An antistatic and high-toughness plastic packaging film and its preparation method

Abstract

This invention discloses an antistatic and high-toughness plastic packaging film and its preparation method, belonging to the field of polymer composite materials technology. The packaging film uses linear low-density polyethylene as the matrix resin, compounded with carbon nanotubes modified by methanesulfonic acid activation, silane coupling agent KH-570 grafting, and PEG-PLA block copolymer, supplemented with antioxidants, lubricants, and tributyl citrate. In the preparation process, the carbon nanotubes are first mildly acidified and activated, and then modified with multiple components. The raw materials are then premixed, extruded using a twin-screw extruder, and formed using casting stretching or blown film processes. This invention solves the problem of carbon nanotube agglomeration through composite modification, improving its interfacial bonding with the matrix, and reducing the surface resistivity of the resulting packaging film to 4×10⁻⁶. 7 With an Ω·cm content, it combines excellent antistatic properties with high toughness, overcoming the shortcomings of traditional carbon nanotube modified packaging films where antistatic and mechanical properties are difficult to coordinate, and is suitable for packaging fields such as food and electronic components.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically relating to an antistatic and high-toughness plastic packaging film and its preparation method. Background Technology

[0002] Plastic packaging films are widely used in the packaging and protection of food, electronic components, precision instruments, and industrial parts due to their advantages such as light weight, good flexibility, low cost, and convenient processing. Ordinary plastic packaging films are insulating materials with extremely high surface resistivity. During production, transportation, and use, static electricity easily accumulates due to friction and contact. On the one hand, this attracts dust and impurities, affecting the packaging's appearance and product cleanliness; on the other hand, electrostatic discharge can easily damage electronic components and pose safety hazards to flammable and explosive materials. Therefore, antistatic modification is an important research and development direction for plastic packaging films.

[0003] Carbon nanotubes, with their ultra-high aspect ratio, excellent electrical conductivity, and mechanical strength, have become ideal fillers for antistatic modification of plastic packaging films. A small amount can create conductive pathways, achieving long-lasting antistatic effects. However, in practical applications, directly adding carbon nanotube fillers has two major technical drawbacks: First, the inertness and poor interfacial compatibility of the original carbon nanotube surface make them prone to aggregation in the plastic matrix, forming stress concentration points. This leads to a sharp decrease in the toughness and elongation at break of the packaging film, making it prone to cracking and damage, failing to meet the flexibility requirements of packaging films. Second, simple acidification or coupling agent modification of carbon nanotubes only improves dispersibility and cannot simultaneously address the interfacial bonding with the flexible plastic matrix, making it difficult to synergistically improve antistatic performance and mechanical toughness. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an antistatic and high-toughness plastic packaging film and its preparation method, solving the technical problems of traditional carbon nanotube modified plastic packaging films being unable to simultaneously achieve antistatic performance and toughness, as well as the tendency of carbon nanotubes to agglomerate and weak interfacial bonding.

[0005] This invention constructs a composite modified carbon nanotube filler that combines dispersibility, interfacial compatibility, and flexible segments through carbon nanotube acidification and activation, grafting with silane coupling agent KH-570, and PEG-PLA block copolymer. Specifically, methanesulfonic acid gently activates and preserves the carbon nanotube wall structure and conductivity, while introducing active hydroxyl groups; KH-570 coupling agent enables preliminary organic grafting of carbon nanotubes, improving compatibility with the plastic matrix; the PEG-PLA block copolymer, with its flexible PEG and PLA segments, effectively embeds into the plastic packaging film matrix resin, significantly enhancing interfacial bonding. Simultaneously, the flexible segments release internal stress and inhibit crack propagation, addressing the problem of decreased film toughness caused by the addition of carbon nanotubes.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An antistatic, high-toughness plastic packaging film, by weight, comprises the following components: 90-95 parts of matrix resin, 2-5 parts of composite modified carbon nanotubes, 0.3-1 part of antioxidant, 0.2-0.8 parts of lubricant, and 0.5-1.5 parts of plasticizer.

[0007] A method for preparing an antistatic, high-toughness plastic packaging film includes the following steps: S1. Carbon nanotube acidification and activation: Prepare a 1.5%-2.5% (w / w) methanesulfonic acid aqueous solution. Add carbon nanotubes to the solution at a mass ratio of 1:(5-8) and activate by stirring at a constant temperature of 90-100℃ for 3-5 hours. After activation, filter the solution and wash the filter cake repeatedly with distilled water until the filtrate is neutral. Dry the filtrate under vacuum at 60-75℃ for 20-24 hours to obtain activated carbon nanotubes. This step uses mild acid etching, which only introduces active hydroxyl groups on the surface of the carbon nanotubes without damaging their wall structure and aspect ratio, thus preserving their electrical and mechanical properties.

