Packaging odor is a common complaint issue for flexible packaging products. Most of the odors come from the residual substances and by-product products of the polyurethane laminating adhesive system. Food, baby care, and daily care packaging have extremely high requirements for odor. Even a slight odor can lead to product downgrade and return. Therefore, accurately controlling the odor of the adhesive is a key link in the quality control of flexible packaging.
Polyurethane Adhesive odors can be classified into three types: solvent residual odor, free monomer odor, and reaction by-product odor. If the solvent-based adhesive is not dried thoroughly, ethyl acetate residue will bring a pungent solvent smell. Excessive curing agent or insufficient curing will leave free isocyanate, generating irritating odor. At the same time, if the humidity in the workshop is too high, the isocyanate and water vapor will react to form small molecules, resulting in musty and rotten smells.
Low-odor polyurethane adhesives mainly include three types of odors: solvent residual odor, free monomer odor, and reaction by-product odor. If the solvent-based adhesive is not dried thoroughly, ethyl acetate residue will bring a pungent solvent smell. Excessive curing agent or insufficient curing will leave free isocyanate, generating irritating odor. At the same time, if the humidity in the workshop is too high, the isocyanate and water vapor will react to form small molecules, resulting in musty and rotten smells.
Low-odor polyurethane adhesives use low-residue formulations, select high-purity raw materials, and reduce the content of free monomers, reducing odor substances from the source. Combined with a reasonable lamination process, segmental temperature drying and controlling the appropriate machine speed can completely volatilize solvents and low-molecular impurities. Sufficiently constant temperature curing can promote complete cross-linking of the adhesive, allowing residual active substances to fully react, significantly weakening the odor of the finished product.
Production practice shows that the combination of raw material selection, process parameters, and curing control can achieve low-odor or even odor-free effects for flexible packaging, meeting the industry entry standards for high-end food and light-scent packaging.
