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Technology Trends In The Powder Coating Industry

Posted on Monday, November 27, 2017

This past year brought a slew of innovations in the powder coating industry. In this Buyers Guide edition of Powder Coated Tough, we take a glimpse at recently commercialized advances and emerging technology in the powder coatings industry, specifically within the following segments: powder coating technology, powder formulation (raw materials and pigmentation), and instrumentation.

Powder Coating Technology

Corrosion resistance was a big topic this past year. Axalta Coating Systems introduced two new high-temperature, corrosion-resistant internal pipe coatings to its Nap-Gard® functional coatings collection. The new Nap-Gard 7-0017HT and 7-0017VHT Black Beauty FBE products are thermosetting epoxy powders designed to provide excellent chemical resistance when operating in temperatures up to 392°F (200°C). Corrosion caused by carbon dioxide (CO2) and hydrogen sulfide (H2S), often found in sour crude oil, is a major challenge for the oil and gas industry. Axalta’s introduction of these high glass transition (Tg) temperature internal pipe coatings are designed to combat this problem. When properly applied with Nap-Gard 7-1808 primer, Nap-Gard 7-0017HT and 7-0017VHT exhibit extreme corrosion protection against high levels of H2S and CO2, as well as methane (CH4) even at high temperatures and pressures.

Evonik debuted coatings for extreme environments based on innovative polyether ether ketone (PEEK) powders VESTAKEEP®. These coatings reduce the wear and tear of components in demanding industrial applications. The PEEK powders of Evonik’s VESTAKEEP brand are particularly suitable for applications that are subjected to extreme requirements, like mechanical, thermal and chemical exposure. The coating material is able to withstand permanent operating temperatures of up to 482°F (250°C) and is characterized by its unique ability to resist abrasion and chemicals.

Due to the excellent tribological performance of coatings made from these specially developed powders, the friction between sliding surfaces is significantly reduced, which in turn increases efficiency and economy of operation—for example: lower fuel consumption and lower CO2 emissions in combustion engines, extended service life of bearings, or higher turbine speeds.

These coatings also allow for employing more cost-efficient substrate materials for components used in applications with sliding friction. The various VESTAKEEP PEEK powders are composed of particles with average particle sizes ranging from 5 to 110 µm. They can be applied by flame and electrostatic spraying methods, or as aqueous dispersions. With electrostatic application, layer thicknesses can range from 20 to 300 µm.

New coating technology for alternate substrates such as medium density fiberboard (MDF) and natural wood was introduced in 2017. IGP announced that its IGP-RAPID powder coatings are based on new raw materials combined with IGP technology, enabling a revolution in low-temperature powder coatings. The range of baking temperatures from 266°F (130°C) and curing times of 3 minutes are a breakthrough compared to existing powders on the market. IGP explains that the coater benefits in several ways— from an ecological coating, low curing temperatures, and from powder coatings that enhance product design and provide long-term functional protection. The seamless all-around coating enables coverage of edges and areas in one work step. Three-dimensional (3D) geometries display a homogenous, aesthetic surface.

DVUV introduced its UVMax® line of opaque semi-smooth finishes for MDF claiming it provides a one-of-a-kind finish on components. Powder-coated MDF allows design freedom and durability, all with zero volatile organic compounds (VOCs), the company adds. Ideal markets for powder-coated components include retail store fixtures, healthcare, education and office furniture.

Major advances in architectural coatings were delivered by fluoropolymer companies in 2017. Arkema announced the addition of new Kynar polyvinylidene difluoride (PVDF) powder coatings that offer extreme resistance to chemicals, ultraviolet (UV) exposure, acids and bases. Included in the new powder product line are Kynar Flex 2850 PC and Kynar ADX Flex 281, targeting applications that require varying levels of flexibility, adhesion and differing application methods. Both spray and dip coating options are available as well as primerless options using Arkema’s patented Kynar ADX technology. Kynar Flex 2850PC can be spray applied in thicker layers than most fluoropolymers, making it a “process friendly” powder coating. The new Kynar PVDF powder coatings are designed for the protection of small metal chemical storage tanks, high purity manufacturing components, valves, pumps, ducts, and other chemical handling or mining equipment subjected to acids, halogenated chemicals, petrochemicals, continued abrasion and continuous exposure temperatures of up to 203°F (95°C). Kynar Flex 2850 PC powder coatings may be safely used on parts intended for repeated contact with food per Title 21, Code of Federal Regulations, Chapter 1, part 177.2600, and is USP Class 6 compliant for applications in the biotech industry.

