A transparent polypropylene resin and a method for producing the same

Abstract

The present application provides a kind of transparent polypropylene resin and its preparation method, comprising the following steps: A) propylene is polymerized under the action of main catalyst, macromolecular nucleating agent, cocatalyst and external electron donor;B) the pre-polymerization product, propylene, ethylene and hydrogen are carried out polymerization reaction, and polypropylene powder is obtained;C) polypropylene powder, propylene, ethylene and hydrogen continue to carry out polymerization reaction, and polypropylene resin powder is obtained;D) polypropylene resin powder, antioxidant, halogen absorber, antistatic agent and sorbitol nucleating agent are mixed uniformly, and mixture is obtained;E) the mixture is extruded by extruder, and transparent polypropylene material is obtained;The temperature of the highest temperature zone of extruder is 230-240 DEG C.The present application realizes the replacement of three generations nucleating agent to four generations nucleating agent, and the obtained transparent effect is equivalent to four generations nucleating agent, and mechanical property is also improved.This greatly reduces the preparation cost of transparent polypropylene, and improves the market competitiveness of product.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a transparent polypropylene resin and a preparation method thereof. Background Art

[0002] Polypropylene is a semi-crystalline polymer widely used as one of the three major general-purpose plastics due to its low density, excellent optical and heat resistance, superior chemical resistance and dielectric strength, excellent water vapor barrier properties, and low odor. Random copolymer polypropylene offers excellent transparency and toughness, making it suitable for the production of transparent products. Existing transparent polypropylene plastics typically use random copolymer polypropylene as the base resin and incorporate sorbitol-based nucleating agents to enhance product transparency.

[0003] Currently, sorbitol-based transparent nucleating agents have reached their fourth generation. The first generation of sorbitol nucleating agents lacks any substituents on the benzene ring, with Milliken's Millad 3905 ((1,3:2,4)-di(3,4-dimethyldibenzylidene) sorbitol, abbreviated as DMDBS) representing a representative example. This nucleating agent is low-cost, has moderate nucleation effectiveness, and is unstable at high temperatures, easily degrading and releasing the parent aldehyde. Second-generation products feature para-substituted benzene rings with chlorine, methyl, or other groups, with Milliken's Millad 3940 ((1,3:2,4)-di(p-methyldibenzylidene) sorbitol, abbreviated as MDBS) representing a significant improvement in transmittance enhancement efficiency, but still exhibit a strong odor. The third generation, Millad 3988, boasts significant improvements in transmittance enhancement, nucleation performance, and odor, making it the most widely used transparent nucleating agent. However, polypropylene materials prepared using these third-generation nucleating agents typically exhibit a haze of 8-10%, making it difficult to produce highly transparent polypropylene with a haze less than 6%.

[0004] The fourth-generation nucleating agent, Millad NX 8000, is a benzyl sorbitol derivative. This fourth-generation nucleating agent exhibits significantly better melt dispersion than the third-generation nucleating agent. Therefore, the fourth-generation nucleating agent NX8000 can be used to produce highly transparent polypropylene products. However, its high price increases the production cost of transparent polypropylene. Furthermore, a common problem with nucleating agents is that while they can significantly improve the transparency of polypropylene at a certain dosage, after reaching a certain effective content, such as when the addition level of third- and fourth-generation nucleating agents exceeds 3000 ppm, they have no significant effect on improving the transparency of the polypropylene resin. Furthermore, they are unable to optimize mechanical properties. Summary of the Invention

[0005] The object of the present invention is to provide a transparent polypropylene resin and a preparation method thereof. The transparent polypropylene resin of the present invention has low cost, significantly reduced haze, and improved rigidity, toughness and heat resistance.

[0006] The present invention provides a method for preparing a transparent polypropylene resin, comprising the following steps:

[0007] A) prepolymerizing propylene under the action of a primary catalyst, a polymer nucleating agent, a co-catalyst and an external electron donor;

[0008] The polymer nucleating agent includes one or more of polyvinylcyclopentane, polyvinylcyclohexane, polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, poly-3-ethyl-1-hexene, poly-3-methyl-1-pentene and polystyrene; the mass ratio of the main catalyst to the polymer nucleating agent is 1:(1-2);

[0009] B) subjecting the prepolymerized product, propylene, ethylene and hydrogen to polymerization to obtain polypropylene powder;

[0010] C) continuing to polymerize the polypropylene powder, propylene, ethylene and hydrogen to obtain a polypropylene resin powder;

[0011] D) uniformly mixing the polypropylene resin powder, antioxidant, halogen absorbent, antistatic agent and sorbitol nucleating agent to obtain a mixture;

[0012] The sorbitol nucleating agent includes one or more of 1,3:2,4-dibenzylidene sorbitol, 1,3:2,4-di(4-methylbenzylidene) sorbitol, 1,3:2,4-di(4-ethylbenzylidene) sorbitol and 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol; the mass ratio of the polymer nucleating agent to the sorbitol nucleating agent is 1:(75-150);

[0013] E) extruding the mixture through an extruder to obtain a transparent polypropylene material;

[0014] The temperature of the highest temperature zone of the extruder is 230-240°C.

