Low-temperature-resistant multilayer co-extrusion polypropylene composite material, preparation method and application thereof

Abstract

The application belongs to the field of high polymer packaging materials, and discloses a low-temperature-resistant multilayer co-extrusion polypropylene composite material and a preparation method and application thereof. The composite material is a five-layer symmetric co-extrusion structure, which is composed of an outer layer, a secondary outer layer adhesive layer, a middle barrier layer, a secondary inner layer adhesive layer and an inner layer. The outer layer and the inner layer are a toughened polypropylene composition composed of a copolymerized polypropylene and a polyolefin elastomer, the middle barrier layer is an ethylene-vinyl alcohol copolymer, and the adhesive layer is a maleic anhydride grafted polypropylene adhesive resin. In the application, the composite material is prepared by an extrusion blowing forming process, and is stable and has no adhesion after high-low temperature cycles. The composite material has excellent low-temperature toughness, high barrier property and normal-temperature rigidity, and is suitable for cold-chain food, medicine and other packaging products.

Description

Technical Field

[0001] This invention belongs to the field of polymer packaging materials technology, and particularly relates to a low-temperature resistant multilayer co-extruded polypropylene composite material, its preparation method and application. Background Technology

[0002] Polypropylene (PP) materials are widely used in packaging products for food, pharmaceuticals, and daily chemicals due to their excellent processing and mechanical properties. With the rapid development of the cold chain logistics industry and the increasing demand for low-temperature storage and transportation of food and pharmaceutical products, stringent requirements have been placed on the low-temperature resistance of polypropylene packaging materials. At the same time, in order to ensure the shelf life of the contents, multilayer co-extruded polypropylene composite materials with barrier properties have become the mainstream products in the industry.

[0003] Existing technologies typically employ toughening modification by adding polyolefin elastomers to polypropylene. For example, Chinese patent application CN119613870A discloses a low-temperature resistant, high-transparency reinforced material, its preparation method, and plastic parts and equipment. This material improves its low-temperature resistance and transparency by using propylene-butene copolymer as the resin raw material and adding toughening agents and other additives. CN120737490A discloses a low-temperature resistant, impact-resistant modified polypropylene material, which is prepared by using homopolymer polypropylene, ethylene-butene copolymer elastomers, and other raw materials to obtain a composite material with good low-temperature impact resistance, tensile properties, flexural properties, and high-temperature properties. However, this approach has significant limitations: insufficient elastomer addition cannot achieve effective toughening at -20℃; excessive elastomer addition leads to a significant decrease in the crystallinity and rigidity of the material matrix, resulting in soft products, insufficient stiffness, and poor dimensional stability, failing to balance low-temperature toughness and room-temperature rigidity.

[0004] For multilayer structures, interlayer adhesion performance also needs attention, as it is a crucial factor determining the overall mechanical properties, barrier properties, and service life of the material. In existing technologies, on the one hand, toughening modifications to the polypropylene layer to improve low-temperature resistance easily lead to the formation of weak boundary layers at the interface, causing delamination and debonding during processing and use. On the other hand, in existing multilayer co-extrusion processes, the large differences in melt flow rates between layers easily result in melt instability and uneven layer thickness at the interface, further exacerbating interface defects. More importantly, most existing solutions only focus on the material's room-temperature adhesion performance, neglecting the impact of low-temperature freezing and high-low temperature cycling on interface performance in cold chain scenarios. In long-term storage at -20℃ or in alternating high-low temperature environments, the difference in the thermal expansion coefficients of the layers generates continuous cyclic stress at the interface, leading to a sharp decline in interlayer adhesion strength.

[0005] Therefore, developing a multilayer co-extruded polypropylene composite material that combines excellent low-temperature toughness, high barrier properties, and good interlayer adhesion stability after high and low temperature cycling remains an urgent problem to be solved. Summary of the Invention

[0006] This application provides a low-temperature resistant multilayer co-extruded polypropylene composite material, its preparation method, and its application. By selecting a specific toughened polypropylene composition as the inner and outer layers, maleic anhydride-grafted polypropylene adhesive resin as the secondary outer and secondary inner adhesive layers, and ethylene-vinyl alcohol copolymer as the intermediate barrier layer, a multilayer co-extruded polypropylene composite material with excellent low-temperature toughness, high barrier properties, and good interlayer adhesion stability after high and low temperature cycling is prepared.

[0007] This invention provides a low-temperature resistant multilayer co-extruded polypropylene composite material. The low-temperature resistant multilayer co-extruded polypropylene composite material has a five-layer symmetrical co-extruded structure arranged sequentially from the outside to the inside, consisting of an outer layer, a second outer adhesive layer, a middle barrier layer, a second inner adhesive layer, and an inner layer. The outer and inner layers are toughened polypropylene compositions, which, by weight, consist of the following components:

[0008] 100 parts by weight of copolymerized polypropylene; 12-18 parts by weight of polyolefin elastomer; The total thickness of the composite material is 300-800 μm, of which the outer layer accounts for 25-35% of the total thickness and the inner layer accounts for 25-35% of the total thickness. After being frozen at -20℃ for 2 hours and then held at 40℃ for 2 hours, the oxygen permeability of the composite material was changed by ≤10% after 10 cycles of high and low temperature cycling. Under conditions of 23℃ and 50%RH, the oxygen permeability of the composite material was ≤0.5cc / (m³). 2 • 24h·atm); The impact strength of the composite material at -20℃ unnotched cantilever beam is ≥5kJ / m 2 Flexural modulus at room temperature ≥1100MPa.

