FREQUENTLY ASK QUESTION
Virtually all powder coatings emit 0 or near 0 VOC. Volatile Organic Compounds are chemicals that will evaporate into the atmosphere when a product, such as a coating, is being applied. In the case of liquid coatings, most all contain some type of solvent, which is usually a VOC.
With powder coatings, there are no solvents, and generally no liquids involved in either the manufacture or usage of the powder. Thus, they are 0 VOC products. This can be measured in powder coatings by weight loss measurement of the powder itself when being baked.
For example, starting with 100.0g of powder, the powder can be baked, and re-measured for weight after baking. If there are VOC’s in the powder, they will vaporize, leaving only the powder itself. Generally most powder coatings will maintain 99.0% to 99.5% of their weight after baking. Approximately 0.5% of any powder is water (water is not considered a VOC).
The only exception to zero VOC would be with some specialty products and types of urethane chemistry. Some urethanes are cured with a blocked IPDI. When “unblocking” the blocking agent will evaporate from the coating, forming a potential VOC. This can be sometimes seen as “smoke” coming from the part, the smoke being caprolactam. However, even urethanes are considered near 0 VOC, as the VOC emitted tends to be less than 0.5%.
Here at EPC, we don’t manufacture any coatings that would be considered high temperature.
To start with, the temperature range needs to be defined. High temperature coatings are generally used for applications such as barbecues, fireplaces and stoves, or automotive parts such as tailpipes. For these applications temperatures must be withstood in the range of 500F to 1500F.
The only type of powder coatings that will work in this range (500F – 1200F) are silicone powder coatings. These products are difficult to use, and can contaminate other products.
EPC does manufacture a line of products for medium heat applications, used on items such as heating system parts, or lighting. These products are generally used in applications maxing out to about 150C (300F).
There are a number of products we manufacture for elevated temperatures.
At 200F, a hybrid is probably the better choice (of course, there will be variations in temp, so it\’s hard to be definitive). A glossy hybrid, of course, not matted. Matted hybrids perform much worse than semi-gloss and gloss hybrids. A polyester is excellent, although a standard polyester can start to bloom at those temperatures, so you could get a milky haze on it after some time. It will eventually disappear, but might not look great in the mean time. A superdurable polyester finish, of course, won\’t bloom.
At 300F, the polyester is clearly the better product, but conversely, at 200F the hybrid is comparable, maybe slightly better than the polyesters.
Color is very important, the darker the color, the less any yellowing will show. We have a number of customers that manufacture heaters, such as electric water heaters, that have operating temperatures in this range, and a (glossy or semi-gloss) hybrid works very nicely.
At 300F, the options are much more limited than at 200F. As the temperature goes up, it limits some types of coatings and chemistry’s, which simply don’t withstand higher temperatures.
The best coating in this range is a pure, glossy polyester. A superdurable finish is usually at the high performance end, along with some specially manufactured polyesters for higher heat resistance.
Gloss and color are very important. Some colors, such as reds, will not withstand the temperatures on the pigments – which makes the color of the powder – and thus will change color quickly. Gloss is also very important – glossy products will do better in general than matted products. This is due to the additional chemicals added to the coatings to reduce gloss, some of which have poorer heat resistance than the rest of the coating.
EPC specializes in manufacturing fast cure, and low cure, powder coatings. We are fortunate to have equipment that has excellent manufacturing profiles for producing fast cure / low cure powders. When producing these types of coatings, they cure quickly (goes without saying?). But powder coatings
are manufactured by heating a mixture of plastic through an extruder – and the heat when making the powder can make the system react pre-maturely. EPC has specialty extruders that keep the temperature
profile to a very low level.
There are several options for faster cure or lower cure coatings. Some things need to be defined, such as:
- Do you need fast cure or low cure – the two aren’t necessarily the same thing.
- Interior or exterior?
- What other product specs are most important to you?
As with anything, there is always a give and take. For a fast cure powder coating, the most common trade offs are color stability, smoothness and / or storage stability.
Color stability can be a problem with many fast cure coatings due to accelerants or additives used to speed up the cure, some of which may not be color stable.
Smoothness and storage stability are opposite ends of the same problem. As products are sped up, smoothness becomes tougher to achieve, and the products will generally show orange peel. At times and when sped up to the limit, these accelerated coatings can end up looking like a rolling texture. One of the things that can be done to limit this problem is lowering of the Tg (softening point) of the powder coating, which allows for a smoother finish. However, this also reduces the storage stability of the product. This can become a balancing act between lowering the Tg (and increasing smoothness) and increasing the speed of the product (but making it more orange-peeled).
