Metal Tin Printing & Finishing: Offset Litho, Embossing & FDA Food-Contact Guide

Overview #

Metal tin packaging sits at the intersection of print quality, structural integrity, and regulatory compliance — and getting any one of those wrong creates problems that are expensive to fix after tooling is cut. This guide covers the quality parameters, inspection protocols, and compliance documentation we apply across our metal tin production lines, with particular focus on food-contact and cosmetic tin categories where FDA 21 CFR and EU 10/2011 requirements directly affect material selection and coating specification. Brand partners in food, confectionery, tea, cosmetics, and gift packaging will find the most relevant detail here. The single most common brief gap we see from new brand partners is specifying a decorative finish without confirming whether the tin will hold a food product — that one omission changes the entire coating system.

Print Quality Parameters: Offset Litho on Metal Substrates #

Printing on tinplate and aluminium is not the same as printing on paper or board. The substrate is non-absorbent, dimensionally rigid, and thermally conductive — all of which affect ink lay, cure, and register control.

On our sheet-fed offset litho lines for metal decoration, our standard register tolerance is ±0.15mm for process colour work and ±0.10mm for fine-line or brand logo elements. Ink film thickness on metal typically runs 1.5–3.0 µm per colour pass; going above 3.5 µm risks blocking during stacking and smearing at the slitting stage. We cure UV inks at 120–160 mJ/cm² depending on ink chemistry and substrate gauge — under-cure at below 80 mJ/cm² leaves surface tack that contaminates the next sheet in the stack.

Tinplate used in our standard tin production is electrolytic tinplate (ETP) to GB/T 2520 specification, with tin coating weights of 2.8/2.8 g/m² (equal coating, both sides) for general decorative tins, or 5.6/2.8 g/m² (differential coating) for tins requiring higher corrosion resistance on the interior. Aluminium sheet for lightweight promotional tins runs 0.20–0.30mm gauge; tinplate for structural food tins runs 0.18–0.25mm.

Colour accuracy is measured against Pantone Matching System references and verified using a spectrophotometer to ΔE ≤ 1.5 against approved colour standard. For brand partners with G7 Master-certified press requirements, we can provide G7 press characterisation data on request.

Embossing, Debossing & Surface Finishing on Metal Tins #

Embossing on metal tins is a cold-forming operation, not a heat-and-pressure process like paper embossing. The metal deforms plastically, so the depth and radius of the emboss must be engineered against the substrate gauge — push too deep and the metal thins at the emboss shoulder and cracks.

For tinplate at 0.20mm gauge, our maximum emboss depth is 0.8mm with a minimum corner radius of 0.5mm. At 0.23mm gauge we can go to 1.2mm depth. Attempting a sharp-cornered emboss (radius below 0.3mm) on tinplate below 0.22mm is a tooling rejection risk we flag at the brief stage — we have seen brand partners arrive with artwork specifying a 2.0mm deep logo emboss on a 0.18mm gauge lid, which is not manufacturable without substrate cracking.

Surface finishing options and their production parameters:

• Matte varnish overlay: Applied at 3–5 g/m² dry weight; reduces gloss to 15–30 GU (60° geometry). Must be food-contact compliant if applied to interior surfaces.
• Soft-touch coating: Applied at 5–8 g/m² dry weight; tactile friction coefficient 0.4–0.6 µ. Not recommended for interior food-contact surfaces.
• Spot UV: Applied over matte base coat at 4–6 µm; gloss contrast ratio minimum 3:1 against matte base to be visually effective.
• Metallic ink / hot foil stamping: Foil adhesion tested per ASTM D3359 tape test; minimum 90% foil retention after tape pull.

All exterior varnish and coating systems are tested for blocking resistance at 50°C / 85% RH for 24 hours before production approval — this simulates container shipping conditions in tropical climates relevant to our Southeast Asia and Middle East brand partners.

Food-Contact Compliance: FDA 21 CFR, EU 10/2011 & Interior Coating Specification #

This is where we spend the most time in pre-production review for food and beverage tin clients. The interior coating of a food-contact tin is a regulated material, not a decorative choice.

For tins destined for the US market, interior coatings must comply with FDA 21 CFR 175.300 (resinous and polymeric coatings for food-contact use). We use epoxy-phenolic or polyester-based interior lacquers from approved suppliers with full FDA compliance documentation. For EU market tins, the applicable regulation is EU Regulation 10/2011 on plastic materials in food contact, and we require migration test data (overall migration limit: 10 mg/dm² or 60 mg/kg food simulant) from our coating supplier for each batch.

For tins containing dry foods (tea, confectionery, spices), we specify a minimum interior lacquer coat weight of 5.0–7.0 g/m² dry film. For tins that may contact oily or acidic foods, we increase to 8.0–10.0 g/m² and specify a two-coat application to eliminate pinholes. Pinhole testing is conducted using the electrolytic porosity test method per ASTM A90 — we accept zero pinholes per 100 cm² on food-contact interior surfaces.