[0015] Preferably, the main catalyst is a titanium tetrachloride catalyst supported by magnesium chloride, the main catalyst is an alkyl aluminum, and the external electron donor is an alkoxysilane.

[0016] Preferably, the temperature of the prepolymerization is 15 to 25° C., and the residence time of the prepolymerization is 10 to 20 minutes.

[0017] Preferably, the polymerization reaction temperature in step B) is 70-75° C., the polymerization reaction residence time is 30-50 min; the total flow rate of ethylene and propylene is 20-40 t / h, the mass ratio of ethylene to propylene is (2-5):(98-95), and the hydrogen concentration is 2000-3000 ppm.

[0018] Preferably, the polymerization reaction temperature in step C) is 70-75° C., the polymerization reaction residence time is 10-30 min; the total flow rate of ethylene and propylene is 10-20 t / h, the mass ratio of ethylene to propylene is (2-5):(98-95), and the hydrogen concentration is 2000-3000 ppm.

[0019] Preferably, in the step D), the polypropylene resin powder is 100 parts, the sorbitol nucleating agent is 0.15-0.35 parts, the antioxidant is 0.1-0.3 parts, the halogen absorbent is 0.01-0.2 parts, and the antistatic agent is 0.01-0.1 parts.

[0020] Preferably, the antioxidant includes a primary antioxidant and a secondary antioxidant;

[0021] The mass ratio of the primary antioxidant to the secondary antioxidant is 1:(1-4);

[0022] The main antioxidant includes one or more of antioxidant 2246, antioxidant 1010, antioxidant 1076 and antioxidant 1330; the auxiliary antioxidant includes one or more of antioxidant 168, antioxidant 626 and antioxidant 9228.

[0023] Preferably, the halogen absorbing agent includes one or more of sodium stearate, calcium stearate and zinc stearate;

[0024] The antistatic agent includes one or more of glyceryl monostearate, polyol fatty acid ester, polyethylene oxide, and propylene oxide copolymer.

[0025] The present invention provides a transparent polypropylene resin, which is prepared according to the above preparation method.

[0026] Preferably, the transparent polypropylene resin has a melt mass flow rate of 22 to 30 g / 10 min, an ethylene content of 3.0 to 3.5 wt %, and a haze of 5 to 10%.

[0027] The present invention provides a preparation method of a transparent polypropylene resin, comprising the following steps: A) prepolymerizing propylene under the action of a main catalyst, a polymer nucleating agent, a cocatalyst and an external electron donor; the polymer nucleating agent comprises one or more of polyvinylcyclopentane, polyvinylcyclohexane, polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, poly-3-ethyl-1-hexene, poly-3-methyl-1-pentene and polystyrene; the mass ratio of the main catalyst to the polymer nucleating agent is 1:(1-2); B) polymerizing the prepolymerized product, propylene, ethylene and hydrogen to obtain polypropylene powder; C) continuing to polymerize the polypropylene powder, propylene, ethylene and hydrogen to obtain Polypropylene resin powder; D) uniformly mixing the polypropylene resin powder, an antioxidant, a halogen absorbent, an antistatic agent and a sorbitol nucleating agent to obtain a mixture; the sorbitol nucleating agent includes one or more of 1,3:2,4-dibenzylidene sorbitol, 1,3:2,4-di(4-methylbenzylidene) sorbitol, 1,3:2,4-di(4-ethylbenzylidene) sorbitol and 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol; the mass ratio of the polymer nucleating agent to the sorbitol nucleating agent is 1:(75-150); E) extruding the mixture through an extruder to obtain a transparent polypropylene material; the temperature in the highest temperature zone of the extruder is 230-240°C.

[0028] Compared with the existing technology, the beneficial effects of this technical solution are as follows:

[0029] ① Significant cost-effectiveness: The production of transparent polypropylene using a fourth-generation nucleating agent is expensive, while using a third-generation nucleating agent is less expensive, but the haze is higher than that of polypropylene produced using a fourth-generation nucleating agent. The transparent polypropylene resin composition of the present invention replaces a fourth-generation nucleating agent with a third-generation nucleating agent, while achieving a transparency comparable to that of the fourth-generation nucleating agent NX8000. This significantly reduces the production cost of transparent polypropylene and improves the product's market competitiveness.

