Publications

In addition to scribing the Powder Coatings: Foundation for the Novice Formulator (BNP Media, 2004), Kevin Biller has been a rather prolific writer through the years. He is currently the technical editor of the newly revamped on-line magazine FinishingTalk (link) where he stimulates discussion with his provocative monthly editorial viewpoint, The Last Word. Biller won an APEX journalism award when he was the technical editor for Finishing Today magazine from 2006 through 2008. For years he has contributed to Paint & Coatings Industry magazine (link) as an editorial advisor. You can find his world renown Q&A column, Ask Joe Powder, in Metal Finishing magazine He has been published in North America, Asia, and Western Europe. Feel free to browse these archives.

Ask Joe Powder

picture of Joe Powder

05-01-2007Overcure Protection Additive

Dear Joe,

I have been told by my distributor that many powders contain an overcure protection additive. What is this additive, and is there a way to find it on an MSDS?
--Karl Wagenbrenner

Hi Karl,

Overcure is a problem with hybrid and epoxy-based powder coatings. The polyester and polyurethane types inherently have fairly good overcure protection to about 425ºF. Hybrids and epoxies have epoxy resin as part of the composition. Epoxies are great for hardness, scratch resistance, flexibility and chemical resistance, but they’re lousy for overcure and weatherability. They gradually yellow with extended bake cycles or excess heat. The additive your supplier is referring to is commonly known as an antioxidant. A pinch of this in an epoxy-containing formula provides some overbake resistance. It has to be incorporated as the powder is being made, so don’t try to add some to an already made powder. Good formulators always add an antioxidant to hybrid and epoxy powders.

MSDSs (material safety data sheets) are required by law to list hazardous ingredients. Antioxidants at the levels used in powders aren’t considered hazardous, so they don’t make it onto the MSDS. The best way to determine overcure performance is to check out the product data sheet (sometimes called a technical data sheet) associated with the material in question. Your supplier should furnish one at your request. Most data sheets will contain a reference to the overbake performance. If it doesn’t, ask the supplier directly. If you don't get a satisfactory answer, you may want to consider switching to a more forthcoming supplier.

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05-01-2007The Best Everyday Solvent

Dear Joe,

What is the best “everyday” solvent? We do a complete pretreat and also media blast, but what should we use as a touch-up prior to powdering for items that might have gotten dirty after the pretreat or blast process? We have been using denatured alchohol. Are there any other solvents that we can use safely, economically and effectively?
--Chuck Bell, Atlantic Powder Coating

Hello Chuck,

I’ve always been a methyl ethyl ketone (MEK) kind of guy. MEK is relatively inexpensive, fairly non-toxic and probably one of the best working solvents for a powder coating operation. That being said, I thought I would perform a little research on what constitutes the best choice of solvent for an operation such as yours. As a business person, you want the best performance at the most reasonable cost. As a conscientious corporate citizen, you need to consider the impact that a process decision has on your operators and the environment.

My criteria for “best” solvent were effectiveness, cost, flammability, toxicity and whether it is a volatile organic compound (VOC). VOCs create air pollution when released into the atmosphere. Here’s a summary of what I found:

      -- Denatured Alcohol: Decent effectiveness, but not the strongest of the bunch. Relatively economical, fairly flammable, low toxicity. It’s considered a VOC.

      -- Lacquer Thinner: Strong solvating ability. More expensive, very flammable, can cause neurological damage and is considered a VOC.

      -- Mineral Spirits and Naptha: These petroleum distillates are decent solvents but not the strongest. They’re inexpensive, somewhat flammable, relatively non-toxic and are considered VOCs.

      -- n-methyl Pyrrolidone: Decent solvating ability. Expensive, high boiling (less flammable), medium toxicity and is considered a VOC but evaporates slowly. I’ve found that it leaves a greasy residue that needs to be removed.

      -- Xylene and Toluene: Strong solvents, inexpensive, flammable with moderate toxicity. Both are considered VOCs.

      -- DiBasic Esters (DBE): Moderate solvating ability, expensive, low flammability and considered a VOC. Leaves a residue.

      -- d-Limonene: A citrus-based solvent with decent solvating ability but not the best. More expensive, flammable, relatively non-toxic and is considered a VOC.

      -- MEK: Very good solvating ability, reasonable in price, flammable, low toxicity and considered a VOC.

