High-transparency and high-gloss metallocene polypropylene resin as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and discloses a high-transparency and high-gloss metallocene polypropylene resin and a preparation method and application thereof.The molecular weight distribution value of the polypropylene resin is 2-3, the xylene soluble matter content is 0.4-1.8 wt%, the haze is 2.3-8.2%, the glossiness is larger than or equal to 120.8%, and the melt flow rate is 1-3g / 10min. The polypropylene resin is narrow in molecular weight distribution, high in isotacticity and good in transparency. Precipitates and volatile matters are low, and the application field is wide.

Description

Technical Field

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

[0002] Polypropylene resin has the advantages of low density, excellent comprehensive performance, easy processing, green and non-toxic, and has developed rapidly. With the continuous improvement of the optical properties of polypropylene, its application areas have been further broadened, and the demand in the food, pharmaceutical, household goods and other industries has continued to expand, such as household items, storage boxes, thin-walled containers, syringes, beverage bottles and other transparent plastic products.

[0003] Polypropylene is a semi-crystalline polymer with a spherulite structure. The crystallization is slow and the spherulites are coarse. Because the size of polypropylene spherulites is much larger than the wavelength of visible light, it will inevitably cause light scattering when light passes through, making the transparency of polypropylene products poor. The coarse spherulites also increase the unevenness of the product surface. The increase in surface roughness reduces the gloss of polypropylene products, further affecting the transparency of the products.

[0004] In order to improve the optical properties of polypropylene, in addition to adding a transparent agent, when using traditional Ziegler-Natta catalysts to produce polypropylene, ethylene and other α-olefins are generally used for random homopolymerization with propylene to reduce the regularity of the polypropylene chain, making its crystallization ability worse and the size of the spherulites smaller. However, the molecular weight distribution of polypropylene produced by this process is wide, and ethylene and other α-olefins are inserted unevenly in the polypropylene molecular chain. The ethylene content in the polypropylene component with a lower molecular weight is high, which increases the number of random polypropylene products; the ethylene content in the polypropylene component with a higher molecular weight is low, and this part of the polypropylene chain has good regularity and larger spherulites, which affects its optical properties such as transparency and gloss.

[0005] The invention provides a highly transparent and high-gloss metallocene polypropylene resin, which, compared with a Ziegler-Natta polypropylene resin, has a narrow molecular weight distribution, low precipitates and volatiles, few large spherulites, and high transparency and gloss. Summary of the invention

[0006] The object of the present invention is to provide a highly transparent and high gloss metallocene polypropylene resin, which, compared with a Ziegler-Natta polypropylene resin, has a narrow molecular weight distribution, low precipitates and volatiles, few large spherulites, and high transparency and gloss.

[0007] A highly transparent and high-gloss metallocene polypropylene resin, wherein the molecular weight distribution value of the polypropylene resin is 2-3, preferably 2.3-2.8.

[0008] Preferably, the xylene soluble matter of the polypropylene resin is 0.4 to 1.8 wt %, preferably 0.4 to 0.8 wt %.

[0009] Preferably, the haze of the polypropylene resin is 2.3-8.2%.

[0010] Preferably, the glossiness of the polypropylene resin is ≥120.8%, preferably the glossiness is 120.8-137.4%.

[0011] Preferably, the melt flow rate of the polypropylene resin is 1 to 3 g / 10 min, preferably 1.5 to 2 g / 10 min.

[0012] In order to obtain a highly transparent and high-gloss metallocene polypropylene resin, the technical solution of the present invention provides a method for preparing a highly transparent and high-gloss metallocene polypropylene resin, comprising the following steps:

[0013] 1) subjecting propylene, a main catalyst and a co-catalyst to a prepolymerization reaction to obtain a propylene prepolymer;

[0014] 2) subjecting the propylene prepolymer of step 1) to polymerization reaction with propylene and hydrogen to obtain a propylene polymer;

[0015] 3) sequentially performing gas-solid separation, deactivation and drying of the propylene polymer in step 2) to obtain homopolypropylene;

[0016] 4) The homopolymerized polypropylene, antioxidant, acid neutralizer and clarifier in step 3) are mixed and melt-extruded at 170-250° C. to form granules.

[0017] In a preferred embodiment, the weight ratio of propylene, main catalyst, co-catalyst and hydrogen in step 1) and step 2) is 100: 0.0035-0.015: 0.015-0.075: 0-0.005.

[0018] In a preferred embodiment, the main catalyst in step 1) is a supported metallocene catalyst.

[0019] In a preferred embodiment, the co-catalyst in step 1) is an alkyl aluminum type co-catalyst, selected from at least one of triisobutyl aluminum, triethyl aluminum, trimethyl aluminum, and tri-n-hexylaluminum.

[0020] In a preferred embodiment, the prepolymerization reaction conditions in step 1) are: polymerization temperature 10-20° C., polymerization pressure 3.0-3.9 MPa, and polymerization residence time 0.15-0.25 h.

[0021] In a preferred embodiment, the polymerization reaction conditions in step 2) are: polymerization temperature 60-75° C., polymerization pressure 3.0-3.9 MPa, and polymerization residence time 0.8-1.2 h.

[0022] In a preferred embodiment, the gas-solid separation conditions in step 3) are: gas-solid separation at 1.6-2.0 MPa and degassing at 0.04-0.08 MPa; the deactivation is to deactivate the catalyst with 0.01-0.06 MPa steam; and the drying is to dry with circulating hot nitrogen at 70-110°C.

[0023] In a preferred embodiment, the weight ratio of the homopolypropylene, antioxidant, acid neutralizer and clarifier in step 4) is 100:0.08-0.30:0.02-0.10:0.10-0.40.

[0024] In a preferred embodiment, the weight ratio of the homopolypropylene, antioxidant, acid neutralizer and clarifier is 100:0.10-0.20:0.03-0.08:0.10-0.40.

