Maya Ellison
Plastic is a versatile material with a wide range of applications, from shopping bags to engineering components. The appearance of plastic is an important consideration in product design and manufacturing, with color being a key factor. While plastics are often associated with bright, vibrant colors, non-colored or natural plastics also have their own unique appearance. The natural color of plastic varies depending on the type of plastic and can range from white to light tan. In some cases, the natural color of plastic is altered to achieve a specific finish or to meet functional requirements. Understanding the natural appearance of plastics and the process of incorporating color is essential for designers, manufacturers, and consumers alike.
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What You'll Learn
Natural plastics are white, light tan or grey
Natural plastics are white, light tan, or grey. The colour of plastic is determined by the raw materials used and the manufacturing process. For instance, natural acetal, ABS, polypropylene, and polyethylene plastics are white, while natural nylon appears light tan.
The colour of plastic is an important consideration in the manufacturing process. Coloured plastic can be achieved through the addition of colourants or by allowing the plastic to retain its natural colour. In some cases, the colour of plastic is chosen for aesthetic reasons, while in other cases, it may be selected for functional purposes, such as providing a visual cue to distinguish between different parts or creating contrast against a specific background.
Additionally, the colour of plastic can impact its properties and behaviour. For example, the interaction between polycarbonate and titanium dioxide, a common ingredient in white colourants, can lead to rapid degradation when exposed to high temperatures.
Furthermore, plastic's colour can change over time due to various factors. Discolouration can occur due to UV exposure from sunlight or artificial light sources, resulting in non-uniform changes in colour. This phenomenon is commonly observed in vintage plastic items, where yellowing or browning can take place.
The process of colouring plastic involves scientific complexities that require careful consideration. The viscosity of the colourant, for instance, can significantly impact the final product. Additionally, the long-term objective of many industries is to achieve the desired finish and durability by incorporating colour directly into the polymer rather than relying solely on painting or surface treatments.
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Black non-appearance plastic parts are common
In some cases, there is a good reason for specifying the natural colour, such as providing a simple visual cue for identifying two different parts that may otherwise look identical. Using natural plastic can also provide a contrast against a dark background for poke-yoke vision systems. However, based on the experience of AGS Technology, Inc., this line of reasoning seems to be the exception rather than the rule.
The primary reason why black non-appearance plastic parts are more common than natural plastic parts is that natural, virgin materials often cost less than their black, virgin counterparts. In the virgin resin world, plastic materials come out of the polymerization reactor in their respective natural colours. To make virgin materials black, an additional manufacturing step is required, which adds cost.
In the recycled plastic world, the bulk of recovered post-industrial and post-consumer scrap materials have already been pre-coloured. Black colour concentrate is added to these multi-coloured feedstocks to end up with a consistent-looking material. Interestingly, customers have shown the greatest resistance to converting from virgin, natural resin to an AGS Injectoblend recycled alternative when the new colour is black. This may be because there is a perception that there must have been an engineering basis for the original colour.
Despite its prevalence, black plastic has been labelled as "bad news" by some commentators. Black plastic makes up 15% of all plastic recyclables, but the vast majority is not recycled because the technology used by recycling facilities to sort plastics relies on infrared light, which carbon black absorbs, so the facilities cannot "see" the colour black. As a result, most black plastic items end up in landfills, incinerators, or littered in the environment after just a single use.
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Coloring plastics is a complex science
The process of creating resin colour is a complex science that the plastics industry has been working to improve since its inception. Coloured plastics are used in a multitude of industries and applications, but few know how manufacturers achieve different hues.
Firstly, it's important to note that the colourant chemistry must be able to survive the temperatures at which the material will be processed. For example, a colourant used for polyethylene or polypropylene may be unsuitable for polycarbonate or polysulfone due to the higher temperatures required for processing.
Secondly, there should be no chemical incompatibility between the polymer and the colourant system. Chemical reactions occur more rapidly at higher temperatures, and the injection moulding process involves significantly elevated temperatures. Therefore, any negative chemical interactions between the polymer and colourant will occur very rapidly during processing.
