Polypropylene material for capacitor film and preparation method thereof

Abstract

The invention provides a polypropylene material for a capacitor film and a preparation method of the polypropylene material. The preparation method comprises the following steps: carrying out bulk polymerization on propylene under the action of a catalyst to obtain a polymerization product system; separating a polypropylene product from the polymerization product system; washing the polypropylene product by using a detergent subjected to dehydration and / or deoxidation treatment under anhydrous and anaerobic conditions, and drying the washed product to obtain polypropylene powder; and spraying a compound agent solution containing a free radical capturing agent, a peroxide decomposing agent and an acid absorbent to the polypropylene powder, and drying and granulating the polypropylene powder to obtain the polypropylene material for the capacitor film. The obtained polypropylene material for the capacitor film is lower in ash content, and good in performance indexes such as isotacticity, oxidation induction time parallelism, polymer molecular weight and the like.

Description

Technical Field

[0001] The invention relates to a polypropylene material for capacitor film and a preparation method thereof, belonging to the field of polypropylene. Background Art

[0002] With the continuous expansion of the application scope of polypropylene, low-ash polypropylene resin plays a role in the fields of electronics, electrical appliances, textiles and medical treatment. Among them, the development and application of polypropylene capacitor film has greatly improved the quality and performance of electronics and capacitors. In addition to the performance of ordinary polypropylene, the electrical grade low-ash polypropylene special material also has the advantages of high cleanliness, low ash content, and low dielectric loss factor. The film processed from this polypropylene has good thickness uniformity, high compressive strength, high mechanical strength, high insulation resistance, and high dielectric strength. It can be widely used in low-voltage parallel power capacitors, capacitors for AC motors, DC capacitors, power electronics, lamps, anti-interference, filtering, and power capacitors.

[0003] At present, the ash content of general products of existing polypropylene production technology is about 200-500ppm, which is significantly higher than the ash content of polypropylene capacitor special material resin, which is generally required to be below 100ppm, preferably below 30ppm (CN102040690A). The ash content of polypropylene mainly comes from catalysts, co-catalysts, external electron donors and various additives added during the granulation process. In the industry, the methods for reducing the ash content of polypropylene in related technologies at home and abroad are mainly carried out from three aspects. First, strengthen the refining of propylene and other raw materials, reduce the content of harmful impurities such as water, oxygen, sulfur, arsenic, etc., to increase the activity of the catalyst and reduce the use of alkyl aluminum; second, use high-activity catalysts, reduce the introduction of titanium and magnesium compounds, and minimize the addition of alkyl aluminum and external electron donors; third, use organic compound additives that do not produce ash as much as possible during the granulation process, and use closed systems in the production, processing and transportation processes to avoid the introduction of external impurities (for example, CN103965380A, CN111019025A, CN112979845A). Although the above measures can improve the ash content of polypropylene resin to a certain extent, it is usually difficult to meet the requirements of polypropylene capacitor special material resin. For example, Sinopec Zhongyuan Petrochemical uses ultra-high activity catalyst (HA type catalyst) in the second-generation ring tube process to prepare polypropylene through liquid phase bulk polymerization. Although the ash content of polypropylene has been reduced, its molecular weight and its distribution, isotacticity, melting point, crystallinity and other performance indicators still need to be improved (Science and Technology Innovation and Application, 2018, 18: 166-167.; Insulation Materials 2022, 55 (10): 33-37.), especially in the film forming process, the migration of small molecules produces obvious smoke, which causes pollution to the clean production workshop and brings troubles to downstream film manufacturers. Patent CN109912734 reports a method for deashing a polymer by four heating washings. The process is cumbersome, and each washing requires heating, which consumes a lot of energy. CN 115124635 A reports that "first, the polyolefin resin material to be treated is immersed and / or dissolved in a hydrocarbon solvent, and then an acidic agent is added and immersed and / or dissolved again to obtain a pretreated compounding agent solution; then the pretreated compounding agent solution obtained in the above steps is subjected to a metal complexing reaction with a complexing agent, and then eluted with an eluent to obtain a deashed polyolefin resin material". Although this method has a certain deashing effect, the use of multiple mixed solvents and the addition of a large amount of acidic solvents and complexing agents make solvent recovery difficult and economical.

[0004] Therefore, it is necessary to provide a new preparation scheme for low-ash polypropylene resin to improve the above problems. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a polypropylene material for capacitor film and a preparation method thereof, wherein the polypropylene material for capacitor film not only has a lower ash content, but also has better performance indicators such as isotacticity, parallelism of oxidation induction time, and polymer molecular weight.

[0006] To achieve the above object, the present invention provides a method for preparing a polypropylene material for a capacitor film, which comprises the following steps:

[0007] Propylene is polymerized under the action of a catalyst to obtain a polymerization product system;

[0008] separating a polypropylene product from the polymerization product system;

[0009] Under anhydrous and oxygen-free conditions, a polypropylene product is washed with a detergent that has been subjected to dehydration and / or deoxygenation treatment, and the washed product is dried to obtain a polypropylene powder;

[0010] After spraying a compounding agent solution containing a free radical scavenger, a peroxide decomposer and an acid absorber onto the polypropylene powder, the polypropylene powder is dried and granulated to obtain a polypropylene material for a capacitor film.

