Flexography and gravure printing

In short

Flexography and gravure are the two roll-fed (web) printing processes that dominate packaging. Flexography prints from a flexible relief (raised-image) photopolymer plate inked by a cell-engraved anilox roller; gravure prints from an intaglio (sunken-image) engraved copper cylinder whose cells are wiped clean by a doctor blade. Between them they carry almost all of India's flexible packaging, labels, corrugated boxes, cartons, lamitubes, wallpaper and cigarette packs — Uflex, Huhtamaki India, Cosmo Films, Jindal Poly, Parksons, TCPL, EPL and ITC's Packaging & Printing division all run them. In university printing-technology papers (Jadavpur, Anna University, GJUS&T Hisar, PVG Pune, SIES Graphic Arts, Manipal) and in placement rounds for press, pre-press, cylinder-making and QC roles, the examined core is ink transfer through anilox/cell volume, plate and cylinder making, press configuration, register, defect diagnosis and the solvent/food-safety rules that govern packaging.

Explained

Flexography — principle and press anatomy

• Relief process: only the raised image carries ink; the plate is a flexible photopolymer or rubber sheet mounted on a cylinder with double-sided cushion-mounting tape, so it prints on almost any substrate at light pressure ("kiss impression").
• Ink train: modern presses use a chambered doctor-blade system — ink is pumped into a sealed chamber against the anilox; a reverse-angle metering blade wipes the surface, a containment blade seals the exit. Older presses use a two-roll (rubber fountain roll + anilox) train, which cannot meter accurately at speed.
• Anilox roller: ceramic (chrome-oxide plasma-sprayed) sleeve, laser-engraved with cells. Specified by line screen (lpi or l/cm), cell volume (BCM/in² or cm³/m²) and cell geometry (60° hexagonal standard; channelled/elongated for coatings).
• Rule of thumb: anilox screen ≥ 4-5.5 × plate screen ruling, else the smallest halftone dots sit in cell openings and print dirty or drop out.
• Press configurations:
  1. Stack press — decks stacked in vertical columns; cheap, used for paper/polythene bags, poor register on stretchy film.
  2. Central impression (CI) press — all colours print against one large chilled drum; the web never leaves the drum between colours, so register on thin stretchy film is excellent. Standard for flexible packaging.
  3. Inline press — separate units in a line; used for labels, cartons, corrugated and for combining print with die-cutting, lamination, cold foil.
• Impression setting: too much pressure spreads the dot and causes a halo and dot gain; bounce/gear marking arises from plate-to-cylinder gaps and resonance.

Flexo plate making and pre-press

1. Plate types: sheet photopolymer 0.76-1.70 mm for film/label/carton; 2.84-3.94 mm for corrugated post-print. Hardness 25-70 Shore A — soft plate for rough corrugated, hard plate for fine screen on film.
2. Analogue route: negative film in vacuum contact → back exposure (sets floor) → main UV-A exposure → solvent washout → drying (2-4 h, long) → light finishing/detack → post-exposure.
3. Digital route (now standard): laser ablates the black LAMS (laser-ablatable mask) layer on the plate — no film; then main exposure, washout (solvent or thermal, which is fast and nearly solventless), detack, post-exposure.
4. Screening technology: digital plates give a 1:1 dot and, with flat-top-dot and surface-screening technologies (HD/Full-HD/Crystal type), hold 1% highlights and support 150-175 lpi on film and expanded-gamut (fixed-palette) 7-colour printing.
5. Distortion: the plate is wrapped round a cylinder, so the image stretches in the print direction; the artwork must be shrunk by the distortion factor before imaging (not needed for plates imaged in the round, i.e. sleeves).
6. Mounting: optical/video mounters or pin-register systems; tape density (soft, medium, hard) is chosen by job — soft tape for solids, hard tape for fine process work.
7. Inks: solvent-based (nitrocellulose/PU for film), water-based (paper, corrugated, and increasingly film), UV-curable (labels, shrink sleeves). All are low-viscosity, measured in seconds on a Zahn #2 / DIN 4 mm cup (typically ~16-24 s; always set to the ink supplier's data sheet).

