An environmentally stress crack resistant packaging film material and method of making the same

Abstract

This invention relates to the field of packaging film materials technology, and in particular to a packaging film material resistant to environmental stress cracking and its preparation method. The packaging film material comprises the following raw materials: linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, crack-resistant filler, crack-resistant elastomer, crack-resistant copolymer resin, antioxidant, and lubricant. This invention uses different matrix resins to construct a synergistic system, improving molecular chain flexibility and media resistance, laying the foundation for improving the environmental stress cracking resistance of the packaging film material at the substrate level. Simultaneously, modified heavy calcium carbonate is incorporated into the substrate, along with different crack-resistant modifying components, forming a multi-faceted modification mechanism involving interface reinforcement, stress dispersion, and crystallization regulation. This effectively improves the environmental stress cracking resistance of the packaging film material, enabling it to maintain good structural morphology and mechanical stability even under complex operating environments.

Description

Technical Field

[0001] This invention belongs to the field of packaging film material technology, and in particular relates to a packaging film material resistant to environmental stress cracking and its preparation method. Background Technology

[0002] Packaging film materials, as an indispensable basic consumable in the modern commodity circulation system, are widely used in the transportation and preservation of food, daily chemicals, medical, electronic, and industrial products. With the rapid development of the packaging industry towards lightweight, thin, and high-functionality, the market is placing increasingly stringent requirements on the mechanical reliability of packaging films. Among various polymer film substrates, polyethylene (PE) has become one of the most widely used thermoplastic resins in the packaging film field due to its excellent processing performance, good chemical stability, low cost, and recyclability. However, polyethylene packaging films and other commonly used packaging film materials generally face the technical challenge of environmental stress cracking (ESC) in actual use. Pure polyethylene substrates have high molecular chain regularity and high crystallinity. When in contact with external environmental media such as oils, chemical liquids, acids, and alkalis, the media easily penetrate into the material, reducing intermolecular forces. Simultaneously, under heavy loads, bending, and localized compressive stress, the material is prone to microcracks that propagate rapidly, leading to film cracking and liquid leakage, especially under low temperature and long-term pressure conditions.

[0003] Patent application CN104387653A discloses a high-temperature retort packaging film and its preparation method. This film comprises the following components by weight percentage: 50-60% HDPE and 50-40% LLDPE. The preparation method is as follows: each component is weighed according to the above weight percentages, mixed evenly to obtain a mixture, and then blown into a double-layer co-extrusion blown film machine to obtain the high-temperature retort packaging film. While this high-temperature retort packaging film can withstand a 70-minute retort time at 125-130℃ without damage, exhibiting excellent heat-sealing and processing properties suitable for industrial production, this patent only uses a simple blend of HDPE and LLDPE. HDPE has high crystallinity and inherently poor resistance to environmental stress cracking. The formulation does not include any modifiers to improve this, resulting in a significant shortcoming: poor resistance to environmental stress cracking in the packaging film. Therefore, it is necessary to provide a packaging film material that can withstand environmental stress cracking to solve the problem of poor resistance to environmental stress cracking in existing packaging film materials. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a packaging film material resistant to environmental stress cracking and its preparation method, aiming to solve the problem of insufficient environmental stress cracking resistance in existing packaging film materials.

[0005] To achieve the above objectives, the present invention provides a packaging film material resistant to environmental stress cracking, comprising the following raw materials in parts by weight: 70-85 parts by weight of linear low-density polyethylene, 10-20 parts by weight of low-density polyethylene, 5-12 parts by weight of ethylene-vinyl acetate copolymer, 3-8 parts by weight of metallocene linear low-density polyethylene, 2-5 parts by weight of crack-resistant filler, 8-12 parts by weight of crack-resistant elastomer, 10-15 parts by weight of crack-resistant copolymer resin, 0.3-0.8 parts by weight of antioxidant, and 0.2-0.6 parts by weight of lubricant.

[0006] This invention constructs a synergistic system using linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, and metallocene linear low-density polyethylene, effectively improving the flexibility of the molecular chain and the resistance to media. This lays the foundation for improving the environmental stress cracking resistance of packaging film materials at the substrate level. At the same time, modified heavy calcium carbonate is incorporated into the substrate, along with different crack-resistant modifying components, forming a multi-faceted modification mechanism that enhances interface, disperses stress, and regulates crystallization. This effectively improves the environmental stress cracking resistance of packaging film materials, enabling them to maintain good structural morphology and mechanical stability even under complex usage environments.

[0007] In some embodiments of the present invention, the crack-resistant filler comprises modified heavy calcium carbonate; The crack-resistant elastomer includes Vistamaxx™ 6202 elastomer, which is a propylene-ethylene random copolymer mainly composed of propylene and ethylene monomers. This structure endows it with many excellent properties such as high transparency, thermoplasticity and chemical resistance. Vistamaxx™ 6202 elastomer can maintain good toughness at low temperatures and can also effectively resist the erosion of a variety of chemicals. In addition, it provides extremely high processing flexibility during processing and is suitable for a variety of processing techniques. The Vistamaxx™ 6202 elastomer incorporated in this invention forms an "island structure" by uniformly distributing spherical particles in the matrix resin. When the material is subjected to external stress or environmental erosion, the Vistamaxx™ 6202 elastomer can disperse and dissipate concentrated stress, preventing cracks from rapidly propagating into destructive fractures. More importantly, the Vistamaxx™ 6202 elastomer can insert into the crystalline regions of the matrix resin, disrupting the regular arrangement of molecular chains, inhibiting nucleation and crystal growth, reducing the crystallinity of the matrix resin, and transforming the material from a brittle crystalline state to a more flexible state, thereby improving its resistance to environmental stress cracking. The crack-resistant copolymer resin includes block copolymer polypropylene, which contains an elastic intercalation phase formed by the interaction of ethylene and propylene. Therefore, its addition to the system can introduce elastic block segments into the system and play a stress buffering role in the matrix resin, delaying the initiation and propagation of microcracks. At the same time, the block copolymer polypropylene also contains ethylene components, which can be well compatible with the matrix resin to form a good interfacial bonding state, reducing defects such as phase separation, voids, and interfacial debonding in the blend system, which is beneficial to improving the environmental stress cracking resistance of the auxiliary system. The antioxidant includes at least one of antioxidant 1076, antioxidant 1010, antioxidant 168, and antioxidant THP-24; The lubricant is polyethylene wax.