[0011] First, the present invention adopts bulk polymerization to carry out propylene polymerization reaction, which significantly improves the polymerization activity of the catalyst, can better match the existing conventional polypropylene production equipment, and avoids the use of organic solvents in the polymerization process. Secondly, the present invention uses a detergent that has been dehydrated and / or deoxygenated to wash the polypropylene product under anhydrous and oxygen-free conditions, and further removes impurities such as small molecules, oligomers, random substances and residual ash in the polymer product. Moreover, the present invention also reduces the introduction of ash from the source of raw materials. Furthermore, the present invention adopts free radical scavengers, peroxide decomposers and acid absorbents as low-ash processing aids to reduce the introduction of exogenous ash as much as possible in the granulation stage. In particular, the present invention sprays the free radical scavenger, peroxide decomposer and acid absorbent on the outer surface of the polypropylene powder in the form of a compounding agent solution for mixing, which effectively solves the problem that the processing aid and the powder are difficult to mix evenly due to the large difference in particle size. Based on this, the processing aids can form a good bonding force, avoiding the migration and precipitation of the polypropylene product in the subsequent film drawing process, thereby solving the problems of high ash content, uneven ash distribution, and poor parallelism of oxidation induction time of polypropylene film used for capacitor film.

[0012] In a preferred embodiment, the solvent in the compounding agent solution is an organic solvent. Further, the organic solvent is selected from one or more combinations of substituted or unsubstituted alkanes, aromatic hydrocarbons, ketone compounds and alcohol compounds. Unsubstituted alkanes are selected from one or more combinations of pentane, hexane, heptane, octane, isooctane, n-nonane, n-decane and methylcyclohexane; substituted alkanes are selected from halogenated alkanes, and halogenated alkanes are selected from chloroform; aromatic hydrocarbons are selected from one or more combinations of toluene, ethylbenzene, xylene, trimethylbenzene, etc.; ketone compounds are selected from one or more combinations of acetone, butanone and phenylacetophenone; alcohol compounds are selected from one or more combinations of ethanol, isopropanol, and n-butanol. Further, the way in which the free radical scavenger, peroxide decomposer and acid absorber are dissolved in the above-mentioned organic solvent includes but is not limited to heating stirring and / or ultrasonic dissolution.

[0013] In a preferred embodiment, the detergent comprises one or more of an inert alkane, an inert aromatic hydrocarbon and a C1-C8 organic alcohol. Preferably, the inert alkane is selected from one or more of n-hexane, n-heptane and petroleum ether; the inert aromatic hydrocarbon is selected from one or more of toluene, xylene, chlorobenzene and dichlorobenzene; the C1-C8 organic alcohol is selected from one or more of ethanol, isopropanol and isooctyl alcohol. The above-mentioned detergent can achieve a high-efficiency deashing effect by washing once, avoiding the use of commonly used water, acid and metal ion complexing agent, greatly simplifying the washing operation and saving costs.

[0014] In a preferred embodiment, the detergent can be dehydrated and / or deoxygenated by a conventional method in the art, such as a purification column, to reduce the water content in the detergent to less than 50 mg / kg and / or the oxygen content to less than 50 mg / kg. After washing, the detergent can be recycled after separation and purification.

[0015] In a preferred embodiment, the preparation method further comprises the step of refining propylene before bulk polymerization. By refining propylene, the introduction of ash into the polymer is further reduced from the source.

[0016] Furthermore, the refining method includes one or a combination of two or more of dehydration, deoxygenation, desulfurization, dealcoholization, carbon monoxide removal and carbon dioxide removal. For example, the commercial polymerization-grade propylene raw material can be further dehydrated, deoxygenated, desulfurized, dealcoholized, carbon monoxide removed and carbon dioxide removed by a conventional method in the art, such as a purification column, so that the water content of the refined propylene is less than 0.5 mg / kg, the methanol content is less than 0.5 mg / kg, the oxygen content is less than 0.5 mg / kg, the total sulfur content is less than 0.1 mg / kg, the carbon monoxide content is less than 0.1 mg / kg, and the carbon dioxide content is less than 0.1 mg / kg.

[0017] In a preferred embodiment, the polymerization activity of the catalyst (polymerization activity = polymer weight / weight of the main catalyst in the catalyst) is more than 120,000 times, and the use of ultra-high activity catalysts can reduce the introduction of ash in the polymer from the source. In some optional embodiments, the catalyst is selected from the Ziegler-Natta catalyst system; the Ziegler-Natta catalyst system includes a main catalyst, a co-catalyst and an external electron donor; the main catalyst is a supported titanium-containing Ziegler-Natta main catalyst; the co-catalyst includes alkyl aluminum and / or halogenated alkyl aluminum; the external electron donor includes an organosilicon compound.

[0018] Furthermore, in the catalyst, the molar ratio of Al in the co-catalyst to Ti in the main catalyst is 200-50, for example, 200, 100, 50, preferably 50; the molar ratio of Si in the external electron donor to Ti in the main catalyst is 10-2, for example, 10, 5, 2, preferably 2.

[0019] In some optional embodiments, the co-catalyst includes one or a combination of two or more of triethylaluminum, triisobutylaluminum and diethylaluminum chloride; more preferably, the co-catalyst is triethylaluminum.

[0020] In some optional embodiments, the external electron donor includes one or a combination of two or more of diisobutyldimethoxysilane, cyclohexylmethyldimethoxysilane, dicyclopentyldimethoxysilane, diisopropyldimethoxysilane and n-propyltriethoxysilane; further preferably, the external electron donor is dicyclopentyldimethoxysilane.

