Acrylic Resins

General

Acrylic resins are produced by the Addition Reaction route. The most common addition polymers are polymers such as polyethylene, polypropylene etc with their subsequent use in plastic bags and large plastic tanks, respectively. However, as these two types of polymers are basically insoluble in any solvent, they are of little use in surface coatings. On the other hand, polymers made in a similar manner from acrylic monomers find a wide range of applications in surface coatings, most notably because of their excellent resistance to sunlight and overall durability.

Acrylic types

Acrylic resins used in surface coatings can be divided into 3 groups, Thermoplastic, Room temperature cured, and Oven Cured

• Thermoplastic acrylic coatings dry by the loss of the solvent they contain. There is no other drying mechanism involved. As such, any coating based on thermoplastic acrylics can be removed by using the same, or similar, solvent contained in the original coating. Thus they are unsuitable for use in any application area in which they might come into contact with solvents.
• Room temperature cure acrylics are used in what are generally termed '2 pack paints' (aka '2K Paints'). The coating system comes in 2 packs, one, the acrylic paint, and a second, specialised, catalyst. An acrylic resin based paint is mixed with a specific quantity the catalyst just before use and sprayed onto the desired surface (application by roller is possible, in some instances, but fairly unusual).The initial stage of the drying process is simple solvent evaporation, the same as for thermoplastic acrylic resins. However, as the catalyst reacts with the acrylic resin at room temperature, a highly 'crosslinked' polymer network is formed producing a cured coating that is no longer soluble in the original solvent(s). The curing process produces polymers with enhanced properties, when compare to the thermoplastic acrylics, such as visual properties like gloss retention, together with improvements in the mechanical strength and coating durability
• Oven cured acrylics are used in what are generally termed 'stoving' (or baking) coatings. They are similar to the room temperature cure resins in that paints based on these acrylic resins also contain a catalyst, but one that only reacts with the acrylics polymer at high temperatures, generally from 120°C upwards, depending on the specific catalyst used. As the curing mechanism requires above ambient temperatures, the catalyst is often added to the coating by the paint manufacturer, rather than immediately before use. After a suitable 'flash-off' time, to allow the solvents to evaporate,the coating has to be 'baked' after it is applied to the required surface to ensure that the acrylic resin fully reacts with the catalyst. Similar to the room temperature cure acrylics, the reaction of the acrylic with the catalyst produces a more highly 'crosslinked' polymer that is impervious to the original solvents used in the coating manufacture and has enhanced properties, such as mechanical strength and durability, when compared to thermoplastic acrylics.

A synopsis of the different Acrylic types is presented in the following table:

In terms of 'Drying Speed', the focus is more on the 'surface drying', the time it takes for the surface to be 'dry to the touch', rather than the fully dried state, which can take a much longer time.

Chemistry

To be completed at a later date