[0008] In some embodiments of the present invention, the modified heavy calcium carbonate is prepared by first ultrasonically hydrolyzing dried heavy calcium carbonate with isopropyl tris(dioctyl pyrophosphate) titanate ethanol solution to obtain modified material A; then, under nitrogen protection, the surface of modified material A is coated with a mixture of butyl acrylate and ethylene glycol dimethacrylate to obtain modified material B; finally, propyl gallate is added for subsequent processing to obtain the final product.

[0009] In some embodiments of the present invention, the preparation method of the modified heavy calcium carbonate specifically includes the following steps: S1. Isopropyl tris(dioctylpyrophosphoryloxy)titanate and ethanol solution are ultrasonically dispersed and hydrolyzed at room temperature to obtain hydrolysate for later use; butyl acrylate and ethylene glycol dimethacrylate are mixed to obtain mixed solution for later use. S2. Dry heavy calcium carbonate and hydrolysate are stirred in a temperature-controlled oil bath, filtered, and the filter residue is dried under controlled temperature to obtain intermediate modified material A. S3. Mix sodium dodecyl sulfate, deionized water and intermediate modifier A, stir at a controlled speed, then disperse ultrasonically, adjust pH, replace air with nitrogen, add potassium persulfate under controlled temperature in a nitrogen atmosphere and stir, then add the mixture dropwise, keep the temperature controlled after the addition is complete, cool to room temperature, filter, take the filter cake and wash it with deionized water first and then with anhydrous ethanol, dry under controlled temperature to obtain intermediate modifier B; S4. Add intermediate modified material B to deionized water and stir at a controlled speed. Add propyl gallate and stir at a controlled speed again. Filter, take the filter residue, wash with deionized water, and dry at a controlled temperature to obtain modified heavy calcium carbonate.

[0010] In some preferred embodiments of the present invention, the isopropyl tris(dioctyl pyrophosphate) titanate in step S1 is 0.75-1 parts by weight, the ethanol solution is 100 parts by weight, the butyl acrylate is 13.5-16 parts by weight, and the ethylene glycol dimethacrylate is 0.3-0.45 parts by weight. The alkoxy groups in isopropyl tris(dioctylpyrophosphoryloxy)titanate and the hydroxyl functional groups on the surface of heavy calcium carbonate can form a partially covalently bonded and network-structured film that coats the heavy calcium carbonate. In other words, an organic coating layer is formed on the surface of the heavy calcium carbonate. Because the surface of the coated heavy calcium carbonate is covered with an organic layer, the surface energy is reduced, the hydrophobicity is reduced, and the oleophilicity is increased. At this time, adding the coated heavy calcium carbonate to the system is beneficial to the dispersion of heavy calcium carbonate in the system, and further improves the interfacial compatibility between heavy calcium carbonate and matrix resin. This reduces internal defects in the system, and the filled heavy calcium carbonate particles can transfer some energy, disperse local stress concentration, avoid the tendency of the material to brittle fracture, and thus improve the stress cracking resistance of the finished product. Butyl acrylate is coated onto the surface of heavy calcium carbonate via emulsion polymerization to form a coating layer. The low glass transition temperature of the coating layer endows the surface of heavy calcium carbonate with excellent elasticity and interfacial compatibility. At the same time, the flexible coating layer can act as a buffer layer. When a crack encounters the coated particles in the system, it will be deflected, bifurcated or terminated, instead of directly passing through the heavy calcium carbonate particles or propagating along the interface.

[0011] Furthermore, the mass concentration of the ethanol solution in step S1 is 90-95%.

[0012] In some preferred embodiments of the present invention, the ultrasonic dispersion time in step S1 is 20-30 min; the room temperature hydrolysis time is 1.5-2 h.

[0013] In some preferred embodiments of the present invention, the drying of heavy calcium carbonate in step S2 is to dry the heavy calcium carbonate at 75-80°C to a constant weight.

[0014] Furthermore, the heavy calcium carbonate is 2000 mesh with an average particle size D50 (μm) = 3 ± 0.5, and was purchased from Henan Xintai Calcium Industry Co., Ltd.

[0015] In some preferred embodiments of the present invention, the amount of dried heavy calcium carbonate in step S2 is 50-53 parts by weight, and the amount of hydrolysate is 100 parts by weight.

[0016] In some preferred embodiments of the present invention, the temperature of the temperature-controlled oil bath stirring in step S2 is 60-65°C and the time is 2.5-3 hours; the temperature of the temperature-controlled drying is 75-80°C and the time is 3-5 hours.

[0017] In some preferred embodiments of the present invention, the sodium dodecyl sulfate in step S3 is 0.75-0.9 parts by weight, the deionized water is 250-300 parts by weight, the intermediate modifier A is 50-55 parts by weight, the potassium persulfate is 0.25-0.3 parts by weight, and the mixture is 14-16.5 parts by weight.

