1、Item No. 24249 NACE International Publication 43113 This Technical Committee Report has been prepared by NACE3 International Task Group (TG) 378,* “Waterborne Coatings on Railcars.” Waterborne Coatings on Railcars February 2013, NACE International This NACE International (NACE) technical committee r
2、eport represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone from manufacturing, marketing, purchasing, or using products, processes, or procedures not included in this report. Nothing cont
3、ained in this NACE report is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by letters patent, or as indemnifying or protecting anyone against liability for infringement of letters patent.
4、This report should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this report intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this report in specific instances. N
5、ACE assumes no responsibility for the interpretation or use of this report by other parties. Users of this NACE report are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this report prior to its use
6、. This NACE report may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this report. Users of this NACE report are also responsible for establishing appropriate
7、health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this report. CAUTIONARY NOTICE: The user is cautioned to obtain the latest edit
8、ion of this report. NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE reports are automatically withdrawn if more than 10 years old. Purchasers of NACE reports may receive current information on all NACE International publications by
9、contacting the NACE FirstService Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +1 281-228-6200). Foreword This NACE technical committee report reviews the current information available concerning the application of waterborne coatings to railcars. It is not intended as an
10、all-encompassing technical document, but as an overview of general trends and a description of the current generic products and equipment involved. The report is intended to benefit railcar fleet owners, operators, manufacturers, and repair personnel who are contemplating the use of waterborne coati
11、ngs for their equipment and are seeking more information on their history and applicability to this industry. This report was prepared by NACE Task Group (TG) 378, “Waterborne Coatings on Railcars.” The TG is administered by Specific Technology Group (STG) 43, “Transportation, Land.” It is also spon
12、sored by STG 02, “Coatings and Linings, ProtectiveAtmospheric.” It is issued by NACE under the auspices of STG 43. _ * Chair Randy Carter, Sherwin Williams, Chicago, IL. NACE International 2 NACE technical committee reports are intended to convey technical information or state-of-the-art knowledge r
13、egarding corrosion. In many cases, they discuss specific applications of corrosion mitigation technology, whether considered successful or not. Statements used to convey this information are factual and are provided to the reader as input and guidance for consideration when applying this technology
14、in the future. However, these statements are not intended to be requirements or recommendations for general application of this technology, and must not be construed as such. Background This report covers waterborne coatings that are most commonly used in the railcar industry and their advantages an
15、d disadvantages, according to the end users polled. Waterborne coatings, particularly acrylic emulsions, have become one of the leading alternatives to solvent-borne railcar coatings, both by the original equipment manufacturer (OEM) and in contract shops and repair facilities. Other waterborne coat
16、ings include waterborne epoxies, acrylic latexes, and waterborne urethanes. As the name suggests, waterborne coatings primarily use water instead of organic solvents to deliver the components to the substrate. Even though waterborne coatings use water as the carrier, usually a small amount of organi
17、c cosolvent is needed to promote film formation (coalescence). Waterborne volatile organic compound (VOC) levels range between 0.0 and 0.42 kg/L (0.0 and 3.5 lb/gal); solvent-based ranges between 0.02 and 0.6 kg/L (0.2 and 5.0 lb/gal). Although water is a solvent, for the purposes of this report, th
18、e term “solvent” refers to organic solvents. Railcar builders and shops realized that by switching to waterborne products, when possible, they could help meet VOC requirements and improve plant environments. Possible benefits may include lower disposal costs for paint waste, easier cleanup, and redu
