High-transparency high-toughness polypropylene composition and preparation method thereof

Abstract

The invention discloses a high-transparency and high-toughness polypropylene composition and a preparation method thereof. The high-transparency and high-toughness polypropylene composition is prepared from the following components in parts by mass: 100 parts of polypropylene matrix resin; 0 to 0.3 part of an antioxidant; 0.02 to 0.15 part of a halogen absorbent; the polypropylene matrix resin is syndiotactic polypropylene powder, and the molar percentages of a syndiotactic five-unit group [rrrr] and a syndiotactic two-unit group [r] measured by a C13-nuclear magnetic resonance spectrum are 62-94% and 80-98% respectively; the heat stability and oxidation resistance of the polypropylene composition are improved by adding a proper amount of antioxidant, and halogen and residual catalyst in polypropylene matrix resin are eliminated by using the halogen absorbent. The high-transparency and high-toughness polypropylene composition has excellent comprehensive performance, the minimum haze (thickness of 1 mm) is 6.8%, the simply supported beam notch impact strength (23 DEG C) is higher than 70 kJ / m < 2 >, and the high-transparency and high-toughness polypropylene composition is suitable for molding processes such as injection-stretch-blow, multi-layer co-extrusion, tape casting, fused deposition 3D printing and the like and can be applied to the fields of medicine packaging materials, heat-sealing films, tooth retainers and other medicines and foods.

Description

Technical Field

[0001] The present invention belongs to the field of high-performance synthetic resins, and particularly relates to a syndiotactic polypropylene-based highly transparent and highly tough polypropylene composition and a preparation method thereof. Background Art

[0002] As a semi-crystalline polymer, the aggregate structure of polypropylene is anisotropic, resulting in poor surface gloss and transparency of products, lack of aesthetic appearance, and restricting its application in the fields of transparent packaging and daily necessities. After transparent modification of polypropylene, it can not only inherit its advantages of light weight, low cost, hygiene, easy molding and processing, etc., but also its transparency and surface gloss can be comparable to those of transparent resins such as polyester, polyvinyl chloride, and polystyrene. Moreover, it shows good moisture barrier property, heat resistance and chemical corrosion resistance, and has unique advantages in the packaging fields of dry food, medicine, hot drinks, microwave cookware and disposable tableware. In recent years, the domestic demand for transparent polypropylene has been rising continuously, becoming one of the polypropylene varieties with relatively fast growth in added value. However, the self-sufficiency rate of the market is seriously insufficient, and a large amount of special materials for transparent polypropylene used in high-end packaging fields such as food and medicine rely heavily on imports.

[0003] The research and development of transparent polypropylene in China started relatively late. It mainly realizes high performance and high transparency by adding transparent nucleating agents to ordinary polypropylene (produced by Ziegler-Natta catalysts) to reduce the grain size. There is a large gap compared with foreign countries in the synthesis, performance optimization, application development of high-efficiency transparent nucleating agents and the types of high-transparency polypropylene products and market consumption. The market application is also mostly limited to the field of low-value-added plastic products. Yanshan Petrochemical Corporation has successively developed grades such as K4818, K4808, and K4902, which can be used for products such as extrusion sheets, thermoforming, blow molding, and injection molding; products such as B4808 and B4902 developed have excellent comprehensive properties and are suitable for injection stretch blow molding processes, and are widely used in the fields of medical large infusion packaging, hot filling beverage packaging, and dairy product packaging. Shanghai Petrochemical Company has successively developed homopolymer and random copolymer transparent polypropylene series products, including M250E, M450E, M800E, M1200E, M3000E, M250T, etc. In addition, Maoming Petrochemical, Qilu Petrochemical, Yangzi Petrochemical, Shanghai Secco, Dushanzi Petrochemical, Lanzhou Petrochemical, etc. have also launched a number of transparent polypropylene products. The polypropylene base resin produced by traditional Ziegler-Natta catalysts has high haze and poor transparency, and needs to add nucleating agents for transparency enhancement, which increases the production cost to a certain extent. At the same time, the impact toughness of homopolymer and random copolymer polypropylene is poor, and it is difficult to meet the requirements of high-end application fields for impact toughness.

