A polyolefin elastomer for photovoltaic encapsulation films, its preparation method and application

Abstract

This invention discloses a polyolefin elastomer for photovoltaic encapsulation films, its preparation method, and its application. The polyolefin elastomer simultaneously meets the following requirements: a) residual metal element content <100 ppm, b) total grain content <2% with a grain thickness Lc > 4 nm as continuously measured by differential scanning calorimetry (SSA). When applied to the preparation of photovoltaic encapsulation films, the polyolefin elastomer proposed in this invention maintains the advantage of fewer film-forming crystal points even at high casting speeds, while also helping to reduce additive absorption time, demonstrating advantages in both production cost and product performance.

Description

Technical Field

[0001] This invention relates to a photovoltaic encapsulation film material, and more particularly to a polyolefin elastomer for photovoltaic encapsulation films, its preparation method, and its application. Background Technology

[0002] With the rapid development of the photovoltaic industry, photovoltaic encapsulation film, as a key material for photovoltaic modules, directly affects the power generation efficiency and lifespan of these modules. Polyolefin elastomer (POE), due to its excellent light transmittance, weather resistance, and electrical insulation properties, has become the main raw material for photovoltaic encapsulation films.

[0003] Currently, polyolefin elastomers used in photovoltaic encapsulation films are mainly copolymerized from ethylene and α-olefins. Their molecular structure, molecular weight, and molecular weight distribution have a significant impact on the performance of the final encapsulation film. Existing research has proposed numerous solutions to improve the applicability of POE through adjustments to product indicators and processes. For example, patent application CN120365466A, by preparing bimodal distributed ethylene and α-olefin random or block polymers and combining them with crosslinking agents, solved the problems of uneven dispersion and failure in improving the transmittance of photovoltaic films, achieving high transmittance and high-efficiency power generation in photovoltaic cells. Patent application WO2025043950A1, by preparing POE particles with special microstructures and optimizing their soluble content, solved the degradation problem of photovoltaic films under PID effects, achieving photovoltaic compositions with high transmittance and high anti-PID performance, thus improving the stability and lifespan of photovoltaic modules. Patent application WO2025043950A1, through a dual-reactor tandem solution polymerization process, combined with dynamic chemical crosslinking agents and initiators, and optimized catalyst ratios, solved the problems of complex preparation processes and poor performance control of dynamically crosslinked polyolefin elastomers, achieving the preparation of high-performance dynamically crosslinked polyolefin elastomers.

[0004] However, existing polyolefin elastomers still present some problems when applied to photovoltaic encapsulation films. Firstly, crystal point issues severely impact product quality and performance during photovoltaic encapsulation film processing. While patent application CN119410295A achieved high light transmittance and high cross-linking degree in photovoltaic encapsulation films by adjusting the molecular weight, molecular weight distribution, and long-chain content of the polyolefin elastomer, it failed to effectively solve the crystal point problem. These crystal points reduce the film's light transmittance, thereby affecting the photovoltaic module's absorption and conversion efficiency of sunlight.

[0005] Secondly, as the photovoltaic industry continues to demand higher production efficiency, encapsulant film processing companies need to increase production line speeds to reduce unit energy consumption and production costs. However, the processing performance bottlenecks of existing materials severely restrict breakthroughs in production efficiency, especially under high-speed processing conditions, which are more prone to crystal point defects and are difficult to adapt to ultra-high-speed casting processes (such as line speeds > 15 m / min). Summary of the Invention

[0006] To address the above technical problems, this invention proposes a polyolefin elastomer for photovoltaic encapsulation films, its preparation method, and its application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] Based on the first aspect of the present invention, a polyolefin elastomer for photovoltaic encapsulation film is first proposed, characterized in that the polyolefin elastomer simultaneously meets the following requirements: a) residual amount of metal elements <100ppm, b) total grain content with grain thickness Lc >4nm as continuously measured by differential scanning calorimetry (SSA) <2%.

[0009] In a preferred embodiment, the polyolefin elastomer has a molecular weight (Mw) of 40,000-100,000, a PDI of 2-2.5, and a density of 0.87-0.878 g / cm³. 3 .

[0010] In a preferred embodiment, the olefin elastomer is prepared by solution polymerization of ethylene and α-olefin;

[0011] Preferably, the α-olefin is an olefin with 3-13 carbon atoms, and more preferably one or more of propylene, butene, hexene, octene, nonene, and decene.

[0012] During their ongoing research, the inventors unexpectedly discovered that by adjusting the residual amount of metal elements and the total content of Lc>4nm grains in polyolefin elastomers within a specific range, the processing performance and crystal point level of photovoltaic encapsulation films can be effectively improved. In particular, when increasing the casting line speed during the photovoltaic encapsulation film processing, good low crystal point characteristics can still be maintained. This is further manifested in the accelerated absorption rate of additives by POE particles, demonstrating significant application performance advantages.

