This image was created with artificial intelligence – marked under Art. 50 of the AI Act, Regulation (EU) 2024/1689. It is a placeholder until the company's photos arrive.How are engineering plastics coloured?
How are engineering plastics coloured? Methods such as masterbatch, compounding and the best pigments for stable, uniform colours.
The importance of colouring engineering plastics
Engineering plastics are used in a wide range of industries – from the automotive industry to medical technology. Not only the functionality of the materials plays a role here, but also their visual design. Colouring plastics therefore fulfils far more than an aesthetic purpose: colours serve for identification, safety, brand building or the visual differentiation of different components.
Particularly in the case of the industrial identification of thermoplastics, different colours can, for example, visually distinguish material variants, functional areas or component groups from one another.
In order to achieve consistent colour quality, UV resistance and compatibility with the respective material when colouring plastics, colouring processes and pigments for plastics must be selected to suit the application.
Processes for colouring plastics
Engineering plastics can be coloured in different ways. Which process is suitable depends, among other things, on the plastic, the desired colour, the quantity and the requirements for colour consistency and processing.
1. Masterbatch process
A masterbatch – often also referred to as a colour batch for plastic – is a concentrated preparation of colourants and a suitable carrier material. The colour granulate is added to the plastic in metered quantities during processing.
Masterbatches are used, among other things, in injection moulding, blow moulding and extrusion. Their advantages include good meterability, reproducible colour results and high process reliability.
Anyone looking for plastic colour granulate therefore often means a colour masterbatch that is specifically matched to the plastic to be processed.
2. Direct pigmentation (dry blending)
In this method, colour pigments are mixed directly with the plastic granulate. Direct pigmentation can be economical, but places higher demands on an even distribution of the pigments.
An insufficient mix can cause colour differences or uneven colouring. The process is therefore suitable above all for applications in which suitable metering and mixing technology is available.
3. Liquid colour
Liquid colours consist of colourants that are dispersed in a liquid carrier system. They are added in a controlled manner before or during plastic processing.
With suitable metering technology, even small amounts of colourant can be distributed evenly. However, storage, metering and process control must be matched to the colour system used.
4. Compounding
In compounding, pigments are incorporated into the plastic in a controlled manner together with other additives. As a result, colour and material properties can be specifically matched to the later application already during the production of the compound.
The process offers a high degree of control over the formulation and is particularly suitable for technical applications with defined requirements for colour, resistance and material properties.
Further information on the function of stabilisers, flame retardants, pigments and other additives can be found in our article on additives for plastics.
Selecting pigments for plastics correctly
When colouring plastics, the choice of colourants depends on the desired colour depth, the processing temperature, the later operating conditions and the respective polymer.
A fundamental distinction is made between dyes and pigments. Dyes dissolve in the respective medium, while pigments are present as insoluble colourants. Pigments play a particularly important role in the colouring of plastics.
Typical groups are:
- Organic pigments: enable intense and brilliant colour tones. Temperature, light and UV resistance depend strongly on the respective pigment.
- Inorganic pigments: often offer high thermal and chemical stability.
- Effect pigments: produce, for example, metallic, pearlescent or other optical effects.
Also in the development of plastic pigments and individual colour formulations, compatibility with the base plastic must be taken into account. Pigments must not be selected solely on the basis of the desired colour tone. Processing temperature, UV exposure, chemical stress and other additives can also be relevant.
Colouring plastic black
Black is one of the particularly widespread colourings for engineering plastics. Carbon black is used, among other things, as a black pigment. In addition to colouring, carbon black can, depending on the formulation, also help to improve UV resistance, as it absorbs UV radiation.
However, whether a black colouring is suitable for an engineering plastic depends on the material and the requirements of the finished component. Colourants and concentration should therefore always be considered together with the other material properties.
Can plastic be coloured subsequently?
When considering the question of whether plastic can be coloured subsequently, a distinction must be made between colouring the entire material and subsequently modifying the surface.
Masterbatch, direct pigmentation, liquid colour and compounding colour the plastic during or before its shaping. The colourant is incorporated into the material in the process.
If a component has already been produced, this complete colouring of the material cannot simply be carried out afterwards. A subsequent colour change instead takes place via suitable surface processes. Whether a coating or another surface treatment is possible depends strongly on the respective plastic.
Factors influencing the colour result
The colour result in the colouring of engineering plastics is influenced by various factors. A central aspect is the plastic type, as polymers differ with regard to their inherent colour, processing temperature and interaction with colourants.
The processing parameters such as temperature, pressure and shear stress also influence how evenly the colour pigments are distributed in the plastic. Excessively high processing temperatures can impair unsuitable pigments or dyes.
A further factor is the use of additives. Reinforcing materials, stabilisers or flame retardants can influence the visual appearance and the interaction between colourants and polymer.
The later operating conditions also play a role. UV radiation, moisture, temperature or aggressive media can cause colour changes in the long term. For technical applications, colourants should therefore be used whose properties match the plastic and the intended operating conditions.
In practice, tests with different formulations and processing parameters can be useful in order to achieve a reproducible colour result.
Comparison of the processes for colouring plastic
| Process | Advantages | Possible disadvantages | Typical areas of application |
|---|---|---|---|
| Masterbatch | Good meterability, reproducible colouring, simple handling | Different variants must be kept in stock | Injection moulding, extrusion, blow moulding |
| Direct pigmentation | Direct use of pigments, flexible formulations | Even distribution more demanding | Suitable mixing and processing processes |
| Liquid colour | Good meterability, flexible colouring | Additional metering and handling technology required | Industrial plastics processing |
| Compounding | Precise formulation setting, combination with additives possible | Additional production step | Technical and application-specific compounds |
Which method is suitable for colouring plastic?
Which method is suitable for colouring plastic cannot be determined solely on the basis of the desired colour tone. Decisive factors include the type of polymer, the processing temperature, the production process, the quantity and the requirements for UV, temperature and chemical resistance.
For reproducible industrial plastic colouring, colourants and processes should therefore be selected together with the material and process requirements.
Frequently asked questions about colouring plastics
Which pigments are suitable for plastics?
That depends on the plastic, the processing temperature, the desired colour and the later operating conditions. Organic, inorganic and effect pigments have different properties and must be compatible with the respective polymer.
What is a colour batch for plastic?
A colour batch or colour masterbatch is a concentrated colourant preparation in a carrier material. It is added to the base material during plastics processing and enables controlled colouring.
Can plastic be coloured subsequently?
A plastic component that has already been produced can normally no longer be coloured all the way through as in the case of colouring during processing. Depending on the plastic, however, suitable processes for subsequent surface colouring are possible.
What is the difference between pigments and dyes?
Pigments are colourants that are insoluble in the respective medium, while dyes are soluble. Which variant is suitable for a plastic depends, among other things, on the material, processing and the desired colour result.
Can plastic be coloured?
Yes. Colloquially, people often speak of "colouring plastic". In industrial plastics processing, colouring is carried out, for example, with masterbatches, pigments, liquid colours or compounds that are already coloured.
The right colouring for engineering plastics
The colouring of engineering plastics combines visual requirements with material and process properties. A suitable colour tone alone is therefore not enough. Pigment or colour system, base plastic, processing and later operating conditions must be matched to one another.
In this way, engineering plastics can not only be designed in terms of colour, but also reliably identified and clearly differentiated for different applications.