Master a Few Points to Easily Solve Common 'Troublesome Issues' with UV Inks
Following up on the previous article (How to Choose and Use UV Inks? A Quick Overview), the author briefly explains some key points and precautions when selecting and using UV inks. However, during the use of UV inks, problems often arise, such as poor curing, weak adhesion, and ink piling, which can baffle label printing companies. In this article, the author will briefly discuss these issues.
01
Poor Curing Phenomenon and Solutions
When UV ink is not fully cured, the ink layer has poor adhesion, which can cause the ink to stick to the back of adjacent prints during printing, resulting in smudges. At the same time, the ink surface will be less resistant to abrasion and can easily be scratched during post-processing or use, seriously affecting print quality.
The most thorough way to solve incomplete curing of UV ink is to switch to a UV ink with a faster curing speed. You can also use ink with higher color density and apply a thinner ink layer to achieve the desired color, which improves curing efficiency and ensures complete ink curing. In some cases, without changing the ink, adding a small amount of surface lubricant additive or curing assistant can improve UV ink curing efficiency and achieve complete curing. However, generally, adding additives is not recommended to avoid chemical reactions.
02
Weak Adhesion Phenomenon and Solutions
Poor ink adhesion is not always caused by the ink itself; it is closely related to the surface properties of the substrate. When changing or adjusting the ink does not solve the problem and changing the substrate is not an option, printing companies have two solutions to choose from.
Solution 1: Before printing the color ink, apply a transparent medium with excellent adhesion using printing, which improves the surface properties of the substrate and allows UV ink to adhere well. This method is applied in the first unit of the printing press using UV curing.
Solution 2: Coat the substrate surface with a water-based varnish before printing to resolve adhesion issues like ink splattering or spreading. The water-based varnish is applied by roller coating and dried with infrared. This solution is designed for substrates like metallic or holographic cardboard, which have unstable UV ink adhesion.
03
Ink Piling Issue Analysis and Solutions
Ink piling refers to ink accumulating on the blanket, printing plate, and rollers, causing poor ink transfer and resulting in blurry images on the printed material (see Figure 4). The main causes include poor ink flow, poor ink transfer, paper dust mixing with the ink, insufficient ink fineness, and in offset printing, emulsification of ink by fountain solution.
To solve ink piling, use tack reducers or anti-set-off agents to adjust the ink's tack and viscosity. For offset printing, use ink with good water resistance and avoid using too much water during printing.
Generally, the faster the UV ink cures, the harder the ink layer surface, the lower the flexibility, the weaker the adhesion on the substrate, and the lower the gloss of the print. Additionally, many ink suppliers offer inks suitable for different substrate surface properties.
In short, label printing companies should consider all factors carefully when choosing and using UV inks and make balanced decisions. When printing problems occur, it's crucial to target the solution appropriately.