A modified montmorillonite and a polypropylene film

Abstract

The present invention relates to a modified montmorillonite and a polypropylene film comprising the modified montmorillonite. The modified montmorillonite is prepared by chemically reacting a crown ether and metal ions with the montmorillonite. The present invention also provides a polypropylene film comprising polypropylene, a hindered amine flame retardant, and the modified montmorillonite. The present invention utilizes efficient coordination and chelation between the crown ether and the metal ions to enable the montmorillonite to exert a nano-enhancement effect while also achieving condensed-phase flame retardancy through carbonization by the crown ether and catalytic carbonization by the metal ions. Simultaneously, the hindered amine flame retardant in the polypropylene film achieves gas-phase flame retardancy by capturing active free radicals in the gas phase during combustion.

Description

Technical Field

[0001] The invention belongs to the technical field of polypropylene, and in particular relates to modified montmorillonite and a polypropylene film comprising the modified montmorillonite. Background Art

[0002] Cast polypropylene (CPP) film is a PP film produced through a cast extrusion process. It boasts excellent transparency, high gloss, heat and moisture resistance, easy heat sealing, and low cost. Since its successful development in the 1960s, CPP film has been widely used in packaging for food, medicine, clothing, and daily necessities. With the annual increase in China's CPP production capacity, competition in the market for standard CPP film has become increasingly fierce, leading to the development of high-performance CPP film. In recent years, with the rapid development of emerging industries such as new energy and high-strength composite materials, high-strength and flame-retardant CPP film has begun to be widely used. Specifically, the packaging films for new energy soft-pack lithium-ion batteries place high demands on film strength and flame retardancy. Currently, commercially available soft-pack lithium-ion battery packaging films primarily achieve flame retardancy and strength through the use of embedded aluminum foil and a multilayer composite material. However, the complex production process and significant cost increase for this film have limited the widespread application of soft-pack lithium-ion batteries. Summary of the Invention

[0003] The purpose of the present invention is to provide a modified montmorillonite with good flame retardant and reinforcing properties in order to solve the above technical problems, and to use the modified montmorillonite in polypropylene film to obtain a polypropylene film with high strength and high flame retardancy.

[0004] The above-mentioned object of the present invention is achieved through the following technical solution: a modified montmorillonite, wherein the modified montmorillonite is prepared by chemical reaction of crown ether and metal ions with montmorillonite.

[0005] Montmorillonite is a natural material with a nano-layered structure. The present invention uses crown ethers and metal ion salts to modify the montmorillonite. When the crown ether is introduced into the montmorillonite through adsorption, a large number of O or N atoms in the crown ether molecule can further coordinate and chelate with the metal ions, thereby introducing different metal ions into the modified montmorillonite. This not only greatly improves the strength of the modified montmorillonite and plays a reinforcing role, but also the crown ether and rare earth metal ions or transition metal ions inserted into the modified montmorillonite can catalyze carbonization during combustion, thereby improving the flame retardant effect.

[0006] In the above-mentioned modified montmorillonite, the preparation method of the modified montmorillonite is specifically as follows: first, natural montmorillonite is dispersed in an aqueous solution, and then an acetone solution of crown ether is slowly added dropwise to the montmorillonite aqueous solution, and continuously stirred. After the reaction is completed, the mixture is filtered and dried to obtain intermediate 1; intermediate 1 is added to a metal salt solution, and continuously stirred. After the reaction is completed, the mixture is filtered, washed with water, and dried to obtain modified montmorillonite.

[0007] In the modified montmorillonite, the reaction temperature is 20-50° C. Preferably, the reaction temperature is 30° C. If the temperature is too high, greater than 50° C., the crown ether may volatilize excessively, resulting in incomplete reaction.

[0008] In the modified montmorillonite, the reaction time is 4-48 hours, preferably 24 hours.

