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Tuesday, December 09, 2008

Mold Release and Silicon or Polysilane Oil Removal

Question:
How do you remove silicon mold releases and polysilane oils from stainless steel, plastic and glass?

Answer:
Silicon mold releases and polysilane oils are very difficult to remove filmy residues. Mold release agents on glass act as a protective film on the glass attempting to clean them off with very aggressive acid or alkaline cleaners, the cleaning agent etches around the edges of the mold release agent and the un-coated sections of the glass, leaving behind a shadow of where the mold release was or had been. Even if the cleaner does eventually remove the mold release, there is a permanent shadow of where it had been due to the etching that occurred where the mold release had been. This same effect has also been with fingerprints on glass. If there is a silicon mold release agent on the glass, remove it with ultrasonic cleaning with extremely hot (over 170 deg F or over 77 deg C) 2% Alconox followed by a thorough rinse. Ideally, make sure the first rinse is with extremely hot water. Typically 10-20 minutes in ultrasonics is adequate to remove the residue. Alconox is a mild cleaner and will not etch the glass under normal cleaning conditions. On plastic first make sure your plastic is compatible with exposure to these temperatures. As we best understand it, many polysilanes have a softening point at somewhere in the 160-170 deg F (72-77 deg C) range. Above that softening point, the polysilanes can be more readily emulsified by a strong emulsifier. A 2% Alconox solution is a strong emulsifier and has been successfully used to remove difficult silicon oil residues. Once the polysilane is emulsified, you want to rinse it with hot water so that cold rinse water does not break the emulsion and redeposit the silicon oil before it has a chance to be rinsed away. The cleaning temperature is critical here. If this is a smooth, cleanable and easily rinsed surface, you can often get away without having to use a very hot water rinse. If there are crevices, blind holes or other features to the glass that would slow down the rinsing, then the very hot first rinse is critical tool Once you have done an initial static or running water initial very hot rinse, then subsequent rinses can be usually be done with ambient temperature water. Note that if extremely high purity deionized or reverse-osmosis water is used for the first very hot rinse, this water can etch glass; although at least it should be a uniform etch because there should no longer be a mold release mask on the glass. To avoid this, use tap water for the first very hot rinse, followed by cooler or ambient temperature higher purity water if a high purity water rinse is required to avoid water spots or other tap water residues. Note that as far as removing the mold release is concerned, tap water rinses will work just fine. The reason to use any higher purity water rinse is to avoid water spots or other tap water residues. These tap water residues can also be minimized by physically removing the tap water and not allowing it to evaporate and deposit - this can be done by blowing off the rinse water, wiping it off, or removing it using a drying solvent like isopropyl alcohol.

To view the technical bulletin for Alconox, Powdered Precision Cleaner, please download this PDF.

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