Have a question about PPG powder coatings solutions? We’ve answered some of the most frequently asked questions below. Still need information? Please contact us. We’re happy to help.
During the curing cycle, volatile ingredients may be emitted from the surface which can cause surface contaminants and imperfections in the finish coat. Potential sources of volatiles other than the powder ingredients include primer coatings that may be underneath the powder coating, metal pretreatment conversion coatings, and oils, moisture, or other contaminants that are on or in the substrate prior to coating. If excessive amounts of volatile substances are generated late in the cure cycle, they may create defects in the forming film.
Preheating of a part prior to painting may eliminate enough volatile substances from the part to permit it to be painted without the occurrence of defects from outgassing. The time and temperature of preheating required to minimize outgassing must be determined by trials. Generally painting needs to be done shortly after preheating is carried out, since volatiles substances may recur, either by absorption from the environment or migration for the substrate interior.
While there is no powder coating product that can eliminate all occurrences of outgassing in severe cases, there are ways to reduce outgassing occurrences during the application process, and there are products PPG makes that are designed to reduce the chances outgassing occurs. We call these Anti-Outgassing, Gas-Free or Anti-Gas powder coatings.
PCMB70106 Gray Anti-Gas Epoxy Primer
PCS79102OG Gray Anti-Gas Polyester HAA Primer
PCMT70101OG Ultra Gray ESD Epoxy Primer
PCTA99171 Gloss Black AOG Ultra-durable TGIC Polyester
PCMA90111 Flat Black AOG Epoxy
Optimum conditions should be defined on a product-specific basis. Every powder product has an individually defined shelf life rating that is related to its storage temperature. You’ll find this information on the product data sheet.
Typically, low temperature has no harmful effect on powder performance properties. In fact, refrigerated storage of powders is a recommended method for maximizing the physical and chemical shelf life of a powder. However, cold powder acts as a condensation site when exposed to higher temperature, humid air. For this reason it is recommended that bulk containers of powder coating be allowed to equilibrate to application room temperature for at least several hours prior to opening of the container. This precaution is especially important during winter in northern climates when powder may have been transported or stored at very low temperatures, below 32°F (0°C).
Powder may form lumps in bulk containers, possibly caking together to form substantial agglomerates that cannot be pumped or easily broken by powder handling equipment. Heat may also be detrimental to the chemical stability of many powder products.
While there are no safety concerns if the powder is stored at high/low humidity, there are application issues that could arise:
A cure curve is a graphical representation of the thermal conditions required to insure that an applied thermoset powder coating is completely cured, i.e. essentially all available resin and curing agent reactive groups are chemically reacted together.
No, each powder product manufactured by PPG has a cure curve associated with it, the specification of which is primarily determined by the formulation of its resin and curing agent system. However, there are commonalities between technologies, so it’s not unusual to see a family of related powder products sharing a single cure curve.
Yes. The simplest cure curve is one that specifies the minimum thermal conditions that must be provided to cure a powder during its baking process. Graphically, it is a single line or curve. Conditions of shorter time or lower temperature, i.e. those which fall below the cure curve line, are not recommended due to the likelihood of less than optimal cured film performance.
The following minimum (simple) cure curve is for a low temperature cure polyester TGIC product line.
A more complex cure curve will graphically represent both minimum and maximum thermal conditions, and thus is a two-dimensional area, rather than a line.
The complex (area) cure curve below is for the same low temperature cure polyester TGIC product line as shown above, and has identical minimum cure data points (blue line), but with the addition of a maximum cure conditions line (red).
Annotations can be added to complex cure curves indicating details of how they were determined or displaying the powder film properties or potential failure modes that are associated with various cure chart areas.
In the case of multi-film coating systems that undergo two or more heat-curing processes, cure curves for each applied coating layer need to be cross-referenced to account for the cumulative thermal experience of the system.
Historically, the laboratory determination of minimum bake time and temperature using standard pretreated metal test panels has been found to correlate well with customer experience. Often film flexibility or chemical resistance falls off dramatically once baking conditions fall below a certain point.
Unfortunately, the determination of maximum time and temperature bake schedules for curing powder coating products does not always correlate well between PPG's laboratory experiments and customer experience due to the fact that:
1. Powder coatings are remarkably heat resistant at common baking temperatures. They do not typically undergo embrittlement or chemical decomposition when exposed to 100% or even 200% of their standard baking times at a recommended temperature. Those properties of a powder coating that are significant for defining an overbake condition can be highly application specific (e.g. recoat, touch-up repair, silk screening, pinstriping, decal application, etc.), and different customers will evaluate the various properties in different ways (e.g. color and gloss tolerances vary widely across applications and industries).
