Print Materials, Inks and Substrates
This domain covers what you print on and what you print with. Questions test paper grading, sheet sizes and yield, conditioning, ink types and drying, and how ink and substrate interact to produce faults.
Core rules
- Paper grades: woodfree (chemical pulp, stable, archival) versus mechanical (newsprint, yellows with light); coated gloss, silk and matt; uncoated offset and bond; recycled grades with variable whiteness.
- Measured properties: grammage (gsm), caliper (µm), bulk = caliper ÷ gsm, opacity, whiteness (ISO 2470), smoothness and grain direction. gsm is not thickness.
- Sheet sizes: A-series with the √2 ratio, A0 = 1 m², 841 × 1189 mm; SRA3 = 320 × 450 mm; B1 = 707 × 1000 mm; B2 = 500 × 707 mm. Always check yield, not just fit.
- Conditioning: 20–23 °C and 45–55% RH before printing; paper takes on or loses moisture and develops wavy edges or tight edges, which cause register and feeding faults.
- Boards: FBB (folding boxboard), SBS (solid bleached sulphate), recycled GD/GT, and corrugated flutes B, E and F.
- Inks: process CMYK, spot PMS, opaque white, metallic, fluorescent; drying by absorption, oxidation, heatset evaporation, UV/EB curing. Ink tack runs from high to low down the unit sequence.
- Ink–substrate interaction: coated stock has high hold-out, giving sharp dots and gloss; uncoated absorbs more, raising dot gain and giving a chalky look; non-porous films need corona treatment or primer for adhesion.
- Compliance: FSC and PEFC chain of custody, EU food-contact rules (1935/2004 plus migration testing), low-migration inks for food packaging.
Worked example
A carton needs caliper of at least 350 µm. Supplier A offers 300 gsm FBB with bulk 1.3 → 300 × 1.3 = 390 µm: passes. Supplier B offers 280 gsm SBS with bulk 1.15 → 322 µm: fails, despite being the same visual grade. Supplier A is chosen and the grain direction is checked against the crease lines so the carton folds without cracking.
Traps that cost marks
Treating gsm as a thickness measure; assuming recycled board prints like virgin board; ignoring grain direction; over-inking coated stock so the pile sets off; using standard inks on a food wrapper without low-migration certification.
Key points
- Bulk = caliper ÷ gsm; thickness matters in packaging.
- B1 = 707 × 1000 mm, B2 = 500 × 707 mm, SRA3 = 320 × 450 mm.
- Condition stock at 20–23 °C and 45–55% RH before running.
- Coated stock holds ink out; uncoated absorbs and gains dot.
- Drying routes: absorption, oxidation, heatset, UV/EB.
- Food packaging needs low-migration inks and migration testing.