[0030] ② Significantly Improved Transparency: The transparent polypropylene resin composition of this invention utilizes a specific ratio of a polymer nucleating agent and a sorbitol nucleating agent (3988). The synergistic effect of these two nucleating agents significantly enhances the transparency of the polypropylene. Even at low nucleating agent levels (1500ppm), a significant transparency effect is achieved. This also increases the upper limit of transparency enhancement for third-generation transparent nucleating agents (raising the upper limit of haze for nucleating agents added at levels of 3000ppm or greater from 8-10% to 5-6%).

[0031] ③ Improved mechanical properties: While improving the transparency of polypropylene products, the mechanical properties are also improved, with rigidity and toughness increased by about 10%, and heat resistance improved. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing a transparent polypropylene resin, comprising the following steps:

[0033] A) prepolymerizing propylene under the action of a primary catalyst, a polymer nucleating agent, a co-catalyst and an external electron donor;

[0034] The polymer nucleating agent includes one or more of polyvinylcyclopentane, polyvinylcyclohexane, polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, poly-3-ethyl-1-hexene, poly-3-methyl-1-pentene and polystyrene; the mass ratio of the main catalyst to the polymer nucleating agent is 1:(1-2);

[0035] B) subjecting the prepolymerized product, propylene, ethylene and hydrogen to polymerization to obtain polypropylene powder;

[0036] C) continuing to polymerize the polypropylene powder, propylene, ethylene and hydrogen to obtain a polypropylene resin powder;

[0037] D) uniformly mixing the polypropylene resin powder, antioxidant, halogen absorbent, antistatic agent and sorbitol nucleating agent to obtain a mixture;

[0038] The sorbitol nucleating agent includes one or more of 1,3:2,4-dibenzylidene sorbitol, 1,3:2,4-di(4-methylbenzylidene) sorbitol, 1,3:2,4-di(4-ethylbenzylidene) sorbitol and 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol; the mass ratio of the polymer nucleating agent to the sorbitol nucleating agent is 1:(75-150);

[0039] E) extruding the mixture through an extruder to obtain a transparent polypropylene material;

[0040] The temperature of the highest temperature zone of the extruder is 230-240°C.

[0041] The invention uses propylene as a raw material, magnesium chloride-loaded titanium tetrachloride catalyst as a main catalyst, alkyl aluminum as a co-catalyst, alkoxysilane as an external electron donor, a polymer nucleating agent, and a spheripol polymerization process. Hydrogen is used as a molecular weight regulator, and ethylene is added into a reactor to prepare polypropylene resin powder. The polypropylene resin powder, a main antioxidant, an auxiliary antioxidant, a halogen absorber and a sorbitol nucleating agent are uniformly mixed, and the mixture is extruded through an extruder to prepare a transparent polypropylene material with a melt mass flow rate of 22-30 g / 10 min and an ethylene content of 3.0-3.5 wt%.

[0042] In the present invention, the main catalyst is a titanium tetrachloride catalyst supported on magnesium chloride, the main catalyst is an alkyl aluminum, preferably triethyl aluminum, and the external electron donor is an alkoxysilane, such as methylcyclohexyldimethoxysilane; the polymer nucleating agent is preferably one or more of polyvinylcyclopentane, polyvinylcyclohexane, polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, poly-3-ethyl-1-hexene, poly-3-methyl-1-pentene and polystyrene; the mass ratio of the main catalyst to the polymer nucleating agent is preferably 1:(1~2), more preferably 1:(1.2~1.8), such as 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, preferably a range value with any of the above values ​​as the upper or lower limit.

[0043] The present invention firstly adopts continuous pre-contact and pre-polymerization to ensure the stability of polymer quality and prevent device fluctuation.

[0044] In the present invention, the flow rate of propylene is preferably 2 to 2.8 t / h, more preferably 2.2 to 2.6 t / h, such as 2 t / h, 2.1 t / h, 2.2 t / h, 2.3 t / h, 2.4 t / h, 2.5 t / h, 2.6 t / h, 2.7 t / h, 2.8 t / h, preferably a range value with any of the above values ​​as the upper or lower limit; the mass ratio of the co-catalyst to propylene is preferably (0.1 to 0.15) g / kg, such as 0.1 g / kg, 0.2 g / kg, 0.3 g / kg, 0.4 g / kg, 0.5 g / kg, preferably a range value with any of the above values ​​as the upper or lower limit; The mass ratio of the co-catalyst to the external electron donor is preferably (3-5):1, more preferably 4:1, the mass ratio of the main catalyst to the co-catalyst is preferably 1:(10-20), more preferably 1:(12-18), such as 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, preferably a range value with any of the above values ​​as the upper or lower limit; in the present invention, the temperature of the prepolymerization is preferably 15-25°C, more preferably 20°C, and the residence time of the prepolymerization is preferably 10-20min, more preferably 15min.

