What is Enamel Lacquer? An Essential Guide to Food Can Coatings
Enamel lacquer, often simply called lacquer, is a crucial protective coating applied to the inside of metal food containers. This liquid substance is made from a resin, such as oleoresinous, vinyl, epoxy, phenolic, or polyester, combined with a solvent. The primary purpose of this enamel lacquer is to prevent harmful chemical reactions between the metal of the can and the food inside. This is vital for several reasons:
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Preventing Food Discoloration: The enamel lacquer prevents dissolved metal from mixing with the food, which could change its natural color.
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Preventing Corrosion: It acts as a robust barrier, protecting the metal canister from corrosion caused by the food’s acidity.
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Preventing Hydrogen Gas Formation: By stopping these chemical reactions, the enamel lacquer prevents the buildup of hydrogen gas, which can cause the can to swell.
Types of Lacquer Coatings
The Thai Industrial Standard (TIS 735) for “Lacquer for use with food containers” outlines two main types of enamel lacquer based on their application.
Type 1: For Cans Undergoing Heat Processing
This type of enamel lacquer is used for cans that will be sterilized by heat after being filled. It is further categorized into three types:
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Acid-resistant: For highly acidic foods like tomatoes and fruits.
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Sulfur-resistant: For foods with a high sulfur content, such as meat or corn, which can cause black staining.
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General purpose: For all other canned foods.
Type 2: For Cans Not Undergoing Heat Processing
This type of enamel lacquer is for cans used with dry foods, beverages, or pharmaceuticals that are not subjected to thermal processing.
Common Enamel Lacquer Compositions
While many different formulations exist, several common compositions are used for enamel lacquer coatings on food cans.
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Oleoresinous Lacquer: Although less common today, this enamel lacquer is still used for some fruits and vegetables. Zinc oxide is often added to it to prevent sulfide staining.
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Vinyl Lacquer: Known for its high adhesion and flexibility, this type of enamel lacquer is often used as a second coating layer for beverages and dry foods because it is odorless and tasteless, though it cannot withstand high sterilization temperatures.
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Phenolic Lacquer: This enamel lacquer is highly chemically resistant and ideal for coating cans containing meat and fish due to its low permeability to sulfide ions.
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Acrylic Lacquer: Due to its high heat resistance, this enamel lacquer is suitable for cans that undergo heat processing and provides a clean, white internal finish.
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Epoxy-Phenolic Lacquer: This is the most widely used enamel lacquer today. It offers a superior combination of acid resistance, flexibility, strong adhesion, and high heat resistance, making it suitable for a wide range of products from juices to soups and meats.
