UV varnish common problems and solutions

UV varnish common problems and solutions

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1. Poor gloss and insufficient brightness

Main reasons:

1. The viscosity of the UV varnish is too low, resulting in an overly thin coating.
2. Excessive dilution with non-reactive solvents such as ethanol.
3. Uneven application of the UV varnish.
4. The paper has high absorbency.
5. The anilox roller mesh is too fine, resulting in insufficient varnish supply.

Solution:
Appropriately increase the viscosity and coating thickness of the UV varnish according to the paper type. For highly absorbent paper, apply a base coat first.

2. Poor drying, insufficient light curing, and sticky surface

Main reasons:

1. Insufficient ultraviolet light intensity.
2. Aging UV lamps with reduced output.
3. Excessively long storage time of the UV varnish.
4. Excessive addition of non-reactive diluents.
5. Excessive machine speed.

Solution:
When the curing speed requirement is less than 0.5 seconds, ensure that the power of the high-pressure mercury lamp is not less than 120 W/cm, and replace aging lamps in a timely manner. If necessary, add an appropriate amount of UV curing accelerator to improve drying speed.

3. UV varnish cannot be applied smoothly; surface appears rough or hairy

Main reasons:

1. Low viscosity of UV varnish and insufficient coating thickness.
2. Excessive varnish or drying oil content in the ink.
3. Crystallization on the ink surface.
4. Presence of anti-adhesive materials (such as silicone oil or powder spray) on the ink surface.
5. The rubber-coated roller is too thin.

Solution:
When printing products that require UV coating, appropriate preparatory measures must be taken. Increase the coating thickness during UV varnishing. If necessary, apply a base oil or replace it with a special varnish.

4. White spots and pinholes in UV coating

Main reasons:

• The coating layer is too thin.
• The anilox roller mesh is too fine.
• Excessive use of non-reactive diluents (such as ethanol).
• Dust contamination on the surface of the printed material.

Solution:
Keep the production environment and the surface of printed materials clean, and increase the coating thickness. A small amount of leveling agent may also be added. Reactive diluents that participate in curing are preferred.

5. Uneven coating surface, streaks, or orange peel

Main reasons:

1. Excessively high viscosity of UV varnish.
2. Coating roller surface is too rough or uneven.
3. Uneven pressure distribution.
4. Excessive coating amount.
5. Poor leveling performance of the UV varnish.

Solution:
Reduce the viscosity and coating amount of the UV varnish. Adjust the pressure evenly. Grind and polish the coating roller if necessary. A suitable leveling agent may be added.

6. Poor adhesion of UV varnish

Main reasons:

1. Crystallization of the printed ink surface.
2. Incompatible auxiliary materials in the printing ink.
3. Insufficient adhesion properties of the UV varnish itself.
4. Improper photocuring conditions.

Solution:
Glazing requirements should be considered during the printing process. A primer that enhances adhesion should be applied before UV coating.

7. UV varnish thickening and gelling

Main reasons:

1. Excessively long storage time of the UV varnish.
2. Incomplete protection from light during storage.
3. Excessively high storage temperature.

Solution:
Pay attention to the effective service life of UV varnish and strictly avoid light exposure during storage. The recommended storage temperature is 5°C to 25°C.

8. Strong residual odor

Main reasons:

1. Incomplete drying and curing.
2. Insufficient ultraviolet light intensity or aging lamps.
3. Poor oxygen inhibition resistance of the UV varnish.
4. Excessive addition of non-reactive diluents.