[0025] In a preferred embodiment, the antioxidant is a mixture of a hindered phenol antioxidant and a phosphite antioxidant, wherein the weight ratio of the hindered phenol antioxidant to the phosphite antioxidant is 1:1-4, preferably 1:1-2.

[0026] In a preferred embodiment, the hindered phenol antioxidant is selected from: 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, and pentaerythrityl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionate.

[0027] In a preferred embodiment, the phosphite antioxidant is selected from: tris(2,4-di-tert-butylphenyl)phosphite and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite.

[0028] In a preferred embodiment, the acid neutralizer is calcium stearate or hydrogenated talc.

[0029] In a preferred embodiment, the transparent agent is di(3,4-dimethyldibenzylidene)sorbitol, bis[2,2′-methylene-bis(4,6-di-tert-butylphenyl)phosphate]hydroxyaluminum, or 1,3-2,4-di-allylbenzylidene sorbitol.

[0030] In addition, the present invention also provides the application of the above-mentioned high-transparency and high-gloss metallocene polypropylene resin in the fields of food, medicine, household products, etc.

[0031] Without violating the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0032] The positive improvement effect of the present invention is that compared with the prior art, the high-transparency, high-gloss polypropylene resin of the technical solution of the present invention has the following beneficial effects:

[0033] The present invention provides the composition, proportion and preparation method of highly transparent and high gloss polypropylene resin. Compared with the existing Ziegler-Natta catalyst technology, the polypropylene resin of the present invention has a narrow molecular weight distribution, few large spherulites, high transparency and gloss, and can be applied to highly transparent products. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the molecular weight distribution diagram of polypropylene in Example 11 DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solutions in this application, the present invention will be further described below in conjunction with embodiments. Obviously, the described embodiments are only part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used to implement or test the present invention, preferred methods and materials are described herein. For purposes of the present invention, the following terms are defined below.

[0037] Supported Metallocene Catalysts

[0038] The supported metallocene catalyst of the present invention comprises a carrier and a metallocene component supported on the carrier. The carrier may be a known carrier used for metallocene catalysts, including silicon dioxide and aluminum oxide; the metallocene component comprises zirconocene dichloride and methylaluminoxane.

[0039] Molecular weight distribution value

[0040] The molecular weight distribution value of the present invention is used to represent the index of the dispersion degree of molecular weight distribution. The molecular weight distribution value is equal to the weight average molecular weight divided by the number average molecular weight. When the molecular weight distribution value is equal to 1, it is a polymer with uniform molecular weight. The larger the molecular weight distribution value is than 1, the wider the molecular weight distribution is and the greater the degree of polydispersity is.

[0041] As used herein, the term "about" refers to an amount, level, value, dimension, size, or amount that differs by up to 30%, 20%, or 10% compared to the amount, level, value, dimension, size, or amount of a reference product. Percentages used herein, unless otherwise indicated, are by weight.

[0042] Throughout the specification and claims, unless otherwise required, the following words "comprise" and variations "comprising" and "including" will be understood to imply the inclusion of a stated integer or step, or a group of integers or steps, but not the exclusion of any other integer or step, or other group of integers or steps.

[0043] The present invention will be described in detail below through examples. The raw materials used in the examples of the present invention can be obtained commercially.

[0044] Experimental Materials:

[0045]

[0046]

[0047] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0048] Example 1: Preparation of homopolymer polypropylene

[0049] 100 parts by weight of propylene, 0.0065 parts by weight of a metallocene catalyst, and 0.06 parts by weight of triisobutylaluminum are introduced into a prepolymerization reactor for prepolymerization reaction. The prepolymerization reaction conditions are temperature 15° C., pressure 3.4 MPa, and residence time 0.2 h to obtain a propylene prepolymer;

[0050] The propylene prepolymer, 100 parts by weight of propylene and 0.0001 parts by weight of hydrogen are introduced into a loop reactor for polymerization reaction. The polymerization reaction conditions are temperature 67° C., pressure 3.3 MPa, and residence time 1 hour to obtain a polymerization reaction propylene homopolymer.

[0051] The polymerization reaction propylene homopolymer is heated through a flash tube and then discharged into a flash tank for gas-solid separation at a pressure of 1.8 MPa, and then the homopolymer is sent to a low-pressure degassing tank for further degassing at a pressure of 0.06 MPa; the separated homopolymer is deactivated with 0.05 MPa, 120°C steam for 8 minutes to completely inactivate the catalyst; it is dried with 0.03 MPa, 90°C circulating hot nitrogen for 8 minutes to remove moisture, and the obtained homopolymer polypropylene is set aside.

[0052] Example 2: Preparation of homopolymer polypropylene

[0053] 100 parts by weight of propylene, 0.0065 parts by weight of a metallocene catalyst, and 0.06 parts by weight of triisobutylaluminum are introduced into a prepolymerization reactor for prepolymerization reaction. The prepolymerization reaction conditions are temperature 15° C., pressure 3.4 MPa, and residence time 0.2 h to obtain a propylene prepolymer;

[0054] The propylene prepolymer and 0.0003 parts by weight of hydrogen per 100 parts by weight of propylene are introduced into a loop reactor for polymerization reaction. The polymerization reaction conditions are temperature 67° C., pressure 3.3 MPa, and residence time 1 hour to obtain a polymerization reaction propylene homopolymer;

[0055] The propylene homopolymer of the polymerization reaction is heated through a flash tube and then discharged into a flash tank for gas-solid separation at a pressure of 1.8 MPa, and then the homopolymer is sent to a low-pressure degassing tank for further degassing at a pressure of 0.06 MPa; the separated homopolymer is deactivated with 0.05 MPa, 120°C steam for 8 minutes to completely deactivate the catalyst; it is dried with 0.03 MPa, 90°C circulating hot nitrogen for 8 minutes to remove moisture, and the obtained homopolymer polypropylene is set aside.

