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

Screen Printing

Overview

There are about 40,000 graphic art screen printing and textile printing shops in the United States. These mostly small- and medium-sized businesses perform diverse functions ranging from the printing of billboard advertisements, greeting cards, art books, clothing and posters to printing onto electronic equipment (US EPA, 1995a).

Screen printing is probably the most versatile of the printing techniques, as it can place relatively heavy deposits of ink onto practically any type of surface with few limitations on the size and shape of the object being printed. The ability to print variable thicknesses of ink with a high quantity of pigment allows for brilliant colors, back lighting effects, and durable products which are able to withstand harsh outdoor weather conditions or laundering. Unlike many other printing methods, substrates for screen printing can include all types of plastics, fabrics, metals, papers, as well as exotic substrates such as leather, masonite, glass, ceramics, wood, and electronic circuit boards. While screen printing does compete with other printing techniques for some products (especially for small paper substrate products), it has a specialized market niche for many graphic art materials and textile printing applications. Comparatively low equipment investment costs allow for low-cost short production runs (US EPA, 1994a).

Screen printing uses a porous mesh screen with an ink-resistant image on its surface as a template to transfer ink to substrates. The type of material used to make a screen depends on the substrate being used as well as the desired appearance of the product. Screen preparation begins by tightly stretching and securing the material in a rigid frame so that it is level and smooth. Non-image areas of the screen must be blocked and image areas open to allow ink to pass through to the substrate (Figure 8).

 

Figure 8. Principle of Screen Printing

 

The image can be transferred to the screen manually, but it is more common to use a direct coating photomechanical stencil, which consists of an emulsion of bichromated gelatin or bichromated polyvinyl alcohol (PVA) applied to the screen's surface. The emulsion is spread and leveled either manually with a squeegee or automatically. When the coating has hardened, a stencil is applied and the screen is exposed to UV light, that causes a photochemical reaction and makes the emulsion insoluble. The unreacted emulsion, which is still water soluble, is rinsed off. A rubber-type blade (squeegee) is swept across the screen surface, pressing ink through the uncovered mesh to print the image defined by the stencil. Many screen printing facilities reclaim their screens for reuse because the screen material is valuable and costly to replace (US EPA, 1994a).

Screen reclamation has three steps. First, any residual ink must be removed with a solvent, usually sprayed directly on the screen. Some common ink removal solvents are d-limonene-based products, glycol ether and dibasic ester blends, mineral spirits, methyl ethyl ketone, acetone, butyl celusol, cyclohexane, toluene, and methyl isobutyl ketone (Jendrucko, 1994). If the image on the screen is not going to be reused, the emulsion that blocks the non-image area needs to be removed. Emulsion remover is generally sprayed onto the screen then brushed into its pores. Typical emulsion removers contain sodium metaperiodate or salts of periodic acid. After the ink and emulsion have been removed, there is often a ghost image that remains on the screen. A haze remover, which usually contains potassium hydroxide and aliphatic ether alcohols, is applied to the affected areas to remove the ghost. The use of these screen reclamation products, however, can pose potential risks to the people who work with them and to the environment (US EPA, 1995a).

The number of workers exposed to screen reclamation products in the graphics section of the screen printing industry is estimated to be as low as 20,000 or as high as 60,000 depending on how many workers at each facility spend part of their time reclaiming screens (US EPA, 1994a). A Workplace Practices Survey for screen printers, conducted by the Screenprinting and Graphic Imaging Association International (SGIA), reported that almost 36 percent of the respondents had implemented changes in workplace practices to reduce their use of ink removal/reclamation products (US EPA, 1994b).

Prepress

Stencils and Screen Preparation

Several types of emulsions or stencils, such as indirect or direct photo stencils, are used in transferring an image to a screen. Most direct stencils are water-soluble, and thus incompatible with water-based inks. However, chemical curing of water-soluble stencils can improve their resistance to water. A water-resistant stencil must accompany a solvent-based ink, and a solvent-resistant stencil must accompany a water-based ink. Solvent and UV curable inks are typically coupled with water-resistant emulsions. Thus, a commercial facility using 90 percent solvent-based inks and 10 percent UV curable inks can use the same water resistant emulsion systems for both inks. If, however, the screen printing facility wants to replace some of its solvent-based inks with water-based inks, a new type of solvent resistant emulsion will have to be used to complement the water-based inks. Using solvent-resistant emulsion with water-based inks will cause the emulsion to erode quickly and pinholes will show up in the stencil.

Press

A simple way to reduce waste is to keep the various waste segregated. Do not mix various waste streams in an effort to conserve space. This will cause problems and cost money in the disposal or recovery of reusable materials from the wastes.

Ink

Ink categories include traditional solvent-based inks (which include enamels), ultraviolet (UV)-curable inks, water-based inks, and plastisols (for textile printing).

The most common screen printing inks are solvent-based. They dry through solvent evaporation, which produces VOC emissions. Depending on the quantity of ink used, VOC emissions can create regulatory problems for printers, especially those located in nonattainment areas as designated under the Clean Air Act Amendments (CAAA) of 1990 (Jendrucko, 1994).

Water-based inks include water, emulsion resins, other resins, pigments, and additives. Many printers observe that these water-based inks have more vibrant colors and print more crisply than their solvent-based counterparts. The sharper definition possible with water-based inks allows printers to use finer dot patterns in screened process printing. Water-based inks do not require organic solvents when cleaning the presses and, if free of heavy metals, do not produce hazardous wastes. They are usually less expensive than solvent-based inks and are similar in quality, gloss, and adhesion. However, water-based inks require a longer drying time than solvent-based inks (Alaska Health Project, 1987).

Excess ink used in the screen printing process is currently recaptured. The ink left on the screen is squeegeed back into the can prior to washing the screen. This not only reduces the amount of ink used but also decreases the amount of cleaning emulsions needed to wash the screen (Alaska Health Project, 1987).

Postpress

Screen Reclamation

While screen reclamation techniques may vary significantly from one screen printer to another, two basic functions must be performed in order to restore a used screen prior to reuse: removal of ink and removal of emulsion (stencil). A third step, removing any remaining "ghost image" or haze, may be required depending upon the type of ink used, effectiveness of ink removal and/or emulsion remover products, and the length of time that ink and stencil have been on the screen (US EPA, 1994a).

Screen reclamation activities generate solvent waste and wastewater. VOC emissions may also be associated with the solvent used to remove inks (Jendrucko, 1994).

Ink removal (also called screen washing or screen cleaning) precedes stencil removal so that excess ink does not interfere with removal of the stencil. Ink is also removed at other times prior to screen reclamation (for example, when dust gets into the ink and clogs the screen mesh, or at lunch break, to avoid ink drying on the screen). This "process cleaning" usually occurs at press side, in a separate ink removal area of the shop, or in an area where emulsion and haze are removed.

