Solution for some attachment failures of UV inks

What is the role of UV ink adhesion promoter?

When the adhesion of UV ink to the substrate is poor, adding the additive can increase its adhesion to the substrate, and the added amount is generally not more than 3%.

What are the reasons for the incomplete UV ink curing and surface stickiness and how to solve it?

(1) Lamp aging. Flexographic UV inks absorb UV light at wavelengths of 200-400nm, and generally require more than 150W/cm to completely cure. The medium-pressure mercury lamps currently used have an average service life of 1,000-1500 hours, gradually decomposing as the electrodes of the lamps are used. The inner wall of the lamp tube is deposited, and the transmittance of the transparency and ultraviolet light is gradually weakened. Therefore, the lamp tube should be tested regularly and the lamp tube should be replaced in time.

(2) The power of the light source is not enough. The fast printing speed is also the cause of incomplete UV ink curing and surface stickiness. This can reduce the printing speed or increase the power of the light source.

(3) The UV ink itself cures slowly. Can add photo-curing accelerators, reduce printing speed or find ink suppliers to solve.

(4) Some manufacturers use ethanol to dilute UV inks, and excessive ethanol will affect the degree of light curing, resulting in incomplete photocuring and surface stickiness. Therefore, it should be avoided to use ethanol dilution. If it is necessary to reduce the viscosity of ink, UV ink thinner can be used.

Why does the phenomenon of unsatisfactory adhesion occur when UV inks are used to print films such as PE, BOPP, and PET?

(1) The corona treatment on the surface of the film is not enough. Generally, the surface tension should be 3.8x10N-2/m or more in order to obtain good adhesion of the ink.

(2) UV ink is not cured enough. Therefore, it is necessary to ensure that the UV ink is completely cured.

(3) UV ink shrinkage greatly affects adhesion. Adding a certain amount of monofunctional reactive diluent or a small amount of filler can increase the adhesion.

In addition, the addition of a UV ink adhesion promoter can increase the physical adsorption of UV inks and substrates, thereby increasing adhesion.

How to solve the problem of poor stability during UV ink storage?

(1)UV inks are exposed to light or heat-prone to cross-linking. Therefore, direct light irradiation should not be used during use, and long-term storage in environments above 30C is not allowed. It must be ventilated under 16-28C and protected from light.

(2) In order to increase the speed of photo-curing, adding an excessive amount of photoinitiator also affects the stability of the UV ink. Therefore, excessive photoinitiators should be avoided.

(3) Improper mixing of UV inks produced by different manufacturers can also cause changes in the stability of UV inks. Therefore, when the ink needs to be mixed, it must be tested first, and it can be mixed without any reaction.