Originally flexographic inks used coal tar or aniline dyes dissolved in alcohol. Although the coal tar has been replaced with other pigments, alcohol and other organic solvents are still commonly used in ink formulated to print on plastic film, metallics, and paper or paperboard. Drying on press occurs by evaporation and is aided by dryers placed between print stations on press and a final tunnel dryer. Solvents are chosen primarily for appropriate drying rates, good solubility of the resin vehicle and good flow of the ink system.
The solvent used in ink may be organic solvent, water or a mixture. Organic solvents are usually volatile organic compounds (VOCs). Printers are required by law to control emissions of VOCs. Some solvent-based inks exceed 80 percent solvent.
Commonly found VOCs in inks are ethanol, ethyl acetate, ethylene glycol, glycol esters, hexane, isopropanol, nmethanol, methyl ethyl ketone, mineral spirits, naphthas, normal propyl acetate, normal propyl alcohol, toluene and xylene. Concentrations of these chemicals should be listed on the Material Safety Data Sheet (MSDS), which accompanies the ink or solvent.
Best Management Practices & Pollution Prevention
If a facility is located in an area where VOC emissions must be reduced, there are usually two control options: use inks that have a low VOC content, such as water-based or radiation cured inks; or install an emission control device to destroy VOC emissions. In some cases, a permanent total enclosure (PTE) may be required to increase capture efficiency of VOC emissions.
In some situations, the use of a water-based or radiation cured (UV/EB) ink as a compliance option is just not possible. The inks may not meet the performance criteria that come into play with different substrates, such as plastic films, heavier gauge films, and metalized surfaces, and with certain demanding end uses such as frozen food packaging, liquid packaging and retail carry bags with heavy ink coverage. However, printers can often reduce emissions of VOCs to some degree, by implementing some general improvements.
Sequencing like color jobs to minimize cleanup
For access to vendors who may supply alternative materials and equipment, see the PNEAC Vendor Directory.
Solvent is the primary pigment carrier in solvent-based inks and aids in the drying process. The solvent in solvent-based inks is considered a VOC (a.k.a. VOM). When the solvent evaporates due to ink drying either due to ambient exposure (can left open) or mechanical drying (press dryers) the VOC's are emitted. The emission of these VOC's is an air pollutant that is regulated by the state environmental regulatory and Federal EPA whether or not there are vents or stacks directly releasing the emissions or not. An air emission permit may be required by the state and/or federal EPA depending on the amount of VOC and hazardous air pollutant (HAP) that is emitted from the entire facility.
Subsequently records of the monthly emissions based on usage of VOC containing products (inks, additives, cleaning products, parts washers, maintenance products, etc.) must be maintained. This information is then used to calculate actual annual emissions based on VOC content of the product. These records must be maintained to prove continued compliance and verification of whether or not a permit is required.
If a permit is required, typically the permit will have specific record keeping and reporting conditions. These conditions may include the requirement to submit a summary report of the VOM and HAP emissions for the previous calendar year. Additionally, the printing facility is required to verify that they are in compliance with the permit limits based on record keeping requirements. If the facility exceeds the interim (i.e. monthly VOM emission limit), then the state or federal regulatory agency must be notified and appropriate follow-up reports filed. An exceedance of an air emission limit does not necessarily mean that a fine will be assessed.
Toluene, a hazardous air pollutant (HAP) under the Clean Air Act, was traditionally used as a solvent in solvent based inks. Toluene and other solvents (isopropyl acetate, toluol, etc.) commonly used in solvent-based inks are strictly regulated due to air contamination, health hazards and hazardous waste.
Under Section 112r of the CAA, facilities that actually emit or have the potential to emit considering controls, in the aggregate, 10 tons per year or more of any hazardous air pollutant or 25 tons per year or more of any combination of hazardous air pollutants are subject Title V permitting and emission control requirements.
The U.S. EPA has developed and published guidelines for state/local air pollution control agencies that enable them to ascertain which technologies are acceptable to reduce the impact of pollutants in the process. These are called Control Technology Guidelines (CTGs). CTGs set the minimum air pollution control requirement for a given industry or process. The basic CTG for flexographic printers was promulgated in 1978 and provides for three control technologies: add-on controls, high solids ink, and water-based ink. The carrier, water, must represent at least 75% of the liquid volume of the ink as applied. These requirements are applied to only certain printing operations, those designated as "major sources". The definition of a major source depends upon the geographic location of the facility and its actual and potential emissions of VOCs. All states have set the emission levels for major sources.
For additional information:
Understanding Air Pollution Permits
Most solvent-based ink waste is hazardous because it exhibits a low flash point or is a listed waste based on the type of solvent being used. For information about ink waste see the Waste Disposal section (Link to section)
Depending on the pigments in the waste, which may contain regulated metals, the waste may be classified as hazardous for regulated metals as well, i.e. nickel, barium, etc. The regulated metals differ among each state.
RCRA Section 313
All ink has the potential to contain chemicals and metal compounds that are regulated under EPA's RCRA Section 313 regulations. Product manufacturers are required to list Section 313 reportable ingredients and the percent by volume in the product on the MSDS. The MSDS should be carefully to determine which products contain reportable materials. Appropriate calculations to determine the amount stored and consumed each calendar year must be maintained.
There are various reporting thresholds depending on the chemical or metal regulated by Section 313. The printer must be aware of the reporting limits and the amount stored and consumed at the facility to determine whether a report must be filed with the state environmental regulatory agency or Federal EPA.
Ink waste may be considered a hazardous waste if it exhibits a flashpoint of 140 degrees Fahrenheit or less or contains F-Listed solvents.
Health & Safety
Most solvents present a fire hazard, and it is important to take note of flash points and explosive limits.
Use explosion-proof tools in ink rooms or press areas where flammable liquids are being used or stored.
Never use electric extension cords in explosion proof areas where solvent or solvent based ink is stored.