[0009] In the modified montmorillonite, the crown ether is one or more of 15-crown-5 ether (structural formula I below), diaza-15-crown-5 ether (structural formula II below), 18-crown-6 ether (structural formula III below), diaza-18-crown-6 ether (structural formula IV below), phenyl-18-crown-6 ether (structural formula V below), diphenyl-18-crown-6 ether (structural formula VI below), and cryptand (structural formula VII below);

[0010]

[0011] In the modified montmorillonite, the ratio of the crown ether to the natural montmorillonite is (100-300) mmol / 100g. Preferably, the ratio of the crown ether to the natural montmorillonite is 150 mmol / 100g.

[0012] In the modified montmorillonite, the metal ions are obtained by adding a metal salt, wherein the metal salt comprises a transition metal salt. Preferably, the metal salt comprises one or more of lanthanum nitrate, cerium nitrate, cesium chloride, rubidium chloride, nickel nitrate, zinc nitrate, and copper chloride.

[0013] The second object of the present invention is to provide a polypropylene film, which comprises polypropylene, a hindered amine flame retardant and the modified montmorillonite.

[0014] As is well known, the flame retardant properties of polypropylene are relatively poor, and the addition of flame retardants will significantly deteriorate the mechanical properties of the film, making it unable to meet the high flame retardant requirements of industries such as soft-pack lithium-ion batteries and high-strength composites for film. The present invention adds hindered amine flame retardants and modified montmorillonite to polypropylene. The nanosheet structure of the modified montmorillonite itself can, on the one hand, play a nano-enhancement role and improve the mechanical properties of polypropylene, and on the other hand, play a covering barrier role and improve the flame retardant properties of polypropylene. In addition, the crown ether present in the modified montmorillonite can act as a carbonizing agent during the combustion process, and the metal ions can play a catalytic carbonization role during the combustion process, and the efficient catalysis promotes the formation of the carbon layer, and then play a flame retardant role in the condensed phase, while improving the flame retardant and mechanical properties of the polypropylene film, meeting the high flame retardant and mechanical properties requirements of industries such as soft-pack lithium-ion batteries and high-strength composites for film.

[0015] The polypropylene film comprises 84-93 wt% polypropylene, 5-15 wt% modified montmorillonite, and 1-2 wt% hindered amine flame retardant. While the flame retardancy of the polypropylene film increases with the addition of the flame retardant, its mechanical properties are significantly reduced, rendering it of no practical value. The reason for adding a hindered amine flame retardant rather than a conventional flame retardant is that the combined effect of 1-2 wt% of the hindered amine flame retardant and 5-15 wt% of the modified montmorillonite not only imparts improved flame retardancy to the polypropylene film without affecting its mechanical properties, but also significantly improves its mechanical properties.

[0016] In the above-mentioned polypropylene film, the hindered amine flame retardant is one or both of NOR116 and T-NOR. The specific structural formulas of NOR116 and T-NOR are as follows:

[0017]

[0018] Compared to existing technologies, the present invention produces high-strength, flame-retardant cast polypropylene film through integrated flame retardancy and reinforcement. This invention utilizes crown ether-modified montmorillonite. Through the efficient coordination and chelation between the crown ether and metal ions, rare earth metals or transition metal ions are introduced into the montmorillonite. This allows the montmorillonite to both exert its nano-reinforcement properties and achieve condensed-phase flame retardancy through carbonization by the crown ether and catalytic carbonization by the metal ions. Simultaneously, the hindered amine flame retardant in the polypropylene film achieves gas-phase flame retardancy by capturing active free radicals in the gas phase during combustion. The condensed-phase-gas-phase synergistic flame retardancy achieved by the modified montmorillonite and hindered amine flame retardant significantly improves the flame retardancy of polypropylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the infrared spectrum of the montmorillonite modified with cerium chelate 18-crown 6 ether in Example 2 of the present invention. DETAILED DESCRIPTION

[0020] Below by specific embodiment and accompanying drawing, technical scheme of the present invention is further described explanation, it should be understood that specific embodiment described herein is only for helping to understand the present invention, is not used for specific limitation of the present invention.And accompanying drawing used herein, is only for better illustrating the disclosure of the present invention, does not have limiting effect on protection scope.If no special instructions, the raw materials adopted in the embodiment of the present invention are all raw materials commonly used in this area, and the method adopted in the embodiment is all conventional method in this area.

