Introduction

This article focuses on the current design and materials engineering practices employed by major appliance manufacturers in the United States for developing a new suite of household appliances. Alternative finishes challenging stainless steel are emerging as a highly marketable feature. Today’s unprecedented consumer demand for customizable appliance colors and textures (with decorative hardware finishes) that are integral to warm and inviting home interiors is likened to the wildly popular 1970s “harvest gold era.” Years of above GDP growth in new construction and home remodeling are drivers. Remodeling demand, in particular, is partly driven by home renovation-themed TV shows featuring celebrity hosts who, year after year, inspire multigenerational audiences to improve and update their living spaces.

As outlined in the scope of the U.S. Market Analysis’ Chapter 10, Appliance Finishes, original equipment manufacturer (OEM) appliance finishes include powder coatings, coil coatings, and liquid coatings. Appliance finishes are used to protect and decorate interior and exterior plastic and most metal substrates (e.g., ranges, freezers, washers), heating equipment (furnaces), industrial furnaces and ovens, and air conditioning equipment. Stainless steel, by comparison, was historically unpainted but is now commonly coated with an anti-fingerprint coating, while the newer black stainless appliances have a unique finish process that varies by OEM.

Appliance Design and Home Interiors

Customer Segmentation

Appliance OEMs are segmenting and tracking business trends that fall under three consumer categories: single appliance replacement (largest by volume), home renovation, and the U.S. builder distribution market comprising the design and construction of new homes.

Appliance shopping for most consumers is driven by a need to replace a single aging or unrepairable appliance. In this category, consumers are seeking to closely match the finish of a new kitchen or laundry appliance with their existing models, such as matching the color and finish of a new refrigerator to that of an existing stove and dishwasher. Far less frequently, consumers are investing in a suite of appliances for the kitchen and laundry either for a newly renovated space or in preparation for a move to a recently built or existing home. The move or renovation may entail a first-time appliance purchase or replacing existing (possibly aging) appliances that no longer fit the consumer’s new space or must be left behind due to a real estate agreement. Buying factors will vary, but the appliance suite sale is king.

Timely interior design input from production builders as they build homes for a large, diverse audience across the United States is extremely valuable to appliance designers. Appliance designers walking alongside builders in each phase of a new home design springboards mutual creativity as builders conceptualize and design interior finishes for kitchens, laundry rooms, and adjoining spaces. Appliance design is required to fit in with the builders’ vision for style, color palette, textures, and finishes. Beyond aesthetics, the appliance designer considers durability for the typical 10- to 15-year life of most major appliances.

Appliance Design and Finishes

In 2011–2012, GE embarked on a full year of consumer research, recognizing that the kitchen had become the hub of the home—that kitchen appliances, the refrigerator, stove/cooktop, dishwasher, and oven were integral to, and should complement, the surrounding décor. Wall coverings and cabinet finishes took on a warmer tone similar to a living room aesthetic. Moreover, the popularity of stainless steel was waning. GE set out to develop an alternative to stainless-steel in response to a gap in the market (an unmet need among consumers) for ease of wiping off, or ideally preventing, oily fingerprint smudges and water droplets that continually marred the surface of their stainless-steel appliances—otherwise known as “stainless steel fatigue.”

In late 2012, on a limited basis, the appliance industry introduced new alternative finishes like frost white and black stainless. From GE’s perspective, their year-long consumer research uncovered a preference for metallic surfaces with fingerprint resistance, while the traditional pure white, almond, and glossy black finishes had faded in popularity. Flooring such as laminates featured a warmer wood tone. In response to changing interiors and consumer preferences, GE landed on what it called Slate, marketed as “a rich matte appearance that naturally hides fingerprints and smudges to maintain its beauty,” and GE sales took off. During shipping, however, the low-gloss, slate coating soon began to burnish around the appliance corners. According to ChemQuest vice president David Cocuzzi, this burnishing effect is an inherent concern with low-gloss (matte) coatings technology.

At about the same time, LG launched a brushed stainless finish that caught on.

By 2014, “black stainless” was introduced—a brush metal effect that shines through a translucent darker color. While a year earlier Slate was designed to complement cabinets and other features in a kitchen, by contrast, black stainless was designed to make a bold statement. The “black” in black stainless is a coating with a small amount of black pigment to create a transparent, dark coating.

Shortly thereafter, the Café line of high-end GE appliances with customizable hardware was introduced, featuring new colors such as pearl bright white.

GE’s Monogram series followed. These appliances use physical vapor deposition (PVD) technology, which produces an exceptionally hard, scratch-resistant coating. PVD coatings are, by end user’s standards, exceptionally expensive. PVD technology is principally nitride coatings, according to Cocuzzi, comparable to tungsten carbide in toughness, and equally tough to work with. After all, appliances, with a relatively long life verses consumer electronics and smartphones, are subjected not only to a fair number of fingerprints and smudges, but also door slams and other use considerations.

The net effect is that consumers and interior designers have a great deal more to work with to create their very own “dream kitchen.” Moreover, anti-fingerprint coatings are now commonly used on stainless-steel appliances.

In-home Consumer Research

“We did consumer research the old fashion way,” says Lou Lenzi, recently retired design director for GE Appliances. “GE Appliances’ design research team spent time with consumers in their homes during daily activities like meal preparation. It’s one thing to observe and ask questions through the one-way glass in a focus group setting, but quite another to actually go into the consumer’s home and observe and witness how people live their lives in the kitchen and how they congregate.”

Designers bring miniature versions of appliance designs under development in the form of paper models, reminiscent of paper doll fashion accessories with foldable tabs for attachment. This was one of many methods GE used to obtain consumer feedback—adhering paper models to the front surfaces of a refrigerator, dishwasher, and wall oven. The consumer stood in front of their current appliances and offered feedback. GE dedicates a lot of time, attention, and detail to its in-home consumer research because the outcomes drive the company’s understanding of where consumers are headed. Consumers are certainly influenced by magazines, social media, and cable TV shows, and that crossover effect is experienced in homes.

