tank to 6 bar. The temperature was maintained at 70°C, and the reaction was allowed to proceed for 30 minutes. After the polypropylene homopolymerization stage, the water bath temperature was adjusted to 80°C. Simultaneously, a vacuum pump was used to remove the n-heptane solvent from the tank until the pressure inside the tank reached -0.9 bar, at which point the vacuuming process was stopped.

[0048] Then, the gas-phase homopolymerization stage proceeds. In the first stage, the polypropylene matrix is ​​separated by a separator and enters reactor R2. Simultaneously, two pre-mixed ethylene / propylene gases are added to the bottom of the reactor. The gas-phase polymerization stage involves alternating between two ethylene / propylene gas mixtures with different E / P ratios: 3:1 and 1:3, respectively. The total reaction residence time is 20 minutes. First, 10 minutes of ethylene / propylene copolymerization with a 3:1 E / P ratio is carried out, followed by 10 minutes of ethylene / propylene copolymerization with a 1:3 E / P ratio. Before switching gases, a vacuum pump is used to remove residual gas from the reactor before introducing gas for the next stage. The gas-phase reaction temperature is 70°C, and the pressure is 5 bar. After the second polymerization stage, the product is obtained by cyclone separation.

[0049] The high-impact copolymer polypropylene prepared in the examples and comparative examples was tested for ethylene content, rubber content, and molecular weight, and the results are shown in Table 1:

[0050] Table 1

[0051]

[0052] As shown in Table 1, the mechanical properties of the polypropylene composition prepared by the dynamic switching polymerization method for olefin polymerization in the impact-resistant polypropylene polymerization process of this invention are significantly better than those of the comparative example. With the increase of the switching frequency, the low-temperature toughness (-30℃) is significantly improved, from 5.19 kJ / m... 2 Increased to 38.96 kJ / m 2 Meanwhile, the flexural modulus only decreased from 932 MPa to 874 MPa. Therefore, the present invention has significant technical advantages.

[0053] While the specific embodiments of the present invention have been described in detail above, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims. Those skilled in the art can make appropriate modifications to these embodiments without departing from the technical concept and spirit of the present invention, and these modified embodiments are obviously also included within the scope of protection of the present invention.

Claims

1. A method for preparing a polypropylene resin with excellent low-temperature toughness, characterized in that: The method includes the following steps: 1) The pressure is controlled at 1~30 bar, the temperature is controlled at 10~50℃, the partial pressure of propylene is 0.1~0.2MPa, and the partial pressure of hydrogen is 0.01~0.1MPa, for propylene prepolymerization; 2) The pressure is controlled at 1~100 bar, the temperature is controlled at 40~90℃, the propylene pressure is 0.5~0.6MPa, and the reaction time is 10~50min to carry out propylene homopolymerization; 3) The temperature is controlled at 40~90℃ and the pressure is controlled at 1~100 bar. The fractions of ethylene monomer and propylene monomer in the reaction environment are changed periodically to carry out ethylene-propylene copolymerization. In step 3), the fraction of ethylene monomer in the reaction environment varies from 10% to 90%, and the fraction of propylene monomer varies from 90% to 10%. Before changing the reaction environment, the remaining raw material gas in the reactor from the previous polymerization step is purged and evacuated. The switching time required to change the ratio of ethylene monomer and propylene monomer from one set ratio to another is 0.1 to 10 minutes; the frequency of periodically changing the concentration ratio of ethylene monomer and propylene monomer in the reaction environment is 24 to 60 times / hour; the difference in the ethylene fraction in the reaction environment before and after the change is not less than 30%.

2. A polypropylene resin with excellent low-temperature toughness, characterized in that: Its toughness loss at -20℃ compared to 20℃ is less than 10%, and its toughness loss at -30℃ compared to 20℃ is less than 20%. It is prepared using the method described in claim 1.

3. The polypropylene resin according to claim 2, characterized in that: It contains 10-100% by mass of ethylene-propylene copolymer, wherein the xylene-soluble component in the ethylene-propylene copolymer accounts for 40-90 wt% by mass.

4. The polypropylene resin according to claim 2, characterized in that: The glass transition temperature of the copolymer in the polypropylene resin is -40℃ to -60℃.

5. The polypropylene resin according to claim 2, characterized in that: The content of the fraction obtained by rinsing and classifying the polypropylene resin at elevated temperatures is in the range of 5-40 wt%, the content of the fraction at 80℃ is in the range of 1-10 wt%, and the content of the fraction at 100℃ is in the range of 5-25 wt%.

6. The polypropylene resin according to claim 2, characterized in that: The melt index of the polypropylene resin is 0.3 g / 10 min to 200 g / 10 min, and the isotacticity is 95 to 99.9%.

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