What are dry laminators, solventless laminators, and flexo adhesive laminators?

The Three Pillars of Precision Coating Technology: An In-Depth Analysis of Dry Lamination, Solventless Lamination, and Flexo Adhesive Lamination

In numerous industrial fields such as flexible packaging, decorative materials, and electronic films, firmly bonding two or more substrates (e.g., films, aluminum foil, paper) into a single unit is a key process for manufacturing high-performance composite materials. This process is called "laminating". The core equipment enabling this process is the laminating machine. Among them, dry laminators, solventless laminators, and flexo adhesive laminators, with their distinct working principles, technical characteristics, and applicable fields, constitute the three major pillars of modern precision coating and laminating technology. This article will provide a deep analysis of these three types of equipment, presenting a professional and detailed technical picture.

I. Dry Laminator: Classic Technology, Wide Application

Dry lamination is the earliest developed, most mature, and most widely used laminating process, and it still holds significant importance globally.

Core Working Principle

Its process can be summarized as a "dry method" process, with specific steps as follows:

Coating: First, a layer of solvent-based or water-based polyurethane adhesive is precisely coated onto the first substrate (e.g., BOPP, PET film) using a gravure roller or coating blade.

Drying: Subsequently, the coated substrate enters a multi-section (typically 3 sections) drying oven. Under the influence of hot air, the solvent (or water) in the adhesive is completely evaporated, leaving only a dry, reactive adhesive layer. This is the origin of the name "dry".

Laminating: The dried substrate is pressed together with the second substrate (e.g., CPP, PE film, or aluminum foil) between a heated steel roller and a rubber roller. Under certain temperature and pressure, the dried adhesive layer melts and forms a strong bond with the surface of the second substrate, completing the lamination.

Curing: The laminated roll must then rest in a specialized curing room for a period (typically 24-72 hours). During this time, the adhesive undergoes a complete chemical cross-linking reaction, ultimately achieving the designed optimal bond strength and various resistances (e.g., heat resistance, media resistance).

Technical Advantages

Strong Versatility: Can laminate almost all types of plastic films, aluminum foil, and paper, with an extremely wide adaptability to substrates.

Mature Process: Long history, well-established process parameter database, experienced operators, and high production stability.

High Bond Strength: By selecting different types of adhesives, extremely high final peel strength can be achieved, meeting the demands of high-end packaging.

Relatively Lenient Substrate Surface Requirements: Compared to other laminating methods, the requirements for substrate corona treatment level are slightly lower.

Limitations

Environmental Pollution: If solvent-based adhesives are used, VOCs (Volatile Organic Compounds) are emitted during the drying process, requiring expensive exhaust gas incineration or recovery systems, which increases operational costs and environmental pressure.

High Energy Consumption: The drying oven process consumes a large amount of thermal energy, leading to significant energy costs.

Safety Hazards: Solvents are flammable and explosive substances, requiring extremely high fire and explosion prevention standards in the workshop.

Risk of Solvent Residue: If process control is inadequate, trace amounts of solvent may remain, affecting the safety of food and pharmaceutical packaging.

Production Efficiency: Requires curing time, which extends the production cycle.

II. Solventless Laminator: Green, Eco-Friendly, Efficient, and Energy-Saving

Solventless lamination is a new laminating technology developed in line with the global trend of green manufacturing. With its outstanding environmental friendliness and economic efficiency, it is becoming one of the mainstream processes.

Core Working Principle

Solventless lamination uses 100% solid content polyurethane adhesives. These adhesives have high viscosity at room temperature and consist of two components (main agent and curing agent) mixed in precise proportions by specialized equipment.

Metering and Mixing: High-precision gear pumps and static mixers are used to meter and uniformly mix the two-component adhesive according to a set ratio (e.g., 100:75).

Coating: The mixed adhesive is transferred to an applicator roller and, through a very precise four-roller or five-roller coating system, an extremely thin and uniform adhesive layer is coated onto the first substrate.

Laminating: The coated substrate does not need to pass through a long drying oven but is directly pressed together with the second substrate at the laminating roller.

Curing: The laminated roll similarly needs to enter a curing room to allow the adhesive to complete the chemical reaction between the substrates, forming a strong bond.

Technical Advantages

Absolutely Eco-Friendly: No solvent emissions whatsoever, completely eliminating VOC pollution, compliant with the strictest environmental regulations.

Extremely Energy Efficient: Eliminates the energy-intensive drying oven, reducing overall energy consumption by approximately 70%-80% compared to dry lamination.

High Economic Efficiency: The adhesive application amount is very low (typically only 1/2 to 1/3 of dry lamination), resulting in lower laminating cost per unit area.

