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How are spray paints cans produced? We found a nice video that shows the production process of spray paint at Montana Cans. This gives you a good overview of the steps that are taken in the factory of a manufacturer. If we look at the stages represented in Life Cycle Assessment, this video shows the birth of the spray can. It resembles the 'cradle to gate' of spray paint. This means the production phase to the point of the factory gate of the spray paint manufacturer.

In the following sections you can find information about the global production of spray paint. The second section handles the spray can and all relevant components and in the last section we dive into the spray paint itself.

  1. 01. Global production figures
  2. 02. Spray can components
  3. 03. Spray paint components

01. Global production figures

The worldwide aerosol production figures are staggering. Europe is the world's leading region in producing aerosol products. With over 5.3 billion aerosols produced in 2020. The USA is the second-largest producer with over 3.75 billion aerosols produced according to the FEA, the European Aerosol Federation. The paints and varnishes aerosol products represent a relatively small amount of this European total with 5.68%.

This means that in Europe roughly 284.000.000 spray paint cans are produced. So far we have not found out which share is related to graffiti spray paint. However, for the purpose of informing all artists using spray paint cans. This is a crazy amount of cans filled with paint, right?

In the following section we dive into how spray cans work and the main components it consist of. In the third section we dive into the details of the actual paint inside a can, called spray paint.

02. Spray can components

First, let's handle the can. The packaging of "the product" spray paint.

Spray cans are usually made from light-gauged or tin plated steel (cold-formed sheets) or aluminium. Roughly 75% of aerosol can are made from tin-plated steel. Aluminium accounts for roughly 25%. In general aerosol product aluminium is used for more expensive products.

Other important spray can components are: the valve, a dip tube and a pea [1].

Spray paint works the way it does because it's actually a combination of paint and a gas propellant. During the manufacturing process, the cans are first filled with paint and then injected with the gas propellant.

The valve is then crimped, making sure that the highly compressed compound stays within the confines of the can. Thus, the spray paint can is sealed with a valve that controls how the paint is dispensed.

The top of the valve holds the cap (button or actuator) which controls the shape of the spray. The cap is attached to the valve body. Which acts as a mixing chamber for the liquid paint concentrate and the propellant [1].

At the bottom of the valve a plastic tube (the dip tube) is attached that carries the paint upward from the bottom of the can. The pea is a small bead, used to mix the paint when shaken.

03. Spray paint components

We have found some basic information that gets us familiar with spray paint, its main components and information regarding the production of paint. The four main ingredients or components of spray paint are:

  1. Pigments
  2. Solvents
  3. Propellants
  4. Binders

The solvent is added to the paint as a liquid used to carry the components of the paint from its container, in aerosols the solvent is used to maintain the consistency of the paint as it is sprayed from the can. The solvent can either be water-based or a form of organic solvent. The binder is used within the liquid paint to enable the process of hardening and production of the hard film that remains when the solvent has evaporated. Solid particles make up the pigment that gives the paint its color and opacity. Finally, additives are added to a can of aerosol paint to increase certain properties of the paint, which can include storage time, application and production qualities [1,2,4].

Pigments

Pigments are used in spray paint to provide color and opacity.

"There are four basic types of pigments used in spray paint. White pigments such as titanium dioxide are used to scatter light and make the painted surface more opaque. Color pigments, as the name implies, provide color to the paint mixture. These include a variety of synthetic chemicals. Inert pigments are used as fillers that alter the film characteristics of the paint. Finally, functional pigments provide extra performance characteristics such as imparting protection from ultraviolet rays. Such as extenders which are larger pigment particles which are added to improve adhesion, strengthen the film and save the amount of binder that is used.

Pigments must be chosen carefully because they can also affect certain formulation characteristics such as viscosity. If the pigments are not properly dispersed they may agglomerate, that is they may come together to form larger clumps that will settle to the bottom of the container. When this occurs the pigments are not able to be separated into small enough particles to spray through the valve [2]".

A white color is mostly made possible by using the pigment titanium dioxide (TiO2), red originates from Iron Oxide (Fe2O3). A broad range of pigments that give a yellow color like: zinc, cadmium, bismuth and a few more. Blue pigments are mainly from: cobalt, azurite and complex sulphurs. More historical background information on pigments can be found Webexibits.org.

Solvents

"Solvents are the liquids that carry the rest of paint ingredients. While water is a good solvent for many materials, it is slow in drying and tends to cause corrosion in metal cans. Therefore, non-aqueous, quick drying solvents are used. Solvent selection can also affect the stability of the pigment dispersion.[2]."

Solvents are sometimes also called a thinner. Either an organic solvent or water is used to give viscosity to the paint and improve the application. Water based paints are replacing some paints that use volatile organic compounds (VOC's) such as the hydrocarbons which are harmful to the atmosphere. Don't worry we will explain VOC's in more detail here.

Propellants

"Propellants are gasses that force the paint out of the can by expanding rapidly when the valve is opened. Chlorofluorocarbon gasses (CFCs) were originally used as propellants but these were banned from use in 1978 because it was discovered that they deplete the ozone layer. Other gasses like butane and propane were used as replacements for CFCs.

These hydrocarbons are classified depending on the amount of pressure they create in the can. Butane 40, for example, is a mixture of butane and propane and has a vapor pressure of 40 psi per square inch. Hydrocarbon propellants were used as primary propellants until the 1980's when the California Air Resource Board determined that these chemicals contribute to smog. They passed regulations that limited the amount that could be used in spray paint. To solve these problems, a new class of propellants known as Hydrofluorocarbons (HFCs) where developed for use in aerosols [2]."

Binders

Binders are ingredients that provide a binding effect that holds the pigments together to create a dry film on the surface. A paints binder is the key ingredient that directly relates to a paints performance, including adhesion, wash-ability, scrub resistance, fade resistance or gloss retention [5]. Binders are made from polymers, often referred to as resin, the resin forms a matrix and holds the pigment in place.

Additives

Other ingredients are included in the formula to stabilize the pigment dispersion, to control pH and viscosity and to prevent corrosion in the can. They are called additives. The binder (resin) and solvent together are sometimes known as the vehicle. Depending on the type of paint and intended use, additives may include [4]:

  • Dispersants separate and stabilize pigment particles
  • Silicones improve weather resistance
  • Thixotropic agents give paints a jelly-like consistency that breaks down to a liquid when stirred or when a brush is dipped into it
  • Driers accelerate drying time
  • Anti-settling agents prevent pigment settling
  • Bactericides preserve water based paints in the can fungicides and algaecides and to protect exterior paint films against disfigurement from molds, algae and lichen.
References
  1. Howstuffworks
  2. MadeHow.com
  3. Homesteady
  4. The constituents of paint
  5. DunnEdwards - What's in your paint