AGC Chemicals presented interesting findings with fluoroethylene vinyl ether (FEVE)-based powder coatings. Coatings based on this copolymer offer excellent UV durability, typically enduring 20 or more years in a South Florida environment without exhibiting significant chalking or coating degradation. The fluoroethylene monomer in the resin backbone protects the vinyl ether groups from degradation, whereas the vinyl ether moieties allow the polymer to be functionalized. In this case, it provides a site to attach a hydroxyl group, which can be crosslinked with diisocyanate curing agents. Powder coatings based on AGC’s FEVE resins cured with blocked aliphatic isocyanates have withstood more than 10 years exposure in both Okinawa and South Florida with greater than 50 percent gloss retention. The same formulations pass 10,000 hours exposure to QUV-B (ASTM D4587) and 3,000 MJ/m2 EMMAQUA accelerated testing (ASTM D4364).

Additionally, superdurable polyester resin can be blended with FEVE polymer to provide advantages in metallic-containing formulations. Their studies show that the polyester component stratifies below the fluoropolymer, leaving the metallic at the interface between the FEVE and polyester. This phenomenon protects aluminum flake from degradation from hydrolysis commonly seen with exposure to outdoor environments. AGC presented energy dispersive x-ray spectroscopy (EDX) cross sectional analysis to verify this stratification. Not only does this formulation system exhibit exceptional UV durability, but also excellent corrosion resistance as evidenced by AGC’s 4,000-hours salt fog test results.

AGC also proffers formulation tips on achieving matte finishes with FEVE based powder coatings. The incorporation of 8 percent by weight of silicone microparticles (Tospearl from Momentive) produced a 60° gloss of 30 gloss units (GU). Impact resistance, adhesion and UV durability were not compromised by this matting technique.

The most common powder application technique involves electrostatically charging the powder to facilitate attraction to a conductive (e.g., metal) surface. It is, therefore, rare to encounter an application to a non-conductive surface such as glass. A dynamic custom coater in California has thought outside of the box to develop a technique to powder coat glass bottles for high-end consumer goods such as fragrances, nail polish and spirits. The company, Bottle Coatings, Inc., is the brainchild of Shivie Dhillon and is a spin-off of his primary business, SunDial Coatings. The success of Bottle Coatings relies mainly on a patented two-coat process that allows the powder to be applied evenly to the vitreous substrate. Glass bottles are preferred to ceramic packaging as glass provides more precise closure tolerances.

This innovative process blocks the entire spectrum of UV light, including UVA, UVB and UVC wavelengths. Keeping UV light out of a packaged product is critical to the shelf life of nail polish, especially the higher end polishes that use UV energy to cure or harden the finish. Initial attempts were made to filter the UV light with inhibitors or absorbers; however, these materials eventually lose their functionality and the contents of the bottle suffer. Dhillon designed a technique to block UV light and therefore protect the contents indefinitely. In addition to application consistency and UV blocking, this process delivers chemical resistance to the aggressive solvents, plasticizers and additives commonly found in nail polish.

Raw Materials

A surprising number of this year’s innovations were introduced by the raw material world. Many of the advancements are from newcomer chemical suppliers focused on entering the powder coating industry.

One of the most interesting developments is self-healing coating technology by Autonomic Materials Inc. (AMI), whose products are autonomic—which means that they repair themselves automatically upon incurring damage. These products are microcapsules based on core-shell morphology. The microcapsules are dispersed evenly into the powder coating as a post-blend additive. The coatings are applied conventionally and cured at conditions appropriate for the thermoset binder. The initial work is based on epoxy binders.

Upon damage to the coating film, AMI’s microcapsules rupture and fill the damage with a healing polymeric material. From a functional perspective, this healing mechanism reseals the film and thereby provides protection to the substrate from environmental attack, specifically corrosion. Dr. Gerald O. Wilson, AMI’s vice president of technology, has demonstrated excellent examples of performance of damaged vs. “healed” films in ASTM B-117 salt fog corrosion testing. Coatings were applied to cold rolled steel and scribed with a 500 micron-wide tool. Epoxy powder coating films containing AMI microcapsules repaired the breach in the coating and significantly outperformed the control powder coating, which did not contain the microcapsules. The control powder began to exhibit significant creep from the scribe after about 750-hours salt fog exposure, whereas the formula modified with the microcapsules resisted scribe creep until 4,000 hours in the salt fog environment.