[0009] Furthermore, the copolymer polypropylene is a random copolymer of propylene and ethylene, with an ethylene content of 3wt%-6wt%; the melt flow rate at 230℃ and 2.16kg is 1.0-3.5g / 10min, and the flexural modulus is ≥1100MPa.

[0010] Furthermore, the polyolefin elastomer is an ethylene-propylene copolymer elastomer with a melt flow rate of 2.0-5.0 g / 10 min at 230°C and 2.16 kg, and an ethylene content of 10-16 wt%.

[0011] Further, the preparation method of the toughened polypropylene composition includes: adding the copolymerized polypropylene and polyolefin elastomer to a high-speed mixer in a certain proportion, mixing at 60-80℃ for 10-15 min to obtain a premix; adding the premix to a twin-screw extruder, melt-extruding at 180-220℃, water-cooling, pelletizing, and drying to obtain the toughened polypropylene composition.

[0012] Furthermore, the outermost adhesive layer and the innermost adhesive layer comprise maleic anhydride-grafted polypropylene adhesive resin, wherein the melt flow rate of the maleic anhydride-grafted polypropylene adhesive resin is 1.0-4.0 g / 10 min at 230°C and 2.16 kg.

[0013] Furthermore, the intermediate barrier layer is an ethylene-vinyl alcohol copolymer with a melt flow rate of 3.0-6.0 g / 10 min at 210°C and 2.16 kg, and the melt flow rate ratio with that of the maleic anhydride-grafted polypropylene bonding resin is 0.8-1.5.

[0014] This invention also provides a method for preparing a low-temperature resistant multilayer co-extruded polypropylene composite material, comprising the following steps: Step 1: Add the toughened polypropylene composition as the inner layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene bonding resin as the secondary inner layer bonding layer to the multilayer co-extrusion extruder, add the ethylene-vinyl alcohol copolymer as the intermediate barrier layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene as the secondary outer layer bonding layer to the multilayer co-extrusion extruder, and add the toughened polypropylene composition as the outer layer to the multilayer co-extrusion extruder. Perform co-extrusion to obtain a five-layer co-extruded melt. Step 2: The five-layer co-extruded melt is blow-extruded, cooled and shaped, and the scrap is removed to obtain the low-temperature resistant multilayer co-extruded polypropylene composite material.

[0015] Furthermore, the inner layer extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, the second inner layer adhesive layer extrusion temperature is 190-230℃, the middle barrier layer extrusion temperature is 190-230℃, the second outer layer adhesive layer extrusion temperature is 190-230℃, and the outer layer extrusion temperature is 180-235℃.

[0016] The present invention also provides a packaging article comprising the aforementioned low-temperature resistant multilayer co-extruded polypropylene composite material.

[0017] The beneficial effects of this application are as follows: This invention's toughened polypropylene composition achieves a highly efficient balance between low-temperature toughness and room-temperature rigidity by selecting specific propylene-ethylene random copolymer polypropylene and combining it with a polyolefin elastomer of specific dosage, melt flow rate, and ethylene content. This avoids the technical problems of poor toughening effect and easy material cracking at low temperatures caused by insufficient elastomer addition, while also avoiding the defects of a significant decrease in polypropylene matrix crystallinity, softness, and insufficient stiffness and dimensional stability caused by excessive elastomer addition. This allows the material to maintain excellent impact resistance under long-term low-temperature storage conditions.

[0018] This invention also precisely controls the melt flow rate of each layer in the multilayer co-extrusion system, limiting the melt flow rate ratio of the intermediate barrier layer (ethylene-vinyl alcohol copolymer) to the outermost and innermost adhesive layers (maleic anhydride-grafted polypropylene adhesive resin). Simultaneously, it achieves rheological property matching between the inner and outer toughened polypropylene compositions, the adhesive layer, and the barrier layer. This fundamentally solves the problems of melt instability, uneven layer thickness, and weak boundary layer formation at the interface caused by excessive differences in melt flow characteristics among the layers during multilayer co-extrusion. It avoids the cyclic stress generated at the interface due to differences in the thermal expansion coefficients of the layers damaging the adhesive performance and causing a significant decrease in barrier performance, thus achieving long-term stability of interlayer adhesion and barrier performance under high and low temperature alternating environments. Detailed Implementation

[0019] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Example 1 This embodiment provides a low-temperature resistant multilayer co-extruded polypropylene composite material, which is a five-layer symmetrical co-extruded structure arranged from the outside to the inside, namely an outer layer, a second outer adhesive layer, an intermediate barrier layer, a second inner adhesive layer, and an inner layer; the outer layer and the inner layer are both made of toughened polypropylene composition, and the multilayer composite material is prepared by a multilayer co-extrusion extruder through extrusion at different extrusion temperatures between different layers. The total thickness of the low-temperature resistant multilayer co-extruded polypropylene composite material is 550 μm, of which the outer layer accounts for 30% of the total thickness and the inner layer accounts for 30% of the total thickness. In this embodiment, the toughened polypropylene composition comprises the following components by weight: 100 parts by weight of copolymerized polypropylene and 15 parts by weight of polyolefin elastomer; The copolymer polypropylene is a random copolymer of propylene and ethylene, wherein the mass fraction of ethylene structural units is 4 wt%, the melt flow rate at 230℃ and 2.16 kg is 2.2 g / 10 min, and the flexural modulus is 1300 MPa. The polyolefin elastomer is an ethylene-propylene copolymer elastomer with a melt flow rate of 3.5 g / 10 min at 230°C and 2.16 kg, and an ethylene content of 13 wt%. The method for preparing the toughened polypropylene composition includes: adding the copolymerized polypropylene and polyolefin elastomer to a high-speed mixer in a certain proportion, mixing at 70°C for 13 minutes to obtain a premix; adding the premix to a twin-screw extruder, melt-extruding at 200°C, water-cooling, pelletizing, and drying to obtain the toughened polypropylene composition.

