POLLUTION PREVENTION OPPORTUNITIES IN SCREEN PRINTING OPERATIONS: A CASE STUDY

Transcription

1 POLLUTION PREVENTION OPPORTUNITIES IN SCREEN PRINTING OPERATIONS: A CASE STUDY Presented by: Lisa F. Wilk, P.E. Associate and Senior Environmental Engineer Capaccio Environmental Engineering, Inc. 75 Union Avenue Sudbury, Massachusetts Tel. 508/ Fax at: Pollution Prevention for the Printing Industry Conference Sponsored by U.S. EPA, PINE, and MA OTA September 30, 1993 ABSTRACT With the the increasing regulatory emphasis on pollution prevention through both federal and state regulations and policies as well as concern for economic efficiency, printers are interested in identifying practical solutions to minimize pollutant generation. The focus of this presentation will be a case study example of implementation of pollution prevention at a screen printing facility. The emphasis will be on providing practical, cost-effective pollution prevention information for the printer. REGULATORY BACKGROUND The Resource Conservation and Recovery Act (RCRA) of 1976 established the regulatory framework for management of hazardous waste. With the reauthorization of RCRA in 1984, greater emphasis was placed on minimizing waste generation. As originally defined, the term waste minimization referred to source reduction, recycling/reuse, and some forms of alternative treatment. Source reduction is defined as minimizing or eliminating waste at the point of generation via chemical substitution, process modification, et al. Recycling/reuse refers to returning the wastestream, sometimes with additional treatment, to process operations (either the same process - I -

2 where generated or another process operation). The United States Environmental Protection Agency (US EPA) identified source reduction as the preferred means of achieving waste minimization, and recycling/reuse as the next preferred method of achieving waste minimization. Alternative treatment was identified as the least preferred means of achieving waste minimization because often it is just a transfer of pollutants from one environmental medium to another (e.g., from land to air, land to water). Alternative treatment is only acceptable as a means of achieving waste minimization if it facilitates recovery/reuse and/or reduces the volume and toxicity of the wastestream without utilizing dilution. Although the initial regulatory focus was on minimization of solid and hazardous waste, with the enactment of the Pollution Prevention Act (PPA) of 1990 the concept of waste minimization has been expanded to include all environmental media (land, air, water). The term waste minimization has been replaced with the term pollution prevention to emphasize the multimedia focus as well as source reduction as the most effective means of achieving the goals of the PPA. With the enactment of the Toxics Use Reduction Act (TURA), Massachusetts has taken pollution prevention even one step further by focusing on reducing the use of toxics in process operations to achieve reductions in waste generation., OVERVIEW OF SCREEN PRINTING PROCESS In screen printing,, sometimes referred to as silk screening, a stencil is created photomechanically or manually on either a porous fine screen mesh or frame-mounted stainless steel. Typically, the non-printing areas are protected by the stencil. Ink is forced through the screen. Due to the larger quantities of ink applied by screen printing processes (versus other types of printing), the use of hot air drying and UV curing ink improves the efficiency of the process. Screen printing can be done manually or via automatic presses. Rotary screen presses allow faster and continuous operation. One advantageous feature of screen printing is that it can be done on virtually any type of surface, and is therefore used for clothing, art prints, posters, greeting cards, menus, program covers, wallpaper, tablecloths, shower curtains, billboards, decals, and labels. The electronics industry also utilizes screen printing techniques to print electronic circuit boards. CASE STUDY: SCREEN PRINTING COMPANY A screen printer in the New England area was faced with increasing costs for disposal of solvent wastestreams generated by cleaning of fine mesh screens. Although treatment of the wastestream would potentially reduce disposal costs, the company preferred to investigate potential pollution prevention opportunities which could provide even greater savings as well as more environmentally sound solutions. A team consisting of both in-house personnel and outside consultants was created to identify potential improvements. -2-

3 POLLUTION PREVENTION OPPORTUNITIES IDENTIFIED & IMPLEMENTED lnput 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 to installed to achieve more efficient usage 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. SUMMARY 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 significant cost savings in cleaning chemistry purchase costs, water and sewer costs, and wastestream disposal costs. In addition, the printer helped contribute to an improved environment by reducing its use of toxic chemistries and generation of hazardous wastestreams. 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. -3-

4 POLLUTION PREVENTION OPPORTUNITIES IN SCREEN PRINTING OPERATIONS: A CASE STUDY Presented by: Lisa F. Wilk, P.E. Associate and Senior Environmental Engineer Capaccio Environmental Engineering, Inc. Sudbury, MA Tel. 508/ , Fax. 508/

