Washes: Aromatic or aliphatic is the question? - The Avinash Kawadkar blog

There are many claimed benefits that one can derive from using this or that type of wash but often the user experience doesn’t quite match up to the hype. What then are the facts?

But to delve further into it, let’s first look at some basic chemistry.

Aromatic and aliphatic are terms that describe a particular sort of hydrocarbon. Simply put, it is a mix of carbon and hydrogen as the name says and it is like kerosene, petrol and diesel oil. The molecular structure, however, is different and this makes a big difference in its performance and interaction with other chemicals.

From the table, you can see the significant differences with respect to their working on ink, blanket and roller coverings, paintwork, skin, eyes and mucous membranes. 

The strong solvent action stems from greater penetrating power. It also means that wet ink films are penetrated quickly resulting in a rapid reduction in viscosity and then is cleaned with the cloth/rags which is a mechanical process. As seen earlier in this article, quick penetration is true for rubber as well as skin, resulting in possible irritation. Rapid penetration of blanket and roller covering compounds shows up as swelling.

Biodegradable is a term that needs to be always with a prefix like – non, readily or inherently. Poor biodegradability of aromatics tends to kill the microorganisms that usually act in the process of biodegradation. Thus, aromatic hydrocarbons can be considered to be non-biodegradable. And due to its reaction with the skin, it needs to be used with proper care. Use of hand gloves (not latex) therefore is strongly recommended.

As clearly seen in the table, aliphatic hydrocarbons are poor at penetrating, thus slower to work on wet ink films meaning that more mechanical energy is required for the removal of ink from substrates with aliphatic-based washes. To overcome this, automated wash-up systems for roller train and blankets is recommended. Everything else however is a positive, which is - lower odour, low skin irritation potential, low toxicity, low swell characteristics on roller and blanket coverings when compared to aromatic containing washes and most importantly are readily biodegradable.

World trend: Offset printing industry worldwide is changing over to the use of washes made from aliphatic hydrocarbons.

Factors to be considered by manufacturer and user can be summarised as: Solvency power and drying speed.

Solvency power affects the speed that the solvent works at and is controlled by the manufacturer by varying the ratio of aromatic to aliphatic hydrocarbons that is blended together.

Drying speed is directly proportional to flash point, which we have seen needs to be greater than 60 deg C to qualify for OEM approval. So, to reiterate, aromatic solvent washes dry faster and aliphatic solvent washes dry slower.

Machine operators using manual cleaning prefer aromatic washes because they require a minimum effort and dry faster.

Issues with fast drying: solvent evaporates quickly leaving a dry surface; it also means that the air steadily becomes full of that solvent vapour, which in an extreme case can cause both a fire hazard and a health hazard. 

Issues with slow drying: solvent remains in contact with the substrate longer which may become an issue if the blend contains aromatic hydrocarbons as this can mean a greater risk of damage to the rubber compounds used in the roller/blankets. These washes are less efficient allowing the buildup of oxidised ink vehicle glaze on roller surfaces. Therefore, when choosing it, the maintenance schedule of deglazing is needed. Glaze is a separate subject in itself, please look forward to a separate article on same in this space in coming weeks.

Conclusion: Using of aliphatic hydrocarbon-based washes, preferably with automatic washup systems are recommended owing to environment and safety. It is relatively easier to manage the efficiency related and its peripheral issues stated in this article over non-biodegradable and high irritancy potential material. Automation to using wash-up systems will, of course, allow it to happen faster.

 

Chris Searle
Chris Searle is the author of the article. He is an industrial chemist who has been working in graphic arts industry for over 30 years. Chris has been spearheading TechNova’s technological advances in chemical business for years, the objective has been to offer its customer with new solutions. He spends significant amount of time in India to work with team TechNova.