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The latest in coatings technology Long-life fluoropolymer resins

SEPTEMBER – OCTOBER 2006

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luoroethylene vinyl ether (FEVE) resinswere developed in the early 1980s in Japan.Unlike other fluoropolymer resins, FEVEresins are thermoset, which means they canbe applied in the field or in the shop andcured under ambient conditions.

Fluoropolymers offer a number of desirable prop-erties, among them excellent stability against UVlight and the elements, corrosion resistance, andchemical resistance. FEVE resins are no different;they are used to formulate coatings that offer 20years or more of resistance to weathering andcorrosion in the most severe environments.Because they can be field-applied, coatings madewith FEVE resins are used for structures such asbridges, water towers, monumental buildings, andother assets that are difficult to paint.

FEVE coatings derive their properties from thechemical structure shown below in Figure 1.

The fluorinated segment of the moleculeimparts weather resistance, durability, and chemicalresistance to the polymer. The vinyl ether segmentsallow the polymer to be dissolved in solventscommonly used in coatings, and to be chemicallyset with standard coating crosslinkers. Physicalproperties like hardness, chemical resistance, flexi-bility, and toughness can be altered by changing thestructure of the polymer.

FEVE-based coatings offer excellent weather-ability under the worst of conditions. The weatherresistance of coatings often is tested by placingcoated metal coupons on a test rack in South Floridafor extended periods of time. The high levels of UVlight, humidity, and salt in this environment willdegrade many coatings inside of a year. There are

several architectural coating specifications thatrequire at least 50-percent gloss retention after 10years of South Florida weathering. As shown inFigure 2 below, FEVE-based coatings offer excel-lent gloss retention, even after 10 years.

The traditional reasons for using FEVE resins incoatings have been aesthetic: The coatings retaintheir appearance and gloss for more than 20 years inmany cases. Minimizing changes in coating appear-ance over time is of interest in markets other thanarchitectural. For industrial maintenance applica-tions, such as coatings for bridges, protection of thestructure from corrosion also is important.

Recent test results from panels coated with fluo-rourethane coatings made with FEVE resins indi-cate that these coatings offer superior corrosionresistance as well. A marine platform off the coastof Japan near Tokyo has been set up by Japan’sMinistry of Land, Infrastructure and Transport.This platform is used by coating manufacturers toget real-time corrosion data on their products.Coated panels were placed on the platform in 1988,and were periodically inspected. The coatingsystem was a four-coat system: an inorganic zincprimer (75μm, 3 mils), two epoxy midcoats (120μm,and 30μm, total of 6 mils), and a fluorourethanetopcoat (25μm, 1 mil).

Coating thickness was monitored carefullyduring the 16 years of exposure on the platform. AsUV light degrades a topcoat, the degraded productswill be removed from the surface of the coating bywind and rain. If enough of the topcoat is lost, thelikelihood of corrosion is increased. In the platformtest, it was determined that the fluorourethanecoating suffered no change in thickness for the firstseven years of exposure. In years 8-16, the average

F

Long-life fluoropolymer resinsfor bridge coatings By Winn Darden

Unlike other fluoropolymer resins,

FEVE resins are thermoset,which means they can

be applied in the field orin the shop and cured

under ambient conditions.

Figure 1: Chemical structure of FEVE polymer.

Fluoroethylene SegmentWeatherability, durability,chemical resistance

Vinyl Ether SegmentsR1 = Clarity, gloss, hardnessR2 = FlexibilityR3 = Crosslinking site (-OH) Solubility

Figure 2: South Florida weathering test resultsfor FEVE-based coating.

120100

80604020

0

Gloss

Reten

tion %

0 1 2 3 4 5 6 7 8 9 10

OcherClear

Exposure Time (years)

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change in thickness was 0.38μm (0.015 mils) peryear. This means that the average remaining coat-ing thickness of the FEVE-based coating after 16years was 21.6μm (0.85 mils). By comparison, theaverage change in coating thickness for a urethanecoating was more than 2μm (.079 mils) per year,beginning in year two, meaning that a 2-mil-thickurethane topcoat would lose more than half of itsthickness during the time span of the test. Becauseof variability in coating thickness and phenomenasuch as inadequate coating thickness on edges,reducing topcoat thickness by this amount can leadto initiation of corrosion.