[0021] Both the outermost and innermost adhesive layers are maleic anhydride-grafted polypropylene adhesive resins, and the melt flow rate of the maleic anhydride-grafted polypropylene adhesive resins at 230°C and 2.16 kg is 3 g / 10 min. The intermediate barrier layer is an ethylene-vinyl alcohol copolymer with a melt flow rate of 4.0 g / 10 min at 210°C and 2.16 kg, which is 1.3 times the melt flow rate of the maleic anhydride-grafted polypropylene bonding resin.

[0022] This embodiment also provides a method for preparing a low-temperature resistant multilayer co-extruded polypropylene composite material, including the following steps: Step 1: Add the toughened polypropylene composition as the inner layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene bonding resin as the secondary inner layer bonding layer to the multilayer co-extrusion extruder, add the ethylene-vinyl alcohol copolymer as the intermediate barrier layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene as the secondary outer layer bonding layer to the multilayer co-extrusion extruder, and add the toughened polypropylene composition as the outer layer to the multilayer co-extrusion extruder. Perform co-extrusion to obtain a five-layer co-extruded melt. Step 2: The five-layer co-extruded melt is blow-extruded, cooled and shaped, and the scrap is removed to obtain the low-temperature resistant multilayer co-extruded polypropylene composite material.

[0023] In this embodiment, the inner extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, divided into 4 temperature zones, wherein the temperature of the first temperature zone is 180℃, the temperature of the second temperature zone is 195℃, the temperature of the third temperature zone is 210℃, and the temperature of the fourth temperature zone is 235℃.

[0024] The extrusion temperature of the innermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃.

[0025] The intermediate barrier layer of the multi-layer co-extrusion extruder has an extrusion temperature of 190-230℃, divided into 4 temperature zones, with the first temperature zone at 190℃, the second temperature zone at 200℃, the third temperature zone at 215℃, and the fourth temperature zone at 230℃.

[0026] The extrusion temperature of the outermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃.

[0027] The outer extrusion temperature of the multi-layer co-extrusion extruder is 180-235℃, divided into four temperature zones: the first zone is 180℃, the second zone is 195℃, the third zone is 210℃, and the fourth zone is 235℃. The die temperature of the multi-layer co-extrusion extruder is 200℃.

[0028] Example 2 This embodiment provides a low-temperature resistant multilayer co-extruded polypropylene composite material, which is a five-layer symmetrical co-extruded structure arranged from the outside to the inside, namely an outer layer, a second outer adhesive layer, an intermediate barrier layer, a second inner adhesive layer, and an inner layer; the outer layer and the inner layer are both made of toughened polypropylene composition, and the multilayer composite material is prepared by a multilayer co-extrusion extruder through extrusion at different extrusion temperatures between different layers. The total thickness of the low-temperature resistant multilayer co-extruded polypropylene composite material is 300 μm, of which the outer layer accounts for 25% of the total thickness and the inner layer accounts for 25% of the total thickness.

[0029] In this embodiment, the toughened polypropylene composition comprises the following components by weight: 100 parts by weight of copolymer polypropylene and 12 parts by weight of polyolefin elastomer.

[0030] The copolymer polypropylene is a random copolymer of propylene and ethylene, wherein the mass fraction of ethylene structural units is 3wt%, the melt flow rate at 230℃ and 2.16kg is 1.0g / 10min, and the flexural modulus is 1100MPa. The polyolefin elastomer is an ethylene-propylene copolymer elastomer with a melt flow rate of 2.0 g / 10 min at 230°C and 2.16 kg, and an ethylene content of 10 wt%. The method for preparing the toughened polypropylene composition includes: adding the copolymerized polypropylene and polyolefin elastomer to a high-speed mixer in a certain proportion, mixing at 70°C for 13 minutes to obtain a premix; adding the premix to a twin-screw extruder, melt-extruding at 200°C, water-cooling, pelletizing, and drying to obtain the toughened polypropylene composition.

[0031] The method for preparing the toughened polypropylene composition includes: adding the copolymerized polypropylene and polyolefin elastomer to a high-speed mixer in a certain proportion, mixing at 60°C for 15 minutes to obtain a premix; adding the premix to a twin-screw extruder, melt-extruding at 180°C, water-cooling, pelletizing, and drying to obtain the toughened polypropylene composition.

[0032] The outermost and innermost adhesive layers are made of maleic anhydride-grafted polypropylene adhesive resin, and the melt flow rate of the maleic anhydride-grafted polypropylene adhesive resin is 4.0 g / 10 min at 230°C and 2.16 kg. The intermediate barrier layer is an ethylene-vinyl alcohol copolymer with a melt flow rate of 4.0 g / 10 min at 210°C and 2.16 kg, which is 1.0 times the melt flow rate of the maleic anhydride-grafted polypropylene bonding resin.

