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

Gravure

Overview

Gravure printing process is used for long runs of multi-colored, high quality jobs at high press speeds. Examples of gravure printed products include art books, greeting cards, advertising, currency, stamps, wall paper, wrapping paper, magazines, wood laminates and some packaging. Gravure printing is a direct printing process that uses a type of image carrier called intaglio. Intaglio means the printing plate, in cylinder form, is recessed and consists of cell wells that are etched or engraved to differing depths and/or sizes. These cylinders are usually made of steel and plated with copper and a light-sensitive coating. After being machined to remove imperfections in the copper, most cylinders are now laser engraved. In the past, they were either engraved using a diamond stylus or chemically etched using ferric chloride which creates pollution. If the cylinder was chemically etched, a resist (in the form of a negative image) was transferred to the cylinder before etching. The resist protects the non-image areas of the cylinder from the etchant. After etching, the resist was stripped off. The operation is analogous to the manufacture of printed circuit boards. Following engraving, the cylinder is proofed and tested, reworked if necessary, and then chrome plated (US EPA, 1990). Often corrections and touch-ups are still done using the old process.

In direct image carriers such as gravure cylinders the ink is applied directly to the cylinder and from the cylinder it is transferred to the substrate. Modern gravure presses have the cylinders rotate in an ink bath where each cell of the design is flooded with ink. A system called a "doctor blade" is angled against the cylinder to wipe away the excess ink, leaving ink only in the cell wells. The doctor blade is normally positioned as close as possible to the nip point of the substrate meeting the cylinder. This is done so ink in the cells has less time to dry out before it meets the substrate via the impression rollers. The capillary action of the substrate and the pressure from impression rollers draw/force the ink out of the cell cavity and transfer it to the substrate (Figure 10).

Figure 10. Principle of Gravure Printing

Gravure printers usually use solvent-based inks, although use of water-based is increasing due to regulatory issues. Processes that continue to use solvent inks can run considerably faster than processes that have changed to water-based inks. The nature of solvent evaporation allows the inks to dry much quicker and allows for faster press runs. This is especially true on multi-color jobs where the basic process color scheme, CMYK (cyan-magenta-yellow-black [or key]) is used to produce many different hues, shades, and colors. This is commonly called process color printing.

Rotogravure presses use the gravure process to print continuously on long rolls rather than sheets of paper. Unlike lithography and flexography, gravure printing does not break solid, colored areas into minute dots (half tones) to print the areas, which makes it ideal for reproducing high-quality continuous tone pictures, especially when using glossy inks. Many state-of-the-art printing presses are now able to run 8 to 10-color jobs at high speeds.

The basic raw materials used in most gravure printing techniques are those of a substrate, either in sheet or web(roll) form; a direct transfer or mechanically engraved etched cylinder; impression cylinders; ink systems; ink viscosity control; solvent recovery system; drying ovens; in-line cutting and stripping to remove excess margin waste; quality control systems or procedures to control the quality of the product, and a finished product that ends in sheet form or roll form.

Substrates have an impact on several parts of the printing process. Substrates can affect how the ink is transferred to the surface, how the ink lies on the surface, how well the ink dries and is absorbed by the surface, and how well the press operator can control the register of the finished product. Common substrates include coated and non-coated papers, coated and non-coated board, release papers for the food industry, foils, and metallized papers. Less common substrates are cellophane, polyurethanes and tissues. Coated papers and board probably make up the bulk of the more common printing substrates. One of the more popular coatings used is a clay coating. This coating is generally applied when the paper or board is manufactured. There are single, double, one-sided, and two-sided coated papers. The end use is generally decided by end product/customer specification and the manufacturing process.

Engraved cylinders are stored by the printer until the job is scheduled on the press. Cylinders (only one if a single color) are then mounted on the press and matched with the correct size and hardness of impression rollers. When all of the cylinders have been mounted in the press, each printing unit is set with the correct inks and rollers. A proof is then pulled by the press crew (sometimes on a proof-press). Press proofs can be done on non-virgin substrates or obsolete paper and end rolls to reduce waste and pollution. Color adjustments and registration corrections are made. Once customer approval is obtained, the press run begins. When the press run is completed the cylinders are removed from the press, cleaned, wrapped and placed in protective boxes (normally constructed of aluminum or heavy pine) and then moved to a designated storage area. Cylinders are stored for future press runs or placed back into the process to be dechromed, copper plated, and re-etched with new designs.