We offer most all of our chemistries in slip resistant product lines.
There are two things that will increase slip resistance of any coating. One is working on the chemical end of the powder coating, and the other is working on the physical form of the coating after cure.
Chemically, things like rubber compounds have excellent slip resistance. Many rubber compounds are used specifically for slip resistance because of this. EPC has added a chemical component (trade secret!) that has excellent “grab” and allows much better slip resistance on the powder coating than any others we have seen or tested.
Physically, EPC makes sure that the coating has a textured finish. This gives the product natural slip resistance.
Most all powder coatings have different shelf lives.
First, what is a definition of shelf life? We define shelf life as the length of time that a coating can sit “on the shelf” under defined storage conditions (temperature, humidity) and not show any significant loss in its properties – either properties of the powder itself or of the finished product coating, if it was to be sprayed and cured.
This deterioration of the properties of the powder could be:
• Agglomeration or clumping of the powder in the box
• Poor chargeability of the powder when spraying
• Loss of impact or other properties of the finished powder
• Decrease of cure speed of the coating
• Seeds showing up in the finished coating
One of the most important things that affect how the powder stores, is how it is stored. Under what conditions. Powder coatings will last a long, long time, if they are stored in good conditions – closed packaging, with heat at a maximum 80F (25C) and low humidity.
Powder coatings will attract moisture and humidity, and with the packaging left open, they will degrade far quicker than when the packaging is fully closed. We can’t describe how many times our sales people have gone into our customers plants and found boxes being stored with the packaging (box top and plastic liner) completely open to the air, or boxes being stored next to the ovens. This not only leaves the powder with a much shorter shelf life, but also leaves the powder open to contamination.
The different powder coating chemistry’s have different shelf lives. Specialty products, like some of our SEFA grade products, have very poor shelf lives, and will start to degrade after 6 months or less. Many of the standard powder coatings, however, have shelf lives that are usually rated at 1 year, but generally will extend far, far beyond 12 months. It is not uncommon for us to test very old powder (5 – 10 years old) of products such as standard hybrids or polyester powders, and find almost no degradation at all of these products, even when they haven’t been stored in the most ideal conditions.
There are a number of common problems that our sales people find at customers spraying powder coatings. The most common problems are often easy to fix, but simply don’t get fixed due to a lack of understanding of some of the problems and their consequences.
I’ve listed a couple of the most common problems, but we also have a publication about common problems and fixes.
1. Ground Issues: Probably the most common problem is ground issues. It is absolutely essential that the metal being sprayed is fully grounded. We often find very poor ground on the production line at our customers, as powder build up on the hooks, lack of grounding thru the equipment, or not having a true ground at all is often an issue. The problem with this is that the powder wont’ spray well, and efficiency (powder on the part) will be low. So not having a ground is like throwing money away.
2. Contamination Issues: This is usually seen as either defects in the finished coating such as craters, or visually by color (specs) cross-contaminating one powder coating to the other. Contamination has several causes, but the answer usually comes down to good or improved house cleaning. There are some other actions that can help quite a bit as well. For example, if a customer is using several powder coatings that may not be compatible with each other, a relatively inexpensive and easy solution might be having a second set of product delivery hoses for the incompatible product.
3. Curing Issues: Curing problems go both ways: over-cure and under-cure. Over-curing can lead to problems with color, or in severe cases, physical damage to the coating. Under-curing powder can lead to poor adhesion, the wrong gloss and flexibility problems. The root cause is often a lack of understanding of the recommended cure cycles (which generally cite “metal
temperature” which is very different from “oven temperature”), problems or breakdowns in the oven itself, or changing of part parameters, such as part thickness, which leads to big changes in metal temperature. This can usually be resolved fairly quickly by using an oven temperature logger, along with testing of the paint after it exits the oven, along with knowledge of the production line process learned over time.
There are two answers to this question. In general, we divide our product range at EPC into 2 parts. We have custom manufactured orders, and stock products.
Stock products are products that Erie has “on the shelf” ready for sale. This is a defined list of products that are on our color card, for example, but also includes a number of other products that may not have made it onto our color card but we manufacture frequently, and products such as our large choice of black powders. The stock products are generally sold in 25kg minimum orders, but for customers needing / wanting smaller volumes, we have our “smart pack” program, where we will individually custom pack products to the customers requested weight, whether that is 5lbs or 25lbs.
Custom manufactured products make the rest of our product line. These products are also generally manufactured to a 25kg (55lb) minimum. However, we will on request manufacture some products in smaller volumes still, down to any volume requested.
