Gypsum Board with Improved Moisture Resistance
Foundation chemistry for silicone-grafted hydrophobization of the dihydrate crystal surface.
- Assignee
- United States Gypsum (USG)
- Jurisdiction
- United States
- Filed
- 1997-08-21
- Published
- 2002-01-29
- Status
- Granted
Discloses an emulsion of poly(methylhydrogensiloxane) (PMHS) injected into the slurry that, upon contact with the alkaline calcium environment, hydrolyzes and grafts a methyl-silicon shell directly onto growing dihydrate crystals, producing a board with bulk water absorption below the Type WR threshold.
Wax emulsions sit in the pore network as a physical barrier; silicone bonds chemically to the crystal. The performance difference shows up in long-term cycling and elevated-temperature service, where wax can migrate and bloom while silicone holds. Below the 4.5% absorption threshold, silicone has effectively won.
- Claim 1
PMHS emulsion active range and slurry pH window required for graft completion.
- Claim 2
Minimum residual moisture in the board at kiln exit to allow full reaction — over-dried boards do not develop full hydrophobicity.
- Claim 3
Composition of the activator co-additive that triggers PMHS hydrolysis at the desired point in the line.
If you have converted to silicone hydrophobization and your absorption test drifts upward, look at kiln exit moisture before you accuse the supplier. Silicone needs trace water to finish the reaction. Tighten the kiln too aggressively and the chemistry is starved.
- · USPTO Patent Full-Text Database, US 6,342,284 B1
- · ASTM C1396 / EN 520 Type H specifications