[0021] In a preferred embodiment, the reaction raw material for propylene polymerization further comprises a molecular weight regulator; more preferably, the molecular weight regulator comprises hydrogen.

[0022] Furthermore, the total amount of the free radical scavenger, the peroxide decomposer and the acid absorbent is 0.2-0.5 wt %, preferably 0.3-0.4 wt %, of the weight of the polypropylene powder.

[0023] Furthermore, the weight ratio of the free radical scavenger, the peroxide decomposer and the acid absorbent is 1:0.5-2:0.01-0.05.

[0024] In some optional embodiments, in the compound solution, the total amount of the free radical scavenger, the peroxide decomposer and the acid absorber is 3 to 4.5 g based on 100 mL of solvent.

[0025] Further, the free radical scavenger is selected from hindered phenol compounds. In some optional embodiments, the free radical scavenger is selected from one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester (antioxidant 1010), β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate n-octadecyl alcohol ester (antioxidant 1076), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanuric acid (antioxidant 3114), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene (antioxidant 330) and tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate (antioxidant 1790), IRGANOX B225 and IRGANOX B215.

[0026] Further, the peroxide decomposer is selected from phosphite-containing compounds and / or organic sulfur-containing compounds. In some optional embodiments, the peroxide decomposer is selected from one or a combination of two or more of trisnonylphenyl phenyl phosphite (TNPP), dioctadecyl pentaerythritol diphosphite (antioxidant 618), tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168), bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite (antioxidant 626), dilauryl thiodipropionate (DLTP) and dioctadecyl thiodipropionate (DSTP).

[0027] Further, the acid absorbent is selected from stearate compounds and / or hydrotalcite compounds containing intercalated structures. In some optional embodiments, the acid absorbent is selected from one or a combination of two or more of calcium stearate, zinc stearate, sodium stearate, magnesium stearate and magnesium aluminum hydrotalcite.

[0028] In a preferred embodiment, the free radical scavenger is selected from pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1010), the peroxide decomposer is selected from dioctadecanol thiodipropionate (DSTP), and the acid absorber is selected from calcium stearate.

[0029] Furthermore, the washing temperature is between 70 and 90°C.

[0030] Furthermore, the weight ratio of the detergent to the polypropylene product is 2 to 10:1.

[0031] In an optional embodiment, before washing, the preparation method further comprises separating a polypropylene product from a polymerization product system. The polymerization product system comprises polypropylene and unreacted propylene raw material, the polypropylene is in a solid state, and the unreacted propylene raw material is in a liquid state, the unreacted propylene in the polymerization product system is vaporized to obtain gaseous propylene which can be reused after liquefaction; the solid polypropylene product is separated from the polymerization product system, and the solid polypropylene product enters a washing kettle under nitrogen pressure for washing treatment.

[0032] Furthermore, during the polymerization of propylene under the action of the catalyst, the polymerization reaction temperature is 70-80°C, the time is 2-4 hours, and the pressure is 3-5 MPa. More preferably, the polymerization reaction temperature is 78°C, the time is 2 hours, and the pressure is 3.5-4.2 MPa.

[0033] In some optional embodiments, the polymerization reaction is carried out in a polymerization reactor, which includes a tank reactor and / or a loop reactor; preferably, the polymerization reactor includes a tank reactor.

[0034] The present invention also provides a polypropylene material for capacitor film, wherein the polypropylene material for capacitor film is prepared by the above-mentioned preparation method of the polypropylene material for capacitor film.

[0035] Furthermore, the ash content of the polypropylene material for capacitor film of the present invention is less than 20ppm, the isotacticity is higher than 98%, the mass average molecular weight is 350,000 to 450,000, the molecular weight distribution is 6 to 8, the melt index is 2.5 to 4.0g / 10min, the tensile elastic modulus is greater than 1500MPa, the tensile yield stress is greater than 34MPa, the melting temperature is greater than 165°C, the oxidation induction time (200°C) is greater than 35min, and the volume resistivity is greater than 3×10 15 Ω·m, dielectric loss factor is less than 5×10 -4 The polypropylene material for capacitor film has excellent performance indicators, and when it is subsequently used in the fields of electronics and capacitors, it can greatly improve the quality and performance of the product. DETAILED DESCRIPTION

[0036] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0037] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0038] The materials, reagents, etc. used in the following examples can all be obtained from commercial sources. The specific information is as follows:

[0039] High-purity hydrogen: Beijing Huanyu Jinghui Jingcheng Gas Technology Co., Ltd.

[0040] High purity nitrogen: Beijing Huanyu Jinghui Jingcheng Gas Technology Co., Ltd.

[0041] Polymer grade propylene: Beijing Huanyu Jinghui Jingcheng Gas Technology Co., Ltd.

[0042] Main catalyst: Customized (titanium content 3.4%, commercial catalyst)

[0043] Co-catalyst triethylaluminum: AR, Aldrich

[0044] External electron donor cyclohexylmethyldimethoxysilane: AR, Aldrich

[0045] External electron donor dicyclopentyldimethoxysilane: AR, Aldrich

[0046] Hexane: AR, Inokane

[0047] Isopropyl alcohol: AR, Inokane

[0048] Propylene purification column: Dalian Kona Science and Technology Development Co., Ltd.

[0049] Hexane purification column: Dalian Kona Science and Technology Development Co., Ltd.

