Types of Printing Inks · The Complete Guide

The type of ink used in printing is not a background variable, it determines the press configuration required, the substrates that can be printed, the finishing processes that are compatible, the food safety status of the finished product, the environmental impact of the production, and the cost structure of the job. Selecting the wrong ink system for an application is not a minor error, it can produce a product that fails technically, fails regulatory compliance, or simply fails to meet the client's quality expectations despite a technically correct print.

In Indian press rooms, the dominant ink system is conventional oxidative-drying offset ink, the same fundamental chemistry that has been used in offset printing since the 1950s. UV and LED-UV printing are growing rapidly, driven by packaging quality requirements and the need for instant-dry productivity. Food-safe inks are increasingly specified as brand owners and retailers become more aware of migration regulations. Understanding each system, and the critical incompatibilities between them, prevents the most costly ink-related errors in production.

Conventional offset inks are oil-based, paste-consistency inks that dry by oxidative polymerisation, a chemical reaction between the linseed or soya oil vehicle and atmospheric oxygen. This is the dominant ink system in Indian sheetfed offset printing, used on the vast majority of commercial brochures, catalogues, annual reports, and packaging cartons produced in India.

How they work

The ink vehicle is a combination of vegetable oils (predominantly linseed or soya) and alkyd resins dissolved in petroleum or vegetable oil solvent. Metal drier salts (cobalt, manganese) catalyse the oxidative reaction. After printing, oxygen from the atmosphere diffuses into the ink film and triggers crosslinking of the oil molecules, the liquid ink becomes a solid polymer film. This process takes 4–12 hours for surface cure and 12–24 hours for full through-cure, depending on ink formulation, substrate, coverage, temperature, and humidity.

Advantages

• Works on virtually every substrate, coated and uncoated papers, boards, labels
• Compatible with all standard offset press configurations, no special press equipment required
• The widest range of colours, formulations, and special effects available in any ink system
• Lower ink cost per kilogram than UV or LED-UV inks
• The industry standard, all press operators, prepress professionals, and finishing operators are familiar with conventional ink behaviour

Limitations

• Slow drying, 4–12 hours before the printed pile can be handled for finishing. On heavy coverage jobs, longer. This limits production speed and requires careful pile management with anti-setoff powder.
• Drying is humidity and temperature dependent, in India's monsoon season, slow-drying conventional inks can cause significant production delays (see the Fountain Solution guide for the India-specific context)
• Lower scuff resistance than UV-cured inks, printed solids can be scratched during handling, particularly on uncoated substrates
• Contains VOCs (volatile organic compounds) from the petroleum-based solvents, not relevant to most Indian regulatory requirements currently, but increasingly relevant as Indian sustainability standards evolve

Soya-based and vegetable oil inks

Soya inks replace the petroleum-derived vehicle solvent with soybean oil. The environmental benefit is genuine, lower VOC emissions, easier de-inking for recycling, but modest from a carbon perspective. Print performance is equivalent to mineral oil inks for most applications. Soya inks dry slightly more slowly. They are increasingly specified by brand owners with sustainability reporting requirements. They do not inherently improve food safety, food safety is determined by the pigment and binder chemistry, not the vehicle oil source.

UV (ultraviolet) inks contain no drying oils. Instead, they contain reactive monomers, oligomers, and photoinitiators. When exposed to UV light (200–400nm wavelength) from a UV lamp mounted in the press delivery, the photoinitiators absorb the UV energy and trigger radical polymerisation, the liquid ink film crosslinks almost instantaneously into a solid polymer. The entire curing process takes milliseconds as the sheet passes under the lamp.