Most emulsion removers are packaged in a water solution or as a powder to be dissolved in water; the water acts as a carrier for the actual reclaiming chemical. The predominant chemical in an emulsion remover is often sodium metaperiodate. Because periodate needs water as a carrier to reach certain chemical groups in the emulsion, it is more difficult to reclaim a water-resistant emulsion than one which is only solvent-resistant. Most commercially available emulsion removers are able to remove either water resistant or solvent resistant emulsions. High pressure water spray can also facilitate emulsion removal and may lower the quantity of emulsion remover required. The rinse water should be evaluated for recycling possibilities since the major contaminant would be suspended solids. Special care must be taken to ensure that the emulsion remover does not dry on the screen, as the screen will become almost impossible to clean even with repeated applications of the remover, thus adding to regulated waste quantities (US EPA, 1994a).

A haze or ghost image is sometimes visible after the emulsion has been removed. This results from ink or stencil being caught in the knuckle (the area between the overlap of the screen threads) or dried/stained into the threads of the screen. Staining of the mesh frequently occurs when petroleum-based solvents are used in the ink removal process. The solvent dissolves the ink, leaving behind traces of the pigment and resin in the screen. The residual pigment and resin bonds to the screen after the solvent evaporates, leading to haze accumulation. Ghost images are especially common when dark inks (blue, black, purple and green) are used, or if an excessively long time period elapsed prior to ink removal from the screen. A ghost image is particularly likely when using solvent-based ink systems, as opposed to other ink systems. If the ghost image is dark or will interfere with later reimaging or printing, a haze remover product can be applied until the image disappears or fades. The level of cleanliness required at the end of the process varies depending on the kind of printing job that the screen will be used for after reclamation. Some printers can use screens with light ghost haze, others cannot. Haze remover can potentially damage the screen mesh, particularly caustic haze removers that are traditionally used in the industry. The excessive use of these products, such as applying the chemical and leaving it on the screen too long, can weaken the mesh (US EPA, 1994a).

The major health impact on the general population for screen reclamation products is probably their release of VOCs that may be detrimental to the worker's health and contribute to the formation of smog in the air. The traditional products, because of their volatility, are likely to have a much greater impact than the alternative products on ambient air quality. The major benefit identified for switching from traditional screen reclamation methods to alternative methods is a significant reduction in inhalation risks to workers (US EPA, 1994a).

Issues which are important in the selection of chemical alternatives are: risk, performance, disposal, quantity used (is more required to do the same job), cost, employee acceptance (perceived benefit), effectiveness (cleaning time), effect on substrate (detrimental effects to the screen), and effect on print quality.

Equipment Modification

Several types of equipment can be used in screen reclamation to prevent pollution. Many of these systems can save money as well as reduce regulatory requirements, facilitate compliance and reduce the amount of chemicals used in screen reclamation. Each printer needs to examine his or her particular process to determine the applicability of any or all of these equipment modifications. In addition, printers should consult their operating permit and applicable water and waste disposal regulations to ensure compliance before making equipment changes (US EPA, 1994a).

The current practice of screen printers is the use of hand held pump bottles to apply screen reclamation chemicals to the used screen which can help reduce emissions and potential exposures with more effective application (US EPA, 1994a). By allowing the screen reclaimer to control the amount and direction of ink remover, emulsion remover, and/or haze remover, pump bottles effectively minimize the amount of solution used and reduce chemical waste at the source. Other sprayer/application systems are also on the market, but the printer will be the one to best determine what will work for their shop.

To further minimize chemical throughput, the more complex systems frequently combine solvent recirculation systems with a spray applicator system. For the smaller printer who spends minimal time in reclamation, the relatively inexpensive spray bottle might be the most cost effective. However, companies that spend a substantial amount of time and effort in reclamation might find the more extensive spray systems a viable option. While the initial costs may be substantially higher, some or all of the cost may be recovered through decreased solvent use. Further, these systems may decrease labor costs because they tend to be quicker and easier methods for cleaning screens. In addition to surveying product literature, a printer may wish to check with several suppliers as well as other printers to determine feasability for their situation (US EPA, 1994a).

A washout booth can also minimize exposures and waste by containing the reclamation process in a confined area and collecting spent chemicals for proper reuse or disposal (US EPA, 1994a). The premise of the washout booth is that concentrating the ink and/or emulsion remover within a specific area will minimize the quantity of solvent necessary for reclamation, while maximizing the cleaning potential of the quantity used. Consequently, these booths are built to focus the cleaning solution in a small semi-contained area (usually box shaped). Although some booths consist of multiple cleaning areas to separate the ink and emulsion removal functions, single unit booths are equipped to remove both ink and emulsion. Waste solution is usually funneled into a drain where it may be recycled or disposed of in several ways.

A booth can be made to specifications; however, the price increases according to size and level of complexity. For the small printer that reclaims very few screens, such an apparatus may not be a prudent or feasible investment. However, for printers with a sizeable reclamation operation, a washout booth may be a positive addition. Printers should consider their individual situations as well as other sources of product information to make a choice that remains consistent with good business practices (US EPA, 1994a).

Filtration systems can be used to remove specific substances from the waste stream, facilitating compliance and allowing reuse of some chemicals (US EPA, 1994a). They work by several different processes. Used independently, these products may not provide unique pollution prevention opportunities; however, when used in conjunction with a recirculator/recycler, the filtration of solvent may allow for substantial decreases in the quantity of solvent used. A filtration system's function within the solvent recirculation process is to filter out particulates (filters), heavy metals (nanofiltration, reverse osmosis), hydrocarbons (ultrafiltration), and other waste products. This process of treating the effluent makes it possible for conditioned solution to recirculate back for reuse in subsequent reclamation.

By screening the effluent resulting from the reclamation process, filtering systems also facilitate compliance with effluent guidelines. The cost of these systems should be carefully considered by a printing facility. Printers should also consider potential savings generated by reducing the use of chemicals and by avoiding fines that could result from noncompliance with federal, state, and local environmental regulations (US EPA, 1994a).

A recirculation system, through a combination of several technologies, allows a printer to minimize solvent usage, and consequently, minimizes pollution at the source. Its purpose is to filter contaminants from the cleaning solution so that the filtered solution can be reapplied to future screens. Generally, a recirculation system consists of an applicator/sprayer system, a filtration unit, and a recirculating mechanism.

A recirculation system can take on a variety of different forms. From a simple ink remover recirculator, to a system that involves complete reclamation, these systems can be made to fit almost any operation. If a printer decides that this is an appropriate method of pollution prevention, he/she should carefully consider the vast array of options in order to properly match the system to their facility. Further, printers should keep in mind that recirculation systems are not closed systems. Printers should consult applicable water and wastewater disposal regulations to ensure compliance (US EPA, 1994a).

Distillation devices that can be used to reclaim used solvent represent another alternative for addressing screen reclamation waste issues. These devices separate the contaminants from screen reclamation effluent and provide an effective way to recycle and reuse spent solvent. Thus, like a filtration and recirculation system, these solvent distillers provide an opportunity to reduce solvent use, raw materials purchased, and operating costs.

Distillation units can provide a cost-effective method to reclaim solvent used in screen reclamation, and this may result in other benefits as well (lower cost, compliance benefits). Differential distillers can vary in size (two to three gallon capacity up to 250 gallons) as well as in cost. The relatively high cost may prohibit many small printers from utilizing this technology. When purchasing these units, printers should consider cost, relevant environmental regulations, and changes in the Uniform Fire Code affecting the availability and use of distillers (US EPA, 1994a).

