This article will be available as a reprint, SecondSight No. 85. To order, call 1-800- Keep Your True Colors: 662-3916 or order Lightfastness and Weatherability Testing online at www.gain.net. by Julie Lucas

he job is printed, the spectro- mouths and they lose confidence in usually responsible for most of the photometer and densitometer your company.” degradation to more durable materials, Lightfastness and weatherability such as many substrates. Treadings match the specs, everyone agrees that “it looks are obvious objectives for Inkware, Testing for light stability and great.” Then, one day the customer since most of its products are used out- weatherability is typically done in the calls to complain that the job you doors on large billboards, signs, and research and development stage and/or printed has faded. Perhaps the ink banners. A manufacturer of piezo the quality control stage. “We test in faded on a storefront poster exposed inkjet inks, the Las Vegas-based com- the R&D stage and in conjunction with to sunlight, or maybe an expensive pany works hand in hand with VUTEk our customers’ ongoing test programs,” brochure that was stored under fluo- (www.vutek.com), manufacturer of says Matt Creegan, dry offset product rescent lights in “protective” packag- inkjet printers that digitally produce manager at Zeller + Gmelin, producer ing changed color or faded. If, as massive outdoor signs. of specialty UV-cured inks. Richard Harold says earlier in this As many industry professionals are “Testing gives us confidence issue, “Appearance is the foremost discovering, however, it’s not just out- that our products will meet customer and most impressive product mes- door materials that should be tested. expectations. And customers do tell sage,” then a product’s appearance Bright interior lighting and sunlight you what they expect, such as a product over time—its lightfastness and through window glass can be surpris- that will last at least a year in the field, weatherability—can also be crucial. ingly damaging. “Testing for light sta- for instance.” Based in Richmond, In this article, Julie Lucas of Q-Panel bility really does make a difference,” Virginia, Zeller + Gmelin manufactures Lab Products (www.q-panel.com) says Johnston. “You’d be surprised at inks for lithography, dry offset, and explains what types of tools are how much light infiltrates a bottle of flexography. available for testing lightfastness ink on a shelf.” And, of course, durabil- Because of the push in recent years and weatherability, while Ian John- ity of appearance is a big issue for inks toward graphic arts materials that are ston of Inkware LLC (www.inkware. and artists’ materials. Maintaining “per- not only durable but also environmen- com) and Matt Creegan of Zeller + manent records” or enduring works of tally friendly and nontoxic, testing has Gmelin (www.zeller-gmelin.com) art is not possible if your materials do become even more important. “When describe what this kind of testing not last. you are dealing with organic pigments, has meant to their companies. Damage to products from indoor it’s really hard to find good reds and lighting and the outdoor elements yellows, especially yellows,” says Cree- cause billions of dollars in losses every gan. “We must have tested a few dozen Why should you test products for year. This damage may include fading to find the right one that works with lightfastness and weatherability? Ian of inks and color change, hazing, crack- our system.” Johnston, director of research and ing, peeling, delamination, gloss loss, A balance between good color development for Inkware LLC sums it chalking, and oxidation of substrates. and good weatherability is the goal up in a sentence: “It helps us to sleep Bright indoor lighting, sunlight at Inkware, says Johnston. “There are better at night.” through window glass, and direct natu- nicer looking colors we could use, but While many in the graphic arts ral sunlight are the main causes of it’s a compromise between what will industry still think of this kind of test- this damage. Different wavelengths look good and what will work outdoors ing as a luxury, to Johnston and many affect materials differently. In general, for the next several years. We try to others, it is crucial. “Weatherability is longer wavelength ultraviolet (UV) make sure our colors look good and our number one concern,” he says. “A and visible light are most harmful to have the widest color gamut possible, lot hinges on the appearance of our graphic arts materials because they while remaining weatherable,” he products. When appearance degener- tend to cause fading and color change. says. The way to accomplish that ates, it leaves a bad taste in consumers’ Short-wavelength UV radiation is goal? Testing.

May/June 2001 GATFWorld 13 Keep Your True Colors:Lightfastness and Weatherability Testing

