What is packaging laminating production technology?

A Detailed Look at Packaging Laminated Production Process: The Art of Precision "Welding" for Multi-layer Materials

In the modern packaging industry, we often encounter packaging materials with exceptional performance: they effectively block oxygen and moisture while withstanding high-temperature retorting; they are lightweight and flexible yet possess sufficient mechanical strength; they feature gorgeous, exquisite printed patterns while preserving the original flavor of the contents. These seemingly contradictory performance requirements are often beyond the capability of a single material. The secret behind them lies in the composite production process – an engineering technology that precisely and reliably "welds" two or more substrates with different characteristics into one, thereby creating a high-performance composite material system.

This article will delve into the core of the packaging laminated production process, systematically explain its principles, main methods, process control, and future trends, presenting a complete panorama of packaging composite technology.

I. Core Principles and Value of the Laminating Process

The essence of the composite process is synergy and complementarity. Its basic principle is to use adhesives or other media to firmly combine substrates with different properties (such as plastic films, aluminum foil, paper, etc.), forming a multi-layer composite material. Each substrate plays a unique role, collectively building a complete protection system.

Barrier Layer: Typically made from aluminum foil, metallized film, polyvinylidene chloride (PVDC) film, ethylene-vinyl alcohol copolymer (EVOH) film, etc., it is primarily responsible for blocking oxygen, water vapor, light, and odors, ensuring the shelf life and safety of the contents.

Strength Layer: Such as paper, biaxially oriented polypropylene (BOPP), biaxially oriented polyester (BOPET), etc., it provides the material's mechanical strength, tensile resistance, tear resistance, and impact resistance, ensuring the integrity of the packaging during transportation and circulation.

Seal Layer: Usually low-melting-point materials like cast polypropylene (CPP) or polyethylene (PE), located on the inner side of the packaging, responsible for achieving a strong seal through heat melting during bag-making or filling and sealing.

Printing Layer: Such as BOPP, BOPET, and other materials with excellent surface properties, providing a high-quality display interface for brand information and patterns.

Through the composite process, a typical three-layer structure (e.g., BOPP/AL/CPP) can simultaneously achieve exquisite surface printing, high barrier properties, and reliable sealing performance. Its value far exceeds the simple sum of its individual layers.

II. Detailed Explanation of Mainstream Composite Production Process Methods

Depending on the type of adhesive used and the method of combination, mainstream composite production processes can be divided into the following major categories, each with its unique application scenarios and process requirements.

Dry Lamination

This is currently the most widely used and mature composite process.

Process Flow:

Coating: A solvent-based or water-based polyurethane adhesive is uniformly coated onto the surface of the first substrate (e.g., BOPET) using a gravure roller.

Drying: The coated substrate is sent into an oven where the solvent (or water) in the adhesive is completely evaporated under a specific temperature gradient. Controlling residual solvent is crucial in this step.

Lamination: At the oven outlet, the dried but still tacky adhesive layer is immediately pressed together with the second substrate (e.g., CPP) through heated steel and rubber rollers.

Curing: The laminated roll is placed in a curing room where, under specific temperature and time conditions (e.g., 40-50°C, 48-72 hours), the adhesive undergoes sufficient cross-linking and curing reactions to achieve the final bond strength.

Advantages: Wide application range, high bond strength, high production efficiency.

Disadvantages: Risk of solvent residue (when using solvent-based adhesives), high energy consumption, relatively long process flow.

Applications: Suitable for almost all common flexible packaging composite materials, such as snack packaging, pharmaceutical packaging, retort packaging, etc.

Solvent-free Lamination

As the mainstream direction for green and environmentally friendly production, solvent-free composite technology is rapidly gaining popularity.

Process Flow:

Mixing and Coating: Two-component, 100% solid content polyurethane adhesive (Component A and Component B) is proportionally mixed via precision metering pumps and a static mixer, and immediately coated uniformly onto the first substrate.

Lamination: The coated substrate, without needing drying, is directly pressed together with the second substrate under the lamination roller.

Curing: A curing process is still required to allow the adhesive to complete its cross-linking reaction.

Advantages: No solvent emissions, safe and environmentally friendly; low energy consumption, high speed; no risk of solvent residue.

