| Hydrophilically modified, aliphatic polyisocyanate based on hexamethylene diisocyanate (HDI). As the hardener/binder component for high-quality waterborne polymer dispersions and as an additive to improve the property level of waterborne coating and adhesive systems. With respect to its composition, the product corresponds to the following sections of the U.S. FDA ’s guidelines Title 21 CFR: Section 175.105. Properties / Applications: Because of its hydrophilic character, Bayhydur® 304 can be easily emulsified in the aqueous phase. It is used mainly as the crosslinking partner for waterborne polyol binders (Bayhydrol®) and as a crosslinker for largely pH-neutral waterborne polymer dispersions, including polyurethane (Dispercoll® U), polyvinyl acetate, polyacrylate and synthetic rubber dispersions. After addition of Bayhydur® 304, the ready-to-use two-component formulation must be used within the pot life. This is not only governed by the polymer content but also by its other constituents (resin, thickener, plasticizer, etc.). Within many dispersions, the end of this pot life – usually several hours – is not marked by gelling. The addition of 3 – 10 % Bayhydur® 304 is recommended to crosslink adhesive dispersions containing 40 – 60 % polymer. Effective mechanical stirring is required to emulsify Bayhydur® 304 in adhesive dispersions. Manual stirring by hand is not sufficient to ensure good homogenization, especially in the case of low-viscosity adhesive dispersion. Inadequate dispersion may result in the formation of granular deposits in the adhesive. Should Bayhydur® 304 be modified with an additive, this may contain no groups which react with isocyanate and no secondary components which may do so. In particular, any additives used must be free of secondary components which are alkaline or have a catalytic effect on isocyanate groups. Even at very low concentrations, these can cause an increase in viscosity or even solidification. Information provided by Covestro |