Use of an automatic screen washer for ink removal may significantly reduce air emissions of certain volatile ink remover components, although the amount of reduction depends on the chemical components of the formulation (US EPA, 1994a).

Totally enclosed systems are commercially available for ink, emulsion, and haze removal or ink only removal. These systems can reduce the quantity of chemicals necessary for screen cleaning and reduce air emissions. Labor involved with screen cleaning will also be reduced. These systems are currently expensive and may be cost prohibitive for small printers (Jendrucko, 1994).

Process Modifications

Many printers have found that by making simple process modifications they can reduce solvent use, waste disposal costs and employee exposure to harmful chemicals.

Whenever possible, avoid delays in cleaning and reclaiming the screen. The quantity of chemicals needed to remove ink, emulsion, and haze can be reduced if screens are cleaned promptly (US EPA, 1994b).

A printer in Minnesota reported that he had identified chemical overspray not directed at the screen during emulsion and haze removal as one of the biggest sources of chemical loss. Employees built a simple "catching frame" to place around the screen during the chemical application steps. The catching frame is used to capture the overspray, which is then recycled or reused (US EPA, 1994a).

A printer in New York said his facility keeps chemicals in safety cans or other sealed containers to minimize solvent loss from evaporation. They used to use a pump and spray unit to apply ink degradant and emulsion remover, followed by a high-pressure water wash. They only use haze remover if it is absolutely necessary. This facility has now gone to manual, spot application of the ink degradant and manual application of the emulsion remover, followed by a low-pressure rinse. A final high-pressure water blast follows this rinse step. Results of industrial hygiene monitoring at the facility indicate that this new method of applying chemicals results in no overspray of chemicals and reduced worker exposure, since the high-pressure water blaster no longer disperses the chemicals as a mist in the air. They have also reduced the accidental discharges from crimped or cracked discharge lines in the pump system. This printer estimates that the new methods of applying chemicals to the screen have resulted in a 15 percent reduction in material use (US EPA, 1994a).

An alternative technique for ink removal is to use a high-pressure water blast. The high velocity fluid impacting the screen loosens the emulsion and increases the removal efficiency. Pressures up to 4,000 psi have been used without damaging screens. The combination of this and previous measures could potentially reduce emulsion remover use by as much as 75 percent (Jendrucko, 1994). Precautions will have to be taken to protect the employees from the noise generated by the high pressure jet.

Using haze remover can cause screens to become brittle and tear more easily. It also contributes chemicals to the wastewater stream. Therefore, it is beneficial to minimize its use. Several simple techniques can be used to accomplish this reduction:

  • Apply haze remover only to the affected area instead of over the entire screen
  • Avoid allowing used screens to sit for a long period of time before reclamation because the longer ink and emulsion remain on the screen the more likely "ghost" images will form
  • Apply an ink degradant to the screen before reclamation to prevent "ghost" image formation (Jendrucko, 1994).

Screen Disposal

Many screen printing facilities reclaim their screens for reuse because the screen material is valuable and costly to replace. Screen fabric can be one of the most expensive supplies that a screen printer uses and can have a large impact on cost of operations. For example, the most commonly used fabric, polyester, costs $10 to $40 per square yard. A shop that wastes $100 -$200 per week in fabric costs from ruining screens or failing to reclaim them, increases its production costs by as much as $5,000 to $10,000. The average monthly expense for fabric is $360. In addition, reclaiming screens has the advantage of saving labor time needed for stretching mesh across the frame and adjusting it to the correct tension. Some printers believe that using retensionable frames when stretching the mesh "work hardens" the fabric, improving the printability and longevity of the screen. Other printers note that reusing screens for other jobs, instead of storing them in an imaged screen inventory, saves both screen fabric costs and storage space often needed for presses (US EPA, 1994a).

Some screen printers with long production runs and extremely small screens, such as those used to print on medicine bottles, simply cut the screen mesh out of the frame after completion of the production run. By simply disposing of the screens, printers could eliminate the high cost of reclamation chemicals and labor time associated with screen reclamation, as well as reduce the risk associated with occupational and population exposure to these chemicals. However, printers have to dispose of more screens, some of which may be designated as hazardous waste due to the chemicals applied to them during imaging and printing. Due to the different types of source reduction involved in these two options, they are difficult to directly compare in terms of pollution prevention. Based on Design for the Environment (DfE) analysis, it is clear that screen disposal is not a cost-effective option for a majority of screen printing facilities. However, printers should not view this cost estimate as a final analysis, because the operations of any one facility can be different from the assumptions used in generating this analysis. Screen disposal would be more cost-effective in circumstances where production runs approach the useful life of a screen and where the size of the screen is relatively small (US EPA, 1994a).

References Used

Alaska Health Project. "Waste Reduction Assistance Program (WRAP) On-Site Consultation Audit Report: Printing Company." 21 p., 1987.

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

US EPA "Designing Solutions for Screen Printers." Design for the Environment Printing Project Factsheet. US EPA. 1995. 2p.

US EPA, 1994a "Cleaner Technologies Substitutes Assessment: Industry: Screen Printing Use Cluster: Screen Reclamation (Draft)" US EPA, Washington, DC, 1994.

US EPA, 1994b "Work Practice Alternatives for Screen Reclamation-Case Study 4: Screen Printing." Design for the Environment Printing Project Factsheet. US EPA. 1994. 4 p.

Annotated Bibliography

"Chemical Alternatives for Screen Reclamation-Case Study 5: Screen Printing." Design for the Environment Printing Project Factsheet. US EPA. 1994. 4 p.

Factsheet compares chemical alternatives for screen reclamation to traditional systems (includes only chemical composition of alternative, not product name). Tests were conducted at two facilities--includes performance, risk and cost data.

"Designing Solutions for Screen Printers." Design for the Environment Printing Project Factsheet. US EPA. 1995. 2p.

Factsheet gives overview of DfE project, gives no information about results of study.

"Reducing the Use of Reclamation Chemicals in Screen Printing: Screen Printing" Design for the Environment Printing Project Factsheet. US EPA. 1993. 4 p.

Very good factsheet. Case study of Romo Incorporated gives lots of good basic ideas, some easy and inexpensive to apply--includes cost and waste reduction data.

"Technology Alternatives for Screen Reclamation-Case Study 2: Screen Printing." Design for the Environment Printing Project Factsheet. US EPA. 1994. 4 p.

Factsheet discusses three alternative technologies for screen reclamation--compares risk, performance and cost to traditional methods.

US EPA. 1994a. "Cleaner Technologies Substitutes Assessment: Industry: Screen Printing Use Cluster: Screen Reclamation (Draft)" Washington, DC: United States Environmental Protection Agency, 1994.

Massive technical document including lots of data. Compares alternative and traditional screen reclamation products, technologies, and processes in terms of environmental and human health exposure and risk, performance and cost. Includes general screen printing information and good overall pollution prevention opportunities. An executive summary is available.