PrePress

Cylinder Preparation

Gravure cylinders are made by engraving or etching a design on a steel/copper and aluminum/copper base that is chromed after the design is proofed. The chromed cylinder surface is hard enough to resist image breakdown on long press runs, which would occur with softer material. Solvent-based ink cylinders vary in the depth and style of engraving or etching compared to water-based ink cylinders. Generally, the engraving or etching has a shallower cell micron depth for water-based inks. In each process a design is mechanically or laser engraved into the surface of the cylinder. The circumference of the cylinder depends on the type of press and the repeat of the design, if any.

Depending on the press, cylinders can be made of copper-plated steel or aluminum. In preparation for plating, cylinders are heated in warm water and then put into a muriatic acid bath that strips the chrome plating and rust from the cylinder. They are then rinsed clean. Steel cylinders are nickel-plated to promote the bonding of the copper, and the aluminum cylinders are zinc-plated for the same reason. Aluminum cylinders are also treated with cyanide prior to copper plating. The final process after engraving is to chrome plate each cylinder and ready it for proofing (EPA/600/S-93/009). If the printer does not make its own cylinders, they are proofed at the manufacturer before shipment to the printing company. During proofing, design, engraving and color separation approvals are given.

Press

Process Modification

There are several methods available to address pollution prevention and waste reduction in gravure printing environments. Each method should be evaluated for its practical application, both in cost and resource consumption. Caution should be used to ensure that a prevention program or waste reduction program is not discarded based solely on cost.

In conjunction with shallower ink pans, improved doctor blade technology results in reduced ink usage. Vapor recovery systems can be one of the largest contributors to reducing pollution in solvent-based operations. These systems need to be matched to the specific environment and have been successfully carried out in many printing companies. In addition, alternative chemical solutions can significantly reduce pollution. Test runs and trial projects should be considered when searching for safe alternatives.

Printers need to develop partnerships with each of their major raw material suppliers. Within these partnerships there needs to be a clear understanding of the printers needs matched with materials so a quality finished product is achieved. Suppliers have technical assistance available to their customers so an acceptable product can be manufactured with as little pollution and waste as possible. Development of partnerships with ink vendors is essential so that use of the technical assistance that the ink and solvent suppliers can provide is used. Partnerships with ink vendors allows printers to take advantage of an ink technician's assistance with "ink kitchens" that automatically mix inks to the correct color and quantity thereby reducing the opportunity for waste and pollution.

Post Press

Equipment Modifications

There are many types of equipment modifications that printers can use to help reduce pollution. The type and degree of modification depends upon the company goals, financial health, commitment to improvement, and availability of new technology. Printing press makers have taken advantage of new technology and installed several types of process improvement controls on their equipment. After market items that improve the printing process are also available to modify existing equipment. High temperature ovens, solvent and vapor recovery systems (afterburner) can be improved or modified to reduce pollution. In many cases the improvements used to reduce pollution result in increased manufacturing output that justifies the capital expenditure for these projects. Any reduction in wasted resources will improve the overall pollution prevention program.

Process Modification

The degree to which vegetable oils can replace petroleum oils in inks to reduce VOCs depends on several things, including the type of press, the type of substrate, and the type and color of the inks. Gravure presses generally use heatset inks, which are inks that are set by going through an oven or dryer. These inks generate the most VOCs because they tolerate only the smallest amount of vegetable oil content. The drying temperature needed to set vegetable oil inks will normally scorch the substrate and ruin the product. Vegetable inks dry slower than conventional inks - especially on coated papers.

The absorbency of the substrate will determine the amount of vegetable oil content that can be used in the ink. Absorbent papers hold the ink in the substrate so less VOCs are released as compared to coated papers which normally need heat to dry the inks - thereby releasing VOCs. Soy and vegetable based inks provide beneficial printing properties - but dry slower than petroleum based inks.

Water-based inks, while environmentally friendly, pose their own special kinds of concerns in gravure printing. As a rule, water-based inks dry slower than solvent-based inks resulting in initial obstacles when making a switch to water-based. They are more abrasive and cause increased cylinder wear and they require somewhat different engraving and etching processes. Water-based inks tend to have surface adhesion and lay-down problems that solvent-based inks do not have. Printing process adjustments are needed to maintain the quality of finished product.

Some of the more common solvents used in solvent-based gravure printing are toluene, xylene, methyl ethyl ketone (MEK), methyl isobutyl ketone, acetone, methylene chloride, isopropyl and normal-propyl alcohol. All pose risks that are inherent in a solvent-based system. Alternative materials with less risk associated to their use should be considered.

