Printing Industry

Table of Contents  Keys to Using Guide  U.S. Domestic Printing Industry  Emerging Technologies   P2 Practices in Printing  Lithography  Screen Printing  Flexography  Gravure

Common Pollution Prevention Practices in Printing

The composition of wastes from each printing type varies, but overall, source reduction of these wastes will benefit printers by reducing raw material needs and disposal costs, and by lowering the long term liabilities associated with waste disposal. The pressures from government and local citizens to reduce wastes and the emission of pollutants has led to changes in the operation of many printing facilities. Traditionally, pollution control focused on end of pipe controls. Changing this focus to process improvement will help to prevent pollution and promote profits.

Major Wastestreams

The three major types of wastes in the printing industry include:

1. Solid Wastes - In a general printing environment solid waste could consist of the following: empty containers, used film packages, outdated materials, damaged plates, developed film, dated materials, test production, bad printing or spoilage, damaged products, and scrap paper.

2. Wastewater - Wastewaters from printing operations may contain lubricating oils, waste ink, cleanup solvents, photographic chemicals, acids, alkalis, and plate coatings, as well as metals such as silver, iron, chromium, copper and barium.

3. Air Emissions - Printing operations produce volatile organic compound (VOC) emissions from the use of cleaning solvents and inks, as well as alcohols and other wetting agents (used in lithographic printing). Larger plants can be the source of NO_x and SO₂ emissions.

Hazardous wastes, defined and regulated by federal, state, or local governments, can be a subset of any of the three major wastestreams.

This section will provide a general overview of pollution prevention options applicable to any type of printing facility.

How to Reduce Waste

Start at the Beginning-Graphic Design

Waste can be reduced most efficiently from the inception of the printing project through graphic design choices. Preparing layouts that use the most efficient image size to the press sheet size reduces paper waste at the later stages of cutting and binding. Designers should also be made aware of inks containing heavy metal or other hazardous pigments and provided with information on non-toxic alternatives. Other graphic design options to consider include decreasing the amount of ink coverage of the layout and using non-coated, non-bleached paper, and recycled papers.

Job Planning

Thorough planning of the overall job load will reduce wastes. Planning allows for scheduling of the daily runs to reduce color changes and to run inks from lighter to darker. Both techniques reduce heavy cleaning steps. Planning also allows the press operator to prepare only the amount of ink needed for the day's jobs. Using a computer controlled mixing program equipped with a digital scale for weighing inks can help reduce waste. These programs allow the printer to custom mix any ink color from colors already on hand thus decreasing the purchase of new colors and increasing the use of existing inventory. A digital scale makes the entire process more accurate and decreases the amount of ink wasted as a result of "guesstimation" errors. Increased attention to the amount of ink mixed for specific jobs improves material use efficiency.

Best management practices (BMPs) are the most cost-effective way to decrease the amount of waste generated. BMPs require building employee commitment and interest in pollution prevention, as well as managerial support, to encourage participation in pollution prevention programs. This includes careful control of raw materials, practical scheduling, and job management. For example, a good housekeeping and maintenace program helps to ensure that all machinery and processes are working well with no leaking valves, tanks, etc. Wise planning of a print job through the entire process accomplishes the task with a low margin of error, consequently decreasing waste generation.

With any substrate, consistency is key. Inconsistent quality of substrates is a major factor in problematic quality of finished product. Once a process is set with the correct inks, paper and machine conditions, changes in the substrate affect all parts of the process. Many ancillary resources are wasted due to inferior and inconsistent substrates. All printing companies need to be vigilant in the identification of quality and consistency of incoming raw materials.

Vendor certification programs on all raw material sources should be strongly evaluated as a tool to help reduce waste. Each supplier needs to know how their products are used in the printing process and the expectations of the printer so they can recommend process improvements. Developing partnerships with vendors can allow the printer to have access to the technical assistance and experience of each supplier.

Material Handling and Storage

As with best management practices, wise material handling and storage can contribute to less waste generation. These procedures can virtually eliminate wastes from spoilage and improper storage.

By limiting purchasing authority to a specified individual, a company may be able to avoid duplicate purchasing. In addition, a printer could have an environmental manager provide an approved list of materials to the purchasing agent. To avoid unwanted materials that will eventually have to be disposed, the printer can adopt a policy of not accepting any material samples without authorization.

