Low-haze linear low-density polyethylene resin as well as preparation method and application thereof

Abstract

The invention provides low-haze linear low-density polyethylene resin as well as a preparation method and application thereof, and the preparation method comprises the following steps: (1) adding ethylene, propylene, hydrogen and a catalyst system into a first reactor, and reacting to obtain a first-step polymerization product; (2) adding the first-step polymerization product, ethylene, butylene and hydrogen into a second reactor, and reacting to obtain a second-step polymerization product; (3) adding the second-step polymerization product, ethylene, propylene and hydrogen into a third reactor, reacting to obtain a final polymerization product, and post-treating the final polymerization product to obtain linear low-density polyethylene powder; and (4) mixing the linear low-density polyethylene powder with polyvinyl acetal and an auxiliary agent, and carrying out extrusion granulation to obtain the low-haze linear low-density polyethylene resin. Linear low-density polyethylene is prepared through a three-section reactor, polyvinyl acetal is added for blending modification, and the low-haze linear low-density polyethylene resin is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyethylene resins, and relates to a low haze linear low density polyethylene resin, a preparation method thereof, and an application thereof. Background Art

[0002] As one of the five general-purpose plastics, polyethylene has excellent properties such as good mechanical properties, chemical corrosion resistance, low density, non-toxic and harmless, and is widely used in many production and living fields, such as automotive applications, packaging applications, household applications, storage applications, etc. In recent years, in the production fields such as agricultural greenhouse films, the demand for special low haze polyethylene materials has been increasing day by day. As is well known, the production volume and coverage area of agricultural greenhouse films in China rank first in the world. However, compared with the world's advanced level, there is still a large gap in the development level of agricultural greenhouse films in China. These gaps are not only reflected in the quantity and variety, but also in the performance indicators such as haze (>20%) and low light transmittance (<90%). The reason is that the greenhouse film covering materials produced by the polyolefin industry in China generally adopt high-pressure low density polyethylene (LDPE) / linear low density polyethylene (LLDPE) or metallocene polyethylene / linear low density polyethylene blended resins. Among them, linear low density polyethylene is produced by using Ziegler-Natta catalysts and is composed of copolymerization of ethylene and 1-butene. Its molecular structure is linear, with short side chains and wide distribution on the main chain, and there are many macromolecules. Therefore, during the blown film processing, when the resin changes from the molten state to the glassy state, large-sized crystals are easily formed, and the crystal region distribution is uneven, resulting in irregular light refraction and scattering on the film surface, causing high haze and poor transparency of LLDPE films. In recent years, with the development of the economy, people's requirements for the transparency of greenhouse films have become higher and higher.

[0003] In the prior art, generally, methods such as adding nucleating agents, transparent resins, and micro-crosslinking modification are currently used to improve the transparency of polyolefin films. Commonly used nucleating agents include organic types such as sorbitol, phosphate esters, and hexahydrophthalates, as well as inorganic small molecules such as talc powder, silica, and mica. For example, CN101268132A discloses a film product including a polyethylene polymer or copolymer and a cycloaliphatic metal salt (including a compound containing stearate, such as zinc stearate), which reduces the haze of the film product during the blow molding and casting of polyethylene films to a relatively low level. CN1280145A uses 0.1 - 0.6 parts by mass of sorbitol and aluminum hydroxide nucleating agents and 20 - 100 parts by mass of low-density polyethylene to obtain a polyethylene resin composition with good transparency and low-temperature impact resistance. CN1324887A discloses a polyolefin resin composition containing a polyolefin resin and an acetal-based nucleating agent, and the product produced by this composition has superior optical, mechanical, and thermal properties. CN101796103A discloses a nucleating agent masterbatch for polyolefin resins composed of an aromatic phosphate metal salt nucleating agent and a fully hydrogenated petroleum resin. This masterbatch can improve the transparency and mechanical strength of polyolefin resins and has excellent heat resistance and coloring properties. CN1384139A discloses an agricultural greenhouse film composed of 50 - 90 parts by mass of ordinary low-density polyethylene and 10 - 50 parts by mass of metallocene linear low-density polyethylene, which has excellent light transmittance and right-angle tear strength. Patent CN103627070A discloses a method for achieving micro-crosslinking of polyolefins by adding a compound crosslinking aid containing peroxide, thereby improving the dispersion of nucleating agents in polyolefins to increase the crystallization rate, reduce the crystal size, improve transparency, and reduce haze. However, the haze of the polyolefin resins prepared by the above prior art still needs to be further reduced.