[0018] In some preferred embodiments of the present invention, the stirring speed in step S3 is 300-400 rpm for 25-30 min; the ultrasonic dispersion time is 30-40 min; the pH adjustment is performed by adjusting the pH to 8-10 with 0.5-1 mol / L NaOH solution; the temperature for adding potassium persulfate and stirring is 70-75°C for 20-30 min; the mixture is added dropwise at a uniform rate over 1-1.5 h; the temperature for maintaining the temperature is 70-75°C for 1-1.5 h; the washing with deionized water is performed 2-3 times, and the washing with anhydrous ethanol is performed 1-2 times; the temperature for drying is 60-65°C for 3-5 h.

[0019] In some preferred embodiments of the present invention, the intermediate modifier B in step S4 is 5-6 parts by weight, the deionized water is 100-120 parts by weight, and the propyl gallate is 0.75-1 parts by weight. Propyl gallate contains a strong coordinating group, pyrogallol, which can adsorb particles on the surface. At the same time, the alkyl chain in the propyl gallate molecule extends outward to provide steric hindrance, effectively inhibiting the agglomeration between heavy calcium carbonate particles and improving the dispersibility between heavy calcium carbonate particles.

[0020] In some preferred embodiments of the present invention, the speed of the controlled stirring in step S4 is 1500-2000 r / min for 30-35 min; the speed of the re-controlled stirring is 1000-1500 r / min for 30-35 min; the number of times the deionized water is washed is 2-3 times; and the temperature-controlled drying is carried out at a controlled temperature of 60-65°C until constant weight is achieved.

[0021] The present invention also provides a method for preparing the above-mentioned environmental stress crack-resistant packaging film material, which specifically includes the following preparation steps: (1) Raw material pretreatment: Linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, crack-resistant filler, crack-resistant elastomer, crack-resistant copolymer resin, antioxidant and lubricant are mixed at controlled temperature according to the formula ratio to obtain premix; (2) Melt extrusion granulation: The premixed material is melted and extruded into granules using a twin-screw extruder to obtain the masterbatch material; (3) Blow molding: After the masterbatch material is dried at controlled temperature, it is added to the hopper of the blown film machine, and after plasticizing extrusion, blowing and traction, blown into film, cooled and shaped, and wound up, a packaging film material resistant to environmental stress cracking is obtained.

[0022] In some embodiments of the present invention, the linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer and metallocene linear low-density polyethylene mentioned in step (1) are all dried at 65-80°C to a moisture content of ≤0.05%; In some embodiments of the present invention, the temperature of the temperature-controlled mixing in step (1) is 40-60°C and the time is 10-15 min.

[0023] In some embodiments of the present invention, in the twin-screw extruder described in step (2), the screw speed is 200-300 r / min; The temperature parameters for each zone are as follows: Zone 1: 160-170℃, Zone 2: 175-185℃, Zone 3: 180-190℃, Head unit: 185-195℃.

[0024] In some embodiments of the present invention, the temperature of the temperature-controlled drying in step (3) is 75-80°C and the time is 6-8 hours; In the blown film machine, the barrel temperature is 170-190℃, the die head temperature is 190-200℃, the blow-up ratio is 1.5-2.5, the traction ratio is 4-6, and the film thickness of the blown film is 0.1-2mm.

[0025] The beneficial effects of this invention are: (1) Pretreatment of heavy calcium carbonate with isopropyl tris(dioctyl pyrophosphate) titanate is beneficial for n-butyl acrylate to form a composite core-shell structure on the surface of heavy calcium carbonate through emulsion polymerization. At the same time, the flexible segments provided by n-butyl acrylate can effectively buffer the local stress of the composite material, reduce the initiation of microcracks, inhibit the further slow propagation of cracks, and alleviate the tendency of creep cracking of the composite material. On this basis, this application also uses a small amount of propyl gallate adsorbed on the surface of heavy calcium carbonate to generate a steric hindrance effect, which significantly improves the dispersibility of heavy calcium carbonate in the matrix resin. This good particle dispersion state can effectively enable the finished packaging film material to obtain better environmental stress cracking resistance.

[0026] (2) Vistamacxx™ 6202 elastomer achieves stress dispersion through the "island structure" and also takes into account the crystal region regulation, which disrupts the regular arrangement of the matrix resin molecular chains and reduces the crystallinity; while the elastic block segments of block copolymer polypropylene play a stress buffering role through good compatibility with the matrix resin and interfacial bonding state. Both enable the finished packaging film material to improve the overall flexibility of the material when facing complex stress environment through the "island structure" and crystal region regulation mechanism of Vistamacxx™ 6202 elastomer, and reduce internal defects by means of the improved interfacial compatibility of block copolymer polypropylene, thereby comprehensively improving the environmental stress cracking resistance of the finished packaging film material. Detailed Implementation

[0027] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0028] Information on some of the raw materials used in this invention is as follows: Linear low-density polyethylene, grade: 1001XV, purchased from: Nanjing Praxair New Material Technology Co., Ltd. Low-density polyethylene, grade: FT6230, purchased from: Nanjing Praxite New Material Technology Co., Ltd.; Ethylene-vinyl acetate copolymer, VA content: 33wt%, melt flow rate: 18g / 10min, grade: UL01833, purchased from: Lianhong New Material Technology Co., Ltd.; Metallocene linear low-density polyethylene, grade: GM1835CAX01, purchased from: Dongguan Jinshixiang Plastic Raw Materials Co., Ltd. Heavy calcium carbonate, 2000 mesh, average particle size D50 (μm) = 3 ± 0.5, purchased from: Henan Xintai Calcium Industry Co., Ltd. Vistamaxx™ 6202 elastomer, melt flow rate: 20g / 10min, grade: 6202, manufacturer: ExxonMobil, purchased from: Shanghai Yushi Plastics Co., Ltd.; Block copolymer polypropylene, melt flow rate: 2.5 g / 10 min, grade: K8003, purchased from Shanghai SECCO Petrochemical Co., Ltd. The above will not be elaborated upon further.