A prime location for waste reduction is in the receiving area. The acceptance of unusable or damaged materials results in unnecessary wastes. All materials should be inspected and the unacceptable goods returned to the manufacturer or supplier. The savings here are twofold, the expense of the damaged goods and their subsequent disposal. Use a first-in, first-out (FIFO) inventory system, check expiration dates and heed storage specifications particularly for photosensitive film and paper.

Proper storage of chemicals should, at a minimum, meet the label specifications. By meeting the required conditions, the shelf life of a chemical can be guaranteed and the likelihood of spoilage decreased. With paper, proper storage will avoid damage from temperature, humidity, and spills as well as physical damage. It may also be necessary to restrict access to the storage area. By reducing traffic flow, damage from dust, dirt, and spills is avoided. All storage areas should be clearly labeled as to content.

Once solvent-based cleaners have been opened, they should be stored safely. Attention must be paid to flammability and flash point. As a guideline, consult OSHA regulations on flammable storage (29CFR1910.106). Clearly written guidelines should be made available for workers on correst usage and storage. Safety precautions such as grounding containers and bonding wires should be considered. These guidelines should be included in all training programs and posted near equipment. All volatile solvents should be stored in closed, air-tight containers. If a drum is being used for waste solvent, it is important to cover any funnels or openings. Open waste solvent containers that contain hazardous materials can result in a violation of the open container rules under federal hazardous waste regulations as well as increased VOC emissions (Price 1994, Cross 1989).

Waste Segregation, Recycling, and Reuse

Recycling plays an important role in any printer's waste management program. Materials reported in the literature as being recycled by printers include paper, solvents, ink containers, reusable plate or cylinder boxes, pallets, and sometimes ink. Using returnable/refillable items or large totes, when available, can also cut down on packaging waste. Vendors or suppliers can be requested to provide returnable/refillable containers as part of their contract with the printer.

Cloth cleaning rags/wipes (also called shop towels) covered in ink and solvent can be reused by sending them to an industrial laundry service. It is advisable to remove the majority of liquids by a gravity drain, a wringer, or a centrifugal extractor prior to shipping. Many states now require this step. Use caution in doing this, as the solvents used may be ignitable or flammable. The extractor must be explosion proof. This recovered solvent can be used initially for parts washing, recaptured, then distilled for reuse or sent out for fuel blending. The wipes should be stored in an air-tight, self-closing, flame resistant container marked for recycling.

Contaminated wipes may be regulated as hazardous waste and can be a source of regulatory problems. Also, significant VOC emissions and personnel exposure are associated with press cleaning operations. If the shop towels are laundered, make certain that the towels are being handled properly. Dry cleaning may also be an option for used shop towels. An annual visit to the laundry facility should be part of the waste management program in order to review the handling procedure for your wipes. The printer may need guidance from a technical assistance person on what to ask and how to interpret the answers. Check with the local POTW (publicly owned treatment works) that services the laundry to determine if the laundry is complying with sewerage discharge limits. A written description of how the printer's towels are handled should be requested from the laundry and kept on file. Note that the regulations about shop towels have been changing in recent years. Check with the proper regulatory authorities for the latest statutes.

Solvent recycling can also be done in plants of all sizes. The most common method is to install clearly marked drums on the plant floor. Always make sure that the solvent is actually spent before it is exchanged for new solvent. Do not commit to a scheduled solvent replacement program unless it is proven through in-plant trials that solvent is completely spent after a specifically measured amount of time.

The solvents collected from the cleaning operations and recovered from the rags can be recycled on-site or sent to a professional recycler. Many large firms keep solvent storage baths for each process ink color, thereby allowing multiple reuse prior to recycling. In the cases where on-site recycling is done, companies generally use distillation. Distillation is the boiling off of waste solvent to leave behind a sludge of ink, paper dust, and lint. The vaporized solvent condenses within the still and collected for reuse. It should be noted that all equipment in this process must be explosion proof. A variety of different sized stills are now on the market making this technology applicable to the majority of printers. Some states may require a permit, so check with the appropriate regulatory agency. Each printer will have to crunch numbers to determine if a particular still system is an economically sound option for them.