Appliance Design and Engineering

Appliance OEMs’ materials engineers focus on materials, materials processes, application of finishes, testing, validation, and qualifying the finishes, to meet internal specifications and industry standards. At GE and Electrolux, designers work with materials engineers who are part of the R&D team, and materials engineers work hand-in-hand with the production engineer in kitchen (especially dishwashing) and laundry products. Electrolux’s material engineer also interacts with Purchasing, Manufacturing, and Quality Assurance, according to Tim Jones, recently retired after 40 years as Electrolux’s materials engineer.

Lenzi would accompany GE’s materials engineers to meetings with coating suppliers occasionally for a firsthand understanding of their world. Design leaders are like sponges when it comes to information—they track consumer interest, trends and durable goods, automobile design, and fashion design. Beyond design, they seek to understand what is on the leading edge with supplier partners who are challenging their own R&D teams to innovate new approaches. In the appliance OEM’s design studio, coating suppliers (and major retailers) are exposed to design and material concepts, and observations are exchanged on the appliance suite from every angle, which ensures a good leg up on the development process. The consumer’s need for aesthetic attributes is a top priority, followed by the technical properties and processes recommended by materials engineers. Appliance designers must understand color coating, powder coating, and films while leaving technical decisions to the engineering team.

The laundry room is, much like the kitchen, becoming a softer, more inviting environment. Here, the industrial design team works closely with the design research team, the materials engineers, and, of course, the production engineers, to ensure that a specified finish will reflect an appliance brand and its values.

Certain properties such as scratch resistance and burnish require packaging engineers’ expertise. From a packaging engineer’s perspective, safely delivering a 21½-cubic-foot refrigerator to the consumer’s home without scratches requires an appropriate package design including core blocks, the inner packed materials, and the corrugated carton, that collectively become a critical component of the finish specification. Otherwise, during delivery, if a finish burnishes due to rubbing inside the container, the team turns to the manufacturing engineer. Obviously, no team member wants to hear of their new appliance unboxed in the home with the customer’s first reaction being, “What is this scratch or discoloration?.” On the front of the refrigerator, you have injectable to plastic patch overlays for the control services. The side panels are often color-coated or powder-coated. How do you achieve consistent visual harmony across multiple materials and processes? The short answer is that it is a team effort to pull off.

Similarly, retailers display a lineup of various brands of appliances on the show floor, which prompts appliance manufacturers to assess their competitor’s features, brands, and price points against their own in a mock shopping exercise. All the design criteria, material qualifications, and manufacturing decisions are on full display by their channel customer—the retailer. Still, the moment of truth is when the product is unboxed in the consumer’s kitchen—here an appliance manufacturer strives to deliver on its promises to retailer customers.

Otherwise, the retailer hears from the customer, and the complaint runs down the line, but the buck stops with the appliance manufacturer’s internal design and engineering team.

The Technical Side of Appliance Finishes

Qualification of a New Powder Paint Supplier: at the OEM or Job Shop

In his tenure with Electrolux, Jones’ role overseeing supplier and material qualification in the St. Cloud, MN plant was a high priority.

From a logistics standpoint, Electrolux’s newest plant is in Memphis, TN (slated to close by end of 2020). Electrolux manufactures dishwashers in Kinston, NC; freezers in St. Cloud, MN (closing in late 2019); and refrigerators in Anderson, SC and Ciudad Juárez, Mexico. Charlotte, NC is a major hub for Electrolux appliance design, fabric care R&D, and its Global Technology Center, and is its corporate headquarters in North America.

Jones perfected the following steps, over many years of trial and error, to qualify a new powder paint supplier. The qualification is being driven by the appliance manufacturer, usually for a cost advantage. (Click on link below to view steps.)

Qualification of a New Powder Paint Supplier

Finding one or two new powder paint manufacturers may hinge on formulator expertise. Materials engineers can learn from application equipment suppliers who specialize in and use large quantities of powder paint, but chemists formulating new powder paint products have a deeper knowledge not only of their own portfolio, but of technology in general. Appliance OEMs are trying to learn from their supplier partners how to improve performance/cost through innovative materials, new technology, and application methods.

According to the Powder Coating Institute, electrostatic spray deposition (ESD) is commonly 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 that 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 crosslink density. These molecular chains are resistant to breakdown. Sometimes a powder coating is applied during a fluidized bed application. Preheated parts are dipped in a hopper of fluidizing powder—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.

In a week-long trial of a new powder coating for appliances, Jones’ ideal is to use two or three separate batches of production-grade paint to ensure the quality of the new powder paint manufacturer’s process and end product is consistent batch to batch. Climatizing, which takes up to three days, cannot be overlooked—so the three batches can be received on the same day before the trial begins. Humidity is an equally important consideration albeit difficult to control. Excessive heat and moisture can cause powder paint to clump, gel, or otherwise affect its quality. Powder paint exposed to seasonal cold temperatures and low humidity during winter also requires climatization for quality control. Most jobs shops have little, if any, ability to control humidity. Typically, humidity is best controlled in the appliance OEM’s powder paint room using a very sophisticated humidifier.

Whenever possible, appliance suites are manufactured without changing the type of powder paint, hardware, and accessories for design and bulk pricing considerations. Qualifying the same technology for use in multiple facilities in and outside North America can be a strategy, depending on logistics. Standardizing physical property requirements such as material specifications, test specifications, and the finished specification may warrant using the same powder paint coating design and specific powder paint formula. A paint manufacturer who has plant locations and a reliable channel strategy in the same countries as the appliance OEM may have an advantage for this reason.

The volume of powder paint varies by plant, depending on the type of appliance manufactured at that location. When manufacturing, for example, in the United States and Europe, an appliance OEM may invest $10,000 to $20,000 to qualify a new powder paint product in the United States to gain a modest cost savings of $50,000 in their U.S. location and a $200,000 savings in Europe.