[0050] 3A molecular sieve: Shanghai Lvqiang New Materials Co., Ltd.

[0051] Antioxidant 1010: BASF

[0052] Antioxidant 330: BASF

[0053] Antioxidant 168: BASF

[0054] Antioxidant DSTP: BASF

[0055] Antioxidant DLTP: BASF

[0056] Calcium stearate: BASF

[0057] Example 1

[0058] This embodiment provides a method for preparing low-ash polypropylene for capacitor film, which comprises the following steps:

[0059] (1) Material refining

[0060] Propylene raw material refining: After polymerization-grade propylene is dehydrated, deoxygenated, desulfurized, dealcoholized, decarbonated and decarbonated in a propylene purification column under a certain pressure, refined liquid propylene is obtained and enters a propylene metering tank for standby use; in the refined liquid propylene, the water content is ≤0.5mg / kg, the total sulfur content is ≤0.1mg / kg, the carbon dioxide content is ≤0.1mg / kg, the methanol content is ≤0.5mg / kg, the oxygen content is ≤0.5mg / kg, and the carbon monoxide content is ≤0.1mg / kg;

[0061] Detergent refining: n-hexane is circulated through a n-hexane purification column for 4 to 8 hours and then pressed into a metering tank for standby use. The water content and oxygen content of the refined n-hexane are ≤50 mg / kg and ≤50 mg / kg respectively. Isopropanol is soaked in 3A molecular sieve for 24 hours before use (water content is ≤50 mg / kg).

[0062] (2) Bulk polymerization

[0063] First, evacuate the 5L reactor, replace it with nitrogen 3 times, and finally replace it with propylene once, and keep the propylene atmosphere slightly positive pressure. When the reactor temperature drops to room temperature, add 1000g of the above-mentioned refined liquid propylene under the stirring state (100r / min), add 0.014mmol cyclohexylmethyldimethoxysilane (Si / Ti=2), 0.35mmol triethylaluminum (Al / Ti=50) and 10mg main catalyst (0.007mmolTi) to the catalyst feed tank in sequence under the protection of nitrogen slightly positive pressure, then rinse the main catalyst feed tank with 500g refined liquid propylene, close the feed valve, and then add 0.16g hydrogen and close its valve. Adjust the stirring rate to 600r / min. Use a circulating water bath to heat the reactor to 78℃ and maintain for 2h, at which time the liquid propylene is basically consumed.

[0064] (3) Washing:

[0065] The circulating water was set to refrigeration mode, and the polymerization kettle was cooled with circulating cold water. After the temperature in the polymerization kettle dropped to room temperature, the vent valve was slowly opened to release the unreacted propylene, and the gas in the reactor was replaced with nitrogen. The operation was repeated 3 times. The polymer product was pressed into a washing kettle under nitrogen pressure, and then 2.4 kg of the above-refined n-hexane and 0.6 kg of the above-refined isopropanol (V) were added to the washing kettle. 正己烷 :V 异丙醇 ≈5, so that the solubility parameter of the mixed solvent is close to the solubility parameter of polypropylene to achieve the best washing and deashing effect), and stirred at 80°C for 2h, then cooled to room temperature and discharged into a centrifuge, and after solid-liquid separation, the polypropylene powder was further dried in a vacuum drying oven to constant weight. In this example, 1410g of polypropylene powder was obtained.

[0066] (4) Processing and granulation:

[0067] Preparation of premix of polypropylene powder and compounding agent: Add 2.0g antioxidant 1010 (2000ppm), 1.0g peroxide decomposer 168 (1000ppm) and 0.08g acid absorbent calcium stearate (80ppm) to 100mL chloroform, then dissolve by ultrasonic vibration for 20min, so that the three components are fully dissolved in chloroform to obtain compounding agent solution. Weigh 1000g polypropylene powder in a small mixer, then start stirring, and use a nozzle at the upper end to evenly spray the compounding agent solution on the surface of the polypropylene powder, so that the polypropylene powder and the compounding agent are fully mixed to obtain a premix of polypropylene powder and compounding agent, and place the premix in a vacuum drying oven to dry to constant weight.

[0068] Preparation of polypropylene pellets: The dried premix is ​​added to the co-rotating twin-screw extruder in batches, melt-extruded according to the set processing conditions, and underwater granulated to obtain polypropylene pellets. The extrusion granulation conditions are: the first stage set temperature is 170°C, the second stage set temperature is 200°C, the third stage set temperature is 220°C, and the fourth stage set temperature is 200°C.

[0069] Example 2

[0070] This embodiment provides a method for preparing low-ash polypropylene for capacitor film, which comprises the following steps:

[0071] (1) Material refining

[0072] Propylene raw material refining: After polymerization-grade propylene is dehydrated, deoxygenated, desulfurized, dealcoholized, decarbonated and decarbonated in a propylene purification column under a certain pressure, refined liquid propylene is obtained and enters a propylene metering tank for standby use; in the refined liquid propylene, the water content is ≤0.5mg / kg, the total sulfur content is ≤0.1mg / kg, the carbon dioxide content is ≤0.1mg / kg, the methanol content is ≤0.5mg / kg, the oxygen content is ≤0.5mg / kg, and the carbon monoxide content is ≤0.1mg / kg;

[0073] Detergent refining: n-hexane is circulated through a n-hexane purification column for 4 to 8 hours and then pressed into a metering tank for standby use. The water content and oxygen content of the refined n-hexane are ≤50 mg / kg and ≤50 mg / kg respectively. Isopropanol is soaked in 3A molecular sieve for 24 hours before use (water content is ≤50 mg / kg).

