For us, we simply attach a thin Teflon film to protect the silicone from contacting the resin directly so as to extend the lifetime of resin container. You might think that Teflon is a non-stick material. In general, it is true, but some cured resin materials can stick on the Teflon film firmly and are very hard to separate. The followings are the reasons why a cured layer could be hard to separate.

1. Some cured resin has a strong Van Der Waals’ force with Teflon. When the cured area is large, the separation force is high.
2. Over-cured resins tend to have a much higher adhesion to Teflon.
3. Hollowed model without vent holes could introduce tremendous suction force.
   
4. Bulk shrinkage in a tapered solid region could turn a flat layer into a bowl like shape that could also introduce tremendous suction force. A thin cone shape is more likely to happen. This phenomenon often happens when:
   • a. Material itself has a high native shrinkage
   • b. Fast curing ( < 1 second) due to strong light intensity or more photoinitiator concentration could introduce higher shrinkage for the same material
   • c. For a fast resin, low separation speed introduce more on-going curing after the light is turned off. Low separation height does not mix the resin near the curing area with fresh resin outside the curing area well enough so the viscosity becomes higher in the curing area gradually. The combination of the above two could introduce differential shrinkage between layers and across the layer and form a strong suction effect. The situation is more severe when printing repeated patterns. This suction force may result in a phenomenon where the cured layer suddenly sticks to the Teflon and does not come apart (as shown in the photo). To provide an example, suppose a certain resin has a normal exposure time of 1 second. During the printing process, the resin has absorbed photons from both background and scattering exposure near the exposed area. Please note that the resin in the build area close to the vat floor tends to have higher viscosity when partially cured and tends to stay near where it is. If the accumulated absorbed dosage is equivalent to 0.5s of normal exposure, the next print layer will technically be over cured for 1.5 seconds (1 second for the exposure time + 0.5 second from already being cured due to background and scattering exposure). During the buildup of the partially cured resin, the effective over-curing will keep increasing the adhesion between the cured layer and the Teflon film. If you cannot use another slow resin instead, you would need to increase the lifting speed and lifting height to slow down the buildup.
     

How will the above affect your print? They will significantly affect the consistency of the separation force and increase the failure rate. Even if the print survives, the surface quality may be deteriorated. They will affect both the Teflon film lifetime (please refer to the PSP resin container blog ) and the printing quality.

Knowing the reasons as to why high adhesion occurs and the solution to it will greatly smooth out your printing process. Even if your print did not come out the way you expected, it is important to understand why it happened. This way, you know what the cause of the problem is and learn to avoid it next time. Learning from failed print is perhaps one of the best way to quickly learn and understand more about SLA printing!

What is a PSP Resin Container?

PSP stands for Passive Self-Peeling. This is the key component to the “secret” of Kudo3D’s high-resolution 3D printer. Instead of forcibly pulling the printed layers apart from the vat floor, the flexible PSP resin container greatly reduces the separation force between each layer by passively peeling it apart. There is no extra motor to pull the container away and the bending of the container mimics the action of peeling a piece of tape away from a hard surface. This greatly reduces the separation force and thus results in a faster speed as well as the ability to print large models and fine details compared to other types of layer separation mechanism. The vat floor is formed with a layer of elastic clear silicone to assist in peeling. It is well known that clear silicone tends to react with resins and become cloudy after one or two prints on the same spot. Depending on the resin used and number of layers in a model, silicone could permanently bond with the cured layer when reacting with the resins. Therefore, we cover the silicone with a thin layer of Teflon to protect the silicone. By doing so, the lifetime of the container is greatly extended.

Brief History of Kudo3D’s Different Generations of PSP Resin Container

First Generation to Third Generation Resin Container.

During Kudo3D’s Kickstarter campaign, back in May 2014, we released the first generation of PSP resin container along with the Titan 1. It was a fairly simple design: acrylic container with silicone and Teflon, along with 2 thin plastic side walls. These side walls were first held together with double sided tape and sealed with silicone. Though it fulfilled everything that it promised, there was a slight problem with this container. When the container is lifted too much, the silicone sealant may not work. The resin may get to the adhesive through the gap between the silicone and the side walls. The resin weakened the holding between the side walls and resulted in a leakage after using for a while. Although first generation container has such a problem, it was easy for DIYers to make it by themselves.

