Frequently Asked Questions

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.

What is outgassing?

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.

What substrates are prone to outgassing?

  • Metal castings
  • Sheet molding compound
  • Galvanized Steel
  • Bulk molding compound
  • Hot rolled steel
  • Fiber reinforced plastic
  • Molded plastic

What can be done to minimize the detrimental effects of outgassing?

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.

Is there a powder coating that eliminates outgassing?

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.

What factors influence outgassing defects associated with painting?

  • Structural quality of the substrate
  • Age of substrate and storage conditions (humidity)
  • Pretreatment process, including pre-heating
  • Rust (oxidation) on substrate
  • Chemistry and film type (smooth, texture, metallic, etc.) of the powder coating
  • Thickness of coating applied
  • Substrate heat up rate
  • Bake oven temperature
  • Film appearance criteria for quality acceptance

Are there generalizations about how to best counteract outgassing?

  • Low temperature cure is more likely to be successful than higher temperature bake.
  • Either very fast cure (short gel time) or very slow cure (long gel time) may be successful.
  • Preheating of parts prior to powder coating should be at a temperature equal to or higher than that at which the powder is subsequently baked.
  • Application of a powder coating “primer” may help seal the substrate against outgassing prior to a second coating application.
  • Applying the powder at the recommended mil thicknesses, you allow the air or contaminant vapors to pass through the coating while in gel state, burst and flow out smoothly. Too many mils may make it difficult for the air to release and coating to flow out.

What are some common PPG powder coatings to help protect against outgassing?

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


What is outgassing? >

What are the optimal storage conditions for powder coatings?

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.

If temperatures are below 60°F (15°C) 

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).

If temperatures are above 80°F (27°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:

If humidity is too low (0% - 20% RH)

  • Accumulated electrostatic charges increase the risk of the mixture explosion. 
  • Electrostatic charging of particles becomes much less efficient. As a result, first pass transfer efficiency decreases significantly.
  • Grounding of conveyor, part hangers, and associated spray booth equipment becomes a more critical factor than usual, since extremely dry air does not facilitate charge migration to ground.
  • Sparking may be seen in transport hoses due to frictional charging. In some cases, frictional charging is counter productive to electrostatic charging efficiency at the spray gun electrodes.
  • Back-ionization (electrostatic rejection) may occur at lower film thicknesses than usual, particularly when powder is applied over a primer.

 If humidity is too high (80% - 100% RH)

  • Fluidization in feed hoppers and reclaim hoppers may deteriorate due to moisture absorption on particle surfaces leading to agglomerates.
  • Impact fusion buildup and plugging of injector block feed pumps are aggravated by the presence of water.
  • Electrostatic charges may decay more rapidly from particles, resulting in reduced transfer efficiency. In severe cases, loss of dry particle adhesion may occur when particulate coated parts are mechanically conveyed subsequent to spray application but before melting in the bake oven can be achieved.
  • In some cases, film properties may suffer due to the presence of water on particle surfaces. There may be a reduction in gloss, perhaps associated with noticeable out-gassing, pinholing, or “solvent” popping, film defects created by the pressure of water vapor driven from the powder during the cure process.
  • In severe cases, high water levels may affect film adhesion to the substrate or promote flash rusting of substrates prone to oxidation.


What are the optimal storage conditions for powder coatings documentation? >

What is a cure curve?

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.

Do all products from the same chemistry follow the same cure curve?

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.

Are there different types of cure curves?

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.

Why are so many of PPG’s recommended cure curves just a single simple line?

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:

  • Type of gas used in the oven
  • Oven gas burner flame efficiency
  • Airflow speed and makeup air turnover rates in the oven
  • Presence of hot or cold spots in the oven
  • Size of the oven relative to the metal mass of parts that are run through the oven
  • Presence of chemicals or curing byproducts from other coating materials that may be used in the same oven or in areas of the production plant near the powder curing oven

How would a customer determine a maximum bake cure curve line?

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.

Are there any generalizations that can be made for customers who are working with a minimum recommended bake (single line) cure curve?

  • Many PPG powder products are able to tolerate 100% overbake based on time, using the minimum time as a starting point. For example, a product with recommended minimum bake of 15 minutes at 375°F (191°C) would be expected to fully perform with a bake of 30 minutes at 375°F (191°C).
  • In general, dark color products should be studied through testing of several key properties (for example, adhesion, gloss, and topcoat-ability) for overbake resistance properties when peak part metal temperature in the production oven reaches a temperature of 425°F (218°C).
  • In general, light color products should be studied through testing of several key properties for overbake resistance properties when peak part metal temperature in the production oven reaches 400°F (204°C). In particular, color should be monitored for overbake yellowing.
  • PPG does not recommend baking of typical powder coating products at temperatures of 500°F (260°C) or more.

Doesn't baking at conditions of the minimum cure curve line help detect marginal or poor quality product batches?

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.

Does PPG recommend that customers bake parts at the recommended minimum time and temperature conditions as specified by the cure curve referenced on its product data sheet?

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.


What is a cure curve documentation? >

What is an anti-graffiti coating?

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.

What is the key property of an anti-graffiti powder coating?

Excellent chemical resistance. PPG powder coating product lines with exceptional chemical resistance are the best candidates for anti-graffiti applications:

  • Envirocron® PCU
  • Envirocron® PCE
  • Envirocron® XCR

Which PPG powder coatings are the best candidates for anti-graffiti applications?

  • PCUT10100: Anti-graffiti high gloss clear
  • PCUT80108: Anti-graffiti high gloss white
  • PCTT90311: Anti-graffiti high gloss black

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.

What are some common end-use markets for anti-graffiti powder coatings?

  • Road signs
  • Garbage cans
  • Park benches
  • Bus stations
  • Construction equipment
  • White boards

What graffiti removal process does PPG recommend for these products?

  1.  Apply "Bulk Stripper 870GC"* liquid cleaner with a soft brush
  2. Wait approximately five minutes
  3. Loosen the graffiti paint / ink with the brush
  4. Remove the cleaning solution and graffiti remnants with a soft absorbing cloth
  5. Rinse off remaining cleaner with water
  6. Dry the surface with a soft absorbing cloth

*Source of the Bulk Stripper 870GC cleaner is: Bulk Chemicals Inc., P.O. Box 186, Mohrsville, PA 19541, 1-800-338-2855


What is an anti-graffiti coating documentation? >

What is Underwriters Laboratories?

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.

What are common end-use products that may require UL listed powder coatings?

  • Circuit breaker boxes
  • Metal cases for consumer electronics
  • Metal enclosures that house motors or generators

What corrosion tests are involved in UL 1332 recognition?

  • 600 hours of "standard" (ASTM B117) 95F (35C) 5% neutral salt fog spray resistance
  • 1,200 hours of 95F (35C) 1% carbon dioxide/1% sulfur dioxide/98% moist air (CO2/SO2) “acid rain” resistance

How long does UL 1332 recognition take?

  • At least 1,200 hours for the longest test
  • In practice, 10-12 weeks is a more typical turn-around time for a project, allowing for purchase order, material submission, and report-writing activities

What is an all-color recognition?

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.

Which PPG products are recognized for UL 1332 compliant components?

PPG has all-color approval for:

  • PCF epoxy-polyester hybrid
  • PCT polyester-TGIC
  • PCU urethane polyester

How can PPG customers verify UL 1332 all-color recognition?

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.


What is Underwriters Laboratories documentation? >