[0045] After the prepolymerization is completed, the present invention introduces the prepolymerization product, propylene, ethylene and hydrogen into a first reactor to carry out a polymerization reaction to obtain polypropylene powder.

[0046] In the present invention, the temperature of the polymerization reaction is preferably 70-75°C, such as 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, and preferably a range value with any of the above values ​​as the upper or lower limit; the residence time of the polymerization reaction is preferably 30-50min, more preferably 35-45min, such as 30min, 35min, 40min, 45min, 50min, and preferably a range value with any of the above values ​​as the upper or lower limit.

[0047] In the present invention, the total flow rate of ethylene and propylene in the first reactor is preferably 20 to 40 t / h, more preferably 25 to 35 t / h, such as 20 t / h, 25 t / h, 30 t / h, 35 t / h, 40 t / h, preferably a range value with any of the above values ​​as the upper or lower limit, wherein the mass ratio of ethylene to propylene is preferably (2 to 5): (98 to 95), more preferably (3 to 4): (97 to 96), such as 2:98, 3:97, 3.5:96.5, 4:96.5, 5:96.5, 6:96.5, 7:96.5, 8:96.5, 9:96.5, 10:96.5, 11:96.5, 12:96.5, 13:96.5, 14:96.5, 15:96.5, 16:96.5, 17:96.5, 18:96.5, 19:96.5, 20:96.5, 21:96.5, 22:96.5, 23:96.5, 24:96.5, 25:96.5, 26:96.5, 27:96.5, 28:96.5, 29:96.5, 30:9 :96,5:95, preferably, the concentration of hydrogen in the first reactor is controlled to be 2000-3000ppm, such as 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm ...

[0048] In the present invention, the first reactor is preferably a first loop reactor.

[0049] After the polymerization reaction is completed, the obtained polypropylene powder, propylene, ethylene and hydrogen are introduced into a second reactor to continue the polymerization reaction to obtain polypropylene resin powder. New materials are introduced into the first reactor to react, and the cycle continues.

[0050] In the present invention, the temperature of the polymerization reaction is preferably 70-75°C, such as 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, and preferably a range value with any of the above values ​​as the upper or lower limit; the residence time of the polymerization reaction is preferably 10-30min, more preferably 15-25min, such as 10min, 15min, 20min, 25min, 30min, and preferably a range value with any of the above values ​​as the upper or lower limit.

[0051] In the present invention, the total flow rate of ethylene and propylene in the second reactor is preferably 10 to 20 t / h, more preferably 12 to 18 t / h, such as 10 t / h, 11 t / h, 12 t / h, 13 t / h, 14 t / h, 15 t / h, 16 t / h, 17 t / h, 18 t / h, 19 t / h, 20 t / h, preferably a range value with any of the above values ​​as the upper or lower limit, wherein the mass ratio of ethylene to propylene is preferably (2 to 5): (98 to 95), more preferably (3 to 4): (97 to 96), such as 2: 98, 3:97, 3.6:96.4, 4:96, 5:95, preferably a range value with any of the above values ​​as the upper or lower limit, controlling the concentration of hydrogen in the first reactor to be 2000-3000ppm, such as 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm, preferably a range value with any of the above values ​​as the upper or lower limit.

[0052] In the present invention, the second reactor is preferably a second loop reactor.

[0053] After obtaining the polypropylene resin powder, the present invention uniformly mixes the polypropylene resin powder, an antioxidant, a halogen absorbent, an antistatic agent and a sorbitol nucleating agent to obtain a mixture.

[0054] In the present invention, the polypropylene resin powder is an ethylene-propylene random copolymer polypropylene resin, and the weight proportion of the polypropylene resin powder is preferably 100 parts.

[0055] In the present invention, the antioxidant preferably includes a primary antioxidant and a secondary antioxidant; the mass ratio of the primary antioxidant to the secondary antioxidant is 1:(1-4), preferably 1:(2-3); the primary antioxidant includes one or more of antioxidant 2246, antioxidant 1010, antioxidant 1076 and antioxidant 1330; the secondary antioxidant includes one or more of antioxidant 168, antioxidant 626 and antioxidant 9228; the weight portion of the antioxidant is preferably 0.1-0.3 parts, more preferably 0.15-0.25 parts, such as 0.1 parts, 0.15 parts, 0.2 parts, 0.25 parts, 0.3 parts, preferably a range value with any of the above values ​​as the upper or lower limit.

