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This article explores the different types of common plastics and materials that require coating, the typical issues faced, and the various types of pretreatments required for successful results. There are many types of plastic to consider, and this article will discuss the differing approaches needed to achieve adhesion to the chosen substrate.
One common description of plastic is "a polymeric material that has the capability of being moulded or shaped, usually by the application of heat and pressure". The word plastic was first used in the English language in the 1630s as an adjective meaning "capable of shaping or moulding a mass of matter" from the Latin plasticus, and from the Greek plastikos meaning to"grow"orlorm". The word evolved from its adjective meaning and started to be used as a noun in the early 20th century, and used in this sense to describe Bakelite, commonly considered as the world's first entirely synthetic plastic.
The plastics industry has a long and rich history that dates back further than you may think; the Horners Company of London were first mentioned in 1284 with horn and tortoiseshell considered as natural plastics, used to produce all manner of products from combs to piano keys and billiard balls. By the middle of the 19th century, some animal-derived materials were in short supply leading to species, such as turtles and elephants, facing extinction due to increasing demand for tortoiseshell and ivory. Industrialists realised the scale of this environmental and economic problem and set about inventing new semi-synthetic materials based on chemically modified natural substances, such as cork, milk and even blood.
Semi-synthetic materials made way to fully man-made materials, such as Bakelite, invented in 1907 by Belgian chemist Leo Baekeland. In 1920 Hermann Staudinger proved the existence of polymers, in doing so creating a new industrial field of chemistry. Now, the term polymer can be used to describe any plastic and other naturally occurring organic compounds, such as DNA.
In the early decades of the 20th century, the chemical and petroleum industries began to form alliances, driven by the desire to make use of by-products created by processing crude oil and natural gas. Some of these companies are recognisable and supply the coatings industry today, such as BASF, Dow and DuPont. The post-war consumer boom, driven by affordable products made from differing plastics, also spurred development in this field, but discerning consumers also wanted decorative effects and functionality, so coatings would have to be used. Although many plastics are coloured by masterbatch additives or fully pigmented, there are many applications that require the use of coatings, but as will be explained many plastics can be difficult to coat successfully without a certain level of preparation. |
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An introduction to different plastics and approaches to coating them in SURFACE COATINGS INTERNATIONAL, Vol. 106.1 (01-02/2023)