[0013] In this invention, the grain thickness Lc of the polyolefin elastomer is obtained through SSA thermal grading measurement. Specifically, DSC is applied to the sample for SSA treatment, causing copolymer segments with different sequence structures to form lamellar crystals of varying thicknesses based on differences in crystallinity. Subsequently, the lamellar crystals of different thicknesses exhibit multiple melting peaks during the final temperature scan of the DSC. The grain thickness of each component is calculated from the peak temperatures of the multiple melting peaks according to the Thomson-Gibbs equation, thereby characterizing the distribution of the copolymer chain crystallization sequence.

[0014] The mass fraction of each component corresponding to different grain thicknesses is obtained by multiplying its corresponding melting peak area fraction by 293 / AHm(T) and normalizing, where AHm(T) is the melting enthalpy of each component. The total content of grains with a grain thickness Lc > 4 nm is obtained by summing the mass fractions of the components.

[0015] Based on a second aspect of the present invention, a method for preparing a polyolefin elastomer as described above is also proposed, characterized in that an organic solvent and an α-olefin are added to a reaction vessel, ethylene gas is introduced to the reaction pressure, and a main catalyst and a co-catalyst are added and stirred to react.

[0016] After the reaction is completed, the reactants are inactivated to obtain a reactant solution. After removing the volatile components, the reactants are granulated in an aqueous solution containing a nucleating agent and dried to obtain polyolefin elastomer particles.

[0017] Preferably, the nucleating agent is one or more of sodium benzoate, sodium adipic acid, and sodium phenolate;

[0018] Preferably, in the aqueous solution, the mass ratio of nucleating agent to water is (0.5-3):1000.

[0019] To obtain polyolefin elastomers with a residual amount of metal elements of <100ppm as specified above, this can be achieved by increasing the activity of the main catalyst and reducing the actual amount of main catalyst or co-catalyst added, or by using or combining post-treatment methods such as chelation adsorption. This invention does not impose any restrictions on this.

[0020] As feasible methods to improve the activity of the main catalyst, one can choose a metallocene catalyst or post-metallocene catalyst with high copolymerization activity, or choose a metallocene catalyst or post-metallocene catalyst with good high-temperature stability in conjunction with a high-temperature polymerization process, or combine a co-catalyst to reduce the amount of metal elements added, especially the co-catalyst combined with organoborides to significantly reduce the amount of metal-containing main catalyst and co-catalyst, etc., which are easy for industry technicians to adjust.

[0021] As a feasible post-treatment method, such as chelation adsorption disclosed in CN114950368B and CN114989331B, the residual amount of metal elements can be advantageously controlled to below 100 ppm.

[0022] In order to control the total content of larger crystals to below 2%, this invention, based on the consideration of simple and convenient operation, preferably introduces a nucleating agent during the granulation process after the polymerization reaction. The nucleating agent provides crystallization nuclei during particle forming, enabling the polymer to form small and dense crystals, reducing the generation of large-sized crystals, and making the product structure controllable.

[0023] As a preferred embodiment of the above preparation method, the main catalyst is a metallocene catalyst or a post-metallocene catalyst, preferably dimethicyl(N-tert-butylamino)(tetramethylcyclopentadienyl)titanium chloride, dimethicyl(N-tert-butylamino)(tetramethylcyclopentadienyl)dimethyltitanium, dimethicyl(N-tert-butylamino)(fluorenyl)titanium chloride, (pentamethylcyclopentadienyl)trimethoxytitanium, diphenylmethylene(cyclopentadiene)(9-fluorenyl)zirconium chloride, dimethyldimethylalkylbis(2-methyl-4-phenyl-1-indenyl)zirconium chloride, mesodimethylsilylbis(1-indenyl)zirconium chloride, (bis(methylcyclopentadiene)zirconium chloride), (bis(1,3-dimethylcyclopentadienyl)zirconium chloride, (cyclopentadienyl)(1,2-dimethoxyethane)zirconium chloride, diphenylsilyl(cyclopentadiene) One or more of the following: (9-fluorenyl)zirconia, racemic dimethylsilylbis(2-methyl-1-indenyl)zirconia, diphenylmethylenecyclopentadiene(2,7-di-tert-butyl-fluorenyl)zirconia, di-p-tolymethylenecyclopentadiene(2,7-di-tert-butyl-fluorenyl)zirconia, dimethylbis(propylcyclopentadienyl)hafnium, bis(n-butylcyclopentadiene)hafnium, dimethylsilylbis(2-methyl-4-phenylindenyl)zirconia, and dimethylsilane(tert-butylamino)tetramethylcyclopentadienyldimethyltitanium. Typically, the amount of the main catalyst added can be adjusted from 0.1 to 10 ppm by weight of the polymer.