Alternative Materials

Looking for alternative materials that generate less waste and/or are less toxic in terms of human health, can provide a printer with economic as well as environmental benefits. Searching for alternative materials, however, can be a long-term and often frustrating process requiring continued initiative on the part of the printer. Trials may be required of new chemicals or processes and additional personnel training may be necessary. Working closely with vendors and pollution prevention technical assistance providers, within the constraints identified by the printing client, can lead to useable alternative materials or processes.

Solvents

New solvent alternatives for cleaning are continually entering the marketplace. These materials are made of glycol ethers and other heavier hydrocarbons. The hazard rating of these solvents are low due to their high flashpoints (usually above 140 °F) and low toxicity. The alternative solvents can be used for cleaning all equipment contaminated with ink, while detergent and water can be used for non-ink cleaning. Problems associated with the new low hazard solvents include longer drying times, more difficulty in cleaning, residual film on carriers, and an extremely strong odor. Alternative solvents may have a low VOC content but that does not always guarantee they will have an overall lower human toxicity or REL. Always check the MSDS for this information. However, the most recent releases in alternatives have overcome these problems but workers are slow to accept the products due to the past performance of their predecessors and the uncertainty of changing an accepted practice.

For a successful substitution, unlike with solvent based cleaners, it is important to select cleaners specific to the purpose, the cleanliness goal, or in some cases the type of printing done or equipment owned. The technical assistance provider will have to work closely with the printing facility, especially the press operators, to find the right alternatives for their situation. While environmentally sound, the use of alternative solvents is the most difficult pollution prevention technique to implement from a worker standpoint.

Prepress

Chemical process vendors should be contacted when attempting to alter pre-press chemistries. Some alterations in pre-press chemistries that are "home-grown" will result in invalidation of any pre-existing service or guarantee should the in-house chemistry change not work. Often the vendor can suggest ways to help extend the life of their products and will work with the shop as they "experiment" with the best approaches.

Photochemistry

Processes that employ photography in the reproduction of artwork and/or copy can employ a number of techniques to reduce waste generation. Materials used in photo reproduction include paper, plastic film, or an emulsion which is covered with a light sensitive coating. Emulsions are usually composed of silver halide salts including silver chloride, silver bromide, and silver iodide.

After an emulsion (film) has been exposed to light it must be developed. Developing solutions usually contain benzene derivatives, along with accelerating agents (to increase the speed of the developing process), a preservative to control oxidation damage to the developer, and a restrainer which prevents the image from fogging.

The developing action must be stopped in a fixing bath to prevent over exposure. Small amounts of silver enter the bath from the emulsion each time a photographic film is immersed in a fixing bath. To prevent insoluble compounds from forming, fixer must be diluted before the silver concentration reaches the maximum among the fixer can work on. After exceeding this level, these compounds cannot be removed from the emulsion, leaving an often unusable image.

Once the image has been properly fixed to the emulsion, it must be washed to prevent residual chemicals from reacting and damaging the image. In some photoprocessing emulsions, the image contrast must be reduced or increased by additional chemical steps, in order to touch-up the image. Reducers oxidize some of the silver, while intensifiers add silver or mercury to the developed grains of silver in the emulsion.

A variety of techniques can be used to reduce photoprocessing waste generation. For example, in hand-processing, squeegees can be used to wipe off excess liquid to prevent chemical carryover from one process bath to the next; in color processing, iron-EDTA can be substituted for ferrocyanide bleaches as iron-EDTA is less toxic and eliminates costs associated with the treatment or disposal of toxic bleaches. The photoprocessing department can also reuse rinsewater as long as possible, use fog nozzles and sprays, use still rinsing, use rinse bath agitators, use automatic flow controls, and remove sludge frequently.

Typical wastes generated from the photoprocessing stage include: developed films, acids, alkalis, solvents, spent fixer, silver, waste paper, out-dated material, contaminated rinse water, spent developer, and sludge.

Siver Recovery

The most concentrated silver-containing waste in film and image processing is spent or excess fixer bath solution. In film developing, fixer solution is replenished continuously to maintain solution strength. The overflow has varying concentrations of silver, but frequently exceeds 5.0 mg/L. Because of this high silver consentration, silver recovery from the fixer solution is cost effective (Department of Defense, 1995).

When the film is moved from the fixer to the rinse, it carries small amounts of silver, usually as silver thiosulfate complexes, that are very stable. Environmental regulations prohibit discharge of untreated rinse water if the silver concentration exceeds regulatory or POTW limits. Silver recovery technologies include precipitaiton, ion exchange, metallic replacement, reductive exchange, electrolytic recovery, reverse osmosis, and electrodialysis.