[0004] Therefore, in the art, there is a desire to develop a polyolefin resin with low haze. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a low-haze linear low-density polyethylene resin, its preparation method, and its application. Based on ethylene as the basic raw material and a small amount of butene and propylene as raw materials, a linear low-density polyethylene copolymerized with ethylene, propylene, and butene is prepared through a three-stage reactor, and through blending and modification by adding polyvinyl acetal, a linear low-density polyethylene resin with ultra-low haze is prepared. The polyethylene resin provided by the present invention has many advantages such as high transparency, good continuous productivity, high production efficiency, etc., and at the same time has good mechanical impact performance and processing fluidity, fully meeting the production needs of polyethylene greenhouse film manufacturers and the usage requirements of downstream customers, and greatly expanding the application scope of the product.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a low haze linear low density polyethylene resin, the preparation method comprising:

[0008] (1) Adding ethylene, propylene, hydrogen and a catalyst system into a first reactor, reacting to obtain a first-stage polymerization product;

[0009] (2) Adding all of the first-stage polymerization product obtained in step (1), ethylene, butene and hydrogen into a second reactor, reacting to obtain a second-stage polymerization product;

[0010] (3) Adding all of the second-stage polymerization product obtained in step (2), ethylene, propylene and hydrogen into a third reactor, reacting to obtain a final polymerization product, and performing post-treatment on the final polymerization product to obtain linear low density polyethylene powder;

[0011] (4) Mixing the linear low density polyethylene powder obtained in step (3) with polyvinyl acetal and an auxiliary agent, and extruding and pelletizing to obtain the low haze linear low density polyethylene resin.

[0012] Compared with the traditional single-reactor production method, the present invention innovatively adopts a mode of connecting three reactors in series, introducing propylene into the reaction system in the first and third reactors, and introducing butene into the reaction system in the second reactor, reducing the crystallinity of the polyethylene main chain, increasing the proportion of amorphous polyolefin, and improving the randomness of the polyolefin, thereby achieving the goal of reducing the haze of polyethylene; after synthesizing the polyethylene powder, by adding a high molecular weight polyvinyl acetal substance, using its compatibility with polyethylene and its high melting point characteristics, realizing some functions of it as a nucleating agent, increasing the crystallization sites, reducing the crystal size, and further reducing the haze of polyethylene, thereby obtaining a low haze linear low density polyethylene resin.

[0013] Preferably, the mass ratio of the ethylene, propylene and hydrogen in step (1) is (20-40):1:(5-20), 20-40 can be, for example, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, etc., 5-20 can be, for example, 5, 6, 8, 10, 12, 14, 16, 18, 20, etc., and preferably (30-40):1:(10-20).

[0014] Preferably, the catalyst system comprises a Ziegler-Natta catalyst system.

[0015] Preferably, the Ziegler-Natta catalyst system comprises a Ziegler-Natta catalyst and triethylaluminum.

[0016] Preferably, the mass ratio of ethylene to the Ziegler-Natta catalyst in step (1) is (8-12):1, such as 8:1, 9:1, 10:1, 11:1, 12:1, etc.

[0017] Preferably, the mass ratio of ethylene to triethylaluminum in step (1) is (8-12):1, such as 8:1, 9:1, 10:1, 11:1, 12:1, etc.

[0018] Preferably, the first reactor includes a vertical stirred tank reactor.

[0019] Preferably, the temperature of the reaction in step (1) is 50-65°C, such as 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, etc.

[0020] Preferably, the pressure of the reaction in step (1) is 0.3-0.44 MPa, such as 0.3 MPa, 0.31 MPa, 0.32 MPa, 0.33 MPa, 0.34 MPa, 0.35 MPa, 0.36 MPa, 0.37 MPa, 0.38 MPa, 0.39 MPa, 0.4 MPa, 0.41 MPa, 0.42 MPa, 0.43 MPa, 0.44 MPa, etc.

[0021] Preferably, the reaction time in step (1) is 0.3-0.8 h, such as 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.7 h, 0.8 h, etc.