US EPA. 1994b. "Work Practice Alternatives for Screen Reclamation-Case Study 4: Screen Printing." Design for the Environment Printing Project Factsheet. US EPA. 1994. 4 p.

Very good factsheet lists general pollution prevention opportunities including process improvements and materials management/inventory control.

"A Guide for Screen Printers." Washington State Department of Ecology, Environmental Management and Pollution Prevention, 94-137, September 1994.

A good primary resource for the screen printer. Has good checklists of Do's and Don'ts for each major wastestream.

Pollution Prevention for Printers and Photoprocessors, Metro-Dade County Department of Environmental Resources Management, October 1995.

A good booklet on general pollution prevention practices applicable to all types of printing broken down by process.

Factsheets

"Removing solvent and ink from printer shop towels and disposable wipes" MnTAP 1991, 6 p.

Presents options for removing solvent from shop towels and management of disposable wipes, includes some vendors.

Office of Waste Reduction Fact Sheet, Washington State Department of Ecology Nov 1988, Printing Shops, 4 p.

A listing of general pollution prevention opportunities for all types of printers.

Center for Hazardous Materials Research "Pollution Prevention: Strategies for the Printing Industry," 4 p.

Reasons to practice pollution prevention and general tips for all types of printers.

"Waste Reduction for the Commercial Printing Industry" California Department of Health Sevices Toxic Substances Control Division Alternative Technology Division, Aug 1989, 6 p.

Waste reduction incentives, requirements and alternatives including inks and solvents.

"Waste Reduction Checklist" Office of Waste Reduction Services, State of Michigan, Departments of Commerce and Natural Resources, Dec 1989, 6 p.

Checklist of general pollution prevention opportunities for all types of printers.

"Management of Solvents and Wipes in the Printing Industry" SHWEC Waste Education Series, May 1994, 4 p.

Proper management of cleanup wipes and methods of reducing solvent waste.

"Hazardous Waste Reduction Facts: General Commercial Printers" City of Santa Monica Department of General Services, 2 p.

General pollution prevention tips for all types of printers.

"Pollution Prevention Opportunities in Printing" USEPA Region 3, Oct 1990

General pollution prevention tips for all types of printers.

"Lithographic Ink Wastes: How to Reduce, Reuse, and Recyle Ink Waste" SHWEC Waste Education Series, Aug 1995, 6 p.

Discusses ink management techniques including 2 case studies and some ink recycling services providers.

"Waste Reduction Opportunities for Printers" SHWEC Waste Education Series, Aug 1994, 4 p.

Lists potential sources and types of printers' waste and to waste and emission reduction opportunities for printers.

Case Studies

Case Study 1

"Reducing the Use of Reclamation Chemicals in Screen Printing"

Design for the Environment Printing Project Case Study 1
US EPA, 1995, 4 p.

Romo Incorporated of De Pere, Wisconsin is a commercial screen printer that produces a wide variety of products including decals, banners, point-of-purchase displays, and original equipment manufacture. About 60 percent of the company's printing uses traditional solvent-based inks and 40 percent uses ultraviolet (UV) curable inks.

Romo began looking for pollution prevention opportunities in the screen reclamation process. Since screen reclamation is crucial to screen durability and the quality of printing, but also requires a number of expensive and harsh chemical products, the process seemed to provide a large potential to prevent pollution and save money. They concentrated on all three parts of screen reclamation: ink removal (screen cleaning), emulsion removal, and haze or "ghost image" removal. The company searched for ways to reduce chemical risk and prevent pollution through three strategies:

  • reducing the volume of all products used
  • testing alternative application techniques
  • experimenting with alternative formulations of traditional products.

In-process recycling

Romo was using between 20 to 40 gallons of solvent per day. Used screen cleaning product drained through a trough into an open tank, then was lightly filtered and hosed back onto the screen. Unfortunately, the open tank allowed large quantities of solvent to evaporate, and an inefficient filtering system left the recovered solvent dirty and ineffective. Romo reduced their use of solvent to 55 gallons every three or four weeks by installing an in-process recycling still for a one-time cost of $2,900. This investment was recovered within seven weeks through reduced solvent costs. The new still is a closed system that uses a heating and filtering system to remove pigment before pumping the solvent back for reuse. The 5-gallon still is cleaned once or twice a week. The same 55-gallong solvent container lasts for 3 to 4 weeks. When the solvent becomes too dirty to clean effectively, Romo disposes of the ink-contaminated solvent as hazardous waste. This saves the company $83 per day or $20,750 per year in solvent procurement costs alone.

Alternative application techniques

For years the screen cleaning solvent was applied by hosing the solvent onto the screen. Romo added an adjustable spray nozzle in order to provide more direct and efficient application of the product. The nozzle, paired with better use of brushes to loosen the ink, was able to reduce the amount of solvent needed for each screen. Further reductions in solvent use were made by creating a pressure control device for the spray nozzle. The device was simply a small piece of wood secured under the handle of the nozzle by a locking band. Since the wood prevented the screen reclaimers from pushing the nozzle past a certain release point, the amount of solvent being sprayed was controlled.

Alternative products for toxics use reduction

By making the switch to a new press-side screen cleaning product, Romo was able to reduce its use of toluene and methyl isobutyl ketone by approximately 70 percent. Although the new product was expensive ($13 per gallon versus $3 per gallon for the old solvent) it performed well, and Romo decided to use this less hazardous product for press-side cleaning. Savings generated by using less reclaiming solvent with the new spray nozzle were used to fund the increased cost of the new press-side cleaning product.

New emulsion remover approach

Romo tested and then bought an extremely high-pressure water blaster (290 pounds psi) for $2,450 that harnessed the physical power of water pressure to reduce the amount of chemical emulsion remover product used on each screen. Romo was concerned that the increased pressure might disturb screen tensioning or deteriorate the mesh. After five years of use, they were confident enough that the equipment did not deteriorate the mesh that they bought another even higher pressure (1,500 psi to 4,000 psi) blaster for $4,900. Another way Romo reduced the amount of emulsion remover needed was by diluting it with water before applying it to the screen and creating a new applicator for emulsion remover. Formerly, employees dipped a scrub brush into the sliced-open top of an emulsion remover containers before bringing the brush to the screen. Now, the 15-gallon drum has been modified by adding a spray nozzle to evenly mist the emulsion remover onto the screen.

The plant engineer estimates that the combination of the change in emulsion remover application technique, dilution of the emulsion remover, and use of the high-pressure water blaster has resulted in a 75 percent reduction in emulsion remover use. This reduction saves the company almost $3,800 per year.

Haze remover use change

Romo has taken several steps to reduce the use of haze remover. First, the screen reclaimer applies haze remover precisely to the part of the screen that is stained. Second, employees try to remove ink and emulsion as quickly as possible. Third, Romo is looking for alternative chemicals that will eliminate the ghost images and the need for haze remover. The company is also testing a method that the Screen Printing Technical Foundation believes can eliminate the need for a haze remover. The techniques requires that the operator degrease and apply ink degradant to the screen before applying emulsion remover.