5 MOTIVATION FOR POLLUTION PREVENTION ASSESSMENT REDUCE COSTS FOR WASTE DISPOSAL REDUCE ENVIRONMENTAL LIABILITY ACHIEVE MORE EFFICIENT PROCESS OPERATION IMPROVE WORKER SAFETY IMPROVE PUBLIC RELATIONS BE ENVIRONMENTALLY PRO-ACTIVE

6 POLLUTION PREVENTION OPPORTUNITY ASSESSMENT: SCREEN PRINTING OPERATION MOTIVATION FOR POLLUTION PREVENTION DESCRIPTION OF SCREEN PRINTING PROCESS GUIDELINES FOR WM/PP ASSESSMENT PLANNING & ORGANIZATION ASSESSMENT FEASIBILITY ANALYSIS IMPLEMENTATION

7 POLLUTION PREVENTION OPPORTUNITY ASSESSMENT: SCREEN PRINTING PROCESS SUMMARY IDENTIFIED POLLUTION PREVENTION OPPORTUNITIES IMPLEMENTED POLLUTION PREVENTION TECHNIQUES ACHIEVED SIGNIFICANT COST SAVINGS - CLEANING CHEMISTRY COSTS - WATER & SEWER USE COSTS - DISPOSAL COSTS REDUCED ENVIRONMENTALLIABILITY IMPROVED WORKER SAFETY IMPROVED ENVIRONMENT ENCOURAGED TO CONTINUE ASSESSMENTS

8 POLLUTION PREVENTION OPPORTUNITY ASSESSMENT IMPLEMENTATION PHASE IMPLEMENT RECOMMENDATIONS - CHEMICAL SUBSTITUTION: AQUEOUS CLEANER - RINSE PROCESS MODIFICATION: FLOW RED. - CLEANING PROCESS MODIFICATION: USE CCR EVALUATE PERFORMANCE SELECT NEW TARGETS

9 POLLUTION PREVENTION OPPORTUNITY ASSESSMENT FEASIBILITY ANALYSIS PHASE TECHNICAL EVALUATION OF ALTERNATIVES ECONOMIC EVALUATION OF ALTERNATIVES ALTERNATIVE DISPOSAL ALTERNATIVE CLEANING CHEMISTRY PROCESS MODIFICATIONS RECYCLE/REUSE (CA, AS, EVAP) SELECTION OF OPTIONS ALTERNATIVE CLEANING CHEMISTRY PROCESS MODIFICATIONS

10 POLLUTION PREVENTION OPPORTUNITY ASSESSMENT ASSESSMENT PHASE IDENTIFY CONSTITUENTS OF CONCERN - TOLUENE - ACETONE - CHLORBENZENE - 1,3-DICHLORBENZENE - ETHYLBENZENE - TOTAL SUSPENDED SOLIDS (TSS) IDENTIFY SOURCES OF CONSTITUENTS OF CONCERN COLLECT & REVIEW DATA: PROCESS, MSDS, ETC. GENERATE OPTIONS P O T E N T I A L C H E M I C A L SUBSTITUTIONS/ALTERNATIVES POTENTIAL PROCESS MODIFICATIONS: o STAGNANT RINSES o COMPRESSED AIR SPRAY o SOLVENT SPRAY o FLOW RESTRICTORS o HIGH TEMPERATURE RINSING o COUNTERCURRENT RINSING o PROCESS EQUIPMENT UPGRADE RECYCLE/REUSE: o RINSEWATER (CA, AS, EVAP) o SOLVENT (CA; DISTILLATION)

11 POLLUTION PREVENTION OPPORTUNITY ASSESSMENT PLANNING & ORGANIZATION PHASE MANAGEMENT COMMITMENT IDENTIFY TARGET AREA(S) SET GOALS SELECT POLLUTION PREVENTION TEAM

12 SCREEN PRINTING PROCESS IMAGE MOUNTED ON POROUS SCREEN MESH NON-PRINTING AREAS PROTECTED BY BLOCKOUT INK APPLIED WITH SQUEEGEE (UV-CURABLE INK) PRINT BY FORCING INK THROUGH SCREEN HOT AIR DRYING CLEAN SCREENS IMMERSE IN LACQUER THINNER ENZYME TO REMOVE FILM FROM SCREEN WATER RINSE TO REMOVE ENZYME 2ND LACQUER CLEAN & WATER RINSE AIR DRY

13 POLLUTION PREVENTION OPPORTUNITY ASSESSMENT PLANNING & ORGANIZATION PHASE MANAGEMENT COMMITMENT IDENTIFY TARGET AREA(S) SET GOALS SELECT POLLUTION PREVENTION TEAM