Polyurethanes Silane additives

Abstract— The use of organosilanes as adhesion promoters for surface coatings, adhesives and syntactic foams is described and reviewed in the light of published work. Data are presented on the beneficial effect of silanes, when used as pretreatment primers and additives, on the bond strength of two pack epoxide and polyurethane paints applied to aluminium and mild steel. It is shown that silanes when used as additives to structural epoxide and polyurethane adhesives are less effective than when used as pretreatment primers on metals but are highly effective on glass substrates. The compressive properties of glass microballoon/epoxide syntactic foams are shown to be markedly improved by the addition of silanes. 

Effect of silanes as additives on the bond strength of a two-pack polyurethane paint Silane wt% - direct pull-off. All panels grit-blasted only... 

As it had been shown that silanes were effective as pretreatments for a variety of coatings and particularly so when used as additives, selected silanes were examined as pretreatments and additives in conjunction with a two pack polyamide cured epoxide adhesive (Epikote 828/Versamid 115, 1/1) and a structural polyurethane adhesive based on diphenylmethanediisocyanate and a polyester resin. 

Comparison of silanes as pretreatments and additives for a rigid polyurethane adhesive Butt tensile, grit-blasted metal, 2 wt% as pretreatment and additive... 

Polyurethane Methanol 1. Abrasion followed by brushing. Grit or vapor blast or 280-grit emery cloth followed by solvent wipe. 2. Incorporation of a chlorosilane into the adhesive elastomer system 1% by weight is usually sufficient. Chlorosilane is available commercially. Addition to adhesive eliminates need for priming and improves adhesion to glass and metals. Silane may be used as a surface primer... 

LDPE coating to polyester film, clay-coated liner board, and aluminum foil was improved by an addition of calcium carbonate. Adhesion increases as the amount of calcium carbonate is increased and at a 30% level it is doubled. The adhesion of SBR to a polyurethane adhesive was substantially improved (400%) by the addition of silica but only when the surface was roughened. The amount of silica did not affect adhesion of unroughened SBR. The use of MgO with silane coupling increased adhesion of bromobutyl liner by a factor of four. Generally, in the reported data, surface roughening of the filled composite contributes to a better adhesion to other substrates joined by adhesives. 

Figure 2 shows the reactivity, measured as tack-free time in STP-S polymer systems (see below) of systems terminated with different NCO-silanes. The new a-silanes show dramatically enhanced curing rates. Additionally, the curing rates of compounds made from these polymers can be varied over a wide rage, using different amounts of catalyst (usually tin) and water scavengers (usually alkoxysilanes). Comparable results were achieved in silane-terminated polyethers and polyurethanes. 

Allyl glyddyl ether is a monoglycidyl derivative, used as a reactive epoxy diluent for epoxy resins. As an impurity, it was considered as the sensitizing agent in a plastic industry worker allergic to 3-glycidyloxy-propyltrimethoxysilane, an epoxy silane compound used as a fixing additive in silicone and polyurethane. 

Additives can also be used to improve the hydrolytic stability of polyester polyurethanes. Glycol-cured materials are reported to be stabilized with cyclic imines. Substituted ureas or thioureas ethylene-diaminetetraacetic acid-derived chelating agents oxycarbonyl isocyanates epoxies carbodiimides, alone " or in combination with silica silanes " substituted phthalimides and an undisclosed combination of additives have all been cited as stabilizers for polyester polyurethanes. 

---