[0004] Due to the characteristics of metallocene catalysts having a single active center, the stereoregularity, relative molecular mass, relative molecular mass distribution, and the content and distribution of comonomers of the molecular chain can be more precisely controlled, effectively regulating the crystallization behavior and the aggregate structure, and high-end polypropylene products with high strength, high toughness, high transparency, etc. can be obtained. Among them, syndiotactic polypropylene produced using metallocene catalysts, due to the alternating arrangement of methyl groups in the molecular chain, has relatively weak crystallization ability compared with isotactic polypropylene, and the crystal grain size is smaller. It is expected to obtain high transparency without adding a clarifying agent. Syndiotactic polypropylene products have good radiation resistance, do not degrade after sterilization, and their properties do not change significantly, and are expected to be used in the production of liquid medicine containers, infusion tubes, liquid guiding tubes, and medical device housings, etc. The multi-layer laminated film material made with syndiotactic polypropylene as the sealing layer has good heat-sealing property and hot tackiness, high transparency, and a low coefficient of friction between each other, and is more suitable for automated mechanical packaging. In addition, syndiotactic polypropylene has better softness and resilience, and the non-woven fabric made has a better hand feeling and no loose sagging phenomenon. Currently, foreign companies have carried out industrialization attempts to produce transparent syndiotactic polypropylene resin using metallocene catalysts. However, there is no long-term stable operation of metallocene polypropylene in China, and all syndiotactic polypropylene products rely on imports, which seriously restricts the development of downstream consumer products.

[0005] Chinese Patent CN202211371894.6 discloses a low melt index transparent polypropylene resin for blow molding and its preparation method. Specifically, it includes the following components in parts by mass: 100 parts of random polypropylene powder; 0.05 - 0.15 parts of a primary antioxidant; 0.05 - 0.4 parts of a secondary antioxidant; 0.02 - 0.1 parts of a halogen absorber; 0.03 - 0.1 parts of an antistatic agent; 0.1 - 0.3 parts of a transparent nucleating agent; 3 - 10 parts of a polyolefin elastomer. This invention uses the random polypropylene powder produced by traditional Ziegler - Natta catalysts as the matrix resin, still uses a transparent nucleating agent for enhancing transparency, reducing the haze to below 15%; by adding a polyolefin elastomer, the impact toughness is increased to above 20 kJ / m 2 The above. Transparent polypropylene is obtained by means of physical blending modification, which to a certain extent increases the production cost, and there are also problems with the compatibility and dispersibility of multiple components. The haze and impact toughness of the obtained product are not as high as the values of this invention.

[0006] Chinese Patent CN202211371896.5 discloses a super-transparent polypropylene resin that meets food-grade packaging requirements and its preparation method. Specifically, it includes the following components in parts by mass: 100 parts of random polypropylene powder; 0.02 - 0.1 part of a primary antioxidant; 0.02 - 0.5 part of a secondary antioxidant; 0.01 - 0.1 part of a halogen absorber; 0.05 - 0.1 part of an antistatic agent; 0.02 - 0.1 part of a light stabilizer; 0.3 - 0.4 part of a transparent nucleating agent. However, this polypropylene resin uses random polypropylene powder produced by a traditional Ziegler-Natta catalyst as the matrix resin, adds 3000 - 4000 ppm of a transparent nucleating agent to increase transparency, and reduces the haze to below 7%; the Izod notched impact strength (23 °C) is above 5 kJ / m 2 2. However, this method obtains transparent polypropylene by physical blending modification, and the added nucleating agent has a high concentration, resulting in problems with nucleating agent dispersion and selectivity.

