Electropaints

As the surface smoothing and levelling effects are somewhat limited, the use of acid cleaners prior to anodising or electropainting, where surface defects can be enhanced, is not common. 

Fig. 14.1 Typical plant layout for electropainting (courtesy Stein, Atkinson Stordy Ltd.)...

After rinsing and dry-off, the primer is applied. In most modern plants this means electrodeposition of the primer (Section 14.1). The most widely used primers are cathodic. The body shell is made the cathode and current flows between it and inert anodes in the electropaint bath. The paint is formulated so that the resin is basic and, when neutralised with an acid such as lactic acid, becomes positively charged. The most widely used resins are epoxy-amine adducts ... 

Ultrafiltration (UF) is used for the separation and concentration of macromolecules and colloidal particles. Ultrafiltration membranes usually have larger pore sizes than RO membranes, typically 1 to 100 nanometer (nm). Operating pressures are generally low (30-100 psig). Applications include electropaints, gray water, emulsions, oily wastes, and milk, cheese, and protein processing. 

These facts are different demonstrations of the same event degradation reactions occur simultaneously with electropolymerization.49-59 These reactions had also been called overoxidation in the literature. The concept is well established in polymer science and consists of those reactions between the pristine polymer and the ambient that promote a deterioration of the original polymeric properties. The electrochemical consequence of a strong degradation is a passivation of the film through a decrease in the electrical conductivity that allows a lower current flow at the same potential than the pristine and nondegraded polymer film did. Passivation is also a well-established concept in the electrochemistry of oxide films or electropainting. 

The development of new paint technology has mandated further improvements in the performance of non-chrome rinses. Greater use of a final water rinse in treatment applications has taken place particularly with the advent of anodic and cathodic electropainting which require the use of a deionized rinse to prevent paint contamination. High solids paints which tend to be more... 

Concn/purification of organic pigment slurries separation of solvents, etc. from pigment/resin in electropaints concn of pigments in printing effluents... 

To achieve the main process requirements (ability to be applied by different methods by hand, spray, electropaint), and to provide the necessary decorative, physical, and mechanical properties, organic solvents are used in concentrations up to of about 50% to modify the viscosity and other rheological characteristics of the some polymer compositions. During the application and formation of the coating, the solvents evaporate into the atmosphere as pollutants. This serious disadvantage of formulations based on the use of solvents as "intermediate" carriers has provided the incentive to develop polymer compositions and application technologies which yield the required rheological characteristics either without solvents, or at least with low concentrations of them. 

Through this process, very small particles of metal ions can be filtered to be used in electrophoretic psiint industry. The retained big-size particles are returned to the electropaint tank for reuse. 

The technology that is now known as electrodeposition of coatings, electropainting, electrocoating, etc., uses synthetic, waterborne oligomers. (See References 1-10.)... 

Metallic objects are first cleaned to remove impurities and materials associated with metal forming, welding, temporary rust protection, etc. In many instances phosphate and/or chromate treatments are applied. Overall, any electrically conductive surface preparation will impart benefits to electropainted articles similar to the benefits imparted to spray painted or dip-coated articles. The workpieces go from pretreatment to the electrocoating tank either water wet or dried. 

Yeates, R. L. "Electropainting" Robert Draper Ltd. Teddington, England, 1970. 

Machu, W. "Handbook of Electropainting Technology" Electrochemical Publication, Ltd, Ayr, Scotland KA7 IXB, 1978. 

Membrane technology is presently an established part of several industrial processes. Well known is its relevance in the food industry, in the manufacture of dairy products as well as in the automotive industry for the recovery of electropainting baths. Membranes make possible the water supply for millions of people in the world and care for the survival of the large number of people suffering from kidney disease. The chemical industry is a growing field in the application of membranes, which, however, often requires membrane materials with exceptional stability. The first part of the book will discuss the currently available membranes for different processes, which are suitable for the chemical industry. Information on different methods of membrane preparation will be given. Different materials will be compared, taking into account physical characteristics and chemical stability. 

Power depends on target species and configuration water treatment 1.8 kJ/L permeate food application 32 kJ/L permeate electropaint 60 kJ/L permeate. Configuration hollow fiber 6 kJ/L plate and frame 9 kJ/L spiral 3-6 kJ/L tube 15 kJ/L or hollow fibers 100-280 W/m plate and frame 180-280 W/m spiral wound 25-120 W/m. ... 

Commercial electropainting only dates from the early 1960s and the first processes to be introduced used anodic deposition. Some typical paint formulations would contain (i) polycarboxylic acids based on acrylic acid as monomer solubilized by an organic amine, (ii) alkyds, i.e. branched polyesters based on naturally occurring long-chain carboxylic acids and polyalcohols, e.g. glycerol, and (iii) epoxy resins based on phenols, e.g. 

On the other hand, it is obviously only possible to electropaint conducting surfaces and hence the process is limited to a single coat. Also, the colour range is more restricted than with conventional painting. 

---