Hazards of solvents and low-quality resins in laminating adhesives
Adhesives are compounds used for sealing and packaging, and they can migrate into food during packaging or storage. The adhesives commonly used in the packaging industry include hot melt polyurethanes, cold seal, pressure-sensitive, and acrylic adhesives, which can be water-based, solvent-based, or solventless.
The selection of adhesives should be based on the type of packaging and the characteristics of the food product. For example, using hot melt adhesive for packaging milk chocolate pieces is inappropriate. Laminated films are typically made from two or more single-layer films bonded together using adhesives, so that printing inks and adhesives are positioned between the films. Although the organic solvents present in the adhesive, printing ink, and thinners do not come into direct contact with food, they may migrate through the films under specific conditions, posing a threat to human health.
Laminating adhesive for flexible packaging
According to a survey conducted by adhesive manufacturers, a list of over 360 substances was compiled to illustrate the hazards of solvents and low-quality resins in laminating adhesives and potential chemical migrants from adhesives to foods. A subsequent study focused on the chemical composition and migration levels of polyurethane-based adhesives. Migrating residues (e.g., polyethers, polyols, and cyclic reaction products derived from polyesters) were identified at concentrations of 10-100 micrograms per square meter.
Resins
Most liquid resins can be mild to moderately irritating to the skin, eyes, and mucous membranes. The potential for irritation increases due to their sticky nature, leading to prolonged contact with the skin. These resins generally cause mild to moderate skin sensitization in susceptible individuals.
Polyurethane laminate adhesive
Solid resins are not easily absorbed through the skin, reducing the risk of skin irritation. Direct contact with solutions of these resins may cause mild to moderate irritation to the skin and eyes, primarily because solvents can strip away the protective fatty layer on the skin’s surface. When finely powdered, most resins should be considered as irritating dusts, and inhalation or skin contact should be avoided. Solid resins are generally regarded as low to mild sensitizers.
Resins modified by adding thinners or reactive solvents can be more serious irritants. These resins should be handled with the same precautions as those used for chemical solvents. Their sensitizing potential increases with decreasing molecular weight.
Solvents
Solvents commonly used in adhesive or sealant applications pose a fire hazard. Additionally, these solvents carry specific health risks. Contact with solvents causes “degreasing” and drying of the skin, which increases the likelihood of skin irritation. Some solvents are absorbed directly through the skin, and absorption increases if there is abrasion or irritation. These solvents also have the ability to dissolve other chemicals in the epoxy resin system and transport them through the skin. Inhalation of solvent vapors or dust may cause respiratory irritation and central nervous system depression.
Fillers
The hazardous nature of fillers depends on the type of filler and how it is used in production. Fillers pose a potential inhalation and skin contact hazard. They can cause mechanical damage to the skin, which may exacerbate the irritating effects of other chemicals and additives. When fillers are used in a liquid matrix or in a baked matrix, the inhalation risk is low. However, inhalation exposure to fillers can occur when they are in a dry state. Inhalation exposure to fillers such as crystalline silica or fiberglass may lead to delayed lung damage.