Melt blown polyethylene resin and method for making same

Abstract

The application discloses a preparation method of melt-blown polyethylene resin, which comprises the following steps: adding a metallocene catalyst, an activator, ethylene and a comonomer, and a molecular weight regulator into a polymerization reactor to perform a polymerization reaction, so as to obtain a polyethylene copolymer; and performing degassing and granulation on the polyethylene copolymer, so as to obtain the melt-blown polyethylene resin; the metallocene catalyst comprises an inorganic carrier, polyethylene polyol and a cocatalyst methylaluminoxane (MAO) adsorbed on the inorganic carrier, and a metallocene compound combined with the MAO. In the preparation method of the melt-blown polyethylene resin, the metallocene catalyst is used, the metallocene catalyst can catalyze the ethylene polymerization reaction at a high temperature, has high catalytic activity, and the polymerization reaction is not sticky in the kettle, and the ultrahigh melt flow rate polyethylene can be prepared through hydrogen regulation in the polymerization process.

Description

Technical Field

[0001] This invention belongs to the field of meltblown polyethylene technology, specifically relating to a technique for preparing meltblown polyethylene using a metallocene-supported catalyst containing polyethylene polyol. Background Technology

[0002] Metallocene catalysts represent another major breakthrough following the Ziegler-Natta catalyst. Since Professor Kaminsky of the University of Hamburg, Germany, first discovered the high activity of the metallocene / MAO catalyst system for olefin polymerization in the early 1980s, this catalytic system has been a hot topic of research for scientists and is currently gradually replacing Zn catalysts. Metallocene compounds offer many advantages as catalysts for olefin polymerization. They exhibit higher activity, and the polymers produced have better homogeneity, tensile and tear strength, and impact resistance. Furthermore, the resulting polymers have uniform comonomer distribution, low soluble content, and good transparency. However, the polymers produced by directly using these metallocene compounds for olefin polymerization often have poor morphology, severe reactant adhesion to the reactor, and difficult product handling. These problems limit the industrial application of metallocene catalysts. A solution is to load metallocene catalysts onto inert porous particulate supports. Common supports include inorganic supports such as silica gel, magnesium chloride, alumina, clay, and molecular sieves, as well as polymer supports and inorganic / organic composite supports.

[0003] Metallocene catalysts, compared to traditional Ziegler-Natta catalysts, exhibit better hydrogen regulation performance and are more effective in preparing low-molecular-weight, high-melt-flow-rate polyolefins. Meltblown polypropylene can be used to produce ultrafine fibers, which are already widely used in masks and protective clothing. Polyethylene fibers, compared to polypropylene fibers, have better flexibility and thermal conductivity, making them more comfortable for use in masks and protective clothing. However, to date, there is no suitable preparation method for meltblown polyethylene resin, and no commercially available meltblown polyethylene resin products exist.

[0004] Meltblown polyethylene processing requires polyethylene with ultra-high melt flow rates. Current polymerization processes using Ziegler-Natta catalysts to produce ultra-high melt flow rate polyethylene require the addition of large amounts of hydrogen during polymerization, employing a hydrogen-modified method. However, large amounts of hydrogen lead to reduced catalyst activity and increased fine powder content in the polymer. Therefore, to produce ultra-high melt flow rate polyethylene products, it is essential to develop highly hydrogen-sensitive catalyst systems and corresponding polymerization processes.

[0005] Chinese Patent 201610835700.1 discloses a supported metallocene catalyst, its preparation method and application, and a method for preparing methyl acrylate. The support is prepared using the following method: (1) providing a mesoporous molecular sieve material with a cubic cage-like pore structure or preparing a filter cake of a mesoporous molecular sieve material with a cubic cage-like pore structure, as component a; (2) providing silica gel or preparing a filter cake of silica gel, as component b; (3) mixing component a and component b and performing a first ball milling, mixing the resulting first ball mill slurry with water to form a paste, then performing a second ball milling to obtain a second ball mill slurry, spray-drying the second ball mill slurry, and then screening it using cyclone separation technology; the support is heated at 300-900℃ for 7-10 hours to directly support the metallocene. However, this supported metallocene catalyst is not applicable to olefin polymerization in the esterification reaction of acrylic acid and methanol.