[0056] In the present invention, the halogen absorbing agent is preferably one or more of sodium stearate, calcium stearate and zinc stearate; the weight portion of the halogen absorbing agent is preferably 0.01 to 0.2 parts, more preferably 0.1 to 0.15 parts, such as 0.01 parts, 0.05 parts, 0.1 parts, 0.15 parts, 0.2 parts, preferably a range value with any of the above values ​​as the upper or lower limit.

[0057] In the present invention, the antistatic agent is preferably one or more of glyceryl monostearate, polyol fatty acid ester, polyethylene oxide, and propylene oxide copolymer; the weight portion of the antistatic agent is preferably 0.01 to 0.1 parts, such as 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.07 parts, 0.08 parts, 0.09 parts, 0.1 parts, preferably a range value with any of the above values ​​as the upper or lower limit.

[0058] In the present invention, the sorbitol nucleating agent preferably includes one or more of 1,3:2,4-dibenzylidene sorbitol, 1,3:2,4-di(4-methylbenzylidene) sorbitol, 1,3:2,4-di(4-ethylbenzylidene) sorbitol and 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol, more preferably 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (i.e., the third-generation nucleating agent 3988). The weight percentage of the sorbitol nucleating agent is preferably 0 .15 to 0.35 parts, more preferably 0.15 to 0.2 parts, such as 0.15 parts, 0.16 parts, 0.17 parts, 0.18 parts, 0.19 parts, 0.2 parts, 0.21 parts, 0.22 parts, 0.23 parts, 0.24 parts, 0.25 parts, 0.26 parts, 0.27 parts, 0.28 parts, 0.29 parts, 0.3 parts, 0.31 parts, 0.32 parts, 0.33 parts, 0.34 parts, 0.35 parts, preferably a range value with any of the above values ​​as the upper or lower limit.

[0059] In the present invention, by compounding a polymer nucleating agent and a sorbitol nucleating agent, the transparency of the polypropylene product is improved while taking into account the improvement of mechanical properties. The mass ratio of the polymer nucleating agent to the sorbitol nucleating agent is preferably 1:(75-150), more preferably 1:(100-125), such as 1:75, 1:80, 1:85, 1:90, 1:95, 1:100, 1:105, 1:110, 1:115, 1:120, 1:125, 1:130, 1:135, 1:140, 1:145, 1:150, preferably a range value with any of the above values ​​as the upper or lower limit. That is, based on 100 parts by weight of the polypropylene resin powder, the weight portion of the polymer nucleating agent is preferably 0.002 to 0.005 parts, more preferably 0.002 to 0.004 parts, such as 0.002 parts, 0.003 parts, 0.004 parts, 0.005 parts, preferably a range value with any of the above values ​​as the upper or lower limit.

[0060] In the present invention, the mixing is preferably a conventional mixing method. In the present invention, the polypropylene resin powder, antioxidant, halogen absorbent, antistatic agent and sorbitol nucleating agent are preferably added to an extruder and blended in the extruder to obtain a mixture.

[0061] After obtaining the mixture, the present invention extrude the mixture through an extruder to obtain a transparent polypropylene resin.

[0062] In the present invention, the temperature of the highest temperature zone of the extruder is preferably 230-240°C, such as 230°C, 231°C, 232°C, 233°C, 234°C, 235°C, 236°C, 237°C, 238°C, 239°C, and 240°C, preferably a range value with any of the above numerical values ​​as the upper or lower limit; the extruder in the present invention is provided with a plurality of temperature zones, and the overall setting trend is that the temperature of the two temperature zones is low and the temperature of the middle temperature zone is high. In the present invention, it should be ensured that the temperature of at least one middle temperature zone can exceed 230°C, and 2 to 3 middle temperature zones can also be provided with a temperature ≥ 230°C. When the temperature of only one temperature zone exceeds 230°C, the temperature zone is the highest temperature in all temperature zones. Temperature zones. Specifically, in an embodiment of the present invention, the temperature zones can be set to nine zones: Zone 1 175-185°C, Zone 2 185-195°C, Zone 3 205-215°C, Zone 4 225-235°C, Zone 5 230-240°C, Zone 6 225-235°C, Zone 7 205-215°C, Zone 8 195-205°C, and Zone 9 185-195°C; more preferably, Zone 1 180°C, Zone 2 190°C, Zone 3 210°C, Zone 4 230°C, Zone 5 235°C, Zone 6 230°C, Zone 7 210°C, Zone 8 200°C, and Zone 9 190°C. In this temperature zone setting, the highest temperature zone is Zone 5, and the temperatures of Zones 4, 5 and 6 are ≥230°C.

