With the introduction of solvent inkjet printers in the 1990s, the digital printing industry first faced the term “VOCs”. There has been much written about VOCs and inkjet inks. This has resulted in a lot of confusion about what they are, the dangers they present in our industry and how a user of the technology must deal with them to conform to safety and air quality regulations. Today, many different ink chemistries are used in this industry. Printer manufacturers and ink companies make claims of all kinds about their inks and the “VOC” consequences of using them. I will try to clarify here what VOCs mean and the consequences with the various ink types currently in use.
WHAT IS A “VOC”?
The American Solvents Council, made up of a group of petrochemical giants like Exxon/Mobil and Shell Oil, has summarized this subject very succinctly in a white paper from which I quote extensively.
The term “VOC” is an acronym for “Volatile Organic Compound.” In inkjet terms, those are the solvents used in the inks that contain carbon and evaporate into the air both during the printing process and when an ink container is opened. Water is not a VOC, but just about all the other materials that evaporate from ink are. Essentially, all inkjet inks have some organic compounds that evaporate. This includes UV-curable and water-based inks. The important issues to the user of inkjet inks are: which VOCs are in the ink, how much of each evaporates, and what do they do to people and the environment. Another important issue is compliance with local, state or national laws governing their emission.
Because VOCs are subject to regulation, the question “What is a VOC?” is a critical one. The EPA has established a very broad general definition of a VOC. “Any volatile compound of carbon” is classified as a VOC for regulatory purposes unless it appears on a list of compounds that have been specifically exempted. This gets very complicated, since state lists of exempt compounds vary. If you use large amounts of inks, you will need to consult the local regulations governing VOCs to determine what you need to do to comply with the law.
VOCS AND OZONE FORMATION
Emissions of VOCs, in and of themselves, don’t necessarily give rise to health or environmental concerns. In many geographic areas, however, they react with nitrogen oxides in the presence of heat and sunlight to form ground-level ozone — the primary component of smog. For that reason they are regulated under the federal Clean Air Act and similar state laws.
In order to reduce ozone levels, federal and state agencies have developed regulations to reduce VOC emissions from a variety of sources, including products that contain solvents. In some cases, regulations require the installation of a control device such as an incinerator, a catalytic reactor or a solvent recovery system. This is usually the case in urban areas where large amounts of solvent inks are used.
One significant new development in the regulation of VOCs involves the use of “relative reactivity” to rank a chemical’s potential to contribute to the formation of ground-level ozone. A solvent with low potential to form ozone produces less smog, so the government allows more of it to be released without the need for emission control devices. To determine how you may be affected, consult your ink supplier and local regulations.
SOLVENT AND MILD SOLVENT INKS
The largest source of VOCs in the inkjet industry is the grand-format strong solvent printer user who consumes many liters of ink per day. These solvents are fairly high in the “relative reactivity” rankings, and, depending on the geographic area in which they are used, may require installation of a control device to meet local VOC emission requirements. Mild solvent inks are less reactive and are usually used in much smaller amounts. From an EPA perspective, these are much less important; they can be important from an OSHA perspective unless the printers are properly vented.
Solvent ink systems vary widely. Since many grand-format printer companies select inks from third party ink providers, and some are imported from outside the U.S., one should always request an MSDS on each ink and study it carefully. In the MSDS, the ink supplier should disclose the major solvent components in the ink. In some cases, the MSDS does not specify ingredients that are considered proprietary and are kept as trade secrets. They must, however, indicate the nature of the materials and the hazards they present to both the user and the environment. If they do not provide this information, request it before using the ink. Some imported inks may contain ingredients with significant health risks. It pays to be cautious.
Some of the new “green” solvent inks contain bio-degradable materials, like ethyl lactate, which decompose in the atmosphere and do not react to form ozone. These represent a particularly desirable class of solvents from a safety and environmental perspective since they pose only a very limited hazard.
WATER-BASED AND UV-CURABLE INKJET INKS
Contrary to popular beliefs, there are VOC components in nearly all water-based inks used in wide-format printing. These are largely glycols and alcohols. However, unlike solvent inks, where the VOC components may represent up to 95 percent of the ink by weight, in water-based inks the VOC components rarely make up more that 25 percent of the ink by weight. As a result of generally lower ink consumption, and a lower percentage of VOC components, these printers rarely cause concern for VOC emissions. In addition, the solvents used are not very toxic to humans, and present a low level hazard from an OSHA perspective as well.
UV-curable inks are a different story. They contain VOC compounds when in liquid form, some of which are very toxic to humans. Care should be taken to avoid allowing the inks to evaporate, and to be sure they completely cure during the printing process. If this is done, VOC compounds are no longer volatile and no VOCs will remain to evaporate.