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TECHNOLOGY FEATURE

The growth of powder coatings has been dramatic during the last decade with new applications continually being developed, including plastics. Innovations in processes and materials have opened previously unimaginable opportuni-ties. Although environmental advantages have been a strong motivating factor for the conversion of liquid coatings to powder coatings, the bottom line for many companies is increased profitability. Leading manufacturers of powder coating technology foresee untapped potential in plastics applications including automotive, appliances, and many more.

The technology for coating products with dry powder rather than conventional liquids has been used since the 1950s. The powder used for the process is a mixture of finely ground particles of pigment, polymeric resin, and fillers. The powder can be sprayed electrostatically onto the substrate surface, or the substrate (product) can be dipped into a fluidized bed of suspended powder. During post heat curing, the particles flow and fuse into a strong adhering coating. The result is a high quality cosmetic finish with excellent durability.

Polyester TGIC coatings utilize the epoxy functional crosslinker TGIC (triglycidyl isocyanurate). Use of this low molecular weight, multifunctional crosslinker enables polyester TGIC formulations to contain 90 percent or greater resin within the binder system. Weathering of polyester

TGIC powders is comparable to polyester urethane coat-ings. Polyester TGIC coatings typically offer faster or lower temperature curing than polyurethanes. Unlike urethane coatings, TGICs maintain excellent mechanical properties at film builds above three mils with no outgassing. Addition-ally, TGIC coatings provide superior edge coverage when sharp edges are present.

The powder coating process involves finely ground particles of pigment and resin that are sprayed onto a substrate. Once the particles are applied, the part is cured, which causes a chemical reaction that bonds the powder to the work piece (substrate). The result is a uniform, high quality, and du-rable finish. This finish is more attractive than conventional methods due to the elimination of runs, drips, and uneven drying associated with liquid paint. The powder that does not adhere to the part is recovered and reused, generating a maximum efficiency of 98 percent material usage. This compares with a 30 to 80 percent utilization rate for most other spray coating processes.

The most common technique used for powder coating is the electrostatic spray application process. The process involves a feed hopper and a spray gun, which incorporates the electrostatic charge of the particles. There are two types of spray guns, a corona and a tribo charged. The corona gun uses a voltage supply to charge the powder particles, while

Powder Coating Recent Advancements for Industrial Plastics Applications

Figure 1: Electrostatic Spray Application System

Figure 2:Tribostatic Gun Layout

By Scott Sabreen, The Sabreen Group, Inc.

Graphic Dies, Inc. imag-ing@graphicdiesinc.com

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OCR data can be transmitted to external computers with da-tabases of card information, for secure and efficient trackingof personalized cards. This enables card manufacturers tomanage card production and when desired, create internalcontrols on secure printing facilities. For more information onthe new UV and bar code add-on modules, contact Spartanicsat (847) 394-5700 or visit: www.spartanics.com.

Sericol, Inc. Introduces UviPak UCDSericol, Inc., Kansas City, KS, introduces its newest innovationin the UV screen container decorating family. UviPak UCD’sinnovative formulation was specifically developed to provide asingle UV ink solution for the diverse plastics used in the directcontainer decorating market. UviPak UCD is specifically de-signed for printing PETG, PET (both pretreated and untreated),polycarbonate, styrene and pre-treated polyethylene and polypro-pylene containers. This new product offers a 100% NVP-freesolution, advanced multi-substrate adhesion, improved chemicaland scuff resistance and consistent fluid gel structure. UvipakUCD is now available in a wide variety of intense matchingcolors providing bolder, more opaque color solutions to meet theever-increasing graphic demands of the packaging marketplace.For more information on Sericol’s UviPak UCD, call toll free(800) 255-4562 or visit: www.sericol.com.

New Breed of FOBA Turnkey Laser Marking Systems NowAvailable from VirtekVirtek, Waterloo, Ontario, brings to North America a new breedof FOBA laser marking systems - Vario. Launched in Ger-many in 2002, the system has proven ideal for all-purposemarking and serialization for the automotive and electronicsindustries, as well as plastics decorating and lacquer removal(day/night marking). Vario is a versatile, turnkey, Class 1 lasermarking system that is equally suitable for processing high prod-uct mixes in fixtures and trays or large production runs. Vario’srobust, modular design and compact footprint (68 x 35 x 63” –length x width x height) means it can be customized for al-most any manufacturing environment and marking application.

Vario is equipped with a choice of high quality solid-state la-sers manufactured in Virtek’s FOBA Germany facility andcan handle everything from the simplest, surface-marking ap-plication to the high-power engraving of metals. For moreinformation on Virtek’s latest laser marking system – Vario,call (617) 283-4364 or visit: www.virtek.ca.

New Pad Printing Machine from TNT DistributorsTNT Distributors, Inc. is proud to offer the newU.S. built SM 35 pad printing machine. TheSM 35 is a small, bench mount, 90mm closedcup machine. Standard features on the ma-chine include a 90mm closed ink cup and heightadjustable tooling table. Additional features in-clude ink mixing and an automatic print cycle.The machine is capable of 2000 cycles per hourwith minimal air requirements. The new SM35 is 100 percent American made and is avail-able for immediate shipment via UPS for only$3,995.00. For more information, contact TNTat (512) 260-6222.

