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The core challenge of low-temperature packaging lies in the compatibility of material properties with low-temperature environments. Traditional films are prone to embrittlement and reduced barrier properties in an environment of -18℃ to -25℃, resulting in oxidation of contents, microbial growth or physical damage. Functional composite technology introduces specific functional materials into the 7-layer asymmetric co-extruded low-temperature film to solve these pain points in a targeted manner, and promote the evolution of low-temperature packaging from "single barrier" to "multi-dimensional protection".
Technical necessity:
Antibacterial demand: In cold chain logistics, the risk of microbial contamination of perishable foods such as meat and dairy products has increased significantly. Traditional packaging relies solely on low temperature to inhibit microorganisms, but cannot completely block cross-contamination.
Odor control: Chemical raw materials, frozen foods, etc. are prone to release volatile organic compounds (VOCs) during storage, resulting in the accumulation of odors in the packaging, affecting product quality.
Temperature fluctuation management: Temperature fluctuations in cold chain transportation (such as short-term temperature rise during loading and unloading) will accelerate the deterioration of contents, and traditional packaging is difficult to actively adjust the microenvironment inside the package.
The antibacterial function is achieved through two technical paths: silver ion antibacterial agent and activated carbon layer.
Silver ion (Ag⁺) achieves antibacterial effect by destroying microbial cell membranes and interfering with DNA replication. In the 7-layer asymmetric co-extruded low-temperature film, silver ion antibacterial agents are usually embedded in the EVOH or PA layer in the form of nanoparticles, or formed into a unilateral antibacterial coating through asymmetric coating technology.
Broad-spectrum antibacterial: Effective against Gram-positive bacteria, Gram-negative bacteria and some fungi.
Durability: Silver ions form stable chemical bonds with polymer substrates, and the antibacterial effect can last for 6-12 months.
Safety: Nano-encapsulation technology is used to control the release rate of silver ions and avoid heavy metal residues.
Application scenarios: High-risk food packaging such as cold fresh meat, dairy products, and seafood can reduce the risk of contamination by pathogenic bacteria such as Listeria and Salmonella.
Activated carbon removes odor molecules (such as trimethylamine, hydrogen sulfide, etc.) in packaging through physical adsorption. In the film, the activated carbon layer is usually co-extruded with the EVA or PE layer to form a composite structure, or embedded in the asymmetric layer as an independent functional layer.
Efficient adsorption: The specific surface area is 500-1500 m²/g, which can quickly adsorb odor molecules.
Reversibility: Activated carbon can be regenerated by heating or decompression to extend the service life.
Synergistic effect: When used in combination with antimicrobial agents, it can inhibit microbial growth and odor accumulation at the same time.
Application scenarios: Frozen seafood, coffee beans, spices and other commodity packaging that is prone to odor.
Phase change materials (PCM) achieve dynamic balance of temperature in the package by absorbing or releasing heat during the solid-liquid phase change process. In the 7-layer asymmetric co-extruded low-temperature film, PCM is usually embedded in the EVA or elastomer layer in the form of microcapsules to form a "temperature buffer layer".
Phase change temperature: Select the phase change temperature of PCM (such as -5℃ to -15℃) according to the characteristics of the contents to ensure that it continues to play a role in cold chain transportation.
Encapsulation technology: The microencapsulation process is used to wrap PCM in a polymer shell to avoid direct contact with the contents, while improving the flexibility and processability of the material.
Asymmetric distribution: The PCM layer is usually located in the middle of the film or close to the content side, and the heat conduction path is optimized through gradient design.
Heating stage: When the temperature in the package rises briefly, the PCM changes from solid to liquid, absorbs excess heat, and slows down the temperature rise rate.
Cooling stage: When the temperature drops, the PCM solidifies from liquid to solid, releases the stored heat, and avoids over-freezing of the contents.
Dynamic balance: Through the phase change cycle of PCM, the temperature fluctuation range in the package is reduced to within ±2℃, significantly extending the shelf life of the contents.
Cold chain transportation: Reduce temperature shock during loading and unloading, and protect temperature-sensitive commodities such as frozen foods and biological preparations.
Long-term storage: In cold storage, PCM can offset the temperature difference between night and day, reducing the risk of deterioration of the content.
Functional compounding is not a simple superposition, but a synergistic effect achieved through material design and process optimization.
Antibacterial + temperature buffer: PCM may release trace moisture during the phase change process, and the activated carbon layer can absorb this moisture to avoid the growth of microorganisms caused by excessive humidity.
Deodorization + barrier property: The activated carbon layer is combined with the EVOH barrier layer to remove odor molecules and isolate external oxygen, forming a double protection.
Compatibility issues: Antimicrobial agents, activated carbon or PCM may react chemically with the substrate, and the interface bonding needs to be optimized through surface modification or compatibilizer.
Processing window: The introduction of functional materials may change the melt fluidity or heat sealing performance of the film, and the extrusion process parameters (such as temperature and screw speed) need to be adjusted.
Cost control: The price of functional materials is higher than that of traditional polymers, and costs need to be reduced through material substitution (such as partial use of recycled materials) or large-scale production.
Functional compounding technology is developing towards intelligence and greenness.
Thermosensitive color change: Add thermosensitive dyes to the PCM layer. When the temperature exceeds the threshold, the color of the film changes, which intuitively indicates the packaging status.
Antimicrobial response: Develop pH-sensitive antimicrobial agents. When microbial contamination in the package causes pH changes, the antimicrobial agents are automatically released.
Bio-based materials: Replace some petroleum-based materials with bio-based polymers such as PLA and PHA to reduce carbon footprint.
Degradable PCM: Develop PCM that can be degraded in the natural environment to reduce the burden of discarded packaging on the environment.