Modification

Advantages

Disadvantages

Sprayer/applicator systems
  • Minimize cleaning solution used
  • Reduce chemical waste at the source
  • May decrease labor costs because screen cleaning will be faster and easier
  • Cost of sprayer system
Washout booths
  • Minimize exposures and waste
  • Expense of systems
Filtration systems
  • Minimize cleaning solution used
  • Recycle solutions
  • Disposal of filter and/or concentrate
Recirculation systems
  • Reclaim solvent for reuse
  • Expensive and prohibitive for small printers
  • Disposal of sludge
Distillation units
  • Reclaim solvent for reuse
  • Expensive and prohibitive for small printers
  • Disposal of sludge
Automatic screen washers
  • Reduces air emissions
  • Reduce quantity of chemicals used
  • Labor will be reduced
  • Expensive and prohibitive for small printers

 

Case Study 2

"Infrared Ink Curing Boosts Productivity for Indianapolis Apparel Decorator"

EPRI Journal, October/November 1994

In collaboration with Indianapolis Power & Light Company (IP&L), EPRI's Center for Materials Fabrication recently evaluated the energy savings potential of on-line infrared ink-curing ovens at Logo 7, Inc., a major Indianapolis apparel decorator. Four IR panels, each rated at 4.8 kW, were installed on a 12-stage silk-screening machine and were evaluated through a series of tests. The tests demonstrated that inks could be fully cured while still on the machine, eliminating the need for a convection oven. Energy consumption was reduced 23 percent compared with convection oven curing--a reduction that translates to annual energy cost savings of nearly $900 per silk-screening machine.

 

Case Study 3

"Conversion to Low VOC Technologies"
Pollution Prevention for the Printing Industry

Screenprinting and Graphic Imaging Association, Intl., US EPA, Printing Industries of New England and Massachusetts Office of Technical Assistance
September 1993

A screen printing facility switched to inks with low amounts of volatile organic compounds (VOC) from inks with high VOC levels. This change allowed the company to continue to operate and expand its operations in an area of ever increasing air pollution control programs.

Traditionally, the screen printing facility primarily printed with solvent based ink systems. The facility is printing a wide variety of point-of-purchase products, banners for indoor and short term outdoor use, and all types of window decals. Due to the regulatory environment that was forcing reductions in the amount of volatiles emitted, the facility began the transition to low VOC technologies.

Ninety-five percent of the inks used by the facility are low VOC. The facility uses both UV curable and water based ink systems depending on the printing requirements. Employee training in the use of both ink systems was required. Originally, the facility moved into UV technology and then into the use of water based technology.

The facility phased in the use of water based technology over a period of nine to twelve months. They began by doing parts of a print run with water based inks. Working with these low VOC ink systems has required this facility to become more sophisticated in its approach to the screen printing process.

The following are SGAI's recommendations and work practice modifications for effective use of water-based technology.

  • Ensure that films are clear of scratches, splices, and improperly developed areas. Any of these problems tend to cause a weak stencil.
  • When haze removers were used to remove dried on water-based ink, screens were flushed completely with a strong water wash and degreaser before new stencil application. Caustic based cleaners, if not thoroughly removed, tend to re-wet the screen and break down the stencil.
  • Screen stencils needed to be completely and thoroughly dried before exposure. Maintain a low humidity (below 60 percent RH) and warm air (up to but not exceeding 100 degrees F) to assure thorough drying. Drying cabinets, under these conditions, will complete the drying in less than two hours, regardless of screen size. The facility has found that screens for water-based inks should not be coated as thick (one-third less) as ones used for solvent based inks.
  • To assure thorough and complete exposure of the stencil, an exposure unit rich in actinic light (correct spectral intensity in UV) was used. The wattage output was not the concern here, duration of spectral intensity expressed in real time, minutes or seconds, was. The facility is now using a 7500 watt lamp.
  • Stencils used for long runs are chemically hardened.
  • After developing the stencil a sufficient amount of drying needs to occur. Using warm air and low humidity conditions, the drying times were less than two hours.
  • If pinholing the stencil after exposure is necessary, the same photo emulsion used to coat the screen must be used again and re-exposed. Caution must be exercised not to use an excessive amount, regardless of technique, of brush or flat applicator.
  • Press operators must have spray bottles of water to mist on flooded screens to replace water that evaporates.
  • Pre-lubricate the squeegee with a very oily safety solvent to double or triple the number of impressions obtained prior to resharpening the squeegee.
  • Water-based inks may be very difficult to remove from the stencil, and the use of haze removers may be necessary.

A major concern with the use of water based inks is the weather, or the ability of the air to draw the water out of the ink. The facility has found that as shop conditions change throughout the day, printing conditions may change as well. For example, the print run in the morning may only thin with water, and as temperatures increase, more solvent based retarders may be used. However, in both hot and cool humid conditions, care must be taken to use water as a thinner since water based inks loaded with too much retarder are difficult to dry.

The following are SPAI's recommendations and work practice modifications for effective use of UV technology.

  • 360 and up mesh counts are used.
  • The durometer of the squeegee changes. A harder squeegee is used to print UV inks.
  • Prior to running the actual job, a radiometer is used to measure the intensity of the lamp. In addition, an ink cure analyzer is used to test the degree of cure that is achieved.

The facility has found that employee training is crucial to the effective use of low VOC technologies in a production setting. By reducing the amount of solvent based inks used by 95 percent, the facility realized a 70 percent emission reduction from ink emissions alone.

The use of UV technology does require the purchase of new equipment. A typical cure unit, depending on belt width, costs $12,000 to $24,000. However, UV curing equipment is more compact and can reduce the amount of space required for a facility's print area.

While the cost of UV ink is higher than traditional solvent based ink, the UV ink provides a larger amount of coverage. 2,700 square feet from a gallon of UV ink, as opposed to 1,500 from a gallon of solvent based ink.

Water-based inks behave more like solvent based ink, and no new equipment was required to introduce this ink system into the facility. The costs of water based ink are similar to the solvent based ink, so there was no appreciable difference in overhead.

The facility did not find that water-based ink systems require more energy to dry as compared to similarly used solvent based ink systems. Overall, the facility is pleased with the change to water based products. They are easy to work with, there is very little odor associated with the system, but they are difficult to dry.

 

Case Study 4

"Screen Printing Case Study-Waste Water Issues"
Pollution Prevention for the Printing Industry

Screenprinting and Graphic Imaging Association, Intl., US EPA, Printing Industries of New England and Massachusetts Office of Technical Assistance
September 1993

The screen printing facility produces a wide variety of products with both solvent and UV curable ink systems. Upon relocation to a new facility, the screen printing operation was required to install and institute new programs for all operations producing a waste water stream to comply with state and federal regulations.

Prior to the move, the facility was using a solvent based material to clean and reclaim screens. Today, the facility is using a water soluble product for both ink removal and reclaiming.

A silver recovery/wash water recirculating system was installed in the darkroom. This unit reduces the amount of silver contained in the waste stream to acceptable levels, and reduces the amount of waste water that must be disposed in a hazardous waste treatment facility.