19、ced insurance premiums. Information on these topics can be found at various Internet Web sites, such as the “Environmental Protection Blog” site.1 The first waterborne products introduced to the rail and transportation market in the 1960s were mostly primers (see Appendix A). In subsequent decades,
20、regulations increased the pressure on applicators and coating manufacturers to reduce air pollution by further reducing VOCs, and in the 1990s, the hazardous air pollutant (HAP) content of their formulations. Realizing these regulations would only become more restrictive, many companies began invest
21、igating the formulation of low-VOC waterborne coatings. In the late 1980s and into the early 1990s, waterborne locomotive coating systems evolved into color base coats of a direct-to-metal (DTM) acrylic emulsion (latex) copolymer followed by the application of a waterborne single-package urethane cl
22、ear coat. From the mid-1990s until the present, waterborne locomotive coating systems have been color base coats of latex acrylic epoxy, and clear finish coats have been of solution urethanes. The evolution of freight car coatings progressed through extremely low- and zero-VOC high-molecular- weight
23、(1) terpolymer acrylic latex (TAL) materials, epoxy reactive acrylic latex polymers (ERALs), and urethane reactive acrylic latex polymers (URALs), leading to the materials available today for various corrosive and general services applications (see Appendix A). Definitions Cosolvent: During chemical
24、 processing, a second solvent is added to the original solvent, generally in small concentrations, forming a mixture with enhanced solvent powers because of synergism. Terpolymer: The product of simultaneous polymerization of three different monomers. Technology Appearance is a factor in marketing a
25、 railcar. Customers demand their railcars arrive with a durable, aesthetically pleasing coating. The coating products used have an impact on how well these goals are achieved. New technology coatings meet the customers aesthetic requirements while reducing VOC emissions. This allows shops and other
26、applicators to better meet regulatory standards for air quality and requirements for a safe work environment for employees. (1) The molecular weight of the polymer is a simple but critical property of the resin. A polymer is a large molecule made up of repeating structural units or atoms. A large mo
27、lecule is one with a molecular weight of at least 1,000 or one containing 1,000 structural units or more. A resin is composed of a number of these polymers. It is generally accepted that the higher the molecular weight, the stronger and more durable the resin. NACE International 3 Understanding the
28、chemistry and behavior of waterborne coatings may help remove the mystery surrounding them. Chemically, waterborne coatings are similar to solvent-based coatings. They differ in curing mechanism (oxidation solvent evaporation versus coalescence) and in basic polymer makeup. The primary ingredient of
29、 the coating system is the resin. The resin determines the physical properties and film integrity of the dry film. The function of water, as a constituent, in a waterborne coating is to create a pathway for the water and cosolvent to dissipate out of the film, while deformation of the resin molecule
30、s takes place in the process of forming a film. In addition, cosolvents control the application characteristics and the appearance of the applied film. Components Waterborne coatings have six basic components: ResinsPolymers are the backbone of the coating. Typical resins are alkyd, acrylic, epoxy,
31、rubber, vinyl, urethanes, silicon, fluoropolymer, polyvinyl acetate (PVA), and mixtures of these. WaterWater is the primary solvent used to eliminate flammability and reduce the coating, allowing easier application. Dissolves or disperses the film-forming constituents and then evaporates during dryi
32、ng, and is therefore not part of the dried film. Controls the application characteristics and the appearance of the applied film. PigmentsSeveral types, powders, whose purpose is to give color, opacity (coverage), restrict or alter flow, help improve corrosion resistance, or merely extend the coatin
33、g. CosolventsSpecial solvents used to soften the polymer particles, swelling them so they stick together as the water evaporates from the paint. This is known as coalescence. Types of solvents include alcohols, glycols, or glycol derivatives. AdditivesUnique additives or monomers, which may reduce f
34、oam, improve gloss and flow, change viscosity, etc. In air-dry solution resins, driers are used as in solvent-based coatings. In baking resins, catalysts are used to reduce bake cycles, or lower bake temperatures. Amine Used to neutralize the polymer to render it water soluble or compatible. Acts as