[0056] Example 3: Preparation of homopolymer polypropylene

[0057] 100 parts by weight of propylene, 0.0065 parts by weight of a metallocene catalyst, and 0.06 parts by weight of triisobutylaluminum are introduced into a prepolymerization reactor for prepolymerization reaction. The prepolymerization reaction conditions are temperature 15° C., pressure 3.4 MPa, and residence time 0.2 h to obtain a propylene prepolymer;

[0058] The propylene prepolymer and 0.0005 parts by weight of hydrogen per 100 parts by weight of propylene are introduced into a loop reactor for polymerization reaction. The polymerization reaction conditions are temperature 67° C., pressure 3.3 MPa, and residence time 1 hour to obtain a polymerization reaction propylene homopolymer;

[0059] The propylene homopolymer of the polymerization reaction is heated through a flash tube and then discharged into a flash tank for gas-solid separation at a pressure of 1.8 MPa, and then the homopolymer is sent to a low-pressure degassing tank for further degassing at a pressure of 0.06 MPa; the separated homopolymer is deactivated with 0.05 MPa, 120°C steam for 8 minutes to completely deactivate the catalyst; it is dried with 0.03 MPa, 90°C circulating hot nitrogen for 8 minutes to remove moisture, and the obtained homopolymer polypropylene is set aside.

[0060] Example 4: Preparation of homopolymer polypropylene

[0061] 100 parts by weight of propylene, 0.0065 parts by weight of a metallocene catalyst, and 0.06 parts by weight of triisobutylaluminum are introduced into a prepolymerization reactor for prepolymerization reaction. The prepolymerization reaction conditions are temperature 15° C., pressure 3.4 MPa, and residence time 0.2 h to obtain a propylene prepolymer;

[0062] The propylene prepolymer and 0.0007 parts by weight of hydrogen per 100 parts by weight of propylene are introduced into a loop reactor for polymerization reaction. The polymerization reaction conditions are temperature 67° C., pressure 3.3 MPa, and residence time 1 hour to obtain a polymerization reaction propylene homopolymer;

[0063] The propylene homopolymer of the polymerization reaction is heated through a flash tube and then discharged into a flash tank for gas-solid separation at a pressure of 1.8 MPa, and then the homopolymer is sent to a low-pressure degassing tank for further degassing at a pressure of 0.06 MPa; the separated homopolymer is deactivated with 0.05 MPa, 120°C steam for 8 minutes to completely deactivate the catalyst; it is dried with 0.03 MPa, 90°C circulating hot nitrogen for 8 minutes to remove moisture, and the obtained homopolymer polypropylene is set aside.

[0064] Example 5: Preparation of compound antioxidant

[0065] Tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionate pentaerythritol ester and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite are mixed at a weight ratio of 1:1.5 to obtain a composite antioxidant for standby use.

[0066] Example 6: Preparation of polypropylene resin

[0067] 100 parts by weight of homopolypropylene prepared in Example 1, 0.12 parts by weight of the compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and an aspect ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were 190℃, 200℃, 210℃, 220℃, 230℃, 220℃, the screw speed is 220RPM, the material is sheared and heated in the screw and barrel of the extruder, and after shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, the water cooling temperature is 53℃, and after centrifugal drying and dehydration, a highly transparent and high-gloss polypropylene resin is prepared for use. The polypropylene resin is a cylindrical particle with a particle size of 3.5mm and a height of 3mm.

[0068] Example 7: Preparation of polypropylene resin

[0069] 100 parts by weight of homopolypropylene prepared in Example 2, 0.12 parts by weight of the compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and an aspect ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were 190℃, 210℃, 220℃, 230℃, 240℃, 230℃, the screw speed is 220RPM, the material is sheared and heated in the screw and barrel of the extruder, and after shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, the water cooling temperature is 53℃, and after centrifugal drying and dehydration, a highly transparent and high gloss polypropylene resin is prepared for use. The polypropylene resin is a cylindrical particle with a particle size of 3.5mm and a height of 3mm.

[0070] Example 8: Preparation of polypropylene resin

[0071] 100 parts by weight of homopolypropylene prepared in Example 3, 0.12 parts by weight of the compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and an aspect ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were 190℃, 200℃, 210℃, 220℃, 230℃, 220℃, the screw speed is 220RPM, the material is sheared and heated in the screw and barrel of the extruder, and after shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, the water cooling temperature is 53℃, and after centrifugal drying and dehydration, a highly transparent and high-gloss polypropylene resin is prepared for use. The polypropylene resin is a cylindrical particle with a particle size of 3.5mm and a height of 3mm.

[0072] Example 9: Preparation of polypropylene resin

[0073] 100 parts by weight of homopolypropylene prepared in Example 4, 0.12 parts by weight of compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and an aspect ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were 170℃, 180℃, 190℃, 200℃, 210℃, 200℃, the screw speed is 220RPM, the material is sheared and heated in the screw and barrel of the extruder, and after shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, the water cooling temperature is 53℃, and after centrifugal drying and dehydration, a highly transparent and high-gloss polypropylene resin is prepared for use. The polypropylene resin is a cylindrical particle with a particle size of 3.5mm and a height of 3mm.

[0074] Example 10: Preparation of polypropylene resin

[0075] 100 parts by weight of homopolypropylene prepared in Example 1, 0.12 parts by weight of the compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.40 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and an aspect ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were 190℃, 200℃, 210℃, 220℃, 230℃, 220℃, the screw speed is 220RPM, the material is sheared and heated in the screw and barrel of the extruder, and after shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, the water cooling temperature is 53℃, and after centrifugal drying and dehydration, a highly transparent and high-gloss polypropylene resin is prepared for use. The polypropylene resin is a cylindrical particle with a particle size of 3.5mm and a height of 3mm.

