I’m trying to print molds for silicone pieces, and I’ve found that something in standard resin acts as a cure-inhibitor for platinum-cure silicone. I could use tin-cure silicone, but it is not skin-safe and would not work for my application.
I’m wondering if, because the dental resin does not contain VOC’s, and is bio-compatible, if maybe that would allow for the silicone to cure better. I would imagine the VOC’s in other resins are interacting with the platinum.
Let me know your thoughts!
Are you UV curing your parts thoroughly?
At first we had only luck with condensation-cure silicone(tin cure) and silicone based on addition-cure(platinum) simply didn’t want to harden. However, after a long UV cure of the pieces and adding a PVA mould release, we didn’t have any issues anymore with curing of the addition-cure silicone.
On very big pieces we sometimes use a thin coating of lacquer as this improves the surface quality as well. Might this be an option?
I use Dental Model and always have to Coat or Seal before using Platinum Silicone. Just not willing to risk it anymore. 90% of the time now I just use Smooth-on XLS II or Max 10 for deep undercut parts with great results. (Outside of my hands killing me on the demold due to the 30a of the XLS )
We use dental model resin for our moulds. We cast SMOOTHON SORTA CLEAR 40, 18 (12 to follow). We also cast SMOOTHSIL 950 and 960, ECOFLEX 00-50 (00-30 to follow) and BLUESIL RTV 147 A+B
Where the silicone is in contact with the mould, the mould wall thickness is between 0.3 and 0.4mm
We wash in clean IPA every time 5 mins wash followed by 5 mins rinse using manual agitation and jetting using a syringe.
We follow this by drying at 40 deg C (fan assisted) for 35 mins.
Finally UV cure under glycerine for 40 mins
When demolding, we do get some mechanical bonding between the mould and the silicone, bit with gentle teasing it comes out whole and we have no problems. We never have a problem with uncured silicone.
Just a note, but I am sure you have this covered, Do not use latex gloves when using platinum cure silicone. It interferes with the curing process.
We are looking to use CLEAR and DENTAL SG in the future so if any one has experience of these please shout out. We use the DENTAL MODEL because of the high quality of print output.
This is great news because I’m actually using SORTA CLEAR 18 in my molds. When you say that you UV cure under glycerin, do you mean that you actually have a tub of glycerin that’s under a UV light? I’ve never heard of this process before so I’m curious what it does.
I just ordered some applylabwork dental resin so I’ll see how that goes. What kind of printer are you using?
Thanks for the reply! What kind of coating do you use? Do you mean mold release?
Exactly that. The parts I make are really small so I have a small clear glass jar of glycerine preheated to approx 40 degrees C that I pop my parts in then put it on a turn table next to my UV light source, UV passes through glass and glycerine.
The idea of the glycerine is to keep the oxygen (air) away from the surface during curing so that you are not left with a sticky surface. There has been many a debate on the forum about this and many people use water. I use glycerine after seeing it being used at a dental lab. I personally think it helps the uv get to blind holes by using the glycerine as a “light guide”
Oh the note about not using latex gloves, it is the sulphur in them that inhibits the platinum silicone curing, Check for other possible contamination sources. like modelling clays.
As parts get smaller you have to become more anal about precision and exactness and process as the margin for error disappears!!
I am using a FORM 2 and waiting for the FORM 3 to become available in the UK.
Good luck and let me know how you get on
All the best
Thank you for the great information. I had no idea I was supposed to be curing parts in water. If you don’t mind, what kind of mold release do you use?
It is not generally necessary to cure under water or glycerine, but we have found that it does help.
We do not use any release agents to prevent cross contamination that causes problems when we bond silicone parts together.
Awesome. I just got my dental resin today, and a UV lamp that can stay on continuously for hours at a time. My plan is to do the following:
Is there anything you’d do differently or add to that, to increase the chances of getting a good cure on the platinum silicone, such as heat, barriers (I can’t use a shelaq or anything that will fill cavities, since the mold has small details).
I would add an air dry or warm air dry after the IPA rinse to evaporate any residual or absorbed IPA, No more than about 40 deg C. for 30 to 40 mins.
Don’t forget to give the resin a good agitation before use, There is a lot of dense filler in the resin and it can settle out. I rock my resin cartridges from side to side for 10 mins with the screw top and bite valve at the top so there is no chance of the resin splashing out!!
If you leave your resin in the tray, again agitate to get the filler mixed in. I use a silicone spatula.
Smoothon Sorta clear 18A is quite forgiving, but follow their recommendations exactly ie weigh accurately, mix, pour into new mix cup and mix again. If you don’t want bubble you will need to degas. I have some clients who had “sticky” silicone and it was because they had not mixed their silicone thoroughly and the other reason was they were using latex gloves.
Our moulds are tiny and we mix only 30ml of silicone at a time so any bubble will fail our moulding.
Some people like brushing the silicone into the mould to wet the mould surface before pouring. We don’t as it is an extra process and we will get through a fortune in disposable brushes! We actually inject our silicone at high pressure.
Without seeing your mould I cant advise.
I never use heat on my moulds as this distorts the mould and secondly it affects the shrinkage rate of the silicone.
I don’t use any form of barrier as it may affect the later processes when we bond to the silicone.
Your UV cure time seems long, but it will be dependant on your UV out put power and frequency distribution (405nm??) there are many good blogs on this forum on uv cure. Most of my know how came from there then I added the science!
Good luck and let me know how you get on.
ATB
Platinum Silicones are infamous for being inhibited by nearly everything.
Its a very finicky material.
However- if you hunt around, Some formulations are far less sensitive than others.
You should get samples of a wide variety of silicones and test them on your parts- with parts variously treated- some with barrier coats- some without.
For most tin cured silicones- Acrylics. themselves are a perfect separation agent.
But most things that work for tin cure systems will inhibit platinum.
The watch word in any kind of moldmaking is TESTING.
Apart from submerging in Glycerin, I tried molding Sorta Clear 18 in the Model Resin and no joy. Very tacky, pulls apart etc.
Formlabs have released a number of new resins since this thread was posted and I am wondering if anyone has had success with molding Platinum Catalyst silcone (food grade) using a different resin?
Thanks.