[0021] Example 1: Modified montmorillonite

[0022] First, natural montmorillonite was dispersed in an aqueous solution, and then a 3 wt % diaza-15-crown-5 ether acetone solution was slowly added dropwise to the montmorillonite aqueous solution to eventually form 200 mmol crown ether / 100 g montmorillonite. The mixed solution was reacted at 30°C for 24 hours, filtered, and dried to obtain intermediate 1. Subsequently, intermediate 1 was added to a 5 wt % lanthanum nitrate solution, stirred at room temperature for 24 hours, filtered, washed with water three times, and dried to obtain modified montmorillonite.

[0023] Example 2: Modified montmorillonite

[0024] First, natural montmorillonite was dispersed in an aqueous solution, and then a 3 wt % 18-crown-6 ether acetone solution was slowly added dropwise to the montmorillonite aqueous solution to eventually form 150 mmol crown ether / 100 g montmorillonite. The mixed solution was reacted at room temperature for 24 hours, filtered, and dried to obtain intermediate 1. Subsequently, intermediate 1 was added to a 5 wt % cerium nitrate solution, stirred at room temperature for 24 hours, filtered, washed with water three times, and dried to obtain modified montmorillonite.

[0025] Example 3: Modified montmorillonite

[0026] First, natural montmorillonite was dispersed in an aqueous solution, and then a 3 wt % 18-crown-6 ether acetone solution was slowly added dropwise to the montmorillonite aqueous solution to eventually form 300 mmol crown ether / 100 g montmorillonite. The mixed solution was reacted at room temperature for 24 hours, filtered, and dried to obtain intermediate 1. Subsequently, intermediate 1 was added to a 5 wt % nickel nitrate solution, stirred at room temperature for 24 hours, filtered, washed with water three times, and dried to obtain modified montmorillonite.

[0027] Example 4: Modified montmorillonite

[0028] First, natural montmorillonite was dispersed in an aqueous solution, and then a 3 wt % diphenyl 18-crown 6 ether acetone solution was slowly added dropwise to the montmorillonite aqueous solution to eventually form 150 mmol crown ether / 100 g montmorillonite. The mixed solution was reacted at 50°C for 48 hours, filtered, and dried to obtain intermediate 1. Subsequently, intermediate 1 was added to a 5 wt % cesium chloride solution, stirred at room temperature for 24 hours, filtered, washed with water three times, and dried to obtain modified montmorillonite.

[0029] Example 5: Modified montmorillonite

[0030] First, natural montmorillonite was dispersed in an aqueous solution, and then a 3wt% cryptand acetone solution was slowly added dropwise to the montmorillonite aqueous solution to eventually form 150mmol crown ether / 100g montmorillonite. The mixed solution was reacted at 40°C for 36h, filtered, and dried to obtain intermediate 1. Subsequently, intermediate 1 was added to a 5wt% cerium nitrate solution, stirred at room temperature for 24h, filtered, washed with water three times, and dried to obtain modified montmorillonite.

[0031] Example 6: Modified montmorillonite

[0032] First, natural montmorillonite was dispersed in an aqueous solution, and then a 3 wt % 18-crown-6 ether acetone solution was slowly added dropwise to the montmorillonite aqueous solution to eventually form 150 mmol crown ether / 100 g montmorillonite. The mixed solution was reacted at 20° C. for 10 h, filtered, and dried to obtain intermediate 1. Subsequently, intermediate 1 was added to a 5 wt % zinc nitrate solution, stirred at room temperature for 24 h, filtered, washed with water three times, and dried to obtain modified montmorillonite.

