Metal Packaging vs Plastic Packaging: 3 Food Safety Comparisons — Cans / Metallized Films / Composite Pouches — Printers Most Often Stuck on Free Phenol in Metallized Adhesive

In March of this year, a pickle-making client in Zhejiang sent me samples from 3 suppliers and asked me to help judge which one to choose. The three samples were: a tinplate can, a metallized stand-up pouch, and a PET/PE composite pouch — all filled with the same spicy sauce, labeled with a 12-month shelf life. I opened all three samples, examined the test reports on the labels item by item, and ultimately recommended the metallized stand-up pouch — on the condition that the supplier be switched, because the free phenol report on the metallized adhesive had exceeded the limit by 0.4 times.

When it comes to food contact packaging, the question clients ask most often is "is metal better or plastic," but that is a false question. The three types of packaging (tinplate can / metallized composite / plastic composite) have no absolute "which is safer" in food safety — only "which process path carries lower risk for which product." When clients ask me "which is safe," I counter with three questions: product moisture content / whether it is high-oil or high-salt / whether high-temperature sterilization is needed. Different answers to these three questions lead to entirely different recommendations.

Metal Cans: Interior Coating Curing Degree Determines BPA Migration Risk

What worries people most about tinplate cans (food cans) is the interior coating — typically an epoxy coating that contains Bisphenol A (BPA). China's GB 4806.10-2016 sets the BPA Specific Migration Limit (SML) at 0.6 mg/kg, and the EU 10/2011 sets the same 0.6 mg/kg — but EU 2018/213 tightened this limit to 0.05 mg/kg, a 92% reduction. This is the fundamental reason the EU market has been densely rejecting metal cans since 2025.

The printer's key process point: the curing degree of the epoxy coating.
- Curing temperature must reach 200-220°C, sustained for 10-15 minutes;
- Insufficient curing → BPA residue + migration exceedance;
- Over-curing → coating embrittlement, easy to flake off upon contact with contents.

Last July, a client in Guangdong making eight-treasure porridge came to us. Their supplier of 5 years had suddenly been detected by SGS with BPA migration at 0.85 mg/kg, 17 times over the EU limit. A post-mortem revealed: the supplier had rushed orders during that period, lowering oven temperature from 210°C to 195°C, and cutting curing time from 12 minutes to 8 minutes — invisible to the naked eye, but the lab doesn't lie.

The printer/canmaker's baseline action on this point: curing temperature and time must not be adjusted to rush orders; any fine-tuning must be sent for testing first. GB 4806.10 Section 5.2.2 requires that "the coating shall be fully cured," but does not give hard numbers — specific parameters belong in the process card — the process card is a legal document, changing one item requires redoing a compliance assessment; it is not something the workshop can change on a whim.

Metallized Composite Pouches: The Hidden Risk of Free Phenol in Adhesive

Metallized composite pouches (structures like VMCPP/PE / VMPET/PE) are the workhorse structure for mid-range snacks, sauces, and stand-up pouch seasoning packs. Their food safety risk point is not in the aluminum layer (GB 4806.9-2016 sets the migration limit for aluminum at 5 mg/kg), but in the adhesive (glue).

Polyurethane adhesive (PU glue) generates free phenol (mainly Bisphenol A or Bisphenol S) during curing. GB 4806.15-2015 sets the overall migration limit for food contact adhesive at 10 mg/dm², but in most cases there is no mandatory number for the Specific Migration Limit (SML) of free phenol — this is the gray zone where printers most easily get stuck.

Last year, an e-commerce nut client in Dongguan sent samples of metallized pouches from 5 suppliers. We tested free phenol using GC-MS: 4 of them came in between 0.3-0.6 mg/kg, and 1 hit 1.2 mg/kg directly — 24 times over the EU client's internal control line of 0.05 mg/kg. The problem lay in adhesive selection: that supplier used ordinary industrial-grade PU glue, with incomplete curing and simultaneously high residual solvent and free phenol.

The printer's practical response:
1. Adhesives for metallized/composite pouches must be food-grade PU glue (explicitly GB 4806.15 compliant);
2. Composite process curing temperature ≥ 50°C, maturation time ≥ 48 hours;
3. Send for free phenol + overall migration testing before shipment;
4. For clients exporting to the EU and US, the adhesive must avoid the BPA and BPS families — switch to acrylate adhesive (water-based, BPA-free).

The Zhejiang client's metallized pouch problem came down to item 3 — free phenol was not sent for testing before shipment; only overall migration and sensory tests were done. Out of 10 indicators, only 7 were tested, and one of the 3 missed was free phenol.