[0022] Preferably, the mass ratio of ethylene, butene, and hydrogen in step (2) is (20-40):1:(5-10). 20-40 can be, for example, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, etc., and 5-10 can be, for example, 5, 6, 7, 8, 9, 10, etc. Preferably, it is (25-30):1:(5-10).

[0023] Preferably, the second reactor includes a vertical stirred tank reactor.

[0024] Preferably, the temperature of the reaction in step (2) is 70-85°C, such as 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, etc.

[0025] Preferably, the pressure of the reaction in step (2) is 0.3 to 0.43 MPa, such as 0.3 MPa, 0.31 MPa, 0.32 MPa, 0.33 MPa, 0.34 MPa, 0.35 MPa, 0.36 MPa, 0.37 MPa, 0.38 MPa, 0.39 MPa, 0.4 MPa, 0.41 MPa, 0.42 MPa, 0.43 MPa, etc.

[0026] Preferably, the time of the reaction in step (2) is 0.8 to 1.8 h, such as 0.8 h, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, etc.

[0027] Preferably, the mass ratio of ethylene, propylene, and hydrogen in step (3) is (20 to 40):1:(5 to 10). For 20 to 40, it can be, for example, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, etc.; for 5 to 10, it can be, for example, 5, 6, 7, 8, 9, 10, etc. Preferably, it is (30 to 35):1:(5 to 10).

[0028] Preferably, the third reactor includes a gas-phase fluidized bed reactor.

[0029] Preferably, the temperature of the reaction in step (3) is 70 to 85 °C, such as 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C, 80 °C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, etc.

[0030] Preferably, the pressure of the reaction in step (3) is 0.3 to 0.4 MPa, such as 0.3 MPa, 0.31 MPa, 0.32 MPa, 0.33 MPa, 0.34 MPa, 0.35 MPa, 0.36 MPa, 0.37 MPa, 0.38 MPa, 0.39 MPa, 0.4 MPa, etc.

[0031] Preferably, the time of the reaction in step (3) is 0.1 to 0.5 h, such as 0.1 h, 0.2 h, 0.3 h, 0.4 h, 0.5 h, etc.

[0032] Preferably, the post-treatment in step (3) includes degassing, steaming, and drying.

[0033] Preferably, the polyvinyl acetal in step (4) includes a polymer formed by the polycondensation reaction of polyvinyl alcohol with any one or at least two of butyraldehyde, valeraldehyde, and glutaraldehyde.

[0034] Preferably, the polyvinyl acetal in step (4) includes any one or a combination of at least two of polyvinyl butyral, polyvinyl valeral, or polyvinyl glutaral.

[0035] Preferably, the acetalization rate of the polyvinyl acetal described in step (4) is 60% - 90%, such as 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc., and preferably 60% - 80%.

[0036] Preferably, the dosage of the polyvinyl acetal described in step (4) is 2000 - 10000 ppm of the mass of the linear low density polyethylene powder, such as 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, etc.

[0037] Preferably, the dosage of the auxiliary agent described in step (4) is 400 - 4600 ppm of the mass of the linear low density polyethylene powder, such as 400 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 4600 ppm, etc.

[0038] Preferably, the temperature of the extrusion granulation described in step (4) is 170 - 240 °C, such as 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, etc.

[0039] Preferably, the auxiliary agent described in step (4) includes any one or a combination of at least two of a transparent nucleating agent, an antioxidant, an acid absorbent, or an antistatic agent.

[0040] Preferably, the transparent nucleating agent includes any one or a combination of at least two of an inorganic transparent nucleating agent, an aryl phosphate transparent nucleating agent, a sorbitol transparent nucleating agent, a rosin-like transparent nucleating agent, or a carboxylic acid metal salt transparent nucleating agent, and preferably sorbitol-based and carboxylic acid metal salt-based transparent nucleating agents.

[0041] For the above nucleating agents, the inorganic transparent nucleating agent is selected from talc, calcium carbonate, mica, kaolin, etc., and preferably talc or mica; the aryl phosphate transparent nucleating agent is selected from NA10, NA11, NA12, or NA21, etc.; the sorbitol transparent nucleating agent is selected from DBS, MDBS, DMDBS, 3988, or NX8000, etc., and preferably 3988 or NX8000; the rosin-like transparent nucleating agent is selected from dehydroabietic acid, rosin acid salt, rosin acid, or rosin amide, etc.; the dehydroabietic acid and its salt-based transparent nucleating agent is selected from KM1300, KM1500, or KM1600, etc.; the carboxylic acid metal salt transparent nucleating agent is selected from sodium benzoate, aluminum hydroxy p-tert-butylbenzoate, calcium hexahydrophthalate, and its homologues, etc.

