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How to process Premium White and other 3D-printed resin parts to get non-sticky finished parts?

Liqcreate Premium White is an opaque white photopolymer with excellent UV-stability. 3D-printed parts from this material show no discoloration and stay perfectly white, even after long-term UV exposure. Liqcreate Premium White is easy to use on all open source LCD and DLP 3D-printers in the range of 385 – 420nm. This material has excellent properties like low shrinkage and low odor, which makes it ideal for the production of medical models, architectural scale models and miniatures. In some cases the parts feel sticky after post-processing. In this article we try to explain why a 3D-printed part can feel sticky and how to prevent this.

Premium white liqcreate white resin for LCD, MSLA, DLP SLA 3D-printers 3dprint 3dprinting material resins resina 3ddruck

 

Why are 3D-printed resin parts sometimes sticky?

One of the biggest differences between SLA-based 3D-printing in regard to other 3D-printing technologies is that a chemical reaction has to occur to create a layer. The reaction that occurs is a light induced polymerization of monomers. This specific chemical reaction is a very controlled reaction, leading to the high accuracy of which SLA is known for. However, one of its disadvantages is that the reaction is sensitive to oxygen, which means that an oxygen rich environment may disrupt the reaction.

When too many reactive particles are reacting with oxygen, a half-cured resin will be the end-result leaving a sticky or tacky surface. During a top-down SLA, DLP or MSLA / LCD printing process, the resin is cured on the bottom of the resin tank and there is not enough oxygen present to disrupt the process. However, oxygen is present during post-curing (in air), which will be the main cause of surface stickiness.

How to reduce stickiness of Premium White and generally all 3D-printed resin part?

There are a few methods to reduce stickiness of a resin 3D-printed part. It is best to follow them all if you are facing issues with sticky parts. The methods are based on:

  • – 3D-print process settings
  • – Washing process
  • – Post-curing process
  • – What not to do?

3D-Print process settings

The most important step to reduce stickiness, is to fine-tune your printing parameters. Check out our list of printers and parameters here. If you are over-curing or under-curing your part, the surface quality is poor and difficult to post-process it into tack-free parts. Under-curing leads to not completely formed layers giving a sticky surface. Over-curing leads to a softer outer surface, which is almost impossible to wash off and will leave a sticky surface. It is therefore important that the exposure, especially for highly opaque materials like Premium White, is spot on. Feel free to contact us at info@liqcreate.com if you are having difficulties in this step, or have any other questions.

 

Washing process

After getting a high quality 3D-printed object, the parts need to be cleaned and post-cured. Washing is an important step. The washing step ensures that all residual unreacted resin is washed off and can’t react with oxygen during post-curing. We advise to wash with IPA, Ethanol (preferably >85%) or the Liqcreate resin cleaner. Resin cleaner instructions can be found here. For Ethanol and IPA it is advisable to use 2 rinsing baths. One with used solvent and one with fresh solvent. Wash the parts preferably ultrasonic, and otherwise under agitation for 2 minutes in the used solution, followed by 3 minutes in the fresh Ethanol/IPA. The second rinse in fresh IPA/Ethanol will make sure no resin is left on the surface.

 

Post-curing process

After a part is washed properly, it should be UV post-cured. But is very important that before post-curing, the part should be completely dry. This can be done by putting it on a bench and wait 30 minutes, by (slightly) heating up the parts or by blowing with compressed air. The dry parts should already feel quite non-sticky and can be post-cured. Read this article to know more about the best UV post-curing parameters of a specific resin.

In the medical field, often a more professional method is used to eliminate oxygen during post processing and thus reduce stickiness of 3D-printed parts. Often the parts are post-cured in a Nitrogen chamber. This will result in completely non-sticky objects. For more difficult processable resins, like our Flexible-X, we would recommend to post-cure in an oxygen free atmosphere. This would be either in a Nitrogen chamber, or immersed in water or glycerol. Some companies aim to post-cure in a vacuum, which theoretically works by reducing the amount of oxygen in the chamber.

 

What not to do?

There are a few things that would definitely give sticky parts. The first step not to do is to rinse a part that is not completely clean with water. Water and resin won’t mix and give a dirty, sticky surface. Next to water, post-curing not completely clean or dry parts will also lead to  a sticky surface. Once a part is UV Post-cure, it is nearly impossible to get the sticky / tacky surface off. It is therefore advised to give a bit extra focus to the whole process to prevent printing parts again.

If there are still questions after reading this article, feel free to send us an email at info@liqcreate.com

 

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