Offset printing ink is vital in the printing industry as it directly affects the color and quality of printed items. To understand it better, let’s focus on five key technical aspects.
Firstly, consider ink concentration, which is assessed by measuring color strength. Higher ink concentration leads to richer colors, especially noticeable in large solid areas.
Next, let’s talk about ink density. This aspect reflects the particle size and uniform distribution of pigments and fillers in the ink. Finer ink results in more stable properties and produces prints with fuller and stronger dots. Conversely, poor fineness can cause issues like low plate resistance, ink pile-up, weak dots, and uneven dot expansion.
Moving on to ink viscosity, which is measured using an ink viscosity tester. It refers to the force required to separate the ink film between two rolls of the viscosity tester. Both excessively high and low ink viscosity can affect print quality. It’s important to adjust the relative viscosity of inks based on the printing sequence. While ink viscosity typically doesn’t need adjustments under normal conditions, additives can be selected based on viscosity and thickness if necessary.
The fourth aspect is ink gloss, which is the ratio of reflected light from an ink sample under specific light and angle conditions to the reflected light from a standard plate, expressed as a percentage. Higher gloss usually means better printing results. Although printing gloss is influenced by factors like dampening solutions and paper absorbency, ink composition, especially binders and pigments, plays a primary role. Ink binders and pigments should have good printing compatibility, and resin itself contributes to high gloss. Only with such ink can prints achieve a high gloss on paper.
Lastly, ink drying properties are crucial. The drying process of offset printing ink on paper involves transforming from a highly fluid non-polar gel into a fixed state. This is typically measured by ink fixation speed and surface drying indicators.
Most offset printing inks are resin-based, offering fast fixation speeds. Faster initial drying is theoretically preferable. From a drying and surface formation perspective, there are two main types:
- Conventional ink dries through oxidation, penetration, and solvent evaporation, which can take considerable time, especially for large-area prints.
- UV ink, a solvent-free ink cured by ultraviolet light, polymerizes rapidly upon UV light exposure, forming a cured ink film with high gloss and abrasion resistance. However, it comes at a relatively higher cost.
Understanding these five technical aspects of offset printing ink helps industry professionals choose suitable inks, ultimately enhancing print quality and efficiency.