There are two general types of powder coatings, thermoplastic coatings and thermoset coatings. The defining feature of these two types of powder coatings are the way they react after heating. As you can tell by the name, thermoplastic coatings remain “plastic” after heating, whereas thermoset coatings “set”, or cure, after heating.
EPC only manufactures thermoset coatings. Thermoset coatings cover the large majority of powder coatings sold in the market.
Thermoplastic coatings have some excellent properties, such as wear resistance, but are used only in fairly specialized applications, such as dishwasher racks, due to a number of reasons including high cost and generally poor adhesion. These types of coatings include PVC coatings and Nylon.
Thermoset coatings cure, or cross-link when heated to sufficient temperature. Because they cure, a chemical reaction takes place that gives these coatings truly exceptional properties that are impossible to match in thermoplastics, such as impact resistance, adhesion and flexibility. And the cost tends to be much lower and controllable.
Generally, yes, you can spray most any powder coating on your production line. Of course, there are always exceptions. However, most of EPC’s customers spray a variety of different products and chemistry’s with only minimal problems and changeover costs.
When considering changing from one product to another, there are two large factors. These are the color change, and the chemistry change.
The color change is a pretty obvious obstacle. Obviously going from white to black can cause some problems. However, with good cleaning, this can be done on most any powder line with some care. Additionally, many powder coating equipment manufacturers have spent a lot of time, money and resources on developing systems and equipment that makes this job easier. Mainly, this comes down to ensuring that none of the powder particles from the previous color come into contact with the new product, if the color is vastly different. If the colors are close, this problem will often take care of itself.
As far as chemistry goes, this is an issue that can cause some problems on the production line. Changing from one chemistry to another, say from a polyester TGIC to a hybrid, for example, can be done relatively easily, but the customer should be relying on their own experience, on the equipment
manufacturer, and the powder supplier for answers on how to do these product change-overs.
With chemistry, “compatibility” is the key. Compatibility refers to how well two powders get along chemically when mixed together. Many powders have excellent compatibility together, and will cause no problems when mixed. As far as compatibility goes (leaving aside color),
1. Perfectly compatible powders: Can be mixed with no noticeable changes
2. Mostly compatible powders: Can be mixed with only a slight drop in gloss noticeable.
3. Somewhat incompatible powders: Will show significant gloss drop, often sparkly finishes
4. Highly Incompatible Powders: Will often lead to pinholing, and cratering, gloss drops
Because of this, it is important to know what is compatible, and what isn’t. Your powder supplier will likely be able to help with this, either with direct knowledge of the products, or by testing the powders you are looking at with a “compatibility ladder”. A compatibility ladder is basically mixing two powders together at defined quantities, spraying, curing, and checking the results for compatibility.
Most standard powder coatings, even from different suppliers, will usually be compatible, or slightly incompatible. However, some specialty powders, such as rolling textures, will often be incompatible, and can cause real issues.
Some chemistry’s, such as acrylics and silicone based powders, are highly incompatible, and generally cannot be used in the same production line, or even the same production facility, due to contamination issues.
This is a very large question, that has many answers. For this answer, I only look at the metal coating industry, as this is where powder coating has been used for the most part. Other industries that do use powder coatings, such as MDF and some plastic applications, have different economies. Industries such as wood coatings, floor coatings, and house paint are obviously not touched by current powder technology, so no comparison is valid on these types of products.
In metal finishing, based on the number of companies that formerly sprayed liquid coatings, and have over the last 20 or 30 years switched to powder coatings, the answer must obviously be that powder coatings are less expensive or we simply wouldn’t have seen that trend.
There are still some areas where liquid coatings have an advantage. These include lower curing temperatures, and generally lower film build.
However, there are a number of costs associated with liquid coatings that are reduced or eliminated with the usage of powder. These include waste and waste disposal, safety aspects, ability to apply easily without needing specialized work staff, handling ability in plant, and long term durability. Powder coatings show very significant advantages in all of these areas.
Generally for metal finishing, the advantages of powder coating far outweigh any advantages from liquid coating.
For a more in depth analyses using numbers, we would highly recommend using the Powder Coating Institute (PCI) website, www.powdercoating.org, which has an excellent liquid to powder cost comparison under the “Store and Resources” section.
RoHS stands for Restriction of Hazardous Substances, is a European initiative covered under EU directive 2002/95/EC. It covers the usage of a number of hazardous ingredients that might be used in the manufacture of products. This directive covers the usage of materials such as lead, cadmium, PBDE, etc.
Erie Powder / EPC does not use any of the RoHS materials in the manufacture of its products.