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True colours
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Colour is a powerful marketing tool. So it is no surprise that, used strategically, colour sells. Yet as consumers we are notoriously fickle about colour - green is considered to be unlucky for some, while hospitals use it everywhere because they say it has a calming effect on patients. Smart marketers use colour to create brand awareness and maintain edge in highly competitive and fast-moving consumer and industrial markets.
Modern plastics come in a riot of colours, of every shade and hue imaginable. One of the best known authorities on colour is Pantone. Founded in 1963 by Lawrence Herbert in the US, the company provides a system that facilitates the selection of colour and the sharing of this information to reproduce any shade choice across a variety of industries. A special tool, the Pantone Plastics Color System, allows designers, manufacturers and suppliers to select, specify, control and manufacture hundreds of colours using a set of colour chips ranging from opaque to translucent.
Such an impressive array of colours was not always possible. Discovered in the mid-1800s plastics offer some unique properties, but originally colour was not a feature.
Alexander Parkes' cellulose nitrate material, first shown at the Crystal Palace International Exhibition in 1862, could be `made of the most brilliant colours', but was not.
Researchers generally agree that most material breakthroughs came in the early 1900s. In 1907 Leo Baekeland, a New York chemist, produced phenol formaldehyde, the first truly synthetic plastic, known today as Bakelite. Although famed for its `fishy' smell when hot, Bakelite was widely used for electrical fittings in the 1930s, but again these were not particularly colourful items.
Mouldings cast from phenol formaldehyde, made as rods and cut into usable objects such as napkin rings and toast racks, were normally amber coloured. In the UK, British Cyanide introduced a formaldehyde moulding powder that could be produced in white and hence various pale shades. Casein was also popular at this time and its ability to accept colours led to its use for coloured fountain pens and fashion buttons. In the 1940s walnut effect brown was still popular for radio sets although ivory, black, jade-green, bottle-green, red and some interesting mottled-effect colours were beginning to attract attention.
The period 1935 to 1945 witnessed the introduction of a whole raft of thermoplastic materials including PVC, PA, PE, PMMA and PS. Processing methods developed too and in the early 1950s the extrusion technique for film gave birth to the ‘polythene bag’ industry.
Colourful plastics as we know them today, however, did not really take off until after the war. Following the restrictions and privations of World War II, demand for brighter and more colourful accessories increased dramatically. The population craved bright cheerful clothing, kitchens, cars and domestic appliances. Plastics were popular because they could be converted into many forms and would accept virtually any colour.
Remember Formica - a laminated plastic widely used for worktops and offered in an amazing array of patterns? Not to be outdone, the ceramic industry adopted colourful plastics as a direct replacement for existing materials and American designer Russell Wright introduced melamine tableware in 1953.
Over the past 50 years the development of plastic materials, processing techniques and applications has continued virtually unabated. Blues and greens are always popular colours followed by yellows and reds after which come violet shades.
Despite the impact of all these colours, however, there is one surprising fact. Colours account for less than 10 per cent of pigment consumption worldwide and white is the most popular colour by a substantial margin, closely followed by black.
Pigments & dyes
Plastics are coloured by adding pigments or dyes. Pigments tend to be opaque and are virtually insoluble in plastics whereas dyes are generally transparent and soluble (in most plastics but not polyolefins). In general pigments are associated with a particle size range of ~0.01 to ~1 µm. Primary pigment particles obtained during production tend to mass together to form aggregates and subsequently agglomerates, the size and distribution of which are responsible for colour properties. Agglomerates have to be broken down (colour development), wetted by the base polymer and distributed homogeneously (dispersion).
Colouring with dyes involves dissolving the dyes in the polymer. In every case solubility depends on the host plastic and the processing conditions likely to be encountered.
Other factors that affect colour are the nature of the plastic and the temperature at which it is processed.
