Waterborne Bonding Systems

The use of waterborne bonding systems has been driven forward by the worldwide concern about environmental pollution emanating from the use of solvents by industry in general. 

By changing from solvent degreasing to aqueous degreasing systems a 25% reduction in pollution can be achieved. To meet the next target reduction of 67% solvent emission it will be necessary to use only waterborne bonding systems for rubber to substrate bonding. 

Waterborne bonding systems do not have the same ability as organic solvents to wet out the metal surface or solubilise any greasy contamination during bonding agent application to the metal surface. Another factor is quick evaporation of the alternative carrier from the applied adhesive film. Use of water requires higher temperatures for its removal from a deposited film of adhesive. Incomplete removal will result in porous adhesive layers, or even in underbond corrosion at the metal surface. 

N.B. Use of waterborne bonding systems has some major requirements which differ from the way solvent-based systems are handled. Failure to follow the following rules may well result in significant bond failure problems ... 

In present-day high-speed assembly line operations, adhesives are applied robotically. The adhesive bead is apphed quickly and evenly to parts on a conveyor line just prior to being fitted. These operations, especially the need to handle the adhered substrates soon after assembly, demand fast-curing adhesive systems [65]. Two-component adhesives are used to bond metals to plastics in automobiles, to laminate panels in the construction industry, to laminate foams to textiles, to laminate plastic films together, and to bond poly(vinyhdene chloride) films to wood for furniture. A commercial waterborne two-component adhesive is sold by Ashland under the trademark ISOSET. This system is used for exterior sandwich panels by recreational vehicle manufacturers and is composed of a water-emulsiliable isocyanate and a hydroxy-functionalized emulsion latex. 

Uses Lubricant, rub resist, aid, water resist, aid, adhesion aid in textiles, leather bonds dissimilar fibers, provides water resist, in fiberglass mfg. Features Provides adhesion, durability, heat sealability at low temps., exc. water and solv. resist, to waterborne systems usable pH 1+ low... 

In most cases the silane is applied to the filler neat or in diluted form. Typically the silane or silane solution is sprayed onto the filler as it is being agitated. Most important commercial silane coating processes are continuous, with high throughput rates, but application may also be performed in batches. Control of silane addition, dwell time, and temperature within the system is essential for a suceessful coating. Evolution of volatiles (VOC) must be monitored. To remove reaction byproducts, solvents, and water, and to bond the silane to the filler surface, further heat treatment may be necessary. For those fillers typically processed as a slurry, aqueous treatment with waterborne silanes is also possible. 

Some adhesives solidify simply by the evaporation of a carrier liquid (water or solvent). Others harden as a result of going from a molten liquid to a cooled solid. Still others solidify by means of a chemical reaction. Some adhesive systems may require several mechanisms to harden. For example, thermosetting waterborne adhesives require the water carrier to first evaporate and then chemical cross-linking occurs before a final bond is achieved. 

Certain waterborne systems are available which are capable of PV bonding. 

Figures 3.15, 3.16 and 3.17 show two NR compounds, an SBR and an NBR bonded with solvent-borne Chemosils 211/220, a hybrid solvent-borne primer Chemosil 211 with waterborne top coat Chemosil XW7484 and a waterborne system of Chemosil XW1180 primer and XW7484 top coat. Boiling water tests (95 - 98 °C for 2 hours) show 100% rubber retention in all cases (see Figure 3.19).

Bonding Rubber to Metals with Waterborne Adhesive Systems... 

With the advantages and disadvantages of these systems it is still going to be difficult to convince customers that the reliability of the bonded products using waterborne adhesives will be as good as for products produced with solvent-based systems. 

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