Eco-friendly — Analysis of the Production and Application Characteristics of Solvent-free Polyurethane Adhesives

In recent years, China's adhesive market has grown rapidly. Today, adhesive manufacturers are seeking innovative solutions that can meet high standards in terms of quality, durability and sustainability, so as to maintain an advantageous position in the increasingly competitive adhesive market.

Since 2010, guided by relevant national laws and regulations, solvent-free lamination technology has developed rapidly in the domestic flexible packaging industry thanks to its many advantages such as safety, health, environmental protection, energy saving, high efficiency and low cost. Especially in the past two years, both solvent-free lamination production lines and the adhesives they use have been growing exponentially.

The application of solvent-free polyurethane adhesives will not only drive the development of the adhesive industry alone, but will also drive the rapid development of the machinery manufacturing industry. This article briefly analyzes the production and application characteristics of solvent-free polyurethane adhesives, in the hope of being helpful to the industry.

Production and Application Characteristics of Solvent-free Polyurethane Adhesives

1. Good usability

At the operating temperature, the mixed viscosity of solvent-free polyurethane adhesive is below 1000mPa•s, and the actual pot life is more than 30min, which makes up for the shortcoming of previous solvent-free adhesives that required high-temperature heating for coating; it has a certain strength of adhesion to a variety of composite materials, such as the mutual lamination and bonding of films including PE, BOPP, CPP, PET, NY and PVDC; it has good resistance to 100℃ boiling water (121℃ retort), acid, salt and oil, and can be cured by heat or at room temperature, offering convenient operation and good application performance.

1. Safety and hygiene

Dry lamination uses solvent-based adhesives, generally using a drying tunnel at about 80℃ to quickly dry the coated adhesive layer before lamination. During drying, a large amount of organic solvent volatilizes into the environment, causing environmental pollution. The residual unvolatilized organic solvent is trapped in the laminated film, which on the one hand reduces the bond strength of the laminated film, and on the other hand slowly migrates to the inner surface of the laminated film, contaminating the food in the inner packaging.

The use of solvent-free polyurethane adhesives completely eliminates organic solvent volatilization and any irritating odor; there is no residual solvent problem in the laminated products, no odor or toxicity issues, and the erosion of printing ink by organic solvents is eliminated. At the same time, the use of solvent-free polyurethane adhesives enables clean production and is conducive to environmental protection. In addition, since solvent-free polyurethane adhesives contain no organic solvent, there is no risk of fire or explosion, no explosion-proof measures are required, and the equipment and warehouse for solvent storage are also eliminated.

It is worth mentioning that the raw materials used in solvent-free polyurethane adhesives must comply with the provisions of US FDA 175.105 and China's national standard GB 9685-2003 'Hygienic Standard for the Use of Additives in Food Containers and Packaging Materials', i.e., there are no additives or additions toxic or harmful to the human body, and each batch of raw materials must undergo strict inspection before use to ensure that all performance indicators fully meet the standards before production.

1. Energy saving and cost reduction

The use of solvent-free polyurethane adhesives can significantly reduce the production cost of laminated films, mainly in the following aspects:

(1) Compared with dry lamination equipment, solvent-free lamination equipment eliminates the bulky and complex heating and blowing and exhaust gas devices; the equipment is simple, occupies a small area, saves raw materials, has low maintenance costs and low investment cost.

(2) During lamination, there is no need to pass through a drying tunnel to remove organic solvents from the adhesive, resulting in significant energy savings.

(3) The adhesive application weight per unit area is low (only 1.5–2.0g/m2), so the adhesive consumption cost is low. The adhesive application weight per unit area of solvent-free lamination is about two-fifths of that of dry lamination; therefore, although the price of solvent-free lamination adhesive may be 70% higher than that of dry lamination adhesive, the adhesive consumption cost per unit area of solvent-free lamination is about 30% lower than that of dry lamination.

(4) The production line speed is significantly improved. The maximum speed of solvent-free lamination can reach 480m/min, and generally is also above 200m/min.

Based on the above reasons, the production and processing cost of solvent-free lamination is much lower than that of dry lamination, about 50% or less.

If in the next 10–20 years the share of solvent-free lamination technology in China's lamination market can reach 80%–90% as it has abroad, the economic and social benefits brought by solvent-free adhesives will be enormous.