Bookmark and Share

Standardization News Search
Feature
Courtesy of Diamond Vogel Paints
The Coating: Thin as a Dollar Bill

The Value: High as a Stack of Twenties

Subcommittee D01.51 on Powder Coatings

by Jeff Hagerlin

Take a dollar bill from your pocket and note how thin it is. Made of something other than paper, would you consider this suitable armor for protection from attack? Perhaps not, but that bill is the thickness of an effective protective coating on many fine products—a mere 65 micrometres.

A paint layer has many important obligations that it must fulfill throughout its existence that relate directly to the object it covers. The paint must provide a proper appearance, ample protection, adequate functionality, and sufficient longevity. It is the influence of the paint on the value of the end product that makes its properties so important that they must be characterized, measured, understood, and controlled at each step from raw material manufacture through paint manufacture, storage and final application to a product or component.

The obligations of the paint film are prioritized in many different ways depending on the intended purpose of the item and the economics of the market being served.

Proper Appearance
The paint layer, often the most visible aspect of the item, can be a significant factor in the perceived value of the article. Regardless of a product’s good design or quality construction, if the paint on it is not of consistent quality or is not in good condition, the article itself will not receive consumer interest nor uphold the value it might otherwise be due.

Appearance involves those things we see such as color or clarity, gloss or sheen, smoothness or texture, and the uniformity of each. Value perceived.

Ample Protection
The paint layer is the first line of defense against the natural forces that would harm the underlying object. This relatively thin layer must be the enduring barrier between the outer environment and the vulnerable material of which the product is made.

Protection prevents destruction such as corrosion of metal or staining and rotting of wood. Value maintained.

Adequate Functionality
Aside from having a certain look and being protective, the paint layer may also be required to do something physical day after day. Functional performance of the paint surface often relates to friction, for example non-slip or high-slip, or sometimes mar or wear resistance.

Functionality is a physical quality the paint provides that may not exist in the underlying material, enhancing the product when in use. Value added.

Sufficient Longevity
The many values provided by the paint layer must remain at an acceptable level for a period of time that is similar to the intended usage term, the life of the product.

Longevity of the paint layer is important to sustained appearance of the product over its anticipated life. Enduring value.

Adjectives Work—For a While

“Proper,” “ample,” “adequate,” and “sufficient” each infer a level of acceptable performance that would be fine in summary of what happened or what was delivered: “The paint on the outdoor storage system provided ample protection from the wet weather as no rust has occurred.” We know what that means but it gives us no real detail.

So such phrases do not work well when used or implied as a specification between buyer and seller: “We need a grey paint for our racking system that will give us ample protection.” As it relates to providing the right material for the job, this phrase is now meaningless. As you know, herein lies the value of standards, the defined means by which we communicate expectations for a material between buyer and seller.

There are many different properties of the paint that must be present to provide ample protection for the outdoor racks, each the subject of an ASTM standard. Standards help us convert the words of acceptability to scaled or ranked values that can be agreed to, leading to satisfaction for both buyer and seller.

Paint or Coating?

So far we have addressed only that thin layer composed of polymers, pigments and minerals that covers virtually every manufactured thing around you, inside or outside. Really, look around. Do you find any manufactured object that is not painted? (There are some products made of inert metal or durable plastics that stand bare with their own design appeal, but they are few by comparison.)

Actually, this is a trick question. Strictly speaking there are likely many products around you that are not painted. Rather they are coated, powder coated. You can’t often tell by the finish what type it is or how it was applied. As long as the finishing material was selected with an understanding of its capability relative to the use of the product, you are well served.

By tradition, “paint” refers to the liquid material, to the act of applying the material to a surface, and also to the final dried layer. The less specific term “coating” has come into use in modern times as other forms of “paint” have evolved that may not be liquid. The terms are often used interchangeably, but you will usually find “paint” as liquid and “coating” as powder.

Emerging Through Need: ASTM D01.51

During the first half-century of work, ASTM Committee D01 brought into use many fine standards that addressed paint technology from raw materials through film properties. These standards are the basis of technical communication within the industry to define and use paints.

Sometime early in the second half-century for D01, a new form of paint emerged that was based upon solid polymers and did not utilize liquid solvents to facilitate dispersion and application. The new “powder paint” was provided in powder form and was initially applied by immersing a heated metal item in a bed of powder fluidized by air. While most of the final film properties were the same as those already established and defined by D01 standards, there were now new characteristics that had not been addressed when paint was only liquid.

Perhaps the typical seed for a new ASTM subcommittee, a small group of interested parties needed to focus on standards for this new technology. Hence Subcommittee D01.51 on Powder Coatings came into existence.

Since that time, the number of companies providing coating powders in North America has grown from a handful to over 70(1) suppliers now producing or importing powder to a growing market.

Today powder amounts to a still small but growing share of the overall coatings market. The global production of powder in 2001 is estimated at 800,000 metric tons with 20 percent of the total in North America. (1) (See Figure 1.)

The growth of powder, most years in double digits, was initially driven by the need to comply with environmental regulations. As the marketplace learned more about using this friendly new coating, other incentives such as overall economics, ease of application and coating performance became factors in its selection.

Going to Press

The first standard developed by D01.51 was D 3451, Standard Practices for Testing Polymeric Powders and Powder Coatings, published in 1975. It was a comprehensive collection of specialized tests that are important to the technology and represented the monumental effort of the founding group. D 3451, published today as a guide after significant revision and updating, is still the core document for D01.51. Current standards within D01.51 are listed in Table 1.