[0074] (2) Bulk polymerization

[0075] First, evacuate the 5L reactor, replace it with nitrogen 3 times, and finally replace it with propylene once, and keep the propylene atmosphere slightly positive pressure. When the temperature of the reactor drops to room temperature, add 1000g of the above-mentioned refined liquid propylene under the stirring state (100r / min), and add 0.014mmol dicyclopentyldimethoxysilane (Si / Ti=2), 0.35mmol triethylaluminum (Al / Ti=50), 10mg main catalyst (0.007mmolTi) to the main catalyst feed tank in sequence under the protection of nitrogen slightly positive pressure, then rinse the main catalyst feed tank with 500g refined liquid propylene, close the feed valve, and then add 0.18g hydrogen and close its valve. Adjust the stirring rate to 600r / min. Use a circulating water bath to heat the reactor to 78℃ and maintain for 2h, at which time the liquid propylene is basically consumed.

[0076] (3) Washing:

[0077] The circulating water was set to refrigeration mode, and the polymerization kettle was cooled with circulating cold water. After the temperature in the polymerization kettle dropped to room temperature, the vent valve was slowly opened to release the unreacted propylene, and the gas in the reactor was replaced with nitrogen. The operation was repeated 3 times. The polymer product was pressed into a washing kettle under nitrogen pressure, and then 2.4 kg of the above-refined n-hexane and 0.6 kg of the above-refined isopropanol (V) were added to the washing kettle. 正己烷 :V 异丙醇 ≈5, so that the solubility parameter of the mixed solvent is close to the solubility parameter of polypropylene to achieve the best washing and deashing effect), and stirred at 80°C for 2h, then cooled to room temperature and discharged into a centrifuge, and after solid-liquid separation, the polypropylene powder was further dried in a vacuum drying oven to constant weight. In this example, 1445g of polypropylene powder was obtained.

[0078] (4) Processing and granulation:

[0079] Preparation of premix of polypropylene powder and compounding agent: Add 2.0g antioxidant 1010 (2000ppm), 2.0g peroxide decomposer DSTP (1000ppm) and 0.07g acid absorber calcium stearate (70ppm) to 100mL chloroform, then dissolve by ultrasonic vibration for 20min, so that the three components are fully dissolved in chloroform to obtain compounding agent solution. Weigh 1000g polypropylene powder in a small mixer, then start stirring, and use a nozzle at the upper end to evenly spray the compounding agent solution on the surface of the polypropylene powder, so that the polypropylene powder and the compounding agent are fully mixed to obtain a premix of polypropylene powder and compounding agent, and place the premix in a vacuum drying oven to dry to constant weight.

[0080] Preparation of polypropylene pellets: Add the dried polypropylene powder and compounding agent premix into a mixer-extruder for melt granulation. The mixer-extrusion granulation conditions are: the mixer temperature is set at 200°C, the rotor speed is 50r / min, and the mixer time is 10min; the first stage of the single screw extruder is set at 180°C, the second stage is set at 200°C, the third stage is set at 230°C, and the fourth stage is set at 200°C.

[0081] Example 3

[0082] This embodiment provides a method for preparing low-ash polypropylene for capacitor film, which comprises the following steps:

[0083] (1) Material refining

[0084] Propylene raw material refining: After polymerization-grade propylene is dehydrated, deoxygenated, desulfurized, dealcoholized, decarbonated and decarbonated in a propylene purification column under a certain pressure, refined liquid propylene is obtained and enters a propylene metering tank for standby use; in the refined liquid propylene, the water content is ≤0.5mg / kg, the total sulfur content is ≤0.1mg / kg, the carbon dioxide content is ≤0.1mg / kg, the methanol content is ≤0.5mg / kg, the oxygen content is ≤0.5mg / kg, and the carbon monoxide content is ≤0.1mg / kg;

[0085] Detergent refining: n-hexane is circulated through a n-hexane purification column for 4 to 8 hours and then pressed into a metering tank for standby use. The water content and oxygen content of the refined n-hexane are ≤50 mg / kg and ≤50 mg / kg respectively. Isopropanol is soaked in 3A molecular sieve for 24 hours before use (water content is ≤50 mg / kg).

[0086] (2) Bulk polymerization

[0087] First, evacuate the 5L reactor, replace it with nitrogen 3 times, and finally replace it with propylene once, and keep the propylene atmosphere slightly positive pressure. When the reactor temperature drops to room temperature, add 1000g of the above-mentioned refined liquid propylene under the stirring state (100r / min), add 0.014mmol dicyclopentyldimethoxysilane (Si / Ti=2), 0.35mmol triethylaluminum (Al / Ti=50) and 10mg main catalyst (0.007mmolTi) to the main catalyst feed tank in sequence under the protection of nitrogen slightly positive pressure, then rinse the main catalyst feed tank with 500g refined liquid propylene, close the feed valve, and then add 0.20g hydrogen and close its valve. Adjust the stirring rate to 600r / min. Use a circulating water bath to heat the reactor to 78℃ and maintain for 2h, at which time the liquid propylene is basically consumed.