Hydroxide precipition is commonly used to recover metal-laden solids from wastewaters. Silver is frequently precipitated from metal wastewater as silver chloride. Sulfide is also widely used to precipitatie silver, both free silver and silver sulfide, but the chemical costs, the need for supplemental heat input, and labor costs make it a relatively costly technique.

Electrolytic silver recovery applies controlled current in an anode-cathode array to remove silver from the wastewater solution. Silver is removed in nearly pure form, but capital costs and lower treatment efficiency (effluents have 100-200 ppm silver) must be considered. Electrolytic and metallic replacement systems are sometimes used in series to reduce the silver concentration in the effluent.

Metallic replacement involves using iron steel wool to react with silver thiosulfate in the wastewaters, whereby the iron replaces the silver in solution and the silver settles out as a solid. The silver is recovered as a sludge of silver salt compounds, which is more difficult to recover than electrolytically reduced silver flake, the chemical recovery cartridges cannot be reused, and the effluent contains high iron concentrations. The advantages to this method are relative low cost and availability, and that no special energy or plumbing connections are needed. Metallic replacement is usually used in conjunction with electrolytic recovery as a polishing step.

Silver removal by ion exchange is accomplished by passing the wastewater through a mixture of anionic exchange resins, or by using a strong base gel anion resin to selectively remove the silver. Automated ion exchange units are usually only practical for larger processing facilities due to their high cost. It is also essential that the correct resin be chosen for efficient operations. The printer, technical assistance provider, and vendor will need to work together to determine the best resin to be used.

Reverse osmosis uses high pressure to force liquid solutions through a semipermeable membrane, separating larger molecular substances from smaller molecular substances. Up to 90 percent of the silver thiosulfate complexes can be removed from wastewaters using this method. Also, reverse osmosis is effective in removing most other chemicals in solution, including color couplers and ferrocyanide, rendering the water suitable for reuse in final rinses. The disadvantage of this method is the high capital investment required.

Silver recovery technologies can result in a net positive economic return because of the metals recovered and the reduced waste disposal costs. Large firms will sometimes make a capital investment to purchase an automated recirculating system which includes silver recovery, waste recovery, and chemical replenishment. These will remove large percentages of silver as they will be able to treat the low concentration rinse waters as well as the higher concentration process waters.

Alternative Prepress Technologies

Electronic imaging and laser platemaking allow text and photos to be edited on a video terminal and color separations to be prepared electronically. This eliminates the need to photograph, edit, re-shoot, and photoprocess several times (Price 1994). Vesicular films that contain silver and diazo films have been used traditionally, but photopolymer films that are now available use carbon black as a substitute for silver, which eliminates the need to send the waste film to a metal reclaimer. Electrostatic films are also silver-free and have resolution and speeds comparable to silver films. However, these silver-free films are not being widely used. Reducing wastewater generation can be accomplished with counter-current washing, or reusing rinse water in the initial film-washing stage, rather than using fresh water at each stage (Price, 1994).

Press

Mechanical Modifications

Improvements and/or modifications to existing printing equipment may be a suitable choice in a pollution prevention and waste reduction program. Changes to press equipment such as automatic registration systems, ink viscosity measuring systems, revised ink pans, revised ink pumping systems, new doctor blade technology in gravure and flexo printing and vapor recovery systems can go a long way in improving the manufacturing processes.

Ink viscosity measuring systems cannot only control the viscosity of the inks to ensure quality printing but can prevent excessive use of solvent thereby reducing the potential pollution. Changing the design of ink pans to a shallower depth on a lithographic press can reduce the amount of ink needed in each printing station and reduce waste ink as a pollutant.

Web break detectors can reduce waste by informing the operator of breaks without creasing or smearing the web. These non-contact electric systems detect web breaks and inform operators to stop production or automatically shut down the presses without damage to the equipment. Installing an ink agitator or an ink leveller on the ink tray or sump to prevent premature oxidation can reduce ink waste and spoilage. UV light can reduce algae, water borne fungi and bacterial growth in fountain solutions, further reducing waste solutions.