[0042] Preferably, the dehydroabietate-based transparent nucleating agent includes a calcium salt-based nucleating agent.

[0043] Preferably, the antioxidant includes a phosphite antioxidant and / or a phenolic antioxidant.

[0044] Preferably, the antioxidant includes a blend of antioxidant 168 and antioxidant 1330, preferably a blend with a mass ratio of antioxidant 168 to antioxidant 1330 of 1:(1 - 2).

[0045] Preferably, the acid scavenger includes calcium stearate and / or zinc stearate.

[0046] Preferably, the antistatic agent includes octadecyl diglyceride.

[0047] Preferably, the diglyceride content of the octadecyl diglyceride is 40% - 60%, such as 40%, 45%, 50%, 55%, 60%, etc.

[0048] Preferably, the dosage of the transparent nucleating agent is 100 - 1000 ppm of the mass of the linear low-density polyethylene powder, such as 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, etc.

[0049] Preferably, the dosage of the antioxidant is 100 - 2000 ppm of the mass of the linear low-density polyethylene powder, such as 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, etc.

[0050] Preferably, the dosage of the acid scavenger is 100 - 1000 ppm of the mass of the linear low-density polyethylene powder, such as 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, etc.

[0051] Preferably, the dosage of the antistatic agent is 100 - 600 ppm of the mass of the linear low-density polyethylene powder, such as 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, etc.

[0052] As a preferred technical solution of the present invention, the preparation method of the low haze linear low density polyethylene resin comprises:

[0053] (1) Add ethylene, propylene, hydrogen and Ziegler-Natta catalyst system into the first reactor, and react at 50-65 °C and 0.3-0.44 MPa for 0.3-0.8 h to obtain the first-step polymerization product;

[0054] Among them, the mass ratio of ethylene, propylene and hydrogen is (20-40):1:(5-20);

[0055] (2) Add all of the first-step polymerization product obtained in step (1), ethylene, butene and hydrogen into the second reactor, and react at 70-85 °C and 0.3-0.43 MPa for 0.8-1.8 h to obtain the second-step polymerization product;

[0056] Among them, the mass ratio of ethylene, butene and hydrogen is (20-40):1:(5-10);

[0057] (3) Add all of the second-step polymerization product obtained in step (2), ethylene, propylene and hydrogen into the third reactor, and react at 70-85 °C and 0.3-0.4 MPa for 0.1-0.5 h to obtain the final polymerization product. Carry out degassing, steam distillation and drying on the final polymerization product to obtain linear low density polyethylene powder;

[0058] Among them, the mass ratio of ethylene, propylene and hydrogen is (20-40):1:(5-10);

[0059] (4) Mix the linear low density polyethylene powder obtained in step (3) with polyvinyl acetal and additives, and extrude and pelletize at 170-240 °C to obtain the low haze linear low density polyethylene resin;

[0060] Among them, the dosage of polyvinyl acetal is 2000-10000 ppm of the mass of the linear low density polyethylene powder, and the dosage of the additive is 400-4600 ppm of the mass of the linear low density polyethylene powder.

[0061] As a preferred technical solution of the present invention, the conditions of the first-step reaction are medium reaction temperature and low residence time (i.e., reaction time), which improves the hydrogen regulation performance of the catalyst, quickly meets the high melt index requirement in the first-step reaction, and then carries out the second-step and third-step reactions in sequence. A three-step synthesis hydrogen regulation method is adopted. By adjusting the ratios of ethylene, propylene, butene and hydrogen in the three reactors, the purpose of preparing low haze polyolefin powder is achieved. The polyolefin product prepared by the method provided by the present invention has low haze, good mechanical properties and good processing properties.

[0062] In a second aspect, the present invention provides a low haze linear low density polyethylene resin, which is prepared by the preparation method described in the first aspect.

[0063] Preferably, the haze of the low haze linear low density polyethylene resin is 6% - 8%.

[0064] In a third aspect, the present invention provides an application of the low haze linear low density polyethylene resin described in the second aspect in greenhouse films.