[0024] As a preferred embodiment of the above preparation method, the co-catalyst includes one or more of aluminum oxane, alkyl aluminum and their modifiers, preferably one or more of methylaluminoxane, modified methylaluminoxane, triethylaluminum, triisobutylaluminum, trioctylaluminum, monochloroethylaluminum, sesquiethylaluminum, and dichloroethylaluminum.

[0025] Preferably, the cocatalyst also optionally comprises an organoboride, preferably one or more of triphenylmethyltetra(pentafluorophenyl)borate, tri(pentafluorophenyl)boron, N,N-dimethylanilinetetra(pentafluorophenyl)borate, bis(octadecylmethyl)tertiaryaminetetra(pentafluorophenyl)borate, and dihydrotallowylmethyl)tertiaryaminetetra(pentafluorophenyl)borate.

[0026] Typically, the molar ratio (Al / M) of metallic aluminum in the co-catalyst to that of the metal element in the main catalyst can be 1-2000, preferably 1-800; when the co-catalyst contains organoborides, the amount of metallic aluminum can be further reduced.

[0027] Typically, the molar ratio (denoted as B / M) of boron in the organoboride to the metal element in the main catalyst can be 0-8, preferably 1-5.

[0028] As a preferred embodiment of the above preparation method, the reaction temperature is 140-200℃ and the reaction pressure is 3-8MPa.

[0029] As a preferred embodiment of the above preparation method, the granulation temperature is 0-20℃.

[0030] As a preferred embodiment of the above preparation method, the organic solvent is selected from aliphatic hydrocarbon solvents and / or aromatic hydrocarbon solvents;

[0031] Preferably, the aliphatic hydrocarbon solvent is selected from one or more of n-butane, isobutane, n-pentane, cyclopentane, methylcyclopentane, methylenecyclopentane, n-hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, n-heptane, n-octane, n-nonane, and Isopar E; the aromatic hydrocarbon solvent is selected from one or more of benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, and dichlorotoluene.

[0032] Based on a third aspect of the present invention, the application of a polyolefin elastomer as described above or a polyolefin elastomer prepared by the method described above in a photovoltaic encapsulation film is also proposed.

[0033] As a specific example, a photovoltaic encapsulation film is characterized by comprising the following components in parts by weight:

[0034] Polyolefin elastomer, 100 parts

[0035] Crosslinking agent, 0.1-5 parts, preferably 0.5-2 parts.

[0036] Crosslinking agent, 0.1-5 parts, preferably 0.1-2 parts.

[0037] Coupling agent, 0.1-3 parts, preferably 0.1-0.6 parts.

[0038] The polyolefin elastomer is either the polyolefin elastomer for photovoltaic encapsulation films provided above or the polyolefin elastomer prepared by the method described above.

[0039] Preferably, the crosslinking agent is a peroxide-based crosslinking agent, comprising, but not limited to, one or more of the following substances: tert-butyl peroxycarbonate isopropyl ester, 2,5-dimethyl-2,5-(bis-tert-butylperoxy)hexane, tert-butyl peroxycarbonate-2-ethylhexyl ester, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-pentylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-pentylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-pentylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)butane, tert-butyl peroxy-2-ethylhexyl carbonate, tert-pentyl peroxy-(2-ethylhexyl) carbonate, and tert-butyl peroxy-3,3,5-trimethylhexanoate.

[0040] Further, the crosslinking agent is a multifunctional acrylate, including but not limited to one or more of the following substances: trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, triallyl isocyanurate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated glycerol triacrylate, propoxylated glycerol triacrylate, pentaerythritol tetraacrylate, ethoxylated pentaerythritol tetraacrylate, trimethylolpropane tetraacrylate, bis(trimethylolpropane tetraacrylate), bis(trimethylolpropane tetramethacrylate), propoxylated pentaerythritol tetraacrylate, tricyclodecanediethanol diacrylate, propoxylated neopentyl glycol diacrylate, ethoxylated bisphenol A diacrylate, ethoxylated bisphenol A dimethacrylate, 2-butyl-2-ethyl-1,3-propanediol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate;

[0041] Furthermore, the coupling agent is a silane coupling agent, including but not limited to one or more of the following substances: γ-chloropropylmethoxysilane, dimethylvinylethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloyloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidyletheroxypropyltrimethoxysilane, 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate, anilinemethyltriethoxysilane, and octyltrimethoxysilane.

[0042] In this invention, the photovoltaic encapsulation film can be prepared using conventional methods in the art, including, for example, the following steps: high-temperature premixing of raw materials, melt extrusion, casting into a film, cooling and slitting, and winding.

