Inks (Flexo / Gravure / UV)
Printing inks are judged on the printed result, so the colour paste must disperse to a fineness that keeps the anilox cells and gravure engraving clean, and must develop full colour strength at a low dosage. In UV and EB inks the paste also has to be compatible with the acrylate monomer and oligomer phase, because an incompatible carrier either hazes the film or interferes with cure. Press behaviour adds a further constraint, since an ink that prints well in the laboratory can still mottle or dry in on a long run.
Key Requirements in This Application
Fine dispersion for thin ink films
Flexographic and gravure films are only a few micrometres thick, so any agglomerate prints as a speck or a streak. Dispersion must be finer than in a coating, and the particle size distribution has to be narrow enough that the ink does not settle in the pan.
Colour strength and transparency
Ink mileage depends on colour strength per unit of paste, and process colours depend on transparency so that overprints build the intended shade. Both are controlled by pigment selection and by complete dispersion, not by adding more paste.
Rheology and press behaviour
The paste must let down to an ink with the right viscosity and flow for the anilox, doctor blade and gravure cylinder in use. A paste that thickens the ink or thixotropes in the pan causes poor transfer and mottling.
Solvent compatibility
Solvent-based flexo and gravure inks use esters, alcohols and glycol ethers. The carrier must be soluble in that blend and must not precipitate when the ink is diluted at press side.
UV/EB compatibility and cure
In radiation-cured inks the paste must be soluble in the acrylate monomer and must not absorb UV energy or scavenge radicals. An amine-containing carrier can also cause yellowing or odour after cure, so the system has to be checked as a whole.
Substrate adhesion
The same ink may be printed on film, foil, coated paper or board, each with a different surface energy. The paste must not bloom to the surface and reduce adhesion, and it must not plasticise the ink film to the point where rub resistance or lamination bond strength falls below specification.
Plate and cylinder compatibility
Carriers that swell photopolymer plates or attack the cylinder surface shorten plate life and change dot gain over a run. The paste has to be checked against the specific plate and cylinder materials used on the press, not only against the ink formulation.
Recommended DENSON Series
Resin-free carrier pastes that give ink makers freedom over the let-down vehicle and colour strength in solvent-based flexo and gravure inks. Because the carrier adds no resin, the ink maker controls the final vehicle; the carrier contains solvent and is not a solvent-free system.
View seriesUV/EB curable colour pastes for radiation-cured inks, based on a true solvent-free system; the EB route uses no photoinitiator, so the paste does not depend on a photoinitiator package and does not add solvent to the ink.
View seriesOil-based pastes with roughly 20 percent PMA in the carrier, used where a solvent-borne ink vehicle is preferred; they are solvent-based and are not positioned as solvent-free.
View seriesTechnical Considerations
- Grind to the fineness required by the print process, then confirm on the printed web rather than on a draw-down bar.
- Check the dilution ladder at press viscosity, since a carrier that precipitates on let-down will show as gel or haze.
- For UV inks, verify cure response at the specified lamp dose and line speed, and check odour and yellowing after cure.
- For EB inks, confirm that no photoinitiator is required and that the paste does not depend on one.
- Watch settling and hard caking in the ink pan and in storage, because settled pigment changes colour strength across a run.
- Confirm ink stability over a full production run, since a slow viscosity climb changes transfer and dot gain before the colour visibly shifts.
Testing and Compliance
Dispersion and strength
Fineness by GB/T 6753.1, viscosity by GB/T 9751 and particle size distribution to ISO 13320 are combined with a colour-strength comparison against a standard to confirm that the paste develops full strength.
Print performance
Proofs on the target substrate are checked for specking, mottling, transfer and gloss, since these are the faults that dispersion and rheology produce on press.
Cure and film properties
For UV and EB inks, cure is confirmed by solvent rub and adhesion on the substrate, with odour and shade checked after cure to catch interference from the carrier.
Print durability
Rub resistance, adhesion and, where relevant, lamination bond strength are measured on the printed and dried film, because these are the properties that decide whether the print survives the converting process.
Discuss Your Application
Tell us the resin system, process conditions and performance target, and we will confirm the suitable series and starting dosage.
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