      -- Acetone: A very good solvent, reasonable in price, flammable, low toxicity and not considered a VOC.

After my research, my winner is acetone. I like its solvating ability, low toxicity and price. The clincher is that, according to the experts, it doesn't damage the air quality as many of the other alternatives do. However, it’s relatively flammable, so proper handling and storage is a must. Additionally, operators should be trained and required to wear NIOSH-approved respirators and the proper gloves.

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04-01-2007Powder Coating Galvalume

Dear Joe,

We recently sent a truckload of galvalume tubing to be powder coated. The finished product appears to have a bumpy surface that looks like fish eyes. This galvalume consists of 43.4% zinc, 55% aluminum and 1.6% silicon. The coating thickness on this product is approx 1.0 mils, while the powder coating thickness is approx 1.1 mils. Could it be the silicon in the matrix of galvalume?
--Richard Vivian, Bolton Steel

Hello Richard,

One issue that catches my eye is the powder coating thickness — 1.1 mils seems thin. Typically I would recommend a minimum thickness of 1.8 mils for a general industrial application. The thicker film provides increased protection of the substrate and a smoother, more aesthetically pleasing appearance. A 1.1 mil thickness of most powders provides a somewhat orange-peeled (textured) surface. Too thin a film may not be enough to cover the surface of the metal.

I think that it’s also important to differentiate between “bumpiness” and “fish eyes.” Bumps obviously involve raised spots of film. Fish eyes are depressions caused by contaminants that possess a significantly lower surface tension than the powder coating. In the worst scenarios, the defects extend down to the surface of the substrate. Silicones, oils, lubricants, mold release agents and forming compounds are known to cause fish eyes in powder coatings.

Here’s the course of action I recommend:

      1. Re-inspect the defects under low-level magnification to determine whether they are raised or depressed.
      2. Increase your film thickness to a minimum of 1.8 mils.
      3. If you are fairly certain that the defects are fish eyes, rigorously clean the galvalume surface and then apply the powder. By rigorously, I mean scrub/abrade the surface and then apply a strong solvent cleaner with a clean cloth. This should remove any contaminant and eliminate the fish eyes.

If none of these measures eliminates the defects, then the contaminant may be coming from your application/curing environment.

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04-01-2007Disposal of Spent Powder

Dear Joe, We recently began powder coating operations here at our facility. What is the proper way to dispose of the spent powder that we can no longer use? A couple of our powder vendors have told us to bake the powder until it forms a solid and then throw it away with our normal everyday refuse. How would we go about baking it if that is a viable option? I know the material is non-hazardous; however if we threw the material away without solidifying it, wouldn’t the material create an inhalation hazard?
--Sandy Forsyth, McLaughlin Body Co.

Dear Sandy,

I’ve managed a number of powder coating manufacturing sites. Occasionally we would incur an accumulation of obsolete or unwanted powder. In all cases we were able to dispose of the powder in our regular dumpster that was destined for the landfill. Our trash haulers had one stipulation — they wanted to avoid creating a plume as the material was landfilled. We prevented this by securely packaging the obsolete powder in fiberboard drums with tight lids.

Long ago I worked for a major powder coating manufacturer that implemented the solidifying procedure that you mentioned. I lived close to the plant, so at midday I regularly dined at home. Upon my return one day, I encountered a number of fire vehicles encircling my place of employment. Our solidifying process for waste powder had caused a fire in the oven, and hence a visit by the local fire brigade. Large volumes of powder coating can ignite during baking under certain conditions.

I would check with your local waste hauler(s) and get their input before implementing my recommendation. Local regulations may apply, and the waste hauler should be up-to-date with what options exist.

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01-01-2007Glass Transition Temperature and TGIC

Dear Joe,

In polyester/TGIC systems, the Tg is sensitive. Every weight percentage of TGIC reduces the Tg by approximately 1.5 to 2ºC. Why does TGIC reduce the Tg of the coatings? My idea is that TGIC has a very low equivalent weight, and therefore a low crosslinking density. Generally, low equivalent weight hardeners reduce the Tg. The same thing happens with polyester/Powderlink 1174, which also has a low equivalent weight. But this effect does not occur with polyester/hydroxyalkyl amide systems. Why?
--Shiva

Dear Shiva,

Before I answer your question, I would like to define Tg for our readers. Tg refers to “glass transition temperature,” which is reported in degrees Celsius. It is typically measured by exposing a sample to an increasing temperature and measuring the heat flow of the material versus a blank sample. The most common method uses a thermoanalytical test known as differential scanning calorimetry, or DSC. The Tg is relevant because it identifies the temperature at which the material, a powder coating in this case, undergoes a change from a rubbery to a glassy state. In other words, it’s a fancy melt point temperature test.