Dr. Wilson did his homework when characterizing the performance of these microcapsules in powder coatings. He realized that the additive had to maintain integrity during incorporation into the powder coating. Concerns with rupturing the additive in the extrusion process led him to add them via dry-blending after the powder was made. In this process, the particles had to resist agglomeration and sintering. Furthermore, the microcapsules had to remain evenly dispersed throughout packaging and the elec-trostatic application process. They designed the shell material to carry a charge of polarity compatible to common powder coating materials. Finally, the core-shell particles had to resist rupture at high-temperature curing conditions typical for powder coatings.

The significance of this new technology is providing an exceptional improvement in corrosion resistance without the use of heavy metals, hexavalent chromium or other hazardous compounds. These coatings not only exhibit acceptable initial performance, but provide excellent barrier properties even after sustaining significant damage down to the substrate.

Another recent approach to improved corrosion resistance involves powder coating based on epoxy/clay nanocomposite. Epoxy/clay (Closite 30B) nanocomposite samples were prepared by using solution and melt dispersion methods. The quality of clay dispersion in epoxy matrix was evaluated by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The prepared nanocomposite samples were used in epoxy powder coating formulations (named as nano powder coatings). DSC analysis was used to study the curing behavior of samples. The physical, mechanical and thermal properties of prepared samples were evaluated by using tensile, dynamic mechanical thermal analysis (DMTA), microhardness, thermogravimetric analysis (TGA) and loss on ignition (LOI) tests. Finally, the corrosion resistance of prepared epoxy nano powder coatings was determined using the salt spray test. The results illustrated that Closite 30B nanoparticles could be dispersed properly in epoxy resin by melt dispersion methods. It was found that Closite 30B could accelerate the epoxy curing reaction. The results showed that the mechanical properties of nano powder coatings improved when various concentrations of clay nanoparticle (in the range of 1-5 phr) were used in formulation. It was observed that sample with 3 phr clay nanoparticles presented the best thermal- and fire-resistance properties. The salt spray measurements confirmed the superiority of corrosion resistance of epoxy nano powder coatings in comparison to that for neat epoxy powder coating formulations.

Researchers also found that cerium tartrate can be used as an inhibitor pigment for corrosion protection in epoxy coatings. The efficiency of corrosion inhibition of a new pigment, cerium tartrate, on aluminum alloy was studied. The results of release measurements of Ce ions from epoxy coating in 0.05 mol/L NaCl indicate that cerium ions are able to transport through the epoxy coating, which is a key characteristic of inhibitor pigment. The electrochemical impedance spectroscopy (EIS) shows that cerium tartrate is an effective pigment for improving the barrier effect of epoxy coatings on 2024-T3 grade aluminum. The self-healing ability of cerium tartrate in artificial defects was verified by scanning vibrating electrode technique (SVET). Cerium tartrate played a self-healing effect at the defects in epoxy coatings.

Recent studies show that polyaniline grafted basalt plates can improve the corrosion resistance of epoxy coatings. Polyaniline-graft-basalt plates (PANI-g-BP) were prepared based on ϒ-aminopropyltriethoxysiliane-modified basalt plates via in-situ chemical-oxidation polymerization method. Three PANIg-BP samples were prepared by varying the ratio of aniline to BP (1:2, 1:4, 1:6). The results of Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and TGA confirmed that PANI was successfully grafted on the surface of basalt plates. Different coatings were prepared by adding the synthesized PANI-g-BPs or PANI, and were coated on the mild steel subsequently. The water-uptake property, the adhesion strength and the passive properties of the coatings were investigated. In addition, the protective performance of the coatings was tested by EIS (electrochemical impedance spectroscopy) in 12 percent NaCl solution at 203°F (95°C). The results indicated that the coatings with 10 percent PANI-g-BP (1:4) exhibited the best protective performance and its impedance at 0.01 Hz is higher than 1,010 after 80 days immersing.

