FAQ

Powder coatings are solid powder synthetic resin coatings composed of solid resin, pigments, fillers, additives, etc. They exist in a fine powder state and are called powder coatings because they do not use solvents.

This article lists 18 key concepts about powder coatings, which are highly relevant to powder coating production. From a production perspective, you will understand the actual production of powder coatings through these easy-to-understand explanations.

1. Orange Peel:

This refers to the irregular surface structure of powder coatings, resembling the peel of an orange.

2. Impact Resistance:

In some end-use applications, powder coatings need to withstand sudden impacts. Impact resistance refers to the powder coating’s ability to withstand impacts.

The sources affecting impact resistance include substrate type, substrate thickness, substrate treatment method, and the thickness of the powder coating. Simultaneously, impact resistance is also considered a relevant indicator for judging whether the powder coating has fully solidified.

3. Glass Transition Temperature：

There are three common states of matter in nature (solid, liquid, and gas). The glassy state is a special state between solid and liquid, like molten glass, neither solid nor liquid.

The glass transition temperature refers to the critical temperature at which a polymer transitions from a rubbery state (which can be understood as rubbery or solid) to a glassy state, or the transition temperature from the latter to the former. It is commonly represented by G and is an important physical indicator of polymers.

4. Flash Point：

When powder coatings are heated to a certain temperature, their vapor mixes with the surrounding air and comes into contact with a flame, triggering a flash ignition. The lowest temperature at which a flash ignition occurs is the flash point.

5. Slope Flowability：

Slope flowability refers to the flow characteristics of molten thermosetting powder coatings on a slope with a fixed angle of inclination.

6. Melting Range：

The melting point of a substance is not a single point, but a temperature range, called the melting range. The upper and lower limits are called the initial melting temperature and the final melting temperature, respectively. The initial melting temperature is the temperature at which the substance begins to melt, and the final melting temperature is the temperature at which the substance completely melts.

7. Angle of Repose:

The angle of repose of a particle, also known as the dust’s angle of repose or angle of accumulation, is the angle between the generatrix of the cone formed by dust particles continuously falling onto a horizontal plate through a small hole and the horizontal plane. It is related to factors such as the type of dust, particle size, shape, and moisture content. For the same type of dust, the smaller the particle size, the larger the angle of repose; the smoother the surface or the closer the particle is to a sphere, the smaller the angle of repose; the higher the moisture content of the dust, the larger the angle of repose. The angle of repose of dust is one of the dynamic characteristics of dust.

8. Crosslinking Density:

This refers to the number of crosslinking bonds in a crosslinked polymer, usually expressed by the molecular weight of the network chain. The higher the crosslinking density, the more crosslinking bonds per unit volume. A greater degree of crosslinking results in better coating density.

9. Gelation Time:

At a specific temperature, the time it takes for a thermosetting system to reach cross-linking and solidification can be understood as the time required for the material to continuously thicken or agglomerate. The longer the gelation time, the lower the system’s activity; the shorter the gelation time, the higher the system’s activity.

Thermosetting substances, under sufficient temperature and time, will undergo a chemical reaction of solidification and cross-linking, producing a network structure. Increasing the temperature or extending the reaction time will increase the cross-linking density. Once a certain level is reached, it will suddenly become an inmeltable substance and can no longer be easily flowed or drawn into filaments; this indicates that the internal structure of the reaction system has gelled.

10. Corner Coverage:

The ratio of the coating thickness at the corners (90 degrees without chamfering) to the surface thickness of the coating bar under specified planar coating thickness conditions.

11. Coating Porosity:

The number of pinholes and defects in the coating.

12. Epoxy Equivalent and Epoxy Value:

The amount of resin containing one epoxy group (g/equivalent), i.e., the average molecular weight of the epoxy resin divided by the number of epoxy groups per molecule. Epoxy value refers to the equivalent number of epoxy groups contained in 100 grams of epoxy resin, expressed as equivalents/100 grams. The relationship between epoxy value and epoxy equivalent is: Epoxy Value = 100 / Epoxy Equivalent.

13. Corner Coverage:

The ability of powder coating to flow, form, and adhere to sharp bends or corners in practical applications in corrosive environments.

14. Surface Profile:

Any irregular or wavy appearance profile of the powder coating; a specific requirement for powder coatings. The surface profile of a powder coating is primarily determined by the properties of the powder coating itself, but other factors also influence it, such as the substrate, film thickness, drying conditions, and application environment.

15. Acid Value of Polyester:

This indicates the amount of free acid present in organic substances such as oils, polyesters, and paraffin waxes. Specifically, it refers to the mg of potassium hydroxide required to neutralize 1g of sample under test conditions. Polyester acid values ​​are classified as high, medium, and low, and the different acid values ​​determine the type and amount of curing agent required.

16. Hiding Power:

Powder coatings must be opaque to cover the color of the substrate. Hiding power refers to the minimum amount of paint required to evenly coat the surface of an object without revealing the underlying color. Expressed in g/m², the hiding power of a pigment is mainly determined by the following properties:

· Refractive index. The higher the refractive index, the stronger the hiding power.

· Light absorption. The greater the light absorption, the stronger the hiding power.

· Crystallinity. Crystalline forms have stronger hiding power, while amorphous forms have weaker hiding power.

·Dispersion: The greater the dispersion, the stronger the hiding power.

17. Particle Size Distribution (D*):

This is a commonly used parameter in particle size distribution. D represents cumulative, and the following number represents the particle size (µm) at which the cumulative percentage reaches *%. For example, D90 indicates a particle size (µm) where the total number of particles accumulated from the smallest particle to that size accounts for 90% of the total particle size. The greater the difference between D10. D50. and D90. the wider the particle size distribution, meaning a larger variation in particle size. Conversely, the smaller the difference, the wider the particle size distribution. Generally, D50 is close to the average dry particle size. Particle size distribution can be represented by number distribution, surface area distribution, and volume distribution. Each of these distributions has D10/D50/D90 values.

18. L, A, and B Values ​​in a Colorimeter:

Color difference refers to the numerical method used to express the difference in color perception between two colors, usually called the E value. The E-value is the square root of [(standard – L measurement)² + (A standard – A measurement)² + (B standard – B measurement)²]. The L-axis (brightness) represents black and white, with 0 for black and 100 for white.

The B-axis (red/green) represents red with positive values, green with negative values, and neutral with 0.

The B-axis (yellow/blue) represents yellow with positive values, blue with negative values, and neutral with 0.