[0033] This embodiment also provides a method for preparing a low-temperature resistant multilayer co-extruded polypropylene composite material, including the following steps: Step 1: Add the toughened polypropylene composition as the inner layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene bonding resin as the secondary inner layer bonding layer to the multilayer co-extrusion extruder, add the ethylene-vinyl alcohol copolymer as the intermediate barrier layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene as the secondary outer layer bonding layer to the multilayer co-extrusion extruder, and add the toughened polypropylene composition as the outer layer to the multilayer co-extrusion extruder. Perform co-extrusion to obtain a five-layer co-extruded melt. Step 2: The five-layer co-extruded melt is blow-extruded, cooled and shaped, and the scrap is removed to obtain the low-temperature resistant multilayer co-extruded polypropylene composite material.

[0034] In this embodiment, the inner layer extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, divided into 5 temperature zones, wherein the temperature of the first temperature zone is 180℃, the temperature of the second temperature zone is 195℃, the temperature of the third temperature zone is 210℃, the temperature of the fourth temperature zone is 225℃ and the temperature of the fifth temperature zone is 235℃. The extrusion temperature of the innermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃. The extrusion temperature of the intermediate barrier layer of the multi-layer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃. The extrusion temperature of the outermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃. The outer layer extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, divided into 5 temperature zones, of which the temperature of the first temperature zone is 180℃, the temperature of the second temperature zone is 195℃, the temperature of the third temperature zone is 210℃, the temperature of the fourth temperature zone is 225℃ and the temperature of the fifth temperature zone is 235℃. The die temperature of the multi-layer co-extrusion extruder is 190°C.

[0035] Example 3 This embodiment provides a low-temperature resistant multilayer co-extruded polypropylene composite material, which is a five-layer symmetrical co-extruded structure arranged from the outside to the inside, namely an outer layer, a second outer adhesive layer, an intermediate barrier layer, a second inner adhesive layer, and an inner layer; the outer layer and the inner layer are both made of toughened polypropylene composition, and the multilayer composite material is prepared by a multilayer co-extrusion extruder through extrusion at different extrusion temperatures between different layers. The total thickness of the low-temperature resistant multilayer co-extruded polypropylene composite material is 800 μm, of which the outer layer accounts for 35% of the total thickness and the inner layer accounts for 35% of the total thickness. In this embodiment, the toughened polypropylene composition consists of the following components by weight: 100 parts by weight of copolymer polypropylene and 18 parts by weight of polyolefin elastomer. The copolymer polypropylene is a random copolymer of propylene and ethylene, wherein the mass fraction of ethylene structural units is 6 wt%, the melt flow rate at 230℃ and 2.16 kg is 3.5 g / 10 min, and the flexural modulus is 1200 MPa. The polyolefin elastomer is an ethylene-propylene copolymer elastomer with a melt flow rate of 5.0 g / 10 min at 230°C and 2.16 kg, and an ethylene content of 16 wt%. The method for preparing the toughened polypropylene composition includes: adding the copolymerized polypropylene and polyolefin elastomer to a high-speed mixer in a certain proportion, mixing at 80°C for 10 minutes to obtain a premix; adding the premix to a twin-screw extruder, melt-extruding at 220°C, water-cooling, pelletizing, and drying to obtain the toughened polypropylene composition.

[0036] The outermost and innermost adhesive layers are made of maleic anhydride-grafted polypropylene adhesive resin, and the melt flow rate of the maleic anhydride-grafted polypropylene adhesive resin is 2.0 g / 10 min at 230°C and 2.16 kg. The intermediate barrier layer is an ethylene-vinyl alcohol copolymer with a melt flow rate of 3.0 g / 10 min at 210°C and 2.16 kg, which is 1.5 times the melt flow rate of the maleic anhydride-grafted polypropylene bonding resin.

[0037] This embodiment also provides a method for preparing a low-temperature resistant multilayer co-extruded polypropylene composite material, including the following steps: Step 1: Add the toughened polypropylene composition as the inner layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene bonding resin as the secondary inner layer bonding layer to the multilayer co-extrusion extruder, add the ethylene-vinyl alcohol copolymer as the intermediate barrier layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene as the secondary outer layer bonding layer to the multilayer co-extrusion extruder, and add the toughened polypropylene composition as the outer layer to the multilayer co-extrusion extruder. Perform co-extrusion to obtain a five-layer co-extruded melt. Step 2: The five-layer co-extruded melt is blow-extruded, cooled and shaped, and the scrap is removed to obtain the low-temperature resistant multilayer co-extruded polypropylene composite material.

[0038] In this embodiment, the inner layer extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, divided into 5 temperature zones, wherein the temperature of the first temperature zone is 180℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃, the temperature of the fourth temperature zone is 225℃ and the temperature of the fifth temperature zone is 235℃. The extrusion temperature of the innermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 205℃, the temperature of the third temperature zone is 220℃ and the temperature of the fourth temperature zone is 230℃. The extrusion temperature of the intermediate barrier layer of the multi-layer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 205℃, the temperature of the third temperature zone is 220℃ and the temperature of the fourth temperature zone is 230℃. The extrusion temperature of the outermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 205℃, the temperature of the third temperature zone is 220℃ and the temperature of the fourth temperature zone is 230℃. The outer layer extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, divided into 5 temperature zones, of which the temperature of the first temperature zone is 180℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃, the temperature of the fourth temperature zone is 225℃ and the temperature of the fifth temperature zone is 235℃. The die temperature of the multi-layer co-extrusion extruder is 210℃.