Axel Introduces New Water-based, Semi-permanentMold ReleaseAxel Plastics Research Laboratories, Inc., Woodside, NY, re-cently introduced a versatile new water-based, semi-permanentmold release – XTEND W-7283A – which reduces solventsin the workplace. The new mold release is ideal for a broadrange of FRP molding applications, is an aqueous emulsion ofproprietary resins and cross linkers and various surfactantsthat contain no hazardous ingredients. The pleasant smelling,long lasting, release coating can be wiped or sprayed on ambi-ent temperature or warm molds. The water-based releasecoating is designed to dry and cure quickly under most mold-ing conditions and has a strong affinity for the mold, assuringclean, highly cosmetic parts. To learn more about XTENDW-7283A mold release, call toll free (800) 332-AXEL or (718)672-8300 or visit: www.Axelplastics.com.

the tribo gun uses friction generated within the gun barrel. The corona technique negatively charges the particles. This generates electric fields, which causes uneven coating. The tribo gun positively charges the particles. As a result, there is no uneven coating, making it the optimal method for electrostatic spray application.

Initially, the powder particles are stored in a large fluidized bed to keep them continuously suspended. The suspension of the particles prevents clogging in the pick-up tube that leads to the powder pump. The pump pulls the particles from the

fluidized bed into the delivery tube. A second burst of air accelerates the particles, increasing the number of collisions with the Teflon walls and positively charging them (coatings). The tribostatic process is shown in Figure 2 (Tribostatic). The positively charged particles are sprayed out of the gun tip and adhered to the grounded work piece. This process can be seen in Figure 1 (Coatings). The work piece (substrate) is then placed in a furnace and cured at 300º F for 20 minutes (TGIC). The curing process causes a chemical reaction, bonding the powder coating and the substrate.

Advantages DisadvantagesNo solvents, near zero VOCs Thin coatings (< 1.0 mil) are difficult to apply because of

pin holesExhaust air from the coating booth can be returned to the coating room, thus less oven air is exhausted to the outside

Frequent color changes can entail extensive downtime

Over-spray (up to 98 percent) can be retrieved and re-used

Storage and handling of powder requires climate controls

No drying or flash time required so that parts can be racked closer together

Exact color matching and color uniformity is somewhat more difficult than with liquid coatings

Easily adapted to continuous automation processes Uniformity of coating thickness is sometimes difficult to maintain

Operator-friendly Cure temperatures required for some powders are too high for temperature-sensitive parts

Thick coatings are easily achievable; film thicknesses of 1.5 - 5.0 mils generally can be applied on cold products

Conversion from liquid coating processes is expensive

High volume production rates Inside corners can have low film thickness – “Faraday Cage Effect”

Easy clean-up and maintenance Some difficulty with preparing certain types of metallic appear-ances; texture finishes are limited, unlike wet texturing

Powder Coating does not drip or sag; the process is more robust than Liquid Coating

Repairing blemishes in powder coating films can be difficult; matching liquid coating for repairs is not normally viable

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ITW Foils www.itwfoilsplas-ticsandsecurities.com

TECHNOLOGY FEATURE continued from page 33

Of significant importance to plastics applications, UV powders with curing temperatures as low as 250°F have emerged. Such advancements now make it possible to apply powder coatings to some of the most widely used plastics, as either a secondary finishing process or during primary injection molding. For “In-mold” powder coating, the pow-der coating material is sprayed onto a heated mold cavity before the molding cycle begins. During the molding opera-tion, the powder coating chemically bonds to the molding compound and produces a coated product that is chip- and impact-proof.

Not unlike other technologies, powder coating has inherent advantages and disadvantages. (See Table on page 33.)

Recent breakthroughs in powder coating technology have approached the mar performance usually associated with porcelain enamels, as measured by commonly used industry tests. This provides significant value to customers. The final properties of the powder coatings often are superior to liquid coating systems. The reasons for the fast growth of this tech-nology is that powder coatings maximize production, cut costs,

improve efficiencies, and offer maximum compliance with increasingly stringent environmental regulations. The future for broad scope powder coating on plastics is bright. n

References:SpecialChem – Coatings & Inks.•

Coatings.de• . 26 April 2004. Vincentz Network. 08 April 2004.

What Are TGIC Powder Coatings? 26 April 2004. • Caswell. 15 April 2004.

Tribostatic Powder Spray Systems. 26 April 2004. • Nordson Corporation.

Scott R. Sabreen is founder and president of The Sabreen Group, Inc. (TSG). TSG is a global engineering company specializing in secondary plastics manufacturing processes – surface pretreatments, bonding, decorating and finishing, laser marking, and product security. For more information, call toll free (888) SABREEN or visit www.sabreen.com and www.plasticslasermarking.com.