[0006] Chinese Patent 201710166709.2 discloses a supported metallocene catalyst, its preparation method and application, and a method for preparing methyl acrylate. However, the application of this supported metallocene catalyst in the esterification reaction of acrylic acid and methanol cannot be used for olefin polymerization.

[0007] Chinese Patent 201710312252.1 discloses a supported metallocene catalyst, its preparation method and application, and a method for preparing methyl acrylate. The support is prepared using the following method: (1) water glass, polyol, and inorganic acid are mixed and contacted, and the resulting mixture is filtered and / or washed using a ceramic membrane filter to obtain a silica gel filter cake; (2) the silica gel filter cake obtained in step (1) is ball-milled and then spray-dried to obtain a silica gel support; the support is heated at 300-900℃ for 7-10 hours to directly support the metallocene. However, this supported metallocene catalyst is only suitable for the esterification reaction of acrylic acid and methanol and cannot be used for olefin polymerization.

[0008] Chinese Patent 201710312720.5 discloses a supported metallocene catalyst, its preparation method and application, and a method for preparing methyl acrylate. However, the application of this supported metallocene catalyst in the esterification reaction of acrylic acid and methanol cannot be used for olefin polymerization.

[0009] Chinese Patent 99801772.8 discloses a polyethylene nonwoven fabric and a nonwoven laminate made therefrom. The technical description is as follows: A polyethylene (A) with a weight-average molecular weight of 21,000-45,000 and a melt flow rate of 15-250 g / 10 min measured according to ASTM D1238 at 190°C and a load of 2.16 kg is prepared by melt-blowing. The weight ratio of polyethylene (A) to polyethylene wax (B) is 30 / 70-70 / 30. The fiber fineness of the polyethylene nonwoven fabric is below 5 μm. However, by mixing high melt flow rate polyethylene and polyethylene wax, a resin with lower viscosity is obtained for melt-blowing processing. The preparation method of high melt flow rate polyethylene is not clearly defined.

[0010] Generally, the metallocene supported process uses MAO to treat silica gel and then chemically adsorbs metallocene compounds. The supported catalyst prepared by this process has a low content of metallocene compounds and low catalytic activity. Summary of the Invention

[0011] The purpose of this invention is to provide a meltblown polyethylene resin and its preparation method. The meltblown polyethylene resin is prepared using a metallocene catalyst, which can catalyze the polymerization reaction of ethylene at a high temperature, has high catalytic activity, and does not stick to the reactor during the polymerization reaction. Ultra-high melt flow rate polyethylene can be prepared by hydrogen adjustment during the polymerization process.

[0012] To achieve the above objectives, the present invention provides a method for preparing meltblown polyethylene resin, the method comprising the following steps: adding a metallocene catalyst and activator, ethylene and comonomer, and a molecular weight regulator to a polymerization reactor to carry out a polymerization reaction to obtain a polyethylene copolymer; and degassing and granulating the polyethylene copolymer to obtain meltblown polyethylene resin.

[0013] The metallocene catalyst comprises: an inorganic support, a polyethylene polyol adsorbed on the inorganic support, a co-catalyst methylaluminoxane (MAO), and a metallocene compound combined with MAO.

[0014] In the method for preparing meltblown polyethylene resin of the present invention, the inorganic support in the metallocene catalyst accounts for 70%-90% by weight.

[0015] In the method for preparing meltblown polyethylene resin of the present invention, the polyethylene polyol in the metallocene catalyst accounts for 0.05-1.5% by weight.

[0016] In the method for preparing meltblown polyethylene resin of the present invention, the metallocene catalyst contains MAO in a weight ratio of 10%-25%.

[0017] In the method for preparing meltblown polyethylene resin of the present invention, the metallocene catalyst contains a metallocene compound comprising 1.3%-4.2% by weight.

[0018] In the method for preparing meltblown polyethylene resin of the present invention, the inorganic support in the metallocene catalyst can be at least one selected from silica gel, alumina, and molecular sieves, preferably silica gel. The particle size range of the inorganic support is 15-120 μm.

[0019] In the method for preparing meltblown polyethylene resin of the present invention, the metallocene catalyst contains a polyethylene polyol with the general formula -(CH2CH2)n-(CH2CHOH)m-, a molecular weight of 1000-20000 g / mol, wherein the molar content of -OH is 2-30%, n is an integer greater than or equal to 1, and m is an integer greater than or equal to 1.