A system was designed that allows for the recycling of the waste water from screen cleaning activities. This minimizes the use of water as well as disposal costs. After the water is spent, it is placed in holding tanks and transported to a legal disposal facility. To install this waste water recirculating systems, the facility spent $35,000 and will incur an annual operating cost of $8,000.

By making a switch from solvent based to water soluble screen cleaning/reclamation products, the facility realized a savings of $7,000 per year.

Due to the installation of the silver recovery/wash water recirculating system, the facility has seen a 60 percent to 80 percent decrease in the amount of waste that must be properly disposed.

The filter/recirculating system installed in the screen reclamation area has reduced the amount of waste by 75 percent. With the addition of both recirculating/filtration systems, disposal costs for this facility are approximately $9,000 per year.

 

Case Study 5

Pollution Prevention Opportunities in Screen Printing Operations: A Case Study

presented by Lisa F. Wilk
Screenprinting and Graphic Imaging Association, Intl., US EPA, Printing Industries of New England and Massachusetts Office of Technical Assistance
September 1993

A screen printer in New England was faced with increasing costs for disposal of solvent wastestreams generated by cleaning of fine mesh screens.

Input chemical substitution--screen cleaning operations formerly utilized organic solvents (toluene, mineral spirits). Through a product literature search, an alternative aqueous cleaning chemistry was identified. Pilot testing of the alternative cleaner indicated that satisfactory cleaning could be obtained with the aqueous chemistry.

Rinse process modification--spray nozzles were installed to control flow, which improved cleaning and minimized excess wastewater generation from rinsing operations.

Cleaning process modification--a countercurrent cleaning system was installed to achieve more efficient use of cleaners. This is an idea borrowed from the electronics and metal finishing industries, which involves passing the component (e.g., the screen) requiring cleaning (or rinsing) through two or ideally three baths of cleaner (or rinse). Fresh solvent (or rinsewater) is only added to the last bath. The solvent (or rinse) is periodically (or continuously in the case of rinsewaters) transferred from the last container to the previous bath (and from the second bath to the first bath in the case of triple countercurrent systems). Thus, the screen is rinsed in the cleanest bath last. Computer modelling has shown triple countercurrent rinsing to be the most effective in terms of cleaning quality as well as reduction in cleaning solvent (or rinse) required. Adding four or more baths to the system does not achieve measurable improvement over the triple countercurrent system.

Process equipment modification/upgrade--automated cleaning systems were investigated. Due to capital equipment investment requirements, it was decided to postpone this option for further review in the future.

Through a cooperative team effort, a New England Screen Printer was able to identify and implement pollution prevention techniques in its screen cleaning operations. The printer achieved a significant cost savings in cleaning chemistry purchase costs, water and sewer costs, and waste stream disposal costs. In addition, the printer helped contribute to an improved environment by reducing its use of toxic chemistries and its generation of hazardous waste streams. Encouraged by its success with implementation of pollution prevention techniques in screen cleaning operations, the company is now investigating potential techniques for reducing ink usage and waste generation.

 

 

Case Study 6

Technology Alternatives for Screen Reclamation
Design for the Environment Printing Project

US EPA
October 1994
(also available to download from Enviro$ense http://es.inel.gov/)

This is one of a series of case studies focusing on the screen printing industry that EPA has developed to illustrate how the DfE concepts can be incorporated into screen printing operations. This case study focuses on different technologies that can be utilized in screen reclamation. Three screen reclamation technologies that may enable the printer to change both the types and amounts of chemicals used are: high pressure screen washers, automatic screen washers, and sodium bicarbonate (baking soda) spray.

This case study presents:

1) Descriptions of two commercially available technologies that can reduce a facility's usage of traditional solvent-based ink removers.

2) Description of a technology now under development that could further reduce the costs and potential health risks of screen reclamation.

3) Comparative cost, performance and risk information for three reclamation technologies.

The costs and risks for each of the three substitute technologies are compared to the costs and risks of a traditional screen reclamation system. The traditional system used in the comparison consists of lacquer thinner as the ink remover, a sodium periodate solution as the emulsion remover, and a xylene/acetone/mineral spirits/cyclohexane blend as the haze remover. These chemicals were selected because screen printers indicated they were commonly used in screen reclamation. In both the cost and risk comparison, it was assumed that these chemicals were applied manually to 6 screens per day, each 2,127 in2 (approximately 15 ft2) in size.

High Pressure Screen Washers

Two high pressure screen reclamation systems were reviewed. In addition, the performance of one system was evaluated in a print shop as part of the DfE Screen Printing Project. High pressure washers typically work as follows. Excess ink is carded off the screen prior to cleaning. No ink remover is applied to the screen. An emulsion softener or remover is applied and allowed to work, typically for anywhere from ten seconds to less than one minute. The ink and stencil are then removed by a high pressure water blaster sprayed on both sides of the screen at a pressure of up to 3,000 pounds per square inch (psi). If necessary, a haze remover is then applied and allowed to work. Again, the high pressure water blaster is used to rinse off the haze and the haze remover. Cleaning usually takes place in a washout booth where the rinse water can be collected.

While this technology may require significant water use, most emulsion and haze removal products are formulated to allow discharge to sewers. Where ink residues in the rinse water exceed wastewater permit concentration limits, such as for suspended solids, manufacturers also supply a variety of filters. Some improved filtration systems allow rinse water to be reused. Filter wastes are typically disposed of as hazardous waste.

Risk

In general, the benefits of high pressure washes are that they reduced both chemical use (eliminating ink removers) and worker exposure (less scrubbing required). The DfE Screen Printing Project found that the occupational risks of this system were notably lower than the risks associated with the traditional solvent-based reclamation chemicals, particularly with organic solvents, were significant. For the high pressure screen reclamation system, health concerns were related to unprotected skin contact with the reclamation chemicals. Dermal exposures could be reduced dramatically, however, by wearing gloves. Ecological risks from discharges to the water were not a concern for either the traditional system or the high pressure blaster system. General population risks from air releases also were not a concern for either system.

Performance

Performance of a high pressure water blaster were evaluated by DfE staff at a volunteer printing facility where the technology was in place. During the demonstration, the technology's performance was very good. On screens with solvent- and water-based inks, the stencil dissolved easily, leaving no emulsion residue on the screen. Ink stains on these screens were completely removed by the haze remover even before the waiting period or pressure wash. Reclamation results were fairly similar for UV-curable ink as well.

Cost

The DfE Screen Printing Project also estimated the cost of equipment, labor, and chemicals for the high pressure wash. Assuming that 6 screens are reclaimed daily and each screen is 2,127 in2 in size, the cost estimate for the high pressure washer totaled $4.53 per screen. This estimate was compared to that of traditional screen reclamation system. Using the same assumptions, the estimated reclamation cost using the traditional system is $6.27 per screen: 30 percent more that the high pressure wash, with the greatest savings coming from the reduced labor costs for the high pressure washer. Equipment costs, estimated at $5,300 (installed) account for just 12 percent of the per screen costs. This estimate does not include filtration units, which range in price from $1,300 to $12,000, although maintenance and operating costs vary widely.