Reaching Out

The members of D01.51 represent all areas of the industry: raw materials, coating powder producers, application and test equipment, consulting specialists, government, professional associations, universities, standards bodies, and, most importantly, end users. In addition, our members participate in many other ASTM groups, especially within D01, but also in other committees as they may relate to specific areas of interest or profession. The work of the subcommittee pales in comparison to the work accomplished by members between meetings and ballots.

D01.51 has an active link with the Test Procedures/Health and Safety Subcommittee of the Powder Coating Institute (PCI). The two groups have worked together to enhance the publications of each and to avoid duplication of effort on specific subjects. For example, the PCI “Powder Coating Terms and Definitions” was adopted and referenced in D 3451 rather than commence a quite similar compendium. The PCI subcommittee chair also serves as the chair of ASTM Task Group D01.51.08 Liaison to PCI.

Similarly, D01.51 maintains a relationship with International Organization for Standardization (ISO)/TC 35/SC 9/WG 16 on Powder Coatings. Once again the mutual interest and effort has enriched each group. ISO 8130-10, “Spray Characteristics of Coating Powders,” was the first inter-association adoption by D01.51.03 as our task group was in the early stages of developing a comparable method. We share leadership here also as the convenor of the ISO Working Group also chairs Task Group D01.51.09 Liaison to ISO. (Sadly, we have recently learned that the ISO WG may disband having completed 14 standards, though the continued insight and input of its members is welcomed and valued here.)

Next Steps

There are two new task groups in the subcommittee working on important areas of developing interest.
Task Group D01.51.14 on Consideration of Cure Volatiles of Coating Powders was established in January of 2001 and has been working closely with Subcommittee D01.21 on Chemical Analysis of Paints and Paint Materials and with PCI Test Procedures/ Health and Safety Subcommittee. This group plans to establish a standard means to quantify the total amount of volatiles emitted during the oven cure of coating powders and the amount of water vapor released. Once the amount of moisture is taken from the total, the remaining volatile amount may be considered under permitting and emissions regulations.

The value of this proposed method is in providing accurate information for the powder application facility. It will prevent unnecessary restriction or fee expense from false high assumed values or avoid fines from false low assumptions.

Task Group D01.51.15 on Consideration of Pre-Bake Thickness of Coating Powders was established in January of this year and is drafting a new standard for measuring the depth of a freshly applied coating powder prior to melt and cure in the oven. Knowledge of this depth and of the shrinkage factor for the powder during cure provides for accurate prediction of the final film thickness.

The value of this method is in the ability to predict film thickness before curing which will lead to significant savings in the operation of a coating line. All coating powders have a target film thickness range and the coating of objects above or below this range is wasteful. Current film thickness measurement is at the end of the process so adjustments involve trial and error with many pieces and much time involved for each.

Other new subjects on the horizon will address the expanding technology of powder coatings as the needs for standards coalesce and as expertise develops.

Join Us

D01.51 meets during D01 meetings each January and June. Please join us to learn more about powder coatings and to provide your expertise, new ideas or challenges for the group. //

Reference

1 Greg Bocchi, Executive Director, Powder Coating Institute, Alexandria, Va., Summary Report-Worldwide Powder Coating Markets, PCI Annual Meeting, May 2002, www.powdercoating.org.

Copyright 2002, ASTM

Jeff Hagerlin is president of Good Answer, a technical consulting firm in Houston, Texas, and chair of ASTM Subcommittee D01.51 on Powder Coatings. He is formerly vice president, R&D and Data Systems, DuPont Powder Coatings USA, Houston. As a member of ASTM D01.09 US TAG to ISO TC35/SC9, Hagerlin serves as the US delegate to ISO/TC 35/SC 9/WG 16 (Powder Coatings).

Coating Powder or Powder Coating?

The terms “coating powder” and “powder coating” are used throughout D01.51 standards to clarify content for the user. What’s the distinction? Coating powder refers to the material itself, powder coating to the application process and the finished film.

Today most coating powders are applied to cold pieces via air conveyance and differential charge that attracts the powder to the surface and holds it in place. The powder covered pieces are then heated in an oven for five to 30 minutes while the substrate heats and the coating melts, flows and cures. They exit the oven with a powder coating, the protective layer that now resembles paint.

The Powder Family, Larger Than It Looks

The subcommittee described here is focused on only one portion of the powder coatings market. The attention is generally on decorative uses of powder, where appearance and hiding properties are primary, though physical properties are important also. There are other market segments that involve similar but distinct technologies and application methods.

Functional coating powders for construction and transmission are often referred to as fusion bond epoxies (FBEs) and they are primarily tough and durable barriers to corrosion. FBE powders are used on reinforcing steel bars, “rebar,” embedded in concrete road, bridge decks, and structures such as parking garages. This use is addressed through ASTM Subcommittee A01.05 on Steel Reinforcement.

A larger FBE market is the coating of pipe sections for buried pipelines that transmit natural gas from well to user and other petroleum products throughout the process including from offshore wells to onshore facilities. This market is served within ASTM by Subcommittee D01.48 on Durability of Pipeline Coating and Linings.

These two uses for FBE coating powders in the United States consumed an estimated 20,000 metric tons1 in addition to the amounts shown in Figure 1. These coatings are applied to hot substrates at much higher film thickness, 200-1,500 micrometres, depending on the particular end use. They are often very fast-curing materials that are water quenched within 30 seconds of application.