[0020] In the method for preparing meltblown polyethylene resin of the present invention, the metallocene catalyst contains a substituted dicyclopentadiene compound of a Group 4 metal, having the following structure:

[0021]

[0022] R1 to R5 may be the same or different, and are independently selected from H or C1-C4 alkyl groups; M is titanium, zirconium or hafnium.

[0023] Typically, the metallocene compound is at least one of titanium dichlorodicyclopentadiene, zirconium dichlorodicyclopentadiene, hafnium dichlorodicyclopentadiene, di(n-butylcendichloride), and di(n-propylcendichloride).

[0024] The metallocene catalyst of the present invention can be prepared by the following steps:

[0025] (1) The inorganic carrier is subjected to high-temperature treatment under nitrogen protection;

[0026] (2) The inorganic carrier after high temperature treatment in step (1) is reacted with polyethylene polyol and MAO under solvent stirring conditions, and then washed, filtered and dried to obtain a loaded carrier loaded with polyethylene polyol and MAO.

[0027] (3) The supporting support and homogeneous metallocene catalyst from step (2) are reacted and loaded in a solvent under stirring, and then washed, filtered and dried to obtain the metallocene catalyst.

[0028] In step (1), the high-temperature treatment temperature is 400℃-600℃ and the treatment time is 4-6h.

[0029] In step (2), the reaction temperature is 20℃-120℃ and the time is 2-4h.

[0030] In step (3), the temperature of the reaction load is 40-80℃ and the time is 2-4h.

[0031] The method for preparing meltblown polyethylene resin of the present invention includes an activator that is at least one of alkylaluminum and methylaluminoxane; wherein the molar ratio of aluminum in the activator to the metal in the metallocene catalyst is 50-2000.

[0032] The method for preparing meltblown polyethylene resin of the present invention, wherein the comonomer is at least one of propylene, butene, and hexene; and the comonomer accounts for less than 20% of the total molar proportion of polymeric monomers (ethylene plus comonomer).

[0033] The method for preparing meltblown polyethylene resin of the present invention uses hydrogen as a molecular weight regulator, wherein the molar proportion of hydrogen to ethylene does not exceed 20 mol%.

[0034] The method for preparing meltblown polyethylene resin of the present invention wherein the polymerization reaction temperature is 70-100℃, preferably 70-90℃, the reaction time is 30-150min, and the reaction pressure is 0.5-2.0MPa.

[0035] The method for preparing meltblown polyethylene resin of the present invention includes a granulation process in which antioxidants and other components may be added as needed.

[0036] The present invention also provides a meltblown polyethylene resin, wherein the melt flow rate of the meltblown polyethylene resin is 150-750 g / 10 min and the melting point is 115-135 °C.

[0037] When the metallocene catalyst of the present invention for meltblown polyethylene is used for ethylene polymerization, the melt flow rate of polyethylene can reach up to 800 g / 10 min when the amount of hydrogen added is less than 10% of the ethylene content.

[0038] The method for preparing meltblown polyethylene resin of the present invention uses a metallocene catalyst, which has the characteristics of high catalyst activity and high catalyst hydrogen regulation sensitivity. The meltblown polyethylene resin obtained by the preparation method of the present invention has the characteristics of adjustable melt flow rate and non-stick polymer.

[0039] In the preparation method of this invention, polyethylene polyol is introduced as a modifier, allowing the inorganic support to load more MAO, and subsequently more metallocene compounds, thus improving catalytic activity. In the preparation method of this invention, the preparation temperature is close to the polymerization temperature, and the metallocene catalyst is resistant to desorption during polymerization, preventing it from reverting to a homogeneous catalyst due to detachment from the inorganic support. In the preparation method of this invention, hydrogen adjustment allows for a wide range of controllable regulation of the polymer melt flow rate, resulting in polyethylene with ultra-high melt flow rate. Polyethylene with ultra-high melt flow rate can be used for meltblown processing to prepare meltblown fibers. In the preparation method of this invention, adding a small amount of hydrogen is sufficient to prepare polyethylene with ultra-high melt flow rate. Detailed Implementation

[0040] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0041] Source of raw materials or equipment:

[0042] Toluene: Analytical grade, produced by Beijing Chemical Industry, dehydrated and filtered through 3A molecular sieve, with a water content of less than 10 ppm;

[0043] n-Hexane: Analytical grade, produced by Beijing Chemical Industry, dehydrated and filtered through 3A molecular sieve, with a water content of less than 10 ppm;

[0044] Ethylene: Polymer grade, supplied by Beijing Huatong Precision Gas & Chemical Co., Ltd.

