For every product, quality functioning and aesthetics play an important role in public acceptance and eventual success. Coloring, a common form of measuring aesthetics, does this by attracting more people and increasing the chance of product success.
In plastic injection molding, coloring is important for the reasons mentioned above. However, there is also a need for color consistency due to products being mass-produced. Therefore, choosing the correct color for the plastic injection molded part can be a challenging step.
This article will show you the different techniques you can use to color your injection molded parts and tips for selecting the right color.
How To Custom Color Plastic Products
In injection molding, manufacturers can add colors to a plastic product before, during, and after the process. Both ways of coloring are suitable for coloring your products.
However, each one has its advantages and disadvantages, which aids selection. Below are the two categories of coloring plastic products and the methods under each category.
Coloring Plastic Products Before Injection Molding Process
Coloring plastic products can occur at the beginning of the injection molding process. It involves the use of methods such as Masterbatching, solvent coloring, compounding, etc. A detailed explanation is given below.
Masterbatching
A masterbatch is made by encapsulating a pigment or additive in a carrier material. The carrier material can be wax (universal carrier) or a resin that is compatible with the polymer to be colored. For example, injection molding specialists use EVA for nylon and polystyrene for ABS or polycarbonates.
The difference in the plastic polymer and the carrier can lead to the modification of the plastic’s properties. The carrier material on encapsulation undergoes cooling and is cut into the required shape.
Masterbatched colors are solid or liquid additives suitable for coloring raw plastic polymers. They are the suitable method for coloring plastic injection molded parts when other methods result in colorant clumping and insufficient dispersion.
A masterbatch is not ready for injection mold as-is. Instead, you should mix it with uncolored plastic polymers in a ratio of 2% color/volume.
Masterbatching is a common method in injection molding due to its stability, safety, clean production, and long shelf life.
Compounding
Compounded colors are made by blending pigment and raw materials before introducing them into the injection molding machine. Popular examples include the Pantone/RAL colors.
Compounding allows manufacturers to quickly get common colors and make custom colors at ease. While effective, the method is not a cost-effective method as a minimum order of a ton is required.
Solvent Coloring
This method is one of the easiest ways of coloring plastic parts made using injection molding. It involves spraying uncolored pellets with a solvent that contains the required color pigment. Like masterbatch, the ratio of the pigment to plastic must be 2% to get the best results.
Dry Pigment Mixing
Dry pigment mixing is similar to the previous methods. However, mixing occurs in the hopper of the injection molding machine. Here, the dry pigment powder is mixed with plastic pellets in a ratio of 2% by volume and introduced into the injection molding machine.
A major disadvantage of this method is the adherence of the dry pigment powder to the hopper walls and other plumbing. This dilutes the concentration, which makes it harder to get the ratio of dry pigment to plastic pellets.
It also makes maintenance and subsequent use harder as the adherence is hard to clean. In simple terms, there are many variables to consider that hinders getting the right color.
Post-Process/Surface Finishing
These are the most common methods for getting the right color for plastic parts, and it involves using several mechanisms to color or coat the injection molded part. Below are the top methods suitable for custom plastic parts:
Painting
Painting is the coloring method that puts the control in the hand of the operator making it an ideal method for multi-coloring. While you need to pay attention that some plastic materials like Nylon, POM, PTFE can’t be colored by painting. To paint an injection molded part, follow the steps below.
- Allow the plastic part to cool.
- Sand the surface to remove any imperfection.
- Prime the surface with a few thin coats of priming coat/spray.
- Add as many layers of coats of paint until you get what you want.
- Add a topcoat to protect the paint.
Painting is advantageous because it puts more control on the operator’s hand. However, it is a time and cost consuming process based on the number of steps, labor and materials needed. Also, the addition of many layer coats can affect the dimension.
Hydro Dipping
Also known as water transfer printing, this new method involves laying the desired color/pattern on the water together with an activator. The plastic part is then dipped in the container and the activator allows the pattern to adhere to the surface of the part. On removal, the part is allowed to dry.
Hydro dipping is the best method for pattern-coloring of plastic products. However, it requires special equipment and skill for correct coloring.
Dyeing
Dyeing is the most common method of coloring objects all around the world. Here, the plastic part is submerged in a container containing the required dye (care must be taken to ensure compatibility between the dye and the plastic parts).
It is a suitable method for plastic parts that are translucent with porous surfaces. The absorption of color by the part does not affect the dimension of the parts
Tips To Avoid Color Differences
Choosing a color for an injection molded part is not a straightforward process. There are many things you have to consider before choosing the right one. Below are a few tips to take to avoid color differences.
Using A Liquid or Solid Colorant
You should not just choose a liquid or solid colorant based on color only. Choosing any of them depends on the type of materials you are working with, as each is compatible with different types of plastics. Choosing also depends on the effect you desire.
On the one hand, liquid colorants are suitable for PET and PVC plastics, and they give translucent/semi-transparent effects which change based on concentrations. On the other hand, solid colorants are suitable for most materials and they give an opaquer look that changes based on the concentration.
Color Versus Appearance
Color and appearance are what a team in charge of injection molding should be able to discern and help you with. Appearance is a subjective term, i.e., it is different for everybody, and the team must be able to adjust the color in order to get what you want. This is important as describing your product’s appearance can be more important than the color.
Manage Your Acceptance Criteria
You should be able to review and manage the variation that can result in getting the wrong color. Having one hundred percent control of the color you will get is near impossible as factors such as temperature (both machine temperature and ambient temperature), operator, colorant formulation or concentration play roles in your product appearance.
Therefore, you should find a reliable injection molding manufacturer and be closely connected with them to review the samples before mass production.
Conclusion
Injection molding is a popular manufacturing process suitable for the mass production of plastics. In order to improve aesthetics and sometimes quality functioning, there might be a need for coloring.
Coloring in injection molding as a result of mass production requires color consistency, and here you can know several ways of coloring plastic parts.
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