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How is Colour Used in Injection Moulding?

The Role of Colour in Injection Moulding

For some plastic parts, colour is a vital but often overlooked part of the injection moulding process.

While many parts do not have a colour requirement, for some parts the inclusion of colour in the manufacturing process is a crucial element of the component build.

Colour can greatly enhance a product by providing several aesthetic and functional benefits.

Colourful Building Blocks

For some parts, colour can also improve the marketability of a product, making it memorable and appealing. In addition, colour can also serve brand identity and competitor differentiation.

In this article, we will explore these issues in more detail, examining how the process is achieved. We will also ask why colour uniformity is so essential to the success of the operation.

Why Might Colour be Needed for Injection Moulded Parts?

Let’s look in more detail at why colour might be needed for some injection moulded parts:

Aesthetics: Injection moulding allows for a wide range of vibrant and attractive colours. This can make the final product more engaging and aesthetically pleasing to customers.

Branding: Colour can be used to align the injection moulded parts with a specific brand. By using corporate colours, products become easily recognisable and help to reinforce brand identity.

Differentiation: In industries where multiple manufacturers produce similar products, colour can play a crucial role in differentiating one product from another. It allows customers to quickly distinguish between different brands and models.

Safety and warning indications: Colours are frequently employed to convey safety-related information or warning signs on products. For example, injection moulded parts in medical devices may use specific colours to indicate different functions or to easily identify different parts during assembly.

Colourful Plastic Bottles

Product traceability: In certain industries, colour coding is used to track and identify products. By assigning specific colours to different products or manufacturing batches, it becomes easier to manage inventory, track defects, or perform quality control checks.

Functional purposes: Colour may serve a functional purpose. For example, specific colours may be used to minimise heat absorption or to indicate temperature-sensitive parts.

When is Colour Added in the Injection Moulding Process?

Colour can be added to parts during or after the injection moulding process.

During the injection moulding process, colorants can be mixed with the plastic material before it is melted and injected into the mould. This is called “in-mould colouring” or “colour compounding.” The colorants are typically in the form of pellets or granules. These can be pre-mixed with the plastic resin or introduced as a separate stream during the injection moulding process. The melted plastic with the colorants is then injected into the mould cavity, thus producing coloured parts.

Parts can also be coloured through various post-processing methods, including painting, coating, or applying surface treatments. These secondary operations are typically performed after the initial injection moulding process is completed.

The choice between adding colour during the injection moulding process or applying it afterwards depends on factors. These include cost, production volume, desired colour accuracy, and part complexity.

How is Colour Achieved in Injection Moulded Parts?

Colour is achieved in injection moulded parts through various methods, including:

Masterbatch: This is the most common method of adding colour to injection moulded parts. Masterbatch is a concentrated pigment or dye that is mixed with the base polymer material before the injection moulding process. The masterbatch is typically added in small quantities to achieve the desired colour. It disperses uniformly throughout the material during the moulding process, resulting in a consistent and even colour.

Colourful Make Up Products

Colour Compounding: In this method, specific colorants or dyes are mixed with the base polymer during the compounding stage. Colour compounding allows for greater control over the colour and can produce a wider range of shades and hues. It is often used when intricate or custom colour requirements are needed.

Liquid Colorant: Liquid colorants are mixtures of pigments or dyes dispersed in a liquid carrier. They are added directly into the injection moulding machine, either through the hopper or a separate dosing unit. Liquid colorants offer flexibility in colour selection and can be easily changed.

Dry Pigment: Dry pigments, in the form of powders or granules, can be added to the base polymer before the injection moulding process. The pigment particles are typically mixed with the polymer in a blender or mixer. Dry pigments are commonly used for large-scale production where consistent colour is required.

Regardless of the method used, it is essential to maintain proper colour consistency throughout the injection moulding process. This includes controlling factors like temperature, pressure, and residence time, which can affect the colour result. Additionally, colour testing and quality control measures are typically employed. These measures ensure the desired colour is achieved in the final moulded parts.

How is Colour Uniformity Achieved in Injection Moulding?

Colour uniformity is essential to the overall presentation of the final component or product. It can affect perceptions of product quality and customer satisfaction. It is also an essential element of upholding brand status and loyalty.

Colour uniformity in plastic injection moulding can be achieved using several techniques:

Material selection: Choosing a high quality colour masterbatch or pigment which is compatible with the base plastic resin. This ensures consistent colour distribution throughout the moulded part.

Mixing: Properly mixing the colorant or masterbatch with the base resin to achieve colour homogeneity. This can be done using specialised mixing equipment or by ensuring thorough dispersion during the melt phase.

Injection moulding process control: Maintaining consistent process parameters, including temperature, pressure, and injection speed, helps to ensure uniform colour distribution. Optimum processing conditions, including properly calibrated injection moulding machines, helps to prevent degradation of pigments or resin. This can also reduce defects and ensure colour uniformity.

Mould design: An optimised mould design can facilitate uniform flow of melted plastic. It will also minimise any visual blemishes or colour streaking. Consideration must be given to gate locations, cooling channels, and venting to ensure even filling of the mould cavity.

Plastic Polymer Granules with Cables

Material testing: Conducting regular material testing, including melt flow index (MFI) and colour dispersion analysis. This ensures that the colorant or masterbatch performs consistently. The testing helps to identify any variations in colour distribution.

Quality control: Implementing a robust quality control process. This includes regular inspections and colour matching checks to identify and rectify any problems with colour uniformity during production. This can involve visual checks as well as colour measurement using specialised instruments.

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