testing. For the tions. With the recent increases in most compre- new technology, the use of accelerated hensive testing weathering is increasing proportionately. regimen, manu- There are a number of commonly facturers will send used laboratory weathering and light samples to out- stability testers. Each uses a somewhat door weathering different method to reproduce the sites in both damaging effects of sunlight and mois- Florida and ture. Since there are pros and cons to Arizona. each tester, it’s important to evaluate Zeller + them individually before deciding Gmelin and which is best for a particular purpose. Inkware have the Carbon Arcs luxury of testing at their company Enclosed carbon arc testers, the sites, which are oldest form of light stability testers, located in harsh have been around since about 1918. climates. “We do Test samples are mounted vertically on outdoor testing on a carousel that revolves around a pair our own at branch of carbon rods, which are “burned” to locations in Vir- produce light. Because this tester is Figure 1. The appearance of photos may degrade over time due to ginia, Texas, and deficient in short wavelength UV and bright indoor lighting or sunlight through window glass. These photos California,” says is an extremely mild test for today’s are being exposed outdoors at a test site in Florida to check for durable products, it is rarely used permanency. Creegan of Zeller + Gmelin. anymore. What are today’s testing options? Inkware simply takes advantage of its The sunshine carbon arc was intro- There are a number of them, but no Nevada location. Since the company duced in the 1930s as an improvement single testing technique is perfect for was founded seven years ago, Inkware to the enclosed carbon arc. The major all materials and applications. The has been able to compile a lot of out- difference between it and the enclosed approach you choose should depend door test data, according to Johnston. carbon arc tester is the light source. on what you need to accomplish, your “We have one sample still being The sunshine carbon arc emits extre- time frame, and your budget. Each exposed that has already been there mely short-wave UV light, but this type technique has inherent strengths and for 6 1/2 years!” he says. “We are quite of exposure represents an overly severe weaknesses. proud of that one because it’s actually and unnatural exposure condition. As most researchers have found, Natural Exposure Testing held up very well.” (See Figure 2.) The drawback to natural sunlight carbon arcs will give some useful data, Often the most accurate way to test testing is the amount of time it takes. but more accurate ways of testing are products for lightfastness and weather- “With the long lead time you need available. “In the past, we’ve sent sam- ability is simply to expose them to natu- to introduce new products, you can’t ples out to be tested in a carbon arc,” ral sunlight. (See Figure 1.) Materials always wait a couple of years to see if a says Creegan of Zeller + Gmelin, “but can be exposed in a variety of ways, material will last,” says Johnston. How- when it was time to buy our own such as under glass to simulate a bright ever, if you have flexibility in terms of machine, we decided we didn’t want indoor environment. time, outdoor weathering tests are the to own a carbon arc. All of our research Real-time, outdoor testing is usu- most realistic—and they are usually rel- indicated that it’s not the best tester ally done in either Florida or Arizona atively inexpensive. for correlating to the solar spectrum.” because these areas provide extreme climates that accelerate the degrada- Accelerating Results in the Lab Xenon Arcs tion of materials. Florida is known for Many manufacturers have found The xenon arc tester has been high temperatures, high humidity, and success using accelerated laboratory shown to reproduce the full sunlight abundant rainfall, while Arizona has light stability and weathering tests. spectrum most accurately. Xenon high temperatures, high UV concentra- These tests can give fast, reproducible lamps emit UV, visible light, and tion, and extreme dryness. In fact, results. And, by varying the exposure infrared in the same way the sun does, these areas are considered international conditions, lab tests can be correlated and can therefore provide very accu- “benchmark” locations for weathering with outdoor exposures at various loca- rate data. Xenon arc testers may also

14 GATFWorld May/June 2001 dew) causes more be damaging, but also lower intensity wetness than rain. light over long time periods. Acceler- Some testers are ated testing helps you avoid a lot of pit- also fitted with a falls with materials, but it’s not always water spray mecha- apples to apples. Interactions that hap- nism to reproduce pen outdoors can lead to product fail- thermal shock, ure. Moisture and chemical reactions which can be very (caused from pollution) can contribute. damaging to some So, we began to also expose products materials. outdoors as well in a Q-Sun xenon Inkware has tester.” done a lot of testing “We still use the UV bulbs to test,” with fluorescent UV says Johnston. “If we need to make bulbs. “When the quick first cuts on a material, we Figure 2. This photo has been exposed at Inkware’s Las Vegas, company was ini- expose them to UV first. It’s an Nevada, site for the past 6 1/2 years. tially developed, we extreme test, but it’s very quick. After approached testing materials last in this environment, we be equipped with a water spray mecha- from the scientific standpoint that UV put them in the Q-Sun to see which nism to simulate wet conditions. Xenon radiation tends to cause the most dam- holds up better.” arc testers are especially good for eval- age to colors as far as fading,” says UV testers are easier to operate uating resistance to color change and Johnston. “We originally used only and much less expensive than the car- fading because many products fail high-intensity UV bulbs to test. We bon arc or the xenon arc testers. Their when exposed to longer-wavelength knew that if materials lasted at this main weakness is that they do not emit UV and visible light. (See Figure 3.) intensity UV, they would most likely visible light or infrared. This limitation Both Inkware and Zeller + Gmelin last outdoors. But we discovered that can be important for evaluating mate- use xenon arc testers as well as outdoor it’s not only high-intensity UV that can rial colorfastness and fading, which exposures for light stability and weath- ering testing. And, to be confident in their xenon tester results, both corre- late their data. “So far our outdoor data compared with the Q-Sun xenon tester looks pretty close,” says Creegan. John- ston says he has found similar results. The drawback to xenon testers is that some of them can be more costly than other testers or outdoor testing. Fluorescent UV/ Condensation Testers Fluorescent UV/condensation testers utilize lamps that are similar to the common cool white lamps used in general lighting, but which produce UV rather than visible light or infrared. In this way, these testers expose speci- mens to short-wavelength UV, which is generally the most damaging portion of the sun’s spectrum for durable materi- als such as many substrates. UV testers can also simulate mois- Figure 3. The Q-Sun Xenon Test Chamber is an accelerated weathering tester that uses xenon ture through a condensation mecha- arc lamps to simulate the entire spectrum of sunlight. The Q-Sun 3100 (left) has a large spec- imen capacity that will accommodate 3D parts, and is also available with relative humidity nism. This provides a more realistic control. Q-Panel donated a Q-Sun 1000 Xenon Test Chamber (right) to GATF. The realistic test, since studies on outdoor materials simulation of sunlight in both chambers is especially useful for testing printing inks that are have shown that condensation (i.e., sensitive to longer-wave UV and visible light.

