When it comes to formaldehyde, people would first associate paint or new furniture and may feel that there is no chance of contact if they are far away from decoration. Formaldehyde exists in many animals and plants as a kind of body metabolite, and we may often come into contact with it in our daily life. In addition to food, there may be a risk of formaldehyde in the coatings of common metal cans.
Overview of metal cans packaging
Metal cans are widely used in food packaging, including carbonated beverage cans, functional beverage cans, milk powder cans, tea boxes, candy cans, ready-to-eat cooked meat products cans, fruit cans and so on. The advantages of metal cans are obvious. It has good tightness, the long storage period of food, high internal pressure resistance, and good corrosion resistance. As a result, many famous enterprises have vigorously promoted the brand food in metal canning packaging.
There are two types of materials used to make metal cans: aluminum and tin. Aluminum cans are usually two pieces, and the surface is generally passivated. They are mainly used for carbonated beverage packaging. The tin metal can is composed of three metal plates, namely the body, the bottom, and the lid. In contrast, tinned metal canisters usually have an organic polymer coating applied to the surface during oxidation protection. The tin can has good rigidity, high material utilization rate, mature production process and is easy to change size, so it is used for packaging canned food, functional beverage, milk powder, and other food. Due to the existence of the coating, the organic hazardous substances in the coating are easy to migrate to food and have certain potential risks to human health.
Source of formaldehyde in metal canning coatings
At present, the widely used organic coating mainly includes epoxy phenolic resin, epoxy amino coating, epoxy-polyamide resin coating, organic sol coating, vinyl coating, polyester coating, acrylic coating, epoxy ester coating and so on. Due to the excellent chemical resistance, oil resistance and water resistance of epoxy resin, it is often used as the main raw material for coating inside the food tinplate metal cans. Formaldehyde is one of the starting reactants of epoxy resin coating, and the possible contamination of food in metal cans is mainly caused by the process of resin degradation.
Formaldehyde has been listed as a clear human carcinogen by IARC, the International Agency for Research on Cancer. The main harm of formaldehyde is the stimulation to the skin mucous membrane, and long-term chronic contact will lead to gene mutation, as well as the increased risk of human blood cancer, lymphoma, and other cancers.