[0029] Preparation Example 1 This example demonstrates the preparation of modified heavy calcium carbonate using the following steps: 8.1 g of isopropyl tris(dioctyl pyrophosphoryloxy) titanate and 1000 g of 90% ethanol solution were ultrasonically dispersed for 23 min and then hydrolyzed at room temperature for 1.5 h to obtain the hydrolysate for later use. Mix 135g of butyl acrylate and 4.5g of ethylene glycol dimethacrylate to obtain a mixture for later use; Heavy calcium carbonate was dried at 80℃ to constant weight. 515g of the dried heavy calcium carbonate and 1000g of hydrolysate were stirred in an oil bath at 65℃ for 3 hours. The mixture was then filtered. The filter residue was dried at 77.5℃ for 3 hours to obtain intermediate modified material A. Mix 8.3g sodium dodecyl sulfate, 3000g deionized water and 500g intermediate modifier A, stir at 300rpm for 25min, then ultrasonically disperse for 35min, adjust pH to 9 with 0.5mol / L NaOH solution, purge air with nitrogen, add 2.6g potassium persulfate at 70℃ under nitrogen atmosphere and stir for 25min, then add 165g of the mixture dropwise at a uniform rate over 1h. After the addition is complete, keep the temperature at 73℃ for 1.5h, cool to room temperature, filter, take the filter cake, wash it 3 times with deionized water, then wash it once with anhydrous ethanol, and dry it at 60℃ for 3h to obtain intermediate modifier B. Take 55g of intermediate modified material B and add it to 12000g of deionized water. Stir at 1500r / min for 33min. Add 8.1g of propyl gallate and stir at 1000r / min for 30min. Filter the mixture and wash the filter residue twice with deionized water. Dry the residue at 60℃ until constant weight to obtain modified heavy calcium carbonate.

[0030] Preparation Example 2 This example demonstrates the preparation of modified heavy calcium carbonate using the following steps: 7.5 g of isopropyl tris(dioctyl pyrophosphoryloxy) titanate and 1000 g of 90% ethanol solution were ultrasonically dispersed for 20 min and then hydrolyzed at room temperature for 1.5 h to obtain the hydrolysate for later use. 148g of butyl acrylate and 4.13g of ethylene glycol dimethacrylate were mixed to obtain a mixture for later use. Heavy calcium carbonate was dried at 75℃ to constant weight. 507.5g of the dried heavy calcium carbonate and 1000g of hydrolysate were stirred in an oil bath at 62.5℃ for 2.5 hours. The mixture was then filtered. The filter residue was dried at 76℃ for 4 hours to obtain intermediate modified material A. Mix 7.9g sodium dodecyl sulfate, 2500g deionized water and 550g intermediate modifier A, stir at 325rpm for 28min, then ultrasonically disperse for 30min, adjust pH to 8 with 1mol / L NaOH solution, purge air with nitrogen, add 2.5g potassium persulfate at 72.5℃ under nitrogen atmosphere and stir for 20min, then add 146.3g of the mixture dropwise at a uniform rate over 1h. After the addition is complete, keep the temperature at 70℃ for 1h, cool to room temperature, filter, take the filter cake and wash it twice with deionized water, then wash it once with anhydrous ethanol, and dry it at 63℃ for 4h to obtain intermediate modifier B; S4. Take 53g of intermediate modified material B and add it to 1000g of deionized water. Stir at 1750r / min for 30min. Add 7.5g of propyl gallate and stir at 1250r / min for 35min. Filter the mixture and wash the filter residue three times with deionized water. Dry the residue at 62.5℃ until constant weight to obtain modified heavy calcium carbonate.

[0031] Preparation Example 3 This example demonstrates the preparation of modified heavy calcium carbonate using the following steps: 10g of isopropyl tris(dioctyl pyrophosphoryloxy) titanate and 1000g of 95% ethanol solution were ultrasonically dispersed for 25min and then hydrolyzed at room temperature for 2h to obtain hydrolysate for later use. Mix 160g of butyl acrylate and 3g of ethylene glycol dimethacrylate to obtain a mixture for later use; Heavy calcium carbonate was dried at 77.5℃ to constant weight. 523g of the dried heavy calcium carbonate and 1000g of hydrolysate were stirred in an oil bath at 60℃ for 2.5 hours. The mixture was then filtered. The filter residue was dried at 75℃ for 5 hours to obtain intermediate modified material A. Mix 7.5g sodium dodecyl sulfate, 2750g deionized water and 525g intermediate modifier A, stir at 400rpm for 26min, then ultrasonically disperse for 33min, adjust pH to 9 with 2mol / L NaOH solution, purge air with nitrogen, add 2.7g potassium persulfate under nitrogen atmosphere and temperature of 75℃ and stir for 30min, then add 140g of the mixture dropwise at a uniform rate over 1.5h. After the addition is complete, keep the temperature at 71℃ for 1h, cool to room temperature, filter, take the filter cake, wash it 3 times with deionized water and 2 times with anhydrous ethanol, and dry it at 61℃ for 5h to obtain intermediate modifier B; Take 50g of intermediate modified material B and add it to 1100g of deionized water. Stir at 2000r / min for 35min. Add 9.45g of propyl gallate and stir at 1125r / min for 33min. Filter the mixture and wash the filter residue three times with deionized water. Dry the residue at 61℃ until constant weight to obtain modified heavy calcium carbonate.

