Nonmetallic Additives for Protective Coatings
Many metallic surfaces can be protected from corrosion using a variety of available coatings. Their effectiveness, however, is not completely satisfactory because of small imperfections in the material that can cause coating film de-bonding, blistering or undercutting of the coating adjacent to the unprotected area. In addition, physical damage to the coating can also lead to corrosion of the metal. Salt and acid substances in the air often aggravate surface deterioration. Chromates and other heavy-metal additives can improve the protective abilities of coatings but have been proven to be environmentally undesirable.
Other nonmetal synthetic organic derivatives exhibit effective corrosion-inhibiting properties. As an example, macromolecular derivatives produced from the reaction of diamines with benzoquinones exhibit highly effective corrosion-inhibiting properties. When used in conventional protective metal coatings, enhanced corrosion resistance is realized due to the extended coverage by the coating to regions of the metal substrate where small gaps in the coating allow corrosive elements to come in contact with the unprotected surfaces when traditional anti-corrosion pigments are used.
Potentially, these additives offer a variety of benefits. They can reduce the application of hazardous materials as coating additives, be applied in waterborne coatings, be used with a wide variety of coating resins, and be applied in standard coating manufacturing techniques.
Intercoat Adhesion Promoters
In the many decorative and performance applications of coatings, a single applied film is many times not sufficient to meet the coating performance requirements. Thus, it is common to apply several different layered films to provide a specific function to the overall coating performance.As an example, in typical coating applications, primers are often used for substrate adhesion and corrosion protection. In addition, primer surface coatings are used to provide a smooth surface for subsequently applied topcoats. Basecoats and clearcoats are also used to provide a decorative appearance, UV protection and surface gloss properties.
The overall performance of the coating system requires that each layer must have a strong adhesion to the other. Especially in high humidity or after water immersion, individual layers will lose adhesion, leading to film layer de-bonding and peeling. This problem can be controlled using intercoat adhesion promoters.
Typical adhesion promoter additives include metal chelate or complexes, multifunctional oligomeric organic derivatives, and siloxane derivatives. Their application either directly onto a substrate before coating or integration into the applied coating formulation can be effective ways to improve film intercoat adhesion.
Additives Stabilize Dispersed Pigment Particles
What are the differences between a dispersing additive and a grinding resin?Dispersing additives and grinding resins aid in the stabilization of dispersed pigment particles during the milling stage of formulation. Both dispersing additives and grinding resins function by binding to the surface of the pigment, altering the surface of the particles to induce repulsive forces between the pigment particles. In the case of a dispersing additive, the repulsive forces are characteristically electrostatic and/or steric in nature. Grinding resins rely primarily upon steric forces to separate the particles.
Both technologies are effective in producing high primary particle concentrations in the mill grind, and then stabilizing the dispersion in the final paint formulation. Generally, dispersing additives are more efficient than grinding resins in dispersing pigments to a high primary particle concentration due to the greater specific smaller molecule binding per pigment particle. These additives typically disperse a higher pigment loading at a significantly lower concentration of a grinding resin.
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