[0045] Propylene: Polymer grade, supplied by Beijing Huatong Precision Gas Chemical Co., Ltd.

[0046] 1-Hexene: 99%, Aladdin Chemical Reagents Website;

[0047] Hydrogen: 99.999%, Beijing Huatong Precision Gas & Chemical Co., Ltd.

[0048] Polyethylene polyol: Industrial grade, Kuraray Corporation, Japan;

[0049] Methylaluminoxane (MAO): 1.5M toluene solution, manufactured by Arbemarle;

[0050] SiO2 (955 / 2408) silicone: Imported from the USA;

[0051] Alumina: 99.9%, Beijing Innocare Technology Co., Ltd.;

[0052] Bis(n-butylcyclopentadienyl)zirconium dichloride: laboratory synthesis.

[0053] Evaluation and analysis methods:

[0054] Polyethylene thermal properties testing: Performed on a TA Q2000 differential scanning calorimeter (DSC) from the USA. Sample preparation: Weigh approximately 2-5 mg of sample using an electronic balance. Under nitrogen protection, heat the sample from 10°C to 200°C at a rate of 10°C / min, hold at 200°C for 5 min, then cool to 30°C at a rate of 10°C / min, hold at 30°C for 5 min, and finally heat to 200°C at a rate of 10°C / min. The results of the melting and crystallization processes are then derived.

[0055] Melt flow rate (MFR) test: The test was conducted using a melt flow rate tester from Jinjian Company. The experimental conditions were 2.16 kg and 190 °C.

[0056] Example 1:

[0057] Take 20g of 955 silica gel (90% of the particles have a particle size range of 20-70 micrometers), calcine it at 500℃ for 4 hours in a tube furnace under N2 atmosphere, cool it under nitrogen atmosphere, transfer it to a desiccator, dry it and store it separately under nitrogen.

[0058] 2g of heat-treated silica gel was mixed with 20mL of MAO toluene solution (10wt%) and 0.2g of polyethylene polyol (molecular weight 4500g / mol) with 3.5mol% hydroxyl content. The mixture was magnetically stirred at 500rpm and refluxed at room temperature for 3h. After cooling to room temperature, excess MAO was washed with dehydrated toluene at a ratio of 10 (1g silica gel to 10g toluene) twice. Excess toluene was then washed with dehydrated n-hexane at a ratio of 10 (1g silica gel to 10g n-hexane) twice. The mixture was then vacuum dried at room temperature for 4h to obtain MAO-supported silica gel.

[0059] Take 80 mg of metallocene catalyst monomer (bis(n-butylcyclopentadienyl)zirconium dichloride) at a ratio of 4% (1 g silica gel 40 mg metallocene monomer), mix it with 20 mL of toluene at 80 °C for 2 h, and stir magnetically at 500 rpm to obtain solution B;

[0060] 2g of loaded silica gel and solution B were thoroughly mixed at 80°C under a nitrogen atmosphere for 3 hours, and then cooled to room temperature.

[0061] Excess catalyst monomer was washed twice with dehydrated toluene at a ratio of 10 (1g silica gel to 10g toluene). Then, excess toluene was washed twice with dehydrated n-hexane at a ratio of 10 (1g silica gel to 10g n-hexane). The mixture was then dried under vacuum at room temperature for 4 hours to obtain the supported metallocene catalyst SMC-1.

[0062] Example 2:

[0063] Take 20g of type 2408 silica gel (90% of the particles have a particle size range of 30-70μm), calcine it at 500℃ for 4h in a tube furnace under N2 atmosphere, cool it under nitrogen atmosphere, transfer it to a desiccator, dry it and store it separately under nitrogen.