[0008] S2. Carbon nanotube composite modification: Activated carbon nanotubes were mixed with anhydrous ethanol at a mass ratio of 1:(80-120) and ultrasonically dispersed for 20-40 min to obtain a dispersion. Ammonia was added to adjust the pH of the system to 8.5-10.0. Under stirring at room temperature, a mixture of silane coupling agent (KH-570) and anhydrous ethanol was slowly added dropwise. The amount of KH-570 was 40%-60% of the mass of activated carbon nanotubes. The mixture was pre-reacted at room temperature for 1.5-3 h to allow the coupling agent to be fully hydrolyzed and grafted. Then, PEG-PLA block copolymer (20%-35% of the mass of activated carbon nanotubes) was added, and the temperature was raised to 45-60℃. The mixture was kept at this temperature and stirred for 2-4 h for composite modification. After the reaction was completed, the mixture was centrifuged, washed with anhydrous ethanol to remove unreacted additives, and vacuum dried to obtain composite modified carbon nanotubes.

[0009] S3. Premixing of membrane raw materials: According to the formula ratio, the composite modified carbon nanotubes, matrix resin, antioxidant, lubricant, and plasticizer are added to a high-speed mixer and mixed at room temperature and high speed for 10-20 minutes until all components are uniformly mixed to obtain the membrane mixture. The matrix resin is linear low-density polyethylene; The antioxidant is selected as antioxidant 1010, the lubricant is selected as calcium stearate, and the plasticizer is selected as tributyl citrate. The components, by weight, are as follows: 90-95 parts of matrix resin, 2-5 parts of composite modified carbon nanotubes, 0.3-1 part of antioxidant, 0.2-0.8 parts of lubricant, and 0.5-1.5 parts of plasticizer.

[0010] S4. Film Formation Process: The mixture is fed into a twin-screw extruder, and the temperature of each section of the extruder is controlled in stages: Zone 1 160-170℃, Zone 2 170-185℃, Zone 3 185-200℃, and the die head 200-220℃. Forming is achieved using either a casting and stretching process or a blown film process: (1) Casting and stretching: The die head temperature is 190-210℃, and the cooling rollers are temperature-controlled in sections: 25-30℃ for the front section, 30-35℃ for the middle section, and 35-40℃ for the rear section; the longitudinal stretch ratio is 2.5-3.0 times, and the transverse stretch ratio is 3.0-4.0 times. After shaping, traction, and winding, an antistatic and high-toughness plastic packaging film is produced.

[0011] (2) Film blowing: The extrusion die temperature is 180-205℃, the air supply temperature in the bubble tube is 30-38℃, and the traction roller temperature is 28-35℃; the blow-up ratio is controlled at 1.8-2.5, and the traction stretch ratio is 2.8-3.5 times. After air cooling, shaping, traction, and winding, the antistatic high-toughness plastic packaging film is obtained.

[0012] The beneficial effects of this invention are as follows: (1) The present invention adopts a process of mild activation with methanesulfonic acid and composite modification with KH-570 and PEG-PLA block copolymer, which not only solves the problem of carbon nanotube agglomeration and achieves uniform dispersion in the matrix, but also greatly improves the interfacial bonding force between carbon nanotubes and plastic matrix through PEG-PLA flexible segments, avoids the generation of interfacial defects, and overcomes the problem of decreased membrane toughness caused by the addition of antistatic fillers.

[0013] (2) Composite modified carbon nanotubes construct continuous and stable conductive pathways inside the packaging film, reducing the surface resistivity of the film to 4×10⁻⁶. 7 It has a strength of Ω·cm and exhibits excellent long-lasting antistatic properties.

[0014] (3) The flexible segments of PEG-PLA block copolymer can effectively disperse stress and increase toughness, combining high flexibility and impact resistance. Attached Figure Description

[0015] Figure 1 (a) Scanning electron microscope image of carbon nanotubes, (b) SEM image of sample of Comparative Example 1, (c) SEM image of sample of Example 1. Figure 2 Strain curves of the samples in Example 1 and Comparative Examples 1-3. Detailed Implementation

[0016] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely illustrative and explanatory of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the inventive concept, all of which should fall within the protection scope of the present invention. The preparation method of the present invention will be described below through specific embodiments.

[0017] Example 1 S1. Acidification and activation of carbon nanotubes: Prepare a 1.5% methanesulfonic acid aqueous solution, add carbon nanotubes to the solution at a mass ratio of 1:5, and activate by stirring at 90℃ for 5 hours; after activation, filter by suction, wash the filter cake repeatedly with distilled water until the filtrate is neutral, and dry under vacuum at 60℃ for 24 hours to obtain activated carbon nanotubes.

