Resin 3D printing is not a straightforward process. Instead of just clicking “print” and getting a finished object (as with many FDM 3D printing technologies), resin-printed objects need to undergo a sometimes extensive post-processing procedure to prepare it for use.
To correctly wash the resin 3D printed part, isopropyl alcohol (IPA) in concentrations of 90% or greater is typically required. IPA at that concentration, though, can become expensive because each 3D printed part requires at least some fresh solvent during the cleaning process in order to be effectively cleaned.
Fortunately, materials engineers have developed a clever solution to this problem. Water-washable resin is a novel, special type of resin that can be effectively cleaned using water as a solvent, eliminating the need to deal with a large volume of IPA or other solvents. In this article, we’ll explain how it’s different from normal resin.
What Is It?
First, what are water-washable resins and how do they compare to standard resins? Depending on the brand, resins can be wildly different. So, it’s helpful to be able to classify these two resin types before comparing them:
- Standard Resin is any 3D printing resin that does not have any special properties (i.e. flexible, biomedical, or castable) and is designed to be washed in isopropyl alcohol or another organic solvent after printing. These are the most commonly used 3D printing resins in today’s desktop 3D printing market, and they’re sold by virtually every 3D printing resin vendor.
- Water-washable resin is a more recent innovation that allows users to bathe the resin-printed parts in water or low concentrations of IPA to clean off excess resin. This type of resin was invented in 2016 but has since become widely used in desktop resin 3D printing.
Although the most significant difference is the type of solvent required to post-process prints made out of each resin, the difference in solvent has several important implications for the properties of the finished part and the maker’s quality of life.
Physical Properties
Resin formulations can be very different across resin manufacturers, even for the same type of resin. So, it’s difficult to make claims about general differences in material properties between water-washable and standard resins.
However, that doesn’t mean that the material properties of the resins are the same. Within the same brand, water-washable and standard resins will have different properties because of the different chemical compositions. This may impact tensile strength, flexural modulus, and available colors.
An example of this is Anycubic’s standard vs water-washable resin whose tensile strength is 36-45 and 30-45 MPa, respectively. With a higher flexural modulus range than the standard resin, Anycubic’s water-washable resin is more rigid, but differences like these should be taken on a case-by-case basis.
Printing & Post-Processing
Maybe or maybe not surprisingly, water-washable and standard resins print in exactly the same manner. Depending on the brand of resin (and therefore the chemical formulation), standard and water-washable resins will even have similar layer-curing times for the same model of 3D printer.
The big difference, as mentioned above, is the washing process that happens after the prints have been removed from the 3D printer’s build plate. Depending on the brand, the water-washable resin 3D print is submerged inside an aqueous solution of 0-10% IPA. Some brands of resin will require just a touch of IPA, whereas others are truly water washable and require absolutely no IPA to be cleaned of residual liquid resin.
With standard resin, the process is the same. Although, by definition, the solvent consists of between 90-99.9% IPA. Regardless of the resin type, the cleaning time is specified by the manufacturer.
After the washing process, even the final curing process is the exact same. Both standard and water-washable resin should be left under ultraviolet radiation – either in a curing station or in the sun – for an amount of time specified by the resin manufacturer.
Disposal
Regarding solvent disposal, it’s important to note that used cleaning water containing uncured resin cannot be discarded down the drain! It must be disposed of just like used IPA, which means placing it out in the sun and waiting for it to evaporate and leave behind residual resin, which can then be thrown away.
Another alternative is to dispose of the contaminated water according to your community’s local regulations regarding hazardous waste.
Price
Water-washable resin is typically slightly more expensive than its standard counterpart produced by the same resin manufacturer. Additionally, water-washable resins will typically come in different, and sometimes fewer, colors than standard resin.
For example, Sunlu’s standard resin is priced around $27 per kg and comes in eight colors, although you can find as many as 15 at some online retailers. Their water-washable resin will set you back about $31, and you have only 5 colors to choose from, though you can find 10 at Amazon.
The situation is similar to Anycubic’s offerings. Their standard resin costs about $20 and can be found in seven colors, while their water-washable resin is priced at $34 and comes in six colors.
Drawbacks
Water-washable resins will save you from the hassle of purchasing, spoiling, and disposing of more expensive organic solvents. Especially if you’re a hobbyist, water-washable resin is definitely a useful material to have on hand, as your household water tap can supply all of the solvent you’d ever need to use in order to clean your prints.
But, on the other hand, water-washable parts are incredibly susceptible to moisture and water damage. You’ll only want to use it for prints that will not come into contact with water.
Moreover, a big drawback of both water-washable and standard resins is that they’re brittle with water-washable being slightly more brittle than standard. Parts fracture like glass when applied stress exceeds the cured resin’s yield stress. There’s also the danger of residual resin inside hollow prints, which can cause cracks during post-curing.
If water-washable or standard resins don’t meet strength requirements for your models, the good news is that tons of other types of resins exist. Some are flexible, and some are even designed to be ABS-like. And if you’re struggling with achieving great-looking prints, check out our article Resin/SLA Printing Tips: How to Get Perfect Prints
Happy printing!
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