FT Archives

Roobol on Painting

July 2003 Q&A

For Young Readers

I am doing my senior year (grade 12) Chemistry ISU on the synthesis of paint and I have a few questions. Are there many very different processes for the manufacturing of different paints, or are there a few basic steps that are common to most processes? I ask because I am debating whether to select a general paint type (e.g., craft paint, spray paint, etc.) or whether I should do the project on the synthesis of all paints. Do you have any specific Web sites, contacts or books that would be useful? Is there any place where I could find out the reasons that different paints dry at different rates, have different textures, have different reflectivity and other such properties?

The simplest of paints consist of pigment and binder, plus perhaps a little solvent. Pigment is what gives color to paint; in its raw form, it is a fine powder. Binder is what holds the pigment and enables paint adhesion on a surface. The pigment particles are insoluble and merely form a suspension in the binder. There are a great many pigments as well as a great number of binders for pigments. It is the binder resins that give us the many different types of paint, such as oil, acrylic and epoxy. Each chemical resin binder imparts a unique quality and cures in an individual manner, either by one of many types of chemical reaction, or simply by evaporation of the solvent.

“Synthesis” is not the correct term for what you are referencing. Instead, the terms “paint making,” “paint production” or “paint manufacturing” are used. Most liquid paints are made by the same general process of carefully blending together the proper proportions of the select ingredients in that particular paint formula. No chemical synthesis is done in paint making, although paint resin production may involve chemical synthesis procedures. Powder paints are made by a different but still rather similar technique.

I don’t know what books are available to you, so I hesitate to list reference items. Instead, I suggest you look up the terms I’ve given you in a municipal or college library, and you will find ample material for your work. Don’t overlook various encyclopedias as information sources.

Quality Assurance and Mil Thickness

I am involved with quality assurance for an aluminum boat builder. We currently utilize concept topcoats over a wash primer with zinc chromate. The primer is applied at 0.3 to 0.5 mil, and the topcoat we paint at 2.0 to 2.5 mils. Now, my questions are: Are the mil specs appropriate to protect the primer? Are there places to find such parameters? What are the recommended in-house tests to be performed to ensure a quality finish? Any thoughts would be appreciated.

First, it is confusing when you use the term “mil specs” because, to most people, that means “military specifications.” But I understand that you mean to ask about mil thickness.

The phosphoric acid in the wash primer is used to chemically react with the aluminum and thereby provide adhesion for the topcoat, which otherwise would not adhere well to the bare aluminum. Because applying too much wash primer would leave unreacted acid that adversely affects adhesion, it is always recommended that no more than 0.3 to 0.5 mil dry film thickness be used. The wash primer also provides a degree of corrosion resistance to aluminum, since zinc chromate is a strong corrosion inhibitor. The amount of topcoat listed is satisfactory for the aluminum boat. While there are no special references for information on what total topcoat thickness might be required (since there are thousands of different topcoats and wide variations in field conditions), the paint supplier can give you the thickness range they advise, knowing the usage conditions generally experienced by your boats.

Quality-assurance testing on the painted product is a topic that takes far more space than can be accommodated here, so you may wish to consult my book, Industrial Painting & Powder Coating, Principles and Practices. The 3rd edition should be available now. If not, you can get the 2nd edition by phoning Hanser Gardner Publishing at 800-959-8977.