Production Safety: No flammable or explosive solvents, significantly improving production environment safety.

Hygienic Safety: No risk of solvent residue, making it the preferred process for food, pharmaceutical, and hygiene product packaging.

High Production Efficiency: High online speed, and no need to wait for solvent evaporation, although curing time is still required.

Limitations

High Demands on Substrates: Requires substrates to have excellent surface tension and flatness; tension control for easily stretched films like PE is extremely critical.

Low Initial Tack: The initial tack immediately after lamination (commonly known as the "butterfly effect") places higher demands on process control for subsequent slitting and bag-making processes.

High Equipment Investment: The core metering, mixing, and coating systems require extremely high precision, resulting in a relatively high initial equipment investment.

Narrow Process Window: More sensitive to environmental factors such as workshop temperature, humidity, and adhesive working temperature.

III. Flexo Adhesive Laminator: Specialized in Paper-Plastic, Economical and Practical

Flexo adhesive lamination, often referred to as "water-based adhesive lamination", is mainly used in specific fields, offering irreplaceable advantages, particularly in paper-plastic lamination.

Core Working Principle

Its core involves using flexographic printing technology for adhesive application.

Adhesive Application: A water-based adhesive (e.g., PVA, EVA, acrylates) is transferred via an anilox roller (gravure); the cells engraved on the anilox roller carry a metered amount of adhesive, and a doctor blade scrapes off the excess. Finally, the anilox roller transfers the metered adhesive directly to the flexible printing plate, which then coats the adhesive onto the substrate.

Drying: The coated substrate enters a drying oven, where hot air evaporates the water from the adhesive.

Laminating: After drying, it is pressed together with the second substrate. Some simpler machines may omit the drying oven, relying on penetration and natural drying, but strength development is slower.

Technical Advantages

Highly Eco-Friendly: Uses water-based adhesives, no solvent emission issues.

Low Cost: The cost of equipment and consumables (water-based adhesive, printing plates) is usually much lower than the previous two methods.

Capable of Partial Coating: Like printing, it can perform partial, discontinuous adhesive application according to preset patterns, achieving special functions or saving adhesive.

Suitable for Porous Materials: Good penetration into porous materials like paper and non-wovens, resulting in good bonding effects.

Limitations

Limited Bond Strength: The final bond strength of water-based adhesives is generally lower than that of polyurethane adhesives, making it difficult to meet demanding requirements such as high strength and resistance to retorting.

Narrow Application Scope: Mainly used for paper/plastic, paper/aluminum foil lamination, with limited application in the field of plastic/plastic film lamination.

Susceptible to Environmental Influence: Although energy consumption during drying is lower than dry lamination, it still requires energy. The water evaporation rate is greatly affected by environmental humidity.

May Cause Substrate Deformation: For thin plastic films, the moisture in the water-based adhesive and the heat from drying may cause film shrinkage and deformation.

IV. Comprehensive Comparison and Selection Guide

For a more intuitive comparison, we summarize the core characteristics of the three in the following table:

Selection Recommendations:

Choose a Dry Laminator: When you need to laminate a wide variety of substrates with complex structures (e.g., containing metallized film), or when the product requires extremely high media resistance or retort resistance, dry lamination remains a reliable choice. Especially with the ongoing advancement of water-based adhesive technology, it is also evolving towards more environmentally friendly directions.

Choose a Solventless Laminator: For enterprises pursuing green production, aiming to reduce comprehensive costs, and whose product structures mainly involve mainstream plastic/plastic or plastic/aluminum foil lamination, solventless lamination is the current and future inevitable trend. It is the core direction for upgrading high-end flexible packaging production lines.

Choose a Flexo Adhesive Laminator: When your products are mainly paper/plastic lamination (e.g., gift bags, instant noodle bags), paper/aluminum lamination, and the requirements for bond strength are not extreme, while investment cost and environmental protection are major concerns, flexo adhesive lamination is an ideal, economical, and practical solution.

Conclusion

Dry lamination, solventless lamination, and flexo adhesive lamination are not simply substitutive but rather complementary technologies, each excelling in different application scenarios. Dry lamination holds its ground with its classic nature and powerful adaptability; solventless lamination, with its green, efficient, and economical superior characteristics, is leading the future of laminating technology; flexo adhesive lamination occupies a solid position in specific cost-performance markets.

For composite material manufacturers, deeply understanding the essence of these three technologies, and conducting scientific and rational equipment selection and process layout based on their own product positioning, environmental requirements, and investment budget, is the way to build a solid technical barrier and cost advantage in the fierce market competition, ensuring steady and long-term development.