Table of Contents
Types of Powder Coating
Thermoset Powder Coating
UV curable powder coatings
There are literally a plethora of applications for powder coatings. Powder coating is used mainly on metals, so is perfect for industrial parts, medical devices, architectural applications, automotive refinishing, bicycle parts, household appliances, bicycles, motor bikes, furniture, enclosures, trailers, lighting etc. There are so many advantages to using powder coatings – too many to cover in this article – but some of the obvious ones include lack of solvents. This means no volatile organic compounds (VOCs) are released, a great advantage especially when compared to traditional liquid paints. This makes them safer to work with, dispose of and transport and brings unbeatable environmental advantages to you and your customer. Powder coating also offers a wide range of specialty effects that are hard to achieve through traditional methods. The list goes on, and we could get into better scratch resistance, toughness, corrosion resistance and hardness than traditional liquid paints, but let’s take a look at some of the different powders used.
Types of Powder Coating
There are three main categories of powder coatings: thermosets, thermoplastics, and UV curable powder coatings. The UV curable powder coating is a new technology.
Most manufacturers examine costs and potential coating complexity when deciding which type is most appropriate for their application. In each of these classifications, there are a variety of sub-groups, and each individual powder is engineered for specific finish qualities.
The first powder coatings produced were based on thermoplastic polymers which melt at the application temperature, and solidify on cooling. Thermoplastic powder coating is a type of coating which particles coat metals by melting when it reaches desired temperature and it shows mechanical and chemical strength with cooling. Especially in industrial applications, all metal materials are coated with coating materials before usage because of esthetic, endurance and safety reasons. The most important purpose of this coating method is providing protection against corrosion. As well as corrosion preventing coatings like liquid, powder and PVC or polyurethane generally show low performance and provide poor protection, they spread toxic smoke and solvent vapour environmentally in production. Pulron was developed especially for protection of metals against corrosion, impulse and chemical materials and it provides an ideal solution for thermoplastic powder coating materials. Some of the industrially used thermoplastic powder coating are as follows:
Vinyl Powder Coating : Two binders are used for the manufacture of the so-called vinyl powder coatings; polyvinyl chloride (PVC) and polyvinylidene fluoride (PVDF). On the basis of their polymer nature both powder coatings can be included in the same group, although they differ considerably in their performance. While PVC powder coatings are predominantly intended for indoor application because of their limited outdoor durability, PVDF powder coatings are among the best coating systems with respect to their weathering resistance. Vinyl polymers belong to a group of resins having a vinyl radical as the basic structural unit. Polyvinyl chloride and copolymers of vinyl chloride are the most significant members of this group being among the first thermoplastics to be applied by powder techniques.
Poly Vinyl Powder Coating: PVC coatings were introduced on the market in the time when the thermosetting powder coatings were in very early stages of development. These coatings have very good resistance to many solvents, which is a rather poor characteristic of the thermoplastic, combined with resistance towards water and acids. They have excellent impact resistance, salt spray resistance, food staining resistance, and good dielectric strength for electrical applications. PVC Powder coatings engineered via the polymerization of vinyl chloride and is produced by the industry on a large scale. Its basic properties include chemical and corrosion resistance, good physical strength and good electrical insulation. Polyvinyl chloride (PVC) is by nature a brittle polymer, but the flexibility of the material can be easily adjusted by using an appropriate amount of a suitable plasticizer.
Polyester Powder Coating: Polyester coatings weather well, look great and are resistant to abrasions. They find use in outdoor furniture, exposed automobile parts such as leaf and strut springs and are available in a diverse pallet of colors. Some polyester powders are architecturally certified for building exteriors as they shield the elements and maintain their color with only minor fading over the years. Polyester fibers are sometimes spun together with natural fibers to produce a cloth with blended properties. Cotton-polyester blends can be strong, wrinkle- and tear-resistant and reduce shrinking. Synthetic fibers using polyester have high water, wind and environmental resistance compared to plant-derived fibers. They are less fire-resistant and can melt when ignited.
Polyurethane Powder coating: polyurethane powder coatings exhibit properties similar to epoxy powders, but also offer exterior durability and are often more ‘overbake stable’ than epoxies (though not as good as Polyester).
Nylon: Nylon powder coat is extremely durable and impact resistant. It offers excellent protection against chemicals and solvents and is FDA approved for food contact. Parts covered with nylon include food handling and dishwasher baskets. Nylon also has a very low friction coefficient, making it useful as a coating on gears and conveyor equipment.
2.Thermoset Powder Coating
In a powder coating system, the more brittle thermoset resins can be broken up into a very fine powder that can then be fabricated into an exceptionally thin, paint-like film. This film exhibits chemical and physical properties comparable to those of liquid-based coatings. In addition, advancements in thermoset technology have continuously increased the versatility of this material group, allowing for more customization options. In the verge to achieving successful coating results, it is also necessary to match the thermoset formulation with the product’s intended corrosion resistance, curing cycle, texture, and aesthetic properties. One of the most significant developments in thermoset powder coating involves the capacity to engineer resin types with variable properties designed to complement metal finishing treatments. This broader range of characteristics has led to an increase in specialized roles for thermoset powders, with polyesters and acrylics finding greater use in the automotive and appliance industries despite the traditional reliance on epoxy-based coatings. Most thermoset powders can provide a high level of corrosion, temperature, and impact resistance. Below are some industrially consistent Thermoset Powder coatings.
Epoxy: Epoxy coated surfaces are hard and electrically insulative. They are brittle, however, and when exposed to UV light (present in sunlight) they tend to chalk and dull over time. This disadvantage keeps most epoxy-coated items indoors or buried underground as pipe coatings.
Epoxy-Polyester Hybrid: Epoxy-polyester (Hybrid) are general purpose coatings that have limited exposure to sunlight. These are the widely used powder coatings. They offer excellent hardness and have the best chemical and corrosion resistance of all available powders. Another plus point of this type of powder is its ease of use and a wide range of cure schedules. Epoxies adhere to metals extremely well, with various pre-treatments of the metal providing excellent adhesion, including phosphate and sandblasting. Addition of polyester to an epoxy makes a softer plastic that is less likely to chip or crack. Often simply known as “hybrid” coatings, they do slightly better outdoors than straight epoxies, showing less chalking and better weathering. Their properties are similar to pure polyesters in terms of impact resistance and durability. Their applications include office furniture, fire extinguishers and toys.
Acrylic Powder coating: Acrylics require curing temperatures close to those of hydroxyl polyesters, and they combine high quality surface aesthetics with flexibility and impact resistance. They also exhibit excellent alkali resistance, making them well-suited for use on appliances, such as ovens and washing machines. Acrylic powder coatings can be effectively applied through electrostatic spraying and have adjustable thin film characteristics. However, acrylics are more responsive to substrate attributes than most other powder coatings, making them incompatible with certain chemical compounds. Some of the advantages of using Acrylic powder coating are excellent weatherability, Outstanding smoothness, good chemical resistance, optical clarity and water-white color.
3.UV curable powder coatings
Powder coatings cured with UV light offer increased benefits over thermosetting coatings such as faster curing cycles with lower temperature requirements. This allows heat-sensitive substrates such as wood, plastics, and some alloys to be coated using powder. Coating of parts containing both metallic and heat-sensitive substrates becomes possible when UV powder coatings are used. UV-curable powder coatings can facilitate higher line speeds and productivity, and time, energy, and space savings.
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