There's no such thing as "latex paint"
“I can't use latex paint because I have a latex allergy.”
“Some water-based paint is acrylic, and some is latex.”
“Acrylic, vinyl and latex are all different compounds.”
These are all statements that have been spoken to me, and they are all false. Regarding the first one....of course I would never knowingly use a product my client is allergic to. But people with latex allergies are NOT allergic to latex paint.
These statements all reveal a misunderstanding about basic paint chemistry, and I hope this brief article clears these up.
What is latex paint?
In the paint industry, “Latex” (“emulsion” in the UK) is an umbrella term commonly used for a family of water-based coatings with synthetic polymer binders (paint most basically consists of a liquid vehicle, pigment and binders). These binders are typically acrylic or an acrylic-vinyl blend. “100% acrylic,” “styrene acrylic,” polyvinyl acetate (PVA), or vinyl acetate ethylene (VAE) are the most common types found in “latex paint.” Vinyl paints provide the weakest film and are the easiest to use, whereas 100% acrylic paints provide the strongest film and are the most difficult to use generally. There is a water-based type of paint that is stronger than 100% acrylic, which is a waterborne alkyd (sometimes called acrylic-alkyd hybrid, or simply a “Hybrid”), which is Dutch technology where alkyd (oil-based) resin particles are suspended in a water-based vehicle. But waterborne alkyd type paints are not considered latex paints since they are a hybrid.
So here's the million dollar question:
Latex paints contain no latex, so WHY are these paints called “latex?”
Latex is a clear, sometimes milky colored, fluid found in a few species of trees and some flowers in the poppy family. The rubber tree is the most noteworthy of these latex producing plants because latex from the rubber tree is the material that is processed into what we know as rubber. Many products we use on a daily basis contain latex. For example, latex gloves, rubber bands, balloons, adhesives and many shoe soles contain natural latex rubber. Truck tires tend to be made of natural rubber, whereas car tires tend to be made of synthetic rubber.
So why do we have natural rubber and synthetic rubber? World War II was the catalyst for the development of synthetic rubber. Nearly every war machine and piece of equipment, including small arms, contained rubber components. But by 1941 Germany had gained control of around 80% of the world's supply of latex, so with the rubber supply being depleted the Allied nations were pressed to create synthetic latex to continue the war effort. The Germans actually first attempted emulsion polymerization (the process used to produce synthetic latex) prior to the War, but were mostly unsuccessful at that time.
A so-called “chemical revolution” began when Styrene-Butadiene synthetic latex rubber (SBR) was developed, and was first put into production in 1943 by Firestone and Goodrich. This was the first synthetic latex rubber to be put into common use. Glidden was the first paint company to use SBR to create an architectural coating, called “SpredSatin,” in 1948, although another waterborne paint had already been commercially available. Sherwin-Williams had introduced “Kemtone” in 1941, whose binder used casein (milk protein), corn protein, rosin and a small amount of linseed oil in an emulsion with titanium dioxide (white pigment), chalk, clay and mica. Many painters in those days knew this paint as “distemper.”
So the answer to the question of why latex paint is called latex when it contains no latex is that when synthetic latex was developed, it was easier to continue to call things “latex” rather than call each one by its specific type of polymer made by emulsion of petrochemicals. Natural latex was used in some paints, particularly for exterior use, but most paints in this era were oil-based. In the 60's and 70's is when water-based “latex” paint took off because it was much preferable to apply paints that were fast drying and didn't require the use of solvent for cleanup. Painting became more accessible to the homeowner, which is a primary reason why the water-based paint manufacturing industry took off.
I hope this was a helpful explanation.