Job shops will vary in their approach. One job shop may use an appliance OEM’s qualified powder paint product to gain bulk pricing (often the powder paint manufacturer will even accommodate the job shop’s packaging preference), while other shops with multiple OEM customers would not be able to satisfy all of their customers’ requirements using one OEM’s qualified product.

Managing Efficiency in the Major Appliances Supply Chain

Managing efficiency at the factory and among the many tier suppliers is challenging for material engineers. Cost reduction strategies that resonate with coatings practitioners involve the substitution of parts and technologies with lower priced versions or qualifying new suppliers and unseating an incumbent supplier with a low-bid rival. Implementing newer, more efficient application equipment is another strategy employed at the OEM and in job shops. Sometimes, it is a matter of periodically inspecting job shops to ensure compliance with an appliance OEM’s methods and painting practices. When a red flag is encountered, corrective action must be taken or the job shop risks losing its OEM contract. At minimum, improving efficiency reduces operating expenses by significantly reducing scrap and waste. Appliance OEMs prioritize worker health and safety throughout their supply chain. Avoiding downtime on the appliance OEM’s own lines due to inferior parts is critical.

Historically, smaller parts have been outsourced, with wired goods as one of those examples. Poor practices discovered in job shops may involve a prolonged search for reliable and efficient wire suppliers with powder paint capabilities to meet best practices in powder paint booth management, equipment maintenance, part manufacturing including pre-trim surface preparation and painting, and worker safety and training.

A ~$500,000 capital expense for equipment was once recouped in less than a year. To illustrate the savings, consider a wire goods part produced in a job shop. The unpainted part weighs about a half pound. Measuring the pure powder paint coating on the wire part with a film thickness gage, film thickness coverage was in the range of 10 to 20 mils of powder paint. For the Faraday Cage areas film thickness should be around 3 to 5 mils by comparison. In a mismanaged job shop, the total output of powder paint for that part exceeded the acceptable film thickness by three to four times.

Heavy and inconsistent coating thicknesses can lead to surface defects such as orange peel, and the paint may become more brittle and chip during assembly. (Note: orange peel is a surface defect, a non-smooth surface, which creates a poor overall finish appearance. Orange peel has multiple causes and can occur with powder or liquid coatings.) Part fitting into the application can be thrown off. For example, a wire part may not fit into its stud application due to excessive film thickness. In other cases, poorly painted parts may no longer fit into a cabinet.

The new piece of equipment increased a semi-automated operation to 100% automated, which decreased time, materials, labor, waste, and clean-up expenses, and optimized the coating application. Improved quality paid off by producing consistently good coating systems vs the shop’s prior inconsistent results. Not only did the equipment pay for itself in under one year, but these gains compounded every year thereafter.

Part of the qualification process determines the efficiency of the powder paint itself—not only by volume and transfer efficiency to the substrate but also by the degree of hideability achieved for each mil of film thickness. For instance, one powder paint product may produce a level of coverage at 1 mil film thickness achieving a certain level of color and gloss and other physical properties, while a new paint supplier’s product may require 1.5 mils to achieve identical results.

Seasonal energy variations also affect quality and efficiency. The demand for natural gas peaks during winter months for heating in most parts of the United States. In some areas, industrial users may be forced to curtail their use of natural gas when pressure is low, at which point a manufacturer will turn to its Liquefied Petroleum Gas (LPG) source. Material engineers in appliance manufacturing have observed that a change from Natural Gas to LPG as its energy source may cause color changes (often yellowing) with certain chemistries of powder paint. White powder paint is reportedly the most sensitive.

The Future of Appliances

Buying appliances online is also a growing trend: the changing dynamic between brick and mortar and e-commerce sales is fast paced, even though buying an appliance for many consumers is one of the largest investments they will make in their home, and well worth doing in person.

Is Alexa waiting to unveil her hidden talent for preparing fine cuisine? Not that we know of. But the trend towards voice control is thought to be the next big thing in appliances. You may see fewer physical controls on your appliance in the not-so-distant future, which will open the door to more opportunities for new finishes. Eliminating all the buttons and knobs on a high-end front-load washing machine is unlikely anytime soon. However, reducing the number to two or three key buttons combined with more advance controls enabled by a voice mechanism is feasible. As a smartphone technology begins translating controls into a voice interface, the technology will open up these clean, simple, sleek surfaces, making the kitchen feel more like a living space and less like a mechanical environment.

Customization and personalization will continue to transform appliances. Today, GE’s Café line of appliances is customized with mix and match hardware. A consumer may prefer a handle design that has a certain finish and a certain end-cap aesthetic that they want to extend to virtually every appliance.

The kitchen seems destined for an era of video screens popping up (i.e., touch a screen on your refrigerator to shop online), more furniture, larger islands that become the focal point—truly the living area of the home. Any finish or material compatible with the kitchen’s multiple functions—cooking, entertaining, congregating at the end of the day—that adds warmth, functionality, and appeal, will likely be in demand. Yet, coming full circle in a few decades, the dining room and living room may take center stage and the kitchen may once again be relegated to a mere utility room. For now, the kitchen is the hub of the home.

These trends are obvious for appliance designers who attend three important annual trade shows: the annual Consumer Electronic Show (CES), The Kitchen & Bath Industry Show, and The NAHB International Builders’ Show® (IBS).

GE Appliances, according to Lenzi, has relied on powder coatings for years because “you can’t beat the durability and the ease of application; powder coated is a well-liked process.” In 2010, GE put a billion-dollar investment into GE Appliances business unit to reshore its major manufacturing in the United States. Its Louisville, KY site is a 900-acre complex producing refrigerators, dishwashers, and laundry products. In 2018–2019, GE Appliances (acquired by Haier in 2016) invested another $200 million in upgrades to expand the laundry and dishwasher manufacturing in Louisville.

