Offset lithography transfers ink from a planographic plate to a rubber blanket, then to the substrate—leveraging the oil–water repulsion principle. It delivers stable halftone reproduction and excellent color consistency, making it a mainstay for paper-based print and folding cartons at medium–large volumes.
1) How It Works (Brief)
Platemaking (CTP): Image and non-image areas lie on the same plane; image areas are ink-receptive, non-image areas water-receptive.
Dampening & inking: Fountain solution first, ink adheres only to image areas.
Indirect transfer: Plate → blanket → paper, smoothing out surface irregularities.
Drying: Oxidation/penetration for conventional inks; UV for instant curing.
2) Strengths of Offset
High fidelity & detail: Fine screens, crisp micro-text/lines; great for gradients and imagery.
Color consistency: Robust control of gray balance, dot gain, and color sequence across long runs.
Broad substrate range: Coated papers, SBS/FBB cartonboards, specialty stocks, metallized boards.
Cost efficiency at scale: Competitive unit cost for medium to large runs; highly compatible with downstream finishes.
3) Potential Limitations
Very short runs/many SKUs: Frequent plate changes → digital may be more agile.
Large solid coverage: Risk of mottling/banding; consider spot colors, double hits, or alternate processes.
Rough/corrugated direct print: Offset favors smooth facestocks; use litho-lam or preprint when needed.
4) Using Offset for Folding Cartons
Materials
SBS / Ivory Board, FBB / Cartonboard: common 300–450 gsm; coated surfaces favor high-resolution print.
Specialty papers: textures, metallized, pearlescent (may require dedicated inks/primers).
Litho-lam: print on coated paper, then mount to greyboard/corrugated for rigidity and premium look.
Color & Artwork
Color mode: CMYK with optional Pantone spots (brand colors/large solids/metallics).
Screening & resolution: typically 150–200 lpi; supply images ≥ 300 dpi.
Separate layers for foil, spot UV, emboss/deboss, coatings, and dielines.
Proof targets: digital or wet proofs, LAB references, and ICC workflows for press calibration.
Surfaces & Finishing
Lamination/varnish: gloss/matte/anti-scuff films; AQ or UV coatings (flood or spot).
Decorative: foil (hot/cold), spot UV, emboss/deboss, textures, holographic films/transfer.
Die-cut & crease: set rule/crease ratios to board caliper & grain (MD/CD); plan nicks/stripping.
Folding/gluing: define glue flaps and adhesives (hot-melt/dispersion); set QC for fold strength.
Structure & Sizing
Dimensions: standardize on L × W × H (internal); H = opening-to-base depth.
Common styles: Tuck-end (STE/RTE), Crash-lock (auto-lock), Sleeve/Drawer/Lid–Base (rigid).
Strength: Upweight board or switch to crash-lock + inserts for heavier items; validate drop/abrasion.
5) Typical Production Flow
White mockup (structure) → board selection (GSM/caliper/grain)
Color proof (digital/spot wet proof) & process samples (foil/UV, etc.)
CTP plates → make-ready → production run
Surface finish → die-cut/crease → stripping → folding/gluing → QC & packing
6) Quality Control Focus
Dot gain (TVI) & gray balance: managed via curves and target bars.
Color delta: e.g., ΔE2000 targets ≤ 2–3 for brand colors; document ink and dampening settings.
Register accuracy: verify crosshairs, hairlines, and front/back alignment.
Adhesion & durability: pull tests for foil/UV/lamination; rub/sweat/chemical resistance as needed.
Carton performance: crease quality, glue bond strength, lid/bottom reliability.
7) Sustainability & Compliance
Materials: FSC/PEFC options; water-based coatings, solvent-free adhesives; aim for mono-material designs for recyclability.
Inks: low-migration series and statements for food-contact where required; manage VOCs (or use UV offset).
Design for recycling: minimize hard-to-separate laminates; include disposal marks/regulatory info.
8) When to Choose Offset
High-quality images/gradients, fine text/linework.
Medium–large quantities with multiple premium finishes in one pass.
Tight color management and brand consistency requirements.
For very short runs/many SKUs or variable data, consider digital. For extreme solids or ultra-long runs, evaluate gravure/flexo or hybrid strategies.