When you pull out the roller or the brush and start painting your home, the paint's ingredients and how it is made are likely the least of your concerns. Visions of your soon-to-be beautiful living room, bedroom, or kitchen run through your mind, not paint solvents, resins, and pigments being blended in a factory. Yet if you spend enough time painting, you might wonder why paint behaves the way it does. Far from being an esoteric subject remote from all practical applications, the manufacture and makeup of paint begin to take on a significance that applies to your own home.
The Basic Composition of Latex Paint
A gallon of freshly mixed paint in your perfect, chosen color can be a beautiful thing. Pop the lid with the can opener, swirl the paint with the wooden stick, and watch the paint slide off of the stick. Silky, rich, and imbued with vibrant color, the paint appears to be a homogeneous substance. But let that same paint rest for nine months in the basement and it tells a different story, revealing its true structure. On top is a liquid that veers toward clear and bears no resemblance to the representative color dot on the lid. Press the stick to the bottom and you will discover a thick, nearly impenetrable solid mass.
Latex paint, the most widely used paint in homes by do-it-yourself homeowners, is composed of solids and liquids. All paint specifications state how much of the paint is solids or liquids. For example, in one gallon of flat paint, 57-percent of the weight might be devoted to solids. For paint on the other end of the sheen spectrum—semi-gloss—solids' weight might drop to around 51-percent. Already it is evident how paint's make-up applies directly to your own walls. If you have ever wondered why flat or matte paint has a chalky texture, it's because of this: more solids.
Solvents are the liquid body of the paint, the vehicle that carries and dissolves the other ingredients. Water, often called the universal solvent, is used for latex paints. For oil-based paints, mineral turpentine is often used as the solvent. Solvents are the ingredient that account for paint drying time. For water-based latex paint, all of the water in the paint ends up on your wall, ceiling, or other work surface and must fully evaporate for the paint to cure. This is why humid and cold conditions adversely affect paint drying time and, at worst, cause the paint to fail.
If water helps keep the solids in water-based latex paint solvent, it is the resins that bind everything together and help the paint dry after it has been applied to the surface. For many latex paints, these resins come in the form of acrylic emulsion polymers.
Pigments give paint its color. Pigments initially come in powdered form. For example, white pigment is titanium dioxide, black pigment is carbon black, and oranges and yellows are derived from metallic salts. At the paint store when you see the color dispersion machine squirting colors into the paint base, those water-borne pigments are called colorants.
Additives are a loose collection of other ingredients that supplement the paint, mainly to improve its physical properties. Additives might be added to the paint to smooth out brush strokes, inhibit mold growth, promote faster drying, or help the paint to resist sag. It is also possible for the product user, after purchase of the paint, to introduce additives. Penetrol and Floetrol are the brand names of popular additives that smooth down brush marks.
The Process of Making Paint
- Measurement: Raw liquid and dry ingredients are portioned out by bulk weight.
- Mill base creation: Raw pigments are crushed and dispersed, creating a dry substance called the mill base.
- Letting down: In a process called the let-down, resins, solvents, and additives are prepared in a different vat.
- Combining: The mill base and let-down product are combined.
- Shipment to canning area: Prepared materials arrive at the canning section by truck. Liquid materials are piped into storage silos or tanks and dry materials are brought into the receiving area of a warehouse.
- Mixing: Materials are combined in tanks to create the paint.
- Labeling: Empty paint cans arrive in the factory and are run through machines that apply labels to them.
- Filling: Separate machines fill one-gallon paint cans and five-gallon paint cans.
- Palletizing: Cans are sealed up, boxed, and the boxes are placed on pallets for shipment.