[0063] The present invention provides a transparent polypropylene resin, which is prepared according to the preparation method described above.

[0064] In the present invention, the transparent polypropylene resin has a melt mass flow rate of 22 to 30 g / 10 min, an ethylene content of 3.0 to 3.5 wt%, a haze of 5 to 10%, and a crystallization temperature greater than 116°C.

[0065] The present invention provides a preparation method of transparent polypropylene resin, comprising the following steps: A) prepolymerizing propylene under the action of a main catalyst, a polymer nucleating agent, a cocatalyst and an external electron donor; the polymer nucleating agent comprises one or more of polyvinylcyclopentane, polyvinylcyclohexane, polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, poly-3-ethyl-1-hexene, poly-3-methyl-1-pentene and polystyrene; the mass ratio of the main catalyst to the polymer nucleating agent is 1:(1-2); B) polymerizing the prepolymerized product, propylene, ethylene and hydrogen to obtain polypropylene powder; C) continuing to polymerize the polypropylene powder, propylene, ethylene and hydrogen to obtain to polypropylene resin powder; D) uniformly mixing the polypropylene resin powder, antioxidant, halogen absorbent, antistatic agent and sorbitol nucleating agent to obtain a mixture; the sorbitol nucleating agent includes one or more of 1,3:2,4-dibenzylidene sorbitol, 1,3:2,4-di(4-methylbenzylidene) sorbitol, 1,3:2,4-di(4-ethylbenzylidene) sorbitol and 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol; the mass ratio of the polymer nucleating agent to the sorbitol nucleating agent is 1:(75-150); E) extruding the mixture through an extruder to obtain a transparent polypropylene material; the extrusion temperature of the extruder is 230-240°C.

[0066] Compared with the existing technology, the beneficial effects of this technical solution are as follows:

[0067] ① Significant cost-effectiveness: The production of transparent polypropylene using a fourth-generation nucleating agent is expensive, while using a third-generation nucleating agent is less expensive, but the haze is higher than that of polypropylene produced using a fourth-generation nucleating agent. The transparent polypropylene resin composition of the present invention replaces a fourth-generation nucleating agent with a third-generation nucleating agent, while achieving a transparency comparable to that of the fourth-generation nucleating agent NX8000. This significantly reduces the production cost of transparent polypropylene and improves the product's market competitiveness.

[0068] ② Significantly Improved Transparency: The transparent polypropylene resin composition of this invention utilizes a specific ratio of a polymer nucleating agent and a sorbitol nucleating agent (3988). The synergistic effect of these two nucleating agents significantly enhances the transparency of the polypropylene. Even at low nucleating agent levels (1500ppm), a significant transparency effect is achieved. This also increases the upper limit of transparency enhancement for third-generation transparent nucleating agents (raising the upper limit of haze for nucleating agents added at levels of 3000ppm or greater from 8-10% to 5-6%).

[0069] ③ Improved mechanical properties: While improving the transparency of polypropylene products, the mechanical properties are also improved, with rigidity and toughness increased by about 10%, and heat resistance improved.

[0070] In order to further illustrate the present invention, a transparent polypropylene resin and a preparation method thereof provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0071] Example 1

[0072] (1) Using the spheripol polymerization process, propylene was prepolymerized in the presence of a HR catalyst, polyvinylcyclohexane, triethylaluminum, and methylcyclohexyldimethoxysilane, wherein the mass ratio of the HR catalyst to polyvinylcyclohexane was 1:1.2, the mass ratio of the HR catalyst to the cocatalyst was 1:15, the ratio of the cocatalyst to propylene was 0.125 g / kg, the mass ratio of the cocatalyst to the external electron donor was 4, the prepolymerization temperature was 20°C, and the residence time was 15 min;

[0073] (2) feeding the prepolymerized product obtained in step (1), propylene, and hydrogen into a first loop reactor for polymerization reaction to obtain polypropylene powder, wherein the hydrogen concentration in the first loop reactor is controlled to be 2000 ppm, the total flow rate of ethylene and propylene is 30 t / h, the mass flow rate ratio of ethylene to propylene is 3.5:96.5, the reaction temperature is 72° C., and the reaction residence time is 40 min;