References Used

Fleischman, M., Kirsch, F.W., and Looby, G. 1993. "Waste Minimization Assessment for a Manufacturer of Rotogravure Printing Cylinders," US EPA Risk Reduction Laboratory, EPA/600/S-93/009. 1993.

Pferdehirt, W.P. 1993. Case Study: Roll the presses but hold the wastes: P2 and the printing industry. Pollution Prevention Review. Autumn 1993.

US EPA, 1990. "Guides to Pollution Prevention: The Commercial Printing Industry." US EPA Office of Research and Development, EPA/625/7-90/008, August 1990.

Annotated Bibliography

Duzinskas, Donald R. 1983, "The Systems Approach to Pressroom Ventilation in Solvent Recovery," Gravure Research Institute, Report No. M-263.

Information on how one company installed a new ventilation system for its seven rotogravure presses and gives an in-depth description of the system.

Norman, Edward C., 1987, "Recent Developments in the Use of Foamed Aqueous Inks in Rotogravure Printing," Paper presented at the Annual Meeting of the Air Pollution Control Association.

This paper presents technical information on the use of foamed aqueous inks, which can lower VOC emissions significantly in rotogravure operations. Good basic information on this technique, author works for Foamink Company, Inc.

Pferdehirt, W.P. 1993. Case Study: Roll the presses but hold the wastes: P2 and the printing industry. Pollution Prevention Review, Autumn 1993.

A review of the printing industry, including a description of the basic printing processes, is given. Waste reduction opportunities are explained, along with a review of progress that has been made in pollution prevention in the printing industry.

Rosen, D.R. and M.R. Wool, 1986, "Microprocessor Control of Rotogravure Airflow," Office of Research and Development, US EPA, EPA/600/2-85/068.

The report discusses the technical and economic viability of using microprocessor-based control technology to collect volatile organic compound emissions from a paper coating operation. The microprocessor-based control system monitors and controls both the airflow rate and vapor concentration level within the rotogravure printing press dryers. It incinerates the VOC emissions in the plant's existing steam boiler and also saves energy by reducing the amount of dryer and room air that must be heated.

"Guide to Pollution Prevention in the Commercial Printing Industry," U.S. EPA Risk Reduction Engineering Laboratory and Center for Environmental Research Information, 1990, 45 p.

This report covers basics of all printing wastes and pollution prevention efforts; includes worksheets for conducting an assessment of a printing facility.

Related ProcessesJendrucko, Richard J., Thomas N. Coleman, and Gwen P. Looby "Waste Minimization Assessment for Manufacturer of Gravure-Coated Metalized Paper and Metalized Film" Environmental Research Brief, US EPA Risk Reduction Engineering Laboratory, Sept. 1994, EPA/600/S-94/008

A waste minimization assessment was performed for a plant that manufactures gravure-coated metalized paper and film. The team's report, detailing findings and recommendations, indicated that a large quantity of unused coating mixture is wasted. The greatest cost savings can be achieved by the plant through the installation of an automated system for mixing and diluting coating mixtures.

Fleischman, Marvin; Kirsch, F. William and Gwen P. Looby, 1993, "Waste Minimization Assessment for a Manufacturer of Rotogravure Printing Cylinders," US EPA Risk Reduction Laboratory,EPA/600/S-93/009.

Documentation of a waste minimization assessment with good information on the various plating processes used to manufacture rotogravure cylinders. Provides various minimization options suggested to this facility with associated savings in terms of estimated waste reduction, waste management cost savings, raw material cost savings, operating cost, total cost savings, implementation costs and simple payback.

Case Studies

Case Study 1

Waste Minimization Assessment for a Manufacturer of Printed Labels

F. William Kirsch and J. Clifford Maginn
Environmental Research Brief, Risk Reduction Engineering Laboratory
EPA/600/M-91/047

A waste minimization assessment was carried out at a plant producing approximately 14 billion printed labels/yr. Steel printing cylinders are nickel and copper plated, etched with the label patterns to be printed, chromium plated, and then used with ink applied to print the labels. About 75 percent of the cylinders are chemically etched, and the remainder are mechanically etched. Solvents used with ink concentrate and for cleaning press parts are recovered and sold to reclaimers. Spent reagents, filters, cleaning rags, and sludge are shipped offsite for disposal. Process wastewater and rinse water are treated by ion exchange and distillation. The team's report detailing findings and recommendations, indicated that most waste other than water and paper consists of spent solvents, and that the greatest savings could be obtained by using recovered solvent instead of virgin solvents for cleaning at press side.