[0032] Preparation Example 4 This example demonstrates the preparation of modified heavy calcium carbonate using the following steps: 8.7 g of isopropyl tris(dioctyl pyrophosphoryloxy) titanate and 1000 g of 90% ethanol solution were ultrasonically dispersed for 30 min and then hydrolyzed at room temperature for 2 h to obtain hydrolysate for later use. Mix 141g of butyl acrylate and 3.38g of ethylene glycol dimethacrylate to obtain a mixture for later use; Heavy calcium carbonate was dried at 79℃ to constant weight. 500g of dried heavy calcium carbonate and 1000g of hydrolysate were stirred in an oil bath at 61℃ for 3 hours. The mixture was then filtered. The filter residue was dried at 80℃ for 4.5 hours to obtain intermediate modified material A. 9g sodium dodecyl sulfate, 2625g deionized water and 512.5g intermediate modifier A were mixed and stirred at 318 rpm for 30 min, then ultrasonically dispersed for 40 min. The pH was adjusted to 10 with 0.5 mol / L NaOH solution, and nitrogen gas was used to replace the air. Under a nitrogen atmosphere, 3g potassium persulfate was added and stirred for 23 min. Then, 153g of the mixture was added dropwise at a uniform rate over 1.5 h. After the addition was completed, the temperature was maintained at 75℃ for 1.5 h. After cooling to room temperature, the mixture was filtered. The filter cake was washed twice with deionized water and then twice with anhydrous ethanol. It was dried at 65℃ for 3.5 h to obtain intermediate modifier B. Take 60g of intermediate modified material B and add it to 1050g of deionized water. Stir at 1625r / min for 34min. Add 10g of propyl gallate and stir at 1500r / min for 31min. Filter the mixture and wash the filter residue twice with deionized water. Dry the residue at 65℃ until constant weight to obtain modified heavy calcium carbonate.

[0033] Preparation Example 5 This example demonstrates the preparation of modified heavy calcium carbonate using the following steps: 9.4 g of isopropyl tris(dioctyl pyrophosphoryloxy) titanate and 1000 g of 95% ethanol solution were ultrasonically dispersed for 28 min and then hydrolyzed at room temperature for 2 h to obtain hydrolysate for later use. Mix 154g of butyl acrylate and 3.75g of ethylene glycol dimethacrylate to obtain a mixture for later use; Heavy calcium carbonate was dried at 76℃ to constant weight. 530g of the dried heavy calcium carbonate and 1000g of hydrolysate were stirred in an oil bath at 64℃ for 3 hours. The mixture was then filtered. The filter residue was dried at 79℃ for 5 hours to obtain intermediate modified material A. Mix 8.7g sodium dodecyl sulfate, 2875g deionized water, and 537.5g intermediate modifier A, stir at 332 rpm for 27 min, then ultrasonically disperse for 38 min. Adjust the pH to 8 with 0.5 mol / L NaOH solution, purge the air with nitrogen, add 2.9g potassium persulfate under nitrogen atmosphere and temperature of 73℃, and stir for 28 min. Then, add 159g of the mixture dropwise at a uniform rate over 1.5 h. After the addition is complete, keep the temperature at 74℃ for 1 h, cool to room temperature, filter, take the filter cake, wash it three times with deionized water, then wash it twice with anhydrous ethanol, and dry it at 64℃ for 4.5 h to obtain intermediate modifier B. Take 58g of intermediate modified material B and add it to 1150g of deionized water. Stir at 1875r / min for 31min. Add 8.75g of propyl gallate and stir at 1375r / min for 34min. Filter the mixture and wash the filter residue three times with deionized water. Dry the residue at 64℃ until constant weight to obtain modified heavy calcium carbonate.

[0034] Example 1 This example demonstrates the preparation of a packaging film material resistant to environmental stress cracking, comprising the following parts by weight of raw materials: 77.5g of linear low-density polyethylene, 20g of low-density polyethylene, 6.75g of ethylene-vinyl acetate copolymer, 8g of metallocene linear low-density polyethylene, 2g of modified heavy calcium carbonate prepared in Preparation Example 2, 8g of Vistamaxx™ 6202 elastomer, 12.5g of block copolymer polypropylene, 0.3g of antioxidant 1076, and 0.4g of polyethylene wax; The preparation method of packaging film material resistant to environmental stress cracking specifically adopts the following steps: (1) Raw material pretreatment: Linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer and metallocene linear low-density polyethylene were dried at 65°C until the moisture content was less than 0.05%. The dried linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, modified heavy calcium carbonate prepared in Preparation Example 2, Vistamaxx™ 6202 elastomer, block copolymer polypropylene, antioxidant 1076 and polyethylene wax were mixed at 60°C for 13 min to obtain a premix. (2) Melt extrusion granulation: The premixed material is melted and extruded in a twin-screw extruder with a screw speed of 250 r / min at temperatures of 160°C in zone 1, 180°C in zone 2, 185°C in zone 3 and 195°C at the die head to obtain the masterbatch material. (3) Blow molding film: After drying the masterbatch material at 77.5℃ for 6 hours, it is added to the hopper of the blown film machine. After plasticizing extrusion, blowing and traction, blowing into film, cooling and shaping, and winding, a packaging film material resistant to environmental stress cracking is obtained. In the blown film machine, the barrel temperature is 180℃, the die head temperature is 195℃, the blow-up ratio is 1.5, the traction ratio is 5, and the film thickness after blowing is 1mm.

