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Coatings Types and Characteristics

A. Bhatia, B.E.


Course Outline

Coatings are necessary to provide various degrees of protection. This course details and compares the effectiveness of various types of coatings, enabling the reader to find the right paint and coating system for a myriad of application needs. The course progresses from discussions of universal underlying considerations - the principles of coating- then move on to address the different types of coatings. Each category includes the method or methods of application, areas of application, and the performance properties.

This 3-hr course material is based entirely on the US Army Corps of Engineers document EM 1110-2-3400, "Painting: New Construction and Maintenance" and covers Chapter 4; "Coating Types and Characteristics".

The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the reader will understand:

Intended Audience

This course is aimed at students, engineers, designers, maintenance managers, H &S professionals, supervisors, shop foremen, technical and sales representatives and anyone who wants a basic understanding of surface coatings.


Course Introduction

Many factors must be taken into account when selecting the material of construction of a component for a particular application. Such factors include physical and mechanical properties, workability, corrosion resistance, and cost. Many alloys have been developed to resist corrosion; however, the use of these materials may not be practical from the standpoint of cost, based on the specific application. Using paints or other coating materials, less-expensive materials having the requisite physical and mechanical properties can be employed.

There are different types of coatings each having different function and application.

1) Wood stain is a product very similar to paint, except that it is much thinner, and formulated so that the pigment penetrates the surface rather than remaining in a film on top of the surface. Stain is predominantly pigment or dye and solvent (with little or no binder), designed primarily to add color without providing a surface coating.

2) Varnish and shellac provide a protective coating without changing the color. They are essentially coatings without pigment. Unlike paint, which is opaque, varnish and shellac are clear or translucent.

3) Lacquer is usually a fast-drying solvent-based paint or varnish that produces an especially hard, durable finish.

4) An enamel coating is a coating that dries to an especially hard, usually glossy, finish. Enamel can be made by adding varnish to oil-based paint.

In this course, you will learn about the coating types and characteristics.



Course Content

In this course, you are required to study US Army Corps of Engineers document EM 1110-2-3400, "Painting: New Construction and Maintenance":

EM 1110-2-3400, "Painting: New Construction and Maintenance" - Chapter 4 "Coating Types and Characteristics"


You need to open or download above document to study this course.

Course Summary

All coatings - whether used for corrosion protection, to provide good aesthetics or a pleasing appearance or for any other purpose will contain a film forming material called resin. When the resin contains pigments, it is called a binder because it binds the pigment particles together and to the substrate over which it has been applied. Pigments are used to add color to the coating and can also enhance the coating's resistance to heat, abrasion and acid. The solvent is present in the coating to make it liquid for ease of application. After application, the liquid coating solidifies, leaving the binder and pigment as a colored coating.

The chemicals selected to be used for the resin, pigment and solvent influence the properties of the coating. Most importantly, the selection of resin, pigment and solvent will influence how well the coating performs in its intended service environment. Physical integrity of the coating is as important as its chemical barrier properties in many applications. For instance, coatings on impellers that mix abrasive slurries can be abraded quickly; coatings on pipe joints will cold-flow away from a loaded area, if the creep rate is not low; and coatings on flanges and support brackets can be chipped or penetrated during assembly if impact strength is inadequate. Selecting the best coating for an application requires evaluating all effects of the specific environment, including thermal and mechanical conditions. Depending on the type of binder, this hardening may be a result of processes such as curing (in the form of oxidation or cross linking).

Alkyds are the most widely used industrial protective coating by virtue of their ease of application, relatively low cost, color stability and good weather ability in most atmospheric environments. Unmodified alkyds are generally considered unsuitable for chemical exposure applications or on the application on alkaline substrates (concrete) or water immersion services. Modification of alkyds improves the performance characteristics.

The other common binders include epoxy resins Epichlorhydrin [C4H6OCl] and bisphenol-A [C6H5OH]2C3H6] that are commonly derived from monomers used in the condensation reaction. The advantages of these are they improve hardness, impact and abrasion resistance; adhesion, gloss and water resistance. The disadvantages are slow curing and minimum application temperature [>5ºC].

The common urethane resins Isocynate [R-N=C=O] and Polyol [HO-R-OH]; commonly derived from monomers used in the condensation reaction. The advantages of these are similar to epoxy plus UV resistance, color and gloss retention. The disadvantages are cost and toxicity of Isocyanate.

Vinyl coatings are applied as solvent deposited aqueous or organic solutions containing a copolymer of polyvinyl chloride [PVC] and polyvinyl acetate [PVA]. Individual monomers are not used because PVC is inert and insoluble in most solvents and PVA contains a pendant ester group which is susceptible to solvent attack.

Pigments are usually insoluble powders and are used both to provide color, and to make coating opaque, thus protecting the substrate from the harmful effects of ultraviolet light while also increasing coating's hiding power. The most common pigment used today is a mixture of titanium white and zinc oxide (zinc white). The white pigment does not add color, but serves the very important function of increasing opacity and making the coating resistant to UV radiation.

The additives that can be used to accelerate auto-oxidative cross linking in unsaturated polymers are cobalt and manganese or lead napthenates/octanates. The additives that can be used to slow down the cross linking are zinc oxide and lead-containing pigments.

Zinc rich coatings are both organic and inorganic form. The advantages of organic zinc-rich coatings are longer service. The disadvantages are less tolerant of surface preparation, more difficult to apply, upper temperature limits. The advantages of inorganic zinc-rich coatings are elevated temperature service, abrasion and impact resistance. The disadvantages are shorter service life, cracking in thicker applications.

Environmental regulations and safety concerns have had a large influence on the coatings industry in recent years. Legislation limiting the amount of volatile organic compounds (VOC's) in paint has required coating manufacturers to reformulate their coatings to meet environmental regulations. Additionally, the safety concerns associate with such toxic materials as lead and chromate has continuously challenged manufacturers to formulate high-performance coatings using alternative materials.

Selection of the most appropriate coatings is not always straightforward, and the equipment manufacturer or material specialist should be consulted if in any doubt.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.