Additional analytical tests, such as scanning elec-tron microscopy and electron dispersive X-rayanalysis, indicate that the FEVE topcoat preventscorrosion initiators like chloride, water, and oxygenfrom penetrating to the epoxy middle coats and thezinc-rich primer. This means that corrosion of thesteel substrate is not able to occur, even after 16years on the test platform. Corrosion resistance isparticularly important for structures such asbridges that span salt water. The impervious natureof the FEVE topcoat may allow for development oftwo-coat systems, which would result in substantialdecreases in coating application time and costs.

FEVE coatings have been in use in Japan sincethe mid 1980s. In the United States, the primaryuse for FEVE resins has been in the formulation ofarchitectural coatings, and increasingly, of indus-trial maintenance coatings. However, the sameproperties that make FEVE-based coatings usefulon bridges in Japan make them useful for this coun-try. Shown below are a number of examples ofFEVE-based coatings applied to bridges in Japanand in the United States.

Tokiwa Bridge, Hiroshima, JapanThis bridge is in a mountainous area near

Hiroshima. Because of theprevalence of snow, theextensive use of calcium

chloride for deicing the bridge is common. The oldchlorinated rubber coating was removed by blast-ing, and then a three-coat system of epoxyprimer/epoxy midcoat/FEVE topcoat was applied.The new coating system, a portion of which isshown in the picture above, was applied in 1987.After 19 years, the gloss retention of the FEVEtopcoat is greater than 90 percent.

Amadori Bridge, Wakayama Prefecture, JapanThe Amadori Bridge was recoated in 1994. The

bridge is located in a seaside environment, and thusis exposed to large amounts of chloride.Additionally, it is exposed to the typical climate inJapan: hot, humid summers and moderate winterswith rare snowfall. The previous coating wasremoved by blasting to bare metal. A three-coatsystem of a zinc-rich primer/epoxy/topcoat wasapplied to the bridge. Two topcoats were used forcomparative purposes: one a FEVE-based topcoatand a second of chlorinated rubber. The FEVEtopcoat has outperformed the other coating in bothgloss retention and corrosion prevention after 11years of weathering.

Akashi Kaikyo Bridge, Kobe, JapanThe Akashi Kaikyo Bridge (or Akashi Strait

Bridge) currently is the world’s longest suspensionbridge (12,828 feet), spanningthe water between Japan’s main

The same properties that make FEVE-basedcoatings useful on bridgesin Japan make themuseful for this country.

Tokiwa Bridge in 2006, coated in 1987.

Table 1: Coating procedure for Akashi Strait Bridge.

Treatment Coating dry film thickness, µm (mils) Elapsed time before next treatment Coating location

Abrasive blast - - Shop

Inorganic zinc-rich primer 15µm (0.6 mils) 6 months Shop

Abrasive blast - - Shop

Inorganic zinc-rich primer 75µm (3 mils) 7 days Shop

Epoxy mist coat 10µm(0.4 mils) 7 days Shop

Epoxy midcoat 60µm (2.4 mils) 7 days Shop

Epoxy midcoat with MIO 60µm (2.4 mils) 12 months Shop

FEVE-based fluorourethane topcoat 30µm (1.2 mils) 7 days Shop/onsite

FEVE-based fluorourethane topcoat 25µm (1 mil) - Shop/onsite

Total coating thickness 275µm (11 mils) 60 years

The Akashi Kaikyo Bridge in 1997.

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island of Honshu and the island of Shikoku. Thelongest, single span of the bridge is 6,527 feet,while the towers stand at 928 feet. The coatingsystem used on the bridge is more complex thanthose typically used in the United States, consistingof a number of coatings both field- and shop-applied. The application of the coating system isgiven above in Table 1 (page 17). Elapsed time isthe time period between treatments.

The estimated life of the Akashi Strait Bridge is120 years. During that time, the Honshu ShikokuBridge Authority is planning to recoat the bridgeonly once. To accomplish this, the fluorourethanetopcoat was applied at 55μm (2.2 mils), or abouttwice the normal thickness. The Akashi Strait is thesite of frequent typhoons, with substantial wind andrain common in the area, which may lead to highererosion rates than discussed above. However, thiscoating thickness should allow the authority toreach its goals.