Gravure — principle and press anatomy

• Intaglio process: the image is a pattern of engraved cells below the cylinder surface. The cylinder dips in a low-viscosity ink pan, a doctor blade scrapes the non-image surface clean, and a rubber-covered impression roller presses the web against the cylinder; capillary action and pressure pull ink out of the cells.
• Transfer aids: electrostatic assist (ESA) applies a charge across the nip to pull ink out of cells — essential on rough paper/board to avoid missing dots (snowflaking).
• Doctor blade: carbon/stainless steel 0.15-0.20 mm, sometimes with a backing (pre-) blade, set at roughly 55-65° to the cylinder tangent, oscillating sideways to even out wear; blade angle, pressure and setting distance control ink film and streaking.
• Press layout: always unit-type inline — each colour is a separate deck with its own ink pan, cylinder, impression roller and hot-air dryer (solvent must be fully removed before the next colour). Modern presses are shaftless servo-driven (electronic line shaft) instead of mechanically geared.
• Cylinder: steel or aluminium base → copper plated (often as a thin Ballard shell that can be stripped off and replated) → engraved → proofed → hard chrome plated ~6-8 µm, ~900-1,000 HV, for wear and blade resistance. Chrome is stripped for re-engraving and the base is re-used many times.
• Engraving methods:
  • Chemical etching (obsolete for new work): conventional (constant area, variable depth), variable-area variable-depth via halftone-gravure film.
  • Electromechanical engraving (EMG): a diamond stylus cuts pyramidal cells, 4,000-8,000 cells/s (Helio-Klischograph type). Stylus angle 120°/130°/140° sets cell width-to-depth; screen ruling typically 54-80 l/cm for packaging, up to 100+ l/cm for fine work; screen angles 30°/45°/60°, with compressed or elongated cells.
  • Laser (direct) engraving: fibre laser on copper or on a zinc/polymer layer; gives free cell shape, sharper walls, no stylus geometry constraint.
• Cell structure classification: conventional (area constant, depth varies) · variable area + variable depth (EMG standard) · variable area + constant depth (halftone gravure, used for some electronics/decor work).

Comparison, economics and quality control

• Gravure strengths: heaviest and most uniform ink film (continuous tone look, dense solids), very long run life (millions of impressions per cylinder), excellent for metallics, whites on film, decor and cigarette packaging.
• Gravure limits: very high cylinder cost and lead time (each colour a separate engraved, chromed cylinder), uneconomic for short runs, repeat length fixed by cylinder circumference, fine text can show sawtooth edges, heavy solvent load.
• Flexo strengths: cheap plates and fast changeovers, short runs viable, water-based and UV inks available, easy inline converting, sleeve technology for quick repeats.
• Flexo limits: thinner ink film, more dot gain and highlight/shadow compression, plate distortion and impression sensitivity, limited solid density compared with gravure.
• The crossover in India: flexo has taken label, corrugated, carton and a growing share of mid-run flexible packaging; gravure holds long-run flexible packaging, lamitubes, cigarette and decor printing. The practical break-even is job-specific — compare cylinder/plate cost per colour against run length and make-ready waste.
• Standards and measurement: process control uses densitometry, CIELAB ΔE / spectrophotometry, TVI (dot gain) curves and test strips. International process standards: ISO 12647-6 for flexography and ISO 12647-4 for gravure (publication), with ISO 12647-7 for digital proofs; the FTA's FIRST specifications and G7 grey-balance calibration are widely used industry practice. Bureau of Indian Standards work exists on printing inks and packaging materials, but quote an IS number only after checking its current edition — several older printing-related standards have been withdrawn or revised.
• Legal and safety frame (India, current): food-contact printed packaging falls under the Food Safety and Standards (Packaging) Regulations, 2018 (FSSAI) — ink must not come into contact with food, and toluene- and ketone-free, low-migration inks are standard practice for food packs; EuPIA/Nestlé-type exclusion lists are used contractually. Plastic printed packaging carries EPR obligations under the Plastic Waste Management Rules, 2016 as amended (CPCB EPR portal registration). Weight/price/FSSAI declarations are mandated by the Legal Metrology (Packaged Commodities) Rules, 2011. Workplace solvent handling, flammable-store design, LEL monitoring, exhaust and worker safety now sit under the Occupational Safety, Health and Working Conditions Code, 2020 (in force 21 November 2025, replacing the former Factories Act), with VOC/consent conditions from the State Pollution Control Board; solvent recovery (activated carbon) or thermal oxidation is the usual control on gravure lines.

