Archive: Nov 2022

What is Powder Coating?

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Powder coating is a dry finishing process that has become extremely popular since its introduction in North America over in the 1960s. Representing over 15% of the total industrial finishing market, powder is used on a wide array of products. More and more companies specify powder coatings for a high-quality, durable finish, allowing for maximized production, improved efficiencies, and simplified environmental compliance. Used as functional (protective) and decorative finishes, powder coatings are available in an almost limitless range of colors and textures, and technological advancements have resulted in excellent performance properties.

How Powder Coating Works
Powder coatings are based on polymer resin systems, combined with curatives, pigments, leveling agents, flow modifiers, and other additives. These ingredients are melt mixed, cooled, and ground into a uniform powder similar to baking flour. A process called electrostatic spray deposition (ESD) is typically used to achieve the application of the powder coating to a metal substrate. This application method uses a spray gun, which applies an electrostatic charge to the powder particles, which are then attracted to the grounded part. After application of the powder coating, the parts enter a curing oven where, with the addition of heat, the coating chemically reacts to produce long molecular chains, resulting in high cross-link density. These molecular chains are very resistant to breakdown. This type of application is the most common method of applying powders. Powder coatings can also be applied to non-metallic substrates such as plastics and medium density fiberboard (MDF).

Sometimes a powder coating is applied during a fluidized bed application. Preheated parts are dipped in a hopper of fluidizing powder and the coating melts, and flows out on the part. Post cure may be needed depending on the mass and temperature of the part and the type of powder used. No matter which application process is utilized, powder coatings are easy to use, environmentally friendly, cost effective, and tough!

Durability of Powder Coating
Powder coating is a high-quality finish found on thousands of products you come in contact with each day. Powder coating protects the roughest, toughest machinery as well as the household items you depend on daily. It provides a more durable finish than liquid paints can offer, while still providing an attractive finish. Powder coated products are more resistant to diminished coating quality as a result of impact, moisture, chemicals, ultraviolet light, and other extreme weather conditions. In turn, this reduces the risk of scratches, chipping, abrasions, corrosion, fading, and other wear issues.

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Coating Procedures for Plastisol Coatings

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Plastisol coatings are applied to many different products in order to supply them with aesthetic qualities, tactile softness and gripping power. For instance, tools like pliers and screwdrivers are often fitted with plastisol coatings on their handles in order to provide the user with a solid grip instead of sheer metal. Plastisol coatings involve a plasticized resin combined with many PVC particles, which provide the plastisol with increased durability, toughness and thickness. In order to stay affixed to substrates, plastisol must be combined with a primer, which connects the plastisol particles to the substrate. Different kinds of primers are used depending on the adhesion coating method and the intended result. The plastisol itself has many desirable features, including chemical resistance to acids, alkalines, detergents, oils and certain solvents. Plastisol coatings also maintain structural integrity to – 65 degrees Fahrenheit and provide extraction resistance to different oils and detergents. A plastisol coating can perform well for approximately ten years. Plastisol mixtures can be varied to allow differences in gloss, thickness, toughness and other physical properties.

There are many types of coating procedures that work well with plastisols, most all of which involve heating (curing) the substrate and plastisol resin and a cooling period. These different plastisol coating procedures yield a variety of results and differences in the thickness, texture and geometry of the coating. Some coatings are directly applied to a substrate while others are made in molds.

Dip Molding
Dip molding is accomplished in either a hot or cold dip process. In hot dip molding, the substrate is heated and the plastisol resin is heated until bubbles appear, as if it were boiling. The substrate is then slowly dipped straight into the liquid plastisol and then removed slightly faster so the entire piece is coated in plastisol. Cold dip molding is used when the substrate cannot undergo heating, such as in the case of a wooden or fabric substrate, and it is simply dipped into the heated plastisol resin as is. After the dipping procedure, both hot and cold dip molding require the substrate be briefly “cured,” or heated until the plastisol achieves a solid state.

Slush Molding
Slush molding is similar to dip molding but involves an extra step to ensure complete coating of a substrate. The process is generally used in cases where the substrate has a complex geometry and includes nooks and crannies that may be difficult to coat by simply dipping the piece into the plastisol resin. Following the dipping procedure, a substrate undergoes slush molding by being affixed into a centrifuge that spins very quickly. This spinning process ensures that the resin fills in all the parts of the substrate. The substrate is then cured and the resin solidifies as in dip molding.

Rotational Molding
Rotational molding is used to make products that are hollow, such as buoys and balls. A mold of the product is filled with heated resin, and then the mold rotates at slow speed, allowing the liquid within to slowly coat the entirety of the mold. The plastisol eventually solidifies in the shape of the mold.

Casting is similar to rotational molding but does not involve the movement. When a product with a complex geometry needs to be coating in plastisol, a mold can be made of the shape of plastisol needed. The heated plastisol liquid is then poured into the mold and heated until it solidifies. Once it solidifies, the plastisol mold acts as a sleeve for the product, and can be affixed to the substrate with a small amount of adhesive.

Spray Coating
Spray coating is used to apply a very thin film coating of plastisol to a substrate. The substrate is sprayed with heated liquid plastisol by a gun, and then heated to allow the plastisol to solidify.

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