[0043] The beneficial effects of this invention are as follows:

[0044] The polyolefin elastomer proposed in this invention, when used in the preparation of photovoltaic encapsulation films, still has the advantage of fewer film-forming crystal points at high casting speeds, while also helping to reduce the absorption time of additives, demonstrating advantages in both production cost and product performance. Detailed Implementation

[0045] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0046] In this invention, “parts” and “%” are by weight, unless otherwise specified.

[0047] Unless otherwise specified, the raw materials and reagents used in the following embodiments and comparative examples of this invention can be obtained through commercially available channels. Information on the main raw materials is as follows:

[0048] Methylaluminoxane, Akzo, 10% toluene solution;

[0049] Modified methylaluminoxane, Noryon;

[0050] Dimethylsilylbis(2-methyl-4-phenylindidine)zirconium dichloride, Yaodexin Chemical;

[0051] Di(2,7-di-tert-butyl-fluorenyl)zirconium dichloride, Yanfeng Technology;

[0052] Dimethicyl (N-tert-butylamino) (tetramethylcyclopentadienyl)dimethyltitanium, Jiangsu Xinnoco Catalyst Co., Ltd.;

[0053] Dimethylbis(propylcyclopentadienyl)hafnium, Yanfeng Technology;

[0054] Diphenylmethylenecyclopentadiene (2,7-di-tert-butyl-fluorenyl)zirconium dichloride, Yaodexin Chemical Co., Ltd.

[0055] Dimethylsilane (tert-butylamino)tetramethylcyclopentadienyldimethyltitanium, Xinnoco.

[0056] The main performance testing methods and equipment involved in the following embodiments and comparative examples of this invention are as follows:

[0057] (1) Melt index: The tester used was ZwickMflow, and the test standard was ASTM D1238;

[0058] (2) Extruder: Single screw extruder (L / D=35), screw diameter 30mm;

[0059] (3) Molecular weight and insertion rate: The tester used was Polymer Char, GPC-IR;

[0060] (4) Metal residue: After wet decomposition of polyolefin elastomer, it is diluted with pure water and the metal elements are quantified using an inductively coupled plasma atomic emission spectrometer (ICP) - Agilent, USA. The total amount of these elements is taken as the metal residue, in ppm.

[0061] (5) Grain content: The polyolefin elastomer was measured by SSA thermal classification using a DSC analyzer. The specific method was as follows: In the first cycle, the temperature was raised to 150℃, held for 1 minute, and then lowered to -50℃; in the second cycle, the temperature was raised to 120℃, held for 5 minutes, and then lowered to -50℃; in the third cycle, the temperature was raised to 112.5℃, held for 5 minutes, and then lowered to -50℃; the process of raising the temperature and holding it for 5 minutes and then lowering it was repeated as above. The fourth cycle (i.e., in the fourth cycle, the temperature was raised to the highest point of 105℃ at intervals of 7.5℃ and held for 5 minutes and then lowered to -50℃), the fifth cycle (i.e., in the fifth cycle, the temperature was raised to the highest point of 97.5℃ at intervals of 7.5℃ and held for 5 minutes and then lowered to -50℃), the sixth cycle, and so on, until the temperature reached -40℃. The final temperature scan was then performed to obtain the multiple melting peaks corresponding to the lamellar crystals of different thicknesses.

[0062] According to the Thomson-Gibbs equation, the grain thickness of each component was calculated from the melting point of the multiple melting peaks:

[0063]

[0064] In the formula, Tm is the melting point of the melting peak, T 0 m is the equilibrium melting point of the polyethylene flake (418.5 K), and σ is the free energy of the side surface of the infinitely large polyethylene flake (90 × 10⁻⁶ K). -3 J / m 2 ), ΔHv is the enthalpy of fusion of infinitely large polyethylene flakes (293 × 10⁻⁶). 6 J / m 3 ).

[0065] Simultaneously, the mass fraction of each component is obtained by multiplying the melting peak area fraction of each component by 293 / AHm(T) and normalizing, where AHm(T) is the melting enthalpy of each component. The mass fractions of components with grain thickness Lc > 4 nm are summed to obtain the total content of grains with grain thickness Lc > 4 nm as measured by SSA.

[0066] The following Examples 1-8 and Comparative Examples 1-3 were used to prepare different polyolefin elastomers:

[0067] Example 1

[0068] Preparation of polyolefin elastomer A: Solution polymerization was used. 2.8 kg of octene was added to 4.2 kg of n-butane solvent to prepare a solution, which was then added to a reactor. The temperature was raised to 150°C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 3 MPa. 1 mg of the main catalyst, dimethylsilylbis(2-methyl-4-phenylindidine)zirconia, was added to the reactor, along with a co-catalyst (a 1.5 mol / L methylaluminoxane toluene solution) at an Al / Zr ratio of 20. Tris(pentafluorophenyl)boron was also added, with a molar ratio of boron in the organoboronide to the metal element in the main catalyst (denoted as B / Zr) of 2. After stirring for 8 minutes, 30 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed using an aqueous solution of sodium benzoate at a mass ratio of 1000:0.5 and a water temperature of 10°C. The granulated product was dried to obtain the polymer, polyolefin elastomer A (Mw = 69000, PDI = 2.5, density = 0.8712 g / cm³). 3 The metal residue was 75 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm was 1.7%.