[0088] (3) Washing:

[0089] The circulating water was set to refrigeration mode, and the polymerization kettle was cooled with circulating cold water. After the temperature in the polymerization kettle dropped to room temperature, the vent valve was slowly opened to release the unreacted propylene, and the gas in the reactor was replaced with nitrogen. The operation was repeated 3 times. The polymer product was pressed into a washing kettle under nitrogen pressure, and then 2.4 kg of the above-refined n-hexane and 0.6 kg of the above-refined isopropanol (V) were added to the washing kettle. 正己烷 :V 异丙醇 ≈5, so that the solubility parameter of the mixed solvent is close to the solubility parameter of polypropylene to achieve the best washing and deashing effect), and stirred at 80°C for 2h, then cooled to room temperature and discharged into a centrifuge, and after solid-liquid separation, the polypropylene powder was further dried in a vacuum drying oven to constant weight. In this example, 1436g of polypropylene powder was obtained.

[0090] (4) Processing and granulation:

[0091] Preparation of premix of polypropylene powder and compounding agent: Add 2.0g antioxidant 330 (2000ppm), 2.0g peroxide decomposer DLTP (2000ppm) and 0.08g acid absorber calcium stearate (80ppm) to 100mL chloroform, then dissolve by ultrasonic vibration for 20min, so that the three components are fully dissolved in chloroform to obtain compounding agent solution. Weigh 1000g polypropylene powder in a small mixer, then start stirring, and use a nozzle at the upper end to evenly spray the compounding agent solution on the surface of the polypropylene powder, so that the polypropylene powder and the compounding agent are fully mixed to obtain a premix of polypropylene powder and compounding agent, and place the premix in a vacuum drying oven to dry to constant weight.

[0092] Preparation of polypropylene pellets: The dried premix is ​​added to the co-rotating twin-screw extruder in batches, melt-extruded according to the set processing conditions, and underwater granulated to obtain polypropylene pellets. The extrusion granulation conditions are: the first stage set temperature is 170°C, the second stage set temperature is 200°C, the third stage set temperature is 220°C, and the fourth stage set temperature is 200°C.

[0093] Example 4

[0094] This embodiment provides a method for preparing low-ash polypropylene for capacitor film, which comprises the following steps:

[0095] (1) Material refining

[0096] Propylene raw material refining: After polymerization-grade propylene is dehydrated, deoxygenated, desulfurized, dealcoholized, decarbonated and decarbonated in a propylene purification column under a certain pressure, refined liquid propylene is obtained and enters a propylene metering tank for standby use; in the refined liquid propylene, the water content is ≤0.5mg / kg, the total sulfur content is ≤0.1mg / kg, the carbon dioxide content is ≤0.1mg / kg, the methanol content is ≤0.5mg / kg, the oxygen content is ≤0.5mg / kg, and the carbon monoxide content is ≤0.1mg / kg;

[0097] Detergent refining: n-hexane is circulated through a n-hexane purification column for 4 to 8 hours and then pressed into a metering tank for standby use. The water content and oxygen content of the refined n-hexane are ≤50 mg / kg and ≤50 mg / kg respectively. Isopropanol is soaked in 3A molecular sieve for 24 hours before use (water content is ≤50 mg / kg).

[0098] (2) Bulk polymerization

[0099] First, evacuate the 5L reactor, replace it with nitrogen 3 times, and finally replace it with propylene once, and keep the propylene atmosphere slightly positive pressure. When the reactor temperature drops to room temperature, add 1000g of the above-mentioned refined liquid propylene under the stirring state (100r / min), add 0.028mmol dicyclopentyldimethoxysilane (Si / Ti=4), 0.70mmol triethylaluminum (Al / Ti=100) and 10mg main catalyst (0.007mmolTi) to the main catalyst feed tank in sequence under the protection of nitrogen slightly positive pressure, then rinse the main catalyst feed tank with 500g refined liquid propylene, close the feed valve, and then add 0.25g hydrogen and close its valve. Adjust the stirring rate to 600r / min. Use a circulating water bath to heat the reactor to 75℃ and maintain for 3h, at which time the liquid propylene is basically consumed.

[0100] (3) Washing:

[0101] The circulating water was set to refrigeration mode, and the polymerization kettle was cooled with circulating cold water. After the temperature in the polymerization kettle dropped to room temperature, the vent valve was slowly opened to release the unreacted propylene, and the gas in the reactor was replaced with nitrogen. The operation was repeated 3 times. The polymer product was pressed into a washing kettle under nitrogen pressure, and then 2.4 kg of the above-refined n-hexane and 0.6 kg of the above-refined isopropanol (V) were added to the washing kettle. 正己烷 :V 异丙醇 ≈5, so that the solubility parameter of the mixed solvent is close to the solubility parameter of polypropylene to achieve the best washing and deashing effect), and stirred at 85°C for 2h, then cooled to room temperature and discharged into a centrifuge, and after solid-liquid separation, the polypropylene powder was further dried in a vacuum drying oven to constant weight. In this example, 1392g of polypropylene powder was obtained.

[0102] (4) Processing and granulation:

[0103] Preparation of premix of polypropylene powder and compounding agent: Add 1.0g antioxidant 1010 (1000ppm), 2.0g peroxide decomposer 168 (2000ppm) and 0.08g acid absorbent calcium stearate (80ppm) to 100mL chloroform, then dissolve by ultrasonic vibration for 20min, so that the three components are fully dissolved in chloroform to obtain compounding agent solution. Weigh 1000g polypropylene powder in a small mixer, then start stirring, and use a nozzle at the upper end to evenly spray the compounding agent solution on the surface of the polypropylene powder, so that the polypropylene powder and the compounding agent are fully mixed to obtain a premix of polypropylene powder and the compounding agent, and place the premix in a vacuum drying oven to dry to constant weight.