In polyester powder coating formulas, the addition of triglycidyl isocyanurate (TGIC) depresses the Tg of the powder coating. For every percent addition of TGIC, the powder Tg is reduced approximately 1.5 to 2.0ºC because the TGIC is soluble in the polyester resin. As you state, TGIC has a low molecular weight (297 g/mol) and equivalent weight (101 g/mol). However, it is the solubility that causes the depression in Tg.

Cytec’s Powderlink 1174 (tetramethoxy methyl glycoluril) also depresses the Tg of polyester powder coatings due to its solubility in the resin. Its molecular weight is 350 g/mol. Formulations using Powderlink 1174 typically contain higher than normal Tg polyester resins to compensate for the Tg reduction caused by the Powderlink.

Primid crosslinkers (hydroxy alkyl amides, or HAAs) possess limited solubility in the polyester resins typically used to formulate powder coatings. Because of this effect, it is important to achieve adequate dispersion of the HAA in the polyester resin during extrusion as a powder is manufactured. Accordingly, HAA crosslinkers do not depress the Tg of the powder coating. Interestingly, the most common HAA product is Primid XL-552, and its molecualar weight is 320 g/mol.

So Tg depression is caused by the solubility of a material in the base resin, instead of by the molecular or equivalent weight.

Thanks for your interesting question, and good luck formulating powder coatings.

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01-01-2007Wood Bleaching Systems

Dear Joe,

We recently stripped an oval dining table about 17 ft long and approximately 4 ft wide. We are unable to find two-part wood bleach and were advised that it has been put into a more dangerous category and will no longer be available. Why? Is there any other bleaching product available for wood refinishing?
--Louis Baum

Hello Louis,

It sounds like you have a difficult project on your hands. Basically there are three types of wood bleaching systems:

                                    -- Two-part peroxide
                                    -- Chlorine
                                    -- Oxalic acid

They all work well if used correctly. The two-part peroxide system has a limited shelf life because the mixture is neutralized with time. It doesn’t remove the stronger dye stains. Chlorine works well, but you have to make sure the concentration is high enough. Regular laundry bleach is too weak. The oxalic acid system works uniquely. It kills stains caused by the reaction of iron with natural wood tannins. It also lightens graying due to weathering of wood surfaces.

Good luck with your project.

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12-01-2006Powder Overspray Collection System

Hello Joe,

We currently use 1K paint on OEM parts and are planning to build a mini-line to paint powder on class A parts. The size of the booth we want is 3 ft square with a line speed of 2 fpm, running 16 hours per day. How do we build a booth and collection system to capture powder overspray?
--Khem Ramsaran, Paintline - Rollstamp Manufacturing

Greetings Khem,

It sounds like you need a “starter-kit” application booth to allow you to enter powder technology.

To construct one yourself, you will need a box-like structure to act as a target for the oversprayed powder. This can be built with plastic. Clear polycarbonate works well but is expensive; high-density polyethylene can also be used. Alternately, you can have your local tinman fabricate a sheet metal box. The box should be tapered in the back leading to a 3 or 4 in. duct flange. Booth illumination is recommended. A window can be fashioned in the sheet metal or opaque plastic, if used. Clear polycarbonate has obvious advantages for light distribution.

The working component of the booth is a dust collector. This can be purchased either new or used, if you would like to be frugal. I would recommend a small unit that has a minimum of 300 cfm capacity. There are a number of used equipment suppliers that offer these. I would check the websites of Federal Equipment, Aaron Equipment, Ingalls Equipment, Arnold Equipment and HGR Equipment.

The dust collector will have to be connected to the booth with suitably sized piping that is available from your local hardware supplier. I recommend industrial quality ductwork as opposed to residential heating piping. Ductwork and clamps can be ordered from McMaster-Carr and Grainger catalogs if a local source is not available.

These guidelines will allow you to design a spray-to-waste process. If you want to capture and recycle the oversprayed powder, you will need a more sophisticated system from a booth manufacturer. Companies such as Nordson, ITW-Gema, Wagner, Parker Ionics and Deimco can provide an off-the-shelf unit to meet your needs.

