In UV printing, there are often problems with poor ink drying, or ink drying is too fast. We must know the reasons to solve the problem. Let's talk about 6 reasons to help you check in the production process.

1. Too thick ink layer

In large-area printing, due to too much ink and too thick ink layer, the ink on surface of the printed product will be completely dry while the bottom ink is not completely dry. This is called false drying. In addition to the thick ink layer, too fast paper feeding speed and insufficient exposure time of UV light can also cause false drying.

If it occurs, it is easy to cause the ink layer to fall off during the post-processing. The incompletely dried ink has a poor bonding strength with the surface of the substrate, causing the ink to be scraped and fall off under friction.

Solution

If you use spot color UV ink for printing, try to make the ink darker when mixing it, so that the bottom layer of the ink can be completely dried by reducing the amount of ink during the printing. The bonding strength between the bottom layer and the surface of the substrate can be increased.

It is also necessary to ensure a suitable feed speed of paper and sufficient exposure time of UV light. If the paper feed speed is fast, the power of the UV light must be increased to ensure ink drying effect.

2. Insufficient power of UV light

Insufficient power of UV light is also one reason for poor drying of ink. This is related to the daily production.

a. All UV lights have service life (usually 800 to 1000 hours). When the UV light is used for more than its service life, although it can continue to work, the power has been greatly reduced.

b. After replacing the UV light, the usage timer was not reset to zero, resulting in the usage time exceeding its service life without anyone knowing it.

c. You don't pay attention to surface cleaning of UV light. After long-term use, the reflector is too dirty, resulting in the loss of reflected energy of the UV light (the reflected energy can account for about 50% of the power).

d. Unreasonable power configuration of UV light can cause problems. For example, the reasonable power configuration in a full-rotary self-adhesive label printing machine is above 3000W, while the unqualified printing machine is only 2000W.

Solution

a. You must establish a complete and effective management system of UV lights. It ensures that the UV light works within its effective service life. Replace UV lights that have exceeded their service life in a timely manner, and reset the use timer after replacing UV lights.

b. Clean the reflector of the UV light regularly to reduce the loss of its reflected energy.

c. Reasonably configure the power of UV light according to the structural features of the equipment.

3. Ink exceeds its shelf life, or additives are excessive

Generally, if the shelf life is exceeded, the photoinitiator in ink may become ineffective after printing, resulting in poor ink drying.

In printing, to improve the performance of ink, additives such as ink oil and detackifier are often added. If the proportion of additives is too high, the ink may be too thin. It causes poor drying.

UV ink has thixotropy, that is, it will become thinner and thinner under the shear force of the ink roller. Moreover, after the printing equipment has been running for a period of time, the friction between the ink rollers will generate heat, thereby reducing the viscosity of ink.

Solution

a. Ensure that the ink is used within its shelf life.

b. Pay attention to the amount of ink adjuvants and desiccants. The proportion of ink additives should not exceed 3% in summer, and not exceed 8% in winter.