Advantages over conventional

• Instant cure, sheets can be handled, stacked, and sent to finishing immediately after the press. No waiting for drying. No setoff risk. Production throughput can be dramatically higher than with conventional inks.
• No anti-setoff powder required, because the ink is solid by the time it reaches the delivery, there is no wet ink to cause setoff. This improves surface cleanliness and eliminates powder-related finishing problems.
• Superior scuff and chemical resistance, the dense polymer network of UV-cured ink is harder and more resistant to abrasion, moisture, and chemical contact than conventional oxidative-dried ink. This makes UV particularly appropriate for packaging that will be handled heavily in retail environments.
• Higher gloss potential, UV inks can achieve higher surface gloss than conventional inks because the instant cure freezes the ink surface before it can be absorbed into the substrate.
• No humidity-dependent drying issues, UV curing is not affected by ambient humidity or temperature. UV printing in Mumbai's July monsoon produces the same cure speed as December dry season.

Limitations and requirements

• UV-compatible press required, UV inks contain reactive monomers that attack and swell standard nitrile rubber blankets and rollers. A press running UV inks must have UV-resistant rubber components (EPDM or UV-grade formulations). This is not a setting change, it requires replacement of rubber press components.
• UV lamp system required, the press must be fitted with a UV curing unit (typically mercury arc or microwave-powered UV lamps) in the delivery section. Standard presses do not have this.
• Significantly higher ink cost, UV inks cost approximately 3–5× more per kilogram than conventional offset inks. For high-volume commercial work, this cost difference is a significant factor.
• Food safety complexity, some UV photoinitiators (particularly benzophenone and its derivatives) are known migrants and are restricted or banned for food packaging applications. Food-grade UV inks with compliant photoinitiator systems are available but more expensive. Standard UV inks should not be used for food packaging without specific food safety compliance verification.
• Non-absorbent substrates, UV inks do not absorb into the substrate, they cure on the surface. This makes them excellent for non-absorbent substrates (films, foils) but means adhesion relies entirely on surface chemistry. Some substrates require corona treatment or primer before UV printing.

LED-UV is a development of UV printing that uses high-power LED arrays rather than mercury arc or microwave UV lamps. The LEDs emit UV light at a narrow, specific wavelength (typically 365nm, 385nm, or 395nm) rather than the broad UV spectrum of mercury lamps. This requires UV inks formulated with photoinitiators that absorb efficiently at the LED emission wavelength, standard UV inks for mercury arc lamps are not directly compatible with LED-UV systems.

LED-UV advantages over conventional UV

• Energy efficiency, LED-UV lamps consume approximately 60–80% less energy than mercury arc UV lamps. A mercury arc UV system running continuously consumes substantial electricity; LED arrays consume much less. The energy cost saving is significant on a high-volume production press.
• No warm-up time, LEDs reach full output instantly. Mercury arc lamps require 2–5 minutes to warm up and cannot be switched off between jobs without losing their temperature calibration. LED-UV can be switched on and off with each job.
• No mercury, mercury arc lamps contain mercury, which requires careful disposal. LED arrays are mercury-free, simpler to dispose of and compliant with European WEEE regulations.
• Longer lamp life, LED arrays typically last 20,000–50,000 hours versus 1,000–2,000 hours for mercury arc lamps. Lamp replacement cost is significantly lower.
• Lower substrate heat, mercury arc UV generates significant infrared heat that can distort heat-sensitive substrates (thin films, some laminated boards). LED-UV generates substantially less heat, making it suitable for temperature-sensitive substrates.

LED-UV limitations

• LED-UV inks must be specifically formulated for the LED wavelength used. Standard UV inks for mercury arc do not cure under LED-UV. Always verify ink-lamp compatibility when switching to LED-UV.
• Some darker colours (particularly dense blacks and dark blues) can be more difficult to fully cure through the depth of the ink film under LED-UV than under the broader spectrum of mercury arc. Verify cure completeness with a scratch or adhesion test.
• Higher initial investment than conventional UV, LED-UV press conversions cost more than standard UV conversions due to the LED array technology.
• LED-UV in India: adoption is growing but still limited compared to conventional and standard UV. Availability of LED-UV specific inks from Indian ink suppliers is expanding but not yet as broad as conventional or UV options.

Heat-set inks are used exclusively in web offset printing, printing from a continuous roll of paper rather than individual sheets. They contain high-boiling petroleum solvents that evaporate when the printed web passes through a high-temperature drying oven (120–180°C) immediately after printing. The resin in the ink then sets rapidly as the web is chilled by water-cooled rollers, producing a hard, dry, rub-resistant surface.

