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Common Problems and Solutions in the Use of UV Varnish

Release time:

2014-05-27 09:23

Common Problems and Solutions in the Use of UV Varnish
Common Problems and Solutions in the Use of UV Varnish

UV varnishes pose two main challenges for packaging and printing plants: First, they are sensitive to operating conditions during seasons with high temperatures and humidity; second, they are vulnerable to excessive moisture content in the substrate. Under these workshop conditions and given the substrate’s moisture levels, the ink or adhesive film applied during printing or varnishing is highly likely to peel off when initially inspected using adhesive tape, leading to product returns by customers. In addition, there are numerous common issues associated with the use of UV varnishes. What are the primary causes behind these problems? What are their direct manifestations? And what are the effective solutions?

1. Poor luster and insufficient brightness

Main reason:

1. The UV oil has too low viscosity, resulting in a coating that’s too thin.

2. Excessive dilution with non-reactive solvents such as ethanol

3. Uneven UV coating application

4. The paper is too absorbent.

5. The mesh pattern on the glue-coating roller is too fine, resulting in insufficient oil supply.

Solution: Adjust the viscosity and coating amount of the UV varnish appropriately according to the specific characteristics of the paper. For papers with high absorbency, you can first apply a primer coat.

2. Poor drying and incomplete curing result in a sticky surface.

Main reason:

1. Insufficient UV light intensity

2. The UV lamp tube has aged, and its light intensity has weakened.

3. UV varnish has been stored for too long.

4. Excessive addition of diluents that do not participate in the reaction

5. The machine is running too fast.

Solution: When the curing speed is less than 0.5 seconds, the power of the high-pressure mercury lamp should generally be no less than 120 W/cm. The lamp tubes should be replaced promptly, and if necessary, a certain amount of UV varnish curing accelerator can be added to speed up the drying process.

3. The UV varnish cannot be applied to the surface of the printed material, resulting in a mottled appearance.

Main reason:

1. The UV varnish has too low viscosity, resulting in a coating that is too thin.

2. The ink contains too much blending oil or drying oil.

3. The ink surface has crystallized.

4. Excessive anti-sticking materials on the ink surface (silicone oil, spray powder)

5. The mesh lines on the coating doctor blade roller are too fine.

6. Issues with construction techniques (the technical staff aren't very skilled).

Solution: For products requiring UV coating, appropriate measures should be taken during printing to create favorable conditions: the UV varnish can be applied slightly thicker; if necessary, a primer coat can be applied, or a special varnish formulation can be used.

4. The UV coating has white spots.

1. The coating is too thin.

2. The coating doctor blade roller is too fine.

3. Excessive addition of non-reactive diluents (such as ethanol)

4. The surface of the printed material has a lot of dust and other particles.

Solution: Keep the production environment and the surface of printed materials clean; increase the coating thickness; add a small amount of smoothing additive; preferably, use a reactive diluent that participates in the reaction as the solvent.

5. Uneven UV coating, with streaks and an orange-peel texture.

Main reason:

1. The UV varnish has excessive viscosity.

2. The mesh lines on the coating doctor blade roller are too coarse (resulting in excessive coating amount), and the surface is not smooth.

3. Uneven coating pressure

4. UV varnish has poor leveling properties.

Solution: Reduce the viscosity of the varnish and decrease the coating amount; ensure even pressure adjustment; grind and polish the coating rollers thoroughly; add a gloss-leveling agent.

6. Poor adhesion of UV varnish

Main reason:

1. Crystallization on the surface of printing ink

2. The additives in the printing ink are inappropriate.

3. The UV varnish itself has insufficient adhesion.

4. The light-curing conditions are inappropriate.

Solution: The printing process should take into account the varnishing conditions in advance; apply a primer to the already printed products to enhance adhesion.

7. The UV varnish has thickened and exhibits gelation.

Main reason:

1. UV varnish has been stored for too long.

2. The UV varnish was not stored completely away from light.

3. The storage temperature of UV varnish is too high.

Solution: Pay attention to the expiration date of UV varnish and store it strictly away from light. The ideal storage temperature is between 5°C and 25°C.

8. Strong residual odor

Main reason:

1. UV varnish curing is incomplete.

2. Insufficient ultraviolet light or aging UV lamp tubes

3. UV varnish has poor resistance to oxidative interference.

4. Excessive addition of non-reactive diluents in UV varnish.

Solution: UV varnish curing must be thorough, and ventilation should be enhanced. If necessary, the type of varnish should be changed.

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