Acknowledgments

The author extends her special thanks to co-contributors, Tim Jones and Lou Lenzi, FIDSA. Jones retired in April 2018. Over his more than 40-year career with Electrolux Major Appliances, he was involved in qualifying new paint colors and paint products and new application equipment, to satisfy diverse Electrolux internal requirements from its Design Group as well as Purchasing, Manufacturing Engineering, Accounting, and its Quality teams, while working with various paint and coatings vendors seeking qualifications and approval for U.S.-based appliance and part finishes.

Lenzi retired in July 2016 as design director of GE Appliances, where he and his team were responsible for all industrial design, user interface design, and user experience design activities for all GE and GE Monogram-branded major appliance products.

For more information on how to purchase ACA’s The U.S. Market Analysis for the Paint & Coatings Industry (2018–2023) and The Global Market Analysis for the Paint & Coatings Industry (2018–2023), contact  ACA’s Allen Irish.

*For the first time in ACA’s history, both Market Analyses will cover the same five-year period (2018 through 2023). They will be available for purchase by early September 2019 via
/publications-resources/market-analyses-benchmarking/.

©Photo courtesy of GEAppliances.com

CoatingsTech | Vol. 16, No. 7 | July 2019

$1

This article outlines an unmet industry need for formulators to conduct robust testing of their coatings products in real-world or simulated environments that closely resemble an OEM facility’s environmental and processing conditions as coatings are applied and cured. The illustrative examples provided in this article are not hypothetical but are based on actual OEM and end-user processes, widely available coatings products, and current market dynamics.

Application and curing dynamics of paints for factory and field-applied coatings are rarely quantified by coatings practitioners over a wide range of climactic and factory-specific conditions; yet, this information is critical to the long-term performance of the coating in global markets.

For example, there is a growing need to better understand the performance of factory and field-applied coatings exposed to fluctuating humidity and temperature conditions (as shown in Figure 1) during application and curing. For raw material suppliers, formulators, third-party engineers, and applicators, the physics and chemistry of changing climactic conditions during application and curing that impact the durability of a coating system are not well understood. This is primarily due to the disconnect of evaluating coatings performance following application and curing in a highly controlled (small scale) laboratory compared to an evaluation on the scale of an OEM manufacturing environment using similar (if not identical) equipment and techniques.

Humidity and temperature conditions affect fluid dynamics associated with the spray stream, the formation and adhesion of the film on the substrate surface, the curing dynamics, and the long-term performance of the cured film. In addition, the physical and chemical variables introduced during fluid delivery process such as pump mechanics, tubing chemistry, spray applicator geometry and mechanics, and air flow dynamics, introduce further complexities in developing a coating for application in the factory or field; worldwide plant locations that use different types of application equipment and methods will clearly add more variables to the evaluation.

We will examine four illustrative examples of how coatings performance test findings rendered in real-world manufacturing environments differ from standard laboratory coatings evaluations:

• Indoor aerospace production shutdown due to weather changes;
• Pretreatment of automotive plastic parts (application window deviations);
• The effects of part geometry on powder coating curing dynamics; and
• Spray dynamics.

Consolidation’s Role

Historically, smaller and mid-sized paint manufacturers provided custom products and exceptional service by today’s standards to small manufacturers of parts for OEM assemblies, often including a specific paint SKU for a part. Coatings were tested through plant
trials on a part manufacturer’s production line, usually with the coatings supplier on-site at their customer’s location to observe the testing.

If the test results were negative—no matter how small or large of a correction might be required—the mid-size formulator had the capacity, knowledge, experience, and resources to make changes to the formulation or to recommend changes to a customer’s process. The coating formulator’s recommendations were usually tailored to the plant’s specific environmental conditions.

In recent years, inorganic growth (consolidation) has shifted priorities for newly reorganized paint and coatings manufacturers following an acquisition or merger: the exceptional technical service on which smaller (low volume) OEM customers depended, in many cases, was no longer available. A void emerged in the standard protocol for testing and selecting a coating for an OEM part, especially for testing new coatings products. The responsibility for testing a coating for its intended application or use shifted away from the coatings formulator to the part manufacturer. The low-volume part manufacturer had little choice but to adapt by selecting a non-custom (off the shelf) coating product that is not optimized for its intended application, or to switch to toll manufactured coatings.

By comparison, large OEMs with high-volume production continued to receive individualized technical service from multinational coatings formulators. Yet as paint companies grow and begin serving a larger customer-base in new geographic regions (moving away from the smaller regional player’s business model), they are faced with having to produce coatings systems to meet global performance standards. Will a coating originally formulated for use in a midwestern automotive plant in the United States, that is tested in a controlled laboratory, perform as well in Thailand?

The responsibility is squarely on the formulator to test their products over wider environmental ranges, and to formulate their coatings to be more robust to handle those varying conditions. Yet the standard array of lab tests either entirely ignores relative humidity (RH) and temperature (T)—or tests at a single value—when, in fact, a wide set of values is in order.

The solution may involve designing multiple formulas and SKUs for different conditions (i.e., one formula optimized for hot and high humidity climates; another formula for cold temperatures and low humidity). However, pricing pressures and other factors mitigate against that type of compromise.

Alternatively, developing one formula that is not optimized for a single environment, but instead is designed to perform adequately in multiple conditions and environments may be less costly and acceptable for certain end uses. These compromises ultimately result in performance disadvantages. Making formulation decisions to optimize this balance between performance and widening the application window is predicated on being able to develop reliable test data under real-world conditions.

Aerospace Production Shuts Down When Weather Changes

In this scenario, an aerospace manufacturing facility specified a coating with a technical data sheet (TDS) that expressly stated coatings performance could not be guaranteed in application conditions of 40% or less humidity. Consequently, when the facility’s indoor RH dropped below 40% due to outdoor weather conditions, the facility’s painting operation was halted until the indoor RH increased, causing a large loss in production output and associated revenue. The risk of liability associated with applying a coatings system in low humidity conditions that would not be certified by the coatings manufacturer was too great. At issue for the end user was the absence of application testing data for verification purposes that would ensure that the coating would perform at the lower RH levels in their factory using the same type of spray equipment, curing process, etc.