A modified graphene oxide (GO) coating was found to reinforce the corrosion protection properties of epoxy coatings. This coating was prepared by anchoring a prepolymer of urea-formaldehyde resin onto graphene oxide sheets through in situ polycondensation. The modified graphene oxide sheets were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction experiment, Fourier transform infrared spectroscopy, sedimentation test, and electrochemical impedance spectroscopy. One major finding was that the superior compatibility of UF resin with the epoxy resin retained the high dispersion of modified GO sheets in polymer matrix. Results further revealed that the modified GO sheets significantly reinforced the corrosion protection properties of epoxy coatings on carbon steel substrate.

The Lubrizol Corporation announced the availability of new additive technology for powder coating applications with the development of a matting additive. PowderAdd 9553 is a novel matting agent that provides consistently reproducible and uniform matting. It is an easy-to-use additive that is highly efficient and quickly turns glossy powders into matte powders. It can reduce production costs and inventory requirements for small batch manufacture. It works with all standard powder chemistries, allowing for improved manufacturing flexibility.

Researchers found that the roughness and gloss of powder coatings can be tuned with thin Al2O3 films. In this work a method was found to change the surface finish of a standard polyester-based powder coating from gloss to matte by depositing ultrathin films of Al2O3 on the powder coating particles. The coating experiments were performed in a fluidized bed reactor at 1 bar and 81°F (27°C), using a gas-phase coating process of alternating exposure of the particles to the two precursors (trimethylaluminum and water), similar to atomic layer deposition (ALD). The number of coating cycles were varied (1, 2, 3, 5, 7 and 9 cycles) to obtain film thicknesses of the alumina shell ranging from 1 to 30 nm. The average growth per cycle of the process is 3.5 nm, significantly larger than the one for pure self-limiting ALD. When the average alumina shell was thicker than 6 nm, the shell prevented the flow of the core particles, even though the powder particles did soften above its glass transition temperature. With the particles’ morphology intact, this resulted in a rough and matte surface finish of the coating after curing. The surface roughness, with a value around 9 μm determined by surface profilometry, is associated to the alumina coated particles as observed with SEM and EDX analysis. In addition, the matte finish coating showed mechanical resistance similar to that of uncoated powder particles.

Powder coatings provide excellent film performance in a range of harsh environments; however, the presence of polymers in their composition increases the risk of combustion in adverse situations. In this context, a study was made to develop and characterize acrylic-based powder paints with the addition of 2 wt % and 4 wt % montmorillonite clays (MMT) as Cloisite 30B (MMT-30B) and Cloisite 15A (MTT-15A), employed as flame retardants. The characterization of the coatings was carried out by TGA, X-ray diffraction, and scanning electron microscopy. After application of the coatings on carbon steel substrates, flammability tests were performed. The coatings with 2 wt % MMT-30B showed overall better results, especially in the flammability tests. Flames spread less on these coatings than on the other systems. However, when the surface and bottom temperatures were analyzed by the cone calorimeter test, the samples prepared with 4 wt % MMT-15A were considered safer to be applied in fire scenarios.

Nouvex, a new antimicrobial polymer additive that was developed by Purdue School of Materials Engineering and commercialized by Poly Group LLC, has been approved by the U.S. Environmental Protection Agency, Office of Pesticide Programs, Antimicrobial Division as a material preservative. The technology is used to prevent microbial contamination of textiles, thermoplastics, water- and solvent-based coatings and powder coatings. Poly Group intends to keep developing the technology aiming for another approval from FDA and EPA.

Pigmentation

The first new shade of blue in more than 200 years—discovered via happenstance by a team of college scientists—soon will be introduced to the coatings market. Shepherd Color Company has reached a license agreement to market the first amount of YInMn Blue pigment and is seeking business partners to explore its commercial applications. According to Shepherd’s website, YInMn pigment—named as such because it’s based on an oxide made of yttrium, indium and manganese—can be used for artist color materials; building products with high solar reflectance for regulatory approval and reduced energy for cooling; or applications where this particular shade of blue can be useful (high heat and UV stability, infrared [IR] properties, and unique chemical structure and composition).

In 2009, scientists at Oregon State University, led by Material Science Department Chair Mas Subramanian, were exploring the electronic properties of manganese when mixed with different chemicals. When graduate student Andrew Smith heated black manganese oxide, yttrium and indium to 2,000°F (1,093°C), a compound with a striking blue hue was pulled from the furnace.

Energy companies have expressed interest in using YInMn Blue because of its pigment structure. Oregon State says its IR reflectivity is about 40 percent, and when used in roofing materials could help keep a property cool and improve energy efficiency by reducing the need for air conditioning.