[0064] 1 g of heat-treated silica gel was mixed with 20 mL of MAO toluene solution (10 wt%) and 0.15 g of polyethylene polyol (molecular weight 5000 g / mol) with 6 mol% hydroxyl content. The mixture was magnetically stirred at 500 rpm and refluxed at 50 °C for 4 h. After cooling to room temperature, excess MAO was washed with dehydrated toluene at a ratio of 10 (1 g silica gel 10 g toluene) twice. Excess toluene was then washed with dehydrated n-hexane at a ratio of 10 (1 g silica gel 10 g n-hexane) twice. The mixture was then vacuum dried at room temperature for 4 h to obtain MAO-supported silica gel sMAO.

[0065] Take 40 mg of metallocene catalyst monomer (bis(n-butylcyclopentadienyl)zirconium dichloride) at a ratio of 4% (1 g silica gel 40 mg metallocene monomer), and dissolve and mix it with 20 mL of toluene at 50 °C and 500 rpm with magnetic stirring to obtain solution B;

[0066] sMAO and B were magnetically stirred at 500 rpm in a N2 atmosphere at 50°C for 4 hours to ensure thorough mixing, and then cooled to room temperature.

[0067] Excess catalyst monomer was washed twice with dehydrated toluene at a ratio of 10 (1g silica gel to 10g toluene). Then, excess toluene was washed twice with dehydrated n-hexane at a ratio of 10 (1g silica gel to 10g n-hexane). The mixture was then vacuum dried at room temperature for 4 hours to obtain the supported metallocene catalyst SMC-2.

[0068] Comparative Example 3:

[0069] Take 20g of alumina (specific surface area 300m2 / g), calcine it at 500℃ for 4h in a tube furnace under N2 atmosphere, cool it under nitrogen atmosphere, transfer it to a desiccator, dry it and store it separately under nitrogen.

[0070] Take 1g of heat-treated alumina and mix it with 20mL of MAO toluene solution (10wt%). Stir magnetically at 500rpm and reflux at 50℃ for 4h. Cool to room temperature and wash the excess MAO with dehydrated toluene at a ratio of 10 (1g alumina to 10g toluene). Wash twice consecutively. Then wash the excess toluene with dehydrated n-hexane at a ratio of 10 (1g alumina to 10g n-hexane). Wash twice consecutively. Vacuum dry at room temperature for 4h to obtain MAO-supported silica gel sMAO.

[0071] Take 40 mg of metallocene catalyst monomer (bis(n-butylcyclopentadienyl)zirconia) at a ratio of 4% (1 g alumina 40 mg metallocene monomer), and dissolve and mix it with 20 mL of toluene at 500 rpm under magnetic stirring at 50 °C to obtain solution B;

[0072] sMAO and B were magnetically stirred at 500 rpm in a N2 atmosphere at 50°C for 4 hours to ensure thorough mixing, and then cooled to room temperature.

[0073] Excess catalyst monomer was washed twice with dehydrated toluene at a ratio of 10 (1g alumina to 10g toluene). Then, excess toluene was washed twice with dehydrated n-hexane at a ratio of 10 (1g alumina to 10g n-hexane). The mixture was then vacuum dried at room temperature for 4 hours to obtain the supported metallocene catalyst SMC-3.

[0074] Example 4:

[0075] Take 20g of aluminum oxide (specific surface area 350m²) 2 / g), calcined at 500℃ for 4h in a tube furnace under N2 atmosphere, cooled under nitrogen atmosphere, transferred to a desiccator, dried and stored separately under nitrogen;

[0076] Take 1g of heat-treated alumina and mix it with 20mL of MAO toluene solution (10wt%) and 0.1g of polyethylene polyol with 7% hydroxyl content (molecular weight 3200g / mol). Stir magnetically at 500rpm and reflux at 50℃ for 4h. Cool to room temperature and wash the excess MAO with dehydrated toluene at a ratio of 10 (1g alumina 10g toluene). Wash twice consecutively. Then wash the excess toluene with dehydrated n-hexane at a ratio of 10 (1g alumina 10g n-hexane). Wash twice consecutively. Vacuum dry at room temperature for 4h to obtain MAO-supported silica gel sMAO.