The TDS stipulated < 40% RH as the lowest criteria simply due to a lack of adequate application data below this level. The coatings user did not have the ability to conduct the necessary testing given that the conditions inside their factory depend on difficult-to-forecast weather. Therefore, planning a plant shutdown on a low humidity day was not realistic.

However, if the paint manufacturer could test the paint in a simulated manufacturing environment under those low humidity conditions—and assuming the test results met with FAA approval and exhibited overall satisfactory performance—they could confidently modify their TDS based on the new test data. This outcome would pave the way for expanded usability of the coatings manufacturer’s product, resulting in higher sales, increased market penetration, potentially leading to new market opportunities. The end user, in turn, could manufacture for a larger percentage of the year, and achieve higher throughput and profitability.

By comparison, conducting coatings tests on the scale of a laboratory in a small test chamber using standard lab application equipment and curing methods would not render the same findings as a low humidity simulated application and manufacturing environment. This is mostly because laboratory testing assesses temperature and humidity effects only during curing; neither temperature nor humidity is measured during application. The actual testing would need to closely mimic every aspect of the aerospace painting operation, including multiple low humidity values of 10%, 20%, 30%, and 40%—
factoring in the actual substrate types, the spray procedure and equipment (same type of pumps and spray guns), and the same curing method, followed by relevant ASTM tests in plant conditions.

Pretreatment of Automotive Plastic Parts (Application Window Deviations)

Plastic automotive components normally undergo certain surface pretreatment processes prior to application of coatings, adhesives, and foams. These processes are used on low surface energy materials to clean and activate the surface to improve wettability and adhesion. Among other factors, the timing between those two processes will ensure the quality and performance of the finished part. To achieve the required wettability and adhesion properties for this application, a particular automotive tier supplier opted to raise the free surface energy of the plastic substrate by using an open-air plasma pretreatment process.

Conducting tests following pretreatment is a common procedure for assessing to what degree, if any, factory conditions will affect the application window. This assessment is necessary because any type of pretreatment will render an exposed surface vulnerable to local conditions of temperature and humidity prior to applying coatings.

Under typical factory conditions, an approved coating process may include an acceptable window of time between the pretreatment and coating application. For illustrative purposes, we will use a 15-min application window as the norm. Unbeknownst to the tier supplier, that standard 15-min application window may one day shrink to five minutes. This sudden deviation in the application window can be caused by high or low humidity plant conditions, or other factors—which, in turn, can affect the part’s surface energy following pretreatment. The effect of low or high humidity on the substrate performance is not normally known because it may have never been tested, nor is it addressed in the plant’s coatings specification or in the supplier’s TDS.

If these parameters are not established in advance, the factory workers will allow the parts to proceed through the manufacturing process. Therefore, the prepared surface following pretreatment may be left exposed to the current high or low humidity condition for more than five minutes. Consequently, deviations in adsorbed moisture caused by the interaction between the gas phase and the solid phase of the substrate, the temperature of the part, and the dew point of the air, will create a surface condition that may not be amenable to proper coating or adhesive performance.  As a case in point, Figure 2 demonstrates the effects of T and RH on the free surface energy of an exposed low surface energy plastic membrane over time after pretreatment with an open-air plasma treatment process.

Dew point can affect the performance of field-applied and factory-applied coatings, especially in large factories with indoor air conditions that change with the weather. The drop of water on the surface of a pretreated part may be at the atomic or molecular level often not visible to the human eye, unless the part begins to “sweat.” Even a molecular layer of water between the primer and the substrate can interfere with the adhesion of the primer to the substrate. Because of these interrelationships, control of the humidity and temperature during the application process is important to realizing a cured film that has superior physical and chemical performance attributes. In the absence of controls, premature failure of the coatings system may occur as follows:

• Reduced corrosion resistance;
• Changes to free energy of the surface  changes to film formation;
• Blistering, blushing, cracking, delaminating, and blooming defects;
• Loss of adhesion; and
• Degraded chemical resistance.

It is best practice to ensure that the temperature of the substrate is at least 3–5°F above the dew point of the air. Preventative measures when that condition is not met might include raising the temperature of the part to avoid condensation onto its surface prior to painting. However, this measure is impractical in the field, and costly in the factory because it is an added process.

In summary, there is a measurable advantage in a part manufacturer’s process flow to leveraging test findings under a variety of factory conditions.

Effects of Part Geometry On Powder Coating Curing Dynamics

Curing a powder coated part typically involves placing the part in an oven set at a certain temperature and allowing the part to cure for a set time. For example, a powder coating may call for a curing temperature and time of 400°F for 10 min. Most OEMs have ovens that comfortably reach the desired temperature set point. However, what is not normally considered in product and process development is the myriad of sizes, shapes, and mass of parts—all of which affect the ultimate thermal profile that the coating will experience during its trek through the oven. Also, the type of oven and air flow through the oven will affect the thermal profile.

In this scenario, following a supplier’s instructions in the TDS, a particular OEM proceeds to powder coat its part by placing it in a 400°F convection oven. After 10 min, the part is removed from the oven and a visual inspection indicates it is properly cured (no visual defects). Next, the OEM begins conducting standard tests on the part’s coating; tests that may include a mandrel bend test, methyl ethyl ketone (MEK) solvent rub test, followed by more standard test methods for coating adhesion and hardness. One-by-one the coated part fails these tests. Why? What went wrong? Is the chemistry or production process of the powder coating responsible, or is the failure due to differences in thermal mass of the parts, and the temperature profile of the OEMs oven?

An investigation reveals the large thermal mass (e.g., a block of steel) of the part prevented it from reaching 400°F (even though the convection oven did) because a part with a large thermal mass does not heat as quickly as a smaller part. This variation is a function of the geometry of the part—10 min is insufficient to heat this larger part to 400°F.