REACH compliance (EU SVHC list, updated biannually) is verified for all inks, coatings, and adhesives used in our metal tin production. We maintain a full material declaration for each component. For brands selling into the EU under the PPWR (Packaging and Packaging Waste Regulation) framework, we can provide recyclability documentation — tinplate and aluminium are both classified as infinitely recyclable materials under EU recyclability assessment criteria.

FSC chain-of-custody certification applies to any paper or board components (inserts, sleeves, instruction cards) packed with the tin. Our FSC CoC certificate number is available on request.

AQL Inspection System & Defect Classification #

We apply a two-stage inspection protocol on all metal tin orders: inline process inspection during printing and forming, and final AQL sampling inspection before packing.

Our AQL framework follows ISO 2859-1 (Sampling Procedures for Inspection by Attributes). Standard inspection level is General Inspection Level II. AQL levels by defect class:

Lid-to-body fit is measured using a calibrated gauge: acceptable interference fit is 0.05–0.15mm. Below 0.05mm the lid is loose and rattles in transit; above 0.20mm the lid requires excessive force to open and risks deforming the body flange on repeated use.

For orders above 50,000 units, we run 100% automated vision inspection on the print surface using a camera system calibrated to detect register errors above 0.2mm and colour deviation above ΔE 2.0. Below 50,000 units, AQL sampling per ISO 2859-1 applies.

Specification Notes for Brand Partners #

When you brief us on a metal tin project, the first information we need is: (1) product contents and whether they are food-contact, (2) target market — US, EU, or other — because this determines the interior coating specification and compliance documentation package, (3) tin dimensions and gauge preference, and (4) finish requirements for exterior surfaces including any emboss artwork as a vector file.

The most common brief mistake we see is submitting emboss artwork as a raster file or PDF without specifying depth — we cannot tool an emboss die from a visual reference alone. We will ask you to confirm emboss depth and corner radius before die cutting begins.

Our standard sampling process: digital colour proof in 3–5 working days, physical pre-production sample (printed and formed tin) in 15–18 working days, production lead time 30–35 working days after sample approval. For food-contact tins requiring interior coating compliance documentation, add 5 working days for coating batch certification review. MOQ for custom-printed metal tins is typically 5,000 units per SKU, with lower MOQs available for simple one-colour or two-colour designs.

Frequently Asked Questions #

Q1: What interior lacquer coat weight do you specify for a tea tin that will hold loose-leaf tea directly?
A: For dry food contact like loose-leaf tea, we specify a minimum 5.0–7.0 g/m² dry film interior lacquer using an FDA 21 CFR 175.300-compliant epoxy-phenolic or polyester system. We also run electrolytic porosity testing per ASTM A90 and accept zero pinholes per 100 cm² — any pinhole in a food-contact interior is a critical defect and triggers 100% re-inspection of that batch.

Q2: What is your MOQ and lead time for a custom embossed tin with a four-colour printed lid?
A: Our standard MOQ for custom-printed metal tins is 5,000 units per SKU. Lead time from approved sample to production delivery is 30–35 working days, with the physical pre-production sample available in 15–18 working days. Emboss die tooling is included in the sampling stage — we need your emboss artwork as a vector file with confirmed depth specification before we begin.

Q3: Do your tins comply with EU REACH and PPWR requirements for the European market?
A: Yes. We maintain full material declarations for all inks, coatings, and adhesives against the EU SVHC list under REACH, updated biannually. For PPWR recyclability documentation, tinplate and aluminium both qualify as infinitely recyclable under EU assessment criteria, and we provide the relevant material declarations as part of our compliance documentation package.

Q4: Can you combine a matte exterior varnish with a spot UV logo and an interior emboss on the same tin?
A: Yes, this is a combination we run regularly. The matte varnish is applied at 3–5 g/m² dry weight to achieve 15–30 GU gloss, and spot UV is applied over it at 4–6 µm — the gloss contrast ratio needs to be at least 3:1 to read clearly. Interior emboss depth on a 0.20mm gauge tinplate lid is limited to 0.8mm maximum with a 0.5mm minimum corner radius; we review your artwork against these parameters before die tooling.

Q5: What is the most common quality failure you see on metal tin print jobs, and how do you catch it?
A: The most common issue is ink adhesion failure at the emboss shoulder — the metal stretches during forming and if the ink system is not flexible enough, it micro-cracks at the deformation zone. We catch this by running a cross-cut adhesion test per ISO 2409 on formed samples before production approval; we require Grade 0 (zero squares detached). If we see Grade 1 or above, we adjust the ink flexibility modifier and re-test before releasing the job to production.

Planning a metal tin packaging project? Contact our team to request a complimentary specification review and sample quote.