[0039] Comparative Example 1 This comparative example provides a low-temperature resistant multilayer co-extruded polypropylene composite material. The only difference from Example 1 is that the mass fraction of the copolymer polypropylene ethylene structural unit in the toughened polypropylene composition of this comparative example is 2 wt%, the melt flow rate at 230°C and 2.16 kg is 5 g / 10 min, and the flexural modulus is 900 MPa. Other parameters are the same as in Example 1. The specific scheme is as follows: This comparative example provides a low-temperature resistant multilayer co-extruded polypropylene composite material, which is a five-layer symmetrical co-extruded structure arranged from the outside to the inside, namely, an outer layer, a second outer adhesive layer, an intermediate barrier layer, a second inner adhesive layer, and an inner layer; both the outer layer and the inner layer are made of toughened polypropylene composition, and the multilayer composite material is prepared by a multilayer co-extrusion extruder through extrusion at different extrusion temperatures between different layers. The total thickness of the low-temperature resistant multilayer co-extruded polypropylene composite material is 550 μm, of which the outer layer accounts for 30% of the total thickness and the inner layer accounts for 30% of the total thickness. In this comparative example, the toughened polypropylene composition comprises, by weight, the following components: 100 parts by weight of copolymerized polypropylene and 15 parts by weight of polyolefin elastomer; The copolymer polypropylene is a random copolymer of propylene and ethylene, wherein the mass fraction of ethylene structural units is 2wt%, the melt flow rate at 230℃ and 2.16kg is 5g / 10min, and the flexural modulus is 900MPa. The polyolefin elastomer is an ethylene-propylene copolymer elastomer with a melt flow rate of 3.5 g / 10 min at 230°C and 2.16 kg, and an ethylene content of 13 wt%. The method for preparing the toughened polypropylene composition includes: adding the copolymerized polypropylene and polyolefin elastomer to a high-speed mixer in a certain proportion, mixing at 70°C for 13 minutes to obtain a premix; adding the premix to a twin-screw extruder, melt-extruding at 200°C, water-cooling, pelletizing, and drying to obtain the toughened polypropylene composition.

[0040] Both the outermost and innermost adhesive layers are maleic anhydride-grafted polypropylene adhesive resins, and the melt flow rate of the maleic anhydride-grafted polypropylene adhesive resins at 230°C and 2.16 kg is 3 g / 10 min. The intermediate barrier layer is an ethylene-vinyl alcohol copolymer with a melt flow rate of 4.0 g / 10 min at 210°C and 2.16 kg, which is 1.3 times the melt flow rate of the maleic anhydride-grafted polypropylene bonding resin.

[0041] This comparative example also provides a method for preparing a low-temperature resistant multilayer co-extruded polypropylene composite material, comprising the following steps: Step 1: Add the toughened polypropylene composition as the inner layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene bonding resin as the secondary inner layer bonding layer to the multilayer co-extrusion extruder, add the ethylene-vinyl alcohol copolymer as the intermediate barrier layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene as the secondary outer layer bonding layer to the multilayer co-extrusion extruder, and add the toughened polypropylene composition as the outer layer to the multilayer co-extrusion extruder. Perform co-extrusion to obtain a five-layer co-extruded melt. Step 2: The five-layer co-extruded melt is blow-extruded, cooled and shaped, and the scrap is removed to obtain the low-temperature resistant multilayer co-extruded polypropylene composite material.

[0042] In this comparative example, the inner extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, divided into 4 temperature zones, wherein the temperature of the first temperature zone is 180℃, the temperature of the second temperature zone is 195℃, the temperature of the third temperature zone is 210℃, and the temperature of the fourth temperature zone is 235℃.

[0043] The extrusion temperature of the innermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃.

[0044] The intermediate barrier layer of the multi-layer co-extrusion extruder has an extrusion temperature of 190-230℃, divided into 4 temperature zones, with the first temperature zone at 190℃, the second temperature zone at 200℃, the third temperature zone at 215℃, and the fourth temperature zone at 230℃.

[0045] The extrusion temperature of the outermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃.

[0046] The outer extrusion temperature of the multi-layer co-extrusion extruder is 180-235℃, divided into four temperature zones: the first zone is 180℃, the second zone is 195℃, the third zone is 210℃, and the fourth zone is 235℃. The die temperature of the multi-layer co-extrusion extruder is 200℃.

