Transparent polypropylene resin and preparation method thereof

Abstract

The invention provides transparent polypropylene resin and a preparation method thereof. The preparation method comprises the following steps: A) pre-polymerizing propylene under the action of a main catalyst, a macromolecular nucleating agent, a cocatalyst and an external electron donor; b) carrying out polymerization reaction on the prepolymerization product, propylene, ethylene and hydrogen to obtain polypropylene powder; c) continuously carrying out polymerization reaction on the polypropylene powder, propylene, ethylene and hydrogen to obtain polypropylene resin powder; d) uniformly mixing the polypropylene resin powder, the antioxidant, the halogen absorber, the antistatic agent and the sorbitol nucleating agent to obtain a mixture; and E) extruding the mixture through an extruder to obtain the transparent polypropylene material. The temperature of the highest temperature area of the extruder is 230-240 DEG C. According to the method, the fourth-generation nucleating agent is replaced by the third-generation nucleating agent, the obtained transparent effect is equivalent to that of the fourth-generation nucleating agent, and the mechanical property is improved. The preparation cost of the transparent polypropylene is greatly reduced, and the market competitiveness of the product is improved.

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. It is widely used because of its low density, good optical properties and heat resistance, excellent chemical corrosion resistance and insulation strength, excellent water vapor barrier, low odor and other advantages. It has become one of the three major general-purpose plastics. Random copolymer polypropylene has good transparency and toughness and can be used to produce transparent products. Existing transparent polypropylene plastics usually use random copolymer polypropylene as the base resin and add sorbitol transparent nucleating agents to improve the transparency of the product.

[0003] At present, sorbitol transparent nucleating agents have developed to the fourth generation. The first generation of sorbitol nucleating agents does not have any substituents on the benzene ring. Representative varieties include Milliken's Millad3905 ((1,3:2,4)-di(3,4-dimethyldibenzylidene) sorbitol, referred to as DMDBS). This nucleating agent has low cost, general nucleating effect, and is unstable at high temperature and easily degraded to release the parent aldehyde; the second generation product is characterized by the benzene ring being replaced by chlorine, methyl and other groups at the para position. Representative varieties include Milliken's Millad3940 ((1,3:2,4)-di(p-methyldibenzylidene) sorbitol, referred to as MDBS), which has greatly improved the permeability enhancement efficiency, but still has a strong odor; the third generation Millad3988 product has greatly improved in permeability enhancement, nucleation performance and odor, and is currently the most widely used transparent nucleating agent. However, the haze of polypropylene materials prepared using the third generation of transparent nucleating agents is usually 8-10%, and it is impossible to prepare high-transparency polypropylene products with a haze of less than 6%.

[0004] The fourth generation is Millad NX 8000 transparent nucleating agent, which is a benzyl derivative of sorbitol. The fourth generation nucleating agent has a significantly better melt dispersion effect than the third generation nucleating agent. Therefore, the fourth generation transparent nucleating agent NX8000 can be used to prepare highly transparent polypropylene products, but it is expensive, which increases the preparation cost of transparent polypropylene. In addition, the common problem of transparent nucleating agents is that they can significantly improve the transparency of polypropylene at a certain addition amount, but when the effective content reaches a certain level, such as when the addition amount of the third generation nucleating agent and the fourth generation nucleating agent exceeds 3000ppm, there is no significant effect on improving the transparency of the polypropylene resin; and it is impossible to take into account the optimization of mechanical properties. Summary of the invention

[0005] The purpose 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 polyvinyl cyclopentane, polyvinyl cyclohexane, 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 prepolymer product, propylene, ethylene and hydrogen to polymerization reaction 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 absorbing agent, 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 prepolymerization temperature is 15 to 25° C., and the residence time of the prepolymerization is 10 to 20 min.

[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), based on weight, 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 are used.

