Curing system isocyanates

Ionic polymers are also formulated from TDI and MDI (43). Poly(urethane urea) and polyurea ionomers are obtained from divalent metal salts of /)-aminohen2oic acid, MPA, dialkylene glycol, and 2,4-TDI (44). In the case of polyureas, the glycol extender is omitted. If TDI is used in coatings apphcations, it is usually converted to a derivative to lower the vapor pressure. A typical TDI prepolymer is the adduct of TDI with trimethyl olpropane (Desmodur L). Carbodiimide-modified MDI offers advantages in polyester-based systems because of improved hydrolytic stabihty (45). Moisture cure systems based on aromatic isocyanates are also available. 

Curing system. The most common room curing agent is zinc oxide. Isocyanates are also very common. 

The blocked isocyanate systems (with curative present) are latent cure systems. In order to create a latent curing adhesive, the blocked isocyanate is added to a catalyzed polyol component without a reaction occurring at room temperature. In theory, the blocked adhesive system is relatively stable at room temperature. When this system is heated to the unblocking temperature, the chemical reaction, which... 

For polyether-based polyurethane at 70 to 80°C, the properties are only 50% of the original, whereas at 110°C the value drops to about 20%. This gives a normal safe working temperature of 80°C. Figure 7.10 illustrates the aging effect on different cure systems. This working range can be increased by the use of isocyanates such as PPDI in the polyurethane (Chin et al., 1992). 

Recently, hot melt PSA systems have been introduced and radiation curable PSA systems are at the commercial development stage. High solids (50%-70% by wt.) nonaqueous dispersion acrylic PSA systems have also been reported(1). Unlike the hot melt and radiation cured systems which require new capital outlay in coating head and/or curing (drying) equipment, BFG has developed PSA systems, based on Hycar 2100R reactive acrylic liquid polymers and isocyanate terminated prepolymer, which can be processed at 80% solids (by wt.) with equipment presently used in the PSA industry, namely, the reverse roll and knife-over-roll coater. 

Table I summarizes properties of RIM elastomers obtained at a 40% hard segment level. Several isocyanate indices are given. Systems having a 1" suffix, i.e. Al, were not post-cured. Systems with a "2" suffix were post-cured under conditions given. In general, the higher index systems give higher strength properties and lower elongations at break. Ccnparison of non post-cured with post-cured systems indicate little oroperty enhancement upon post-cured.

Other types of curing systems for allyl-terminated urethane polymers were described by Kehr and Wszolek (176). Polyether and polyester urethane-ene systems were prepared by reaction of polyester or polyether dlols with allyl isocyanate or by reaction of isocyanate-terminated prepolymers with allyl alcohol. These urethane-ene systems can be cured by branched monomeric polythiols such as pentaerythritol tetrakis(thioglycolate) C(CH20C0CH2SH)4. 

Features Promotes amino resin/blocked isocyanate dual cure systems ... 

NFPA Health 3, Flammability 1, Reactivity 0 Uses Curing agent for cast PU elastomers, food-contact PU resins epoxy resin curing/hardening agent corrosion inhibitor intermediate for paints, dyes, polymers isocyanate resins polyamides determination of tungsten and sulfates curing system additive for bisphenol A-ep-ichlorohydrin epoxies for food contact antioxidant in food-contact rubber articles for repeated use... 

Heat cure systems are formulated from an isocyanate-terminated prepolymer and a curing agent, in which one of the components is rendered inactive at room temperature. Upon heating, the inactive species becomes active and curing takes place. For energy reasons, it is desirable to formulate such adhesives with a low activation temperature. However, the shelf stability of the formulation will often suffer if this activation temperature is too... 

Curing systems for Kel-F include organic peroxides, polyamines, polyisocyanates and isocyanate-amine combinations. Benzoyl peroxide is effective and convenient. 

---