Simply put, the TDS instructions to heat the part for 10 min in a 400°F oven omitted heating variations for different size parts. The TDS also excluded variations in equipment. Ovens vary tremendously: there are different types of ovens (convection is one type), air flow, and methods of heating (gas, electric, and infrared). The formulator oven cured a powder coated standard grade of metal testing panel that is approximately 2 in. x 4 in., with a thickness of 1/16 in. to 1/8 in. With a low thermal mass, 10 min sufficed to cure the test panel in a 400°F oven, which was the basis for the formulator’s TDS curing criteria. However, the OEM’s large thermal mass part did not meet that criteria.

A conflict between the OEM and powder coating supplier might have been avoided if the supplier would have conducted curing tests on a dozen different sized parts, using various types of ovens. Also, the TDS should have spelled out at least the most commonly encountered variables for a formulator’s customer base.

In summary, a process may technically follow the set point and dwell-time parameters as called for in the TDS, but the surface of the part may still experience an insufficient thermal profile, depending on its residence time, geometry, and thermal mass. Testing cure time for a variety of part configurations (different shapes and thermal masses) using different types of ovens is necessary for quality assurance and is critical for accurately and efficiently troubleshooting a coatings failure for both the coating manufacturer and end user. Being proactive, a formulator may ask customers for examples of what they are coating for possible inclusion in the supplier’s test matrix. The intent is to identify a range of testing samples—the highs and lows that represent the extremes of the process—with the understanding of where every sample in between would fit on the spectrum for a TDS.

These findings are not typically included in standard lab tests, so switching to a simulated manufacturing environment for performance testing of powder coated parts makes good business sense.

Spray Dynamics

Droplet Dynamics

Inherent to all spray technologies, whether they are conventional, HVLP, airless, or air-assisted-airless, is the atomization/aerosolization of the bulk liquid into small microdroplets that are moving at relatively high velocity. The fineness and consistency of the atomized droplets are critical factors in the wetting of the surface and the formation of a uniform, continuous film. If the droplet morphology is not consistent and within the proper range upon impact with the substrate, a film may fail to form properly. If the droplet morphology is such that the film builds too quickly, running, sags, and orange peel can result, as well as extreme variations in dry film thickness that, when cured, will result in heterogenous microstructural variations in the physical performance of the film.

As the drop leaves the spray nozzle, it enters an atmosphere of either stagnant or moving air (see Figure 3). This body of air is represented by three parameters:

1. Air velocity;
2. Temperature; and
3. Relative humidity

The dynamics of the drop as it moves through the body of air are characterized by several key parameters, including (but not limited to):

• Drop size (radius)
• Drop temperature
• Viscosity
• Surface tension
• Drop velocity
• Rate of evaporation at surface
• Heat conduction and convection inside the drop
• Water content
• Solids content
• Solvent content

As the drop moves through the body of surrounding air, each of these parameters affects how the droplet evolves as it moves from the spray nozzle to the substrate. For example, a droplet with a relatively high-water content traveling through a body of air that is at relatively high temperature and low relative humidity will lose its liquid content due to rapid evaporation from the drop. The drop will cool due to evaporative cooling, raising the viscosity of the liquid. As the drop travels toward the substrate, it will continue to decrease in size while the solids content increases. If the droplet’s water content is too low at the time it makes impact with the surface, wetting and film formation may fail to occur properly.

Many water-based paints are designed with coalescing solvents and rheology reagents to finetune both the viscosity and the minimum film forming temperature of the coating. The ratio of water to these coatings additives, as well as the relative rate of evaporation of the water and coalescing agents, determine the overall quality of the final film. The quality of film will dictate the efficacy of the paint post-cure. Therefore, from this one simple thought experiment, it is evident how the RH of the environment can affect the final performance profile of the coating.

In the scenario in which the RH is high and the T is lower, the rate of water accretion will be greater than the rate of evaporation, and the droplet will grow as it picks up water from the surrounding air. This phenomenon can cause the paint to have a water content that is too high, which will affect its viscosity. This, in turn, can lead to loss of film build, increased sagging, and increased curing times. If the downstream curing process does not evaporate this accumulated water, this can introduce significant problems in the performance of the film downstream.

Due to this linkage between environmental conditions, spray dynamics, film formation, and final film performance, it is advantageous to test the spray application of coatings under varying humidity and temperature conditions. Spray testing under five psychometric conditions (low T/low RH; low T/high RH; high T/low RH; high T/high RH; and Intermediate T/Intermediate RH) is a good place to start (see Figure 4). Because temperature and relative humidity are inversely related, achieving low T/low RH and high T/high RH application conditions is a challenge and requires specialized application equipment that is designed to treat and replenish moving air as it becomes laden with solvent and/or water during the application process.

Transfer Efficiency Dynamics

OEMs routinely design application equipment and processes to optimize transfer efficiency and reduce waste. This not only reduces the cost per part due to reduced usage of coating, it also reduces the costs associated with clean up, hazardous waste removal, equipment repair and maintenance, and VOC permitting. Uncontrolled overspray may be removed through a ventilation system or it may adhere to the conveyor or walls of the process equipment. Air pressure, gun-to-part-distance, coatings chemistry and the design, size and settings of the spray nozzle (and even the amount of air in a spray booth) will influence the degree of overspray. Furthermore, transfer efficiency processes are engineered in the plant for recapturing overspray for reuse to reduce waste. One method involves employing squeegees to scrape the liquid coating overspray off the underside of a conveyor belt into a steel container for filtering and reuse.

While paint manufacturers do conduct lab tests to ensure performance they generally are not factoring in their customers’ transfer efficiency methods and sensitivity to these paint characteristics. By testing a formulation in a real or simulated manufacturing environment, a formulation can be optimized to exhibit a higher transfer efficiency and a greater recoverability.