Most plastics can be coloured but thermosetting materials (e.g. phenolic) and high temperature (>260 °C) processing engineering thermoplastics (e.g. PPO), can alter the physical state of pigments, changing or even degrading their colours.
The most widely used white pigment in plastics is titanium dioxide. Other popular pigments for plastics are carbon black, iron oxide (Red 101), phthalocyanine blue (Blue 15), phthalocyanine green (Green 7), plus a number of organic complexes and heavy metal salts.
Consumption
Today the 700,000 t of plastic colorants consumed worldwide each year go to make up to 84m t of coloured plastic compound. Global plastic consumption in 2005 is estimated at 130m t.
It is enormously difficult to put a figure on the quantity of coloured plastics consumed in the UK. This is not too surprising because there are numerous global sources of natural polymer, dozens of pigment suppliers and about 50 masterbatch manufacturers in the UK delivering material into hundreds of trade moulders and in-house processors.
However, most material suppliers and processors agree that over 95 per cent of plastics are coloured and would amount to ca 5m t of coloured plastics consumed every year.
No doubt the digital world will ensure that we have millions of colours to choose from as well as the means to evaluate and translate them into ideas.
Plastic materials and processing technology will continue to deliver end products in any colour we like, although history tells us that the majority will probably be coloured black or white!
Coloured plastics can be supplied as ready-to-use compounds. Alternatively, processors - commonly injection and blow moulders, profile, film, fibre and sheet extruders - can purchase natural polymers and add colour during processing in their own plant by using pigments dispersed in a solid polymer carrier known as a masterbatch.
Masterbatch
Since their introduction in the 1960s masterbatches have steadily penetrated the traditional coloured compound market.
A masterbatch is a solid concentrate of colour and/or performance enhancing additives such as anti-static, UV stabiliser, metal deactivator, etc., that is added to a base polymer to impart these attributes. It is usually supplied in granular form, either as pellets similar in size to most polymers or as miniature pellets, known as micro granules. Alternatively, masterbatch can be delivered in 'rough cut' form - a mixture of small shreds and chunks.
Two main types are offered - polymer specific and universal. Polymer specific masterbatch is produced using the same base polymer group. Universal masterbatch employs a carrier system that is capable of carrying the high quantities of additives necessary to deliver the end use properties required as well as affording the essential compatibility required across a broad range of polymers.
Universal masterbatches are normally readily available from stock, in small quantities and are cost effective if used correctly. However, in terms of compatibility, they are a compromise and processing difficulties can arise with some materials and engineering polymers that may have to be pre-dried. They are not recommended for use at high dosage levels as the appearance or physical properties of the final product may be adversely affected.
Conversely, polymer specific masterbatch, which can be pre-dried with the host polymer, may be added at high loading without compatibility problems. However, only a limited range of colours is generally available and not all engineering polymers lend themselves to conversion to masterbatch.
Masterbatch formulations normally include:
- pigment - up to 65 per cent
- polymer carrier - 35 to 50 per cent
- dispersing aids (waxes/stearates etc) - up to 10 per cent
- inorganic filler
Manufacture
In simple terms masterbatch manufacture is a two-stage process: gathering the ingredients and then mixing them by applying heat and shear to produce an homogenised pellet. Generally high or low speed mixers are used to produce a pre-mix of the additives which is then compounded on roller mills, kneaders, single or twin screw extruders. Even distribution (dispersion) and development (breaking down) of the additives throughout the carrier are essential. This processing depends on several key elements: formulation, the quality of raw materials, mixing and the compounding plant. Finally, the mix is pelletised (die-face or strand cut) or ground.
Contact :
Tony Gaukroger
ColourTone Masterbatch Limited
Pant Glas Farm Industrial Estate
Newport Road
Bedwas
Gwent
NP1 8BJ
Telephone: 01222 888910
Fax: 01222 868487
Press enquiries:
Ian McMath
Copylines
Telephone: 01428 723211
Fax: 01428 722371
Email: ian.mcmath@btopenworld.com
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