|Advances in Coatings Testing
A Look at Subcommittee D01.27 on Accelerated Tests for Protective Coatings
by Eric T. Everett
The next time you admire the luster and durability of a cars finish remember that the accelerated weathering test methods of Subcommittee D01.27 on Accelerated Tests for Protective Coatings are largely responsible. The accomplishments of D01.27 over the years are numerous and noteworthy. This is due in part to a loyal and dynamic membership, comprised of paint and coatings producers, suppliers and other affected parties.
If it were not for the progressive vision started by Committee D01 100 years ago, the many benefits afforded to the paint industry by D01.27 Subcommittee and its membership would never have been realized. Perhaps John Weaver (who joined D01 in 1945) says it best: D01, over the past century, has been a forum where producers and users can openly discuss without fear of collusion.
The improvement in coating performance and durability (that we may take for granted today) is largely a result of the numerous accelerated test procedures created by Subcommittee D01.27. Over the years, exposure test cycles have been improved to better approximate a products end use and service environment. Lets look at a specific historic example.
The D01.27 subcommittee was established in the early 1970s. The subcommittee was formed in response to advances taking place in paint technology and testing. For example, the emergence and popularity of the fluorescent UV/condensation tester for coatings testing created a need for an applicable ASTM D01 material standard. The D01.27 subcommittee answered the call by writing ASTM D 4587, Standard Practice for Fluorescent UV-Condensation Exposures of Paints and Related Coatings.
This impacts the real world in a dramatic way. The reason why exterior coatings are so durable today is because of advances made in developing an accelerated tester that could precisely simulate short wavelength UV and natural moisture, which is responsible for most physical property degradation to coatings.
The scope of D01.27 is to promulgate standards or practices used to evaluate film performance of applied paint and finishes subjected to accelerated deterioration, in normal and abnormal service environments.
Weathering and corrosion testing of paints has come a long way in the past 20 years, and so have the standards for testing, says D01.27 Subcommittee Chairman Doug Grossman, Q-Panel Lab Products. These improvements in durability testing have been a major driver in the tremendous advances weve seen in the actual field performance of paints. Almost any kind of coating you can name is much more durable now than it was 10 years or 20 years ago. And remember that those performance improvements have come despite increasing government regulation of raw materials and despite relentless pressures to reduce costs. But in order to improve durability you must be able to test durability. The unique expertise of the members of D01.27 and their willingness to contribute their valuable time is an invaluable resource for the whole coatings industry.
In recent years, the D01.27.04 Light and Water Task Group has been very active by updating existing accelerated testing standards under its supervision. One of my goals as chair of this task group has been to make our standards technically sound and as user-friendly as possible, comments D01.27.04 Chairman Larry Thieben, of BASF. Over the years, we have been very fortunate to have members that are seriously interested in accelerated weather testing. We have a good mix of equipment suppliers and end-users, which brings varying points of view. Sometimes these different viewpoints bring conflicts, but in the end, I believe we develop well-rounded standards that are easy to use.
Task Group D01.27.04 is also responsible for developing a new xenon arc paint specification that was published by ASTM in 2001. ASTM D 6695, Practice for Xenon-Arc Exposures of Paint and Related Coatings, is intended to simulate the effects of sunlight, moisture and heat on paints. D 6695 is the result of several years work and numerous balloted revisions by the D01.27 Subcommittee. A special recognition should be given to D 6695 project leader, Warren Ketola, of 3M. He is primarily responsible for writing this important new standard and bringing it to publication. According to Ketola, D 6695 represents the culmination of many years of effort. The approval and publication of the performance standards for laboratory test apparatus written by ASTM Committee G03 on Weathering and Durability really advanced and made the development of D 6695 possible.
D 6695 contains a table of exposure cycles from which the user can choose. Typical exposure cycles are specified for general coatings, exterior pigmented stains, exterior wood stains, as well as coatings used for marine and automotive applications. Test conditions range from continuous light to alternating light and dark cycles with either high humidity or water spray. Xenon arc test apparatus used to perform D 6695 need to comply with ASTM performance-based standards G 151, Practice for Exposing Nonmetallic Materials in Accelerated Test Devices that Use Laboratory Light Sources and G 155, Practice for Operating Xenon Arc Light Apparatus for Exposure of Nonmetallic Materials.