• Heat-set web is the production method for high-volume magazines, newspaper supplements, and very large-edition catalogues, runs of 50,000+ copies where the economics of web printing are advantageous
• Not used in sheetfed printing, heat-set is a web-specific ink and process
• Print quality is excellent on coated LWC (light weight coated) paper, the standard heat-set substrate. The rapidly cured ink produces good colour density and relatively low dot gain.
• The high-temperature oven and chilling system are integral parts of the web press, the press and the ink system are inseparable
• India context: India has a number of large-format heat-set web presses in newspaper publishing groups and in specialist print facilities. Most commercial packaging and brochure work in India is sheetfed and uses conventional inks.

Waterless offset printing eliminates the dampening system entirely. Instead of using water-wet non-image areas on a conventional aluminium plate, waterless plates have silicone-coated non-image areas that repel ink by surface chemistry rather than by moisture. Waterless inks are formulated specifically for this system, they have different viscosity and tack characteristics than conventional inks.

• No ink-water balance issues, the most complex variable in conventional offset is eliminated. No fountain solution, no pH monitoring, no conductivity checks, no IPA management. The ink-water balance problem does not exist.
• Lower dot gain, without water emulsification into the ink, dots print at a smaller size and the tone reproduction is more linear than in conventional offset. Very fine screen work and stochastic screening are more reproducible.
• Temperature-sensitive inks, waterless inks have a narrow temperature window within which they perform correctly. Too cool and the ink is too viscous; too warm and it tacks down onto the silicone non-image areas (toning). The press must maintain precise temperature control, typically with chilled inking rollers. This adds press complexity.
• Specialist plates and inks required, standard plates and inks cannot be used. The entire consumable system is specific to waterless printing.
• India context: waterless offset is rare in India. The temperature control requirement is particularly challenging in press rooms without air conditioning. Not recommended for Indian press rooms without climate-controlled environments.

Food-safe inks (also called low-migration inks, LMI, or compliant inks) are formulated specifically for packaging that may contact or be adjacent to food. They use pigments, binders, and photoinitiators (in UV inks) that have been verified to migrate from the printed surface to food content at levels below regulatory limits, typically below 10 mg/dm² total migration and below specific migration limits for individual substances.

Why migration matters

When a printed food carton sits in a warehouse or on a retail shelf, ink components, monomers, pigment particles, solvent residues, photoinitiators, can transfer from the printed surface through the packaging material into the food. This set-off migration (from the outer printed surface to the inner food-contact surface when cartons are stacked) and through-migration (directly through the board) are the primary pathways. FSSAI in India and EU Regulation 1935/2004 set limits on how much migration is acceptable.

Low-migration conventional inks

• Formulated with high-molecular-weight pigments and resins that do not migrate readily through packaging materials
• Free from specific restricted substances: no benzophenone, no ITX (isopropylthioxanthone), no mineral oil MOAH/MOSH aromatic hydrocarbons above permitted levels
• Supplied with a formal Declaration of Compliance (DoC) from the manufacturer, this document, specific to the ink formulation and job conditions, is the evidence of compliance
• Must be applied within the specified coverage and substrate conditions stated in the DoC

Low-migration UV inks

• UV ink photoinitiators are the primary food safety concern in UV packaging printing. Benzophenone-type photoinitiators are highly mobile and have been found migrating into food from UV-printed packaging at levels of concern. They are now banned or severely restricted in food packaging applications in the EU and increasingly in India for major brand exporters.
• LM-UV inks use high-molecular-weight photoinitiators or type II photoinitiators (which become bound into the polymer network on cure and cannot migrate). These inks require verified full cure, partially cured LM-UV ink can still migrate because uncured monomers remain mobile.
• LED-UV systems often have better food safety performance than mercury arc UV for the same inks, because the narrow-spectrum LED output can be optimised to ensure complete cure in the depth of the ink film, reducing residual monomer.