[0104] Comparative Example 1

[0105] This comparative example provides a method for preparing polypropylene, which is basically the same as the method provided in Example 1, except that: in the post-treatment process of step (3), after the unreacted propylene is released, the polypropylene powder is directly discharged into a stainless steel barrel without any washing, and then dried in a vacuum drying oven to constant weight. This comparative example obtains 1418g of polypropylene powder. This polypropylene powder is not processed and granulated.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing polypropylene, which is basically the same as the method provided in Example 1, except that: during the granulation process in step (4), 1000 g of polypropylene powder and 2.0 g of antioxidant 1010 (2000 ppm), 1.0 g of peroxide decomposer 168 (1000 ppm), and 0.08 g of acid absorbent hard calcium (80 ppm) are directly mixed in a mixer for 10 minutes, and then granulated by twin-screw extrusion.

[0108] This comparative example obtained 1425 g of polypropylene powder.

[0109] Comparative Example 3

[0110] This comparative example provides a method for preparing polypropylene, which is basically the same as the method provided in Example 1, except that: during the post-treatment process in step (3), undried n-hexane (water content ≈ 80 ppm) and isopropanol (water content ≈ 600 ppm) are directly used for washing in an air atmosphere; during the processing and granulation process in step (4), only 4.0 g of antioxidant 1010 (4000 ppm) and 0.08 g of acid absorbent hard calcium are added.

[0111] This comparative example obtained 1403 g of polypropylene powder.

[0112] Comparative Example 4

[0113] This comparative example provides an existing polypropylene product, namely, Borealis product HC300BF.

[0114] The polymer analysis and characterization in the examples and comparative examples were measured according to national standards or industry standards:

[0115] (I) Propylene bulk polymerization data

[0116] The polymerization activity was calculated according to the following formula: polymerization activity = polymer mass / main catalyst dosage; the test results are shown in Table 1.

[0117] The polymer melt index (MFR) was measured using a melt index tester (MADSUR) (refer to GB / T3682.1-2018); the test results are shown in Table 1.

[0118] The molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer were measured at 150°C using a PL-GPC220 gel permeation chromatograph (refer to GB / T36214.4-2018); the test results are shown in Table 1.

[0119] The isotacticity of the polymer was measured by the n-heptane extraction method (refer to GB / T2412-2008); the test results are shown in Table 1.

[0120] The melting point (Tm) of the polymer was measured using a DSC (Q2000) differential scanning calorimeter (refer to GB / T19466.3-2004); the test results are shown in Table 1.

[0121] (II) Test data of ash content and composition of polypropylene pellets

[0122] The total ash content of the polymer was determined by calcining more than 100 g of the polymer product using a platinum crucible calcination method (refer to GB / T9345.1-2008). The test results are shown in Table 2.

[0123] The content of each component in the polymer ash was measured by ICP-OES (SH / T1829-2020); the test results are shown in Table 2.

[0124] (III) Mechanical properties analysis data of polymer products

[0125] The polymer tensile strength test was measured according to GB / T1040.2-2006; the test results are shown in Table 3 and Table 4.

[0126] The polymer impact strength test was measured according to GB / T1043.1-2008; the test results are shown in Table 3 and Table 4.

[0127] The polymer bending strength test was measured according to GB / T9341-2008; the test results are shown in Tables 3 and 4.

[0128] The polymer oxidation induction time test was measured according to GB_T19466.6-2009; the test results are shown in Tables 3 and 4.

[0129] The polymer volume resistivity test was measured according to GBT31838.2-2019; the test results are shown in Tables 3 and 4.

[0130] The polymer dielectric loss factor (power frequency) test is measured according to GB_T13542.2-2021; the test results are shown in Tables 3 and 4.

[0131] Table 1

[0132]

[0133] Table 2

[0134] serial number Total ash / ppm Ti / ppm Mg / ppm Al / ppm Si / ppm Ca / ppm Example 1 17.3 0.2 1.1 1.3 0.1 5.2 Example 2 15.1 0.2 1.2 1.1 0.1 4.7 Example 3 17.5 0.3 1.3 0.9 0.2 5.3 Example 4 16.6 0.2 0.9 1.5 0.2 5.1 Comparative Example 1 25.7 0.3 1.5 6.8 0.3 5.3 Comparative Example 2 17.8 0.3 1.3 1 0.1 5.3 Comparative Example 3 25.2 0.4 1.4 6.6 0.3 5.2 Comparative Example 4 18.6 1.7 1.1 1.8 0.2 5.3

[0135] Table 3

[0136]

[0137] Table 4

[0138]

[0139] Note: The “ / ” in the data of oxidation induction time in Table 3 and Table 4 indicates that two test results are separated.