Automatic registration systems are available in several different types and styles. Registration is the precise fitting together of two or more printing images on the same paper in direct alignment with one another. These systems allow the press crew to check and maintain quality registration and high press speeds resulting in less waste and improved process output. With the ability to bring jobs into register quicker and keep them in quality register longer, less inks, solvent and substrate are consumed or wasted. For web-fed presses the consideration of automatic splicing may be evaluated. Using this process improvement will reduce the waste of inks, solvent and paper as well as avoid slowing down press speed.

Installing automatic lubrication systems on the critical rollers, bearings and gears will reduce waste and conserve resources. Self contained lubrication systems which are properly maintained can prevent contamination of the lubricant and extend its useful life.

Other methods to reduce waste involve careful attention to operating parameters and instrumentation: installing automated plate benders, optical scanners to lock onto registration marks, automatic key settings, and ink/water ratio sensors. Another technique for sheetfed printing is to use both sides of the make-ready paper, slipping in clean sheets periodically in order to check registration and print quality.

Quicker make-readies and changeovers can reduce the amount of raw materials that are consumed in getting to the press ready stage. Efficient and effective scheduling plays a major role in how printing companies can reduce waste and practice sound pollution prevention. Constant scheduling changes will adversely affect the best of programs.

The newest printing technology is "computer-to-press," currently available for lithographic sheetfed print. This technology eliminates all wastes associated with prepress photoprocessing wastes. This and other equipment is available from local equipment vendors and increasing numbers of manufacturers are entering the marketplace.

During cleaning operations, equipment can be introduced which will reduce wipe and solvent usage. The least technical of these is the employment of squeegees to remove excess liquids from equipment. This in turn will reduce the quantity of wipes required. Automated cleaning systems can further reduce residual liquids and in turn reduce cleaner consumption. Some examples of these systems are an automated blanket cleaner, roller wash-up blades, and ink blades. The choice of equipment is dependant upon the type of printing operation. Any new equipment will require training of plant personnel as well as their cooperation in changing their working methods.

Inks

Alcohol- and petroleum-based ink systems use various solvents that are major contributors to pollution. However, these alcohol- and oil-based systems allow for faster press speeds then some of the alternatives currently available, longer cylinder wear and (occasionally) better ink transfer to various substrates. Effective solvent recovery systems are needed to develop, implement and maintain sound pollution prevention programs when using alcohol- and oil-based systems. Solvent recovery systems can be internal or external. On-site batch distillation systems can be internal or external. On-site batch distillation systems can be used when justified by volume. Off-site professional solvent recyclers can be an alternative to reclaim solvents.

Recycling Inks

Inks have traditionally consisted of colored pigments and a vehicle or carrier for printing fluidity during application and subsequent pigment binding. Inks are perhaps the most important aspect of the overall process because different ink formulations bestow distinct characteristics to the product and thus affect its performance in relationship to the other press elements. Prior to the mid 1970s most colors in inks were produced by using metals. These metals were often present in amounts that exceeded state and federal regulatory limits, thus rendering the waste ink hazardous. In recent years, ink manufacturers have developed organic color replacements which are not as heavily regulated as their inorganic counterparts. Unfortunately, even if waste ink does not test hazardous, it may require disposal by a licensed hazardous waste management company. Individual states and their industrial waste requirements differ as to whether these petroleum-based materials require special handling.

Some waste ink can be recycled through an ink recycling service or in-shop. Blending colors usually requires some additives such as toner to fine tune the color quality. Recycling allows blending several colors together into darker colors for reuse. Equipment is currently on the market with a wide range of capabilities to filter and distill waste inks. The recycled ink compares favorably to new ink in tests for grind, residue, viscosity, tack, water content, and water pickup. On site recycling has been found to produce satisfactory final products. For large quantity generators there are recyclers who bring mobile recycling units on site to recycle ink, mixed or color separated. By recycling on site, the legal liabilities and regulatory paperwork associated with off-site recycling and disposal can be avoided. Colors can be produced very similar to new inks. Press operators can adjust the ink/water balance and produce results comparable to new inks without experiencing trapping problems. Trapping is the ability to print a wet ink film over previously printed ink. Ink recovery machines currently on the market in a wide range of capacities make on-site reclaiming a viable option for larger printers.