[0047] Comparative Example 2 This comparative example provides a low-temperature resistant multilayer co-extruded polypropylene composite material. The only difference from Example 1 is that the amount of polyolefin elastomer in the toughened polypropylene composition of this comparative example is 25 parts by weight. Other parameters are the same as in Example 1. The specific scheme is as follows: This comparative example provides a low-temperature resistant multilayer co-extruded polypropylene composite material, which is a five-layer symmetrical co-extruded structure arranged from the outside to the inside, namely, an outer layer, a second outer adhesive layer, an intermediate barrier layer, a second inner adhesive layer, and an inner layer; both the outer layer and the inner layer are made of toughened polypropylene composition, and the multilayer composite material is prepared by a multilayer co-extrusion extruder through extrusion at different extrusion temperatures between different layers. The total thickness of the low-temperature resistant multilayer co-extruded polypropylene composite material is 550 μm, of which the outer layer accounts for 30% of the total thickness and the inner layer accounts for 30% of the total thickness. In this comparative example, the toughened polypropylene composition comprises, by weight, the following components: 100 parts by weight of copolymerized polypropylene and 25 parts by weight of polyolefin elastomer; The copolymer polypropylene is a random copolymer of propylene and ethylene, wherein the mass fraction of ethylene structural units is 4 wt%, the melt flow rate at 230℃ and 2.16 kg is 2.2 g / 10 min, and the flexural modulus is 1300 MPa. The polyolefin elastomer is an ethylene-propylene copolymer elastomer with a melt flow rate of 3.5 g / 10 min at 230°C and 2.16 kg, and an ethylene content of 13 wt%. The method for preparing the toughened polypropylene composition includes: adding the copolymerized polypropylene and polyolefin elastomer to a high-speed mixer in a certain proportion, mixing at 70°C for 13 minutes to obtain a premix; adding the premix to a twin-screw extruder, melt-extruding at 200°C, water-cooling, pelletizing, and drying to obtain the toughened polypropylene composition.

[0048] Both the outermost and innermost adhesive layers are maleic anhydride-grafted polypropylene adhesive resins, and the melt flow rate of the maleic anhydride-grafted polypropylene adhesive resins at 230°C and 2.16 kg is 3 g / 10 min. The intermediate barrier layer is an ethylene-vinyl alcohol copolymer with a melt flow rate of 4.0 g / 10 min at 210°C and 2.16 kg, which is 1.3 times the melt flow rate of the maleic anhydride-grafted polypropylene bonding resin.

[0049] This comparative example also provides a method for preparing a low-temperature resistant multilayer co-extruded polypropylene composite material, comprising the following steps: Step 1: Add the toughened polypropylene composition as the inner layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene bonding resin as the secondary inner layer bonding layer to the multilayer co-extrusion extruder, add the ethylene-vinyl alcohol copolymer as the intermediate barrier layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene as the secondary outer layer bonding layer to the multilayer co-extrusion extruder, and add the toughened polypropylene composition as the outer layer to the multilayer co-extrusion extruder. Perform co-extrusion to obtain a five-layer co-extruded melt. Step 2: The five-layer co-extruded melt is blow-extruded, cooled and shaped, and the scrap is removed to obtain the low-temperature resistant multilayer co-extruded polypropylene composite material.

[0050] In this comparative example, the inner extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, divided into 4 temperature zones, wherein the temperature of the first temperature zone is 180℃, the temperature of the second temperature zone is 195℃, the temperature of the third temperature zone is 210℃, and the temperature of the fourth temperature zone is 235℃.

[0051] The extrusion temperature of the innermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃.

[0052] The intermediate barrier layer of the multi-layer co-extrusion extruder has an extrusion temperature of 190-230℃, divided into 4 temperature zones, with the first temperature zone at 190℃, the second temperature zone at 200℃, the third temperature zone at 215℃, and the fourth temperature zone at 230℃.

[0053] The extrusion temperature of the outermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃.

[0054] The outer extrusion temperature of the multi-layer co-extrusion extruder is 180-235℃, divided into four temperature zones: the first zone is 180℃, the second zone is 195℃, the third zone is 210℃, and the fourth zone is 235℃. The die temperature of the multi-layer co-extrusion extruder is 200℃.

[0055] Comparative Example 3 This comparative example provides a low-temperature resistant multilayer co-extruded polypropylene composite material. The only difference from Example 1 is that the intermediate barrier layer in this comparative example is an ethylene-vinyl alcohol copolymer, and the melt flow rate under the conditions of 210°C and 2.16 kg is 9.0 g / 10 min, which is 3 times the melt flow rate of the maleic anhydride-grafted polypropylene bonding resin.

[0056] This comparative example provides a low-temperature resistant multilayer co-extruded polypropylene composite material, which is a five-layer symmetrical co-extruded structure arranged from the outside to the inside, namely, an outer layer, a second outer adhesive layer, an intermediate barrier layer, a second inner adhesive layer, and an inner layer; both the outer layer and the inner layer are made of toughened polypropylene composition, and the multilayer composite material is prepared by a multilayer co-extrusion extruder through extrusion at different extrusion temperatures between different layers. The total thickness of the low-temperature resistant multilayer co-extruded polypropylene composite material is 550 μm, of which the outer layer accounts for 30% of the total thickness and the inner layer accounts for 30% of the total thickness. In this comparative example, the toughened polypropylene composition comprises, by weight, the following components: 100 parts by weight of copolymerized polypropylene and 15 parts by weight of polyolefin elastomer; The copolymer polypropylene is a random copolymer of propylene and ethylene, wherein the mass fraction of ethylene structural units is 4 wt%, the melt flow rate at 230℃ and 2.16 kg is 2.2 g / 10 min, and the flexural modulus is 1300 MPa. The polyolefin elastomer is an ethylene-propylene copolymer elastomer with a melt flow rate of 3.5 g / 10 min at 230°C and 2.16 kg, and an ethylene content of 13 wt%. The method for preparing the toughened polypropylene composition includes: adding the copolymerized polypropylene and polyolefin elastomer to a high-speed mixer in a certain proportion, mixing at 70°C for 13 minutes to obtain a premix; adding the premix to a twin-screw extruder, melt-extruding at 200°C, water-cooling, pelletizing, and drying to obtain the toughened polypropylene composition.