[0140] It can be seen from the data in Tables 1 to 4 that the ash content of the polymer in Comparative Example 1 is relatively high without washing, and the isotacticity is relatively low, indicating the necessity of washing and deashing; the oxidation induction time of the polypropylene pellets in Comparative Example 2 has poor parallelism (the results of the two tests are 13.7 and 41.5 min, respectively), indicating the necessity of improving the uniform mixing of the compounding agent powder and the polypropylene powder; the ash content of the polymer in Comparative Example 3 is relatively high and the molecular weight of the polymer is reduced when the solvent is not refined and washed in an air atmosphere, and the oxidation induction time when only a free radical scavenger and an acid scavenger resin are added is relatively low, indicating the necessity of refining the detergent and washing under inert conditions, and the compounding agent requires the coordinated action of the three components of the free radical scavenger, the peroxide decomposer and the acid scavenger to achieve good antioxidant capacity.

Claims

1. A method for preparing polypropylene material for capacitor film, characterized in that: The following steps are involved: Propylene is polymerized under the action of a catalyst to obtain a polymerization product system; separating a polypropylene product from the polymerization product system; Under anhydrous and oxygen-free conditions, washing the polypropylene product with a detergent that has been subjected to dehydration and / or deoxygenation treatment, and drying the washed product to obtain a polypropylene powder; After spraying the compounding agent solution containing free radical scavenger, peroxide decomposer and acid absorbent onto the polypropylene powder, the polypropylene powder is dried and granulated to obtain the polypropylene material for capacitor film.

2. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: The solvent in the compounding agent solution is an organic solvent; Preferably, the organic solvent is selected from one or a combination of two or more of substituted or unsubstituted alkanes, aromatic hydrocarbons, ketone compounds and alcohol compounds; Further preferably, the substituted or unsubstituted alkane is selected from one or a combination of two or more of chloroform, pentane, hexane, heptane, octane, isooctane, n-nonane, n-decane and methylcyclohexane; Further preferably, the aromatic hydrocarbon is selected from one or a combination of two or more of toluene, ethylbenzene, xylene and trimethylbenzene; Further preferably, the ketone compound is selected from one or a combination of two or more of acetone, butanone and propiophenone; Further preferably, the alcohol compound is selected from one or a combination of two or more of ethanol, isopropanol and n-butanol.

3. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: The detergent comprises one or a combination of two or more of inert alkanes, inert aromatic hydrocarbons and C1-C8 organic alcohols; Preferably, the inert alkane is selected from one or a combination of two or more of n-hexane, n-heptane and petroleum ether; Preferably, the inert aromatic hydrocarbon is selected from one or a combination of two or more of toluene, xylene, chlorobenzene and dichlorobenzene; Preferably, the C1-C8 organic alcohol is selected from one or a combination of two or more of ethanol, isopropanol and isooctyl alcohol.

4. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: Before carrying out the polymerization, the preparation method further comprises the step of refining the propylene; Preferably, the refining method includes one or a combination of two or more of dehydration treatment, deoxygenation treatment, desulfurization treatment, dealcoholization treatment, carbon monoxide removal treatment and carbon dioxide removal treatment; Further preferably, in the propylene after the purification, the water content is below 0.5 mg / kg, the methanol content is below 0.5 mg / kg, the oxygen content is below 0.5 mg / kg, the total sulfur content is below 0.1 mg / kg, the carbon monoxide content is below 0.1 mg / kg, and the carbon dioxide content is below 0.1 mg / kg.

5. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: The polymerization activity of the catalyst is more than 120,000 times; Preferably, the catalyst is selected from a Ziegler-Natta catalyst system; the Ziegler-Natta catalyst system comprises a main catalyst, a co-catalyst and an external electron donor; Further preferably, the main catalyst is a supported titanium-containing Ziegler-Natta main catalyst; the co-catalyst comprises alkyl aluminum and / or halogenated alkyl aluminum; the external electron donor comprises an organosilicon compound; More preferably, in the catalyst, the molar ratio of Al in the co-catalyst to Ti in the main catalyst is 200-50; the molar ratio of Si in the external electron donor to Ti in the main catalyst is 10-2.

6. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: The free radical scavenger is selected from hindered phenol compounds; and / or The peroxide decomposer is selected from phosphite-containing compounds and / or organic sulfur-containing compounds; and / or The acid absorbent is selected from stearate compounds and / or hydrotalcite compounds containing intercalated structures.

7. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: The total amount of the free radical scavenger, the peroxide decomposer and the acid absorbent is 0.2-0.5wt% of the weight of the polypropylene powder; Preferably, the weight ratio of the free radical scavenger, the peroxide decomposer and the acid absorbent is 1:0.5-2:0.01-0.

05.

8. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: The weight ratio of the detergent to the polypropylene product is 2 to 10:

1.

9. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: The washing temperature is 70-90°C.

10. The method for preparing polypropylene material for capacitor film according to claim 1, characterized in that: During the polymerization process, the polymerization reaction temperature is 70-80° C., the time is 2-4 hours, and the pressure is 3-5 MPa.

11. A polypropylene material for capacitor film, characterized in that: The polypropylene material for capacitor film is prepared by the preparation method of any one of claims 1 to 10.

12. The polypropylene material for capacitor film according to claim 11, characterized in that: The polypropylene material for the capacitor film has an ash content of less than 20 ppm, an isotacticity of more than 98%, a mass average molecular weight of 350,000 to 450,000, a molecular weight distribution of 6 to 8, a melt index of 2.5 to 4.0 g / 10 min, a tensile elastic modulus of more than 1500 MPa, a tensile yield stress of more than 34 MPa, a melting temperature of more than 165° C., an oxidation induction time of more than 35 min, and a volume resistivity of more than 3×10 15 Ω·m, dielectric loss factor is less than 5×10 -4 .

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