[0033] Example 7: Polypropylene film

[0034] 93 wt% of polypropylene, 2 wt% of NOR116 and 5 wt% of the modified montmorillonite in Example 1 were mixed in a high-speed mixer, and then the mixture was added to a screw extruder for melt extrusion and passed through a three-roll casting machine to form a CPP film with a thickness of 25 μm.

[0035] Example 8: Polypropylene film

[0036] 89 wt% of polypropylene, 1 wt% of NOR116 and 10 wt% of the modified montmorillonite in Example 2 were mixed in a high-speed mixer, and then the mixture was added to a screw extruder for melt extrusion and passed through a three-roll casting machine to form a CPP film with a thickness of 25 μm.

[0037] Example 9: Polypropylene film

[0038] 84 wt% of polypropylene, 1 wt% of NOR116 and 15 wt% of the modified montmorillonite in Example 3 were mixed in a high-speed mixer, and then the mixture was added to a screw extruder for melt extrusion and passed through a three-roll casting machine to form a CPP film with a thickness of 25 μm.

[0039] Example 10: Polypropylene film

[0040] The only difference from Example 8 is that the modified montmorillonite in this example is taken from the modified montmorillonite prepared in Example 4 and made into a CPP film with a thickness of 25 μm.

[0041] Example 11: Polypropylene film

[0042] The only difference from Example 8 is that the hindered amine flame retardant in this example is T-NOR, and a CPP film with a thickness of 25 μm is prepared.

[0043] Example 12: Polypropylene film

[0044] 88 wt% of polypropylene, 2 wt% of T-NOR and 10 wt% of the modified montmorillonite in Example 5 were mixed in a high-speed mixer, and then the mixture was added to a screw extruder for melt extrusion and passed through a three-roll casting machine to form a CPP film with a thickness of 25 μm.

[0045] Example 13: Polypropylene film

[0046] The only difference from Example 8 is that the amount of modified montmorillonite added in this example is 3 wt %, and a CPP film with a thickness of 25 μm is prepared.

[0047] Example 14: Polypropylene film

[0048] The only difference from Example 8 is that the amount of modified montmorillonite added in this example is 16 wt %, and a CPP film with a thickness of 25 μm is prepared.

[0049] Example 15: Polypropylene film

[0050] The only difference from Example 8 is that in this example, the amount of NOR116 added is 0.5 wt %, and a CPP film with a thickness of 25 μm is prepared.

[0051] Example 16: Polypropylene film

[0052] The only difference from Example 8 is that in this example, the amount of NOR116 added is 2.5 wt %, and a CPP film with a thickness of 25 μm is prepared.

[0053] Comparative Example 1

[0054] Pure polypropylene was added into a screw extruder for melt extrusion and passed through a three-roll casting machine to form a CPP film with a thickness of 25 μm.

[0055] Comparative Example 2

[0056] 98 wt% polypropylene and 2 wt% NOR116 were mixed in a high-speed mixer, and then the mixture was added to a screw extruder for melt extrusion and passed through a three-roll casting machine to form a CPP film with a thickness of 25 μm.

[0057] Comparative Example 3

[0058] Compared with Example 8, this comparative example does not contain NOR116 and only contains 11 wt% of modified montmorillonite.

[0059] Comparative Example 4

[0060] Compared with Example 8, the montmorillonite in this comparative example is natural montmorillonite.

[0061] Comparative Example 5

[0062] Compared with Example 8, NOR116 in this comparative example was replaced with a common flame retardant.

[0063] Comparative Example 6

[0064] Compared with Example 8, NOR116 in this comparative example was replaced with a common flame retardant (triphenyl phosphate).

[0065] The CPP films prepared in Examples 7-16 and Comparative Examples 1-6 were cut into appropriate strips and tested for flame retardancy (LOI and vertical flammability UL-94) and tensile strength. The LOI and vertical flammability UL-94 values were tested according to ASTM D2863-19 and ASTM D4804-20, respectively, while the tensile strength was tested according to GB / T13022-1991. The test results are shown in the table below.