[0077] Take 40 mg of metallocene catalyst monomer (bis(n-butylcyclopentadienyl)zirconia) at a ratio of 4% (1 g alumina 40 mg metallocene monomer), and dissolve and mix it with 20 mL of toluene at 500 rpm under magnetic stirring at 50 °C to obtain solution B;

[0078] sMAO and B were magnetically stirred at 500 rpm in a N2 atmosphere at 50°C for 4 hours to ensure thorough mixing, and then cooled to room temperature.

[0079] Excess catalyst monomer was washed twice with dehydrated toluene at a ratio of 10 (1g alumina to 10g toluene). Then, excess toluene was washed twice with dehydrated n-hexane at a ratio of 10 (1g alumina to 10g n-hexane). The mixture was then vacuum dried at room temperature for 4 hours to obtain the supported metallocene catalyst SMC-4.

[0080] Comparative Example 5:

[0081] Weigh 80 mg of catalyst (SMC-3) into a catalyst tube under nitrogen protection.

[0082] Add 250 mL of n-hexane to a 1 L glass reactor, add 5 mL of MAO toluene solution (1.5 mol / L), stir mechanically at 500 rpm, and heat to 90 °C.

[0083] A catalyst was added, a certain amount of hydrogen gas was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 0.94%, and polymerization was carried out at 90℃ with mechanical stirring at 500 rpm for 1 hour.

[0084] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0085] The resulting polymer had a melting point of 134.9℃ and a melt flow rate of 130 g / 10 min (190℃ / 2.16 kg).

[0086] Example 6:

[0087] Weigh 80 mg of catalyst (SMC-1) into a catalyst tube under nitrogen protection.

[0088] Add 250 mL of n-hexane to a 1 L glass reactor, add 5 mL of MAO toluene solution (1.5 mol / L), stir mechanically at 500 rpm, and heat to 90 °C.

[0089] A catalyst was added, a certain amount of hydrogen gas was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 0.94%, and polymerization was carried out at 90℃ with mechanical stirring at 500 rpm for 1 hour.

[0090] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0091] The resulting polymer had a melting point of 129.5℃ and a melt flow rate of 150 g / 10 min (190℃ / 2.16 kg).

[0092] Example 7:

[0093] Weigh 80 mg of catalyst (SMC-2) into a catalyst tube under nitrogen protection.

[0094] Add 250 mL of n-hexane to a 1 L glass reactor, add 5 mL of MAO toluene solution (1.5 mol / L), stir mechanically at 500 rpm, and heat to 90 °C.

[0095] A catalyst was added, a certain amount of hydrogen gas was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 0.94%, and polymerization was carried out at 90℃ with mechanical stirring at 500 rpm for 1 hour.

[0096] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0097] The resulting polymer had a melting point of 126.4℃ and a melt flow rate of 210 g / 10 min (190℃ / 2.16 kg).

[0098] Example 8:

[0099] Weigh 80 mg of catalyst (SMC-2) into a catalyst tube under nitrogen protection.

[0100] Add 250 mL of n-hexane to a 1 L glass reactor, add 5 mL of MAO toluene solution (1.5 mol / L), stir mechanically at 500 rpm, and heat to 90 °C.

[0101] A catalyst was added, a certain amount of hydrogen gas was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 1.9%, polymerization was carried out at 90℃ with mechanical stirring at 500 rpm, and the polymerization time was 1 hour.

[0102] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0103] The resulting polymer had a melting point of 128.3℃ and a melt flow rate of 300 g / 10 min (190℃ / 2.16 kg).

[0104] Example 9:

[0105] Weigh 80 mg of catalyst (SMC-2) into a catalyst tube under nitrogen protection.

[0106] Add 250 mL of n-hexane to a 1 L glass reactor, add 5 mL of MAO toluene solution (1.5 mol / L), stir mechanically at 500 rpm, and heat to 90 °C.

[0107] A catalyst was added, a certain amount of hydrogen was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 2.54%, and polymerization was carried out at 90℃ with mechanical stirring at 500 rpm for 1 hour.

[0108] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0109] The resulting polymer had a melting point of 129.5℃ and a melt flow rate of 400 g / 10 min (190℃ / 2.16 kg).

[0110] Example 10:

[0111] Weigh 150 mg of catalyst (SMC-4) into a catalyst tube under nitrogen protection.