[0007] Chinese Patent CN202010798707.7 discloses a high-impact transparent polypropylene resin and its preparation method. The preparation method of this polypropylene resin includes: first, carrying out liquid-phase bulk polymerization of propylene in a first loop reactor in the presence of hydrogen and a Ziegler-Natta catalyst system containing an external electron donor; the polymerization product enters a second loop reactor and undergoes liquid-phase bulk random polymerization of propylene in the presence of hydrogen and ethylene; after the polymer product removes unreacted propylene monomer, ethylene monomer, and hydrogen, it enters a third gas-phase reactor and undergoes ethylene-propylene gas-phase copolymerization reaction to prepare a polymer powder; the polymer powder is added with a compounding aid and extruded into pellets to prepare a polypropylene resin with a melt flow rate of 10 - 30 g / 10 min, a haze (1 mm) less than or equal to 13%, a room-temperature impact performance (23 °C) of 15 - 30 kJ / m 2 2, and a low-temperature impact performance (-20 °C) greater than or equal to 3.5 kJ / m 2 2. However, this method uses high-impact polypropylene powder produced by Ziegler-Natta as the matrix resin, and the effective addition amount of the nucleating agent in the added compounding aid is 1000 - 2000 ppm. This invention still needs to add a transparent nucleating agent to increase the transparency of impact polypropylene, rather than directly synthesizing a polypropylene product with good transparency and impact toughness.

[0008] Chinese patent CN202310407824.X discloses a high-strength, low-fog, transparent polypropylene material and a preparation method thereof. The high-strength, low-fog, transparent polypropylene material comprises, by weight: 85-95 parts of random copolymer polypropylene, 8-12 parts of polymethyl methacrylate modified microspheres, 2-5 parts of low-density polyethylene copolymer, 3-5 parts of compatibilizer, 0.2-1 parts of antioxidant, 0.2-1 parts of nucleating agent, and 1-3 parts of lubricant. However, this technology is based on traditional Ziegler-Natta random copolymer polypropylene, and requires the synthesis and addition of polymethyl methacrylate modified microspheres, as well as the addition of low-density polyethylene copolymer, nucleating agent and compatibilizer. The system is very complex. In addition to the nucleating agent that must be added in the traditional method, two transparent polymers must be added, which invisibly increases the types and costs of components. SUMMARY OF THE INVENTION

[0009] The technical problem that the present invention intends to solve is to use metallocene catalysts to develop high syndiotactic polypropylene powder with a specific chemical structure, and obtain a high-transparency and high-toughness polypropylene composition without adding a transparent nucleating agent and a toughening agent; by reducing the temperature of the feeding section and the die area, and adopting underwater pelletizing, etc., the shortcomings of low melting temperature and soft splines are overcome, and the melt extrusion granulation process is reasonably designed to form a preparation method for the high-transparency and high-toughness polypropylene composition.

[0010] In view of the deficiencies in the above-mentioned prior art and market demand, the purpose of the present invention is to provide a high-transparency and high-toughness polypropylene composition and a preparation method thereof. The high-transparency and high-toughness polypropylene composition prepared by the present invention not only has excellent transparency and impact toughness, but also has good rigidity-toughness balance, heat resistance, dimensional stability and heat sealing performance, and is suitable for molding processes such as injection stretch blow molding, multi-layer co-extrusion, casting, and melt deposition 3D printing, and can meet the requirements for raw material performance in the fields of medicine and food such as pharmaceutical packaging materials, heat-sealing films and tooth retainers.

[0011] To achieve the above purpose, the present invention provides a highly transparent and high-toughness polypropylene composition, which is composed of the following components in parts by weight: 100 parts of polypropylene matrix resin; 0-0.3 parts of antioxidant, preferably 0.06-0.21 parts; 0.02-0.15 parts of halogen absorbent, preferably 0.03-0.08 parts;

[0012] The polypropylene matrix resin is syndiotactic polypropylene powder, using carbon 13 -The molar percentages of syndiotactic pentads [rrrr] and diads [r] measured by nuclear magnetic resonance spectroscopy are 62-94% and 80-98%, respectively.

[0013] The high-transparency and high-toughness polypropylene composition of the present invention has an apparent bulk density of not less than 0.35 g / cm​3 , preferably 0.40 - 0.46 g / cm 3 .