Thirdly, attention to detail is crucial in producing a coloured plastic that fits the customer's needs. There are many methods for resin colouring, and careful consideration of the client's needs is essential to choosing the appropriate approach. For example, pre-coloured resins are often used by processors who lack experience handling custom colour matches, as they offer ease of use and fast-matching performance rates.
Finally, the applications of colouring plastic are not limited to enhancing a product's aesthetic features. Products that come into direct contact with food, such as storage containers, cutlery, and dishes, must be designed in alignment with stringent FCS (food contact substances) regulations.
In conclusion, colouring plastics is indeed a complex science that requires a deep understanding of chemistry, materials science, and processing technologies.
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Titanium dioxide is a common white colorant
Natural plastics like acetal, ABS, polypropylene, and polyethylene are white in colour, while natural nylon appears light tan. However, the majority of non-appearance functional plastic parts are black. This is because black colour concentrate is added to the recovered post-industrial and post-consumer scrap materials to create a consistent look.
Titanium dioxide (TiO2) is a common white colourant used extensively in plastics and other applications. It is a synthetically produced white pigment manufactured from naturally occurring ores. It is derived from titanium and has the chemical formula TiO2. When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insoluble in water.
TiO2 is used as a pigment to provide whiteness and opacity to products such as paints, coatings, plastics, papers, inks, foods, supplements, medicines, and toothpastes. It is also used in sunscreen and cosmetics. In foods, it is commonly found in ice creams, chocolates, candies, creamers, marshmallows, chewing gum, pastries, dressings, cakes, and some cheeses.
As of 2024, the US FDA considers titanium dioxide safe for human consumption as long as it is 1% or less of the total food composition. However, the EU EFSA banned the use of titanium dioxide in food in 2021 due to concerns about its potential genotoxicity.
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UV light causes plastic discoloration
Non-coloured plastics, also known as virgin plastics, are those that have not been altered from their natural state. These plastics can vary in colour depending on their chemical composition. For example, natural acetal, ABS, polypropylene, and polyethylene are white, while natural nylon appears light tan.
Now, let's turn our attention to the effects of UV light on plastics. Prolonged exposure to UV light or ultraviolet radiation from sunlight can cause plastic to discolour and turn yellow. This process is known as photodegradation, where the UV light initiates and accelerates a chemical reaction in the polymers, causing them to break down and form shorter, yellow-coloured chains. While yellowing can occur even in the absence of light, UV rays significantly expedite this process.
The impact of UV light on plastics can vary depending on the type of plastic and the intensity and duration of exposure. Automotive parts, for instance, are particularly vulnerable to UV damage. The effects of UV light are primarily observed on the surface layer of the material, and in some cases, it can lead to the failure of the entire component.
To mitigate the effects of UV light on plastics, it is advisable to keep plastic items away from direct sunlight and heat. While yellowing cannot be entirely prevented, taking such precautions can significantly slow down the process. Additionally, storing plastic items in boxes or cupboards can provide some protection from UV exposure.
It is worth noting that other factors, such as extreme temperatures, humidity, and exposure to pollutants, can also contribute to plastic discoloration. However, UV light plays a significant role in accelerating and exacerbating the yellowing process.
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Frequently asked questions
Non-coloured or 'virgin' plastics emerge from the polymerization reactor in their natural colour, which varies depending on the type of plastic. For example, natural acetal, ABS, polypropylene, and polyethylene are white, while natural nylon is light tan.
Coloured plastics are often used to achieve a desired finish and durability. Additionally, colouring can be used to differentiate between parts that may otherwise look identical, or to provide contrast against a dark background.
Yes, plastic can become discoloured over time due to factors such as UV exposure from sunlight or fluorescent lights. This can cause plastics to turn yellow or brown.
Yes, some plastics like acrylic and polycarbonate are known for their transparency and impact resistance.
Yes, plastic can be manufactured in a variety of colours, including fluorescent shades. However, the process of colouring plastic involves scientific complexities and potential negative interactions between colourants and the base polymer.