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12-01-2006Salt Spray Test Failure

Dear Joe,

I have a customer who has pulled steel parts from various areas of the racks to test three colors for salt spray. All colors passed in an earlier salt spray test, but one color failed in the recent test. Film thickness and methyl ethyl ketone (MEK) testing showed the part to be okay. I have explained to the customer that the product will pass if it is pretreated properly, has the correct film thickness and is cured correctly. How would you convince the customer that the powder is okay?
--Salt Spray

Dear Salty,

Your customer is wise to test powders on parts pulled from his pretreatment line. In doing so, he not only tests the powders in real-world conditions as opposed to idealized lab conditions (e.g., using Bonderite® panels), but also measures how well his pretreatment system is performing. You are wise to measure the film thickness and solvent resistance to verify that the powder has been applied and cured correctly.

If the powder demonstrates acceptable film thickness and solvent resistance but exhibits questionable salt spray performance, then the issue to address is the quality of the substrate and pretreatment. Are some of the parts excessively dirty (e.g., smut, forming oils, oxidation)? Is the pretreatment system adequate for the condition of the substrates? Is the pretreatment system adequately maintained? Are the chemicals within the supplier’s specified ranges? Are the rinses clean? Are the spray nozzles all in working order? Are the required solution temperatures being maintained within specification?

From what you’re telling me, I suspect that either the incoming parts vary widely in cleanliness and/or quality, or the pretreatment system is out of control. I suggest that you work closely with this customer to evaluate the quality of the incoming parts and the pretreat system, then rerun the same tests. It doesn’t hurt to include lab test panels as a benchmark alongside the line parts being evaluated.

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11-01-2006Craters in the Powder Shop

Dear Joe,

We’ve been having a nightmare with craters in our powder shop over the last few months. We only spray polyesters in our shop. However, one of our neighbors in our industrial park applies a silicone-based military coating. I’m convinced the overspray mist from our neighbor is causing our trouble. Am I correct in my thinking, and what can I do to remedy this situation?
--Todd

Dear Todd,

Serious contamination of powder coatings can occur from contact with even minute concentrations of silicone-based paints. Mist from a finishing operation involving silicone-based paints can carry long distances and become entrained in the ambient air of a powder coating operation. The mist of silicone-based paint can also contaminate a powder coating finish by depositing itself on the surface of parts before or during the powder coating process. Furthermore, the mist from a silicone-based paint can be deposited on air handling equipment surfaces such as filters and thereby be distributed to the ambient air, compressed air and/or finishing surfaces.

Silicone-based paints cause craters in powder coatings due to the inherently large difference in surface tension between the silicone-based paint and the powder coating. Craters form when a region of very low surface tension resides within the melted film of a powder coating. The surface tension of silicone-based paints is typically measured at 15 to 20 dynes per centimeter. The surface tension of powder coatings is typically 40 to 50 dynes per centimeter. This is a large enough discrepancy to cause fish eyes or cratering. Laboratory studies have shown that concentrations of silicone-based products as low as 0.001% can cause widespread cratering.

Remediation of silicone contamination of a powder coating system requires exhaustive measures. If the source of the contaminant can be identified, the first action is to isolate the cause. The next steps involve the painstaking procedure of cleaning the entire finishing shop. You should thoroughly clean all air handling equipment, including compressed air systems, booth exhaust and oven air handling systems. You should also thoroughly clean all powder handling and application equipment, including guns, hoppers, hoses (these should be discarded if possible) and booth surfaces. The use of denatured alcohol is recommended to clean plastics parts. It can dissolve the silicone residue while leaving the plastic intact. A test application can be conducted at this point. If contamination is not eliminated, then all surfaces in the shop should be thoroughly washed with an industrial cleaner.

Diligent root cause analysis is vital, as is thorough cleaning of the entire powder application system.

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11-01-2006Creating a Woodgrain Finish

Dear Joe,

We are creating a woodgrain finish in our powder coatings by covering the coating with a specially made, paper-like foil prior to curing. I’ve heard that a woodgrain finish can also be achieved by applying a single powder, somewhat like a dry sublimation technique. Can you please tell me how to make this type of powder coating?
--Shiva

Dear Shiva,

I am familiar with the process you are using with the paper. It can create very appealing images on the surface but is rather process-intensive.