Upon learning this, our team quickly found a solution to this problem. Using a stronger chemical bonding to replace double sided tape, we released the second generation of PSP resin container. The interface between the side walls and the acrylic is strong to prevent the resin from seeping through. However, we soon found that 3D-Materials resin could react with the side wall materials and cut through the side walls gradually. The side walls lasted about 120 hours if the container was maintained properly. The 3D-Material resin users experienced a lower resin container lifetime that ultimately could led to leaking containers- if not caught early on.

To extend the lifetime, 3D-Material resin users needed to clean up the container after each use and must monitor the sidewall condition. When using non-3DM materials, the lifetime was much longer for the second generation PSP containers.

To be more compatible with 3DM resins, the PSP resin containers went through another round of testing and development in order to identify a material that resists 3DM resins while still be chemically bonded to the acrylic. Finally, Kudo3D’s R&D team was able to create the third generation of PSP resin container, our current generation, which is deemed “all-resin safe.” We are happy to state that we have been accident-free of leaking resin containers since the release of it over a year ago!

Soft Silicone? Hard Silicone?

Do you see the stickiness of the soft silicone?

But not for the hard silicone!

As you may notice, we offer two types of resin container: soft silicone resin containers and hard silicone resin containers. However, what exactly is the difference and how do you know when to use which type of silicone?

The soft silicone resin container, as the name states, uses a soft silicone with a Teflon sheet on top of the silicone. The adhesion force between the Teflon and silicone is much higher than of the hard silicone. The silicone is extremely sticky. If you touch the silicone (which we do not recommend unless necessary), the silicone will stick to your finger and stretch out, almost like when you try to pull gum off your shoe. This soft silicone resin container is very useful when printing smaller objects, such as rings or miniatures. The separation force, when using this resin container, is much lower and is generally recommended for first time users. The downside of this resin container is that the Teflon film is more susceptible to warpage and is not ideal for larger prints and prints require flat surfaces.

The hard silicone resin container uses a hard silicone and a Teflon film on top. The adhesion force between the Teflon and the silicone is much lower than of the soft silicone. If you were to touch the surface, the surface will feel tougher and will not come up along with the finger. Unlike the soft silicone resin container, the Teflon film on the hard silicone resin container will have less warpage, and users are able to print large objects or objects with a flat surface. The downside is that users will need to print at a lower printing speed, due to the higher separation force.

How Do You Maximize the PSP Resin Container Lifetime?

Although the silicone is protected by the Teflon to increase the lifetime of the container, the Teflon film itself still has a lifetime which is dependent on the separation force. Teflon film starts warping after experiencing a high separation force. Since Teflon and silicone are the two most chemically resistant materials, there is no way to permanently bond them together. Severe warpage could induce a gap between the Teflon film and silicone. The resin can enter through the gap and separate the Teflon from the silicone. If the silicone is not damaged, it is possible to replace the Teflon film. For hard silicone, you would need to use a clear double sided tape to bond a new film. For soft silicone, you would need to peel off the Teflon film　gently to avoid damaging the silicone, and lay a new film down slowly to prevent dusts or bubbles from getting in-between. For details, please refer to our forum.

To maximize the PSP　container lifetime, users must minimize the separation force and avoid model dropping. Please refer to Printing Guide to prevent model dropping. The shrinkage of the cured model could introduce warpage on the Teflon film. When the adhesion between the cured layer and the Teflon is larger, the front of the container will be lifted. If the container is lifted over 5 mm before dropping back down onto the frame, you may need to reorient the model and make some adjustment to the printing parameters. The height being lifted is a good indicator of the separation force.

