The challenge of preventing ink migration from the printed information on food and grocery packaging keeps many chemists, printers and brand executives awake at night.

It’s easy to understand their anxiety. Some regulations, like the Swiss Ordinance and the Nestlé Guidelines on Food Contact materials, require stringent testing to ensure contaminant levels measure below 10 parts per billion. For some perspective on how small an amount this is, consider that one pack of sugar in an Olympic-size swimming pool is a concentration of one part per billion. Now think about measuring for that. To understand how food packaging stays below these contaminant thresholds we must first understand what ink migration is, what causes it and what options there are for preventing it.

What is Ink Migration in Consumer Products?

Ink migration is the transfer or bleed-through of ink substances from the packaging material into consumer goods such as food, medicines or health and beauty products. What’s printed on the outside ends up inside.

Ink migration is not good for several reasons:

• It puts consumer health at risk
• Changes the flavor and odor of products
• It violates regulations
• It can damage the brand reputation

Intentionally Added Compounds: The components of inks — those intentionally added compounds — can be the most significant source of contamination. These include monomers, antioxidants, plasticizers and photoinitiators.

Non-Intentionally Added Substances: No less troublesome are the non-intentionally added substances (NIAS), which are difficult to detect and assess after being identified. The sources of NIAS vary.

Impurities in the raw materials of the ink may introduce non-intentional substances. Another source may be the byproducts of chemical reactions that could happen during packaging, environmental effects during shipping or storage. Consumers may trigger reactions that create dangerous compounds.

The Value of Low-Migration Inks

The market for low-migration inks is strong, with pharmaceuticals accounting for 25% of product demand, according to a Global Market Insights, Inc. report. Total revenue could hit $480 million by 2025 compared to $300 million in 2018.

In North America, the market size for low-migration printing inks is projected to grow at over 7% CAGR, according to the market research report.

Types of Ink Migration

Set-off Migration: Ink migration is “set-off” when it transfers from the printed side of one package to the reverse side of another package.

When roll-printed packaging materials are re-wound, the ink may transfer to the reverse side. Similarly, stacking printed cups or other consumer products has the potential to transfer ink to the inside of the cup.

Diffusion Migration: When ink migrates through diffusion, substances pass through the substrate from the printed side of the substrate to contact the food, medicine or health and beauty product encased in the packaging. The substrate for the consumer product may not block the chemicals in ink. The ink and substrate may interact with environmental conditions to allow migration or introduction of NIAS.

Gas-Phase Migration: Gas-phase ink migration happens when volatile chemicals and compounds in the ink transfer to the interior product through evaporation or from heating, baking or boiling food products.

While the primary packaging of consumer products is the obvious source of gas-phase migration, academic studies have confirmed ink compounds used in secondary packaging have migrated through primary packaging.

Ink Migration Barriers: Glass and metal packaging are considered “absolute” barriers. Any ink can be used on the exterior of these packaging materials because these materials prevent migration. Other materials must be evaluated for the potential of ink migration. Both paper and plastic packaging pose a risk of migration.

What Causes Ink Migration or Contamination?

The following elements must all work in harmony to keep consumers safe and brands protected:

Inkjet Inks: Inks fall into two broad categories.

1. Direct food contact (DFC) inks must be formulated to meet European and U.S. standards and regulations. They must be non-toxic. These inks are not intended to have any chemical effect on the consumer or the product. M&M’S and Skittles are printed with a vegetable-based dye ink.

2. Indirect food contact (IFC) inks don’t contact the food, or health and beauty product. These inks must not pass into the consumer product.

Product packaging relies on low-migration inks, but they are only one part of the equation for preventing contamination. Inks must also be evaluated and tested to identify any external interactions that may produce dangerous contaminants from ink migration.

The U.S. Food and Drug Administration and other regulatory bodies don’t “approve” inks for use in packaging consumer goods. Instead, the FDA approves the materials used in the formulation of inks, and only after extensive testing is submitted.

Packaging Materials: Consumers expect packaging materials to maintain freshness and keep products free of toxic contamination. That’s why testing must ensure the packaging materials and ink choice don’t negatively interact.

The Printing Environment: Contaminants from the equipment used for printing can introduce catalysts that affect either the ink or packaging material — or both. While the ink and packaging material have been verified to prevent dangerous migration, external factors may cause unintended reactions.

Incomplete Curing: Extensive and meticulous ink testing may prove an ink to be safe in ideal conditions. Risk is introduced if the testing conditions are not followed during production. Incomplete curing may introduce toxic materials that would not otherwise exist if the ink had completely dried.

Post-packaging Influences: Environmental conditions introduced during shipping and storage can’t be ignored. The packaging and inks must be tested to meet tolerances of extreme heat, cold and humidity. In the hands of the consumer, the product must remain safe when boiled, frozen or heated in a microwave or conventional oven.

Ink Migration in an Eco-Friendly World: Today, manufacturers are using thinner plastics for packaging, which reduces costs and makes less of an environmental impact. Flexible films are replacing cans, glass, and rigid boxes with interior liners. The introduction of new or reformulated packaging materials requires new testing to ensure continued safety.