[0065] Compared with the prior art, the present invention has at least the following beneficial effects:

[0066] Compared with the traditional single reactor production method, the present invention innovatively adopts a way of connecting three reactors in series, introducing propylene into the reaction system in the first and third reactors, and introducing butene into the reaction system in the second reactor, reducing the crystallinity of the polyethylene main chain, increasing the proportion of amorphous polyolefin, and improving the randomness of polyolefin, so as to achieve the goal of reducing the haze of polyethylene; further, after synthesizing the polyethylene powder, by adding polyvinyl acetal substances to the powder, the main chain of this substance has a similar structure to polyethylene, improving its compatibility with polyethylene and its dispersion in polyethylene; the acetal on its side chain can form a network structure during the high-temperature heating process, forming more crystallization sites, further reducing the polyethylene spherulite size, and thus generating a lower haze. Specific Embodiments

[0067] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0068] The XY-S catalyst used in each embodiment and comparative example of the present invention is purchased from Yingkou Xiangyang Catalyst Company.

[0069] Other raw materials, unless otherwise specified, are obtained through commercial channels in the market.

[0070] Example 1

[0071] In this embodiment, a preparation method of a low haze linear low density polyethylene resin is provided, and the preparation method includes:

[0072] (1) Mix ethylene, propylene, hydrogen, XY-S catalyst, and triethylaluminum and add them into the first reactor (vertical stirred tank reactor), and react for 0.5 h under the conditions of a reaction temperature of 50 °C and a reaction pressure of 0.42 MPa to obtain a first-step polymerization product;

[0073] Among them, the ethylene feed rate is 4.5 kg / h, the propylene feed rate is 0.225 kg / h, the hydrogen feed rate is 0.2 kg / h, the addition amount of XY-S catalyst is 0.45 kg / h, and the addition amount of triethylaluminum is 0.5 kg / h;

[0074] (2) Mix all the first-stage polymerization products, ethylene, butene, and hydrogen obtained in step (1) and add them to the second reactor (vertical stirred tank reactor), and react for 1.2 h under the conditions of a reaction temperature of 70 °C and a reaction pressure of 0.38 MPa to obtain the second-stage polymerization products;

[0075] Among them, the ethylene feed rate is 2 kg / h, the butene feed rate is 0.12 kg / h, and the hydrogen feed rate is 0.2 kg / h;

[0076] (3) Mix all the second-stage polymerization products, ethylene, propylene, and hydrogen obtained in step (2) and add them to the third reactor (gas-phase fluidized bed reactor), and react for 0.3 h under the conditions of a reaction temperature of 70 °C and a reaction pressure of 0.35 MPa to obtain the final polymerization products. Carry out degassing, steam distillation, and drying treatments on the final polymerization products to obtain linear low-density polyethylene powder;

[0077] Among them, the ethylene feed rate is 3 kg / h, the propylene feed rate is 0.07 kg / h, and the hydrogen feed rate is 0.3 kg / h;

[0078] (4) Mix the linear low-density polyethylene powder obtained in step (3) with polyvinyl butyral (grade PVB-7), nucleating agent (3988), antioxidant (1330:168 = 1:1), antistatic agent (octadecyl glycerol diester), and calcium stearate evenly, and extrude and pelletize at 210 °C to obtain the low haze linear low-density polyethylene resin;

[0079] Among them, based on the mass of the linear low-density polyethylene powder being 100%, the dosage of polyvinyl butyral is 2000 ppm, the dosage of the nucleating agent is 1000 ppm, the dosage of the antioxidant is 1500 ppm, the dosage of the antistatic agent is 500 ppm, and the dosage of calcium stearate is 200 ppm.

[0080] Example 2-14

[0081] The difference between Example 2-14 and Example 1 is that the raw material dosages and reaction conditions are changed. The summary of the raw material dosages and reaction conditions of Examples 1-14 is shown in Tables 1 and 2.

[0082] For the content not summarized in Tables 1 and 2 for Example 2-14, it is the same as Example 1.

[0083] Table 1

[0084]

[0085]

[0086] Table 2

[0087]

[0088]

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 14 is only that the dosage of polyvinyl butyral in step (4) is 0 ppm, that is, no polyvinyl butyral is added.

