Materials Scientist Explains Development Process Behind 3D Printing Resin Colors

If you’re interested in using a 3D printer as a production tool at work, and not just as a potentially frustrating but ultimately awesome hobby, you want the best, right?  It’s important to remember that a great 3D printer is only as good as the parts it can produce, which in turn are only as good as the material and its properties. Formlabs knows a thing or two about 3D printing materials: it employs an in-house team of materials scientists that work on creating reliable materials, for multiple industries, to use with its Form 2 3D printer.

In 2016 alone, Formlabs introduced its biocompatible Dental SG resin, announced an updated formula for its Castable Resin, developed two new resins perfect for engineering applications, debuted its Form X experimental product platform and Ceramic Resin, and just today introduced more dental 3D printing materials. In late 2015, Formlabs added its polypropylene-like Durable Resin to its Engineering Materials library, but once it was finally released to the market a few months ago, the color had changed from yellow to frosted clear. Formlabs materials scientist Alex McCarthy recently addressed this color change, and discussed the science behind 3D printing materials and colors, in a Formlabs blog post.

“At trade shows and online, we frequently hear questions about the color of our 3D printing resins,” McCarthy explained. “Why did the color of Durable change during reformulation? What colors are available? Why is this resin that color?”

Durable Resin’s color before and after reformulation

McCarthy explained that they can spend months working with clear liquids when developing new resins, experimenting with various component samples to fine-tune the properties, before ordering the optimal formulation and deciding the final opacity and color. Opaque materials allow people to easily see the print’s details, and the color is pretty consistent from model to model. But, internal features are easier to see when using transparent resins, which are less complicated to develop and good for applications like microfluidics.

A big challenge when adding pigment particles to materials is keeping them from settling, so users won’t have to mix the material first. Additives will prevent clumping, but since every resin is made up of a different chemistry, different additives are used for every Formlabs material. Once the opacity and color are decided, there are five key factors that Formlabs’ materials scientists have to keep in mind when they’re developing a resin’s appearance:

• Resin Stability
• Mechanical Properties
• Application Friendliness
• Repeatability from Past Components
• Cohesive, Differentiated Library

McCarthy notes that the stability of a resin is their first priority during development. Each formulation of a resin base has a specific color, due to its components, so when the scientists start to determine a material’s outward appearance, they will always choose the color with the most stable formulation, even if it’s not the same as its natural base material color. But, the material development doesn’t always stop just because they have “achieved the desired properties.”

Materials Scientist Alex McCarthy [Image: Formlabs via Facebook]

“In the case of the original version of Durable Resin, our formulation included a component that gave the material a yellow hue,” explained McCarthy. “Given the option of adding more pigments to make it black or dark grey to cover that tint, or going with yellow, we decided to own the yellow color and add white pigment to make the resin opaque. Staying close to the original color allowed us to optimize for stability.”

Most of the time, though, it’s more important to focus on the mechanical properties of a resin. Lots of Formlabs’ resins are developed for specific purposes; for example, the Durable and High Temp resins are both part of the Engineering materials family. Obviously, the most important component of the High Temp Resin is its heat resistance.

McCarthy said, “We were concerned that unreacted components in pigments might not withstand high temperatures. We didn’t add any colorants so we could squeeze just a little more heat resistance from the formulation.”

For the first version of the Castable Resin, a less opaque material was used to make print details more visible, since its main application was jewelry. But after additional testing, a second, opaque Castable version was released, to ensure that the pigments did not impact the material’s functionality in a negative manner.

The scientists also consider how people will use the material, and what color would be most appropriate for its applications. The first version of the Flexible Resin was clear, but once the scientists considered what it was being used to model, the second formulation was a dark, opaque grey color, so it resembled rubber.

Flexible Resin is dark grey in color to emulate the rubber parts it’s used to model.

As mentioned previously, each color needs different additives, in order to stabilize the resins. But that doesn’t mean that, in order to speed up release and be positive about a material’s stability, they can’t use the same pigments more than once. The blue pigment used to formulate the Castable Resin was used again for the Tough Resin, with just a little black added in, meaning that the scientists could focus more of their attention on the mechanical properties and less on determining how stable the blue pigment was.

McCarthy has clearly explained that the chosen colors for Formlabs’ resin library are not about aesthetics as much as they are there to help differentiate between functions and materials. But they still keep the overall look in mind while testing materials, and ask themselves if it looks like it fits with the overall library.

“We also need to consider differentiation within our library,” McCarthy said. “Even when we’re re-using the same pigments for different materials for stability’s sake, we need to ensure that the materials are differentiated enough both as a liquid in the tank and in final parts to prevent mixups, since many of our users stock multiple materials.”

Formlabs also offers tutorials on painting and priming, if you’d like to use a color not currently in the resin library to finish a part. Discuss in the Resin Development forum at 3DPB.com.