[0112] Add 650 mL of n-hexane, 15 mL of 1-hexene, and 5 mL of MAO toluene solution (1.5 M) to a 1 L glass reactor. Stir mechanically at 500 rpm and heat to 90 °C.

[0113] A catalyst was added, a certain amount of hydrogen gas was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 0.94%, and polymerization was carried out at 90℃ with mechanical stirring at 500 rpm for 1 hour.

[0114] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0115] The resulting polymer had a melting point of 122.5℃ and a melt flow rate of 300 g / 10 min (190℃ / 2.16 kg).

[0116] Example 11:

[0117] Weigh 150 mg of catalyst (SMC-4) into a catalyst tube under nitrogen protection.

[0118] Add 650 mL of n-hexane, 25 mL of 1-hexene, and 5 mL of MAO toluene solution (1.5 M) to a 1 L glass reactor. Stir mechanically at 500 rpm and heat to 90 °C.

[0119] A catalyst was added, a certain amount of hydrogen gas was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 0.94%, and polymerization was carried out at 90℃ with mechanical stirring at 500 rpm for 1 hour.

[0120] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0121] The resulting polymer had a melting point of 119℃ and a melt flow rate of 380 g / 10 min (190℃ / 2.16 kg).

[0122] Example 12:

[0123] Weigh 150 mg of catalyst (SMC-4) into a catalyst tube under nitrogen protection.

[0124] Add 650 mL of n-hexane, 25 mL of 1-hexene, and 5 mL of MAO toluene solution (1.5 M) to a 1 L glass reactor. Stir mechanically at 500 rpm and heat to 90 °C.

[0125] A catalyst was added, a certain amount of hydrogen gas was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 1.9%, polymerization was carried out at 90℃ with mechanical stirring at 500 rpm, and the polymerization time was 1 hour.

[0126] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0127] The resulting polymer had a melting point of 117.2℃ and a melt flow rate of 600 g / 10 min (190℃ / 2.16 kg).

[0128] Example 13:

[0129] Weigh 150 mg of catalyst (SMC-4) into a catalyst tube under nitrogen protection.

[0130] Add 650 mL of n-hexane, 25 mL of 1-hexene, and 5 mL of MAO toluene solution (1.5 M) to a 1 L glass reactor. Stir mechanically at 500 rpm and heat to 90 °C.

[0131] A catalyst was added, a certain amount of hydrogen was introduced, and ethylene gas was introduced. The pressure in the reactor reached 0.5 MPa, the hydrogen / ethylene partial pressure ratio was 2.54%, and polymerization was carried out at 90℃ with mechanical stirring at 500 rpm for 1 hour.

[0132] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0133] The resulting polymer had a melting point of 115.7℃ and a melt flow rate of 750 g / 10 min (190℃ / 2.16 kg).

[0134] Example 14:

[0135] Weigh 150 mg of catalyst (SMC-4) into a catalyst tube under nitrogen protection.

[0136] Ethylene and propylene are mixed evenly in a mixing tank at a volume ratio of ethylene / propylene = 95 / 5.

[0137] Add 650 mL of n-hexane to a 1 L glass reactor, add 5 mL of MAO toluene solution (1.5 M), stir mechanically at 500 rpm, and heat to 90 °C.

[0138] A catalyst was added, a certain amount of hydrogen was introduced, and an ethylene / propylene mixed gas was introduced. The pressure in the reactor reached 0.5 MPa, the partial pressure ratio of hydrogen to ethylene / propylene mixed gas was 1.9%, polymerization was carried out at 90℃ with mechanical stirring at 500 rpm, and the polymerization time was 1 hour.

[0139] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0140] The resulting polymer had a melting point of 120.5℃ and a melt flow rate of 510 g / 10 min (190℃ / 2.16 kg).

[0141] Example 15:

[0142] Weigh 150 mg of catalyst (SMC-4) into a catalyst tube under nitrogen protection.

[0143] Ethylene and propylene are mixed evenly in a mixing tank at a volume ratio of ethylene / propylene = 85 / 15.

[0144] Add 650 mL of n-hexane to a 1 L glass reactor, add 5 mL of MAO toluene solution (1.5 M), stir mechanically at 500 rpm, and heat to 90 °C.