Another technique involves applying two dry layers of powder — first a dark brown layer, followed by a lighter brown layer. The dry coatings are then disrupted by dragging a comb-like tool over the deposited powders. The coated object is placed into an oven to affect flow-out and cure of the materials. The resultant finish will have a woodgrain look. This technique requires the use of compatible powders of the proper color and gloss. It also helps to experiment with the technique of “combing” the dry surface. The comb apparatus can be fabricated by fixing stiff strands of plastic to a rigid handle. A successful technique requires a little artistry on the part of the applicator. Some of the major powder manufacturers have this technology and would be happy to provide details and materials.

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10-16-2006Powder Coating Wood Substrates

Dear Joe,

We are starting to manufacture and sell our patent pending, ergonomically adjustable computer workstations. We are interested in the powder coating process for wood substrates such as high-density fiberboard (HDF) that have an even core and face. Do powders for wood substrates still need refrigeration? We would also like to find a powder coater of wood substrates in Northern California or near Reno, NV, that does piece work.
--Norman Allen, Infinity Station

Dear Norman,

Powder coating processes for wood substrates are gradually popping up all across the landscape. Some are big OEMs, while others are small to medium jobcoaters. Some have ultraviolet (UV) cure capabilities, whereas others rely solely on thermal cure powder technology. In your neck of the woods, there is a coater called Do-Able Products in Chino, CA, that can powder coat wood.

It sounds like you are also interested in the possibility of eventually installing your own line. You will want to contact a few key powder suppliers and equipment manufacturers. A good starting point would be Finishing Today’s Buyers’ Guide, which is available online at www.finishingtodaymag.com. The 2006 edition will be published in November.

As for the handling of powders designed for application to wood, refrigeration is not normally required. However, careful handling and transport is strongly recommended, since powders for wood usually have lower melt points than conventional powder coatings. For instance, instead of having your vendor ship this type of powder to you on a Friday during the middle of a scorching summer, have it overnighted to you earlier in the week to minimize the possibility of having the product sit at a shipping depot in a dark truck over the weekend. Similarly, don’t store a wood powder next to the cure oven in your plant. I recommend air conditioned storage as opposed to refrigerated handling.

Good luck with your endeavors. It’s always refreshing to hear of someone pushing back the frontiers of coating technology.

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10-16-2006Powder Coating Aluminum Shutters

Dear Joe,

We are considering changing to powder coat finishing from two-part polyurethane for our aluminum shutters. We currently paint over existing factory finished polyester coatings (.007 in. thick) that have been baked on at the factory. I seem to be getting conflicting answers as to whether this will work due to the possible insulating factor of the factory paint. One person says that the factory finish must be conductive, and another says that you just need a good ground. What is your opinion?
--Steve Sutton, Willard Shutter Co.

Hello Steve,

Powder can be applied over existing finishes. A good example is the clear topcoat that BMW applies to its 5 and 7 series automobiles in Germany. Those cars already have an e-coat, primer surfacer and color basecoat before seeing the final coat of powder. That being said, you still might have trouble powder coating over .007 in. of polyester. Even though the polyester has been baked in the factory, can it survive another possibly higher temperature bake for the powder? And will the powder apply evenly on the somewhat insulated polyester surface? Another issue is whether the powder will achieve acceptable intercoat adhesion to the polyester.

Ideally, you should perform a test by applying the powder of choice to a non-critical scrap part. Make sure the part is adequately grounded to achieve the best electrostatic attraction of the powder, and reduce the current on the gun. (If the gun doesn’t allow for current reduction, just reduce the charge to about 50 kVs.) The polyester surface should be clean and free from oils and contamination. I recommend that you wipe the surface with a weak solvent such as VM&P naptha prior to powder application. If you can use a scrap part, test the powder coat adhesion after the part cools by making a cross cut with a razor blade. Apply packing tape to the cut, and pull. The powder coating should adhere 100%.

I hope that this information helps. Let me know how things work out for you.