[0014] For the highly transparent and highly tough polypropylene composition of the present invention, the melt mass flow rate of the syndiotactic polypropylene powder measured at a temperature of 230 °C and a load of 2.16 kg is 1 - 10 g / 10 min, preferably 2 - 6 g / 10 min.

[0015] For the highly transparent and highly tough polypropylene composition of the present invention, the weight average molecular weight of the syndiotactic polypropylene powder measured by high temperature gel permeation chromatography is between 250,000 - 400,000, preferably 250,000 - 350,000; the molecular weight distribution is between 1 - 5, preferably 1 - 3.

[0016] For the highly transparent and highly tough polypropylene composition of the present invention, the melting temperature range of the syndiotactic polypropylene powder measured by differential scanning calorimetry (scanning rate 10 °C / min) is 80 - 140 °C, where the peak melting temperature is 129 ± 3 °C, the melting enthalpy value is between 30 - 40 J / g, and the relative crystallinity is 60 - 80% (the standard melting enthalpy is 50 J / g); the crystallization temperature range is 35 - 85 °C, and the peak crystallization temperature is 69 ± 3 °C.

[0017] For the highly transparent and highly tough polypropylene composition of the present invention, the syndiotactic polypropylene powder is homopolymerized by a bulk polymerization device; using a metallocene catalyst as the main catalyst, a modified methylaluminoxane as the cocatalyst, propylene as the raw material, and hydrogen as the molecular weight regulator.

[0018] For the highly transparent and highly tough polypropylene composition of the present invention, the syndiotactic polypropylene powder is prepared by the following method: introducing hydrogen into the polymerization reactor, charging part of the propylene into the cocatalyst, stirring, and charging the remaining propylene into the main catalyst; raising the temperature, starting the polymerization reaction, and after the reaction ends, flashing and spraying to obtain the syndiotactic polypropylene powder.

[0019] For the highly transparent and highly tough polypropylene composition of the present invention, the stirring temperature is 20 - 30 °C, and the stirring time is 10 - 20 min.

[0020] For the highly transparent and highly tough polypropylene composition of the present invention, the concentration of hydrogen is 100 - 1500 ppm, preferably 300 - 1100 ppm.

[0021] For the highly transparent and highly tough polypropylene composition of the present invention, the temperature of the polymerization reaction is 50 - 65 °C, and the time is 1 - 7 h.

[0022] For the highly transparent and highly tough polypropylene composition of the present invention, the addition amount of the antioxidant is 0 - 0.3 parts, preferably 0.06 - 0.21 parts.

[0023] The high-transparency and high-toughness polypropylene composition of the present invention, wherein the antioxidant is composed of a primary antioxidant and a secondary antioxidant, and the mass ratio of the primary antioxidant to the secondary antioxidant is 1:1 to 1:3, preferably 1:2; the primary antioxidant is at least one of a hindered phenol antioxidant and a thioester antioxidant, preferably at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; the secondary antioxidant is at least one of a phosphite antioxidant and an ester antioxidant, preferably at least one of tris(2,4-di-tert-butylphenyl) phosphite and distearyl thiodipropionate; the primary antioxidant and the secondary antioxidant can be compounded according to the mass ratio and then added, or can be added separately in sequence.

[0024] For the high-transparency and high-toughness polypropylene composition of the present invention, the addition amount of the halogen absorbent is 0.02 - 0.15 parts, preferably 0.03 - 0.08 parts.

[0025] For the high-transparency and high-toughness polypropylene composition of the present invention, the halogen absorbent is at least one of calcium stearate and hydrotalcite powder.

[0026] The present invention also provides a preparation method of a high-transparency and high-toughness polypropylene composition, and the preparation method includes the following steps:

[0027] (1) According to the mass fraction ratio, add the polypropylene matrix resin, the antioxidant and the halogen absorbent into a high-speed mixer and mix evenly to obtain a premix.

[0028] (2) Add the premix into a twin-screw extruder through the main feeding port for melt extrusion granulation, and obtain the high-transparency and high-toughness polypropylene composition after water cooling granulation and drying homogenization.