Alternative Inks

The correct selection of alternative carriers can reduce the amount of waste ink generated without compromising product quality. Ink choice is dependent upon the print process, the substrate, and the ultimate end use of the product. In lithography, for example, petroleum-based inks can be substituted, depending on the application, with EBC (electron beam curable), ultraviolet curable, soy/vegetable, water-based, and/or waterless inks.

Ultraviolet (UV)

Ultraviolet systems consist of a photo-polymerization process that uses mercury vapor lamps for UV photoinitiated monomer inks. This method has high initial costs, high ink/coating costs, low energy costs, and has no hydrocarbon emissions. The driving force to use UV systems is low VOCs. High quality radiation and optimum spectral distribution are the keys in perfecting the use of these systems. There is a wide range of UV-ink "chemistry" available for adhesion to popular substrates in flexographic and screen printing. UV in flexographic printing offers good resistive properties and economical curing or drying. (Rudolph, 1991)

UV-curable inks are widely used in the printing industry for printing primarily on plastic, vinyl, metal and paper substrate. These inks contain low VOCs. Instead, curing is by ultraviolet light-induced polymerization. These inks will not dry on a press or in ink fountains so cleaning requirements may also be reduced. Some reported advantages of UV curables include:

• decreased or eliminated VOC emissions
• less frequent press cleaning and associated solvent use
• reduction in required floor space (eliminates need for drying ovens or racks)
• increased throughput
• elimination of ventilated storage of sheets during oxidative drying
• can be used on web and sheetfed presses.

On the negative side, the following barriers have been reported by screen printers using UV curables:

• performance is not always as good (insufficient opacity and color matching)
• substrates with deeply textured surfaces are not currently suitable for UV-curables
• outdoor durability may be a problem
• UV curables are brittle and finishing operations like die cutting and molding present problems
• a significant capital investment is needed for conversion to UV systems
• small printers may not experience the increased production speed and ink cost/coverage benefits due to shorter average runs (Jendrucko et al, 1994)
• ink costs are often higher
• recycling problems may be encountered with substrate printed with UV inks.

Electron Beam Curable (EBC)

EBC inks consist of low-molecular weight polymers that react with a stream of electrons from a vacuum tube. These inks contain no solvents, and do not cure until exposed to light and may therefore remain in ink fountains for long periods of time, reducing clean-up needs. The electrons drive the reaction, forming polymers and setting the ink. Problems reported with EBC inks include paper degradation and worker exposure to X-ray.

Electron beam dryers use polymerization by electron bombardment to dry liquid and powdered coatings. These dryers have high initial costs and low to moderate operating costs. They are sometimes used for higher gloss coatings and metal decorating applications.

Vegetable Oil-Based Inks

Vegetable oil-based inks are used only in the lithographic industry. Soybean oil inks can replace 20 to 40 percent of petroleum based oils in ink. The soybean oil replacement is said to reduce volatile organic compound content by as much as 80 percent. This advantage is somewhat limited due to the continued use of solvents for cleaning. The soybean oil inks are more expensive than petroleum inks and require somewhat longer drying times in non-heatset applications. The drying times can be shortened by the installation of custom dryers or power sprayers.

Benefits of soy oil-based inks are: VOC emissions into the atmosphere can be reduced on heatset presses because the VOC content of soy oil-based ink is potentially lower than traditional petroleum based inks (based on the percentage of soy oil in the ink); press washes for soy oil-based inks can be water/detergent types, thus reducing or eliminating the need for high VOC solvent formulations; less paper waste from quicker start-ups, as water and ink balance is reached more easily; and spoilage during runs from color or variation in tracking is minimized; quicker and more even ink coverage to the press blanket is achieved. Soy oil-based inks have exceptional transfer properties, minimizing plate scumming. Brighter colors and darker blacks are produced, because soy oil-based inks have greater color retention than do traditional petroleum-based inks. The disadvantages are: longer drying time, ink sitting up on the paper, cost, and substituting other chemicals for the petroleum-based ink processes requires operator adjustment and training.

