Additives for UV Flexo, UV Offset, and Oil-Based Offset
Photoinitiator, hardener, antitack paste, siccative, diluent, and other additives for precise fine-tuning of the printing process. Each printing technology has its own set of additives, and even its own separate hardeners for different applications.
An additive is a substance mixed into ink or varnish in small quantities (typically 0.2–10% by weight) to change a specific property — drying speed, tack, abrasion resistance, or viscosity. Each printing technology has its own set of additives — what works for UV flexo does not always work for oil-based offset, and some additives (such as a hardener) exist in several distinct versions for different applications even within a single technology. Exceeding the recommended dosage does not improve the result — it only increases the risk to food safety and print performance.
Additives for UV Flexo
For flexographic UV inks, OPV varnishes, and primers on non-absorbent substrates
Photoinitiator
Triggers polymerization under UV light. Critical for dark shades, where the pigment absorbs light and slows the reaction
Hardener for Primer
A separate formula specifically for primers and OPV varnishes — improves adhesion of the ink applied over it. A two-component mix with a limited pot life
Hardener for Ink
A separate formula for the flexographic UV inks themselves (not for the primer) — improves adhesion on demanding substrates. A different product with a different code, not interchangeable with the primer hardener
Antitack Paste
Increases resistance to abrasion and scratching. Prevents subsequent varnishing, foil stamping, and thermal transfer
Matt Paste
Produces a matte surface instead of gloss. When added above 10%, requires an additional photoinitiator
Leveling Agent
Improves the varnish's ability to level an uneven substrate surface
Wetting Agent
Improves varnish spreading on the surface
Defoamer
Eliminates foam formation — very low concentration, excess causes surface defects
Reactive Diluent
Reduces viscosity without compromising print performance — unlike regular solvents, it participates in polymerization
Additives for UV Offset
For offset inks with instant UV polymerization
Photoinitiator
Triggers polymerization, especially important for dark colors and high printing speeds
Hardener
Improves adhesion on non-absorbent substrates — film, foil, metallized materials
Antitack Paste
Increases abrasion resistance of the printed surface
Reactive Diluent
Adjusts ink viscosity for the specific printing system and press speed
Additives for Oil-Based Offset
For inks that dry through oxidative polymerization — commercial printing and non-absorbent materials
Siccative (Drier)
Speeds up oxidative polymerization — relevant at lower shop temperatures or slow ink drying
Hardener (for Non-Absorbent Materials)
Speeds up drying and improves scratch resistance on film, foil, and other demanding substrates
Gloss Diluent
Reduces ink viscosity without significant loss of color intensity
Tack Reducer
Reduces ink tack, preventing sheets from sticking together in the stack at high print run volumes
Q&A
Can a primer hardener be used in flexographic ink?
No. The primer hardener and the ink hardener are two separate products with different codes, developed for different systems. Although both have a similar function (improving adhesion) and similar dosage, they are not interchangeable — using the wrong hardener may produce an unpredictable reaction or not work at all. Always check exactly what you are testing — primer or ink.
Which additive should I choose if UV ink does not fully cure?
The most likely cause is insufficient reactivity of the system, especially when printing dark colors at high speed. Add a photoinitiator at up to 5% of the ink's weight. If the problem persists, check the UV lamp's power.
Why do sheets stick together after offset printing?
The typical cause is excess ink tack, especially with large print runs or printing on coated paper in a warm shop. Add a tack reducer at 2–4% dosage, starting with the minimum amount.
What happens if the recommended dosage is exceeded?
Exceeding it does not improve the result — on the contrary, it increases the risk of component migration (critical for food packaging), impairs adhesion of subsequent layers (varnishing, stamping), and may negatively affect the ink's print performance. Always follow the maximum percentage specified by the manufacturer.