[0057] Both the outermost and innermost adhesive layers are maleic anhydride-grafted polypropylene adhesive resins, and the melt flow rate of the maleic anhydride-grafted polypropylene adhesive resins at 230°C and 2.16 kg is 3 g / 10 min. The intermediate barrier layer is an ethylene-vinyl alcohol copolymer with a melt flow rate of 9.0 g / 10 min at 210°C and 2.16 kg, which is 3 times the melt flow rate of the maleic anhydride-grafted polypropylene bonding resin.

[0058] This comparative example also provides a method for preparing a low-temperature resistant multilayer co-extruded polypropylene composite material, comprising the following steps: Step 1: Add the toughened polypropylene composition as the inner layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene bonding resin as the secondary inner layer bonding layer to the multilayer co-extrusion extruder, add the ethylene-vinyl alcohol copolymer as the intermediate barrier layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene as the secondary outer layer bonding layer to the multilayer co-extrusion extruder, and add the toughened polypropylene composition as the outer layer to the multilayer co-extrusion extruder. Perform co-extrusion to obtain a five-layer co-extruded melt. Step 2: The five-layer co-extruded melt is blow-extruded, cooled and shaped, and the scrap is removed to obtain the low-temperature resistant multilayer co-extruded polypropylene composite material.

[0059] In this comparative example, the inner extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, divided into 4 temperature zones, wherein the temperature of the first temperature zone is 180℃, the temperature of the second temperature zone is 195℃, the temperature of the third temperature zone is 210℃, and the temperature of the fourth temperature zone is 235℃.

[0060] The extrusion temperature of the innermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃.

[0061] The intermediate barrier layer of the multi-layer co-extrusion extruder has an extrusion temperature of 190-230℃, divided into 4 temperature zones, with the first temperature zone at 190℃, the second temperature zone at 200℃, the third temperature zone at 215℃, and the fourth temperature zone at 230℃.

[0062] The extrusion temperature of the outermost adhesive layer of the multilayer co-extrusion extruder is 190-230℃, divided into 4 temperature zones, of which the temperature of the first temperature zone is 190℃, the temperature of the second temperature zone is 200℃, the temperature of the third temperature zone is 215℃ and the temperature of the fourth temperature zone is 230℃.

[0063] The outer extrusion temperature of the multi-layer co-extrusion extruder is 180-235℃, divided into four temperature zones: the first zone is 180℃, the second zone is 195℃, the third zone is 210℃, and the fourth zone is 235℃. The die temperature of the multi-layer co-extrusion extruder is 200℃.

[0064] All test specimens in this manual are cut from the finished low-temperature resistant multilayer co-extruded polypropylene composite material. The specimens are free from scratches, wrinkles, pinholes, and mechanical damage. Before testing, they need to be conditioned in a standard environment of 23°C and 50%RH for 48 hours. All tests are performed under the same standard environment (except for test items with specially specified temperatures).

[0065] Test method: Interlayer interface state after high and low temperature cycling: The sample was placed in a high and low temperature alternating test chamber and frozen at -20℃ for 2 hours and kept at 40℃ for 2 hours as one complete cycle. After 10 consecutive cycles, visual observation and cross-sectional observation were performed to determine the condition. The judgment criteria were as follows: no debonding and no warping: the sample had no warping deformation, no interface separation, and no new gaps; local micro-debonding: the sample had local micro-debonding at the edge and no obvious warping; obvious delamination and warping: the sample had large-area delamination, warping, and complete interface separation.

[0066] Oxygen permeability test: The test was conducted in accordance with GB / T31354-2014. The test environment was 23℃ and 50%RH. Three parallel samples were tested for each group of samples, and the arithmetic mean of the results was taken.

[0067] Test of oxygen permeability change rate after high and low temperature cycling: First, test the initial oxygen permeability of the sample. After the sample is subjected to 10 high and low temperature cycles (freezing at -20℃ for 2 hours and holding at 40℃ for 2 hours), test the oxygen permeability after cycling under the same test conditions. Calculate the change rate according to the following formula: Oxygen permeability change rate (%) = (Oxygen permeability after high and low temperature cycling - Initial oxygen permeability) / Initial oxygen permeability × 100%. Test 3 parallel samples for each group of samples and take the arithmetic mean of the results.

[0068] Low-temperature cantilever beam impact strength test: The test was conducted in accordance with GB / T1843-2008, using unnotched specimens, at a test temperature of -20℃. Five parallel samples were tested for each group of specimens, and the arithmetic mean of the results was taken to characterize the low-temperature toughness of the material.

[0069] Flexural modulus test: The test was conducted in accordance with GB / T9341-2008. The test environment was 23℃ and 50%RH. The bending rate was 2mm / min. Five parallel samples were tested for each group of samples. The arithmetic mean of the results was taken to characterize the room temperature stiffness of the material.

[0070] Table 1 shows the properties of the composite materials prepared in Examples 1-3 and Comparative Examples 1-3.

[0071] As shown in Table 1, the low-temperature resistant multilayer co-extruded polypropylene composite materials prepared in Examples 1-3 of this invention showed no interlayer debonding or warping deformation after 10 cycles of high and low temperatures from -20℃ to 40℃. The change rate of oxygen permeability was ≤10%, and the initial oxygen permeability was ≤0.5cc / (m²) under 23℃ and 50%RH conditions. 2 It has excellent low-temperature impact toughness and room-temperature rigidity, achieving a synergistic improvement in low-temperature toughness, room-temperature rigidity, long-term stability of interlayer adhesion and high barrier properties.

