soft or "silky" silicone 3

[crthomps]

Does anyone know what kind of procedures can be done to make a molded silicone part 'smoother'? We recently got some thin-wall diaphragms made and wanted to get a smooth surface similar to an OEM. The company had a procedure where they'd tumble the parts in talcum powder and then have them cured again; it softened them up a bit, but the surface was still a bit 'tacky'. Are there any procedures or materials out there that would give us a silky silicone surface? I appreciate any suggestions!

 

[Demon3]

Additive 23 from Dow Corning is claimed to give a matte silky finish to coatings. It's made up of cross-linked silicone particles.

http://www.dowcorning.com/content/p... and Inks&DCWSS=Additives for Paints and Inks

As you mentioned talc works too. So it seems that you need a microscopically rough surface and low friction for the silky feel.

 

[berti]

Hi all,

some proposals:

One of my customers solves the problem by surface fluorination, that means he sends his diaphragms and O-rings to a service company which uses diluted fluorine gas to treat surfaces. Your local SOLVAY representative should know one. If you are in Europe I can give you adress.Result is really surprising.

VMQ made by addition (platinum ) cure has much more"dry" and less sticky surface. Contact your silicone (or part) supplier for e.g. RAPIDCURE of Dow-Corning or ELASTOSIL R plus from WACKER.

Some effect is also possible by mixing in a lot of -say 20 %- of fillers ( diatomea earth, teflon powder)but this gives quite often bad influence on mechanics.

HTH

Berti

 

[Pud]

Hi,

I am sure I have seen a reference to using liquid CO2 to remove residues from moulded silicone rubber - I am almost sure it was for baby's bottle teats. Apparently it used to be done some other way but this is better.

Sorry cannot be much more help - grey cells quitting one by one...


Rgds


Harry

 

[RSS22]

Have you tried coating the seal with Teflon (PTFE) ov MoS2?

Rubber Suface Solutions (

http://www.rubbersurfacesolutions.com)

is a dry-film applicator for the rubber industry. Silicone can be tricky to coat, but it is worth a try.

I hope this helps.

 

[janwan]

You can add thin layer (spray) of the Xlinker that will react with the surface only. It will definitely decrease the tack, but can increase the hardness since the Xlinker will penetrate deeper, if you add too much. I have done it before it's an old trick.

 

[craigmj]

Ive tried additive 23 from DOW, as Demon3 suggested. I can tell you that in my case after adding from 1-5% mixture (LIM), there was NO huge difference (I was using a Shincore silicone).

There are other things you can do. Dow makes some silicone topcoats which greatly reduce the COF. Mainly these topcoats are used by textile manufactures as a way to make "slick" non-porus fabrics...such as airbags. If you are interested then let me know and I will look up the exact product identification.

Craig

 

[Demon3]

You could try oxidising the surface. I know that when oxidised the silicones can loose their tackiness. For example you could flame treat them.

One problem with silicones (well often it's a benefit) is that they self heal. So when you remove some oligomers from the surface you find that over time new oligomers diffuse from inside the part to replace those lost at the surface. This has been measured for example using surface energy measurements over time.


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[Pud]

I knew I wasn't dreaming:

How to remove residues from silicone rubber:

http://www.nanon.dk/news/archive/purified-and-colorful-baby-pacifiers-and-nipples/

Cheers

Harry