[0091] Comparative Example 2

[0092] This comparative example uses the traditional one-step process to prepare polyethylene resin, as follows:

[0093] (1) Ethylene, butene, hydrogen, XY-S catalyst, and triethylaluminum are mixed and added to a vertical stirred tank reactor, and the polymerization reaction is carried out at a reaction temperature of 60 °C and a reaction pressure of 0.42 MPa for 1.5 h to complete the polymerization reaction, obtaining a polyolefin product. The product is degassed, steam distilled, and dried to obtain polyethylene powder.

[0094] Among them, the ethylene feed rate is 4.5 kg / h, the butene feed rate is 0.12 kg / h, the hydrogen feed rate is 0.2 kg / h, the addition amount of XY-S catalyst is 0.45 kg / h, and the addition amount of triethylaluminum is 0.5 kg / h.

[0095] (2) The polyethylene powder obtained in step (1) is mixed evenly with polyvinyl butyral (grade PVB-7), nucleating agent (3988), antioxidant (1330:168 = 1:1), antistatic agent (octadecyl glycerol diester), and calcium stearate, and pelletized by extrusion at 210 °C to obtain the polyethylene resin;

[0096] Among them, based on the mass of linear low-density polyethylene powder being 100%, the dosage of polyvinyl butyral is 2000 ppm, the dosage of nucleating agent is 1000 ppm, the dosage of antioxidant is 1500 ppm, the dosage of antistatic agent is 500 ppm, and the dosage of calcium stearate is 200 ppm.

[0097] The polyethylene resins prepared in the examples and comparative examples are subjected to blown film forming (using a LE-45-30C blown film machine from LAB TECH, Germany), and the haze is tested (the haze is tested according to GB / T 2410-2008). The test results are shown in Table 3:

[0098] Table 3

[0099]

[0100] As can be seen from Table 3, the linear low density polyethylene resins provided in the embodiments of the present invention all have relatively low haze values (6.32%-7.89%).

[0101] Compared with Example 14, the haze of the linear low density polyethylene resin provided in Comparative Example 1 increased significantly; compared with the examples, the haze of the polyethylene resin provided in Comparative Example 2 was significantly higher.

[0102] The applicant declares that the present invention uses the above embodiments to illustrate the low haze linear low density polyethylene resin and its preparation method and application of the present invention, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a low haze linear low density polyethylene resin, characterized in that, The preparation method includes: (1) Adding ethylene, propylene, hydrogen, and a catalyst system into a first reactor, reacting to obtain a first-stage polymerization product; (2) Adding the first-stage polymerization product obtained in step (1), ethylene, butene, and hydrogen into a second reactor, reacting to obtain a second-stage polymerization product; (3) Adding the second-stage polymerization product obtained in step (2), ethylene, propylene, and hydrogen into a third reactor, reacting to obtain a final polymerization product, and performing post-treatment on the final polymerization product to obtain linear low-density polyethylene powder; (4) Mixing the linear low-density polyethylene powder obtained in step (3) with polyvinyl acetal and an auxiliary agent, and extruding and pelletizing to obtain the low haze linear low-density polyethylene resin.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the ethylene, propylene, and hydrogen is (20 - 40):1:(5 - 20), preferably (30 - 40):1:(10 - 20); Preferably, the catalyst system includes a Ziegler-Natta catalyst system; Preferably, the first reactor includes a vertical stirred tank reactor; Preferably, the reaction temperature in step (1) is 50 - 65°C; Preferably, the reaction pressure in step (1) is 0.3 - 0.44 MPa; Preferably, the reaction time in step (1) is 0.3 - 0.8 h.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the mass ratio of the ethylene, butene, and hydrogen is (20 - 40):1:(5 - 10), preferably (25 - 30):1:(5 - 10); Preferably, the second reactor includes a vertical stirred tank reactor; Preferably, the reaction temperature in step (2) is 70 - 85°C; Preferably, the reaction pressure in step (2) is 0.3 - 0.43 MPa; Preferably, the reaction time in step (2) is 0.8 - 1.8 h.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step (3), the mass ratio of the ethylene, propylene, and hydrogen is (20 - 40):1:(5 - 10), preferably (30 - 35):1:(5 - 10); Preferably, the third reactor includes a gas-phase fluidized bed reactor; Preferably, the reaction temperature in step (3) is 70 - 85°C; Preferably, the reaction pressure in step (3) is 0.3 - 0.4 MPa; Preferably, the reaction time in step (3) is 0.1 - 0.5 h; Preferably, the post-treatment in step (3) includes degassing, steam distillation, and drying.

