Gravure dominates China’s flexible packaging industry — over 94% of all soft packaging printing equipment and 95% of converters use it. The technology delivers speeds above 300 m/min with cylinder life of 3–4 million impressions, producing the richest color density and finest vignettes of any mass-production print method. Here’s the complete technical reference for gravure flexible packaging production.
Substrate Specifications
Print-grade film requirements: smooth surface, free of defects and impurities; non-polar surfaces corona-treated to raise surface energy; shrinkage and elongation under 1%; adequate tensile strength and heat resistance with minimal thermal deformation; abrasion and puncture resistance to protect inner layers.
| Film | Characteristics |
|---|---|
| BOPP | High tensile strength, high elastic modulus, low tear resistance; excellent rigidity, chemical stability, moisture barrier |
| PET | High strength, toughness, transparency; excellent rigidity, hardness, abrasion/fold resistance, dimensional stability; good gas and moisture barrier; wide temperature range |
| PA (BOPA) | Contains repeating amide groups; strong, good barrier in controlled humidity; highly moisture-sensitive |
| PT (cellophane) | Excellent transparency, gloss, printability; non-conductive |
Ink Systems
Surface-print ink uses polyamide resin binder (softening point controlled at 121°C — too low causes blocking in humid season; too high requires heating to dissolve in winter). Diluents: toluene, isopropanol, xylene, butanol (fast: toluene/isopropanol; slow: xylene/butanol). Butanol improves dot reproduction at low addition rates; excess causes drying failure and blocking.
Reverse-print (lamination) ink uses chlorinated polypropylene resin binder — excellent adhesion to OPP, PET, NY. Diluents: toluene, MEK, butanone, ethyl acetate. Never add alcohol solvents — the ink will degrade. Match the ink grade to press speed: high-speed presses need fast-drying formulations; low-speed presses need slow-drying — using the wrong grade either dries in the cells or won’t dry on the substrate.
Retort-grade ink: Two-component system for retort and aluminum foil printing. Standard lamination ink fails under retort conditions — color dilutes, shifts, and loses definition.
Surface energy: Gravure ink surface tension is approximately 36 dyne/cm. PE and OPP untreated are approximately 32 dyne/cm. Corona treatment must raise substrate surface energy to ≥38 dyne/cm for reliable adhesion. Test: tape peel and finger rub — no ink removal = acceptable.
Process Parameters
| Parameter | Value |
|---|---|
| Maximum speed | >300 m/min |
| Cylinder life | 3–4 million impressions |
| Ink particle size (grind) | ≤15 μm |
| Registration tolerance (GB 7707-87) | Front ≤0.3mm, Back ≤0.5mm |
| Pressroom temperature | 25°C |
| Pressroom humidity | 40% RH |
| Doctor blade contact angle (ideal) | 55° |
Color Sequence
- Surface printing: White → Yellow → Magenta → Cyan → Black
- Reverse printing: Black → Cyan → Magenta → Yellow → White
- Spot colors: after black or after process colors, adjustable by production plan.
Tension Settings (Typical)
| Substrate Type | Tension |
|---|---|
| BOPP, PE (high elongation) | ~100 N |
| NY, PET, PT | ~110 N |
| Paper, paper-aluminum composite | ~120 N |
Drying Temperature
Three-way relationship: constant temperature + higher solvent boiling point → reduce speed → lower temperature. Constant boiling point + higher speed → raise temperature. Constant speed + higher boiling point → raise temperature. Also depends on ink coverage, ink film thickness, and ink formulation.
Key Defect: Doctor Blade Streaks
Viscosity drives streaks — higher viscosity directly increases streak probability. Ink particle size: target ≤15 μm; oversized particles lift the blade and produce streaks while damaging both the blade and cylinder. Blade quality, mounting angle, and adjustment determine whether streaking appears or is suppressed. A skilled operator positions the blade to minimize streaks while maintaining overall print quality. Blade grinding quality is critical — well-ground edges produce fewer streaks.
Industry Outlook
China’s gravure equipment manufacturing still lags European competitors in five areas: electronic shaft drive technology, print carriage design, sleeve technology, machine management systems, and remote technical support. Solvent-based ink remains dominant, creating tension with food and pharmaceutical packaging regulations, but water-based and alcohol-soluble ink development is progressing. The equipment trajectory points toward multi-purpose, multi-color, high-speed, automated, integrated, and environmentally compliant systems.
References
- Wikipedia: Rotogravure: Comprehensive overview of gravure printing technology including cylinder engraving, ink systems, and press architecture.
- Wikipedia: Doctor Blade: Doctor blade function, materials, mounting angles, and wear patterns in gravure printing.
- Wikipedia: Flexible Packaging: Overview of flexible packaging structures, materials, and printing technologies including gravure market position.
- Wikipedia: Corona Treatment: Surface energy modification of polymer films for gravure ink adhesion including dyne level requirements.
- Flexible Packaging Association (FPA): Industry resource covering gravure printing technology, market data, and quality standards.