[0069] Example 2

[0070] Preparation of polyolefin elastomer B: 2.6 kg of octene was added to 5 kg of Isopar E to form a solution, which was then added to a reactor. The temperature was raised to 148 °C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 5 MPa. 4.88 mg of the main catalyst, di-p-toluene-methylenecyclopentadiene (2,7-di-tert-butyl-fluorenyl)zirconia dichloride, was added to the reactor. A co-catalyst (a 1.5 mol / L methylaluminoxane toluene solution) was added at an Al / Zr ratio of 40. Tris(pentafluorophenyl)boron was added simultaneously, with a B / Zr molar ratio of boron in the organoboronide to the metal element in the main catalyst of 1.3. After stirring for 10 minutes, 30 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed using an aqueous solution of sodium adipic acid (water to sodium adipic acid mass ratio of 1000:1) at 15°C. The granulated product was dried to obtain the polymer, polyolefin elastomer B (Mw: 57000, PDI: 2.2, density: 0.8750 g / cm³). 3 The metal residue content is 90 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm is 1.9%.

[0071] Example 3

[0072] Preparation of polyolefin elastomer C: Solution polymerization was used. 1.9 kg of butene was added to 5.7 kg of Isopar E to form a solution, which was then added to a reactor. The temperature was raised to 155°C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 3 MPa. 18.4 mg of the main catalyst, dimethylsilyl(N-tert-butylamino)(tetramethylcyclopentadienyl)dimethyltitanium, was added to the reactor. A co-catalyst (7 wt% Al-modified methylaluminoxane Isopar E solution) was added at an Al / Ti ratio of 30. Tris(pentafluorophenyl)boron was added simultaneously, with a molar ratio of boron in the organoboronide to the metal element in the main catalyst (B / Ti) of 4. After stirring for 8 minutes, 30 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed using an aqueous solution of sodium benzoate at a mass ratio of 1000:2.5 and a water temperature of 8°C. The granulated product was dried to obtain the polymer, namely polyolefin elastomer C (Mw = 51000, PDI = 2.15, density = 0.8731 g / cm³). 3 The metal residue was 48 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm was 0.5%.

[0073] Example 4

[0074] Preparation of polyolefin elastomer D: Solution polymerization was used. 3.3 kg of hexene was added to 8.9 kg of Isopar E solvent to prepare a solution, which was then added to a reactor. The temperature was raised to 140°C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 4 MPa. 25.2 mg of the main catalyst, dimethylbis(propylcyclopentadienyl)hafnium, was added to the reactor. A co-catalyst (a 1.5 mol / L methylaluminoxane toluene solution) was added at an Al / Hf ratio of 45. Tris(pentafluorophenyl)boron was added simultaneously, with a B / Hf molar ratio of boron in the organoboronide to the metal element in the main catalyst of 2. After stirring for 7 minutes, 30 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed. The aqueous solution was an aqueous solution of sodium phenolate, with a water-to-sodium phenolate mass ratio of 1000:1.5 and a water temperature of 5°C. After granulation and drying, the polymer, polyolefin elastomer D (Mw: 58000, PDI: 2.25, density: 0.8725 g / cm³), was obtained. 3 The metal residue was 93 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm was 0.2%.

[0075] Example 5

[0076] Preparation of polyolefin elastomer E: Solution polymerization was used. 2.35 kg of octene was added to 4.68 kg of Isopar E solvent to prepare a solution, which was then added to a reactor. The temperature was raised to 160 °C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 3.5 MPa. 20.4 mg of the main catalyst, diphenylmethylenecyclopentadiene (2,7-di-tert-butylfluorenyl)zirconia dichloride, was added to the reactor. A co-catalyst (7% Al Isopar E modified methylaluminoxane solution) was added at an Al / Zr ratio of 10. Tris(pentafluorophenyl)boron was added simultaneously, with a molar ratio of boron in the organoboronide to the metal element in the main catalyst (B / Zr) of 1.5. After stirring for 6 minutes, 30 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed using an aqueous solution of sodium benzoate at a water-to-sodium benzoate mass ratio of 1000:1 and a water temperature of 1°C. After granulation and drying, the polymer, polyolefin elastomer E (Mw: 64000, PDI: 2.34, density: 0.8720 g / cm³), was obtained. 3 The metal residue was 41 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm was 1.1%.