Plastic Composite Pouches: Solvent Residue and rPET Recycled Material

All-plastic composite structures like PET/PE, PET/CPP, PA/PE (without an aluminum layer) have two main risk points: solvent residue + recycled material contamination.

Solvent residue is the combined product of printing inks + composite adhesive. If solvents like ethyl acetate, toluene, and methyl ethyl ketone in the ink are not fully dried, they remain between composite film layers. GB 4806.7-2016 for food contact plastic materials limits overall migration to 10 mg/dm², but there is no unified standard for specific solvent residue — each enterprise uses its own internal controls.

The printer's process countermeasures: raise post-print drying temperature from the usual 60-70°C to 80-90°C, increase airflow, and ensure solvents fully evaporate; in the composite process, add a barrier layer (PET or aluminum layer) between the print layer and the heat-seal layer, so that even if the print layer has residue, it will not migrate to the inner surface.

The recycled material issue is more hidden. After the EU SUP Directive of 2020, food contact plastics are required to have traceability of recycled content. If a printer uses rPET recycled material (masterbatch reprocessed from recycled PET bottle flakes), it must undergo EFSA safety assessment + declaration, with a cycle of 6-12 months and cost increases of 30-50%. Most small and medium printers do not have this capability and can only guarantee the use of virgin material.

Food Safety Priority Comparison of the 3 Packaging Types

Returning to the client's original "which is safe" question, I made him a table:

| Packaging Type | Main Risk Point | Printer-Controllable Action | Client Re-verification Cost |
|---|---|---|---|
| Tinplate Can | BPA Migration | Strictly follow process card for curing temperature/time | Medium (testing 1500-2000 yuan/item) |
| Metallized Composite Pouch | Free Phenol + Solvent Residue | Food-grade adhesive + 48h maturation + pre-shipment testing | Low-Medium (single item 800-1200 yuan) |
| Plastic Composite Pouch | Solvent Residue + Recycled Material Traceability | Higher-temp drying + barrier layer + virgin material commitment | Low (testing 600-1000 yuan/item) |

The metal can risk concentrates on BPA, but as long as the process card is not shortchanged, the risk is lowest; the metallized pouch risk concentrates on adhesive selection, and is where printers most easily step into trouble, because GB standards have no mandatory number for free phenol and only client internal controls can be relied upon; the plastic pouch risk is dispersed — all three lines of printing, compositing, and raw materials must be checked.

Compliance Boundaries: Printers Handle 2 Items / Brand Owners Handle 3 Items

For food contact packaging compliance, there is a division-of-labor convention in practice:

The printer/canmaker is responsible for:
1. Raw material compliance (food-grade certificates + test reports for substrates/inks/adhesives);
2. Process compliance (process parameters such as temperature/time/pressure executed per the process card);

The brand owner/food manufacturer is responsible for:
3. Formula compliance (compatibility testing of contents with packaging);
4. Usage compliance (matching of storage conditions and transport conditions with packaging);
5. Label compliance (ingredient list, shelf life, allergen labeling).

Items 1 and 2 are the printer's responsibility, and items 3-5 are the brand owner's responsibility. If an accident occurs (e.g., a consumer gets sick from BPA migration exceeding limits after eating the product), the legal first line of accountability is the brand owner, but the second line of accountability is often the printer — because the brand owner will counter that "the packaging was supplied by the printer, and our contents are fine." At this point, if the printer has no process card execution records + raw material compliance files, it is impossible to explain.

The Zhejiang client ultimately chose the metallized pouch supplier we recommended (switched to another company), at the cost of 8 fen per piece higher in unit price, but from then on he tested the full 7-item set of free phenol + overall migration with each inspection — he told me "8 fen for peace of mind, one customer complaint costs thousands to settle."

Compliance for food contact packaging is not about any single link "doing 100%" — it is about every link in the entire chain hitting 80-90%, and using a testing closed loop to catch the last 10%. What the printer can do is not to run every test, but to keep the evidence chain for its own share of responsibility — this is the real moat that lets a printer hold its ground in legal disputes.

Further Reading:
• Food Contact Packaging Migration Limits: GB 31604 vs EU 10/2011 — 3 Boundary Differences Printers Most Often Step On
• Food Contact Packaging GB 4806 Testing Projects in Practice: 5 Commonly Stuck Items + 3 Remediation Methods for Failure
• GB 4806.1 to 4806.11 Demystified: How the 5 Core Standards for Food Contact Packaging Are Actually Used
• 3 Barriers for Packaging Exported to the US: What FDA, Prop 65, and CPSIA Each Govern