Common press defects and their causes

• Flexo — dirty print/filling-in: anilox volume too high, impression too heavy, plate relief too shallow, dried ink in cells.
• Flexo — halo/feathering: excess impression squeezing ink out at the dot edge.
• Flexo — bounce/banding (gear marks): plate gap, uneven plate thickness, worn gears/bearers, resonance at a particular speed.
• Flexo — pinholing/poor laydown: surface tension too high, substrate dyne level too low (corona treat; aim typically ≥ 38 dyne/cm for most film inks).
• Gravure — missing dots/snowflaking: poor ink release in highlights on rough stock; fix with ESA, lower viscosity, softer impression roller.
• Gravure — doctor blade streaks/tracking: nicked blade, dried ink or hard pigment particle, dirty ink (filter and recirculate).
• Gravure — hazing/scumming: blade pressure or angle wrong, chrome worn, ink too thixotropic.
• Both — misregister: web tension variation, wrong repeat/distortion, worn impression rollers; corrected by longitudinal (circumferential) and lateral register servos reading a register mark.
• Both — solvent retention/odour: underdried, usually from excessive line speed or low dryer temperature/airflow; measured by GC head-space.

Key points

• Flexography - relief (raised image) rotary web process using flexible photopolymer plates and an anilox metering roller.
• Gravure - intaglio process; image is engraved cells below the surface, wiped by a doctor blade.
• Anilox roller - ceramic, laser-engraved cell roller; the single biggest control on flexo ink film; specified by lpi + volume.
• BCM - billion cubic microns per square inch of anilox cell volume; 1 BCM ≈ 1.55 cm³/m².
• Anilox-to-plate screen ratio - keep anilox ruling at least 4-5.5 times the plate screen ruling.
• Chambered doctor blade - sealed ink chamber with reverse-angle metering blade; the accurate, low-misting way to ink an anilox.
• CI press - central impression drum press; best register on thin, stretchy films.
• Plate distortion factor - the % by which artwork must be shrunk lengthwise before plate imaging, because the plate wraps a cylinder.
• LAMS digital plate - laser-ablated mask gives filmless plate making and a 1:1 dot.
• Shore A durometer - plate/roller hardness; soft plates for corrugated, hard for fine process on film.
• Cell volume - gravure ink carrier; varies by cell area and depth, set by screen ruling and stylus angle.
• Ballard shell - strippable copper sleeve on a gravure base cylinder, enabling re-engraving without losing the base.
• Chrome plating - 6-8 µm hard chrome over engraved copper for wear life against the doctor blade.
• Electrostatic assist (ESA) - charge across the nip that pulls ink out of cells; cures missing dots on rough stock.
• Repeat length - gravure print repeat = cylinder circumference πD; on geared presses it changes only in fixed increments (classically 1/8 in = 3.175 mm per tooth).
• Dot gain / TVI - tonal increase from plate to print; much larger in flexo than gravure and must be compensated in pre-press curves.
• Viscosity control - low-viscosity solvent/water inks measured in Zahn or DIN cup seconds, held automatically by a viscosity controller.
• Process standards - ISO 12647-6 (flexo), ISO 12647-4 (gravure), with FIRST and G7 as industry practice; food packs governed by FSSAI Packaging Regulations, 2018.

Formulas and examples

Example 1 — Flexo anilox, ink film and cost. A CI flexo press runs a white solid with a 4.0 BCM anilox. Ink: solids 35%, density 1.02 g/cm³, ₹310/kg. Transfer efficiency 45%. Job = 12,000 m² at 100% coverage.

• Cell volume = 4.0 × 1.55 = 6.20 cm³/m².
• Wet film transferred = 6.20 × 0.45 = 2.79 µm (2.79 cm³/m²).
• Wet ink mass = 2.79 × 1.02 = 2.85 g/m²; dry coat weight = 2.85 × 0.35 = 1.00 g/m².
• Ink consumed = 2.85 g/m² × 12,000 = 34.2 kg → cost = 34.2 × 310 = ₹10,602 (≈ ₹0.88 per m²).
• If the anilox is changed to 3.0 BCM, wet film falls to 2.09 µm and ink cost to ≈ ₹7,950 — but check opacity before saving.

Example 2 — Flexo plate distortion. Plate 1.14 mm, cushion tape 0.50 mm, print repeat 500.0 mm. The tape raises the cylinder diameter (and so the repeat) but does not add to the distortion, because the plate's dimensionally stable polyester base sits above it and does not stretch.