5. The preparation method according to any one of claims 1-4, characterized in that, The polyvinyl acetal in step (4) includes a polymer formed by polycondensation reaction of polyvinyl alcohol with any one or at least two of butyraldehyde, valeraldehyde, and glutaraldehyde; Preferably, the acetalization rate of the polyvinyl acetal in step (4) is 60% - 90%; Preferably, the dosage of the polyvinyl acetal in step (4) is 2000 - 10000 ppm of the mass of the linear low-density polyethylene powder; Preferably, the dosage of the auxiliary agent in step (4) is 400 - 4600 ppm of the mass of the linear low-density polyethylene powder; Preferably, the temperature of the extrusion and pelletizing in step (4) is 170 - 240°C.

6. The preparation method according to any one of claims 1-5, characterized in that, The auxiliary agent described in step (4) includes any one or a combination of at least two of a transparent nucleating agent, an antioxidant, an acid absorbent, or an antistatic agent; Preferably, the transparent nucleating agent includes any one or a combination of at least two of an inorganic transparent nucleating agent, an aryl phosphate transparent nucleating agent, a sorbitol transparent nucleating agent, a rosin-like transparent nucleating agent, or a carboxylic acid metal salt transparent nucleating agent, preferably a sorbitol type and a carboxylic acid metal salt type transparent nucleating agent; Preferably, the dehydroabietate type transparent nucleating agent includes a calcium salt type nucleating agent; Preferably, the antioxidant includes a phosphite antioxidant and / or a phenolic antioxidant; Preferably, the acid absorbent includes calcium stearate and / or zinc stearate; Preferably, the antistatic agent includes octadecyl diglyceride; Preferably, the diester content of the octadecyl diglyceride is 40% - 60%; 7. The preparation method according to claim 6, characterized in that, The dosage of the transparent nucleating agent is 100 - 1000 ppm of the mass of the linear low-density polyethylene powder; Preferably, the dosage of the antioxidant is 100 - 2000 ppm of the mass of the linear low-density polyethylene powder; Preferably, the dosage of the acid absorbent is 100 - 1000 ppm of the mass of the linear low-density polyethylene powder; Preferably, the dosage of the antistatic agent is 100 - 600 ppm of the mass of the linear low-density polyethylene powder.

8. A preparation method according to any one of claims 1-7, characterized in that, The preparation method includes: (1) Adding ethylene, propylene, hydrogen, and a Ziegler-Natta catalyst system to a first reactor, reacting at 50 - 65 °C and 0.3 - 0.44 MPa for 0.3 - 0.8 h to obtain a first-stage polymerization product; Among them, the mass ratio of ethylene, propylene, and hydrogen is (20 - 40):1:(5 - 20); (2) Adding all of the first-stage polymerization product obtained in step (1), ethylene, butene, and hydrogen to a second reactor, reacting at 70 - 85 °C and 0.3 - 0.43 MPa for 0.8 - 1.8 h to obtain a second-stage polymerization product; Among them, the mass ratio of ethylene, butene, and hydrogen is (20 - 40):1:(5 - 10); (3) Adding all of the second-stage polymerization product obtained in step (2), ethylene, propylene, and hydrogen to a third reactor, reacting at 70 - 85 °C and 0.3 - 0.4 MPa for 0.1 - 0.5 h to obtain a final polymerization product, and performing degassing, steam distillation, and drying on the final polymerization product to obtain linear low-density polyethylene powder; Among them, the mass ratio of ethylene, propylene, and hydrogen is (20 - 40):1:(5 - 10); (4) Mixing the linear low-density polyethylene powder obtained in step (3) with polyvinyl acetal and an auxiliary agent, and extruding and pelletizing at 170 - 240 °C to obtain the low haze linear low-density polyethylene resin; Among them, the dosage of polyvinyl acetal is 2000 - 10000 ppm of the mass of the linear low-density polyethylene powder, and the dosage of the auxiliary agent is 400 - 4600 ppm of the mass of the linear low-density polyethylene powder.

9. A low haze linear low density polyethylene resin, characterized in that, The low haze linear low-density polyethylene resin is prepared by the preparation method described in any one of claims 1 - 8.

10. Use of the low haze linear low density polyethylene resin as described in claim 9 in a greenhouse film.

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