Water-Based Inks

Water-based inks, while more environmentally sound in that there is little need for petroleum-based solvents in the printing process, have several problems associated with in-plant usage. The most noticeable of these is the significant increase in chemical additives required. It will necessitate the training of workers in basic chemistry and during this period the likelihood of costly mistakes is high. If incorrect chemicals or solvents of any kinds are mixed into a waterbased system, the ink will curdle. Surface tension of the water-based ink is high and therefore reduces the transfer efficiency of the ink to substrate. Water-based ink also tends to foam when pumps are running. Another problem with the water-based system is a somewhat limited color choice. Water-based inks require increased energy for drying and there are occasional difficulties in ink spread. Paper curl and shutting down of presses for short periods of time for more frequent cleaning all contribute to the difficulties in using these inks. Another disadvantage is that dried ink on the press and rollers can be very difficult to remove.

Water-based inks, however, do have several advantages. They are often classified as nonhazardous and no special air pollution control equipment is required for emissions. Disposal costs are often reduced and these inks are less toxic to employees.

The best applications for water-based inks are in flexographic printing, gravure printing, as well as textile screen operations. Both low solvent and 100 percent water-based inks are available. Non-VOC containing cleaners can also be used. Inks may still contain heavy metal pigments that may be required to be disposed of as a hazardous waste, however substitutes for these inks are available and should be used. Testing of the ink waste should be done to determine whether it needs to be classified as hazardous or not. De-inking of material printed with water-based inks may be difficult.

Process changes will occur when using a water-based system compared to alcohol- and solvent-based ink systems. There are manufacturing tradeoffs that need to be evaluated when using water-based systems in comparison to the cost of solvent recovery systems.

Water-based ink systems may not allow the same press speeds to be maintained due to the need for extra drying capacity. Because there are no solvents that evaporate and help dry the inks, the water-based inks must be heat-set and dried in various types of ovens. Generally water-based ink systems are run through ovens that are gas fired, re-circulating air ovens.

When presses have limited space available for expansion or modification, the ability to dry the inks has a definite bearing on the press output. Sometimes the press ovens can be changed and lengthened between the printing units to provide a longer drying time in the printing process. When the total length of a press is critical, ovens may be extended by going upwards over each printing unit. Gas ovens that cannot be lengthened to allow the substrate to stay in the drying area longer may be modified. One method would be to add infrared dryers to the oven to help in the drying process. Another method might be to change the oven configuration and baffle design to produce the maximum drying capabilities of each oven.

Water-based inks are capable of receiving various additives that assist ink drying, ink holdout, ink laydown and printability on various substrates. These additives are used by the press crew in different ratios and formulas depending on the desired finished product. Complete water-based ink systems do not have the vapor recovery concerns that the alcohol and solvent-based ink systems have. This might be a strong consideration to evaluate water-based ink systems. Press speeds should be evaluated in the complete cost of each type of ink system.

Waterless Inks

Special lithographic presses or re-fitted presses are needed to run waterless inks and special plates, exposure methods, and plate handling techniqes need to be employed when waterless inks are used.

Waterless inks are high viscosity inks with characteristics similar to petroleum based inks. The major difference in these ink systems is a resin which produces high viscosity, but requires exact temperature controls. The temperature must be controlled with a three stage refrigeration unit. A waterless system requires a high initial capital investment and careful monitoring during operations.

If the printer has an experienced press operator willing to learn about proper mixing of ink with dryers, ink could be purchased without incorporated dryers. Dryers can then be added by the printer only as needed. Purchasing inks without dryers and adding them when the color is mixed will reduce the amount of waste skins.

Operator experience can also be a factor in the success of waste reduction. An inexperienced press operator will often mix more colors than necessary to achieve the desired specialty color. For a new employee, using a digital scale whenever measuring ink will improve accuracy. Planning ahead and using the fewest mixing colors will reduce the amount of waste skins needing disposal.

Once the ink has been mixed, the use of an anti-oxidant spray will prevent ink skinning in the fountain. These substances are physical barriers to oxygen, and inhibit the drying reaction. Once the press is running, the anti-oxidant "burns off" on the ink roller, greatly reducing or eliminating its effect. The inks can then dry on the substrate. A potential drawback is the same ink in the fountain may be wasted during start-up because it doesn't perform as well a non-treated ink.

Cleanup

Care should be taken to not use more solvent than is necessary—only the bare minimum needed to do the job should be used. Reuse the solvent if possible. The reuse of inks and solvents not only prevent pollution through effective use of resources and materials, but can reduce costs. Depending on the job, if solvents are needed to clean press parts, consider using recovered solvents. Solvent tanks and containers should be kept closed to prevent evaporation and emissions.

