In recent years, UV varnishes have been increasingly used after printing patterns using UV printers. As a key post-printing process, this technology not only imparts a high-gloss mirror effect to printed materials, significantly enhancing the visual appeal of the patterns, but also, through its unique curing properties, creates a wear-resistant and scratch-resistant physical protective layer for the printed materials. Simultaneously, it greatly enhances the product's weather resistance, effectively resisting the effects of environmental factors such as ultraviolet radiation and temperature and humidity changes. However, in actual production applications, due to limitations such as equipment precision, process parameter matching, and operational standardization, this technology still faces several technical bottlenecks that need to be overcome.
1. Poor gloss and insufficient brightness
main reason:
(1) The UV varnish viscosity is too low, resulting in a thin coating;
(2) Excessive dilution with non-reactive solvents such as ethanol;
(3) Uneven application of UV varnish.
Solution: Adjust the viscosity and application amount of UV varnish according to the specific materials used.
2. Poor drying, incomplete light curing, and sticky surface.
main reason:
(1) Insufficient ultraviolet light intensity;
(2) The UV lamp tube is aging and its intensity is weakening;
(3) UV varnish has been stored for too long;
(4) Too much diluent that does not participate in the reaction was added;
(5) The printing speed of the machine is too fast.
Solution: If the curing speed requirement is less than 0.5s, the power of the LED curing lamp must be guaranteed to be no less than 120w/cm. The lamp tube (bead) should be replaced in time, and it should not be replaced until it breaks.
3. UV varnish not applying properly to printed materials, or causing uneven coloring.
main reason:
(1) The UV varnish has low viscosity and the coating is too thin;
(2) The ink contains too much ink thinner or drying oil;
(3) The ink surface has crystallized.
Solution: When printing products that require UV coating, apply the UV varnish more thickly. If necessary, the problem can be solved by changing to a special varnish.
4. White spots and pinholes in UV varnish.
main reason:
(1) The coating is too thin;
(2) Too much non-reactive diluent (such as ethanol) was added;
(3) Printed materials have a lot of dust on their surface.
Solution: Keep the production environment and the surface of the printed materials clean, and increase the coating thickness.
5. Uneven coating on the surface, with streaks.
main reason:
(1) The viscosity of the UV varnish is too high;
(2) The coating is too rough and not smooth;
(3) Applying too much product;
(4) UV varnish has poor leveling properties.
Solution: Reduce the viscosity of the UV varnish and decrease the amount applied.
6. Poor adhesion of UV varnish
main reason:
(1) Crystallization of ink surface in printed materials;
(2) The auxiliary materials in the printing ink are unsuitable;
(3) The UV varnish itself has insufficient adhesion;
(4) The light curing conditions are not suitable.
Solution: The printing process should take into account the conditions for applying varnish in advance.
7. UV varnish thickens and gels.
main reason:
(1) UV varnish has been stored for too long;
(2) The varnish was not stored in complete darkness;
(3) The storage temperature was too high;
Solution: Pay attention to the effective shelf life of UV varnish and store it strictly away from light. The storage temperature should be between 5℃ and 25℃.
8. Strong residual odor
main reason:
(1) Incomplete drying and curing;
(2) Insufficient ultraviolet light source or aging lamp tube;
(3) UV varnish has poor resistance to oxygen interference.
Solution: The UV varnish must be thoroughly dried and cured, and ventilation should be improved.
The effectiveness of UV varnish applications depends on the synergy of materials, equipment, and processes. Companies need to establish standardized operating procedures, implement process control using tools such as viscometers, film thickness gauges, and gloss meters, and regularly train operators on varnish characteristics and equipment maintenance. In the future, with the promotion of environmentally friendly products such as water-based UV varnishes and low-migration varnishes, and the integrated application of AI visual inspection systems in coating processes, UV varnishing processes will evolve towards greater efficiency, greener practices, and greater intelligence. Only by continuously refining technical details can we use light as a medium to achieve a dual enhancement of quality and value.