Conclusion

There is a growing need across the paints and coatings value chain to fully understand and plan for a wide range
of variables encountered in field- and factory-applied coatings—variables that are not routinely accounted for in the typical battery of lab tests. Among these variables, temperature and humidity play a crucial role in coatings performance.

Heretofore, data specific to a plant or application has been lacking as well as the technological resources required to conduct spray application trials under user-defined, controlled, environmental conditions. Making a case for proactively obtaining and using this data on behalf of coatings end users would benefit coatings formulators and the value chain in various ways, such as:

Providing needed information to raw material suppliers for the design of new chemistries (resins, solvents, additives, etc.) that operate over a larger range of climactic conditions;

Informing formulators on how to optimize their products for use across disparate climates;

Conveying to end users the best conditions under which to apply coatings and identifying steps they can take to mitigate against defects;

Creating a body of knowledge for writing new standards that correlate product chemistry to best practices for application conditions.

References

Funke, W., “Blistering of Paint Films and Filiform Corrosion,” Prog. Org. Coat., 9 (1) 29-46 (1981).

Erbil, H.Y., “Evaporation of Pure Liquid Sessile and Spherical Suspended Drops: A Review,” Adv. Colloid Interf. Sci., 170 (1) 67-86 (2012).

Voué, M., et al., “Dynamics of Spreading of Liquid Microdroplets on Substrates of Increasing Surface Energies,” Langmuir, 14 (20) 5951-5958 (1998).

Steward, P.A., Hearn, J., and Wilkinson, M.C., “An Overview of Polymer Latex Film Formation and Properties,” Adv. Colloid Interf. Sci., 86 (3) 195-267 (2000).

Nguyen, T., Bentz, D., and Byrd, E., “A Study of Water at the Organic Coating/Substrate interface.” J. Coat. Technol., 66, 39-39 (1994).

Automotive designs are changing in response to increasingly stringent environmental regulations and constantly evolving buyer preferences. Emission and gas mileage requirements in the United States are steadily rising under the CAFÉ standards. Car manufacturers are responding by replacing traditional steel parts with components made from lighter weight materials. Coating vehicles made from myriad substrates bonded together with adhesives rather than welded joints present significant challenges to both formulators and applicators and are driving innovation across the entire supply chain and vehicle coating process.

Numerous Lightweight Options

Car makers are exploring the use of a wide range of lightweight material alternatives to traditional steel. Some technologies in the forefront include aluminum, ultrahigh strength steel (UHSS), magnesium, carbon fiber reinforced polymers, and various high strength plastics. “Each option carries its own set of benefits and unresolved issues,” says Bill Eibon, director of Technology Acquisition for Automotive OEM Coatings with PPG Industries. New alloys and compositions are being developed in each of these categories to create lighter, stronger, more formable materials, and each is being targeted where they are able to contribute the most value in weight reduction, resulting in multiple materials being used on a given vehicle, according to David Fischer, vice president of Market Strategy and Growth for Axalta Coating Systems.

Multi-Substrate Issues

“No single lightweight material stands ready to displace steel as the largest component,” Eibon asserts. “While prudent, this multi-material approach creates its own set of coating issues,” he continues. Areas that must be addressed include the pretreatment process, the potential for corrosion, compatibility with the adhesives and sealants used to join disparate materials, the need for lower curing temperatures to avoid deformation of composites and plastics, and the greater surface roughness of many of these materials. “As the material content changes and alloys evolve, coatings must be adjusted so they continue to provide a uniform, high quality finish across the vehicle,” Fischer observes. How these materials react to paint shop conditions such as thermal expansion must also be addressed, he notes.

Pretreatment Challenges

Pretreatment is the first coating layer on a car body. Existing pretreatments have been optimized for steel substrates. Today, however, rather than welding debris, excess adhesive and sealant materials need to be removed during the pretreatment of parts comprising different substrates. New wax-based lubricants are used to improve the formability of aluminum parts, but can be challenging to remove during cleaning. These different materials often clog existing filtration systems, according to Jim Schafer, lab manager with Durr Systems.

“Pretreatments require reformulation to ensure uniformity of crystal structures deposited on multiple materials to meet current adhesion and performance specifications, while minimizing sludge formation, waste, and operational inefficiencies,” asserts Eibon. He does note that new pretreatments for aluminum have been developed, while numerous solutions for multi-metal pretreatment are being developed to meet the material choices of each auto manufacturer. “There is definitely a learning curve to determine which technologies work best for newer substrates and different combinations of substrates,” observes Schaefer.

It is very challenging to achieve the same coating quality for all components because the quality of the surfaces of some of the newer materials being used today is lower than that of conventional steel.

When developing new pretreatments, formulators must consider how different chemicals will react with each substrate and the different materials used to join them, as well as how the process will impact coating adhesion to each substrate, according to Scott Clifford, principal engineer in the Paint Shop Automation Group of FANUC America Inc. “The move to multi-material components has added significant complexity to the pretreatment process,” he asserts.

New Corrosion Concerns

The coatings industry has made steady improvements in corrosion protection over the years, according to Eibon. The mixed-material approach to lightweighting, however, brings dissimilar metals in contact, thereby increasing the probability of creating a galvanic cell. “Corrosion resistance will need to be optimized and improved to ensure mixed-metal car bodies meet the current industry standards,” he notes. Corrosion protection for UHSS is a new concern as well, because this material is susceptible to hydrogen-induced cracking that occurs over time. “New corrosion protection systems are being formulated to meet changing characteristics as new alloys are introduced, and when multiple metals are processed through a common system,” Fischer agrees.

Adhesion Problems

One way that car manufacturers are reducing vehicle weight while providing the necessary strength is through the incorporation of lightweight polymeric materials inside pillars in car bodies, according to Jim Pakkala, senior engineering manager for Paint and Final Assembly Systems at Durr Systems. “The polymers have high specific heat values, and, therefore, it can be challenging to achieve full curing of coatings on these pillars,” he comments. Durr is evaluating potential modifications to existing equipment that will enable full curing over the entire car body.