As part of its “Cool Roofs” initiative, Shepherd Color Company tested YInMn Blue’s IR reflective properties at its Laboratory for Advanced Innovative Research, near Denver. Using two house models, researchers used a standard dark blue—made with high durability pigments—for one small, metal-paneled roof, and a coating of YInMn Blue on another. Both models were placed outside on a sunny, warm day. Using an infrared imager to test each roof, it was revealed that the standard roof was much hotter than the YInMn Blue model. The imager’s temperature sensing function showed the standard blue roof was 191°F (88°C); the YInMn Blue roof was 168°F (76°C).

Cornelius Group has collaborated to deliver two extender product solutions to market in the wake of the titanium dioxide (TiO2) shortage. The company has partnered with VB Technochemicals SA to offer VB White, which is suitable for the masterbatch market, and with Huber Engineered Materials to provide Zeolex 330 to the paint and coatings market. Huber Engineered Materials’ Zeolex 330 is an amorphous sodium aluminosilicate powder for paint and coatings applications. It acts as a gloss sheen control agent and provides high levels of opacity, whiteness and brightness as well as outstanding flatting and scrub-resistance for interior architectural formulations.

Recently, the European Chemicals Agency (ECHA) proposed labeling titanium dioxide as a potential carcinogen. Their position is based on laboratory studies that demonstrate that rats can develop malignant tumors when exposed to high doses of TiO2. The International Agency for Research on Cancer (IARC) has listed TiO2 as a potential carcinogen since 2006. Please note that the terminology is a “potential” or “suspected” carcinogen and not a “presumed” or “known” carcinogen. “Presumed” classification is largely based on animal studies whereas “known” is based on human evidence. The exposure route and mechanism are said to be respiratory and due to oxidative stress and inflammation.

Where this proposal leads will have far-reaching effects on the industrial coatings industry as well as decorative paints, plastics, paper, cosmetics and even the toothpaste industry. Titanium dioxide has been used as the primary white opacifier in these end uses for more than 50 years. With this history, it is interesting to note that not a single case of cancer has been connected to exposure to TiO2. The Titanium Dioxide Manufacturers Association (TDMA) contends that more than 24,000 workers in their industry have been exposed to TiO2 with nary an epidemiological link to cancer. They, obviously, vehemently oppose such a regulation.

From a powder chemist’s point of view, this would turn our formulations upside down. I would conservatively estimate that over half of all powder coating formulas have at least some titanium dioxide. Alternate white opacifying pigments all fall woefully short of TiO2’s efficiency in making things white. Rutile TiO2 has the highest refractive index of any white mineral, which, in turn, provides the most efficient hiding. Hopefully the EU will carefully solicit industry experts and business stakeholders for their input on which direction to choose whilst maintaining the safety of workers and the general population.

Instrumentation

When the internal epoxy powder coating of land surface oil pipeline (LSP) in Kuwait was completely detached, curling from the substrate, and the production flow line was plugged with the deposit of paint debris after one year of operation in service, the failure was identified by differential scanning calorimetry (DSC) and other surface analytical techniques as curling caused by the improper curing process of the powder coating materials. But, the question of why there was this failure was not answered.

In a recent study by the Construction and Building Materials Program, Energy and Building Research Center, Kuwait Institute for Scientific Research, an experimental investigation was carried out using electrochemical impedance spectroscopy (EIS) by employing a new test cell to find out the reason behind the failure of the internal coating. The EIS was used to analyze the causes of failure of two different batches of the same coated piping—as-received epoxy coating and the failed one—by simulating the necessary environment and operation temperature. The EIS results with the new test cell indicated the compliance of the technique in confirming the hypothesis about the poor quality of the powder coating process and adhesion loss failure, obtained by the DSC, using FTIR, and X-ray photoelectron spectroscopy (XPS) techniques. The study confirmed that the quality of coating could be identified through the impedance value of the intact and failed coatings

Technology Takeaways

The year 2017 offered a host of advancements for the powder coating industry—from commercialized trends to emerging technology in raw materials, pigments and instrumentation. Most interesting is that the source of many of these innovations emanates from new entries to the powder coating industry. We are finding eager researchers who recognize the potential to improve powder coating technology and at the same time envision a path to eventual commercialization. These new developments bode well for our industry.

Author: PCT Editor