Disadvantages: Lower initial tack (T-peel strength), high requirements for equipment and operation; bond strength development for some specific materials (e.g., NY) can be slightly slower compared to dry lamination.

Applications: The preferred process for standard lightweight packaging, and gradually expanding into high-performance areas like high-temperature retorting.

Extrusion Lamination

This process integrates extrusion casting and lamination into one step.

Process Flow:

Melting and Extrusion: Thermoplastic resin pellets (e.g., LDPE, PP) are heated and melted in an extruder.

Cast Coating: The molten resin is extruded through a narrow T-die, forming a thin film.

Press Lamination: While the molten resin has not yet cooled and solidified, it acts as the adhesive, laminating the first substrate (e.g., paper or BOPP) and the second substrate (or acting as the seal layer itself) together under a pressure roller.

Cooling and Setting: The resin layer is rapidly cooled and solidified via cooling rollers, completing the lamination.

Advantages: Lower cost (saves adhesive cost), combines lamination and casting functions, can produce thick films, excellent sealing performance.

Disadvantages: Relatively lower bond strength, limited material selection, narrow process control window.

Applications: Widely used in areas requiring robust seal layers, such as milk packaging, liquid packaging, toothpaste tube laminates.

Co-extrusion Lamination

This is an advanced technology that achieves "lamination" at the source.

Process Flow: Multiple extruders are used to melt different types or colors of resin pellets separately. These melts are then fed into a precise multi-layer co-extrusion die. Inside the die, the individual melt streams flow side-by-side and merge upon exiting the die, cooling to form a multi-layer film in a single step.

Advantages: One-step formation, no solvents, no adhesives, environmentally friendly and cost-effective; interlayer bonding is at the molecular level, eliminating delamination risk.

Disadvantages: High equipment investment cost; layer materials must be compatible or compatibilized polymers, limiting selection; difficult to incorporate non-plastic materials like aluminum foil or paper.

Applications: Primarily used for high-performance plastic flexible packaging, such as heavy-duty sacks, frozen food packaging, liquid packaging liner layers.

III. Key Points for Quality Control in Composite Processes

To produce high-quality composite packaging materials, precise control over the following key points is essential:

Surface Tension: The surface tension of all substrates must be higher than that of the adhesive to ensure good wetting and spreading, which is a prerequisite for achieving high bond strength. Film surfaces often require activation via methods like corona treatment.

Adhesive Selection and Mix Ratio: Select the appropriate adhesive system based on the end-use of the packaging (e.g., water boiling, retorting, chemical resistance) and precisely control the mix ratio for two-component adhesives.

Coat Weight Control: Ensure the adhesive is applied uniformly and quantitatively through precision gravure rollers and coating systems. Excessive adhesive causes waste and slippage, while insufficient amounts lead to inadequate strength.

Drying and Curing Process: The drying temperature profile directly affects solvent residue; curing temperature and time determine the degree of adhesive cure and the final physical properties.

Production Process Monitoring: Real-time monitoring of the laminate's appearance (e.g., gel particles, bubbles, tunneling), initial tack, and final key indicators like bond strength, coefficient of friction, and heat seal strength.

IV. Future Development Trends

Green and Sustainable Development: Further adoption and enhancement of solvent-free lamination; performance optimization of water-based adhesives; development of mono-material recyclable composite structures (e.g., all-PE structures) are becoming core industry topics.

Intelligent and Digital Transformation: Real-time collection of process data via IoT technologies, utilizing big data and AI algorithms to optimize process parameters, enabling predictive maintenance and quality traceability, thereby improving production stability and efficiency.

Functional and High Performance: Development of composite materials and processes suitable for higher temperatures (ultra-high temperature retorting), stronger barriers (high oxygen barrier, high moisture barrier), and new additional functions like antimicrobial, anti-counterfeiting, and smart labels.

Conclusion

Packaging composite production is a precision engineering technology integrating polymer chemistry, fluid mechanics, mechanical engineering, and materials science. Like a skilled tailor, it deftly stitches together distinct "fabrics" to custom-make a safe, reliable, and eye-catching "garment" for products. With technological advancement and evolving market demands, this process will undoubtedly continue evolving towards greater environmental friendliness, intelligence, and diversity, consistently infusing new vitality and value into the packaging industry.