[0018] S2. Carbon nanotube composite modification: Activated carbon nanotubes and anhydrous ethanol were mixed at a mass ratio of 1:80 and ultrasonically dispersed for 20 min to obtain a uniform dispersion. Ammonia was added to adjust the pH of the system to 8.5. Under stirring at room temperature, a mixture of silane coupling agent KH-570 and anhydrous ethanol was slowly added dropwise. The amount of KH-570 was 40% of the mass of activated carbon nanotubes. The mixture was pre-reacted at room temperature for 3 h. Subsequently, PEG-PLA block copolymer (20% of the mass of activated carbon nanotubes) was added, and the temperature was raised to 45℃. The mixture was kept at this temperature and stirred for 4 h for composite modification. After the reaction was completed, the mixture was centrifuged, washed with anhydrous ethanol to remove unreacted auxiliaries, and vacuum dried to obtain composite modified carbon nanotubes.

[0019] S3. Premixing raw materials for membranes: Weigh 95 parts of linear low-density polyethylene, 2 parts of composite modified carbon nanotubes, 0.3 parts of antioxidant 1010, 0.2 parts of calcium stearate, and 0.5 parts of tributyl citrate by weight, add them to a high-speed mixer, mix at room temperature and high speed for 10 minutes until all components are mixed evenly to obtain the membrane mixture.

[0020] S4. Film Forming Process: The mixture is fed into a twin-screw extruder, with precise temperature control in each section: Zone 1 160℃, Zone 2 172℃, Zone 3 188℃, and Die Head 202℃. A casting and stretching process is used for forming, with a die head temperature of 195℃ and segmented temperature control on the cooling rollers: front section 25℃, middle section 30℃, and rear section 35℃. The longitudinal stretching ratio is 2.5 times, and the transverse stretching ratio is 3.0 times. After shaping, traction, and winding, the antistatic high-toughness plastic packaging film is obtained.

[0021] Example 2 S1. Acidification and activation of carbon nanotubes: Prepare a 2.0% methanesulfonic acid aqueous solution, add carbon nanotubes to the solution at a mass ratio of 1:6.5, and activate by stirring at 95℃ for 4 hours; after activation, filter by suction, wash the filter cake repeatedly with distilled water until the filtrate is neutral, and dry under vacuum at 70℃ for 22 hours to obtain activated carbon nanotubes.

[0022] S2. Carbon nanotube composite modification: Activated carbon nanotubes and anhydrous ethanol were mixed at a mass ratio of 1:100 and ultrasonically dispersed for 30 min to obtain a uniform dispersion. Ammonia water was added to adjust the pH of the system to 9.0. Under stirring at room temperature, a mixture of silane coupling agent KH-570 and anhydrous ethanol was slowly added dropwise. The amount of KH-570 was 50% of the mass of activated carbon nanotubes. The pre-reaction was carried out at room temperature for 2 h. Subsequently, PEG-PLA block copolymer (28% of the mass of activated carbon nanotubes) was added, the temperature was raised to 55℃, and the composite modification was carried out by stirring for 3 h. After the reaction was completed, the mixture was centrifuged, washed with anhydrous ethanol to remove unreacted auxiliaries, and vacuum dried to obtain composite modified carbon nanotubes.

[0023] S3. Premixing raw materials for membranes: Weigh 93 parts of linear low-density polyethylene, 3.5 parts of composite modified carbon nanotubes, 0.6 parts of antioxidant 1010, 0.5 parts of calcium stearate, and 1.0 part of tributyl citrate by weight, add them to a high-speed mixer, and mix at room temperature and high speed for 15 minutes until all components are mixed evenly to obtain the membrane mixture.

[0024] S4. Film Forming Process: The mixture is fed into a twin-screw extruder, with precise temperature control in each section: Zone 1 165℃, Zone 2 178℃, Zone 3 192℃, and Die Head 210℃. A casting and stretching process is used for forming, with a die head temperature of 200℃ and segmented temperature control of the cooling rollers: front section 28℃, middle section 32℃, and rear section 38℃. The longitudinal stretching ratio is 2.8 times, and the transverse stretching ratio is 3.5 times. After shaping, traction, and winding, the antistatic high-toughness plastic packaging film is obtained.

[0025] Example 3 S1. Acidification and activation of carbon nanotubes: Prepare a 2.5% methanesulfonic acid aqueous solution, add carbon nanotubes to the solution at a mass ratio of 1:8, and activate by stirring at 100℃ for 3 hours; after activation, filter by suction, wash the filter cake repeatedly with distilled water until the filtrate is neutral, and dry under vacuum at 75℃ for 20 hours to obtain activated carbon nanotubes.