Shelby Street Bridge, Nashville, Tenn.The Shelby Street Bridge originally was built in

1909. Problems with concrete used in its construc-tion led to repairs in the 1920s and again in 1960.

In 1998, the bridge wasdeclared unfit for trafficand was slated for demoli-tion. However, because of

its historic nature, the bridge was not torn down,but was converted into a pedestrian bridge linkingentertainment venues and the coliseum on eitherside of the Cumberland River. At 3,150 feet, it isone of the longest pedestrian bridges in the world.

The bridge was repainted in 2003 with an inor-ganic, zinc-rich primer, a cycloaliphatic amine-cured epoxy middle coat, and a fluorourethanetopcoat. The bridge often is lit with lights of vari-ous colors, often reflecting the season. A graytopcoat was selected because it shows the color ofthe lights better.

Gateway Boulevard Bridge, Nashville, Tenn.The Gateway Boulevard Bridge won the 2005

National Steel Bridge Alliance award for a majorspan. The bridge’s red box structure was coatedwith a FEVE-based coating on those portions withsignificant exposure to sunlight.

To determine the cost effectiveness of FEVE resin topcoats,

lifecycle cost analysis for the entire coating project must be used.

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Shelby Street Bridge in 2003.

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Lifecycle costsIn 2005, the Ministry of Land, Infrastructure

and Transport in Japan, revised the requirement forperformance of heavy-duty coatings. Fluoro-polymer topcoats now are required for use on allbridges in Japan, both for new construction and forrepainting. The Ministry has determined throughextensive real-time testing that the lifecycle cost ofFEVE-based coatings is far lower than that ofcompetitive coatings. It expects a minimum of 30years of life from the FEVE topcoat.

FEVE topcoats are more expensive than tradi-tional topcoats used on bridges. Paints made fromFEVE resins typically sell in the range of $200 to$450 per gallon. To determine the cost effective-ness of FEVE resin topcoats, lifecycle cost analysisfor the entire coating project must be used.

Labor typically is 80 to 90 percent of the cost offield-coating a bridge. This means that materialcosts typically are only 10 to 20 percent of the cost.Bridge coating systems usually are comprised ofthree parts: primer, midcoat, and topcoat. Becausethe FEVE resins are used only in the topcoat,application and material costs for the primer andmidcoat are the same, regardless of the type oftopcoat used. Field experience has shown that thetotal initial application cost of a FEVE coatingsystem is only 6 to 13 percent more expensive thana polyurethane. When lifecycle costs are taken intoaccount, the FEVE coating system offers a 45-percent cost advantage after 10 years, and a 26-percent cost advantage after 18 years. The life-cycle cost analysis is shown below in Figure 3.

This lifecycle analysis doesn’t include additionalcosts that are incurred when a bridge is repainted.Costs to the public, for example, closing lanes onbridges during repainting operations, can also bereduced over time by using FEVE coatings.Further, FEVE coatings can reduce VOC emis-sions over time. Potential liability can be mini-mized by reducing repainting requirements forassets such as bridges and water towers that aredifficult to access, and by limiting exposure to othercosts such as overspray claims. For taxpayer-funded

entities such as Departments of Transportation,investing in FEVE coatings today can reduce theuse of maintenance dollars in the future, freeingthese funds for use on other projects.

FEVE resins have a 20-year history of successfuluse in the field. FEVE coatings can substantiallyreduce lifecycle costs for bridges, while offeringsignificant improvements in appearance and corrosion protection over the life of the coating:Coating life of 30 years or more is typical usingFEVE coatings. While the majority of projects todate have been completed in Asia, FEVE topcoatsare finding more application for bridge coatingshere in the United States.

When lifecycle costs are taken into account,the FEVE coating systemoffers a 45-percent costadvantage after 10 years,and a 26-percent costadvantage after 18 years.

Winn Darden is the business manager for AGCChemicals Americas line of LUMIFLON fluoropoly-mer resins. He has been involved in the sales andmarketing of coatings and coating raw materials formore than 15 years. Darden has authored more than adozen papers, including presentations for the Societyfor Protective Coatings and the National Associationof Corrosion Engineers.

Pedestrian and Vehicular bridgesAISC Certified Fabricator-Major BridgeNationwide delivery

PO Box 1290, Greeley, CO, 806321-800-234-0734

fax: 970-356-9621www.bigrmfg.com

Figure 3: Lifecycle costs, FEVE topcoat v. polyurethane.

Coating Type

RelativeAppliedCost