Automatic Screen Washers

There are several different types of automatic screen washers, and although most are used for ink removal only, automatic systems for emulsion and haze removal are also available. The major benefits of automatic screen washers are reduced solvent losses, reduced labor costs, and reduced worker exposure. The DfE Screen Printing Project identified a wide variety of automatic screen washers on the market and found significant differences in the chemicals used and costs. Costs vary based on the level of automation (such as conveyors), system capacity, and complexity of the equipment.

The basic component of the automatic screen washers is the wash unit, and enclosed box that can house a variety of screen sizes (up to 60 in. by 70 in.). After a screen is clamped inside the wash unit and the top closed, the cleaning process begins. A mobile mechanical arm sprays solvent onto the screen through pressurized nozzles (30 to 150 psi) for any preset number of cleaning cycles. Since the systems are enclosed to reduce solvent losses, volatile solvents, such as mineral spirits, are often recommended because of the efficacy. There are, however, a number of alternative formulations offered by equipment manufacturers. Used solvent drains off the screen and is directed to filtration system to removed particulates (inks and emulsion). Following the filtration step(s), reclaimed solvent is typically reused. Some systems have separate wash, rinse, and air dry cycles or separate tanks for washing and rinsing. Solvent reservoirs must be replenished intermittently and changed once or twice a year. Filter wastes are typically disposed of as hazardous waste.

Risk

Compared to manual application of the traditional screen reclamation chemicals, the DfE risk evaluation of automatic screen washers found that worker inhalation exposures to the volatile organics used in solvents (mineral spirits and lacquer thinner) were reduced by as much as 70 percent. Although the health risks associated with skin contact of the chemicals remained high, these risks could be reduced dramatically if gloves are worn while handling the screens. since the automatic screen washer is used for ink removal only, the risks associated with emulsion and haze removal remained the same as the traditional system's risks for these steps.

Performance

As described above, there are several types of automatic screen washers, and for each type there are several manufacturers. Because of the resources required to do a full demonstration of the equipment commercially available, performance demonstrations of automatic screen washers were not conducted as part of this project.

Cost

The DfE Screen Printing Project estimated costs for two automatic screen washers, assuming that the washers were used for ink removal only and that 6 screens (as above) were reclaimed per day. Screen reclamation costs using an automatic screen washer ranged from a low of $4.13 to $10.14 compared to $6.27 for traditional reclamation. The largest cost component, and the cause of the variability in costs, is typically equipment cost. Additionally, the savings of switching to this technology would be greater if this costing accounted for the labor savings of workers moving on to other tasks once the screen is loaded in the washer. It is important to note that the cost per screen of the more automated, higher cost washer would be much lower if it operated nearer to its capacity of over 100 screens per day.

Sodium Bicarbonate Spray

A sodium bicarbonate (baking soda) spray technology was evaluated by the DfE Screen Printing Project to determine if it is potentially adaptable as an alternative screen reclamation technology. This technology is currently used for removing coating, such as paint, grease, or teflon from metal parts. In these applications, the technology has been successful in replacing hazardous cleaning chemicals. Based on the technology's success in other applications, it appears to be a promising substitute for chemical screen reclamation systems. Because the sodium bicarbonate spray technology had never been tested for screen reclamation, DfE staff conducted a one-day site visit to the equipment manufacturer's facility. Three imaged screens were inked with three types of ink. An inked screen was placed inside an enclosed cleaning booth, and the screen was passed, back and forth, under the sodium bicarbonate spray. No chemicals other than the sodium bicarbonate spray were used during the reclamation.

Risk

The DfE project did not undertake a risk assessment of this spray technology for a number of reasons. Sodium bicarbonate has been shown to be a fairly innocuous chemical and it is not a skin irritant. In addition, it is a common ingredient in baked goods, toothpaste and detergents. If this technology proves to be a viable alternative for screen reclamation in the future, a detailed assessment of the human health and environmental risk should be conducted.

Performance

The performance demonstration showed that cleaning the screen with a pressurized sodium bicarbonate spray alone, without water, resulted in excessive damage to the screen. Performance clearly improved when the sodium bicarbonate spray was combined with a pressurized water spray for screens with solvent-based ink and water-based ink. Typically, the emulsion came off in stringy rolls, and ink flaked off rather than dissolved. A 100 in2 area took approximately 15 minutes to clean. Following this cleaning, there were either significant haze or ink residue sops. Slightly greater spray pressures or slightly longer times resulted in visual screen damage or a ripped screen. Cleaning of UV-curable inks was ineffective. No evaluation of subsequent use of these screens was made.

Based on these limited demonstrations, initial results indicate that with further testing and research, this may be a promising new screen reclamation technology. Some modifications are needed to clean the screens faster and with less possibility of screen damage. For example, the physical support behind the screen greatly reduced the stress on the mesh. Use of hot water was suggested as a means of improving emulsion removal. Other modifications may include decreasing the sodium bicarbonate particle size, or modifying the delivery rate and pressure of the sodium bicarbonate and water sprays. Further testing is needed before a definitive evaluation of performance can be given.

Cost

Since the available equipment was not designed specifically for screen reclamation, it was assumed that the cost of equipment modified for screen reclamation would be similar to the cost of the equipment used in the performance demonstration. The available equipment ranges from $32,000 to $52,000, including a filtration system. The sodium bicarbonate itself costs between $0.65 to $0.75 per pound, based on amount purchased, and approximately 1 pound is sprayed per minute. If this technology proves to be a feasible alternative for screen reclamation after further developments, a more detailed cost analysis can be conducted.

This case study described three distinct screen reclamation technologies that could offer a screen printer the means to reduce employee exposures to chemicals. These technologies may also reduce the total cost of screen reclamation (which included equipment, labor, reclamation products, and waste disposal costs). One of the technologies under development (sodium bicarbonate spray) offers the benefit of using relatively benign chemicals.

 

Case Study 7

Chemical Alternatives for Screen Printing
Design for the Environment Screen Printing Project

Case Studies #5 (EPA 742-F-95-004) and #10 (downloaded from Enviro$ense at http://es.inel.gov/)
US EPA 1995

Printers, EPA, product manufacturers, and the screen printing trade association are all concerned with minimizing the environmental and health hazards of screen reclamation chemicals currently used in printing shops. In response to these concerns, the DfE Screen Printing project worked with printers and selected the screen reclamation process as one of the foci.

Through DfE, these groups worked together to evaluate alternative screen reclamation products. A total of eleven alternative chemical "systems" were evaluated. Most "systems" included an ink remover, an emulsion remover, and a haze remover.

This case study is geared toward getting information to small- or medium-sized printers. It is a compilation of the data presented in DfE Screen Printing Case Studies #5 and #10. Included are: performance evaluations of the alternative system from laboratory tests and from two printing facilities; the health and environmental risks of the alternative system compared to a traditional screen reclamation system; and the cost of the alternative system compared to the cost of a traditional system.

Background

Initiated by industry, this project was entirely voluntary and involved almost all sectors of the screen printing industry. All product systems were evaluated using the same methods. The consistency of the evaluations allows the printer to determine which of the alternatives may be a substitute for their current reclamation products.