[0076] Example 11: Preparation of polypropylene resin

[0077] 100 parts by weight of homopolypropylene prepared in Example 1, 0.12 parts by weight of the compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.20 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and an aspect ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were 190℃, 200℃, 210℃, 220℃, 230℃, 220℃, the screw speed is 220RPM, the material is sheared and heated in the screw and barrel of the extruder, and after shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, the water cooling temperature is 53℃, and after centrifugal drying and dehydration, a highly transparent and high-gloss polypropylene resin is prepared for use. The polypropylene resin is a cylindrical particle with a particle size of 3.5mm and a height of 3mm.

[0078] Example 12: Preparation of compound antioxidant

[0079] 1,3,5-trimethyl-2,4,6-tri(3,5-di-tert-butyl-4-hydroxybenzyl)benzene and tri(2,4-di-tert-butylphenyl)phosphite are mixed in a weight ratio of 1:2 to obtain a compound antioxidant for standby use.

[0080] Example 13: Preparation of polypropylene resin

[0081] 100 parts by weight of homopolymer polypropylene prepared in Example 1, 0.12 parts by weight of compound antioxidant in Example 12, 0.06 parts by weight of hydrogenated talc and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added into a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added into an extruder with a diameter of 327 mm and a length-to-diameter ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were kept constant. The temperature is 190℃, 200℃, 210℃, 220℃, 230℃, 220℃, and the screw speed is 220RPM. The material is sheared and heated in the screw and barrel of the extruder. After shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, and the water cooling temperature is 53℃. After centrifugal drying and dehydration, high-transparency and high-gloss polypropylene resin is prepared for use. The polypropylene resin is cylindrical particles with a particle size of 3.5mm and a height of 3mm.

[0082] Example 14: Preparation of polypropylene resin

[0083] 100 parts by weight of homopolypropylene prepared in Example 1, 0.12 parts by weight of the compound antioxidant in Example 12, 0.06 parts by weight of calcium stearate and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and a length-to-diameter ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were kept constant. The temperature is 190℃, 200℃, 210℃, 220℃, 230℃, 220℃, and the screw speed is 220RPM. The material is sheared and heated in the screw and barrel of the extruder. After shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, and the water cooling temperature is 53℃. After centrifugal drying and dehydration, high-transparency and high-gloss polypropylene resin is prepared for use. The polypropylene resin is cylindrical particles with a particle size of 3.5mm and a height of 3mm.

[0084] Example 15: Preparation of polypropylene resin

[0085] 100 parts by weight of homopolypropylene prepared in Example 1, 0.12 parts by weight of the compound antioxidant in Example 12, 0.06 parts by weight of calcium stearate and 0.20 parts by weight of di(3,4-dimethyldibenzylidene)sorbitol were added into a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added into an extruder with a diameter of 327 mm and an aspect ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were 1 90℃, 200℃, 210℃, 220℃, 230℃, 220℃, the screw speed is 220RPM, the material is sheared and heated in the screw and barrel of the extruder, and after shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, the water cooling temperature is 53℃, and after centrifugal drying and dehydration, a highly transparent and high gloss polypropylene resin is prepared for use. The polypropylene resin is a cylindrical particle with a particle size of 3.5mm and a height of 3mm.

[0086] Example 16: Preparation of polypropylene resin

[0087] 100 parts by weight of homopolypropylene prepared in Example 1, 0.12 parts by weight of the compound antioxidant in Example 12, 0.06 parts by weight of calcium stearate and 0.25 parts by weight of di(3,4-dimethyldibenzylidene)sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and an aspect ratio of 18. The first feeding section of the extruder was not heated, and the temperatures of the remaining sections were 1 90℃, 200℃, 210℃, 220℃, 230℃, 220℃, the screw speed is 220RPM, the material is sheared and heated in the screw and barrel of the extruder, and after shearing, mixing, melting and plasticizing by the extruder, it is extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, the water cooling temperature is 53℃, and after centrifugal drying and dehydration, a highly transparent and high gloss polypropylene resin is prepared for use. The polypropylene resin is a cylindrical particle with a particle size of 3.5mm and a height of 3mm.

[0088] Example 17: Preparation of polypropylene resin

[0089] 100 parts by weight of homopolypropylene prepared in Example 1, 0.12 parts by weight of the compound antioxidant in Example 12, 0.06 parts by weight of calcium stearate and 0.10 parts by weight of bis[2,2′-methylene-bis(4,6-di-tert-butylphenyl)phosphate]hydroxyaluminum were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and a length-to-diameter ratio of 18. The first feeding section of the extruder was not heated. The temperatures of the remaining sections are 190°C, 200°C, 210°C, 220°C, 230°C, and 220°C, and the screw speed is 220RPM. The materials are sheared and heated in the screw and barrel of the extruder. After shearing, mixing, melting, and plasticizing in the extruder, they are extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, and the water cooling temperature is 53°C. After centrifugal drying and dehydration, high-transparency and high-gloss polypropylene resin is prepared for use. The polypropylene resin is cylindrical particles with a particle size of 3.5mm and a height of 3mm.

[0090] Example 18: Preparation of polypropylene resin

[0091] 100 parts by weight of homopolypropylene prepared in Example 1, 0.12 parts by weight of the compounded antioxidant in Example 12, 0.06 parts by weight of calcium stearate and 0.15 parts by weight of bis[2,2′-methylene-bis(4,6-di-tert-butylphenyl)phosphate]hydroxyaluminum were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and a length-to-diameter ratio of 18. The first feeding section of the extruder was not heated. The temperatures of the remaining sections are 190°C, 200°C, 210°C, 220°C, 230°C, and 220°C, and the screw speed is 220RPM. The materials are sheared and heated in the screw and barrel of the extruder. After shearing, mixing, melting, and plasticizing in the extruder, they are extruded through the die head for pelletizing and water cooling. The pelletizer speed is 520RPM, and the water cooling temperature is 53°C. After centrifugal drying and dehydration, high-transparency and high-gloss polypropylene resin is prepared for use. The polypropylene resin is cylindrical particles with a particle size of 3.5mm and a height of 3mm.

