Water Resistant Wood Adhesive derived from Redispersible Polymer Powders

摘要

Many spray dried polymer dispersions are derived from hydrophilic monomers and the water resistance of their derivative coatings is often poor. Consequently they have not found application as formulating bases for water-resistant wood adhesives. Here it is claimed that by designing a polymer phase comprising at least 30 wt% of a hydrophobic monomer (water solubility <0.1% at 20°C) and using polyVOH containing reactive methylene groups (as introduced by acetoacetoxy functionality) as stabilising colloid, dispersions suitable for spray drying and capable of producing water-resistant coatings may be produced. In a preferred form, the polymer phase comprises a St/(meth) acrylic ester copolymer containing a crosslinking monomer (e.g. one containing epoxy, hydroxyl, silyl or acetoacetoxy groups). The functional polyVOH colloid should contain 0.03-"3 mole% acetoacetoxy groups and have a degree of hydrolysis greater than 95%. This type of polyVOH is able to graft onto the growing polymer chains and confer stability. Typically levels of protective colloid are in the region of 4-10%. Once the dispersion is prepared it may be compounded with conventional, partially hydrolysed polyVOH and other additives prior to spray drying. To achieve maximum water resistance an external crosslinker (e.g. an isocyanate-based compound) may be added prior to application.