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
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.
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.
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.
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.
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.
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.
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.