[0145] A catalyst was added, a certain amount of hydrogen was introduced, and an ethylene / propylene mixed gas was introduced. The pressure in the reactor reached 0.5 MPa, the partial pressure ratio of hydrogen to ethylene / propylene mixed gas was 1.9%, polymerization was carried out at 90℃ with mechanical stirring at 500 rpm, and the polymerization time was 1 hour.

[0146] The polymerization reactor is cooled to room temperature and depressurized to atmospheric pressure. The polymer and hexane solvent are then poured out, filtered, and dried to obtain the polymer.

[0147] The resulting polymer had a melting point of 118.5℃ and a melt flow rate of 560 g / 10 min (190℃ / 2.16 kg).

[0148] Comparative Example 5 is a comparative example of catalyst polymerization, and Examples 6-15 are examples of catalyst polymerization. A summary is shown in Table 1.

[0149] Table 1 Results of catalyst polymerization experiments

[0150]

[0151] As shown in Table 1, the above embodiments demonstrate that adding polyethylene polyol compounds to the metallocene catalyst of the present invention during the loading process can improve the catalyst activity. The metallocene catalyst can ensure high catalyst activity while achieving a wide range of controllable adjustment of the polyethylene melt flow rate by adjusting the hydrogen / ethylene partial pressure ratio within a very small range. The metallocene catalyst prepared using polyethylene polyol can achieve controllable adjustment of the polymer's melting point and melt flow rate by adjusting the hydrogen partial pressure ratio, the type of comonomer, and the proportion of comonomers, so as to meet the requirements of the meltblown process for polymer raw materials.

[0152] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing meltblown polyethylene resin, characterized in that, The process includes the following steps: adding a metallocene catalyst and activator, ethylene and comonomer, and a molecular weight regulator to a polymerization reactor to carry out a polymerization reaction, thereby obtaining a polyethylene copolymer; The polyethylene copolymer is degassed and granulated to obtain meltblown polyethylene resin; The metallocene catalyst comprises: an inorganic support, a polyethylene polyol adsorbed on the inorganic support and a co-catalyst methylaluminoxane (MAO), and a metallocene compound combined with MAO. The general formula of the polyethylene polyol is -(CH2CH2)n-(CH2CHOH)m-, and its molecular weight is 1000-20000 g / mol, wherein the molar content of -OH is 2-30%, n is an integer greater than or equal to 1, and m is an integer greater than or equal to 1. The polyethylene polyol accounts for 0.05-1.5% by weight.

2. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The inorganic carrier accounts for 70%-90% by weight.

3. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The MAO content is 10%-25% by weight.

4. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The metallocene compound comprises 1.3%-4.2% by weight.

5. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The inorganic carrier is at least one of silica gel, alumina, and molecular sieve; the particle size range of the inorganic carrier is 15-120 μm.

6. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The metallocene compound is a substituted dicenocene compound of a Group 4 metal, having the following structure: R1 to R5 may be the same or different, and are independently selected from H or C1-C4 alkyl groups; M is titanium, zirconium or hafnium.

7. The method for preparing meltblown polyethylene resin according to claim 6, characterized in that, The metallocene compound is at least one of titanium dichlorodicyclopentadiene, zirconium dichlorodicyclopentadiene, hafnium dichlorodicyclopentadiene, di(n-butylcendichloride), and di(n-propylcendichloride).

8. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The activator is at least one of alkylaluminum and methylaluminoxane; the molar ratio of aluminum in the activator to the metal in the metallocene catalyst is 50-2000.

9. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The comonomer is at least one of propylene, butene, and hexene; the comonomer accounts for less than 20% of the total molar proportion of ethylene and the comonomer.

10. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The molecular weight regulator is hydrogen, and the molar ratio of hydrogen to ethylene does not exceed 20 mol.

11. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 70-100℃, for a reaction time of 30-150 min, and at a pressure of 0.5-2.0 MPa.

12. The method for preparing meltblown polyethylene resin according to claim 1, characterized in that, Antioxidants are also added during the granulation process.

13. A meltblown polyethylene resin, characterized in that, The meltblown polyethylene resin obtained by the preparation method according to any one of claims 1-12 has a melt flow rate of 150-750 g / 10 min and a melting point of 115-135 °C.

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