[0035] Example 2 This example demonstrates the preparation of a packaging film material resistant to environmental stress cracking, comprising the following parts by weight of raw materials: 74g of linear low-density polyethylene, 10g of low-density polyethylene, 10.2g of ethylene-vinyl acetate copolymer, 3g of metallocene linear low-density polyethylene, 3.5g of modified heavy calcium carbonate prepared in Preparation Example 3, 10g of Vistamaxx™ 6202 elastomer, 11g of block copolymer polypropylene, 0.25g of antioxidant 1076, 0.25g of antioxidant THP-24, and 0.2g of polyethylene wax; The preparation method of packaging film material resistant to environmental stress cracking specifically adopts the following steps: (1) Raw material pretreatment: Linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer and metallocene linear low-density polyethylene were dried at 72.5°C until the moisture content was less than 0.05%. The dried linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, modified heavy calcium carbonate prepared in Preparation Example 3, Vistamaxx™ 6202 elastomer, block copolymer polypropylene, antioxidant 1076, antioxidant THP-24 and polyethylene wax were mixed at 50°C for 10 min to obtain a premix. (2) Melt extrusion granulation: The premixed material is melted and extruded in a twin-screw extruder with a screw speed of 200 r / min at temperatures of 165°C in zone 1, 175°C in zone 2, 190°C in zone 3 and 192°C at the die head to obtain the masterbatch material. (3) Blow molding film: After drying the masterbatch material at 75°C for 7 hours, it is added to the hopper of the blown film machine. After plasticizing extrusion, blowing and traction, blowing into film, cooling and shaping, and winding, a packaging film material resistant to environmental stress cracking is obtained. In the blown film machine, the barrel temperature is 170℃, the die head temperature is 190℃, the blow-up ratio is 2, the traction ratio is 4, and the film thickness after blowing is 2mm.

[0036] Example 3 This example demonstrates the preparation of a packaging film material resistant to environmental stress cracking, comprising the following parts by weight of raw materials: 70g of linear low-density polyethylene, 12.5g of low-density polyethylene, 8.5g of ethylene-vinyl acetate copolymer, 4g of metallocene linear low-density polyethylene, 3g of modified heavy calcium carbonate prepared in Preparation Example 1, 12g of Vistamaxx™ 6202 elastomer, 10g of block copolymer polypropylene, 0.4g of antioxidant 1010, and 0.6g of polyethylene wax; The preparation method of packaging film material resistant to environmental stress cracking specifically adopts the following steps: (1) Raw material pretreatment: Linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer and metallocene linear low-density polyethylene were dried at 80°C until the moisture content was less than 0.05%. The dried linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, modified heavy calcium carbonate prepared in Preparation Example 1, Vistamaxx™ 6202 elastomer, block copolymer polypropylene, antioxidant 1010 and polyethylene wax were mixed at 40°C for 15 min to obtain a premix. (2) Melt extrusion granulation: The premixed material is melted and extruded in a twin-screw extruder with a screw speed of 300 r / min at temperatures of 163°C in zone 1, 177°C in zone 2, 180°C in zone 3 and 185°C at the die head to obtain the masterbatch material. (3) Blow molding: After drying the masterbatch material at 80℃ for 6.5h, it is added to the hopper of the blown film machine. After plasticizing extrusion, blowing and traction, blowing into film, cooling and shaping, and winding, a packaging film material resistant to environmental stress cracking is obtained. In the blown film machine, the barrel temperature is 190℃, the die head temperature is 200℃, the blow-up ratio is 2.5, the traction ratio is 5, and the film thickness after blowing is 1.5mm.

[0037] Example 4 This example demonstrates the preparation of a packaging film material resistant to environmental stress cracking, comprising the following parts by weight of raw materials: 85g of linear low-density polyethylene, 15g of low-density polyethylene, 5g of ethylene-vinyl acetate copolymer, 6g of metallocene linear low-density polyethylene, 5g of modified heavy calcium carbonate prepared in Preparation Example 5, 9g of Vistamaxx™ 6202 elastomer, 15g of block copolymer polypropylene, 0.8g of antioxidant THP-24, and 0.5g of polyethylene wax. The preparation method of packaging film material resistant to environmental stress cracking specifically adopts the following steps: (1) Raw material pretreatment: Linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer and metallocene linear low-density polyethylene were dried at 69°C until the moisture content was less than 0.05%. The dried linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, modified heavy calcium carbonate prepared in Preparation Example 5, Vistamaxx™ 6202 elastomer, block copolymer polypropylene, antioxidant THP-24 and polyethylene wax were mixed at 45°C for 12.5 min to obtain a premix. (2) Melt extrusion granulation: The premixed material is melted and extruded in a twin-screw extruder with a screw speed of 220 r / min at temperatures of 170°C in zone 1, 185°C in zone 2, 183°C in zone 3 and 190°C at the die head to obtain the masterbatch material. (3) Blow molding film: After drying the masterbatch material at 76℃ for 7.5h, it is added to the hopper of the blown film machine. After plasticizing extrusion, blowing and traction, blowing into film, cooling and shaping, and winding, a packaging film material resistant to environmental stress cracking is obtained. In the blown film machine, the barrel temperature is 175℃, the die head temperature is 193℃, the blow-up ratio is 2, the traction ratio is 6, and the film thickness after blowing is 1.5mm.

[0038] Example 5 This example demonstrates the preparation of a packaging film material resistant to environmental stress cracking, comprising the following parts by weight of raw materials: 81g of linear low-density polyethylene, 17.5g of low-density polyethylene, 12g of ethylene-vinyl acetate copolymer, 5.5g of metallocene linear low-density polyethylene, 4g of modified heavy calcium carbonate prepared in Preparation Example 5, 11g of Vistamaxx™ 6202 elastomer, 14g of block copolymer polypropylene, 0.35g of antioxidant 1010, 0.35g of antioxidant THP-24, and 0.3g of polyethylene wax; The preparation method of packaging film material resistant to environmental stress cracking specifically adopts the following steps: (1) Raw material pretreatment: Linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer and metallocene linear low-density polyethylene were dried at 76°C until the moisture content was less than 0.05%. The dried linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, modified heavy calcium carbonate prepared in Preparation Example 5, Vistamaxx™ 6202 elastomer, block copolymer polypropylene, antioxidant 1010, antioxidant THP-24 and polyethylene wax were mixed at 55°C for 11 min to obtain a premix. (2) Melt extrusion granulation: The premixed material is melted and extruded in a twin-screw extruder with a screw speed of 270 r / min at temperatures of 167°C in zone 1, 183°C in zone 2, 188°C in zone 3 and 187°C at the die head to obtain the masterbatch material. (3) Blow molding film: After drying the masterbatch material at 78°C for 8 hours, it is added to the hopper of the blown film machine. After plasticizing extrusion, blowing and traction, blowing into film, cooling and shaping, and winding, a packaging film material resistant to environmental stress cracking is obtained. In the blown film machine, the barrel temperature is 185℃, the die head temperature is 197℃, the blow-up ratio is 2, the traction ratio is 5, and the film thickness after blowing is 2mm.