[0092] Comparative Example 1: Preparation of homopolymer polypropylene

[0093] 100 parts by weight of propylene, 0.0045 parts by weight of Ziegler-Natta catalyst, 0.06 parts by weight of triethylaluminum, and 0.02 parts by weight of cyclohexyldimethoxysilane are introduced into a prepolymerization reactor for prepolymerization reaction. The prepolymerization reaction conditions are temperature 15° C., pressure 3.4 MPa, and residence time 0.2 h to obtain a propylene prepolymer;

[0094] The propylene prepolymer, 100 parts by weight of propylene and 0.31 parts by weight of hydrogen were introduced into a tube reactor for polymerization reaction. The polymerization reaction conditions were temperature 70° C., pressure 3.4 MPa, and residence time 1.0 h to obtain a polymerization reaction propylene homopolymer.

[0095] The polymerization reaction propylene homopolymer is heated through a flash tube and then discharged into a flash tank for gas-solid separation at a pressure of 1.8 MPa, and then the homopolymer is sent to a low-pressure degassing tank for further degassing at a pressure of 0.06 MPa; the separated homopolymer is deactivated with 0.05 MPa, 120°C steam for 8 minutes to completely inactivate the catalyst; the homopolymer is dried with 0.03 MPa, 90°C circulating hot nitrogen for 8 minutes to remove moisture, and the obtained homopolymer polypropylene is set aside.

[0096] Comparative Example 2: Preparation of homopolymer polypropylene

[0097] 100 parts by weight of homopolymer polypropylene prepared in Comparative Example 1, 0.12 parts by weight of compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added into a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added into an extruder with a diameter of 327 mm and a length-to-diameter ratio of 18. The first feeding section of the extruder was not heated, and the remaining sections were heated. The temperature is 190°C, 210°C, 220°C, 230°C, 240°C, and 230°C, and the screw speed is 220RPM. The material is sheared and heated in the screw and barrel of the extruder. After shear mixing, melting, and plasticization by the extruder, it is extruded through a die head for pelletizing and water cooling. The pelletizer speed is 520RPM, and the water cooling temperature is 53°C. After centrifugal drying and dehydration, a transparent polypropylene resin is prepared for use. The polypropylene resin is cylindrical particles with a particle size of 3.5mm and a height of 3mm.

[0098] Comparative Example 3: Preparation of homopolymer polypropylene

[0099] 100 parts by weight of propylene, 0.0045 parts by weight of Ziegler-Natta catalyst, 0.06 parts by weight of triethylaluminum, and 0.02 parts by weight of cyclohexyldimethoxysilane are introduced into a prepolymerization reactor for prepolymerization reaction. The prepolymerization reaction conditions are temperature 15° C., pressure 3.4 MPa, and residence time 0.2 h to obtain a propylene prepolymer;

[0100] The propylene prepolymer, 100 parts by weight of propylene and 0.32 parts by weight of hydrogen are introduced into a first loop reactor for polymerization reaction. The polymerization reaction conditions are temperature 70° C., pressure 3.4 MPa, and residence time 1.0 h to obtain a polymerization reaction propylene homopolymer;

[0101] The polymerization reaction propylene homopolymer is heated through a flash tube and then discharged into a flash tank for gas-solid separation at a pressure of 1.8 MPa, and then the homopolymer is sent to a low-pressure degassing tank for further degassing at a pressure of 0.06 MPa; the separated homopolymer is deactivated with 0.05 MPa, 120°C steam for 8 minutes to completely inactivate the catalyst; the homopolymer is dried with 0.03 MPa, 90°C circulating hot nitrogen for 8 minutes to remove moisture, and the obtained homopolymer polypropylene is set aside.

[0102] Comparative Example 4: Preparation of homopolymer polypropylene

[0103] 100 parts by weight of homopolymer polypropylene prepared in Comparative Example 3, 0.12 parts by weight of compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and a length-to-diameter ratio of 18. The first feeding section of the extruder was not heated, and the remaining sections were heated. The temperature is 190°C, 200°C, 210°C, 220°C, 230°C, and 220°C, and the screw speed is 220RPM. The material is sheared and heated in the screw and barrel of the extruder. After shear mixing, melting, and plasticization by the extruder, it is extruded through a die head for pelletizing and water cooling. The pelletizer speed is 520RPM, and the water cooling temperature is 53°C. After centrifugal drying and dehydration, a transparent polypropylene resin is prepared for use. The polypropylene resin is cylindrical particles with a particle size of 3.5mm and a height of 3mm.

[0104] Comparative Example 5: Preparation of homopolymer polypropylene

[0105] 100 parts by weight of propylene, 0.0045 parts by weight of Ziegler-Natta catalyst, 0.06 parts by weight of triethylaluminum, and 0.02 parts by weight of cyclohexyldimethoxysilane are introduced into a prepolymerization reactor for prepolymerization reaction. The prepolymerization reaction conditions are temperature 15° C., pressure 3.4 MPa, and residence time 0.2 h to obtain a propylene prepolymer;

[0106] The propylene prepolymer and 0.32 parts by weight of hydrogen per 100 parts by weight of propylene are introduced into a loop reactor for polymerization reaction. The polymerization reaction conditions are temperature 60° C., pressure 3.4 MPa, and residence time 1.0 h to obtain a first polymerization reaction propylene homopolymer;

[0107] The propylene homopolymer from the polymerization reaction is heated through a flash tube and then discharged into a flash tank for gas-solid separation at a pressure of 1.8 MPa. The homopolymer is then sent to a low-pressure degassing tank for further degassing at a pressure of 0.06 MPa. The separated homopolymer is deactivated with 0.05 MPa, 120°C steam for 8 minutes to completely inactivate the catalyst. The homopolymer is dried with 0.03 MPa, 90°C circulating hot nitrogen for 8 minutes to remove moisture, and the resulting homopolymerized polypropylene is sent to the extrusion granulation system for standby use.