[0026] S2. Carbon nanotube composite modification: Activated carbon nanotubes and anhydrous ethanol were mixed at a mass ratio of 1:120 and ultrasonically dispersed for 40 min to obtain a uniform dispersion. Ammonia was added to adjust the pH of the system to 10.0. Under stirring at room temperature, a mixture of silane coupling agent KH-570 and anhydrous ethanol was slowly added dropwise. The amount of KH-570 was 60% of the mass of activated carbon nanotubes. The pre-reaction was carried out at room temperature for 1.5 h. Subsequently, PEG-PLA block copolymer (35% of the mass of activated carbon nanotubes) was added, the temperature was raised to 60℃, and the composite modification was carried out by stirring for 2 h. After the reaction was completed, the mixture was centrifuged, washed with anhydrous ethanol to remove unreacted auxiliaries, and vacuum dried to obtain composite modified carbon nanotubes.

[0027] S3. Premixing raw materials for membranes: Weigh 90 parts by weight of linear low-density polyethylene, 5 parts by weight of composite modified carbon nanotubes, 1 part by weight of antioxidant 1010, 0.8 parts by weight of calcium stearate, and 1.5 parts by weight of tributyl citrate. Add them to a high-speed mixer and mix at room temperature and high speed for 20 minutes until all components are mixed evenly to obtain a membrane mixture.

[0028] S4. Film Forming Process: The mixture is fed into a twin-screw extruder, with precise temperature control in each section: Zone 1 170℃, Zone 2 185℃, Zone 3 198℃, and Die Head 218℃. A blown film process is used for forming, with the extrusion die temperature at 195℃, the bubble tube air supply temperature at 35℃, the traction roller temperature at 32℃, the blow-up ratio at 2.2, and the traction stretch ratio at 3.2. After air cooling, shaping, traction, and winding, the antistatic high-toughness plastic packaging film is obtained.

[0029] Comparative Example 1 Compared with Example 1, no modification was performed on the carbon nanotubes; the original carbon nanotubes were used directly. The remaining raw material ratios, preparation processes, film-forming temperatures, and process parameters were exactly the same as in Example 1, and a plastic packaging film was prepared.

[0030] Comparative Example 2 Compared with Example 1, carbon nanotubes were only activated with methanesulfonic acid and grafted with KH-570, without the addition of PEG-PLA block copolymer, and the block copolymer composite modification step was omitted. The remaining raw material ratios, preparation processes, film-forming temperatures and process parameters were exactly the same as in Example 1, and a plastic packaging film was prepared.

[0031] Comparative Example 3 Compared with Example 1, no carbon nanotube components were added to the formulation, and the remaining raw material ratios, preparation processes, film-forming temperatures and process parameters were exactly the same as in Example 1, resulting in the preparation of a pure linear low-density polyethylene packaging film.

[0032] Product performance test results

[0033] As can be seen from the surface resistivity data in Table 1, the surface resistivity of the pure polyethylene packaging film in Comparative Example 3 is 8 × 10⁻⁶. 10 It easily accumulates static electricity; In Comparative Example 1, unmodified carbon nanotubes were directly added. Due to severe aggregation, they could not form a continuous conductive path and still behaved as an insulator, with no antistatic effect at all. Comparative Example 2, with a surface resistivity of only 2×10⁻⁶. 11 Ω·cm, the antistatic effect is weak; In Example 1 of this invention, the surface resistivity was stably reduced to 4 × 10⁻⁶. 7 Ω·cm, which is within the ideal antistatic resistivity range.

[0034] This demonstrates that the carbon nanotubes modified by the present invention can construct a continuous, dense, and stable conductive network pathway in the plastic film matrix. A small amount of addition can achieve excellent long-lasting antistatic performance, overcoming the technical shortcomings of ordinary modified carbon nanotubes, which cannot effectively conduct static electricity and have poor antistatic effects.

[0035] Figure 1 (a) shows the original carbon nanotube morphology, which is extremely prone to entanglement and aggregation. Figure 1 (b) is a SEM image of the unmodified carbon nanotube-filled film of Comparative Example 1. It can be seen that the carbon nanotubes are heavily aggregated and accumulated in the polyethylene matrix, with poor dispersion uniformity, and are prone to forming obvious defects and stress concentration points inside the matrix. Figure 1 (c) is a SEM image of the composite modified carbon nanotube filled film of Example 1 of the present invention. After modification, the carbon nanotubes are more uniformly dispersed in the matrix and there is no obvious agglomeration or entanglement.