[0029] In the preparation method of the present invention, the mixing process is carried out in a combination of high and low speeds, the stirring rates are 1500 - 2500 and 3500 - 4500 rpm respectively, and the stirring time at each rate is 1 - 3 min, preferably 2 min.

[0030] In the preparation method of the present invention, the length-diameter ratio of the twin-screw extruder is 20 - 90, preferably 30 - 60; the screw rotation speed is set at 100 - 300 rpm, preferably 150 - 250 rpm, more preferably 180 - 220 rpm; the screw barrel is at least composed of six heating sections, and the temperature setting range is 150 - 250 °C, preferably 160 - 220 °C; the temperature of the first heating zone is 150 - 170 °C to avoid the "bridging" phenomenon caused by a relatively low melting temperature; the temperature of the last die zone is set at 160 - 180 °C to prevent the sticking wall problem caused by excessive viscosity.

[0031] The preparation method of the present invention cannot be cut by strip extrusion and granulation at room temperature due to the relatively high toughness of the polypropylene composition. Therefore, underwater pelletizing is used for the melt extrusion granulation, the cutter speed is ≥ 200 rpm, and the temperature of the cooling circulating water is ≤ 50 °C, preferably ≤ 35 °C.

[0032] Compared with the prior art, the present invention has at least the following advantages and beneficial effects:

[0033] (1) The polypropylene matrix resin used in the present invention is a highly syndiotactic polypropylene powder produced by using a metallocene catalyst. The methyl groups in the molecular chain are alternately arranged, and the molar percentages of the syndiotactic pentad [rrrr] and the dyad [r] are respectively between 62-94% and 80-98%. Moreover, the relative molecular mass and its distribution, melt mass flow rate, crystallization behavior, etc. are precisely controlled. Compared with the isotactic or atactic copolymer polypropylene produced by the Zilegler-Natta catalyst, the syndiotactic polypropylene powder obtained in the present invention has weaker crystallization ability and smaller crystal grain size, which is more conducive to the development of special high-transparency and high-toughness polypropylene materials.

[0034] (2) In the prior art, polypropylene produced by the Zilegler-Natta catalyst is usually used as the matrix resin, and a transparent nucleating agent and a toughening modifier need to be added to obtain a polypropylene composition with both high transparency and high toughness. The present invention uses highly syndiotactic polypropylene as the base resin, and the above-mentioned high-performance polypropylene composition can be obtained without adding a transparency-improving nucleating agent and a toughening modifier. The present invention requires fewer types of additives and lower addition amounts, which not only reduces the production cost, but also reduces the ash content of the product, improves the cleanliness and market competitiveness of the product.

[0035] (3) Since the melting temperature of the polypropylene composition prepared in the present invention is relatively low, to prevent the "bridging" phenomenon during feeding, the temperature of the first heating zone of the twin-screw extruder is set at 150-170 °C. Since the impact toughness of this composition is relatively high, the melt-extruded sample bar is relatively soft and elastic, and it is impossible to carry out extrusion and strip granulation at room temperature. Therefore, underwater pelletizing is adopted in the preparation process of the present invention. By reducing the temperature of the circulating water and increasing the cutter speed, the melt extrusion granulation of the high-transparency and high-toughness polypropylene composition is successfully realized, forming a proprietary preparation method.

[0036] (4) For the high-transparency and high-toughness polypropylene composition prepared in the present invention, when the sample thickness is 1 mm, the haze reaches below 10%, and the lowest is 6.8%, which is equivalent to that of Zilegler-Natta polypropylene added with a transparent nucleating agent; the notched impact strength of the simply supported beam measured at 23 °C is higher than 70 kJ / m 2 , and all are partially fractured (type P); the polypropylene composition of the present invention has excellent comprehensive properties and can be used in pharmaceutical and food fields such as pharmaceutical packaging materials, heat-sealing films, and dental retainers. Detailed implementation mode

[0037] To further understand the present invention, the following will describe the present invention in detail with reference to specific embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0038] Preparation Examples 1 - 12:

[0039] The polypropylene matrix resin is prepared by homopolymerization in an industrial bulk polymerization device. The preparation process specifically includes the following steps:

[0040] Hydrogen is introduced into the polymerization reactor, and a certain amount of propylene is charged into 0.8 L of modified methylaluminoxane cocatalyst and stirred. The remaining propylene is charged with 50 g of the main catalyst (metallocene catalyst PMP - 01 produced by the Petrochemical Research Institute of PetroChina). Hot water is passed into the jacket of the polymerization kettle to raise the temperature to 45°C, then the hot water is switched to cold water. After the temperature and pressure rise to a constant and start to drop, the cold water is switched to hot water to raise the temperature to 60°C. Then the hot water is switched to cold water to maintain the set reaction temperature for polymerization. After the reaction ends, flash spraying is carried out to obtain syndiotactic polypropylene powder. Among them, the polymerization reaction temperature, pressure, time, hydrogen concentration, and propylene addition amount of each preparation example are shown in Table 1. Through Preparation Examples 1 - 4, Preparation Examples 5 - 8, and Preparation Examples 9 - 12, syndiotactic polypropylene powders M - sPP - A, - B, and - C are obtained respectively, and their typical structural performance parameters are shown in Table 1.

[0041] Preparation of Comparative Example 1:

[0042] The polypropylene matrix resin is isotactic polypropylene powder prepared by homopolymerization in a Spheripol process polypropylene device using a Ziegler - Natta catalyst, with a commercial brand name of T30s (ZN - iPP - T30s). The melt mass flow rate of this product is 3.0 g / 10 min, the isotactic index is 97.0%, the weight - average molecular weight is 317240, the relative molecular mass distribution is 4.8, the peak melting temperature is 162°C, the melting enthalpy is 98.6 J / g, and the peak crystallization temperature is 116°C.

[0043] Table 1 Typical polymerization process parameters and some structural properties of the polypropylene matrix resin in the preparation examples

[0044]

[0045]

[0046] Examples 1 - 12:

[0047] The primary antioxidant is octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Antioxidant 1076), and the secondary antioxidant is distearyl thiodipropionate (Antioxidant DSTDP). The mass ratio of the primary antioxidant to the secondary antioxidant is 1:2; the halogen absorber is calcium stearate.

[0048] Preparation of a highly transparent and highly tough polypropylene composition, and the preparation process specifically includes the following steps:

[0049] (1) Weigh the polypropylene matrix resin, primary antioxidant 1076, secondary antioxidant DSTDP, and calcium stearate in sequence according to the ratio shown in Table 2; add the above components to a high-speed mixer and stir for 2 minutes at rotational speeds of 2000 and 4000 rpm respectively to obtain a uniform premix.

[0050] (2) Feed the premix into a twin-screw extruder through the main feeding port for melt extrusion. The length-diameter ratio of the twin-screw extruder used is 40, the screw rotational speed is 200 - 220 rpm, and the barrel has a total of ten heating zones. In the examples, the barrel temperatures are set at 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 200 °C, 190 °C, 180 °C, and 175 °C.

[0051] The granulation process uses underwater pelletizing. The cutter rotational speed is 220 rpm, and the temperature of the cooling circulating water is 25 - 30 °C. After water-cooled pelletizing and drying homogenization, a highly transparent and highly tough polypropylene composition is obtained.

[0052] Comparative Example 1:

[0053] The difference from Example 11 is that the matrix resin of the polypropylene composition uses the isotactic polypropylene powder ZN-iPP-T30s prepared in Comparative Example 1.

[0054] Comparative Example 2:

[0055] The difference from Example 11 is that the matrix resin of the polypropylene composition uses the isotactic polypropylene powder ZN-iPP-T30s prepared in Comparative Example 1, and a commercial transparent nucleating agent NX8000K from Milliken is added, and the addition amount of the transparent nucleating agent is as shown in Table 2.

[0056] Comparative Example 3:

[0057] The difference from Example 11 is that the matrix resin of the polypropylene composition uses the isotactic polypropylene powder ZN-iPP-T30s prepared in Comparative Example 1, and a commercial transparent nucleating agent NX8000K from Milliken is added, and the addition amount of the transparent nucleating agent is as shown in Table 2.

