by the Coatings Industry

Transcription

1 Sol vent Waste Minimization by the Coatings Industry Neil H. Frick Gerald W. Gruber PPG Industries, Inc.

2 Introduction The issue of waste disposal is of national concern. Solvent waste reduction is especi a1 ly relevant in the coatings industry, because the $30MMM worldwide coatings market has traditionally relied upon solvent, in large quantities to manufacture, apply and clean-up coatings. intent today is to develop the reasons for solvent use in Our coatings through looking at the product requirements and then to inform you of the actions being taken by coatings manufacturers together with appl i cati on equipment manufacturers and end users to reduce solvent usage. Coatings can be broadly defined as decorative and/or functional materials which are applied to an object. Inks, adhesives and sealants can be viewed similarly. Some common examples of coated objects are shown on the first slide, - Bridges - Autos - Buildings - Photographic Film - Mirrors - Furniture - Aircraft - Storage Tanks - Wal fcovering - Appliances These examples will help us to illustrate some coatings product re- quirements. A significant fraction of the list employs metal substrates: Corrosion Protection Required - Autos - Aircraft - Bridges - Mirrors - Buildings - Storage Tanks

3 All of these products are subject to corrosion... rust, and it is through coatings that we are able to build long lasting products from metal. Corrosion protection represents one of the most important uses of coatings. Some additional coatings functional properties are shown on the next slide: Properties of Coatings - Corrosion Protection - Chemical Resistance - Aesthetics - Flexibility - Durability - Adhesion Another common denominator on the list shown previously is aesthetics. Each of these product groups has color, gloss and appearance requirements. It is no longer true that you can have your Model T in any color you.want, as long at it's black. The mirror finish of your automobile and the non-reflective finish of a metal building are made possible through coatings. In addition, we expect the appearance of these products to remain unchanged after years of exposure to sunshine, smog and rain. Let's call this durability. Range tops illustrate extremes in temperature with exposure to a variety of aggressive materials ranging from abrasive cleaners to hot grease to spaghetti sauce stains. We're describing thermal and chemical resistance. Aluminum siding is a good example of a flexibility requirement. It is manufactured by painting wide strips of metal, cutting the strips to the appropriate width and forming the final shape. The coating must survive the cutting and forming and then retain color and gloss on your home for many years.

4 -3- House paint is an excellent example of a product which must be field applied on a wide range of surfaces...bare wood, brick, vinyl, metal... new, old, previously painted, wet, dry, hot, cold...y ou get the idea. We expect it to adhere and provide years of protection and beauty. Plastics represent an additional set of opportunities: adhesion, impact resistance, surface defect coverage, barrier properties, weatherabi 1 i ty enhancement and others. So far we've talked only about the functional properties of coatings and briefly about aesthetics. Many additional considerations go into the design of a coating. Coatings Requirements Functional i ty t Product Safety DrylCure Speed Environmental Safety Aesthetics E conomi c s These include product safety, dry or cure schedule, environmental safety and economics. Product safety requires a product which can be manufactured, transported, used and disposed of safely. By way of example, this means extensive testing of raw materials and finished products for health and environmental effects, f 1 ammabi 1 i ty, reacti vi ty, and corros i vi ty. Unacceptable materials are retricted or deleted from candidacy. The mention of paint creates an image of a paint roller and house paint, hard work, several hours to dry and as much as several days to

5 -4- achieve full properties. I would like especially to call your attention to dry time. Model T's required several days for painting. This was a consequence of 'several coats of solvent paint and dry times of hours for each coat. Imagine today's automotive assembly lines producing greater than 60 cars per hour, but being bottlenecked for days while the finish dries and is recoated. Production speed requirements thus have, become another requirement for coatings design. We spoke briefly of aesthetics from the point of view of requirements, but how does one achieve a smooth, sag and pop-free finished product? The answer is that it is a design criterion, just like color or corrosion protection. Products are applied by a wide range of methods. Some examples include spray, di p, roll, curtain and electrodeposition. I should like to add that traditionally, large quantities of solvents have played a major role in achieving acceptable appearance, and that only in recent times have alternatives begun to be available, Early coatings were essentially all solvent reduced products derived from natural products such as lacquer, coal tar and oils such as linseed. These products were severely limited by today's standards in their ability to deliver the required properties of which we have spoken. Excel lent examples are corrosion protection, durability and dry speed. Deficiencies such as these, together with the availability of a wide variety of synthetic organic building blocks have led to the development of a wide variety of synthetic polymers. Some examples include: i

