Development Trends of Solvent-Free Adhesives for Plastic Flexible Packaging mainly include several types, such as general-purpose solvent-free laminating adhesive, high-temperature cooking-resistant solvent-free laminating adhesive, medium-resistant solvent-free laminating adhesive, single-component solvent-free laminating adhesive, and UV-curable solvent-free laminating adhesive.
General-Purpose Solvent-Free Laminating Adhesive: Undoubtedly, general-purpose solvent-free laminating adhesive is the main adhesive used in solvent-free lamination. Especially in the early stages of adopting solvent-free lamination processes, when flexible packaging manufacturers are just introducing solvent-free lamination production lines, they are still becoming familiar with and understanding the entire lamination process. They start with the simplest and most universal materials, gradually becoming familiar with solvent-free lamination processes. When they fully grasp the key points of the solvent-free lamination process, they will confidently use solvent-free lamination for high-end products.
General-purpose solvent-free laminating adhesive, as the first solvent adhesive used by flexible packaging manufacturers when they first encounter solvent-free lamination, must meet several requirements:
Convenient Operation: The general-purpose solvent-free laminating adhesive should be easy to operate, including appropriate viscosity at room temperature for both components and when mixed, with sufficient working time. Many flexible packaging manufacturers initially use manual mixing. If the viscosity of the solvent-free adhesive is too high, it is not conducive to uniform mixing. Additionally, if the working time is too short, it may affect product quality and damage solvent-free lamination equipment. Generally, the working time of solvent-free adhesive should be no less than 30 minutes.
Wide Applicability: Solvent-free lamination is known for its efficiency and fast lamination speed, requiring the solvent-free adhesive to have broad applicability. Flexible packaging products come in various types, and manufacturers often receive different orders, requiring the lamination of various products. If each product requires a different type of adhesive, the cleaning of the solvent-free lamination equipment becomes a burden for flexible packaging manufacturers. Cleaning solvent-free lamination equipment typically takes 1-2 hours, and if manual cleaning is involved, it might take even longer. Broad applicability allows the solvent-free adhesive to be used for most common flexible packaging materials, including transparent materials, printing materials, and aluminum-plated materials, among others.
Appropriate Curing Temperature and Time: The later-stage curing temperature of the solvent-free adhesive is generally controlled between 40°C and 50°C, similar to the curing temperature of dry lamination. The curing time should be around one day. Excessive curing time not only increases energy consumption but also affects the normal progress of subsequent processing steps for laminated flexible packaging materials.
Good Stability: As solvent-free adhesives for food flexible packaging are in the early stages, they must exhibit good stability to withstand market tests. Stability and reliability are crucial for the survival and development of enterprises.
High-Temperature Cooking-Resistant Solvent-Free Laminating Adhesive: High-temperature cooking-resistant bags refer to bags made by laminating PET, PA, Al, CPP, and other film materials using high-temperature cooking-resistant adhesives. These bags are used for packaging food, medical instruments, and can withstand high-temperature steam heating for sterilization. They are also known as steam-cookable flexible packaging or soft canned goods. The three levels of cooking resistance are 121°C, 135°C, and 145°C. The development of solvent-free adhesives that can withstand high-temperature cooking, especially at 135°C, is limited. Developing such adhesives is essential for fully replacing traditional dry lamination processes with solvent-free lamination.
Medium-Resistant Solvent-Free Laminating Adhesive: With the expanding application of composite flexible packaging materials, especially in packaging daily necessities, cosmetics, detergents, sanitary products, pesticides, and some chemical products, there is an urgent demand for functionality. Research and development of solvent-free adhesives with resistance to acid, alkali, spiciness, salt, oil, and corrosion by benzene, toluene, xylene, esters, hydrocarbons, alcohols, surfactants, and mixed solvents with less than 20% DMF are trends for the future. After sufficient curing, the composite film should be able to package liquid pesticides containing toluene, xylene, small amounts of DMF, alcohols, esters, hydrocarbons, etc.
Single-Component Solvent-Free Laminating Adhesive: The main advantage of single-component solvent-free adhesives is their convenient use. They do not require on-site mixing, can be applied at higher temperatures, have a longer shelf life, and exhibit higher initial tack compared to two-component solvent-free adhesives. However, they rely on moisture in the air for curing, making them highly affected by environmental conditions. Proper humidification of the air is necessary to ensure sufficient adhesive curing. During the curing process, carbon dioxide is generated, and if not promptly removed, it may lead to the formation of bubbles in the product.
The future development direction of single-component solvent-free laminating adhesives is primarily for paper-plastic composite products. In the paper-plastic lamination process, paper easily absorbs adhesive. If a general-purpose solvent-free adhesive is used, serious adhesive absorption may occur, affecting the quality and appearance of the laminated product. Single-component solvent-free laminating adhesive, being a high-temperature coating, can effectively solve this problem as the viscosity of the adhesive rapidly increases after lamination, especially when the temperature decreases.
UV-Curable Solvent-Free Laminating Adhesive: UV-curable solvent-free laminating adhesive not only has the characteristics of fast curing, transparency, high bonding strength, and good flexibility but also has the advantages of being solvent-free, non-toxic, non-corrosive, energy-saving, and environmentally friendly. It is considered a new generation of environmentally friendly products that can partially replace traditional solvent-based laminating adhesives. UV-curable adhesives can be used in the rapid production of plastic/plastic, plastic/paper, plastic/metal film laminated products, offering simple and efficient production. This type of adhesive is suitable for high-speed production line processes and is considered the ultimate trend in solvent-free development.