The new plastic and composite systems used today also require adjustments to coating systems to ensure adhesion to modified surfaces without adversely impacting other properties, according to Fischer. “Adhesion to these new surfaces is the largest initial concern that drives coating reformulation today,” Eibon asserts. Electrostatic deposition can be difficult on multi-material components because different capacitances are required to achieve paint adhesion on the different substrates, according to Pakkala. “The industry has to rethink existing solutions and technologies,” he comments. Eibon also notes that the joining and bonding of multiple materials by polymers will require coating solutions that can adhere to these adhesives and sealants and tolerate any materials that off-gas during curing.

Surface Roughness Issues

When multiple substrates are used in a vehicle body, the material joining process is very complicated; creating a uniform body is very challenging, according to Clifford. The surface roughness and existence of residual mold lines on new plastic substrates also negatively impacts the appearance of coatings, and as a result this issue is driving coating reformulation, according to Eibon. “It is very challenging to achieve the same coating quality for all components because the quality of the surfaces of some of the newer materials being used today is lower than that of conventional steel,” Pakkala adds. He notes that additional sanding steps are often included—sometimes of the primer before application of the basecoat, and occasionally of a first clearcoat layer before application of a second. “Sanding creates a lot of additional process work, slows down production, and adds cost—all of which are undesirable,” Pakkala observes.

Low-Temperature Curing Issues

Increasing the content of plastics on cars combined with the desire to coat all assembled parts online requires low-temperature cure coating systems. “The industry is moving rapidly towards an 80°C cure reality,” states Eibon. “All coatings layers will have to be modified as a complete coating system to ensure success of cars cured at this temperature,” he adds. Achieving color matching and uniform leveling and other appearance characteristics for all body parts including those that are baked at lower temperature is challenging, however, according to Schafer. “Paint companies are working closely with OEMs and equipment manufacturers to develop application equipment that can overcome these issues,” he says.

There has already been movement towards the use of two-component coating formulations to decrease curing times and temperatures as well as reduce environmental footprints. FANUC, for instance, has developed a new direct charge rotary atomizer system for the application of 2K waterborne coatings that involves reaction of the polyisocyanate into the water-based basecoat to reduce the curing temperature. “The use of 2K waterborne systems adds a level of complexity that should be considered,” he observes.

Clifford states that if we see more extensive use of plastics and composites in the coming years, we may see less painting in the assembled body position and more parts painted individually or in the “part on fixture” position.

Sustainability Challenges

All of these difficulties must be overcome while maintaining a very high quality coating appearance, without adding cost, and ideally with a reduction in the environmental impact of painting processes. “Painting is the highest cost step in car manufacturing, as well as the process with the highest energy usage and largest environmental footprint. There is consequently significant focus by OEMs on simplifying the process, but without compromising quality. They are looking for higher utilization, efficiency, and productivity despite the significant changes in materials used,” Pakkala explains. In addition to increasing the efficiency of the application process, efforts to reduce the environmental impact of the coating process include reducing the volatile organic compound (VOC) content of the finishes as applied, improving the ability to capture VOCs, and reducing energy use, according to Fischer.

Regulatory Drivers for Innovation

There are a number of different regulatory drivers that coatings manufacturers must be aware of while developing new solutions for multi-material vehicles. In addition to CAFÉ requirements, which are driving a lot of R&D programs for new material development in and outside of coatings, the global trend toward reduction of toxic materials and the use of sustainable and green processes to generate materials and products is influencing coating development, according to Eibon. Fischer adds that eliminating materials of concern continues to be a priority as regulators continue to add new materials to this list. “Negotiating the complex and dissimilar requirements for material registration around the globe is a challenge for all coatings producers and users. The increase in material registration requirements and legislative compliance has been well documented and will continue to drive coatings activities and costs into the future,” Eibon asserts.

Consumer Preferences

Of course, coating manufacturers and car makers must also keep buying preferences at the forefront of any new technology development efforts. “Consumers continue to want to be delighted with new and fresh designs, including colors with unique effects. Development of new color spaces and programs that offer color in new and interesting ways continues to be a focus,” says Fischer.

In fact, the automotive industry has established two-tone and dissimilar color design elements as a way to increase customization for mass produced vehicles, according to Eibon. “A growing number of consumers are willing to select premium colors when the options are available,” he notes. He adds that the resurgence of aggressive-looking muscle cars with 21st century technology brings a need to paint gloss and matte accent stripes. Roof coatings of different colors, geometric designs, or with solar reflectance have become popular recently. “All three of these design concepts currently require complex manual masking and de-masking applications that add cost and slow production. Automotive OEMs, coatings companies, and paint application equipment manufacturers are developing maskless spray technologies to deliver these design concepts without losing capacity. A reduction in paint overspray from different atomizers is predicted, which—if successful—should lead to reduced material waste,” Eibon explains.

Improvements in coating performance would also be beneficial, according to Fischer. “Today’s coatings are not perfect. Improvements in stone-chip resistance, appearance, scratch and mar resistance, and resistance to chemical attack (acid rain, bug proteins, road grime, etc.) can reduce warranty claims and add value through improved consumer satisfaction and higher residual values,” he states.

Coatings for the interiors of vehicles face similar challenges. “As with car exteriors, new and multiple materials are being used in vehicle interiors, and a uniform look and feel is needed across different surfaces. In addition, coatings for vehicle interiors will need to provide high resistance to chemicals such as sunscreens, mosquito repellants, and air fresheners, despite being applied to different substrates,” Fischer observes. He also notes that, in the future, it is anticipated that people will spend more time being entertained and less time driving as autonomous vehicles begin to populate the roads. “These cars may also be shared, leading to different use and maintenance schedules. As a result, coatings for car interiors will also need to be designed for a new driver/passenger experience.”

CoatingsTech | January 2017 | Vol. 14, No. 1