The recommendations for waste minimization included:

Using recovered solvent instead of virgin solvent for cleaning press parts; net annual savings of $284,292.
Using recovered solvent instead of safety solvent for cleaning; net annual savings $59,443.
Automating mixing of ink, extender, and solvent to reduce overmixing and evaporative loss; net annual savings $47,085; implementation costs $288,800; payback years 6.1.
Replacing a cleaning tank lid to reduce solvent evaporation loss; net annual savings $9,604; implementation cost $500; payback years 0.1.
Rinsing spent ink filters with solvent and reuse; net annual savings $5,016.

Case Study 2

R.R. Donnelley & Sons-Mattoon

in Pollution Prevention: Illinois Industry Case Studies
Hazardous Waste Research and Information Center, TN94-039, 1994

R.R. Donnelley operates large printing facilities. In 1990, their Mattoon facility generated 31,700 gallons of waste gravure ink and 17,800 gallons of waste cleaning solvent. By modifying their process, some of the ink and solvent were gradually fed back into the ink supplies for the printing press. This reuse resulted in a total waste volume reduction of 16,900 gallons per year, or 34 percent.

Case Study 3

Case Study: A Gravure Printer

Cannard, Herve, et al.
Spring 1995, Pollution Prevention Review

Constant Services, Inc. (CSI), a gravure printer, worked with the New Jersey Technical Assistance Program, to develop and implement alternatives for TRI-listed solvents and to decrease solvent usage. The company found that substituting alternative solvents for the listed solvents enabled them to eliminate emissions from the room where the company's strike-off press is located as well as reduce fugitive emissions of hazardous air pollutants previously associated with the formulation of their ink pigments. Moreover, by using dry rags instead of solvent-dampened rags to wipe down the presses, CSI not only further reduced solvent use and fugitive emissions, but also realized a substantial cost savings.

The company prints and laminates vinyl webs that are sold primarily as wallpaper. They have five production lines and a room containing a strike-off press which is a slow gravure press used to make proofs. CSI uses an ink that is formulated in-house. The ink binder, a PVC resin, is purchased from a vendor as "dry chips" that are mixed with methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) to form the vehicle. During formulation, the vehicle is added to surplus inks left from previous runs, and to fresh and spent solvent (dirty, spent press wash that is collected after press wash-ups). CSI has the mixing process well organized and uses all spent press wash and almost all surplus inks in new ink blends. Pigments made on-site are added to adjust the color shades. The pigments were previously stored as MIBK solutions. Those applied to the vinyl contains 70-80 percent solvents.

It was believed that partial substitution for TRI-listed solvents would reduce the overall toxicity of the fugitive emissions into the strike-press room.

Changing the Press Wash Procedure

Under the old process, ink trays and doctor blades were "washed down" between production runs in a 1:1 mixture of MEK and MIBK, which was captured in pails for later reuse in ink. The equipment was then cleaned with rags that were soaked with the MEK/MIBK mix.

At the suggestion of an employee, CSI introduced a new cleaning procedure that reduced solvent use and solvent emissions by avoiding the wash down altogether and using dry rags to wipe down the press parts. This new process relies solely on the solvent content of the ink residue to clean the parts. As a result, solvents are now used only to wash the rubber rollers. Roughly, 1,100 pounds of solvents are now being saved by eliminating wash down resulting in a cost savings of $440 per year.

Calculations showed that nearly 60 solvent-laden rags, holding 5.5 ounces of solvent per rag, were thrown away daily. By adopting the use of dry rags, the company not only reduced solvent emissions by 3,600 pounds per year, but also realized cost savings of $1,440.

Cleaning with dry rags instead of washing the press thoroughly also reduced the overall cycle time. Shutdowns which previously lasted 90 minutes have now been reduced to 10-20 minutes. Yearly labor savings of 2,300 hours predicts a cost savings of $23,575.

Switching from TRI-listed to Nonlisted Solvents

Concern about employee health led CSI to change the solvents used to make ink for the strike-off press. The introduction of two non-TRI listed substitutes for the cyclohexanone and MIBK previously used enabled the company to eliminate emissions from the room where the strike-off press is located. In addition, the substitutes have replaced MEK and MIBK in the pigment formulation of the ink used in production processes.