[0039] Comparative Example 1 Compared with Example 2, the difference is that the modified heavy calcium carbonate obtained in Preparation Example 3 is replaced with modified heavy calcium carbonate obtained without the addition of isopropyltris(dioctylpyrophosphate)titanate, while the other operation steps and parameters remain unchanged.

[0040] Comparative Example 2 Compared with Example 2, the difference is that the modified heavy calcium carbonate obtained in Preparation Example 3 is replaced with modified heavy calcium carbonate obtained without the addition of n-butyl acrylate, while the other operation steps and parameters remain unchanged.

[0041] Comparative Example 3 Compared with Example 2, the difference is that the modified heavy calcium carbonate prepared in Preparation Example 3 is replaced with modified heavy calcium carbonate prepared without the addition of propyl gallate, while the other operation steps and parameters remain unchanged.

[0042] Comparative Example 4 Compared with Example 2, Comparative Example 4 differs in that it does not add Vistamacxx™ 6202 elastomer, while all other operating steps and parameters remain unchanged.

[0043] Comparative Example 5 Compared with Example 2, Comparative Example 5 differs in that no block copolymer polypropylene is added, while the other operation steps and parameters remain unchanged.

[0044] Mechanical property testing (1) Environmental stress cracking resistance test: Referring to GB / T 1842-2008, the packaging film materials prepared in Examples 1-5 and Comparative Examples 1-5 were made into samples with a size of 38mm × 13mm (thickness equal to the original packaging film material thickness) and subjected to environmental stress cracking resistance tests. The notch length was 18.9mm, the notch depth was 0.3mm, and the notch direction was parallel to the length of the sample and located at the center of the surface. A 10% (v / v) aqueous solution of nonylphenol polyoxyethylene ether (TX-10) was used as the medium, and the test was conducted in a 50℃ constant temperature water bath. The time when the sample broke in the medium at a rate of 50% was recorded as the environmental stress cracking time (denoted as F). 50 ), Unit: h, F 50 A higher value indicates better resistance to environmental stress cracking, and vice versa; the final results are shown in Table 1.

[0045] (2) Nominal strain test at fracture: Referring to GB / T 1040.3-2006, the nominal strain at break of the packaging film materials prepared in Examples 1-5 and Comparative Examples 1-5 was tested, and the final results are shown in Table 1.

[0046] Table 1

[0047] As shown in Table 1, the environmental stress cracking time (F) of the environmental stress cracking resistant packaging film materials prepared in Examples 1-5 is [data missing]. 50 All of them were above 340h, with F in Example 2 being the most common. 50 The highest value was achieved at 357 h, demonstrating excellent resistance to environmental stress cracking. In contrast, the F values ​​of Comparative Examples 1-5 were significantly lower. 50 The values ​​were all lower than those in the examples. Specifically, Comparative Examples 1-3, by replacing different modified heavy calcium carbonates, showed that their F values ​​were lower. 50 The values ​​were 326h, 320h, and 331h, respectively, indicating that the absence of any one of isopropyl tris(dioctylpyrophosphoryloxy)titanate, n-butyl acrylate, and propyl gallate would affect the environmental stress cracking resistance of the packaging film material; while the F values ​​of Comparative Example 4, which did not contain Vistamaxx™ 6202 elastomer, were significantly lower. 50 The value was the lowest, at only 303h. The F50 value of Comparative Example 5 without added block copolymer polypropylene was 312h, which was significantly lower than 357h in Example 2. This indicates that the absence of Vistamaxx™ 6202 elastomer or block copolymer polypropylene will affect the environmental stress cracking resistance of the final packaging film material.

[0048] Meanwhile, it can be seen that the nominal strain at longitudinal breakage of the packaging film materials prepared in Examples 1-5 is all above 670%, and the nominal strain at transverse breakage is all above 680%, which is higher than that of each comparative example. Among them, the nominal strain at breakage of Example 2 is the best, with a longitudinal strain of 688% and a transverse strain of 696%. This indicates that the packaging film material prepared by the present invention has excellent toughness and tensile elongation properties and can adapt to the stress deformation requirements in the application scenario.

[0049] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A packaging film material resistant to environmental stress cracking, characterized in that, Including the following parts by weight of raw materials: 70-85 parts by weight of linear low-density polyethylene, 10-20 parts by weight of low-density polyethylene, 5-12 parts by weight of ethylene-vinyl acetate copolymer, 3-8 parts by weight of metallocene linear low-density polyethylene, 2-5 parts by weight of crack-resistant filler, 8-12 parts by weight of crack-resistant elastomer, 10-15 parts by weight of crack-resistant copolymer resin, 0.3-0.8 parts by weight of antioxidant, and 0.2-0.6 parts by weight of lubricant.

2. The packaging film material resistant to environmental stress cracking according to claim 1, characterized in that, The crack-resistant filler includes modified heavy calcium carbonate, the crack-resistant elastomer includes Vistamaxx™ 6202 elastomer, the crack-resistant copolymer resin includes block copolymer polypropylene, the antioxidant includes at least one of antioxidant 1076, antioxidant 1010, antioxidant 168 and antioxidant THP-24, and the lubricant is polyethylene wax.