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09-12-2006Inspection Lighting

Dear Joe,

We are running an overhead monorail and have two banks of overhead lights in our inspection area. We have tried using a bank of vertical lights, but I am looking to get the best overall lighting setup for a variety of part shapes and configurations. I am also concerned about the heat generated from the lights for our employees. I tried searching online for light tunnels and inspection lighting but haven’t come up with anything. Can you point me to any good websites or articles?
--Joy Manning, Grand Rapids, MI

Dear Joy,

I have seen really good inspection areas at a number of manufacturers; the best areas use a multitude of lamps. When a high density of light is needed (measured in lumens) without significant heat generation, most people choose fluorescent lamps. They are relatively energy-efficient and come in a variety of colors ranging from warm or neutral to cool or daylight. The lighting typical for the environment in which your product is used will dictate which color is best for your inspection area. (Daylight would probably be best for an automotive trim application.) McMaster Carr provides a good explanation of its fluorescent lamps on page 632 of its online catalog, located at www.mcmaster.com. GE also has an informative website for calculating commercial lighting needs, located at www.gelighting.com/na/business_lighting/education_resources/tools_software/toolkit/.

As for finding a light tunnel to exactly fit your needs, I would rely on your local maintenance people or fabrication shop instead of an off-the-shelf solution. Your inspection area is probably unique in design and dimensions and will be best served with a custom lighting system. I would calculate the number of lumens you need to deliver to the part surfaces and then determine how many lamps will deliver this amount of light. The distance of the light to the part will also impact how many lamps are needed. The lamps should be close enough to provide the required amount of light, but far enough away to be unobtrusive.

Good luck, and let me know how things turn out.

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09-12-2006Exposure to Materials during Pregnancy

Dear Joe,

I work for a company that staffs employees for an industrial plant that coats automotive parts using e-coat, and I am wondering what effects this process might have on pregnancy. The plant has a lot of black dust on the ground, boxes and anything else lying around. You can definitely smell an odor from the paint as well. I am actually only in the plant for up to an hour per day, so I don’t know whether that is long enough for me to be concerned. I am not currently pregnant, but I would like to know of any possible risks beforehand. No one in the plant wears any type of mask or breathing device, so I am assuming this isn’t an issue, but I would feel much better with a final answer. I have tried several other means to figure this out, but have constantly come to a roadblock. Can you help?
--A Concerned Employee

Dear Concerned,

It’s wise to ask questions about exposure to industrial materials, especially if you are in your childbearing years. Industrial suppliers have a system to notify their customers of the handling requirements of their materials. The lynchpin of this system is the material safety data sheet (MSDS). A well written MSDS will contain a wealth of safety and environmental information, including hazardous components, personal protective equipment recommendations, possible decompostion products, exposure limits and disposal strictures.

All suppliers must provide MSDSs to their customers for any materials purchased. Most companies have a specific person who keeps the MSDSs on file. By law these documents are to be available to all employees. You should determine who keeps these on file and ask to review the ones pertaining to the materials currently being used in your plant, preferably with a safety professional.

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08-04-2006Winter vs. Summer Powder

Dear Joe,

I’m kind of new at this powder coating technology thing and heard an unusual description for powders. One of my operators talked about “winter” powder versus “summer” powder. She said that they behave differently so it’s important to adjust your application settings to compensate for these differences. Is this true, or is it just another urban legend in the wonderful world of powder coatings?
--Left Unsure of Manageable Powder Spraying

Dear LUMPS,

Your operator has the story partially correct. Powders do behave differently depending on environmental conditions. The difference in application performance depends more on the environment in your application area than on the environmental conditions when the powder was manufactured. Certainly an arid day in the middle of January will influence your powder’s electrostatics, just as a sweltering, humid day in August will. Cold, dry air allows electrons to hang around longer than warm, moist air. On a cold, dry day, you may experience excess charge accumulation leading to back ionization, which occurs when a negative charge doesn’t dissipate quickly enough when a powder is electrostatically deposited. This phenomenon causes microbursts of powder on the substrate, kind of like mini volcanoes. The resultant coating surface resembles star patterns. Electrostatic powder seems to enjoy a certain amount of humidity. High relative humidity has a calming effect on the application properties. The only real enemy is excessive heat. Ambient temperatures over 100?F can spell trouble with caking and sintering of powder coatings.

The other thing to avoid when handling powder is storing it in a very cool environment and then transferring it quickly to a hot and humid environment. Cool powder exposed to humid air will essentially act as a desiccant and adsorb the moisture from the air.

So there really isn’t a phenomenon of “winter” and “summer” powders. It’s the application environment that influences the performance, not the date that it was made.

