Different Applications in Electrophoretic Lacquers and Electrophoretic Coatings

Electrophoretic Lacquers Electrophoretic coatings, defined as the deposition of polymer or oligomer in stable emulsion form onto a surface through pH change and subsequent baking, have been in use for over 40 years. Early products operated anodically, with pH reduction causing precipitation, but acidic attack on the coated part resulted in surface discoloration and stability problems due to high metallic contamination in the electrolyte. Over time, the shift from anophoretic to cataphoretic lacquer application has overcome many of these issues, and for over 25 years has continued under constant commercial development. A significant portion of these improvements has been realized in the United Kingdom, with many applications currently in existence. The basic polymers used in these processes are acrylic uretanes, though the primary polymer creating the coatings described below is polyurethane. While epoxy from other polymers exhibits good properties, it typically cannot provide a balanced combination of the appearance, hardness, corrosion resistance and substrate adhesion expected from the final lacquer layer.

Electrophoretic coatings are currently used in two very different applications, each with distinctly different technological requirements;

• Functional coating of large, complex-structured parts such as automobile chassis and doors, • Decorative coating of lighting fixtures, switches, door handles, decorative curtain rails and even jewelry components. The ability to color the decorative systems in question and apply them quickly and simply over low-cost materials such as aluminum and zamak has enabled the production of brass or gold-appearance products at lower cost, creating a new market in the household fixtures and jewelry sectors. This work focuses on the issues preventing full acceptance of lacquers used in decorative applications by the sectors.

These issues are fundamentally;

1. Previously, the uncured lacquer layer exhibited very soft and tacky properties, facilitating the adhesion of airborne particles before baking and resulting in roughening of the final coating. 2. The requirement for post-emulsification of lacquers, combined with high volatile content and low flow, created the need for extensive ultrafiltration both during setup and after any additions, making use difficult. 3. Baking temperatures of 160°C and above prevented the coating of certain materials such as zamak castings and plastics. 4. Especially in dark colors, tone consistency was poor. When pigment was used in the electrolyte, due to poor wrapping power of the lacquer coating process, sharp and corner areas of coated parts received thicker coating, resulting in darker tones in these areas. Subsequent color application was quite difficult and hazardous, as intense, volatile-only solvents were required to achieve color penetration. 5. Pigments used in the colored layer produced lacked ultraviolet resistance, resulting in rapid color and tone loss in outdoor environments. Modern systems are much easier to use and applicable in many other processes. The developments in question began with the creation of low-solvent pre-emulsified products that could be used directly by the operator without requiring post-emulsification. Immediately following this development, the application became easier to use and operate, with improved reliability and consistency.

Another significant advantage of these systems is that due to the low volatile content in the bath, the uncured layer is much less soft, producing harder, more damage-resistant coats, and fewer airborne particles adhere to the surface before baking, resulting in reduced roughness in the final coating.

For these reasons, decorative applicators have rapidly begun using low-volatility pre-emulsified systems, preferring them to the older high-volatility post-emulsification-requiring systems despite the inability to convert back. A further advantage of this latest technology is that due to the very low volatile content in the uncured layer, high volatile content is not required for pigment penetration in the coloring process. This means that after a single transparent lacquer coating station, any number of coloring baths can be added before baking, enabling production of a wide range of colored layers. The layer produced by this method is transparent and acquires quite attractive metallic color. The rate of pigment dissolution within the lacquer layer is the same at all points on the part, resulting in consistent color across the entire surface; conversely, when pigment is used in the lacquer bath, since all areas of the workpiece are not uniformly coated, color inconsistencies appear according to layer thickness. Adsorption rate is shown in the schematic diagram below. [caption id="" align="alignnone"]Electrophoretic Lacquers[/caption]

These new systems have received sector approval, particularly for their adhesion over bright nickel and brass plating, minimal shrinkage after baking, non-yellowing on silver, and additionally for quite easy handling characteristics.

Another problem observed in lacquers was gas release from porous-structure base materials such as casting or zamak casting during high-temperature baking. In the newly developed pre-emulsified technology, cross-linking can be achieved at lower baking temperatures (115 - 120°C) without loss of properties, reducing the risk of spotting and staining. The isocyanates used for cross-linking do not currently allow further risk reduction in today's technology. In the near future, plastic materials plated with metals such as copper and nickel will also be able to be lacquered, and new markets will emerge with the application of paints unaffected by natural light and ultraviolet outdoors. Recent developments have concentrated on cataphoretic systems capable of UV baking to enable coating of plastic, zamak pressure casting or other materials where high temperature baking could present problems. These latest technological developments have emerged from the laboratory and at pilot scale are being tested by numerous OEM (original equipment manufacturer) suppliers who have begun producing parts.

Although these modern polyurethane-based systems offer very good ultraviolet stability, pigments used in coloring still lack ultraviolet resistance, thereby limiting conditions for outdoor use.

Ultraviolet-resistant pigment particles are generally too large and heavy to provide consistent and reliable color. With recent innovations in pigment dispersion production, ultraviolet-stable pigments capable of being added to the lacquer bath have been produced, and QUV testing has yielded durability exceeding 600 hours, equivalent to years of outdoor stability. The nearly unlimited color palette of these pigments, combined with their ability to be mixed with black and white pigments, further expands color options, with pink, gray and silver colors currently available. In light of these developments, modern lacquers are capable not only of coating all conductive materials with a very wide range of colors and effects, but also of providing indoor and outdoor durability. Emrah İnçal Metallurgy Engineer / Customer Relations Manager DEDE Kimya A.Ş. # MAKALE# Analiz# Elektroforetik# Laklar