There are a number of basic differences between lithographic, flexographic, and gravure printing processes. Even though the processes are different, there is much similarity in the equipment, maintenance, waste generation, quality issues, and environmental issues shared by printers that use these processes. Some of the wastes common to most printers are listed below.
- Solid – Paper and plastic substrate trim, boxes, pallets, ink cans, pallet strapping
- Hazardous – Rags, dirty cleaning solvent, leftover ink, photo and plate processing chemicals
- Wastewater – Photo and plate processing (can contain solvent and metals) floor cleaning
- Air Emissions – Solvent emission from drying ink, press cleaning, fountain solutions
Inefficient ink drying and VOC destruction systems are other waste sources resulting in high utility bills. Many of these wastes are significant due to regulations and high cost.
In order to inform printers about ways to reduce waste generation and environmental compliance, a workshop entitled Georgia Printers — Increasing Profits and Reducing Waste was held in January at the Printing Industry Association of Georgia (PIAG) headquarters in Smyrna, GA. Some of the topics discussed were environmental regulations, press cleaning, low-solvent cleaning chemicals, and carbon dioxide blasting.
Regulation of Air Emissions
Printing inks contain about 50% of all solvents used by printers, many of which are considered toxic or hazardous. Ink manufacturers have reformulated their inks in recent years to eliminate most toxic solvents, but inks still contain significant amounts of solvent. As the ink dries, the air emissions are regulated either as a volatile organic compound (VOC) or hazardous air pollutant (HAP) or both under federal NESHAP regulations which may require a Title V permit. For larger printers, some type of treatment technology is often required to comply. Treatment can include incineration systems which destroy VOCs or recovery systems that remove solvents from air discharges and condense them back into liquid for reuse. The goal of most printers is to avoid Title V and the NESHAP rules since compliance and permitting are complex and expensive. Reducing solvent in the ink is part of the solution; however, reducing solvent use in press cleaning is also important. The best way to avoid these regulations is to eliminate VOCs and HAPs from all raw materials used in printing by:
- Purchasing inks that are low in VOCs and HAPs.
- Thinning ink with nontoxic solvents.
- Purchasing low VOC press cleaning solvents.
Press cleaning is perhaps the single most critical printing process and generates much hazardous waste. Hazardous waste regulations are complex and disposal cost is very high. Usually, each person cleaning the press will have their own undocumented cleaning technique. Printing plant management often does not provide direction or supervision of press cleaning operations, and is more concerned with getting the press up and running in the least amount of time possible. Press cleaning is considered the worst job in any printing plant and is often assigned to the newest, most junior employees.
|Cleaning generates almost all printing hazardous waste. Press cleaning is responsible for 50 percent of all solvent used. Cleanliness affects product quality, downtime, and maintenance cost.|
Press Cleaning Management
Tom Cassano of Harper Corporation spends a lot of time helping his customers develop the correct cleaning methods and techniques. He told Georgia Printers workshop attendees that even with the best intentions, proper tools, and training, press cleaners often fall back into bad habits, because they do not follow the prescribed methods and management does not enforce the rules. Press room discipline can only be improved by educating press operators and plant management on the reasons why certain techniques must be used. Print shop management should understand and define cleaning goals. The goals are: to press components that are clean enough for good printing quality, reduce maintenance by preventing excess ink buildup or wear, and comply with all related regulations.
For example, the anilox roller on a flexographic press contains many small dimples that hold ink. In a new roller, the dimples are sharply defined and free of any buildup or wear. Between print jobs, press operators clean the roller to remove old ink and often place the roller in storage for future use. If all of the ink is not removed, some will dry, filling the dimples and causing light printing when the roller is used again. Aggressive cleaning using strong alkalis or acids coupled with ultrasonic baths or blasting may be needed to remove dried ink; but this often causes erosion of the anilox roller, leaving the dimples worn away or irregularly shaped. Print quality problems are the result. Similar situations can occur when cleaning rubber lithographic press blankets or gravure image rollers. Print shop management can avoid these problems by taking the following steps:Specify when press components should be cleaned.
- Specify when press components should be cleaned.
- Specify the methods that should be used to effect cleaning.
- Specify cleaning chemicals to be used.
- Provide the correct cleaning tools.
- Provide a standard tool to determine when parts are clean.
- Provide these instructions in writing to all press operators.
- Train press operators to use the prescribed cleaning methods.
|An example of a cleaning specification:Clean anilox roller within 30 minutes after removal from press, prior to storage. Apply no more than 1 quart of isopropyl alcohol with squeeze bottle and wipe dry. Place used rags in fire safety cans. Examine roller with 30x microscope. If ink still remains, repeat above process.|
Lack of discipline can be seen in many print shops:
- Open buckets of solvent are left sitting on the floor for hours.
- Used rags are left on the floor or placed in the trash can.
- Floors are mopped with solvent and string mops.
- Hazardous and nonhazardous wastes are placed in the same container, creating more hazardous waste.
These practices should be avoided. Floors should never be mopped with solvent. Dry cleanup, using paper or cloth mats around the press to collect small spills, and cleaning with low-solvent cleaners are some alternatives. Keeping all solvent containers tightly closed will result in decreased evaporation of solvent and decreased cost. Blanket washes cost about $8.00 per gallon, and an open gallon container can evaporate in two days. One Georgia company estimates that they are saving $14,000 per year since fitting all solvent containers with tight fitting lids.
Workers need to how to handle solvent-containing waste. Almost all solvent-containing waste is hazardous and should be properly handled onsite prior to being sent to a licensed hazardous waste treatment and disposal facility. Proper onsite handling includes placing hazardous waste in a covered container that is marked with the words “hazardous waste” as well as a description of the contents. Workers that handle hazardous waste must also be trained in proper handling, storage, disposal, emergency, and spill techniques.
Alternative Cleaning Methods
The first alternative is Dry Ice Blasting. Some printers have found that press cleaning can be achieved without using any solvent by using dry ice blasting. Dry ice blasting is similar in technique to sand blasting, except dry ice pellets are propelled against a surface instead of sand.
Mr. Andy Pazahanick of Thomco Equipment — an Atlanta-based manufacturer of dry ice blasting equipment — told the printers attending the Georgia Printers workshop that dry ice blasting works well at a comparable cost to solvent cleaning in some situations. Some characteristics of dry ice blasting are:
- Ink needs to be dry prior to blasting with dry ice.
- Blasting equipment can be purchased for about $25,000.
- Contractors can provide blast cleaning using their equipment.
- The cost of dry ice varies, but is about $0.40 per pound.
- Small blast units use about one pound of dry ice per minute.
- Waste disposal costs are virtually eliminated.
The second alternative is Low VOC Cleaners. One problem with suddenly switching from solvent cleaners to low or zero-solvent cleaners is that the new cleaners work differently than the solvent-based cleaners. A sudden change in chemistry can almost cause a press room revolt. A gradual change in cleaning chemistry is one approach suggested by Mr. Noah Huffman of Printers Service. Some characteristics of low solvent cleaners are: increased drying time; increased liquid waste is collected; and, reduced air emissions and worker exposure.
Alternatives to Hazardous Waste Disposal
Send rags to commercial laundries for cleaning and reuse. Recover solvent from rags by centrifuging the rags. Distill dirty solvent to provide clean solvent for reuse.
Recovering and reusing rags and solvent reduces the amount of new solvent that is purchased as well as reduces the amount of hazardous waste that is disposed. Payback for purchasing a rag centrifuge or solvent distillation unit is often about two years.