2. Many application factors can determine the exact point at which the product begins to lose some of its performance properties because of excess heat exposure. Among these factors, which are specific to each customer's application and production environment, are:
Fortunately, although each customer has their own unique application and baking equipment situation, making it difficult for PPG to determine a maximum time-temperature cure chart line with great precision, most customers have relatively tight process controls and do not typically experience wide variation in bake times or temperatures.
Often it is sufficient for a customer to simulate, perhaps in a validation or PPAP trial, just a few of the "worst case" combinations of time and temperature their "worst case" parts are likely to experience.
A maximum cure curve line constructed from such data points is likely to be conservative relative to the product’s inherent capability, but it is often sufficient for practical, day-to-day process control purposes. Some customers utilize thermal data acquisition hardware ("oven logger") and its associated software (e.g. Datapaq® & Insight; Computer Aided Solutions Grant® & PaintView, etc.) to generate numerical analyses of thermal history for a part, including one or more "%-ofcure" parameters. Such theoretical indices may provide reassurance to a customer who is working only with a minimum recommended bake time/temperature cure curve that a detrimental overbake condition has not been experienced.
No. Many PPG powder products are tested for routine quality control purposes or for performance test specification compliance at conditions of slightly longer baking time and slightly higher bake temperature than the bare minimum.
No. The customer must assume responsibility for verifying that proper cure is applied to the powder product under production conditions. PPG is unable to assess the degree of risk that a customer should assume, in light of the variability that characterizes its baking process. For most powders, there is seldom a problem with baking "above" the cure curve minimum. If anything goes slightly wrong, like cold spots in the oven, racking issues or variations in metal thickness, some parts will have an under cured coating.
Many PPG powder customers deliberately set oven conditions so that there is a comfortable safety margin between the minimum conditions specified in the cure curve and actual. For example, with a specified minimum of 15 minutes at 375°F (191°C), a customer might choose to adjust the oven burners settings so that every part’s temperature profile, measured with an oven recorder, at all positions on the racking system shows at least 21 minutes at 380°F (193°C).
To save time, and thus maximize productivity, many customers set their ovens higher than the maximum peak metal temperature achieved by the parts. For example, a set point of 425°F (218°C) may result in parts reaching a peak metal temperature of 395°F (202°C) just before they come out of the oven. But this approach carries the risk that if there is a conveyor line stoppage, unusually thin gauge metal, or oven "hot spots," some parts might see the temperature as high as the oven set point.
Anti-graffiti coatings resist or minimize the damage associated with application of unauthorized inscriptions, slogans, drawings, or other "artwork" that are scratched, scribbled or painted on a structure or surface, generally public in nature. A typical graffiti material is air-dry paint in an aerosol dispenser. An anti-graffiti coating may prevent the application of such material to its surface or permit easy removal of the material sometime after its application.
Excellent chemical resistance. PPG powder coating product lines with exceptional chemical resistance are the best candidates for anti-graffiti applications:
PPG has the ability to make anti-graffiti powder coatings in a wide range of colors. Not only does this allow the user the flexibility to select the color they need, but it allows the applicator to get the effects of the anti-graffiti performance, without needing the clear coat—eliminating a step in application.
*Source of the Bulk Stripper 870GC cleaner is: Bulk Chemicals Inc., P.O. Box 186, Mohrsville, PA 19541, 1-800-338-2855
Underwriters Laboratories (UL) is an independent, not-for-profit corporation, which focuses on development of safety standards and testing of products to those standards. UL has particular expertise in electrical safety.
Given the significant time and expense involved in qualifying a product to UL1332 requirements, Underwriters Laboratories established a "product line" evaluation process that permits a family of similarly formulated products to receive recognition as a group. The products must utilize the same "organic" components (resins, curing agents, additives), as determined by Infrared (IR) spectroscopy. However, metallics and clear coats must be tested independently.
PPG has all-color approval for:
Underwriters Laboratories' website displays basic information about recognitions, by company to whom the recognition was granted. PPG’s UL file number is MH6892 for Greensboro and Strongsville, MH17729 for Gainesville and MH26707 for Brazil. Click on the link to PPG Industries' UL page for most industrial coatings.
PPG also lists the UL approval on the individual product data sheet.