[0066] Test results of performance parameters of polypropylene CPP films prepared in Examples 7-16 and Comparative Examples 1-6

[0067] Tensile strength (MPa) LOI (%) UL-94 Example 7 26.8 26 VTM-1 Example 8 27.5 27 VTM-0 Example 9 25 28 VTM-0 Example 10 27.3 26 VTM-1 Example 11 26.3 27 VTM-0 Example 12 27 26 VTM-0 Example 13 23.8 25 VTM-1 Example 14 23.5 25 VTM-0 Example 15 25.5 25 VTM-1 Example 16 24.5 27 VTM-0 Comparative Example 1 22.1 18 No level Comparative Example 2 20.8 22 No level Comparative Example 3 24.5 23 VTM-2 Comparative Example 4 23.6 22 No level Comparative Example 5 24.3 20 No level Comparative Example 6 24.5 20 No level

[0068] In summary, compared to pure CPP, CPP containing only a hindered amine flame retardant, CPP containing only modified montmorillonite, or CPP containing conventional flame retardants and unmodified montmorillonite, the polypropylene film of the present invention, incorporating both modified montmorillonite and a hindered amine flame retardant, exhibits significantly improved flame retardancy, achieving an oxygen index as high as 28% and passing the UL-94 flame retardancy rating of VTM-0. This demonstrates the significant role of the condensed-phase-vapor-phase synergistic flame retardancy achieved by the modified montmorillonite and hindered amine. Furthermore, due to the modified montmorillonite's inherent nanosheet structure, the tensile strength of the CPP containing the modified montmorillonite is significantly improved, confirming the present invention's integrated flame retardancy enhancement.

[0069] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the present invention and are not intended to limit the manner in which the present invention is intended to be implemented. Persons skilled in the art may make various modifications, additions, or substitutions to the described embodiments, and it is not necessary or possible to provide a comprehensive list of all possible embodiments. However, any obvious changes or modifications arising from the essential spirit of the present invention remain within the scope of protection of the present invention, and interpreting them as any additional limitations would be contrary to the spirit of the present invention.

Claims

1. A polypropylene film, characterized in that The mass percentages of the components in the polypropylene film are: 84-93 wt% polypropylene, 5-15 wt% modified montmorillonite, and 1-2 wt% hindered amine flame retardant. The hindered amine flame retardant is one or both of NOR116 and T-NOR. The specific structural formulas of NOR116 and T-NOR are as follows: ， ； The modified montmorillonite is prepared by chemical reaction of crown ether and metal ions with montmorillonite. The preparation method is as follows: first, natural montmorillonite is dispersed in an aqueous solution, then an acetone solution of the crown ether is slowly added dropwise to the montmorillonite aqueous solution, and the mixture is continuously stirred. After the reaction is completed, the mixture is filtered and dried to obtain an intermediate 1; the intermediate 1 is added to a metal salt solution, and the mixture is continuously stirred. After the reaction is completed, the mixture is filtered, washed with water, and dried to obtain the modified montmorillonite. The ratio of crown ether to natural montmorillonite is (100-300) mmol / 100g.

2. The polypropylene film according to claim 1, characterized in that The crown ether is one or more of 15-crown-5 ether (structural formula I below), diaza-15-crown-5 ether (structural formula II below), 18-crown-6 ether (structural formula III below), diaza-18-crown-6 ether (structural formula IV below), phenyl-18-crown-6 ether (structural formula V below), diphenyl-18-crown-6 ether (structural formula VI below), and cryptand (structural formula VII below); 。 3. The polypropylene film according to claim 1, wherein The metal salts include transition metal salts.

4. The polypropylene film according to claim 1, characterized in that The metal salt includes one or more of lanthanum nitrate, cerium nitrate, cesium chloride, rubidium chloride, nickel nitrate, zinc nitrate and copper chloride.

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