This case study highlights two alternative systems, referred to as Chi and Epsilon. These systems, as with all systems demonstrated in the project, is a real, commercially available screen reclamation system; however, the names of the products are masked. The actual trade name for these alternative system is not used in this case study or in the final project report. Trade names were masked for several reasons: 1) DfE hopes to encourage printers to discuss the characteristics of the products they use, or are considering using, with their suppliers; 2) since every screen printing shop is different, manufacturers recognize that their product's performance may vary greatly depending on both the operating conditions and the varying options of the different printers using the products. In order to get their full cooperation before the results were available, some manufacturers asked that the product name be masked.

To compare the cost and risk of the alternative systems to a known system, a baseline was established using a traditional solvent-based screen reclamation system. The traditional system used in the comparison consists of lacquer thinner as the ink remover, a sodium periodate solution as the emulsion remover, and a xylene/acetone/mineral spirits/cyclohexanone blend as the haze remover. These chemicals were selected because screen printers indicated they were commonly used in screen reclamation. In both the cost and risk comparisons, it was assumed that these chemicals were applied manually to 6 screens per day, each 2,127 in2 in size.

Promising Performance

Performance was evaluated in two phases: 1) performance demonstrations at Screen Printing Technical Foundation's laboratory evaluated the products under controlled conditions; and 2) field demonstrations at volunteer printers' facilities provided performance information under the variable conditions of production. Each product system was demonstrated in two or three facilities for one month to get a more complete evaluation of performance under a variety of operating conditions.

Laboratory Testing

During laboratory testing, three imaged screens were reclaimed using each alternative system: one that had been inked with solvent-based ink, the second with an ultraviolet-curable (UV) ink, and the third with a water-based ink. Following the ink application, screens were allowed to dry for 15 minutes to simulate a shop situation. After drying, the ink remover was applied according to the manufacturer's instructions. Again the screen was allowed to sit, this time for 24 hours, before applying the emulsion and haze removers.

System Chi

Two applications of the Chi ink remover were required to remove the solvent-based ink. The ink dissolved more easily on the other two screens (UV-curable and water-based ink), however, an ink residue or haze remained on all of the screens after applying the ink remover. On two of the screens, the stencil started to deteriorate during the ink removal process, indicating that this product may not be applicable for in-process ink removal. The emulsion remover easily dissolved the stencil with only light scrubbing, leaving no emulsion residue behind. When additional ink remover was applied (used as a haze remover in this product system), it removed the ink residue and lightened the stains on all three screens.

System Epsilon

The Epsilon ink remover dissolved the ink quickly, was easy to use, and rinsed clean of reside on the screens with solvent-based inks and UV-curable ink. In both cases, a light to moderate ink stain remained on the screen. When the ink remover was used on the water-based ink, more time and effort were needed, but the ink was removed except for a light stain. On all three screens, the emulsion remover dissolved the stencil and there was no emulsion residue on any of the screens after pressure rinsing. In the final step, the haze remover lightened the ink stains of all three screens.

On-Site Demonstrations

Four printing facilities evaluated these alternative systems. Facility A and B used Epsilon for one month, Facility C and D used Chi for one month. Their experience with these systems follows.

Ink Remover Performance
System Chi

At Facility C, the alternative ink remover worked well, although some of the workers who used it thought that it acted more slowly than their standard product (a solvent blend). Facility D found the alternative ink remover worked well, especially on metallic inks.

System Epsilon

At Facility A, the ink remover worked well, although some of the workers who used it thought that it acted more slowly and required more effort on catalyzed inks than on other solvent-based inks. At Facility B, the product removed both UV-curable and solvent-based inks efficiently, but the UV-curable inks was slightly easier to clean than the solvent-based ink. In addition, Facility B found they used significantly less alternative ink remover per screen than their standard product, which was lacquer thinner.

Emulsion Remover Performance

Both emulsion removers worked well at all facilities, dissolving the stencil quickly and easily.

Haze Remover Performance

System Chi

This system did not include a haze remover; instead the manufacturer recommended applying the ink remover again to remove any remaining haze. Facility D found their screens were clean after the emulsion remover and a haze remover was not needed. At Facility C, the haze remover lightened the haze, however, a ghost image remained on the screen that continued to build over time. For light haze, the haze remover was acceptable, but in most cases, this facility needed to dehaze the screen again with another product.

System Epsilon

Both facilities evaluated the haze remover performance as "acceptable," and similar in efficacy to their standard haze removers.

Overall Evaluation

System Chi

At both facilities, the performance of Chi was comparable to the performance of the facilities' standard screen reclamation products. The consistent performance of the product at SPTF and in two print shops demonstrates that this system can work under a variety of operating conditions. When compared to the traditional system described in this case study, a switch to Chi significantly reduced risks and costs while maintaining the screen reclamation performance printers expect from their products. Although the alternative system described, may prove to be a good alternative in many printing shops, it may not be the solution for all types of screen printing operations.

System Epsilon

The performance of Epsilon was similar at both facilities, according to the printers' evaluations. Because the two facilities have very different operations, the fact that Epsilon performed well at both plants demonstrates that this system can work well under a variety of operating conditions. Facility A prints banners and point-of-purchase displays on plastic using a variety of solvent-based inks, a dual cure emulsion, and mesh counts of 83-280 threads/inch. Facility B prints vinyl and mylar labels using both solvent-based and UV-curable inks. They use a direct photo stencil and screens with a mesh count of 355 threads/inch. Even with these differences, Epsilon was successful in reclaiming screens at both facilities. The final proof for the participating printers was that all the reclaimed screens could be reused for future print jobs.

Reduced Risk

The risks associated with inhaling the chemicals in Epsilon are much lower, in Chi were found to be negligible, while there is a clear concern for chemical inhalation risk with the traditional system. Gloves should be worn with both alternative systems as well as with the traditional system.

Cost Savings

The performance demonstrations showed that all of the participating print shops could reduce their costs for screen reclamation by switching to an alternative system. Costs of the alternate systems were compared to costs of using the traditional system. Assumptions included 6 screens reclaimed daily (approx. 15 sq. ft.) in size for both the traditional and alternative systems. The cost estimate for each reclamation system included labor time spent to reclaim the screen, the cost of an average quantity of reclamation products, and the cost of hazardous waste disposal for RCRA-listed waste or RCRA characteristic waste; the RCRA-listing applies to the traditional system ink remover only.

System Chi

For Facility C, their reclamation cost per screen would drop from $6.27 to $3.89/screen. This would lead to annual savings of $3,560. At Facility D, the reclamation of $6.27 would decrease to $3.25/screen. Over a year, the savings would amount to $4,520. The difference in costs between the facilities is due to differences in the quantity of product used and the labor time required per screen as recorded by employees.

System Epsilon

For Facility A, their reclamation cost per screen would drop from $6.27 to $3.08/screen. This would lead to annual savings of $4,775. At Facility B the cost per screen with the alternate system would be $5.29. Over a year, the savings would amount to $1,469. The difference in costs between the facilities is due to differences in the quantity of product used and the labor time required per screen as recorded by employees.