[0074] (3) feeding the polypropylene powder, propylene, ethylene, and hydrogen obtained in step (2) into a second loop reactor to continue polymerization reaction to obtain a polypropylene resin powder, wherein the hydrogen concentration in the second loop reactor is controlled to be 2000 ppm, the total flow rate of ethylene and propylene is 15 t / h, the mass flow rate ratio of ethylene to propylene is 3.6:96.4, the reaction temperature is 72° C., and the reaction residence time is 20 min;

[0075] (4) The polypropylene resin powder obtained in step (3), the antioxidant, the halogen absorbent, the antistatic agent and the nucleating agent are uniformly mixed to obtain a mixture, the formula of which is shown in Table 1, wherein the amount of 3988 nucleating agent (1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol) is 0.15 parts;

[0076] (5) The mixture obtained in step (4) was extruded through an extruder, and the maximum temperature of the extruder barrel was controlled at 235° C. to prepare a polypropylene resin. The performance test results and test methods are shown in Table 2.

[0077] Example 2

[0078] The preparation method is the same as that of Example 1, the only difference being that the amount of 3988 nucleating agent used is 0.2 parts.

[0079] The performance test results and test methods are shown in Table 2.

[0080] Example 3

[0081] The preparation method is the same as that of Example 1, the only difference being that the amount of 3988 nucleating agent used is 0.3 parts.

[0082] The performance test results and test methods are shown in Table 2.

[0083] Comparative Example 1

[0084] The preparation method is the same as that of Example 2, except that the polymer nucleating agent polyvinylcyclohexane (PVCH) is not added in the prepolymerization stage, and the amount of 3988 nucleating agent (1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol) used is 0.202 parts.

[0085] The performance test results and test methods are shown in Table 2.

[0086] Comparative Example 2

[0087] The preparation method is the same as that of Example 3, except that the polymer nucleating agent polyvinylcyclohexane (PVCH) is not added in the prepolymerization stage, and the amount of 3988 nucleating agent used is 0.302 parts.

[0088] Comparative Example 3

[0089] The preparation method is the same as that of Comparative Example 1, the only difference being that 0.202 parts of NX8000 nucleating agent is used instead of 0.202 parts of 3988 nucleating agent in Comparative Example 1.

[0090] Comparative Example 4

[0091] The preparation method is the same as that of Comparative Example 1, the only difference being that 0.302 parts of NX8000 nucleating agent is used instead of 0.202 parts of 3988 nucleating agent in Comparative Example 1.

[0092] Comparative Example 5

[0093] The preparation method is the same as that of Example 2, the only difference being that the maximum temperature of the extruder barrel is controlled at 220°C.

[0094] Comparative Example 6

[0095] The preparation method is the same as that of Example 2, the only difference being that 0.2 parts of NX8000 nucleating agent is used instead of 0.2 parts of 3988 nucleating agent in Example 2.

[0096] Comparative Example 7

[0097] The preparation method was the same as that of Example 2, except that no 3988 nucleating agent was added, the mass ratio of HR catalyst to polyvinylcyclohexane was 1:121.2, and the content of PVCH in the final product was 2020 ppm.

[0098] Comparative Example 8

[0099] The preparation method is the same as that of Example 2, with the only difference being that the polymer nucleating agent PVCH is added in the granulation stage. The amount of 3988 nucleating agent used in the granulation stage is 0.2 parts, and 0.002 parts of PVCH are also added.

[0100] Table 1: Composition ratios and processing conditions of the examples and comparative examples

[0101]

[0102] The transparent polypropylene resins obtained in Examples 1 to 3 and Comparative Examples 1 to 8 were tested for their properties. The results are shown in Table 2.

[0103] Table 2 Performance parameters of transparent polypropylene resin in Examples and Comparative Examples

[0104]

[0105] Performance comparison analysis:

[0106] Comparison of Examples 1 to 3 with Comparative Examples 1 to 2 and Comparative Example 7 shows that the combined use of polymer nucleating agent and 3988 can effectively improve the transparency of PPR (reduce haze); at the same time, it can effectively improve its rigidity, toughness and heat resistance. Specifically, in comparison of Example 2 with Comparative Examples 1 and 7, the total amount of nucleating agent is the same, 2020ppm. However, the crystallization temperature of the polypropylene material obtained in Comparative Example 1 is lower than 116℃, the mechanical properties are significantly reduced, and the haze is 10.7, which is higher than 7.2 in Example 2. The crystallization temperature of the polypropylene material in Comparative Example 7 is also lower than 116℃, the mechanical properties are significantly reduced, and the haze is as high as 30, which is significantly higher than Example 2. This shows that the present invention achieves a better technical effect by combining a polymer nucleating agent with a specific type of sorbitol nucleating agent, and the performance in both mechanical properties and haze are significantly improved. Similarly, the comparison of Example 3 with Comparative Example 2 also reaches the same conclusion.

