| 摘要 |
The invention is an improved hardener for use with phenolresorcinol-formaldehyde wood bonding adhesives. The hardener is conveniently made and shipped as a stable dry powdered material. It is then slurried in water at the point of use for convenience with continuously mixed and dispensed liquid-liquid, two part adhesive systems. The hardener comprises paraformaldehyde or alphapolyoxymethylene, fillers, viscosity and/or rheology control agents, and a solid acidic material. The latter ingredient is a critical component used to adjust the pH of an aqueous slurry to the range of 4.0 to 5.5. Oxalic acid is preferred. In this pH range, the formaldehyde polymers are stable and the slurried hardener does not give off significant formaldehyde odor for periods up to several days. Bonding performance is improved because the characteristics of the hardener and resulting adhesive have very little variation over time.
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