What are the characteristics of UV ink for UV printers and how to use it?
UV ink is an ink that cures instantly after ultraviolet irradiation and forms a film with excellent physical properties.
1. How to use UV ink
UV ink has the property that its viscosity changes with the temperature (high temperature: low viscosity, low temperature: high viscosity). This viscosity change will have a great impact on printing adaptability and printed film thickness. Generally, when the ink temperature drops, the viscosity increases and the film thickness becomes thicker. When the ink temperature rises, the viscosity decreases and the film thickness becomes thinner. Therefore, try to keep a constant temperature during printing. Generally, 18 to 30°C is appropriate.
Some UV inks absorb moisture when the humidity at the printing site is high, which will cause problems such as increased viscosity and gelation. At this time, an air conditioner or dehumidifier is needed to deal with the problem.
2. UV lamp
Common UV lamps include mercury lamps, LED cold light source lamps, and fan-type and water-cooled types for heat dissipation. Fan-type is easier to maintain than the water-cooled type, but its temperature is easy to rise during irradiation, which causes poor adaptability to printing and thermal deformation of plastic materials. UV lamps have a certain service life, and the light intensity of the lamp also gradually decreases. Before the UV lamp reaches its service life limit, the curing and adhesion of the ink will decrease.
3. Factors affecting curing
(1) Type and color of material. Some types of colored materials have the property of absorbing ultraviolet rays, and the curing of these materials will be slow. In addition, the curing properties of the same type of materials will vary depending on the grade.
(2) The color of the ink is particularly absorbing ultraviolet rays, and the curing of UV ink will be slow. Therefore, the concentration of UV curing ink has a certain limit, especially when combining high-concentration white with dark colors (black, blue, and others), full attention must be paid.
(3) Photocuring initiator. Adding a photocuring initiator is an effective way to improve curing. However, adding too much photocuring initiator will hinder curing.
(4) Printing film thickness. The thinner the printing film, the better the curing property. Generally, sufficient curing performance can be obtained within the film thickness range of 10 to 12μm. If the film thickness exceeds 15μm, poor curing will cause a lack of adhesion.
(5) UV intensity W/cm2 and accumulated light volume J/cm2. The criteria for judging hardening are UV intensity and accumulated light volume. The overall judgment of hardening is determined by the accumulated light volume. The most important factor for the internal hardening of the printed ink film is the UV intensity. When the UV intensity is low, increasing the irradiation time and increasing the accumulated light volume cannot improve the internal hardening of the bottom of the printed ink. In this case, the height of the lamp should be lowered or the power of the lamp should be increased.
(6) The temperature during irradiation and the surrounding temperature during preheating UV irradiation have a great influence on the curing of UV ink. The higher the temperature, the better the curing. Therefore, if preheating is used, the curing of the ink will be enhanced and the adhesion will be better.
4. Precautions
(1) Skin irritation. The skin irritation index (PII) is a reference standard for the safety of UV ink.
(PII) value; 0~1.9 (low); 2.0~2.9 (low to medium); 3.0~5.9 (medium); 6.0~8.0 (strong). UV ink is composed of components with a PI value of less than 1.9 and has low skin irritation. However, try not to let it come into contact with your skin during use. If it gets on your skin, please rinse it off with soapy water. Because it has low skin irritation, it will go unnoticed if it gets on your skin. However, some people may develop inflammation or rashes due to prolonged contact, so please be careful.
(2) Storage safety: Please store UV ink in a dark and cool place away from light. Generally, the shelf life of UV ink is about one year after manufacture. If it is stored at a temperature above 30°C, it is easy to cause gelation and viscosity increase of the ink. Once the ink has been used, do not put the ink back into the container.
(3) Stirring the UV ink that has been stored for a long time. When it needs to be poured into a large ink cartridge for use, it needs to be manually shaken to solve the sedimentation and viscosity reduction caused by long-term static.
(4) Mixing of UV inks: Generally speaking, it cannot be mixed with other series of UV inks.