CURING UV

UV ink fails to cure in the correct place on the press.

As UV inks and coatings are exposed to ultraviolet light:

  1. Little or no exposure - ink remains liquid;
  2. Polimerizzazione parziale (di solito si tratta solo della superficie)
  3. Partial curing (usually surface only) with possible 'skinning' and generally poor adhesion to the substrate;
  4. Tacky surface, common to under curing;
  5. 'Correctly cured' with no tack, low odour, flexible and with good adhesion;
  6. Increased surface hardness that can become brittle with poor over printability;
  7. Primary ink surface not receptive to secondary inks resulting in poor adhesion and low  flexibility with flexo and letterpress processes.

 

Causes:

- Direct exposure to sunlight or to general lighting sources;

- Smell from ink;

- Ink is reticulating on top of the first colour (often screen white);

- Cured ink has poor adhesion to the film substrate;

- Lamp problems:

  1. Low lamp power setting;
  2. Weak exposure bulbs;
  3. Dirty lamp reflectors;
  4. Incorrect lamp focus.

 

Solutions: 

- Eliminate direct  exposure to sunlight. Use UV filter covers on light above the press;

- Ink not sufficiently cured. Turn up UV lamp power to a minimum of 100 W/cm and check the lamp and reflectors are clean. Reduce press speed to increase UV lamp dwell time;

- Over curing the white ink. Turn the lamp power down to a point where there is no surface tack but good secondary ink reception;

- Excessive curing of the ink causing shrinkage of the ink film. Turn the power of the lamps down to a minimum and also check the dyne level of the film.

- Lamp Solutions: 

  1. Increase lamp power setting;
  2. Replace exposure bulbs;
  3. Clean lamps reflectors;
  4. Adjust focus to optimal distance.