Defects In Needle Holes Of Flexible Packaging Composite Film And Their Comprehensive Solutions

The needle holes are common microscopic penetrating defects in the flexible packaging composite process, manifested as dense or scattered tiny pinholes on the film surface, which are visible to the naked eye and have obvious light transmission. The needle holes directly damage the packaging barrier property, causing air leakage, water permeation, oil leakage, and significantly reducing the shelf life of food and daily chemical products. They are a key defect that must be strictly controlled in high-barrier packaging production.

 

The presence of pores in the base material is the fundamental cause. Some thin PE and CPP film production has inherent micro pores, while the coating of aluminum film is uneven or the needle holes exceed the standard. After compounding, the defects are magnified and become apparent. Secondly, the influence of glue impurities and coating issues is significant. The Polyurethane Glue is not filtered thoroughly, contains particles, and gel impurities, and forms point-like missed coating during coating. The glue viscosity is inappropriate and the coating amount is too low, preventing the glue layer from fully covering the microscopic pores on the film surface, resulting in the formation of needle holes.

Process and environmental issues can also trigger needle holes. Dust and fluff in the workshop fall and adhere to the film surface, forming point-like vacancies after compounding; the oven temperature is too high, and the surface solvents rapidly evaporate instantly, preventing the glue layer from leveling and closing in time, resulting in fine pore-like needle holes. Solvent-free glue mixed with tiny bubbles, not fully degassed before direct coating, will also form regular needle holes after curing.

 

The rectification needs to be implemented from multiple dimensions. Strictly conduct random inspections of base materials upon entry, filter the glue to eliminate impurities; optimize coating parameters to ensure uniform and full coating; control the cleanliness of the workshop, grade the temperature for drying, and do a good job in glue static deaeration. Systematic control can completely eliminate needle hole defects, ensuring that the barrier performance and appearance quality of the composite film meet the standards.