[0077] Example 6

[0078] Preparation of polyolefin elastomer F:

[0079] Preparation of polyolefin elastomer F: 3.2 kg of octene was added to 4.8 kg of Isopar E to form a solution, which was then added to a reactor. The temperature was raised to 145 °C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 4.5 MPa. 5.12 mg of the main catalyst, di-p-toluene-methylenecyclopentadiene (2,7-di-tert-butyl-fluorenyl)zirconia dichloride, was added to the reactor. A co-catalyst (a 1.5 mol / L methylaluminoxane toluene solution) was added at an Al / Zr ratio of 20. Triphenylmethyltetra(pentafluorophenyl)borate was added simultaneously, with a B / Zr molar ratio of boron in the organoboronide to the metal element in the main catalyst of 3. After stirring for 8 minutes, 50 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed using an aqueous solution of sodium adipic acid (water to sodium adipic acid mass ratio of 1000:1.5) at 12°C. The granulated product was dried to obtain the polymer, polyolefin elastomer B (Mw 49000, PDI 2.3, density 0.8720 g / cm³). 3 The metal residue was 58 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm was 1.7%.

[0080] Example 7

[0081] Preparation of polyolefin elastomer G:

[0082] Preparation of polyolefin elastomer G: Solution polymerization was used. 2.1 kg of octene was added to 5.1 kg of n-butane solvent to prepare a solution, which was then added to a reactor. The temperature was raised to 140°C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 5 MPa. 1.4 mg of the main catalyst, diphenylmethylene(cyclopentadiene)(9-fluorenyl)zirconia dichloride, was added to the reactor, along with a co-catalyst (a 1.5 mol / L methylaluminoxane toluene solution) at an Al / Zr ratio of 45. Triphenylmethyltetra(pentafluorophenyl)borate was also added, with a boron molar ratio (B / Zr) of 3 between boron in the organoboronide and the metal element in the main catalyst. After stirring for 6 minutes, 60 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed using an aqueous solution of sodium benzoate at a water-to-sodium benzoate mass ratio of 1000:2 at 13°C. The granulated product was dried to obtain the polymer, polyolefin elastomer A (Mw 61000, PDI 2.35, density 0.8732 g / cm³). 3 The metal residue content is 75 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm is 1.5%.

[0083] Example 8

[0084] Preparation of polyolefin elastomer H:

[0085] Preparation of polyolefin elastomer D: Solution polymerization was used. 2.8 kg of hexene was added to 8 kg of Isopar E solvent to prepare a solution, which was then added to a reactor. The temperature was raised to 150°C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 3.5 MPa. 20.1 mg of the main catalyst, dimethylbis(propylcyclopentadienyl)hafnium, was added to the reactor. A co-catalyst (a 1.5 mol / L methylaluminoxane toluene solution) was added at an Al / Hf ratio of 35. Tris(pentafluorophenyl)boron was added simultaneously, with a B / Hf molar ratio of boron in the organoboronide to the metal element in the main catalyst of 2. After stirring for 8 minutes, 50 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed. The aqueous solution was a sodium benzoate solution with a water-to-sodium benzoate mass ratio of 1000:2.5 at 8°C. After granulation and drying, the polymer, polyolefin elastomer D (Mw 55000, PDI 2.35, density 0.8735 g / cm³), was obtained. 3 The metal residue was 93 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm was 1.6%.

[0086] Comparative Example 1

[0087] Preparation of polyolefin elastomer D-1: Solution polymerization was used. 4 kg of octene was added to 7 kg of n-butane solvent to prepare a solution, which was then added to a reactor. The temperature was raised to 150°C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 4 MPa. 20.5 mg (approximately 10 ppm) of the main catalyst, dimethylsilane (tert-butylamino)tetramethylcyclopentadienyldimethyltitanium, was added to the reactor, along with a co-catalyst (a 1.5 mol / L methylaluminoxane toluene solution) at an Al / Zr ratio of 1800. The mixture was stirred for 16 min to obtain a reaction solution. 30 g of water was mixed with the reaction solution, and after removing volatiles, underwater granulation was performed at 25°C. After granulation and drying, the polymer was obtained as polyolefin elastomer D-1. Mw was 68000, PDI was 2.5, and density was 0.8720 g / cm³. 3 The metal residue was 169 ppm, and the total content of grains with a measured grain thickness Lc (nm) > 4 nm was 2.4%.