[0036] Figure 2 The stress-strain curves of Example 1 and Comparative Examples 1, 2, and 3 can visually reflect the membrane toughness and elongation at break: Although the pure polyethylene film in Comparative Example 3 has good toughness, it has no antistatic ability. Comparative Example 1 with unmodified carbon nanotubes and Comparative Example 2 with only simple coupling modification. Due to the aggregation of carbon nanotubes, weak interfacial bonding, and a large number of defects in the matrix, the elongation at break decreased significantly, the brittleness increased, and the toughness of the membrane was greatly reduced. The strain curve of Embodiment 1 of this invention shows that the tensile deformation capacity is far superior to that of the comparative examples, and the elongation at break and tensile toughness are significantly improved.

[0037] The PEG-PLA block copolymer flexible segments introduced in this invention strengthen the interfacial bonding between carbon nanotubes and the matrix, eliminating interfacial defects. On the other hand, the flexible segments can disperse internal stress and inhibit crack propagation when subjected to force. While constructing conductive and antistatic pathways, it perfectly solves the industry pain point that the addition of traditional carbon nanotubes leads to a sharp drop in the toughness of packaging films and easy cracking and damage, achieving a synergistic improvement in antistatic performance and high mechanical toughness.

Claims

1. A method for preparing an antistatic, high-toughness plastic packaging film, characterized in that, Includes the following steps: S1. Carbon nanotube acidification and activation: Prepare a 1.5%-2.5% methanesulfonic acid aqueous solution, add carbon nanotubes to the solution at a mass ratio of 1:(5-8), stir and activate at 90-100℃ for 3-5 hours, filter, wash until neutral, and vacuum dry to obtain activated carbon nanotubes; S2. Carbon nanotube composite modification: Activated carbon nanotubes were mixed with anhydrous ethanol and ultrasonically dispersed. The pH was adjusted to 8.5-10.0, and KH-570 anhydrous ethanol solution was added dropwise for pre-reaction. Then, PEG-PLA block copolymer was added and the mixture was heated for composite modification. After centrifugation, washing, and drying, the composite modified carbon nanotubes were obtained. S3. Raw material premixing: The composite modified carbon nanotubes, matrix resin, antioxidant, lubricant and plasticizer are mixed at room temperature and high speed to obtain a mixture; S4. Film forming process: The mixture is extruded through an extruder and shaped using casting stretching or blown film processes to obtain plastic packaging film.

2. The preparation method according to claim 1, characterized in that, In step S1, the vacuum drying temperature is 60-75℃ and the drying time is 20-24h.

3. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of activated carbon nanotubes to anhydrous ethanol is 1:(80-120), and the mixture is ultrasonically dispersed for 20-40 min. The pre-reaction conditions are room temperature reaction for 1.5-3 h, composite modification temperature of 45-60℃, and time of 2-4 h.

4. The preparation method according to claim 1, characterized in that, In step S2, the amount of KH-570 used is 40%-60% of the mass of activated carbon nanotubes; the amount of PEG-PLA block copolymer used is 20%-35% of the mass of activated carbon nanotubes.

5. The preparation method according to claim 1, characterized in that, In step S3, the matrix resin is linear low-density polyethylene; The antioxidant is selected as antioxidant 1010, the lubricant is selected as calcium stearate, and the plasticizer is selected as tributyl citrate. The components, by weight, are as follows: 90-95 parts of matrix resin, 2-5 parts of composite modified carbon nanotubes, 0.3-1 part of antioxidant, 0.2-0.8 parts of lubricant, and 0.5-1.5 parts of plasticizer.

6. The preparation method according to claim 1, characterized in that, In step S4, the extruder is a twin-screw extruder, and the temperatures of each section are: Zone 1 160-170℃, Zone 2 170-185℃, Zone 3 185-200℃, and the die head 200-220℃.

7. The preparation method according to claim 1, characterized in that, In step S4, the casting and stretching process parameters are as follows: die head temperature 190-210℃, cooling roller front section 25-30℃, middle section 30-35℃, rear section 35-40℃, longitudinal stretching ratio 2.5-3.0 times, and transverse stretching ratio 3.0-4.0 times.

8. The preparation method according to claim 1, characterized in that, In step S4, the blown film process parameters are: extrusion die temperature 180-205℃, bubble tube air supply temperature 30-38℃, traction roller temperature 28-35℃, blow-up ratio 1.8-2.5, and traction stretching ratio 2.8-3.5 times.

9. An antistatic, high-toughness plastic packaging film prepared by the preparation method according to any one of claims 1-8.

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