May/June 2001 GATFWorld 15 Keep Your True Colors:Lightfastness and Weatherability Testing

often occur due to exposure to longer- more than one testing method, you can customers can buy the inks and the wavelength light. compare results between them, and substrates as a package that’s known learn which methods work most accu- to work well together.” Choosing a Testing Regimen rately and efficiently for your materials. Creegan and Johnston both say The best testing regimens take into It’s also important to understand that, the best thing to do when you’re account that the more tests you per- that the kind of substrate on which you new to testing is to test as much as pos- form, and the more types of tests you test can make a big difference. “We’ve sible, as many ways as possible. “When perform, the better you’ll understand found that substrates have a dramatic you are first starting out, you probably your products and their strengths and role in the lifetime of an ink,” says want to test all of your product lines,” weaknesses. Both Zeller + Gmelin and Johnston. “The ink needs to stay on the says Creegan. “Start slowly with the Inkware rely on comprehensive testing substrate, and so the substrate itself process. Keep your eyes open for dif- regimens that include both outdoor must be very durable. When compar- ferences in cure condition and sub- and accelerated lab tests. “We have had ing substrates in accelerated testing, strates when testing. Expect it to take some cases where materials did well in we’ve found that they often brown or several years for really meaningful data. accelerated tests, but degraded rapidly yellow due to the UV, or the surface On the other hand, you will reap some outdoors,” says Johnston. “You can be layer deteriorates. We work closely immediate benefits. You will know most confident by doing a wide range with the substrate manufacturers to what’s not going to work for you.” of testing.” In addition, by choosing improve these surfaces so that our “To those new to testing, my advice would be to test, test, test,” says John- What causes fading of outdoor inkjet images? ston. “There is no substitute for a cred- ible range of testing. I would say you “Fading” of inkjet images can be viewed as a simple reduction in color den- need to get involved in some sort of sity over a period of time. The chemistry of fading, however, is not so straightfor- accelerated testing because quick ward. Each pigment has a different chemical composition. A black ink made from results are so essential. But then I carbon black will actually protect the vinyl from cracking and never fades. Most would also get some samples exposed good process cyans are made from organometallic compounds that are almost outdoors, even if it’s on your own roof.” as stable as carbon black. They generally show little fading over time. Of course, customer feedback is The real fading problems in four-color process inks come from the magenta critical as well. “We have inks in about and the yellow. Yellow pigments absorb primarily blue light, which is at the high- 60 countries in all sorts of climates,” energy end of the visible spectrum. Without any protection, yellow will show a says Johnston. “We’re at the point greater loss in density than any other color. where we can get a lot of data from Clear coats containing a UV absorber to reduce the amount of UV light pene- customers about the durability of our trating to the ink layer are being used to try to decrease the fading of the yellow. products and under which conditions Magenta has a different problem. It absorbs green light, and the intensity they last best and worst. of visible sunlight peaks in the green. UV absorbers have little effect on magenta “On the other hand, if we relied fading because they do not absorb green light. Magenta fading is due largely to completely on customers using our absorption of green light. Small changes in magenta density are more visible to products to find out if they last, it could the human eye than similar changes in yellow density. be catastrophic!” he says. Color density loss is not only caused by the discoloration of pigments by In the long run, a comprehensive absorption of light, it also occurs as the direct result of the loss of pigment by testing regimen will pay for itself. Not physical abrasion. Abrasion by particles of grit carried by the wind slowly grind only will you avoid the costs associated away the outer layer of pigment. Areas of an image with the lowest density will be with putting out bad products, but also affected first because there is less pigment there to start with. A clear coat will customers will give you repeat busi- not completely eliminate fading, but it will slow down the process. For outdoor ness, knowing that your products will use in wet climates, a clear coat containing an effective water repellent, such as last. And, like Johnston, you too will be a fluorocarbon, is highly recommended. able to sleep better at night. Rainwater, as it falls, does not have much effect on an image printed with a good solvent-based ink, but the chemistry changes dramatically as the rain Julie Lucas is with Q-Panel Lab Products begins to dry. When the water evaporates, the concentration of pollutants (www.q-panel.com), Cleveland, Ohio. The increases until at the last second of drying, the concentration of pollutants company provides equipment and stan- approaches infinity. The effect on a printed image will depend on the type and dardized substrates for testing the level of air pollution. In any case, it would be better if the rain drops were weatherability and light stability of prod- repelled by the clear coat and ran off, rather than drying on the image. ucts, and also operates outdoor testing Information adapted from Inkware’s website: www.inkware.com/html/vol2_1.html facilities in Arizona and Florida.

16 GATFWorld May/June 2001