[0108] Comparative Example 6: Preparation of homopolymer polypropylene

[0109] 100 parts by weight of homopolymer polypropylene prepared in Comparative Example 5, 0.12 parts by weight of compound antioxidant in Example 5, 0.06 parts by weight of calcium stearate and 0.35 parts by weight of 1,3-2,4-di-allylbenzylidene sorbitol were added to a mixer at room temperature. The mixing screw had a diameter of 500 mm, a length of 4 m and a rotation speed of 50 RPM. The mixed materials were added to an extruder with a diameter of 327 mm and a length-to-diameter ratio of 18. The first feeding section of the extruder was not heated, and the remaining sections were heated. The temperature is 190°C, 200°C, 210°C, 220°C, 230°C, and 220°C, and the screw speed is 220RPM. The material is sheared and heated in the screw and barrel of the extruder. After shear mixing, melting, and plasticization by the extruder, it is extruded through a die head for pelletizing and water cooling. The pelletizer speed is 520RPM, and the water cooling temperature is 53°C. After centrifugal drying and dehydration, a transparent polypropylene resin is prepared for use. The polypropylene resin is cylindrical particles with a particle size of 3.5mm and a height of 3mm.

[0110] Test Example 1: Melt Flow Rate

[0111] The test samples are homopolypropylene prepared in Examples 1-4, polypropylene resins prepared in Examples 6-11, polypropylene resins prepared in Examples 13-18, and polypropylene resins prepared in Comparative Examples 1, 3, and 5.

[0112] The melt flow rate is tested according to GB / T 3682.1-2018 standard: the melt flow rate tester is WL987 from TINUSOLSEN, USA, the test temperature is 210°C, the weight is 2.16 kg, the capillary diameter is 2.095 mm, and the length is 8 mm. A 3-gram polypropylene test sample is placed in the capillary, and the mass extruded within the specified time is tested, which is the melt flow rate, in grams per 10 minutes (g / 10min).

[0113] Table 1 Melt flow rate

[0114] Test samples Melt flow rate g / 10min Example 1 Homopolymer polypropylene 1.0 Example 2 Homopolymer polypropylene 1.0 Example 3 Homopolymer polypropylene 1.0 Example 4 Homopolymer Polypropylene 1.0 Example 6 Homopolymer Polypropylene 1.5 Example 7 Homopolymer Polypropylene 1.2 Example 8 Homopolymer Polypropylene 1.3 Example 9 Homopolymer Polypropylene 1.5 Example 10 Homopolymer polypropylene 1.2 Example 11 Homopolymer polypropylene 1.3 Example 13 Homopolymer polypropylene 1.6 Example 14 Homopolymer polypropylene 1.5 Example 15 Homopolymer Polypropylene 1.4 Example 16 Homopolymer polypropylene 1.2 Example 17 Homopolymer Polypropylene 1.7 Example 18 Homopolymer Polypropylene 1.7 Comparative Example 1 Homopolymer Polypropylene 3.0 Comparative Example 3 Homopolymer Polypropylene 3.0 Comparative Example 5 Homopolymer Polypropylene 3.0

[0115] Melt flow rate indicates the rheological properties of polypropylene melt, and its value indirectly indicates the molecular weight of polypropylene, and estimates the processing performance of polypropylene melt. The larger the molecular weight, the lower the melt flow rate. The size of the melt flow rate should change with the changes in products and processing technology.

[0116] The melt flow rates of the homopolymerized polypropylenes of Examples 1-4, the polypropylene resins prepared in Examples 6-11, and the polypropylene resins prepared in Examples 13-18 of the present invention are 1-1.7 g / 10 min, and the melt flow rates of the homopolymerized polypropylenes of Comparative Examples 1, 3, and 5 are all 3.0 g / 10 min, indicating that the molecular weights of the homopolymerized polypropylenes of Examples 1-4, the polypropylene resins prepared in Examples 6-11, and the polypropylene resins prepared in Examples 13-18 are appropriate.

[0117] Test Example 2: Xylene Soluble Matter

[0118] The test samples are the polypropylene resins of Examples 9-11 and Examples 13-18 and the polypropylene resins of Comparative Examples 2, 4 and 6.

[0119] The xylene solubles are tested according to GB / T24282-2021 standard: 2g of polypropylene test sample and 200mL of o-xylene solution are placed in a flask, stirred and heated to reflux temperature, kept stirring, and heated for 30 minutes to completely dissolve the polypropylene sample; then the flask is naturally cooled to below 100°C at room temperature, placed in a constant temperature water bath at 25°C, cooled for 30 to 32 minutes, and then filtered to obtain a transparent filtrate, evaporate the xylene in the filtrate, obtain the xylene solubles and calculate the content.

[0120] Table 2 Xylene solubles

[0121]

[0122]

[0123] As can be seen from the above table, the detection values ​​of xylene solubles of the polypropylene resins of Examples 9-10 and Examples 13-17 of the present invention are all lower than 1wt%, indicating that the polypropylene resins prepared in these examples have good regularity, low xylene solubles, and high hygienic safety.

[0124] The detection value of xylene solubles of polypropylene in Example 11 is only 1.1wt%, and the detection value of xylene solubles of polypropylene in Example 18 is only 1.8wt%. Although higher than 1wt%, the detection values ​​of xylene solubles are still within a reasonable controllable range compared with Comparative Examples 2, 4 and 6. The detection values ​​of xylene solubles of polypropylene in Comparative Examples 2, 4 and 6 are between 2.9 and 5.6wt%, indicating that the regularity of polypropylene resin in the comparative examples is poor, and the xylene solubles are high, especially the regularity of polypropylene resin in Comparative Example 4 is the poorest, and the xylene solubles are high, while the examples can still maintain low xylene solubles.

[0125] Test Example 3: Haze

[0126] The test samples are the polypropylene resins of Examples 6-11 and Examples 13-18 and the polypropylene resins of Comparative Examples 2, 4 and 6.