• K = 100 × 2π × 1.14/500 = 100 × 7.163/500 = 1.43%.
• Imaged artwork length = 500 × (1 − 0.0143) = 492.8 mm; i.e. the image is pre-shrunk by 7.16 mm in the print direction.
• On a 250 mm repeat the same plate gives K = 100 × 7.163/250 = 2.87% — distortion is larger on small repeats, which is why thin plates are used there (or sleeves imaged in the round, K = 0).

Example 3 — Gravure cylinder repeat. Required print repeat = 450 mm.

• D = 450/π = 143.2 mm outside diameter of the chromed cylinder.
• On a geared press with 1/8 in (3.175 mm) repeat per tooth: 450/3.175 = 141.7 teeth — not available. Nearest repeats are 141 × 3.175 = 447.7 mm or 142 × 3.175 = 450.9 mm; the design must be laid out to the achievable repeat. A shaftless servo press removes this constraint.

Example 4 — Gravure cell volume, ink film and solvent load. Screen 70 l/cm, cell opening 113 µm square, depth 35 µm, pyramidal cells. Ink: 30% solids, density 0.95 g/cm³. Transfer 80%. Web 1.0 m wide at 250 m/min.

• V_cell = (1/3) × 113² × 35 = (1/3) × 12,769 × 35 = 148,972 µm³ ≈ 149 pL.
• Cells/m² = (70 × 100)² = 7,000² = 4.9 × 10⁷.
• Volume per m² = 4.9 × 10⁷ × 1.49 × 10⁵ × 10⁻¹² = 7.30 cm³/m².
• Wet film transferred = 7.30 × 0.80 = 5.84 µm; wet mass = 5.84 × 0.95 = 5.55 g/m²; dry film = 5.84 × 0.30 = 1.75 µm.
• Solvent evaporated = 5.55 × 0.70 = 3.88 g/m². Output = 1.0 × 250 = 250 m²/min → 970 g/min ≈ 58.2 kg/h per deck.
• Dilution air to hold 25% of the LEL (take LEL of ethyl acetate ≈ 2% v/v, so target 0.5% v/v; M = 88 g/mol, 24.45 L/mol at 25 °C): vapour = 58,200/88 = 661 mol/h = 16.2 m³/h → air ≈ 16.2/0.005 = ≈ 3,200 m³/h. This is why each gravure deck has its own dryer and why solvent recovery is sized on kg/h, not on litres of ink.

Example 5 — Make-ready economics, flexo versus gravure. Job: 6 colours on BOPP, 1.0 m web. Flexo plates ₹9,000/colour + mounting; gravure cylinders ₹13,500/colour. Flexo waste 800 m, gravure waste 1,500 m; substrate ₹22/m.

• At 20,000 m run, fixed cost per metre = ₹3.58 (flexo) against ₹5.70 (gravure) — flexo wins.
• At 400,000 m, it is ₹0.18 against ₹0.29 per metre — the difference is now negligible and gravure's ink laydown, speed and consistency decide. (Rates are illustrative; use actual quotations.)

Where it is used

• Flexible packaging (gravure and CI flexo): laminates for snacks, biscuits, oils, spices and detergents — Uflex, Huhtamaki India, Paharpur 3P, Amcor, Constantia, Multiflex; converting plants across Noida, Nashik, Daman, Baddi and Hyderabad.
• Labels and shrink sleeves (narrow-web UV flexo): pharma and FMCG labels on Nilpeter, Mark Andy, Multitec and Webtech presses; shrink sleeves for beverages.
• Corrugated and paper (water-based flexo): pre-print and post-print of shipper cartons for e-commerce and FMCG; paper bags and multiwall sacks.
• Lamitubes and specialities: EPL (Essel Propack) prints tube laminate webs; wallpaper, decor paper, cigarette inner frames and gift wrap on gravure.
• Supply chain roles: cylinder-making and pre-press houses (Janoschka India, Daetwyler-type anilox/cylinder services), ink makers (Siegwerk, Flint, Sakata INX, Hubergroup, DIC/Coates), and press OEMs/service (Bobst, W&H, Comexi, Uteco plus Indian builders such as Pelican Rotoflex and Kohli Industries).
• Jobs examined on this topic: press operator/shift in-charge, pre-press and plate-room technician, cylinder engraving engineer, process/QC engineer (ΔE, dot gain, bond and migration testing), applications engineer with ink and machine suppliers, and PSU security printing roles (SPMCIL units) where intaglio fundamentals are tested.