[0107] By comparing Example 2 with Comparative Example 3, and Example 3 with Comparative Example 4, it can be seen that the combined use of the polymer nucleating agent and 3988 has a better anti-reflection effect than NX8000; at the same time, it has better rigidity, toughness and heat resistance.

[0108] Comparison of Example 2 with Comparative Example 5 shows that controlling the maximum temperature of the extruder barrel at 235° C. is an important condition. If this condition is not reached, the performance of the product will be directly affected.

[0109] Comparison of Example 2 with Comparative Examples 3 and 6 shows that the polymer nucleating agent has a synergistic effect when used in combination with 3988, but when used in combination with NX8000, not only does it have no synergistic effect, but it also affects the optical properties of the product.

[0110] Comparison between Comparative Example 8 and Example 2 shows that PVCH must be added during the polymerization stage to be effective.

[0111] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a transparent polypropylene resin, comprising the following steps: A) prepolymerizing propylene under the action of a main catalyst, a polymer nucleating agent, a cocatalyst and an external electron donor; The polymer nucleating agent includes one or more of polyvinylcyclopentane, polyvinylcyclohexane, polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, poly-3-ethyl-1-hexene, poly-3-methyl-1-pentene and polystyrene; the mass ratio of the main catalyst to the polymer nucleating agent is 1:(1-2); B) polymerizing the prepolymerized product, propylene, ethylene and hydrogen to obtain polypropylene powder; C) continuing to polymerize the polypropylene powder, propylene, ethylene and hydrogen to obtain a polypropylene resin powder; D) uniformly mixing the polypropylene resin powder, antioxidant, halogen absorbent, antistatic agent and sorbitol nucleating agent to obtain a mixture; The sorbitol nucleating agent is 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol; the mass ratio of the polymer nucleating agent to the sorbitol nucleating agent is 1:(75-150); E) extruding the mixture through an extruder to obtain a transparent polypropylene material; The temperature in the highest temperature zone of the extruder is 230-240°C.

2. The preparation method according to claim 1, characterized in that The main catalyst is a titanium tetrachloride catalyst supported by magnesium chloride, the co-catalyst is an alkyl aluminum, and the external electron donor is an alkoxysilane.

3. The preparation method according to claim 1, characterized in that The temperature of the prepolymerization is 15-25° C., and the residence time of the prepolymerization is 10-20 min.

4. The preparation method according to claim 1, characterized in that In step B), the polymerization reaction temperature is 70-75° C., the polymerization reaction residence time is 30-50 min, the total flow rate of ethylene and propylene is 20-40 t / h, the mass ratio of ethylene to propylene is (2-5):(98-95), and the hydrogen concentration is 2000-3000 ppm.

5. The preparation method according to claim 1, characterized in that In step C), the polymerization reaction temperature is 70-75° C., the polymerization reaction residence time is 10-30 min, the total flow rate of ethylene and propylene is 10-20 t / h, the mass ratio of ethylene to propylene is (2-5):(98-95), and the hydrogen concentration is 2000-3000 ppm.

6. The preparation method according to claim 1, characterized in that In parts by weight, in step D), the following ingredients are used: 100 parts of polypropylene resin powder, 0.15-0.35 parts of sorbitol nucleating agent, 0.1-0.3 parts of antioxidant, 0.01-0.2 parts of halogen absorbent, and 0.01-0.1 parts of antistatic agent.

7. The preparation method according to claim 1, characterized in that The antioxidant includes a primary antioxidant and a secondary antioxidant; The mass ratio of the primary antioxidant to the secondary antioxidant is 1:(1-4); The main antioxidant includes one or more of antioxidant 2246, antioxidant 1010, antioxidant 1076 and antioxidant 1330; the auxiliary antioxidant includes one or more of antioxidant 168, antioxidant 626 and antioxidant 9228.

8. The preparation method according to claim 1, characterized in that The halogen absorbing agent includes one or more of sodium stearate, calcium stearate and zinc stearate; The antistatic agent includes one or more of glyceryl monostearate, polyol fatty acid ester, polyethylene oxide, and propylene oxide copolymer.

9. A transparent polypropylene resin prepared according to the preparation method of claim 1.

10. The transparent polypropylene resin according to claim 9, characterized in that The transparent polypropylene resin has a melt mass flow rate of 22 to 30 g / 10 min, an ethylene content of 3.0 to 3.5 wt %, and a haze of 5 to 10%.

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