Glue for flexible packaging is the key material for bonding composite materials, which needs to meet the requirements of hygiene, safety, weather resistance and processing adaptability. The following is the analysis of its main types and characteristics:
1. Solvent adhesive
It is made by dissolving resin in an organic solvent (such as ethyl acetate) and drying to form an adhesive layer. Strong initial viscosity, suitable for common films such as PE and BOPP. However, there is a problem of VOC emission, which requires supporting recycling equipment, and the proportion of use has gradually decreased in recent years.
2. Waterborne adhesive
With water as the dispersion medium, it has outstanding environmental protection and is suitable for food and medicine packaging. Divided into acrylic and polyurethane:
Acrylic: low cost and good light resistance, but the performance may decrease in high temperature and high humidity environment.
Polyurethane: excellent flexibility, can withstand cooking above 100℃, but the drying energy consumption is high.
3. Solventless adhesive
At present, the mainstream technology is curing by polyether/polyester polyurethane prepolymer reaction. Advantages include:
Zero VOC, direct compounding without drying
The coating amount is only 1.5-3g/㎡ (solvent needs 3-5g/㎡).
After curing, the temperature resistance can reach 121℃ (cooking grade)
It is necessary to accurately control the mixing ratio and coating temperature (usually 40-50℃).
4. Functional special glue
Aluminum foil
Composite Adhesive: To solve the passivation problem of aluminum layer, modified polyurethane system is commonly used.
Galvanized film glue: adding polar groups to improve adhesion.
Medium-resistant adhesive: resistant to acid and oil penetration, commonly used in condiment packaging.
Key performance indicators
Hygiene: in line with GB 9685 and other food contact material standards.
Peel strength: ≥2N/15mm (common food bag) to ≥8N/15mm (repackage).
Heat sealing window: match the heat sealing temperature of the substrate by 5℃
Mobility: low molecular weight substance content < 3 mg/DM.
development trends
The proportion of bio-based polyurethane adhesives (such as castor oil derivatives) has increased, and UV curing technology has been applied to transparent packaging. The industry is developing in the direction of ultra-low migration and degradable bonding system, and it is required to adapt to the process stability of high-speed laminating machine (above 300m/min).