There are many factors that has an impact on the separation force and thus the lifetime of a resin container:

1. Exposed area of a slice (reduce cross-sectional area)
2. Pattern of the layer (avoid circle and square patterns that are hard to separate)
3. Orientation of the print (avoid printing same pattern on the same spot)
4. Lifting speed (lower speed reduces separation force)
5. Exposure time (less exposure has less adhesion to the Teflon)
6. Reactivity of the resin (when the resin temperature is higher, the film is more likely to warp)
7. Native adhesion between cured resin and Teflon caused by the Van Der Waals’ force (use resins with less adhesion)
8. Layer thickness (thinner layer with less exposure has also less adhesion to the Teflon)

The golden rule to elongating the lifetime of your resin container is:

Once you understand how to minimize the separation force, it is quite possible to use a single PSP resin container for more than 100 prints. Take it slow and try to understand more about not only Kudo3D’s printer but also about its printing process involved. This will allow you to have a much more successful print.

What do you do with the unused resin in the PSP resin container?

The great news is that you can recycle the unused resin. When removing the resin container or build platform after printing, please cover the venting holes on top of the printer to avoid dripping resin on the projector by accident.

Carefully use a funnel and strainer to pour the resin back into the bottle. It is important to use a strainer to sift out residual pieces of plastic that may have been cured due to a failed or partially failed print and flakes cured by background light. Wash the strainer and funnel after each use to avoid contamination with other resins. If you are using the same resins, you may just need to wipe the strainer and funnel and store them in a dark place.

If the resin does not contain pigments,  you can leave the resin in the container for about a week.    If the resin contains pigments,  do not leave the resin in the container for more than two days as the pigments may settle.  Some pigments settle faster than others so it is better to use a rubber scraper to stir it before printing again if the resin is left in the container.     It is a good practice to recycle the resin back to its original bottle to extend the lifetime of the leftover resin.

How do you clean the PSP resin container?

After recycling leftover resin, the resin container could be washed with mild dish detergent and water if your are going to use a different resin for your next print. Soft resin container can be cleaned with Isopropyl Alcohol (IPA) directly but please do not soak the container in the IPA.  When cleaning the soft resin container,  please be careful not to touch the silicon as the soft silicone is very sticky.   If you plan to print again soon and you recycle the resin,  you can simply store the container in its original packaging box without cleaning. If you plan to store it for more than a couple weeks, then it is better to clean it up and store it. After putting on disposable gloves, gently clean the container using your fingers. Abrasive cleaning supplies, including paper towels, can damage the Teflon film. If needed, you may use a lens wipe instead. Soft vat has a very stick silicone at the bottom of the vat. Please be careful when wiping the vat floor as the paper or cloth can stick on the silicone and hard to be removed.

If you find pieces of cured resin stuck to the resin container, slowly remove the plastic to avoid damaging and lifting the Teflon film. We recommend using a thin plastic blade to separate the cured pieces. Do not exert vertical force to pull the pieces as the Teflon film could be damaged or lifted. To extend the lifetime of the resin container, please also avoid rubbing the edges of the Teflon film and the four corners of the PSP container.

Rinse the container with water several times to completely get rid of the soap and try not to let water run below the vat and leave water stains. If there is resin residue on the bottom surface of the container, you can clean it with IPA (Isopropyl alcohol) and a lens wipe. Fill up half of the resin container with water when rinsing, and tilt the container slowly to drain out the water. The Teflon film should be left mostly free of water since Teflon is a non-stick material.

How do you dry the PSP resin container?

Good question. You should not begin printing with the resin container while it is still wet. To dry the container, you may use a dustless lens wipe or leave the container face down to dry overnight. A fan may speed up the process.

Useful tips:

– If you leave resin sitting overnight, mix it up before printing again, since the pigments could have settled. Settled pigments will affect the resolution of your print. Another good practice is to renew the overnight resin by mixing it with fresh resin. The fresh resin should make up at least 50% of the resin in the PSP container.  

– Got resin everywhere? Isopropyl Alcohol (IPA) is very useful. It’s the same stuff you use to rinse off extra resin, and it cleans the resin off your computer mouse or keyboard just as well. Note: Do not use IPA on printer acrylic covers, because it will cause frosting.

– Cover the projector lens with a piece of paper or business card to avoid collecting dust if your printer model does not come with a shutter

– Make sure the UV blocking cover is on top of the printer.

Still have questions? Leave us a comment below!