Butyl rubber-based adhesives

The elastomers considered in this section have been selected considering the most commonly used in rubber base adhesives natural rubber butyl nibber and polyisobutylenes styrene-butadiene rubber nitrile rubber polychloroprene rubber (neoprene). Typical properties of these rubbers are shown in Table 2. 

Most rubbers used in adhesives are not resistant to oxidation. Because the degree of unsaturation present in the polymer backbone of natural rubber, styrene-butadiene rubber, nitrile rubber and polychloroprene rubber, they can easily react with oxygen. Butyl rubber, however, possesses small degree of unsaturation and is quite resistant to oxidation. The effects of oxidation in rubber base adhesives after some years of service life can be assessed using FTIR spectroscopy. The ratio of the intensities of the absorption bands at 1740 cm" (carbonyl group) and at 2900 cm" (carbon-hydrogen bonds) significantly increases when the elastomer has been oxidized [50]. 

ZDEC is used in the following applications as a fast primary or secondary vulcanization accelerator in NR, SBR, IIR, EPDM and for natural and synthetic latex a stabilizer in butyl, butadiene, and urethane rubbers an antioxidant in rubber-based adhesive systems a stabilizer in cement a heat stabilizer for polyethylene. 

Use of Solvent-based adhesives in seaming stems from the pioneering work of Charles Macintosh in the last century seam bonding with rubber solutions was a method used in the original waterproof coats carrying his name. Developments of the rubber-bonded seams are used in the manufacture of items such as life jackets and life rafts. The following (in cross-linked form) are commonly used Natural rubber-based adhesives, Poiychioroprene rubber adhesives, Poiyurethane and butyl rubber. 

Several elastomers can be used in rubber-based adhesives. The elastomer provides the backbone of the adhesive, so the main performance of the adhesive is provided by the rubber properties. However, several specific properties for application are imparted by adding other ingredients in the formulations. The most common elastomers used in rubber-based adhesives are natural rubber (NR), butyl rubber (BR) and polyisobutylenes, styrene-butadiene rubber (SBR), nitrile rubber (NBR) and polychloroprene rubber Neoprene) (CR). 

Early adhesive uses of butyl rubber generally consisted of solvent-based dispersions, or tape and rope extrusion of formulated solid rubber. Extensive use was made of butyl rubber s inherent tackiness in highly saturated grades of the polymer to make pressure sensitive tapes and precoated films. The polymers are also extensively used as major components of hot-melt adhesives, solid rubber sealing tapes, and caulking grades of sealants and mastics, of which most were high solids content solvent-based formulations. 

Hydrogenated rosin Methyl rosinate Methylstyrene/vinyltoluene copolymer Paraffin, chlorinated Pentaerythrityl hydrogenated rosinate Pentaerythrityl rosinate Polybutene Polydipentene Polyvinyl methyl ether Rosin Sorbeth-20 Terpene resin tackifier, adhesives EVA-based Dipentene-styrene resin tackifier, adhesives rubber-based Dipentene-styrene resin tackifier, amorphous polyolefins C5 hydrocarbon resin, aliphatic tackifier, antifouling paints Methyl hydrogenated rosinate tackifier, butyl rubbers C5 hydrocarbon resin, aliphatic tackifier, caulks C5 hydrocarbon resin, aliphatic tackifier, cement... 

The elastomeric group of adhesives is based on natural rubber latex and its derivatives or totally synthetic rubber known as SBR (styrene butadiene rubber). There is now a wide range of synthetic rubber adhesives based upon SBR including nitrile and butyl rubber. Another elastomeric adhesive is the versatile polyurethane rubber group. 

In the hot-melt type, two principal polymer types are used polyolefin and ethylene co-polymer based and polyester and polyamide type. In the solvent-based type, the most prominent are neoprene (polychloroprene)-based solvent and latex types, and polyvinyl acetate emulsions. For pressure-sensitive adhesives, the most favored are acrylic adhesives and butyl rubber/polyisobutylene types. 

Butyl rubber is an elastomeric polymer used widely in adhesives and sealants, both as primary binders and as tackifiers and modifiers. Butyl rubber is a copolymer of isobutylene with a small amount of isoprene. These materials have relatively low strength and tend to exhibit creep under load. They are useful in packaging apphcations where their low permeability to gases, vapors, and moisture can be exploited. Butyl rubber is also used as an adhesive sealant. It is generally applied from a solvent-based solution. Table 5.1 summarizes some of the important properties of butyl rubber adhesives. 

Plastic foams. Some solvent cements and solvent-containing pressure-sensitive adhesives will collapse thermoplastic foams. Water-based adhesives, based on styrene butadiene rubber (SBR) or polyvinyl acetate, and 100 percent solid adhesives are often used. Butyl, nitrile, and polyurethane adhesives are often used for flexible polyurethane foam. Epoxy adhesives offer excellent properties on rigid polyurethane foam. 

Plasticizers are used in butyl rubber, polyureAane, polysulfide, solvent aerylies, polyvinyl acetate, and silicone rubber adhesives and sealants. The compatibility of the plasticizer depends on base polymer chemistry. Plastieizers for silicone systems are low molecular weight... 

Solvents (A.S.C., 1986 Dick, 1987) - Solvents are used in evaporation type adhesives and sealants. They act as the carrier in which the base polymer is dissolved to provide low viscosity solutions that can accommodate fillers and otheradditives. Butyl rubber solutions are made with 50 to 70% rubber and 30 to 50% solvent. These are the bases of products which vary from unfilled viscous liquids to semi-solid filled sealants. Solvent release sealants generally range from 70 to 80% total solids. The solvent level is chosen so that adhesive or sealant is easy to apply and wets the adherend surface. After application, the solvent evaporates from the glue-line leaving the polymer bonded to the adherend. 

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