35、 a buffer, neutralizing the acid portion of the resin to make it miscible with the water. Once the water, cosolvent, and amine evaporate from an applied coating, these acid groups regain their acidity, allowing cure to proceed, rendering the dried coating water resistant. Types of Waterborne Coating
36、s There are three basic types of waterborne coating resin systems available, which include emulsion or latex, solution or water reducible, and colloidal or dispersion. Emulsion or Latex (a) Two-phase systems with discrete spherical particles dispersed in water. (b) Because these polymer particles ar
37、e only dispersed in water, their presence does not affect the viscosity of the coating. (c) Toughness and abrasion, chemical, and water resistance with typically good outdoor durability. (d) Low cosolvent demand (VOC = 0.0 to 0.19 g/L (0.0 to 1.6 lb/gal). The cosolvent causes coalescence and is esse
38、ntial to film formation. (e) Able to yield gloss ranges between 75 to 85 units at 60 angle of incidence, which is Gloss Level 6, traditional gloss, defined by the Master Painters Institute (MPI)(2) gloss and sheen standard (Level 6).2 (2) Master Painters Institute (MPI), 2800 Ingleton Ave., Burnaby,
39、 B.C., Canada V5C 6G7. NACE International 4 (f) The air-dry resins are thermoplastic and generally hard enough to handle in 15 to 20 minutes. They reach maximum hardness in two to three weeks. For improved hardness and solvent resistance, these emulsions are available in a baked (cross link) form (b
40、aked at 121 to 135 C 250 to 275 F for 10 to 15 minutes metal temperature). (g) No freeze/thaw stability. (h) Resins available are acrylic, alkyd, vinyl, urethane, PVA, rubber, and epoxy. Solution or Water Reducible (a) Copolymers (blend of polymers) formed by polymerization reaction in water/water-s
41、oluble solvents. The acid groups of the resin are then treated with amine to allow reduction in water. (b) Because the resin is soluble and part of the water phase, it reacts very similarly to solvent reducible paints. (c) Molecular weight = 20,000 to 50,000. (d) Being in solution, the higher the mo
42、lecular weight, the higher the viscosity is as in solvent systems, affecting solids at application. The molecular weight is limited to the values shown above. (e) Because of the lower molecular weights, these solution coatings are not as flexible as the emulsions or dispersion resins. (f) Comparable
43、 to solvent epoxy or alkyd in application, flexibility, and abrasion resistance. (g) Available in air dry, low-bake, or high-bake (thermo set) formulations. (h) Has good durability. (i) Able to yield high gloss (85 to 95 units at 60 angle of incidence), which is Gloss Level 7, high gloss and is defi
44、ned by MPI gloss and sheen standard (Level 7) as anything more than 85 units at 60.2 (j) VOC = 0.31 to 0.38 g/L (2.6 to 3.2 lb/gal). (k) In most cases, has freeze/thaw stability. (l) Solvent blend in coatings is 80% water and 20% water-miscible solvent, used for viscosity control. (m) Can be supplie
45、d at high solids, high viscosity, and with no amine or water present. The purpose is to allow reduction in organic solvents or have the option of waterborne or solvent-based use. (n) Available in acrylic, alkyd, epoxy, polyester, and phenolic resin. Colloidal or Dispersion (a) Similar to emulsions,
46、colloidal systems are two-phase systems in water with spherical particles. (b) As with the solution resins, they have chemical groups that are soluble in water. (c) Molecular weights average 20,000 to 300,000. (d) Able to yield traditional gloss (MPI, Level 6) and high gloss (MPI, Level 7) ranges be
47、tween 80 to 90 units at 60 angle of incidence can be achieved.2 (e) Essentially a blend, having both emulsion and solution properties. (f) Use of low levels of cosolvents results in hard film. (g) Available in baking formulations. Baking temperatures range from 107 to 135 C (225 to 275 F) for 10 to
48、15 minutes (metal temperature). NACE International 5 (h) Can sometimes be formulated for freeze/thaw stability. (i) Available in acrylic, alkyd, epoxy, vinyl, phenolic, and polyester resin. Further details of types of waterborne coatings can be found in Dan Lescarbeaus online article titled “Waterbo
49、rne Coatings.”3 Uses The exteriors of many railcar types, such as coil cars, center beam cars, flats, open-top hoppers, gondolas, intermodal well cars, spine cars, boxcars, auto racks, and covered hoppers are now coated with waterborne coatings. Application A commercial blast (NACE No. 3/SSPC(3)-SP 6)4 is typically used for DTM applications. The material is thoroughly mixed using a power agitator until uniform consistency and color are obtained, and all solids that have settled are mixed back into the suspension. Airless spray