[0127] The haze is tested according to GB2410-2008 standard: the test equipment is the haze meter HGM-2DP of Suga Co., Ltd. of Japan, and the injection molding machine is K-TEC85-265 of Milacron of Germany. The injection molding machine is used to make a sample with a length of 50×5×1mm at a temperature of 220℃, and then the sample is put into the haze meter for testing to obtain the result.

[0128] Table 3 Haze

[0129]

[0130]

[0131] The transparency of polypropylene is characterized by haze, which refers to the ratio of the scattered light flux that deviates from the incident light direction by more than 2.5° through the sample to the transmitted light flux. The smaller the value, the less light scattering and the better the transparency, so the smaller the haze, the better.

[0132] The difference between the polypropylene in Example 6, the polypropylene in Example 10 and the polypropylene in Example 11 is that the added amount of the transparent agent 1,3-2,4-di-allylbenzylidene sorbitol is different, indicating that the haze value does not decrease significantly after the added amount exceeds 0.35%, and the haze value is higher when the added amount is 0.2%. Therefore, the added amount of the transparent agent should reach 0.35% or more.

[0133] The difference between the polypropylenes of Examples 6-9 is that the amount of hydrogen added in the process of preparing homopolymerized polypropylene is different, and the amount of hydrogen added is 0.0001, 0.0003, 0.0005 and 0.0007 parts by mass respectively. The haze value of the polypropylene of Examples 6-9 fluctuates between 2.3-4.2 (1 mm) %, indicating that it decreases with the increase of melt flow rate.

[0134] The difference between the polypropylene in Example 13 and Example 14 is that the acid neutralizers are different. Example 13 uses hydrogenated talc as the acid neutralizer, and Example 14 uses calcium stearate as the acid neutralizer. The haze value of the polypropylene in Example 13 is 4.2, and the haze value of the polypropylene in Example 14 is 3.7, indicating that the polypropylene in Example 14 is better than the polypropylene in Example 13, that is, hydrogenated talc is a better acid neutralizer.

[0135] The difference between the polypropylene of Example 14 and Example 15 is that the added amounts of the transparent agent 1,3-2,4-di-allylbenzylidene sorbitol are different. The added amount of the transparent agent 1,3-2,4-di-allylbenzylidene sorbitol in Example 14 is 0.35 parts by mass, and the added amount of the transparent agent 1,3-2,4-di-allylbenzylidene sorbitol in Example 15 is 0.20 parts by mass. Accordingly, the haze value of 3.3 of the polypropylene of Example 15 is better than the haze value of 3.7 of the polypropylene of Example 14, indicating that the haze value does not decrease significantly after the added amount exceeds 0.35%.

[0136] The difference between the polypropylenes in Examples 16 and 18 is that they have different added amounts and different transparent agents. The transparent agent in Example 16 is 0.25 parts by weight of di(3,4-dimethyldibenzylidene)sorbitol, the transparent agent in Example 17 is 0.10 parts by weight of bis[2,2′-methylene-bis(4,6-di-tert-butylphenyl)phosphate]hydroxyaluminum, and the transparent agent in Example 18 is 0.15 parts by weight of bis[2,2′-methylene-bis(4,6-di-tert-butylphenyl)phosphate]hydroxyaluminum. Accordingly, the haze value of 2.3 of the polypropylene in Example 18 is better than the haze value of 3.4 of the polypropylene in Example 16, which is better than the haze value of 8.2 of the polypropylene in Example 17, indicating that the type and amount of additives have a greater influence on the haze.

[0137] In summary, haze is related to the type and amount of transparent agent added. As the amount of transparent agent added increases, the haze decreases and tends to stabilize after a certain amount is added.

[0138] Test Example 4: Glossiness

[0139] The test samples are the polypropylene resins of Examples 9-11 and Examples 13-18 and the polypropylene resins of Comparative Examples 2, 4 and 6.

[0140] Glossiness is tested according to GB / T 8807-1988 standard: the testing equipment is A-4430 of BYK Company of Germany, and the injection molding machine is K-TEC85-265 of Milacron of Germany. The injection molding machine is used to make a sample with a length × width × thickness of 100 × 100 × 1 mm, the temperature is 220℃, and then the sample is put into the gloss meter for testing, and the test angle is 60°.

[0141] Table 4 Glossiness

[0142] Test samples Glossiness (60°) % Example 9 Polypropylene 128.5 Example 10 Polypropylene 126.3 Example 11 Polypropylene 134.1 Example 13 Polypropylene 127.6 Example 14 Polypropylene 128.2 Example 15 Polypropylene 129.1 Example 16 Polypropylene 129.0 Example 17 Polypropylene 120.8 Example 18 Polypropylene 137.4 Comparative Example 2 Polypropylene 110.2 Comparative Example 4 Polypropylene 118.1 Comparative Example 6 Polypropylene 117.6

[0143] Gloss refers to the ability of an object to reflect light when it is illuminated by incident light at a specific angle. It is the ratio of the amount of light reflected by the reference surface and is closely related to the surface flatness of the object. The improvement of gloss means that the fine concave and convex surfaces of the object disappear and form an extremely smooth surface, giving the product excellent optical properties. For the structure of polypropylene itself, the formation of uniform and fine crystals during crystallization can effectively improve the gloss of polypropylene.

[0144] From the above table, it can be seen that the type and amount of the transparent agent affect the glossiness. As the transparent agent content increases, the glossiness increases. Compared with the comparative example, the polypropylene resin of the present invention has a higher glossiness, which indicates that the glossiness is also closely related to the molecular chain structure of the polypropylene itself, so the glossiness is higher.

[0145] Test Example 5: Molecular Weight Distribution

[0146] The test samples are the polypropylene resins of Examples 9-11, Example 13-1 and Comparative Examples 2, 4 and 6.