6 -5- Synthetic Polymer Examples Epox i es Acrylics F1 uorocarbons Polyesters Urethanes Po 1 yam i des These materials provide substantial improvements in corrosion protection, adhesion, durability, flexibility, dry rate and other properties. But this first generation of synthetic polymers did little to reduce the organic solvent requirement. Reduction and elimination of solvents in coatings has been a priority for many years at PPG. One obvious reason is environmental i legislation which limits the allowable solvent emission by industry. EPA Guidelines for Maximum Volatile Organic Content of Coatingst Process Can coating Sheet basecoat & overvarni sh; two-pi ece can exterior TWO-, three-piece can interior body spray, two-piece can exterior end Side-seam spray End sealing compound Coil coating Fabric coating Vinyl coating Paper coati ng Auto and light-duty truck coating Prime Topcoat Repair Metal furniture coating Magnet wire coating Large appl i ance coating Miscellaneous metal parts Wood panel ing Printed interior Natural finish hardwood Class I1 hardboard Limitation (kg/gal) (2.0) 2.8 (3.6) (0) O 'R. W. Tess and G. W. Poehlein, Applied Polymer Science, Second Edition, ACS Symposium Series 285, p. 689.

7 -6- The next slide illustrates an EPA list for the amount of solvent allowed per gallon of paint used in various industries. These guidelines are of very limited use today, because state and local rules, on a case by case basis, provide for more or less solvent usage. Perhaps more importantly the industry has been able to do better than these guidelines in at least some cases. As noted in parenthesis, container spray1 iners, basecoats and varnishes surpass the guide1 ines. Coi 1 coating lends itself to incineration, and this is widely practiced. So clearly there are other motivations for reducing solvent usage. The next slide lists some reasons for the reduction of solvent usage. Motivations for Solvent Elimination Environmental Product Safety Economics Productivity In addition to environmental safety, solvent reduction or elimination can improve product safety through reduced chemical exposure and flammability. Solvents normally do not become part of the finished product, and as such become an expense both in use and disposal, which does not add to the ultimate product value. Finally, Henry Ford used several coats of lacquer because the solids were so low that several coats were required to provide the required properties, and consequently days were invested in painting each car. Improved solids and solventless coatings can provide more film build per coat, and thus also improve productivity by requiring less coats.!'-.-. slide. Some recent advances in coatings technology are listed on the next

8 -f- High Solids Water Reducible Powder 100% Reactive Electrodeposition Application Efficiency Improvements High solids describes coatings with improved volume solids. While natural lacquers and early synthetics could be applied at 20-40% volume solids, high solids products rely not upon drying alone, but also upon polymerizing (curing) as they dry. This allows the use of lower molecular weight materials with reduced solution viscosities and i therefore, volume solids of 60-80% can be achieved. Where high solids coatings have replaced conventional solids materials, solvent reductions on the order of 50% have been achieved. As we shall see later, equipment innovations redouble this improvement. Powder coatings are solventless. These powders melt and fuse into a continuous coating when heated, Obviously, they represent a 100% reduction in solvent usage. They are particularly useful in thick films where excel lent chemical resistance is required. Dishwasher rack coatings represent an excellent application of powder. On the other hand uses which require excellent smoothness, thin films or low cure temperature did not lend themselves to powder in the past. This science has improved in recent years. A technology that does an excellent job of handling thermally sensitive substrates such as plastics, paper and wood, is radiation curable coatings. With this technology, solvent is replaced by reactive molecules which polymerize in place upon activation by ultraviolet light