[0088] Comparative Example 2

[0089] Preparation of polyolefin elastomer D-2: Solution polymerization was used. 2.95 kg of octene was added to 4.92 kg of IsoparE solvent to prepare a solution, which was then added to a reactor. The temperature was raised to 150°C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 4 MPa. 26.2 mg of the main catalyst, diphenylmethylenecyclopentadiene (2,7-di-tert-butyl-fluorenyl)zirconia dichloride, was added to the reactor, along with a co-catalyst (7% Al Isopar E modified methylaluminoxane solution) at an Al / Zr ratio of 2000. After stirring and reacting for 10 minutes, 50 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed using an aqueous solution of sodium benzoate at a water-to-sodium benzoate mass ratio of 1000:1.5 at 6°C. The granulated product was dried to obtain the polymer, polyolefin elastomer E (Mw = 62000, PDI = 2.25, density = 0.8710 g / cm³). 3 The metal residue was 225 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm was 1.4%.

[0090] Comparative Example 3

[0091] Preparation of polyolefin elastomer D-3: 4.15 kg of octene was added to 5.8 kg of Isopar E to form a solution, which was then added to a reactor. The temperature was raised to 145 °C, ethylene gas was introduced, and the pressure inside the reactor was controlled at 5 MPa. 5.12 mg of the main catalyst, diphenylmethylenecyclopentadiene (2,7-di-tert-butylfluorenyl)zirconia dichloride, was added to the reactor. A co-catalyst (a 1.5 mol / L methylaluminoxane toluene solution with Al concentration) was added at an Al / Zr ratio of 60. Tris(pentafluorophenyl)boron was added simultaneously, with a B / Zr molar ratio of boron in the organoboronide to the metal element in the main catalyst of 5. After stirring for 15 minutes, 60 g of water was mixed with the reaction solution for inactivation. After removing volatiles, underwater granulation was performed at 11°C. The granulated product was then dried to obtain the polymer, namely polyolefin elastomer B (Mw = 54000, PDI = 2.28, density = 0.8726 g / cm³). 3 The metal residue was 59 ppm, and the total content of grains with a grain thickness Lc (nm) > 4 nm was 2.87%.

[0092] Application Examples 1-8 and Comparative Examples 1-3

[0093] Using polyolefin elastomer AH and polyolefin elastomers D-1, D-2, and D-3 prepared previously as raw materials, photovoltaic encapsulating films were prepared according to the following methods, corresponding to the preparation of application examples 1-10 and comparative examples 1-3. The specific methods are as follows:

[0094] Add 9g of 2-ethylhexyl carbonate tert-butyl peroxide, 5g of triallyl isocyanurate, 2g of γ-methacryloyloxypropyltrimethoxysilane, and 1g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane to 1000g of polyolefin elastomer. Heat the above raw materials to 50℃ and mix them evenly. Adjust the extruder parameters, setting the temperature from the feed nozzle to the die to 80℃, 90℃, 90℃, 90℃, 90℃, 95℃, 95℃, and 95℃. Adjust the screw speed to 28r / min and the traction speed to 1.4r / min. The extrusion process, including extrusion, casting, cooling, slitting, and rewinding, produces a photovoltaic module encapsulation film with a thickness of 0.55mm. (This process corresponds to a casting linear velocity of 13m / min.)

[0095] Alternatively, the raw materials are mixed and extruded using the same method as described above, with the only difference being the adjustment of the extruder screw speed to 21 r / min, the traction speed to 1.2 r / min, and the winding mechanism to follow the direction of rotation. After extrusion, casting, cooling, slitting, and winding processes, a photovoltaic module encapsulating film with a thickness of 0.55 mm is prepared. (This process corresponds to a casting linear speed of 10 m / min.)

[0096] The absorption time of additives during the production process of photovoltaic encapsulation films in the above application examples 1-10 and application comparative examples 1-3 was tested, and the quantitative evaluation method in the patent application with publication number CN118746677A was used as a reference.

[0097] In addition, the crystal point defect rate of different photovoltaic encapsulation films prepared in the above application examples 1-10 and application comparative examples 1-3 was tested. The test method is as follows: crystal point counting was performed using the ASTM D 3351 standard. An LED backlight detection station was used with an illuminance of not less than 1000 lux. The number of crystal points within a 2 square meter area was detected online, and the final number of defects was obtained.

[0098] Table 1

[0099]

