TECHNICAL INFO




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Acrylic varnishes
More and more widely used, acrylic varnishes have met with great success thanks to their low cost and their ease of use.

Formulation:
There are two types of formulation based on acrylic resins: water based dispersions and solvent based dispersions. Their viscosity is adjusted as a function of the application method.

Use:
Water based acrylic varnishes can be applied using the fount solution tank, a separate varnishing machine or a varnishing unit (the most widely used method is a scraping chamber with an anilox cylinder with a screen ruling of 80-100 l/cm and a capacity of 6, 9 or 13 cm3/m2).
Solvent based acrylic varnishes are dry offset applied using the ink duct.
Acrylic varnishes can be applied in-line over conventional offset / letterpress inks.
In all cases (water or solvent based), it is recommended to use light fast inks because certain pigments may be chemically altered.

Characteristics:
Drying is rapid or even instantaneous (hot air or IR drying).
They are colourless and non-yellowing and they have high gloss.
These varnishes can be glued.

Incidents
 
  1. Hold out / Not smooth

  2. Discoloration of the ink film

  3. Set off

Probable causes and remedies

1. Hold out / not smooth (back to incidents)
 
Cause
Too much anti set-off powder (if wet-on-dry varnishing).
Remedie
Reduce the amount of anti set-off powder. Check the particle size.
Cause
Acrylic varnish over conventional ink.
Remedie
Allow to dry for 24 to 48h before varnishing.
IR or hot air drying of conventional inks is not recommended if
acrylic varnishing.
 
2. Discoloration of the ink film (back to incidents)
 
Cause
Chemical attack by the constituents of the acrylic varnish.
Remedie
Use light fast inks: Rhodamine, Purple, Violet, Blue 072 and Reflex Blue. > See “Fastnesses of inks”.
 
 
Cause
Acrylic varnishing, hot air or IR drying: stack temperature too high.
Remedie
Reduce the amount of IR drying. Maximum recommended stack
temperature: 35°C on the top and 30°C on the reverse side.
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