Interview questions

• Q: What is the fundamental difference between flexography and gravure? A: Flexography prints from a raised (relief) flexible plate inked by an anilox roller; gravure prints from cells engraved below the surface of a cylinder, wiped clean by a doctor blade.
• Q: How is the ink film controlled in flexo? A: Almost entirely by the anilox cell volume (BCM/cm³/m²) and its transfer efficiency, plus ink solids — not by impression pressure, which should be a light kiss.
• Q: Why must the anilox screen be far finer than the plate screen? A: If their rulings are close, small halftone dots land in cell openings instead of on cell walls, giving inconsistent transfer, dirty print or dropout; keep a ratio of about 4-5.5:1.
• Q: What is the plate distortion factor and when is it zero? A: It is the lengthwise shrink applied to artwork because the plate wraps around a cylinder, K = 2π × plate thickness/repeat (tape excluded — the plate's polyester base does not stretch); it is zero for sleeves imaged in the round.
• Q: Why is a central impression press preferred for thin films? A: The web stays held on one chilled drum through all colours, so it cannot stretch or wander between units, giving tight register on extensible film.
• Q: What does electrostatic assist do in gravure? A: It applies a charge across the printing nip so ink is pulled electrostatically out of the cells, eliminating missing dots in highlights on rough paper or board.
• Q: Why is a gravure cylinder chrome-plated, and how is it reused? A: Hard chrome (~6-8 µm, ~900-1,000 HV) resists doctor-blade wear and extends run life; the chrome is stripped, the copper (often a Ballard shell) replaced or re-engraved, and the steel base reused.
• Q: Why does gravure give denser solids than flexo? A: Its cells carry and release a much thicker wet ink film (roughly 4-8 µm against 1.5-4 µm), so more pigment is deposited per pass.
• Q: Diagnose a repeating streak down the web on a gravure deck. A: Almost always a doctor-blade problem — a nicked blade, a hard particle or dried ink under it; filter the ink, oscillate and replace the blade, check blade angle and pressure.
• Q: A flexo job shows a halo round every solid edge. What is wrong? A: Over-impression squeezing ink beyond the image edge; reduce impression to kiss, check plate thickness uniformity and consider a harder cushion tape or lower anilox volume.
• Q: What governs printing inks on Indian food packaging? A: The FSSAI Food Safety and Standards (Packaging) Regulations, 2018 — ink must not contact the food, and low-migration, toluene/ketone-free ink systems are standard practice; customer exclusion lists usually apply in addition.
• Q: When would you still quote gravure over flexo today? A: Very long runs, heavy solid/metallic laydown, large white coverage on film, decor and tobacco work, or where a customer's colour standard is already built on gravure cylinders.
• Q: How do you measure and control colour on a packaging press? A: Spectrophotometer readings against a CIELAB target with a ΔE tolerance, solid ink density and TVI/dot-gain curves on a control strip, with pre-press curves to ISO 12647-6/-4 and G7 calibration.

Common mistakes

• Quoting anilox line screen as the ink-carrying capacity; the volume (BCM or cm³/m²) is what meters ink, and two rollers of the same lpi can differ widely in volume.
• Converting BCM wrongly — forgetting that it is per square inch (1 BCM ≈ 1.55 cm³/m², and 1 cm³/m² = 1 µm of wet film).
• Adding the cushion tape thickness into the distortion calculation (only the plate thickness distorts the image; the tape changes the repeat), or applying distortion to a sleeve imaged in the round.
• Treating impression pressure as a density control in flexo — it produces halo, dot gain and plate wear instead.
• Confusing cell area with cell volume in gravure, or assuming the EMG stylus angle does not change depth-to-width ratio.
• Calling gravure "relief" or flexo "intaglio" in the exam; and claiming letterpress and flexo are identical — both are relief, but flexo uses flexible plates and low-viscosity ink, letterpress rigid plates and paste ink.
• Ignoring solvent balance: computing ink consumption but not the kg/h of solvent the dryers must remove and the LEL/VOC limits that follow.
• Reporting dot gain without naming the measurement condition (screen ruling, patch, instrument) so the number cannot be compared.

Related topics

Offset lithography · Screen and digital printing · Colour science, densitometry and colour management · Pre-press, imaging and screening · Packaging materials, films and lamination · Printing inks, solvents and substrate surface treatment