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

[0021] The mass ratio of the primary antioxidant to the auxiliary 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 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 invention provides 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 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) mixing the polypropylene resin powder, antioxidant, halogen absorbent, antistatic agent and sorbitol nucleating agent uniformly 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 of 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 cost of using the fourth-generation transparent nucleating agent to prepare transparent polypropylene is high, while the cost of using the third-generation transparent nucleating agent to prepare transparent polypropylene is low, but the haze is higher than the polypropylene prepared using the fourth-generation nucleating agent. In the transparent polypropylene resin composition of the present invention, the third-generation nucleating agent replaces the fourth-generation nucleating agent, and the obtained transparency effect is equivalent to that of the fourth-generation nucleating agent NX8000. This greatly reduces the preparation cost of transparent polypropylene and improves the market competitiveness of the product.

[0030] ② Significant improvement in transparency: The transparent polypropylene resin composition of the present invention uses a specific ratio of polymer nucleating agent and sorbitol nucleating agent (3988). The synergistic effect of these two nucleating agents can significantly improve the transparency of polypropylene. Even when the amount of nucleating agent added is low (3988 added at 1500ppm), a significant transparency effect can be obtained; at the same time, the upper limit of the transparency enhancement of the third-generation transparent nucleating agent is also improved (the upper limit of the effect of the 3988 nucleating agent added at 3000ppm or more is increased from 8-10% of the haze value 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 polyvinyl cyclopentane, polyvinyl cyclohexane, 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 prepolymer product, propylene, ethylene and hydrogen to polymerization reaction 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 absorbing agent, 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, and a polymer nucleating agent. After preparing polypropylene resin powder through a spheripol polymerization process, hydrogen is used as a molecular weight regulator, and ethylene is added into a reactor, the polypropylene resin powder, a main antioxidant, an auxiliary antioxidant, a halogen absorber and a sorbitol nucleating agent are uniformly mixed, and 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 2-2.8 t / h, more preferably 2.2-2.6 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 (0.1-0.15) 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 the first reactor to carry out 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, preferably a range value with the above any numerical value 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, preferably a range value with the above any numerical value 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 20-40 t / h, more preferably 25-35 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 (2-5): (98-95), more preferably (3-4): (97-96), such as 2:98, 3:97, 3.5:96.5, 4:98 ... :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 above polymerization reaction is completed, the present invention introduces the obtained polypropylene powder, propylene, ethylene and hydrogen into the second reactor to continue the polymerization reaction to obtain polypropylene resin powder. New materials enter the first reactor for reaction, 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, preferably a range value with the above arbitrary numerical 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, preferably a range value with the above arbitrary numerical 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 10-20 t / h, more preferably 12-18 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 the above arbitrary numerical value as the upper or lower limit, wherein the mass ratio of ethylene to propylene is preferably (2-5): (98-95), more preferably (3-4): (97-96), such as 2: 98, 3:97, 3.6:96.4, 4:96, 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 ...

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

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

[0054] In the present invention, the polypropylene resin powder is 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 proportion 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), and 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 with any of the above values ​​as the upper or lower limit of the range value.

[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 the mechanical properties are improved. 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 into 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, 240°C, preferably a range value with any of the above 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 may 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 among all the temperature zones. Temperature zones, specifically, in an embodiment of the present invention, the temperature zones can be set to nine zones: zone one 175-185°C, zone two 185-195°C, zone three 205-215°C, zone four 225-235°C, zone five 230-240°C, zone six 225-235°C, zone seven 205-215°C, zone eight 195-205°C, zone nine 185-195°C; more preferably, zone one 180°C, zone two 190°C, zone three 210°C, zone four 230°C, zone five 235°C, zone six 230°C, zone seven 210°C, zone eight 200°C, zone nine 190°C. In this temperature zone setting, the highest temperature zone is zone five, and the temperatures of the three temperature zones of zone four, zone five and zone six are ≥230°C.