[0100] 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 and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A polyolefin elastomer for a photovoltaic encapsulant film, characterized by, The polyolefin elastomer simultaneously satisfies the following requirements: a) residual amount of metal elements < 100 ppm, b) total content of crystalline grains with grain thickness Lc > 4 nm < 2% measured by using a differential scanning calorimeter for continuous self-nucleation / annealing (SSA); The polyolefin elastomer has a molecular weight Mw of 40,000-100,000, a PDI of 2-2.5, and a density of 0.87-0.878 g / cm 3 ; The olefin elastomer is prepared from ethylene and an alpha-olefin by a solution polymerization method; the alpha-olefin is an olefin with 3-13 carbon atoms; The total content of crystalline grains is measured by SSA thermal fractionation of the polyolefin elastomer using a DSC tester to obtain multiple melting peaks corresponding to different thickness lamellae; according to the Thomson-Gibbs equation, the grain thickness of each component is calculated from the melting point of the multiple melting peaks: where Tmis the melting point of the melting peak, T 0 m is the equilibrium melting point of the polyethylene lamellae 418.5 K, σ is the lateral surface free energy of the infinite polyethylene lamellae 90 x 10 -3 J / m 2 ; and ΔHv is the enthalpy of fusion of the infinite polyethylene lamellae 293 x 10 6 J / m 3 . Meanwhile, the mass fraction of each component is obtained by multiplying the corresponding melting peak area fraction by 293 / AHm(T) and normalizing, wherein AHm(T) is the melting enthalpy corresponding to each component; the mass fraction of components with grain thickness Lc > 4 nm is summed, which is the total content of crystalline grains with grain thickness Lc > 4 nm measured by SSA.

2. The polyolefin elastomer for photovoltaic encapsulating films according to claim 1, characterized by, The alpha-olefin is one or more of propylene, butene, hexene, octene, nonene, and decene.

3. A method for producing a polyolefin elastomer for a photovoltaic encapsulant film as claimed in claim 1 or 2, characterized by, The organic solvent and the alpha-olefin are added to a reaction kettle, ethylene gas is introduced to the reaction pressure, the main catalyst and the cocatalyst are added and stirred to react; After the reaction is completed, the reaction solution is inactivated, and after removing the volatile matter, it is granulated in an aqueous solution containing a nucleating agent, dried, and the polyolefin elastomer particles are obtained. The nucleating agent is one or more of sodium benzoate, sodium adipate, and sodium phenate. In the aqueous solution, the mass ratio of the nucleating agent to water is (0.5-3):1000.

4. The method for preparing a polyolefin elastomer for a photovoltaic encapsulant film according to claim 3, characterized by, The main catalyst is one or more of dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dichloride, dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dimethyl, dimethylsilyl (N-tert-butylamino) (fluorenyl) titanium dichloride, (pentamethylcyclopentadienyl) titanium trimethoxide, bisphenylmethylene (cyclopentadienyl) (9-fluorenyl) zirconium dichloride, dimethylsilyl bis (2-methyl-4-phenyl-1-indenyl) zirconium dichloride, meso-dimethylsilyl bis (1-indenyl) zirconium dichloride, bis (methylcyclopentadienyl) zirconium dichloride, bis (1,3-dimethylcyclopentadienyl) zirconium dichloride, (cyclopentadienyl) (1,2-dimethoxyethane) zirconium trichloride, diphenylsilyl (cyclopentadienyl) (9-fluorenyl) zirconium dichloride, rac-dimethylsilyl bis (2-methyl-1-indenyl) zirconium dichloride, bisphenylmethylene cyclopentadiene (2,7-di-tert-butyl-fluorenyl) zirconium dichloride, bis-p-tolylmethylene cyclopentadiene (2,7-di-tert-butyl-fluorenyl) zirconium dichloride, dimethyl bis (propylcyclopentadienyl) hafnium, bis (n-butylcyclopentadienyl) hafnium dichloride, dimethylsilyl bis (2-methyl-4-phenylindenyl) zirconium dichloride, dimethylsilyl (tert-butylamino) tetramethylcyclopentadienyl dimethyl titanium.

5. The method for preparing the polyolefin elastomer for photovoltaic encapsulation film according to claim 3, characterized in that, The cocatalyst includes one or more of aluminoxane, aluminum alkyl, and their modifications.

6. The method for preparing the polyolefin elastomer for photovoltaic encapsulation film according to claim 5, characterized in that, The co-catalyst is one or more of methylaluminoxane, modified methylaluminoxane, triethylaluminum, triisobutylaluminum, trioctylaluminum, mono-chloroethylaluminum, sesqui-ethylaluminum, di-chloroethylaluminum.

7. The method for preparing the polyolefin elastomer for photovoltaic encapsulation film according to claim 5, characterized in that, The co-catalyst also optionally comprises an organoboron compound.

8. The method of producing a polyolefin elastomer for a photovoltaic encapsulant film according to any one of claims 3 to 7, characterized in that, The reaction temperature is 140-200°C and the reaction pressure is 3-8 MPa.

9. The method of producing a polyolefin elastomer for a photovoltaic encapsulant film according to any one of claims 3 to 7, characterized in that, The temperature conditions for the granulation are 0-20°C.

10. The method of producing a polyolefin elastomer for a photovoltaic encapsulant film according to any one of claims 3 to 7, characterized in that, The organic solvent is selected from aliphatic and / or aromatic hydrocarbon solvents.

11. Use of a polyolefin elastomer as defined in claim 1 or 2 or produced by the process of any of claims 3-10 in a photovoltaic encapsulant film.

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