An initial search for substitutes led to the introduction of PMA, a glycol ether acetate. Later, a solvent which is a combination of N-methyl 2-pyrrolidone and dipropylene glycol methyl ether (Printsolve�), was added to the ink formulation and used for press cleaning. The company eventually replaced the PMA with DBE, a dibasic ester mixture, also an unlisted solvent. By making these substitutions, CSI has eliminated approximately 2,000 pounds per year in TRI-listed solvents. However, because Printsolve� is more expensive, the additional solvent purchase cost is approximately $3,370 per year.

MIBK solutions used in the formulation of pigments were replaced with the Printsolve�/DBE blend. This reduced the total amount of hazardous air pollutants used in the plant, and the associated fugitive emissions.

In addition, it is estimated that approximately 10,000 pounds per year of MIBK have been replaced with the Printsolve�/DBE blend, at an additional solvent purchase cost of $12,770 per year.

Other P2 Activities

All the spent inks that are too dirty to be reused, as well as the dirty wash solvents, are recovered in an on-site distillation unit. The distillate is reused in the formulation of inks. The dry residue is a nonhazardous waste and is disposed of accordingly.

Ink and solvent containers, which previously remained open to the air, have been covered with hinged lids. As a result, solvent emissions, especially in the ink formulation room, have been drastically reduced.

Ink pans are covered with any available material (often cardboard) to reduce emissions from open ink surfaces.

A policy statement regarding pollution prevention has been distributed to all employees. In addition, the company now posts information on matters such as weekly usage of solvents during production, production totals, job break-downs, and color changes.

Case Study 4

Hampden Papers Reduces Wastewater by 80 Percent, Ends Excessive Zinc Discharge

Toxics Use Reduction Case Study
Massachusetts Office of Technical Assistance

Despite earlier reductions, waste water discharges from Hampden papers specialty operations continued to contain zinc and copper levels above the discharge limits set by the local wastewater treatment authority. Continued excessive discharges could have forced the POTW to mandate installation of a very costly treatment technology.

The waste waters are generated from the printing machines (6 gravure presses and 3 air knife coaters), the coating mixing area, and kettle washup. Discharges from the coating mixing area came from spill cleanup; improved spill prevention was the appropriate action to reduce wastes there. Zinc ammonium carbonate (ZAC), present as a crosslinker which allows aqueous based ink and coating constituents to become waterproof, is a component in 60 percent of Hampden's throughput and is used almost exclusively on the gravure presses. Copper, a pigment in blue and green ink dyes, is only used in about 3 percent of Hampden's production

Cleanup of the gravure presses includes ink being manually reclaimed and presses cleaned with water. Four of the presses require less than 5 gallons per cleanup, the other two require 30 and 45 gallons of water respectively per cleanup. Analysis showed that the two high volume machines generated concentrations that would affect effluent concentrations.

Zinc

There are two possible alternatives to ZAC, as well as an emerging production method that would use dispersion, rather than solution, technology. One of the alternatives was a carcinogen, and therefore ruled out. The other chemical, ammonium zirconium carbonate (AZC), is more expensive than AZC. Trials showed that discharge limits could be met, but print quality standards could not. The dispersion system, though only applicable to certain coatings, was compatible with 85 percent of Hampden's total coating needs. The system was installed for 20 percent of the production, and Hampden plans to increase this to 70 percent.

Copper

Unrestricted hoses used to clean the ink wells on the air knife coaters had a flow of 7.5 gallons/min. for 60 to 90 minutes per cleaning. The ink mixing kettles required 20 to 50 gallons of water per cleanup. Because the kettles are used to mix custom colors, they often need to be cleaned a dozen times per day. Copper concentrations from these cleanups were below detection level only because of the dilution. Colors and carriers were tested for zinc and copper content. Since no substitute could be found for the copper pigment, segregated waste water treatment was a possible temporary solution.

Water Conservation

All leaking hoses and faucets were fixed, automatic shutoffs were installed on all toilets, sinks and hoses. All air conditioning and machinery cooling lines and non contact cooling water discharges were diverted from the sewer line to a nearby river. The cumulative effect of these efforts reduced average daily discharge on production days to 12,000 gallons (from highs of 130,000 gallons); nonproduction days had a flow of zero. The POTW removed Hampden from the significant industrial user list, provided the company continued to seek substitute chemicals and implement improved cleanup practices. Water discharge is now less than 20 percent of 1993 average daily flow. By 1995, zinc will be reduced to 20 percent of previous levels.