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

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

[0065] The invention provides 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 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 cost of using the fourth-generation transparent nucleating agent to prepare transparent polypropylene is high, while the cost of using the third-generation transparent nucleating agent to prepare transparent polypropylene is low, but the haze is higher than the polypropylene prepared using the fourth-generation nucleating agent. In the transparent polypropylene resin composition of the present invention, the third-generation nucleating agent replaces the fourth-generation nucleating agent, and the obtained transparency effect is equivalent to that of the fourth-generation nucleating agent NX8000. This greatly reduces the preparation cost of transparent polypropylene and improves the market competitiveness of the product.

[0068] ② Significant improvement in transparency: The transparent polypropylene resin composition of the present invention uses a specific ratio of polymer nucleating agent and sorbitol nucleating agent (3988). The synergistic effect of these two nucleating agents can significantly improve the transparency of polypropylene. Even when the amount of nucleating agent added is low (3988 added at 1500ppm), a significant transparency effect can be obtained; at the same time, the upper limit of the transparency enhancement of the third-generation transparent nucleating agent is also improved (the upper limit of the effect of the 3988 nucleating agent added at 3000ppm or more is increased from 8-10% of the haze value 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 in conjunction with embodiments, but it should not be construed as limiting the protection scope of the present invention.

[0071] Example 1

[0072] (1) using a spheripol polymerization process, propylene was prepolymerized under the combined action 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 prepolymer product obtained in step (1), propylene and hydrogen into a first loop reactor for polymerization reaction to obtain polypropylene powder, wherein the hydrogen concentration of 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 of 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 polyvinyl cyclohexane (PVCH) is not added in the prepolymerization stage, and the amount of 3988 nucleating agent (1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol) 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 polyvinyl cyclohexane (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 is the same as that of Example 2, except that no 3988 nucleating agent is added, the mass ratio of HR catalyst to polyvinyl cyclohexane is 1:121.2, and the content of PVCH in the final product is 2020 ppm.

[0098] Comparative Example 8

[0099] The preparation method is the same as that of Example 2, 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 added in addition.

[0100] Table 1 Example and comparative example composition ratio and processing conditions

[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] It can be seen from the comparison of Examples 1 to 3 with Comparative Examples 1 to 2 and Comparative Example 7 that the composite use of polymer nucleating agent and 3988 can effectively improve the transparency of PPR (haze reduction); at the same time, it can effectively improve its rigidity, toughness and heat resistance. Specifically, Example 2 is compared with Comparative Example 1 and Comparative Example 7. The total amount of nucleating agent is the same, both are 2020ppm, but the crystallization temperature of the polypropylene material obtained in Comparative Example 1 is lower than 116°C, the mechanical properties are significantly reduced, and the haze is 10.7, which is higher than 7.2 of Example 2. The crystallization temperature of the polypropylene material in Comparative Example 7 is also lower than 116°C, the mechanical properties are significantly reduced, and the haze is as high as 30, which is significantly higher than Example 2. It can be explained that the present invention obtains more technical effects by combining polymer nucleating agent and specific types of sorbitol nucleating agent, and the performance in both mechanical properties and haze is significantly improved; similarly, Example 3 is compared with Comparative Example 2, and the same conclusion is reached.

[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 transmittance-enhancing effect than NX8000; at the same time, it has better rigidity, toughness and heat resistance.

[0108] It can be seen from the comparison between Example 2 and Comparative Example 5 that controlling the maximum temperature of the extruder barrel at 235° C. is an important condition. If it is not achieved, 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 principle of the present invention. These improvements and modifications should also be regarded as 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 primary catalyst, a polymer nucleating agent, a co-catalyst and an external electron donor; The polymer nucleating agent includes one or more of polyvinyl cyclopentane, polyvinyl cyclohexane, 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) subjecting the prepolymer product, propylene, ethylene and hydrogen to polymerization reaction 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 absorbing agent, 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 temperature of 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 main 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: The polymerization temperature in step B) is 70-75° C., the residence time of the polymerization is 30-50 min; the total flow of ethylene and propylene is 20-40 t / h, the mass ratio of ethylene to propylene is (2-5): (98-95), and the concentration of hydrogen is 2000-3000 ppm.

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

6. The preparation method according to claim 1, characterized in that: In terms of weight, 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.

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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