[0147] The molecular weight distribution is measured by gel permeation chromatography GPC: the measurement system is a PL-GPC 220 high performance liquid chromatograph produced by Polymer Laboratories, UK, and the chromatographic column is 3 Plgel 10μm MIXED-B columns connected in series. The solvent and mobile phase are both 1,2,4-trichlorobenzene (containing 0.025% antioxidant 2,6-dibutyl-p-cresol), the column temperature is 150°C, the flow rate is 1.0ml / min, and a narrow distribution polystyrene standard is used for universal calibration. The polypropylene test sample is dissolved in the mobile phase, and the mobile phase flows through three mixed B columns. Due to the difference in the molecular size of polypropylene, molecules of different sizes are eluted and separated from the chromatographic column, and the data is processed by software to obtain the molecular weight distribution.

[0148] Table 5 Molecular weight distribution

[0149]

[0150]

[0151] Polypropylene is a collection of components with different molecular weights. The molecular weight distribution is used to characterize the dispersion of molecular weight. The larger the molecular weight distribution value, the wider the molecular weight distribution, the greater the difference in molecular weight, and the higher the content of low molecular weight components and high molecular weight components.

[0152] As can be seen from the above table, the polypropylenes of Comparative Examples 2, 4 and 6 are all produced by Ziegler-Natta catalyst technology, and the molecular weight distribution of the polypropylenes is wide, and the molecular weight difference is large. The molecular weight distribution of the polypropylenes of Examples 9-11 and 13-18 is 2.3-2.6, and the molecular weight distribution is relatively reasonable, that is, the polypropylene prepared in the embodiments of the present invention is finally a highly transparent and high-gloss polypropylene resin, which not only has excellent optical properties, but also has low precipitates and volatiles, and is particularly suitable for plastic products such as food, medicine, and household products that have high requirements for transparency and hygiene.

Claims

1. A highly transparent and high gloss metallocene polypropylene resin, characterized in that: The molecular weight distribution value of the polypropylene resin is 2 to 3, and preferably the molecular weight distribution value is 2.3 to 2.

8.

2. The polypropylene resin according to claim 1, characterized in that The xylene soluble matter of the polypropylene resin is 0.4-1.8 wt %, preferably 0.4-0.8 wt %.

3. The polypropylene resin according to claim 1, characterized in that The haze of the polypropylene resin is 2.3-8.2%.

4. The polypropylene resin according to claim 1, characterized in that The glossiness of the polypropylene resin is ≥120.8%, preferably 120.8-137.4%.

5. The polypropylene resin according to claim 1, characterized in that The melt flow rate of the polypropylene resin is 1 to 3 g / 10 min, preferably 1.5 to 2 g / 10 min.

6. A method for preparing the polypropylene resin according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: 1) subjecting propylene, a main catalyst and a co-catalyst to a prepolymerization reaction to obtain a propylene prepolymer; 2) subjecting the propylene prepolymer of step 1) to polymerization reaction with propylene and hydrogen to obtain a propylene polymer; 3) sequentially performing gas-solid separation, deactivation and drying of the propylene polymer in step 2) to obtain homopolypropylene; 4) The homopolymerized polypropylene, antioxidant, acid neutralizer and clarifier in step 3) are mixed and melt-extruded at 170-250° C. to form granules.

7. The method according to claim 6, characterized in that The weight ratio of propylene, main catalyst, co-catalyst and hydrogen in step 1) and step 2) is 100: 0.0035-0.015: 0.015-0.075: 0-0.

005.

8. The method according to claim 6, characterized in that The main catalyst in step 1) is a supported metallocene catalyst.

9. The method according to claim 6, characterized in that The co-catalyst in step 1) is an alkyl aluminum type co-catalyst, selected from at least one of triisobutyl aluminum, triethyl aluminum, trimethyl aluminum, and tri-n-hexyl aluminum.

10. The method according to claim 6, characterized in that The prepolymerization reaction conditions in step 1) are: polymerization temperature 10-20° C., polymerization pressure 3.0-3.9 MPa, and polymerization residence time 0.15-0.25 h.

11. The method according to claim 6, characterized in that The polymerization reaction conditions in step 2) are: polymerization temperature 60-75° C., polymerization pressure 3.0-3.9 MPa, and polymerization residence time 0.8-1.2 h.

12. The method according to claim 6, characterized in that The gas-solid separation conditions in step 3) are: gas-solid separation at 1.6-2.0 MPa and degassing at 0.04-0.08 MPa; the deactivation is to deactivate the catalyst with 0.01-0.06 MPa steam; the drying is to dry with circulating hot nitrogen at 70-110°C.

13. The method according to claim 6, characterized in that The weight ratio of the homopolymer polypropylene, antioxidant, acid neutralizer and clarifier in step 4) is 100:0.08-0.30:0.02-0.10:0.10-0.

40.

14. The method according to claim 13, characterized in that The weight ratio of the homopolypropylene, antioxidant, acid neutralizer and clarifier is 100:0.10-0.20:0.03-0.08:0.10-0.

40.

15. The method according to claim 13, characterized in that The antioxidant is a mixture of a hindered phenol antioxidant and a phosphite antioxidant, wherein the weight ratio of the hindered phenol antioxidant to the phosphite antioxidant is 1:1-4, preferably 1:1-2.

16. The method according to claim 15, characterized in that The hindered phenol antioxidant is selected from: 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionate.

17. The method according to claim 15, characterized in that The phosphite antioxidant is selected from: tris(2,4-di-tert-butylphenyl)phosphite and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite.

18. The method according to claim 15, characterized in that The acid neutralizer is calcium stearate or hydrogenated talc.

19. The method according to claim 15, characterized in that The transparent agent is di(3,4-dimethyldibenzylidene)sorbitol, bis[2,2'-methylene-bis(4,6-di-tert-butylphenyl)phosphate]hydroxyaluminum and 1,3-2,4-di-p-allylbenzylidene sorbitol.

20. Use of the highly transparent and high gloss metallocene polypropylene resin according to any one of claims 1 to 5 in the fields of food, medicine, household products, etc.

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