3. The packaging film material resistant to environmental stress cracking according to claim 2, characterized in that, The modified heavy calcium carbonate is prepared by first ultrasonically hydrolyzing dried heavy calcium carbonate with isopropyl tris(dioctyl pyrophosphate) titanate ethanol solution to obtain modified material A; then, under nitrogen protection, the surface of modified material A is coated with a mixture of butyl acrylate and ethylene glycol dimethacrylate to obtain modified material B; finally, propyl gallate is added for subsequent processing to obtain the final product.

4. The packaging film material resistant to environmental stress cracking according to claim 3, characterized in that, The preparation method of the modified heavy calcium carbonate specifically includes the following steps: S1. Isopropyl tris(dioctylpyrophosphoryloxy)titanate and ethanol solution are ultrasonically dispersed and hydrolyzed at room temperature to obtain hydrolysate for later use; butyl acrylate and ethylene glycol dimethacrylate are mixed to obtain mixed solution for later use. S2. Dry heavy calcium carbonate and hydrolysate are stirred in a temperature-controlled oil bath, filtered, and the filter residue is dried under controlled temperature to obtain intermediate modified material A. S3. Mix sodium dodecyl sulfate, deionized water and intermediate modifier A, stir at a controlled speed, then disperse ultrasonically, adjust pH, replace air with nitrogen, add potassium persulfate under controlled temperature in a nitrogen atmosphere and stir, then add the mixture dropwise, keep the temperature controlled after the addition is complete, cool to room temperature, filter, take the filter cake and wash it with deionized water first and then with anhydrous ethanol, dry under controlled temperature to obtain intermediate modifier B; S4. Add intermediate modified material B to deionized water and stir at a controlled speed. Add propyl gallate and stir at a controlled speed again. Filter, take the filter residue, wash with deionized water, and dry at a controlled temperature to obtain modified heavy calcium carbonate.

5. The packaging film material resistant to environmental stress cracking according to claim 4, characterized in that, In step S1, the isopropyl tris(dioctyl pyrophosphate) titanate is 0.75-1 parts by weight, the ethanol solution is 100 parts by weight, the butyl acrylate is 13.5-16 parts by weight, and the ethylene glycol dimethacrylate is 0.3-0.45 parts by weight.

6. The packaging film material resistant to environmental stress cracking according to claim 4, characterized in that, In step S2, the amount of dried heavy calcium carbonate is 50-53 parts by weight, and the amount of hydrolysate is 100 parts by weight.

7. The packaging film material resistant to environmental stress cracking according to claim 4, characterized in that, In step S3, sodium dodecyl sulfate is 0.75-0.9 parts by weight, deionized water is 250-300 parts by weight, intermediate modifier A is 50-55 parts by weight, potassium persulfate is 0.25-0.3 parts by weight, and the mixed solution is 14-16.5 parts by weight. In step S4, the intermediate modified material B is 5-6 parts by weight, the deionized water is 100-120 parts by weight, and the propyl gallate is 0.75-1 parts by weight.

8. The packaging film material resistant to environmental stress cracking according to claim 4, characterized in that, The ultrasonic dispersion time in step S1 is 20-30 min; the room temperature hydrolysis time is 1.5-2 h; The drying of heavy calcium carbonate in step S2 involves drying the heavy calcium carbonate at 75-80℃ to a constant weight; the temperature of the temperature-controlled oil bath stirring is 60-65℃ for 2.5-3 hours; and the temperature of the temperature-controlled drying is 75-80℃ for 3-5 hours. In step S3, the stirring speed is 300-400 rpm for 25-30 min; the ultrasonic dispersion time is 30-40 min; the pH is adjusted to 8-10 using 0.5-1 mol / L NaOH solution; the temperature for adding potassium persulfate and stirring is 70-75℃ for 20-30 min; the mixture is added dropwise at a uniform rate over 1-1.5 h; the temperature for maintaining the temperature is 70-75℃ for 1-1.5 h; the washing with deionized water is performed 2-3 times, and the washing with anhydrous ethanol is performed 1-2 times; the drying temperature is 60-65℃ for 3-5 h.

9. A method for preparing a packaging film material resistant to environmental stress cracking as described in any one of claims 1-8, characterized in that, Specifically, the preparation steps include the following: (1) Raw material pretreatment: Linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, crack-resistant filler, crack-resistant elastomer, crack-resistant copolymer resin, antioxidant and lubricant are mixed at controlled temperature according to the formula ratio to obtain premix; (2) Melt extrusion granulation: The premixed material is melted and extruded into granules using a twin-screw extruder to obtain the masterbatch material; (3) Blow molding: After the masterbatch material is dried at controlled temperature, it is added to the hopper of the blown film machine, and after plasticizing extrusion, blowing and traction, blown into film, cooled and shaped, and wound up, a packaging film material resistant to environmental stress cracking is obtained.

10. The method for preparing the environmental stress cracking resistant packaging film material according to claim 9, characterized in that, The temperature for temperature-controlled mixing in step (1) is 40-60℃, and the time is 10-15 min; In step (2), the screw speed in the twin-screw extruder is 200-300 r / min; The temperature parameters for each zone are as follows: Zone 1: 160-170℃, Zone 2: 175-185℃, Zone 3: 180-190℃, Head unit: 185-195℃; The temperature for temperature-controlled drying in step (3) is 75-80℃, and the time is 6-8h; In the blown film machine, the barrel temperature is 170-190℃, the die head temperature is 190-200℃, the blow-up ratio is 1.5-2.5, the traction ratio is 4-6, and the film thickness of the blown film is 0.1-2mm.

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