[0072] In Comparative Example 1, the melt flow rate, flexural modulus, and ethylene content of the copolymer polypropylene used exceeded the limits of this invention, resulting in insufficient rigidity at room temperature. After high and low temperature cycling, localized micro-debonding occurred, and the oxygen permeability change rate far exceeded 10%, significantly reducing the barrier performance and failing to meet the long-term use requirements of cold chain scenarios. In Comparative Example 2, the amount of polyolefin elastomer added exceeded the limits of this invention. Although the low-temperature impact performance was improved, the crystallinity of the material matrix decreased significantly, the flexural modulus at room temperature decreased significantly, and the interlayer interface bonding force decreased. After high and low temperature cycling, the adhesive stability deteriorated, and both the oxygen permeability and change rate exceeded the limits of this invention. In Comparative Example 3, the melt flow rate ratio of the intermediate barrier layer and the adhesive layer resin exceeded the numerical range limited by this invention. The melt rheological properties were mismatched during multilayer co-extrusion, resulting in obvious delamination and warping after high and low temperature cycling. Oxygen permeation channels were formed between the layers, leading to severe deterioration of the barrier performance. Both the oxygen permeability and the change rate after cycling increased significantly.

[0073] It should be understood that the spirit of the present invention has been described in detail above through preferred embodiments. Those skilled in the art will understand that any modifications, equivalent variations, and alterations made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the present invention.

Claims

1. A low-temperature resistant multilayer co-extruded polypropylene composite material, comprising a five-layer symmetrical co-extruded structure arranged sequentially from the outside to the inside, wherein the five-layer symmetrical co-extruded structure comprises, in sequence, an outer layer, a second outermost adhesive layer, an intermediate barrier layer, a second innermost adhesive layer, and an inner layer, characterized in that, Both the outer and inner layers are toughened polypropylene compositions, which, by weight, consist of the following components: 100 parts by weight of copolymerized polypropylene; 12-18 parts by weight of polyolefin elastomer; The total thickness of the composite material is 300-800 μm, of which the outer layer accounts for 25-35% of the total thickness and the inner layer accounts for 25-35% of the total thickness; After being frozen at -20℃ for 2 hours and then held at 40℃ for 2 hours, the oxygen permeability of the composite material was changed by ≤10% after 10 cycles of high and low temperature cycling. Under conditions of 23℃ and 50%RH, the oxygen permeability of the composite material was ≤0.5cc / (m³). 2 • 24h·atm); The impact strength of the composite material at -20℃ unnotched cantilever beam is ≥5kJ / m 2 Flexural modulus at room temperature ≥1100MPa; The copolymer polypropylene is a random copolymer of propylene and ethylene, with an ethylene content of 3wt%-6wt%, a melt flow rate of 1.0-3.5g / 10min at 230℃ and 2.16kg, and a flexural modulus ≥1100MPa. The outermost adhesive layer and the innermost adhesive layer comprise maleic anhydride-grafted polypropylene adhesive resin. The maleic anhydride-grafted polypropylene adhesive resin has a melt flow rate of 1.0-4.0 g / 10 min at 230°C and 2.16 kg. The intermediate barrier layer is an ethylene-vinyl alcohol copolymer with a melt flow rate of 3.0-6.0 g / 10 min at 210°C and 2.16 kg, and the melt flow rate ratio of the intermediate barrier layer to the maleic anhydride-grafted polypropylene bonding resin is 0.8-1.

5.

2. The composite material according to claim 1, characterized in that, The polyolefin elastomer is an ethylene-propylene copolymer elastomer.

3. The composite material according to claim 2, characterized in that, The ethylene-propylene copolymer elastomer has a melt flow rate of 2.0-5.0 g / 10 min at 230°C and 2.16 kg, and an ethylene content of 10-16 wt%.

4. A method for preparing a low-temperature resistant multilayer co-extruded polypropylene composite material according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Add the toughened polypropylene composition as the inner layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene bonding resin as the secondary inner layer bonding layer to the multilayer co-extrusion extruder, add the ethylene-vinyl alcohol copolymer as the intermediate barrier layer to the multilayer co-extrusion extruder, add the maleic anhydride-grafted polypropylene as the secondary outer layer bonding layer to the multilayer co-extrusion extruder, and add the toughened polypropylene composition as the outer layer to the multilayer co-extrusion extruder. Perform co-extrusion to obtain a five-layer co-extruded melt. Step 2: The five-layer co-extruded melt is blow-extruded, cooled and shaped, and the scrap is removed to obtain the low-temperature resistant multilayer co-extruded polypropylene composite material.

5. The preparation method according to claim 4, characterized in that, In step 1, the inner layer extrusion temperature of the multilayer co-extrusion extruder is 180-235℃, the second inner layer adhesive layer extrusion temperature is 190-230℃, the middle barrier layer extrusion temperature is 190-230℃, the second outer layer adhesive layer extrusion temperature is 190-230℃, and the outer layer extrusion temperature is 180-235℃.

6. A packaging product, characterized in that, Including the low-temperature resistant multilayer co-extruded polypropylene composite material according to any one of claims 1-3.

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