Posted by Paula Hynes | 8/6/15 9:30 PM 1 Comment

August is National Read-A Romance Month so we thought it would be fitting to repost this popular article on the art and science of coloring plastics in manufacturing.  Hope you enjoy this brief summer read.

50 Shades: Redux

How do you achieve just the right shade of grey in your plastic part?  It’s all in the masterbatch.  A masterbatch is a concentrated mixture of pigments and/or additives encapsulated during a heat process into a carrier resin*. The resulting product is used to color raw polymer materials and provide other desired characteristics to the final part such as UV light resistance, flame retardants, slip agents and anti-stat agents.

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We all know the importance color plays in our lives.  And for manufacturers, getting the color right is an integral part of product quality.   Unlike metal or other base materials, plastics lend themselves to a wide array of colors and additives.  They are used in everything from bottle caps to medical devices.  Each plastic application requires specific properties from the chosen polymer.

When is it better to use a masterbatch?

Masterbatching is widely used in high-volume applications.  It is economical and efficient; however it does require some special attention.  Different polymers have different melt rates and molecular weights. The masterbatch must be chemically compatible with the natural material base resin.  The masterbatch pellets should be similar in size to the base pellet to ensure they mix and melt homogeneously in the machine. The feed system that mixes the natural pellets with the masterbatch must be metered or calibrated property for color consistency.  The amount of the masterbatch required to achieve the correct color is called the let-down ratio and is generally between 2 to 5 lbs per 100 lbs of natural resin; making this coloration method the most economical solution for high-volume part producers.

Is masterbatching the only solution?

A masterbatch isn’t the only colorant option in plastic injection molding.  For many applications, a specific color match is required.  Due to some variations that can occur from one cycle to another, a pre-compounded resin may be the best option.  Pre-compounded materials are resins that have been heated and mixed with pigment then extruded.  If you are looking to maintain a specific corporate color, this may be the best choice.  Due to the higher cost, most companies choose this option for smaller production runs. 

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Other coloring options.

For larger generally thin-wall parts, some manufacturers use liquid colorants, and they seem to be growing in popularity.  This material requires a special liquid pump to disperse the color into the resin; however this system is very accurate and helps guarantee color consistency throughout processing and consistent color dispersion throughout the part. It is also often less expensive than other coloring methods, though color changes can be a bit messy.

Color can also be added in a dry powder form to the natural base resin.  Dry resins are most often used in small quantities or prototypes. These powder pigments lend themselves to creating special effects, like adding a pearlescent appearance to a part.  When using a powder form of pigment the product must be mixed homogeneously with the base resin.  Without proper dispersion, the final parts will have an inconsistent appearance.  Powder pigments are often used in rotational molding.

How many shades of grey did you say?

There are many ways to get the color you want in your plastic part.  Color technology in the plastics industry has become very complex.  In a race to meet consumer needs, suppliers are creating new innovative solutions.  Over 10 million tons of pigment  were sold worldwide in the last ten years and that is expected to triple by 2020.  As designers and engineers find advanced applications for plastic, the colorant industry will respond with better, brighter and more versatile products.

If you are planning a new project, be sure to partner with an injection molder who has worked with various resins and masterbatch applications. They will be able to help you get the highest quality part at a cost effective price.

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Topics: Plastic Injection Molding


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