Why ink forms a skin in the ink fountain
Iran Shoraka developed Optima Plus in the Iranian calendar year 1399 (2020–2021). The launch-era article describes resistance to skin formation for 48–72 hours after opening the tin, helping printers reduce waste and cost. The Optima Plus product specification lists resistance to skin formation in the ink duct for up to 48 hours.
What is ink skinning?
Skinning during storage or printing creates several problems: higher ink consumption and printing costs, and lower print quality. Controlling the rate and extent of drying before and during printing is therefore important. Skinning is the formation of a gel-like layer where ink meets air, associated with oxidation, penetration, volatility or evaporation at room temperature. As the ink becomes more concentrated, a surface layer forms. Adding solvent or oil to reduce the concentration does not make the formed skin usable again.
The article estimates that skinning can increase printing costs by 1–4%, creating a significant burden for printers and packaging workshops. The effect on quality also matters. Pieces of skin can be carried into the ink by the blanket and interfere with correct transfer. If they adhere to the plate, ink density varies across the plate and the resulting defects become visible in the printed work.
The main causes of skinning
1. Too much drier in the ink. This may occur during manufacture or when additives are introduced on press. Drier additions need to reflect printing conditions and ambient temperature; otherwise the ink can dry before it is needed.
2. A rise in ink temperature, which speeds surface oxidation. Possible causes include a hot pressroom, excessive pressure between rollers or at the blanket and plate, hot-air leakage from the dryer, or unusual heat generated elsewhere in the press. Skinning is more often observed in summer and in pressrooms without cooling. The article identifies around 20°C as a suitable pressroom temperature for ink flow and transfer. Accurate roller-pressure adjustment also helps limit heat generation and skin formation.
3. Excessive contact with air. Ink components react with oxygen and form a surface skin. Interruptions such as power cuts or press breakdowns are normal possibilities during a run. If the ink skins while the press is stopped, the skin must be separated from the remaining ink and discarded before printing resumes. This wastes both ink and time.
Optima Plus and Optima Plus HD
Resistance to skinning on press is an important ink property. Optima Plus was developed with this performance in mind. The historical article discusses a 48–72-hour period after opening the tin; use the product specification for the stated performance of the selected grade.
Other benefits described for the Optima series are fast drying on the printed work, low tack for printing on uncoated and coated paper, and bright prints with a high-gloss finish.