Migration-Resistant Inks for Food Packaging: Regulatory Requirements and Formulation Strategies

Migration Risk in Food Packaging

When ink is printed on the outside surface of flexible food packaging, ink components can migrate through the packaging material and contaminate the food. Migration occurs by two primary routes: set-off (direct contact between the printed surface and the food-contact surface during winding or stacking) and diffusion through the substrate (permeation of small molecules through polyolefin films or paper).

The consequences of ink migration are severe: consumer safety risks, product recalls, regulatory non-compliance, and brand damage. Since the 2005 isopropylthioxanthone (ITX) photoinitiator crisis — where ITX migrated into infant formula through carton board — the industry has invested heavily in migration testing and low-migration (LM) ink technology.

Regulatory Framework

EU: Framework Regulation (EC) 1935/2004

EU food contact materials legislation requires that materials do not transfer components to food in quantities that endanger human health, cause unacceptable organoleptic changes, or adulterate the food. Printing inks are not currently covered by a specific positive list in EU law — the Notified Bodies framework (e.g., EuPIA Good Manufacturing Practice Guideline) serves as the industry standard.

Swiss Ordinance on Food Contact Materials (RS 817.023.21)

Switzerland has the most prescriptive national standard for printing inks. Annex 10 (effective 2023) lists permitted primary aromatic amines, photo-initiators, and other ink chemicals with specific migration limits. Any ink component not listed requires toxicological evaluation.

Nestlé Guidance Note (NGN) on Printing Inks

The Nestlé Guidance Note is the de facto global industry standard, widely adopted beyond Nestlé. It defines:

A restricted substances list (RSL) of chemicals prohibited in inks used on food-contact packaging
A conditionally acceptable list with migration limits
Functional barrier definitions and testing requirements

US: FDA 21 CFR

FDA food contact regulations use a threshold of regulation (TOR) approach: ink components migrating at < 0.5 ppb dietary concentration are generally exempt from regulation. Components above this threshold require either a food contact notification (FCN) or prior sanction status.

Region	Key Regulation	Approach	Key Limit
EU	EC 1935/2004 + EuPIA GMP	Good Manufacturing Practice	10 ppb specific migration
Switzerland	RS 817.023.21 Annex 10	Positive list	Substance-specific
USA	FDA 21 CFR TOR	Threshold of regulation	0.5 ppb dietary
China	GB 9685-2016	Positive list	Substance-specific
Global brands	Nestlé GN, BRCGS	Industry guidance	RSL-based

Migration Mechanisms and Influencing Factors

Diffusion Through Substrates

Migration through packaging substrates follows Fick's second law of diffusion. Key parameters:

Diffusion coefficient (D): Increases exponentially with temperature. A 10°C rise typically doubles D.
Molecular weight: Compounds below 1000 Da can diffuse through polyolefin films. Above 1000 Da, migration through LDPE is negligible.
Substrate barrier: PET (12 µm) reduces migration by ~95% compared to LDPE at equivalent thickness. Aluminium foil is an absolute functional barrier.

Set-Off Migration

Set-off is the transfer of wet or semi-cured ink components during roll winding or sheet stacking. It is the primary migration route for UV-cured inks where photoinitiator fragments may remain mobile in the cured film.

Prevention strategies:

Ensure complete cure (> 95% monomer conversion) via MEK double-rub test (> 200 rubs) or photoinitiator conversion by FTIR
Allow adequate cooling before winding (substrate temperature < 35°C)
Use functional barriers: lamination with adhesive + 12 µm PET eliminates set-off to inner surface

Low-Migration (LM) Ink Formulation

Photoinitiator Selection for UV Inks

Conventional Type I photoinitiators (benzophenone, ITX, DEAP) are volatile, lipophilic, and diffuse readily into food. LM photoinitiators are designed with high molecular weight (> 400 Da), low vapour pressure, and limited lipophilicity.

Photoinitiator	MW (Da)	Migration Class	Notes
Benzophenone	182	High — restricted	Banned in food packaging in EU
ITX	254	High — restricted	Banned post-2005 crisis
Omnirad 1173	164	High — restricted	Low MW, high volatility
Omnirad 2959	224	Medium	Conditionally acceptable
Omnirad 819	419	LM	Widely used, Nestlé acceptable
Irgacure 369	366	LM	Suitable with functional barrier
Polymeric PI	> 1000	Very low	Best in class, limited cure speed

Polymeric photoinitiators (e.g., Esacure One, MW ≈ 1200) are the gold standard for direct-food-contact applications. Their migration is effectively zero, but their cure response is slower — typically requiring 20–30% higher UV dose compared to monomeric equivalents.

Resin and Monomer Selection

Reactive diluents (monomers) in UV inks must be selected for low volatility and low skin sensitisation risk. Avoid monofunctional acrylates (e.g., IBOA, MW 208) in direct-contact applications. Preferred options:

Difunctional monomers: TPGDA (MW 300), DPGDA (MW 242) — moderate migration risk, use with functional barrier
Higher functionality monomers: PETA (MW 298), DPHA (MW 524) — lower migration due to higher incorporation into network
Polyester acrylate oligomers (MW > 800): Very low migration; form the backbone of LM formulations

Amine Synergists

Conventional amine synergists (e.g., MDEA, MW 163) are low-MW, water-soluble compounds that migrate readily into food. Replace with polymeric amine synergists (MW > 500) such as amine-functional polyester acrylates or bound amine oligomers.

Functional Barrier Approach

When ink composition alone cannot achieve migration compliance, a functional barrier between the printed surface and food contact surface is required. A functional barrier must:

Reduce migration of all ink components to < 10 ppb (EU) or < 0.5 ppb (FDA TOR) at the food contact surface
Be validated for the specific ink system, substrate, and food simulant

12 µm biaxially oriented PET laminated with a 3–4 g/m² adhesive layer provides an effective functional barrier for most ink systems for ambient and chilled storage. For fatty foods or elevated temperature (> 40°C), a 9 µm aluminium foil layer is recommended.

Testing and Validation

Overall Migration (OM) Testing

OM testing per EN 1186 uses standardised food simulants:

Simulant A (10% ethanol): aqueous foods
Simulant B (3% acetic acid): acidic foods
Simulant D2 (vegetable oil): fatty foods

Migration testing at 40°C for 10 days (ambient storage model) or 70°C for 2 hours (hot-fill model) per EU Regulation 10/2011.

Specific Migration (SM) Testing

Targeted GC-MS or LC-MS/MS analysis for known restricted substances (benzophenone, ITX, primary aromatic amines). Detection limits must be at or below the analytical threshold of 0.01 mg/kg.

In-House Screening

For production QC, UV fluorescence scanning and headspace GC can screen for photoinitiator migration and residual monomer. Full migration testing by an accredited laboratory (ISO 17025) is required for regulatory submission.

Summary

Formulating migration-resistant inks for food packaging requires a systems approach: selecting high-MW, low-mobility ink components; validating functional barriers; and testing against the most stringent applicable regulation (Swiss Ordinance or Nestlé GN). UV-curable LM inks using polymeric photoinitiators and high-functionality monomers represent the current best practice for direct-print food packaging without a functional barrier. Chemzip supplies LM photoinitiators, high-MW reactive diluents, and polymeric amine synergists suitable for compliant food packaging ink formulations.