[0058] Table 2 Components and mass parts of the polypropylene composition in the examples and comparative examples

[0059]

[0060] The physical and mechanical properties of the polypropylene compositions prepared in the examples and comparative examples were tested, and the results are shown in Table 3.

[0061] Table 3 Physical and mechanical properties of the polypropylene compositions prepared in the examples and comparative examples

[0062]

[0063]

[0064] As can be seen from Comparative Examples 1-3, when the matrix resin is homopolymer isotactic polypropylene, the impact toughness of the polypropylene composition is poor, and the notched Izod impact strength at 23 °C is only 4.0-5.0 kJ / m 2 , and the specimen was completely fractured during the impact test; when no transparent nucleating agent was added, the transparency of the composition was poor, and the haze was as high as 56.3% when the thickness was 1 mm; when a transparent nucleating agent was added, the haze decreased significantly. When the addition amounts were 0.20 parts and 0.35 parts of the matrix resin, the haze decreased to 13.5% and 8.2% respectively.

[0065] As can be seen from Examples 1-12, when the matrix resin is metallocene syndiotactic polypropylene powder, the polypropylene composition exhibits excellent impact toughness, and the notched Izod impact strength at 23 °C is as high as 70 kJ / m 2 , and all specimens were partially fractured during the impact test; without adding any transparent nucleating agent, the haze of the polypropylene composition can reach below 10%, and the lowest is 6.8%, showing good transparency. Therefore, without introducing a transparent nucleating agent, the present invention can obtain a highly transparent and high-toughness polypropylene composition, which can effectively reduce the cost of additives.

[0066] As can be seen from Examples 1-12, the structural properties of the matrix resin and the addition amounts of the antioxidant and the halogen absorber jointly affect and determine the physical and mechanical properties (melt mass flow rate, mechanical properties, heat resistance, appearance and dimensional stability, etc.) of the prepared polypropylene composition. Comparing Examples 3, 7 and 11, it can be seen that the syndiotactic index and melt mass flow rate of the matrix resin are positively correlated with the rigidity (tensile yield stress, flexural modulus) of the polypropylene composition and negatively correlated with its impact toughness (notched Izod impact strength).

[0067] Comparing Examples 1-3, Examples 5-7, and Examples 9-11, it can be seen that with the addition of antioxidants to the polypropylene composition system and the increase in the added amount, the thermal-oxidative degradation of the matrix resin during the preparation process is effectively inhibited, the melt mass flow rate of the polypropylene composition gradually decreases and tends to be stable, and its physical and mechanical properties change accordingly. In particular, the yellowness index decreases significantly, and the appearance becomes better and better.

[0068] Comparing Example 3 and 4, Example 7 and 8, and Example 11 and 12, it can be seen that different added amounts of calcium stearate have little effect on the mechanical properties, heat resistance, and dimensional stability of the polypropylene composition, but will have a certain impact on the product appearance; with the increase in the added amount, the yellowness index decreases slightly and the haze increases slightly.

[0069] The polypropylene composition prepared by the present invention has excellent physical and mechanical properties, not only has high transparency and high impact toughness, but also exhibits good rigidity-toughness balance, heat resistance, and dimensional stability; at the same time, it is convenient for molding and processing, suitable for various processing methods such as casting, multilayer coextrusion, injection stretch blow molding, and fused deposition 3D printing, meeting the requirements of raw material properties in food and medicine fields such as heat-sealable films, pharmaceutical packaging materials, and tooth retainers.

[0070] The above specific embodiments are illustrative examples of the spirit of the present invention, and the principles and implementation manners of the present invention are elaborated in detail to facilitate those skilled in the art to understand and apply the present invention more accurately. It should be noted that the present invention is not limited to the above specific implementation manners, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the claims of the present invention.

Claims

1. A highly transparent and high-toughness polypropylene composition, characterized in that: The invention is composed of the following components in parts by weight: 100 parts of polypropylene matrix resin; 0-0.3 parts of antioxidant; 0.02-0.15 parts of halogen absorbent; The polypropylene matrix resin is syndiotactic polypropylene powder, using carbon 13 - The molar percentages of syndiotactic pentad [rrrr] and diad [r] measured by nuclear magnetic resonance spectroscopy are 62-94% and 80-98%, respectively.

2. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The apparent bulk density of the syndiotactic polypropylene powder is not less than 0.35 g / cm 3 .

3. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The melt mass flow rate of the syndiotactic polypropylene powder measured at a temperature of 230° C. and a load of 2.16 kg is 1-10 g / 10 min.

4. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The mass average molecular weight of the syndiotactic polypropylene powder measured by high temperature gel permeation chromatography is between 250,000 and 400,000, and the molecular weight distribution is between 1 and 5.

5. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The melting temperature range of the syndiotactic polypropylene powder measured by differential scanning calorimetry (scanning rate 10°C / min) is 80-140°C, wherein the peak melting temperature is 129±3°C, the melting enthalpy value is between 30-40J / g, and the relative crystallinity is 60-80% (the standard melting enthalpy adopts 50J / g); the crystallization temperature range is 35-85°C, and the peak crystallization temperature is 69±3°C.

6. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The syndiotactic polypropylene powder is homopolymerized by a bulk polymerization device; a metallocene catalyst is used as a main catalyst, modified methylaluminoxane is used as a co-catalyst, propylene is used as a raw material, and hydrogen is used as a molecular weight regulator.

7. The high-transparency and high-toughness polypropylene composition according to claim 6, characterized in that: The syndiotactic polypropylene powder is prepared by the following method: hydrogen is introduced into a polymerization reactor, a co-catalyst is injected with part of propylene, the mixture is stirred, and a main catalyst is injected with the remaining propylene; the temperature is raised to start the polymerization reaction, and after the reaction is completed, the material is flash-sprayed to obtain the syndiotactic polypropylene powder.

8. The high-transparency and high-toughness polypropylene composition according to claim 7, characterized in that: The concentration of the hydrogen is 100-1500 ppm; the temperature of the polymerization reaction is 50-65° C., and the time is 1-7 hours.

9. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The added amount of the antioxidant is 0.06-0.21 parts.

10. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The antioxidant is composed of a main antioxidant and a secondary antioxidant, the mass ratio of the main antioxidant to the secondary antioxidant is 1:1 to 1:3; the main antioxidant is at least one of a hindered phenol antioxidant and a thioester antioxidant; the secondary antioxidant is at least one of a phosphite antioxidant and an ester antioxidant; the main antioxidant and the secondary antioxidant are compounded according to the mass ratio and then added, or are added in sequence.

11. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The added amount of the halogen absorber is 0.03-0.08 parts.

12. The high-transparency and high-toughness polypropylene composition according to claim 1, characterized in that: The halogen absorbent is at least one of calcium stearate and hydrated talc.

13. A method for preparing a high-transparency and high-toughness polypropylene composition, characterized in that: The following steps are involved: (1) adding a polypropylene matrix resin, an antioxidant, and a halogen absorber into a high-speed mixer according to a mass ratio and mixing them uniformly to obtain a premix; (2) The premix is ​​fed into a twin-screw extruder through a main feed port for melt extrusion granulation, and then water-cooled, pelletized, dried and homogenized to obtain the high-transparency and high-toughness polypropylene composition.

14. The preparation method according to claim 13, characterized in that: The mixing process is carried out in a combination of high and low speeds, with stirring rates of 1500-2500 and 3500-4500 rpm respectively, and the stirring time at each rate is 1-3 min.

15. The preparation method according to claim 13, characterized in that: The aspect ratio of the twin-screw extruder is 20-90; the screw speed is set to 100-300rpm; the screw barrel consists of at least six heating sections, and the temperature setting range is 150-250℃; the temperature of the first heating zone is 150-170℃; the temperature of the last die zone is set to 160-180℃.

16. The preparation method according to claim 13, characterized in that: The melt extrusion granulation adopts an underwater granulation method, the cutter speed is ≥200rpm, and the cooling circulating water temperature is ≤50°C.

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