Changing from high VOC content cleaning compounds to compounds with low or no VOCs will reduce air emissions. For short print runs, more VOCs are usually released from evaporating press cleaners than from the inks themselves. Segregating and reusing solvent will extend the life of these materials. Installing an on-site solvent distillation unit for solvent recovery can stretch the useful life of the solvent even further. Such a unit may need appropriate permits as well as trained personnel and a capial investment. It is also recommended that aerosol products be replaced with manual pump bottles, especially if the product can be bought in bulk and small containers refilled.

Several simple procedures can reduce the quantity of solvent used for press-side cleaning and the associated VOC emissions:

• Minimize the solvent applied to a rag by using plunger cans or squeeze bottles
• Use press wipes as long as possible before discarding. Use soiled wipes for the initial pass and clean ones for the last.
• Store used solvent-contaminated rags in sealed, fireproof containers labeled "contaminated shop towels" to avoid solvent evaporation and a safety hazard.

Another alternative may be the use of low vapor pressure solvents. While they may have a high VOC content, they evaporate at such a low rate that less solvent is used.

Parts Washers

If parts washers are used to perform maintenance on press parts, use solvents not characterized as hazardous (ignitability: flash point < 140 F) or that are not listed wastes when spent. Install a filtering mechanism in the parts washer to extend the life of the solvent. A solvent still may be an option to reduce the waste and recover/reuse the solvent for the parts washer.

Postpress

Finishing operations may include final trimming, die cutting, folding, collating, binding, laminating, embossing, and assembling operations. Binding methods including stitching (stapling), gluing, and mechanical binding. The primary wastes are binding and laminating chemicals, and scrap paper (Price, 1994).

References Used

Cross, L. 1989. "Ink Waste Disposal," Graphic Arts Monthly 61: 118-120.

Department of Defense. April 1995. "Recycling Photo/X-ray Processing and Printing Wastes," Department of Defense Pollution Prevention Technical Library.

Jendrucko, R.J., Coleman, T.N., and Thomas, T.M. 1994. "Waste Reduction Manual for Lithographic and Screen Printers," University of Tennessee, August 1994.

Legnetti, P. 1992. "Success stories in ink, paint and plastics applications." First annual Conference for Southern States on Hazardous Waste Minimization and Environmental Regulations, Sept. 22-24, 1992.

Massachusetts OTA. 1994. "Toxics Use Reduction Success Story: Deluxe's Solvent-Free Printing System," Office of Technical Assistance, Executive Office of Environmental Affairs, Commonwealth of Massachusetts, 4 p.

Price, R.L. 1994. "Printing and Publishing Industry Pollution Prevention and Recycling. Center for Hazardous Material Research (CHMR) 530-4296-000.

Rudolph, A.C. 1991. "UV-Flexo et al." TAPPO Proceedings Polymers, Laminations & Coatings Conference 1991.

Annotated Bibliography

Campbell, M.E. and W.M. Glenn. 1982. "Printing" in Profit from Pollution Prevention: A guide to Industrial Waste Reduction and Recycling. p. 201-217.

This chapter, which is part of a larger document, gives an overview of the printing industry and the processes involved in the printing. Pollution prevention opportunities discussed include general housekeeping and process control, conserving photsensitive materials, platemaking, inks (types, wastes, and curing), and dirty rag recycling. Brief case studies are included for many of the pollution prevention opportunities discussed.

Legnetti, P. 1992. Success stories in ink, paint and plastics applications. First annual Conference for Southern States on Hazardous Waste Minimization and Environmental Regulations, Sept. 22-24, 1992.

This article discusses the progress that has been made in developing environmentally acceptable pigments. Replacements for lead chromate, barium, and cadmium are listed.

Lewis, B. 1994. The Absence of Waste and Beyond. FLEXO p. 19-22.

This article focuses on the advances in the printing industry and how business and manufacturing principles such as just-in-time and total quality management are being adopted into the industry.

Alternatives to Petroleum- and Solvent-Based Inks. 1994. Fact Sheet 6. Massachusetts Toxics Use Reduction Institute.

This fact sheet covers all the substitute inks available for lithographic, flexographic and gravure printing, including radiation-curable, vegetable oil, and water-based inks. It includes a very comprehensive table that gives the applications, benefits, operational advantages and disadvantages, cost, product quality, and limitations for each alternative.