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08-04-2006Powder Coatings and Food Storage

Dear Joe,

We've been asked to provide a coating for food bins that will be used to store bulk chocolates in a retail environment. Our customer would like these coated in white, orange and a baby blue. I was wondering if powder coatings can be used as a finish on containers that are intended for the storage of confectionary goods. Are there some do’s and dont’s I should be aware of?
--Candy, Hershey, PA

Dear Candy,

I’m glad you asked this question before you coated thousands of containers and then found out that the coating is not acceptable for contact with foodstuffs. Indeed, there is powder coating technology that can be used for finishes coming in contact with food or beverages. The good folks at the Food and Drug Administration (FDA) in Washington, DC, have developed a Code of Federal Regulations that specifically details what components can be used in a coating formula that is used in the food industry. It’s known as Title 21 CFR 175.300 — commonly referred to as the “white list” — and basically outlines what can be used in the resin and binder of the coating. Likewise, the pigments we can use are listed in CFR 178.3297. Powder coating technologists consult these documents when formulating for food contact applications.

As long as your coating supplier can vouch that the coating is based only on ingredients on the white list, then you’re in the clear. Typically this means you will be using either an epoxy or hybrid (epoxy polyester) powder coating. Your choice of color may be limited because not all pigments are listed in CFR 178.3297. Still, the possible color palette is quite broad.

Your next step is to dazzle your powder supplier with your newfound knowledge and get the right powder for your application.

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07-01-2006Superdurable Powder

Dear Joe,

I run a modest powder jobcoating shop. One of my suppliers keeps telling me that I should switch from using hybrids and polyesters to superdurable powders. What are superdurable powders, and should I spend the extra money that these command?

Thank you,
--Lynn Laviere, Hartstown, Pa.

Dear Lynn,

First of all, congratulations on running your own show. Small businesses have all sorts of challenges; hats off to those who take the plunge and live to tell about it.

Hybrid (epoxy polyester) and polyester powder technology are considered the stalwarts of the industry. Hybrids should only be used for applications where there will be no possibility of exposure to the outdoor elements. They are a great economical choice for most indoor applications; however, they will quickly chalk and fade if exposed to sunlight. Conversely, polyesters provide good exterior durability. You can expect to get up to two years of durability in a sun-soaked environment such as southern Florida before observing evidence of coating degradation.

Superdurables typically are polyester based (TGIC in North America and Primid™ in Western Europe) and offer enhanced exterior durability. The resin system alone can survive up to five years in Florida before gloss begins to deteriorate. Pigmented systems usually fade a little sooner, depending on the durability of the pigments used.

Superdurables do command a higher price tag. The resins used are more expensive than conventional polyesters, and the pigmentation can be more costly. In most cases, conventional polyesters will meet the general-purpose needs of a jobcoater. However, if one of your customers has a special application that warrants the higher expense — such as refurbishing a motorcycle or refinishing the exterior parts of a classic car — then I would definitely go with the superdurable technology.

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07-01-2006Silk Screen Adhesion Failure

Dear Joe,

I coat electronic cabinetry for a company that manufactures computer servers. The coating is a textured hybrid powder. Our customer applies a silk screen to the finish to identify control names, and they are having trouble getting the silk screen to adhere to the powder finish. Please help.
--Stan Dubrowski, Parma, Ohio

Jak sie masz (How are you? in Polish), Stan? Perhaps not so good. I have encountered this problem many times in the field. Sporadic adhesion failure to textured powders can be caused by a couple of factors. The red flag in this case is the texture of the powder coating. Often a novice powder formulator will incorporate a texturing agent based on polytetrafluoroethylene (PTFE) (similar to DuPont’s Teflon®), which creates texture because it doesn’t melt. The powder begins to flow and level during the bake cycle; however, the PTFE restricts some of the flow, thereby creating a texture. It’s a nice formulating technique — unless you want something to stick to the finish. As you might have guessed, things don’t stick to PTFE.

Another possible cause could be a gross overbake condition. If the parts being coated are baked significantly beyond the time and/or temperature recommended by the powder supplier, the surface might present adherence challenges. Check to ensure that your bake conditions closely approximate the time and temperature prescribed by your supplier.

I would also ask your powder supplier whether any PTFE is present in the formula. Most powder formulators prefer to avoid discussion about a powder’s ingredients; however, this situation is serious enough to warrant this conversation.

Powodzenia (Good luck), Stan. Let me know how you make out.

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