Reactive Adhesive Systems

In recent years, the use of solvent-borne adhesives has been seriously restricted. Solvents are, in general, volatile, flammable and toxic. Further, solvent may react with other airborne contaminants contributing to smog formation and workplace exposure. These arguments have limited the use of solvent-bome adhesives by different national and European regulations. Although solvent recovery systems and afterburners can be effectively attached to ventilation equipment, many factories are switching to the use of water-borne rubber adhesives, hot melts or 100% solids reactive systems, often at the expense of product performance or labour efficiency. 

As mentioned at the outset, hot melt adhesive s primary advantage is process speed. Fleat resistance and substrate penetration are typically inferior to liquid adhesives (neat reactive systems, solvent, or water-based). Current research and development is therefore focused on maximizing the process advantages of hot melts and minimizing their performance deficiencies. Optimizing hot melt... 

Some catalysts, such as certain Lewis acids, are so reactive that they can provide extremely short gel times with epoxy resins at room temperature.15 For example, BC13, can polymerize epoxy resins, resulting in gel times of less than 60 s. However, these reactive systems result in a very rigid adhesive with low peel strength properties and poor impact strength. As a result, less reactive catalysts are commonly employed in adhesive formulations. 

The adhesive properties of lignin, its reactivity with formaldehyde, and its structural similarity with phenolic adhesives invited investigation of the applicability of lignin in adhesive resin systems. Therefore, during the past several years, numerous attempts have been made to replace the expensive petrochemical resins totally or partially with the renewable raw material lignin (i). 

Consider a non-reactive system consisting of a binary liquid alloy A-B and an oxide substrate such as AI1O3 at constant temperature. A simple statistical thermodynamic model has been developed (Li et al. 1989) to predict the contact angle and the work of adhesion isotherms, 0(XB) and Wa(XB), from the known values of contact angles... 

The adhesive may be solvent or water-based, hot-melt, coldseal or heatseal and pressure sensitive or chemically reactive. So the solidification process may occur via drying of water or solvent-based adhesives, by cooling of hot-melt and heat-seal adhesives, or by curing of chemically-reactive systems. With two notable exceptions - self-adhesive labels used on items of fruit or vegetables, and heat-sealable layers on packaging films - adhesives are in general not intended to touch the packaged food directly. 

Good processing characteristics Adhesives can be supplied as contact bonding types—either in water- or solvent-based systems—hot-melt, pressure sensitive, or as reactive systems—either 100% solids content or solvent based. 

Plywood, parquet flooring, and doors are usually produced using aminoplastic adhesives. The press time necessary for these applications depends on the press temperature, the total thickness of the wood layers which have to be heated through, and the reactivity of the resin glue mix. Traditional adhesive resin systems need rather long press times due to their... 

Uses Water resist, aid for oxidizing oils binder for sealing and adhesive compds., anticorrosion primers, rubber applies., potting compds., impregnations, photo-reactive systems Features Improves dry time, chem. resist. 

CAS 3775-90-4 EINECS/ELINCS 223-228-4 Uses Monomer, antistat, corrosion inhibitor for catephoretic metal primers, vinyl/acryl reactive resins, water-based resins, adhesive resins Features Multifunctional cation-active can be copolymerized with vinyl or acryl reactive systems exc. wet adhesion on metal low volatility Properties APHA 50 max. clear liq. m.w. 185 vise. < 10 mPa s 97.5% min. purity... 

Four reactive systems were studied at varying ratios of the two reactive components. These reactive systems were phenol, bisphenol A, trisphenol, and a mixture of bisphenol A and o-cresol (results from the latter three systems are not shown). An example of the effects of increasing (r) on the reaction time needed to reach the gel point is shown in Figure 4a for phenol. Clearly, the time required to reach the gel point decreases as the ratio of die reactants increases, as predicted by equation 2. The gel time for the other phenolic systems also decreases as the ratio of reactants increases. These model systems show that changing the ratio of reactive sites has the same impact regardless of the functionality of the phenolic system. This is very important as one tries to apply the results from model compound studies to real phenol formaldehyde adhesives that may include complex mixtures of phenolics. 

Diluents. These are generally incorporated to reduce the viseosity of the freshly mixed adhesive to offset the effect of the filler. This may be required to improve handling and spreading characteristics or to allow filler additions which tend to reduce cost. Other properties of the fresh and hardened adhesive can be affected by the use of diluents, for example pot life, flexibility and glass transition temperature. If the diluent is non-reactive, such as solvents which remain in the cured system, the net result is a deterioration of chemical and mechanical properties such as increased shrinkage and reduced adhesion. Reactive diluents containing epoxy compounds are capable of combining chemically with the resin/hardener system. 

The use of adhesives/sealants in both the industrial and consumer spheres has increased dramatically in the past 20 years. In the industrial segment, both reactive and nonreactive systems are used in a wide variety of applications. The increasing use of reactive systems has, however, tended to overshadow that of the nonreactive systems. Most prominent amongst the reactive systems favored in industrial applications are anaerobic sealants (methacrylate ester based), instant adhesives (alkyl cyanoacrylate ester based), acrylic (toughened) adhesives, epoxy resin adhesives, polyurethane/isocyanate-based adhesives, silicone adhesives/sealants, and phenolic resin adhesives. 

Two types that may be considered to be special cases of single-component reactive systems are the Anaerobic adhesives and Cyanoacrylate adhesives. These are similar... 

The setting times for reactive adhesives vary from a few seconds with Cyanoacrylate adhesives to several hours for a typical DIY epoxide cured at room temperature. For a given reactive system, the setting time can be varied by a large factor by changing the temperature and/or catalyst. 

Thermoplastic linear polyurethanes which are usually chain-terminated so that no unreacted free NCO groups remain available. Environmental considerations direct growing attention to these newer non-polluting urethane adhesive forms, e.g. powders, films, aqueous dispersions and 100% solids reactive systems. Some systems do possess blocked diisocyanates which are activated on heating to produce chemically reactive solid systems. 

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