9 -8- or electrons. The weaknesses in this technology include adhesion sensitive substrates and complex shaped articles, although this latter problem is now being addressed with a 3D-UV Milk is an emulsion. curing process. It is comprised of fats, polymers and sugar suspended in water. If allowed to dry, it makes a coating. If it's icing on a cake, it's good, but water will destroy it. This illustrates a traditional problem with waterborne polymers... water sensitivity. again, progress has been made. Cross1 inkable, waterborne polymers, reactive solubilizing groups and improved surfactants r which have allowed the use of waterborne polymers in Humidity variations and flow limitations currently application of these products, especially in spray app But!present advances some industries. prevent ications. broader Where waterborne products can be used, solvent reductions ranging up to 100% can be realized. able. A specialized variety of waterborne coatings are electrodeposit- These coatings are applied by immersing the article to be painted in a coating bath and electrically depositing the paint film on the particle. The process is exceptionally effective at coating obscured areas of complex articles. The coatings can be designed to provide outstanding corrosion protection and, indeed, it largely is responsible for the improved corrosion resistance of today's automobi les. Electrodeposition is limited to electrically conductive substrates. also serves to introduce another concept... transfer efficiency. In the past few years, great strides in spray application efficiencies have been made by close cooperation of the coatings user, equipment manufacturer and coatings supplier. It In the past, it was not unusual for spray efficiencies on automotive lines to be in the range of

10 %, meaning that only 20-30% of each gallon of paint would come to rest on the part. Today, it is not unusual for appl icati on eff ici enci es to be in the range of 65 to 80% with coating so ids near 60%. of The next slide ind coatings used in the cates the improvements in overall efficiencies above case for one ki ogram of dry coating on the automobile. Transfer Efficiency Kg of Reduced Coating Necessary for 1 kg Dry Applied Low Solids (21%) Low Application Efficiency (30%) kg High Solids (60%) High Application Efficiency (65%) kg The difference between the 16 and 2.5 kg of. wet coating supplied amounts to a reduction of about 80% i n the amount of solvent used. This represents a cost saving for the paint user in purchase volume, storage and inventory costs, and disposal costs of liquid and solid waste. Other methods of applying coatings are even more efficient. Electrodeposition of coatings onto metal substrates improves the efficiency in two ways. A more uniform film results from this process (as compared to spraying), and this reduces paint usage, while the engineering of coating tank, rinse recovery system, and chemistry used allows nearly 100% coating application efficiency. Roll coating (for flat substrates) also allows for nearly 100% coating utilization. Advances in polymer mechanical properties has allowed more manufacturers to change from spraying coatings in their facility, to the purchase of precoated stock which is then fabricated and assembled.

11 -10- Solvent Removal Prior to Use Many coatings companies, PPG included, develop new coatings with the objective of reducing the use of solvents by our customers. Systems today, in many cases, need no in-plant dilution with solvents for application. Reactive plasticizers are used as partial or total replacement of solvents in some systems. Many of PPG's cationic electrodeposition systems use solvent in the polymer manufacture, which is removed before final paint shipment. The solvent is then purified and reused in the manufacture of subsequent i systems. This solvent would otherwise need to be disposed of by the coatings user. Recycle and/or Reuse In some cases, where there has been very close cooperation between the coatings user and manufacturer, material that once was considered waste can be recovered and used as raw material for another product. The powder coatings industry has promoted this type of effort for years. The overspray from a powder application can be collected and reused on the same application line, or in other cases used as a raw material for a different product, Concl usions The industry has made great strides in the reduction of solvent use, in the decrease of solvent and other waste streams, and in emissions reductions in the last decade, but more must be done, We, in the industry, are coatings producers and users; but we are also citizens of communities that insist on efficient recycle and reuse of raw materials, and subsequently less use of waste disposal alternatives.

12 -11- We believe that further reduction in both solvent use and waste stream generation w i l l be forthcoming as the new technologies we have described are more widely adopted. Additionally, new technology in electrodeposition, high sol ids, waterborne, powder and radi ati on wi 11 extend the range of applicability of these methods.