The D01.27 Subcommittee is also responsible for the creation of another new standard developed within its D01.27.31 Corrosion Testing (Non-Automotive) Task Group. New Standard D 6675, Practice for Salt-Accelerated Outdoor Cosmetic Corrosion Testing of Organic Coatings on Automotive Sheet Steel specifies an outdoor corrosion test method that produces corrosion much more quickly than previous methods. D 6675 calls for exposing the specimens on outdoor racks facing 45 degrees south, with manual application of a five percent salt solution two times per week at three- to four-day intervals.
Other corrosive solutions can also be used, such as a simulated acid rain. Rusting occurs very quickly, often in a matter of weeks rather than months or years, especially when performed in a warm climate such as Florida. Yet the test maintains a wide variety of natural stresses: natural dew, rain, daily wet/dry cycling, and natural sunlight. The scheduled application of a standardized corrosive solution avoids test variation caused by unpredictable fluctuations in episodes of natural acid rain or storm driven salt.
Task Group D01.27.31 is also responsible for creating a popular combined weathering and corrosion test procedure, D 5894, Standard Practice for UV Exposure/Cyclic Salt Fog of Painted Metal (Alternating Exposures in a Fog/Dry Cabinet and a UV/Condensation Cabinet).
D 5894 effectively blends both conventional fluorescent UV/condensation testing with cyclic corrosion testing. This procedure has been shown to produce more realistic corrosion on industrial maintenance paints. Test specimens are exposed to alternating periods of one week in a fluorescent UV/condensation tester, followed by one week in a cyclic corrosion tester.
This innovative approach to accelerated weathering and corrosion testing has improved the simulation of actual atmospheric exposure for industrial maintenance coatings. For example, such coatings may be applied to bridge structures that are subject to the corrosive force of salt water. Combining the weathering stressors of UV light, condensation, and cyclic corrosion, instead of only subjecting test specimens to continuous salt fog, provides a better simulation of actual service environments for industrial maintenance coatings.
Important work is also under way on other D01.27 task groups. For example, Task Group D01.27.30 on Corrosion Testing (Automotive) is developing a new Guide for Laboratory Cyclic Corrosion Testing. Also, an extensive round-robin study of outdoor exposure of test panels at various benchmark test locations is in process. Task Group D01.27.32 on Electrochemical Impedance is working with its ISO counterpart to develop a new electrochemical impedance standard for coatings testing.
A Special Relationship: D01 and G03
Typically, Committees D01 and G03 on Weathering and Durability meet together twice a year. Many attendees serve on both committees since there is overlap in the issues of interest. Committee G03 is responsible for supervision of the general weathering test specifications for outdoor and accelerated laboratory test exposures.
Many D01 material standards reference G03 weathering standards for guidance on specimen conditioning, preparation, as well as for specifying laboratory accelerated test apparatus and natural outdoor exposure protocols. Additionally, many other ASTM material-specific test procedures for various industries (plastics, roofing, textiles, etc.) also reference the G03 test specifications.
One of Committee G03s significant achievements has been its development of performance-based weathering specifications to replace existing hardware-based specifications. These documents include:
G 151, Practice for Exposing Nonmetallic Materials in Accelerated Test Devices that Use Laboratory Light Sources;
G 152, Practice for Operating Open Flame Carbon Arc;
G 153, Practice for Operating Enclosed Carbon Arc Light Apparatus for Exposure of Nonmetallic Materials;
G 154, Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials; and
G 155, Practice for Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials.
Performance-based standards focus on general performance parameters or conditions needed to comply with the standard, rather than grandly describing construction attributes of test equipment. Such documents foster innovation and facilitate keeping standards up-to-date with rapidly emerging testing technology.
There is much afoot within the confines of the ASTM D01.27 subcommittee meeting room, and theres certainly more exciting challenges ahead. The level of commitment and achievement demonstrated by D01.27 in recent years is laudable and most impressive. It demonstrates the power of effective consensus under the excellent guidance and administration of a world-class standards organization like ASTM. //
Copyright 2002, ASTM