Washful thinking

Recently, while performing a pollution prevention assessment for a medium-sized printer, I completed a study on the pros and cons of using an auto blanket wash system (as opposed to manual cleaning). Even though their Roland press equipment was equipped with an Autowash system, all cleaning of blankets and rollers on the presses is done manually using solvent-soaked rags (printer’s towels).

I found out that this practice is not as unusual as I thought in our industry. Manual cleaning can be an expensive, hazardous and environmentally questionable practice, for several reasons. First, there is a total loss of the solvent. Second, it involves excessive use (at great cost) of printers’ towels, which have to be picked up and laundered off site—the laundry service charges a premium for handling hazardous solvents, an energy surcharge, and an “environmental charge” for solvent disposal (even though it can be recaptured for re-sale). Third, there are greater reportable VOC emissions. Finally, press operators have more contact with hazardous solvents.

This particular print shop did not use their Autowash system because of a problem with the particular solvent used, which created an oily residue that dripped onto the paper stock. Other reasons included the cost of collecting the large amount of used solvent & water mix from the holding tanks and the hazardous nature of the manufacturer-recommended solvent used for their Autowash systems.

A study done many years ago by Baldwin indicated that, on a per-cleaning basis, the volume of solvent required to clean the same area of a blanket was less with an automatic system. I have no real reason to dispute the general claim, but what is interesting is that printers that installed these systems have reported that there was an overall increase in total solvent consumed and emitted. There could be a variety of reasons why this seemingly paradoxical increase in solvent use occurs, but it was clear that overall solvent consumption rose when they installed auto systems.

Benefits to Autowash

Today, the end benefit of using an auto blanket wash system is the ability to recapture, recycle, and reuse the cleaned solvent. This recapturing can save up to 80% (there is always some loss) of the cost for solvent purchases and reduces the corresponding reportable VOC emissions. Recycling units such as those made in Ontario by Uni-Ram are specifically designed to handle water-miscible blanket washes. They distill and separate water from the solvent, rendering clean water for reuse or safe disposal as well as the cleaned solvent. The other benefits to an auto wash is reduction in the number and costs of printer’s towels and the pressman’s reduced contact with hazardous solvents.

There are now many less toxic and lower VOC auto blanket washes available than there were in previous years. On striking a balance between cleaning efficiency, lower VOC emissions and toxicity, I would recommend you consider vapor pressure as the key component. Check the manufacturer’s technical and material safety data sheets for comparisons. Washes with low vapor pressures allow you to have solvency, no oily residue, and minimal employee exposure. A good starting point is to look at washes that have vapor pressure of less then 5 mm Hg at 20 degrees C or 68 degrees F.

Avoid solvents with aromatic content—such as xylene, cumene, toluene, naphthalene etc—because the aromatic solvents have more and greater toxic effects. Finally, consider the flash point. Generally, solvents with high flash points have low vapor pressure. High flash point is also safer, as it is less flammable. My preferred solvent materials are aliphatic petroleum distillates and C11 Cycloalkane. Such solvents have low vapor pressure, high flash points, and low photo-reactivity. Remember that Volatile Organic Compounds (VOC) are smog precursors. By reacting with Ultra Violet rays (sunlight) they create low-level ozone that captures carbon and nitrous oxides and particulate emissions over our cities. Strong sun is why smog is so prevalent in summer.

No one that I know has done any study comparing hand wipe to auto system usage. However, the state of California is pushing to reduce the VOC content of roller and blanket wash to less than 100 grams per liter. I hesitate to recommend any particular solvent because it depends largely on the wash system, rollers, and type of press, but the recommendations that follow are based on my personal experience, for what that is worth.

From the study I conducted of over 50 solvents acceptable for Auto Wash systems; Anchor (Fuji), Day-Varn, and Rycoline have products that meet the above-mentioned criteria. Also, Tower Products and Printers Service (Prisco) have products on or coming on the market in the next month or so. Currently, over three dozen printers in the USA are using vegetable-based solvents out of Europe (Bottcher and Vegra). It seems that because of the chemical makeup of the solvents, printers use much less solvent (50-60 percent) in both hand and auto wash. I have been testing a Canadian product from Eco-Mist that is also vegetable- and tree-extract based. The waste stream depends on the type of solvent used, and the size and number of presses. However, the low vapor pressure, high flashpoint solvents generally generate more waste than their counterparts.

I will be involved with the testing of a number of the newer products in an auto-wash system and will keep you posted. In the meantime, if any reader has experience with an auto-wash solvent (good or bad), please let me know by emailing ecosafe@rogers.com.