Rubber-based adhesives: typical

A general introduction has been given in other articles, Rubber-Based Adhesives and Rubber-based Adhesives Typical Characteristics. Here, one of the most common types of rubber adhesives, contact adhesives, is further considered. Contact adhesives are bonded... 

Natural rubber (NR) is the base polymer for many Rubber-based adhesives. This article is designed to supplement with specific information the more general treatment given in Rubber-based adhesives compounding and Rubber-based adhesives typical characteristics. 

Nitrile rubber, also known as nitrile-butadiene rubber (NBR), is a copolymer of acrylonitrile and butadiene (Fig. 1). As a base polymer for Rubber-based adhesives, it provides a number of specialized properties, which supplement those summarized in the article Rubber-based adhesives typical characteristics. NBR adhesives comprise a range of materials that may differ in proportion of comonomer or may be compounded with other resins. NBR adhesives are characterized by high oil and plasticizer resistance, excellent heat resistance and high adhesion to metallic substrates. 

In addition to the articles cited above, further information is to be found in Rubber-based adhesives typical characteristics and Natural rubber-based adhesives. 

Rubber-based adhesives typical characteristics J M MARTIN MARTfNEZ Advantages... 

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. 

Some typical rubber adhesive formulations are given in Rubber-based adhesives compounding. Specific formulations for NR can be found in the references below. 

In the general introductory article on Rubber-based adhesives, the complexity of formulations for these materials was emphasized. Although considerable experience is necessary for successful formulation, some introductory guidelines and typical formulations can be given this is the purpose of this article. 

Elastomeric adhesives typically contain an elastomer and a tackifying or modifying resin as key components, but in general, other ingredients are also included. The formulation of rubber-based adhesives may contain nine, or even more, different components (Table 1). Typical formulations of various types of adhesives are given in Tables 2-5. 

In solvent-borne rubber adhesives, a variety of solvents can be chosen to control drying rate, adjust viscosity and dissolve important ingredients. Resins can be added to improve tack, wetting properties, heat resistance, bond strength and oxidation resistance. The most common resins nsed in rubber-based adhesives are rosins, rosin esters, and terpene, coumarone-indene, hydrocarbon and phenobc resins. Plasticizers and softeners reduce hardness, enhance tack and decrease cost of rubber adhesive formulations. Paraffinic oils, phthalate esters and polybutenes are typical plasticizers. Fillers are not often added to rubber adhesive formulations because they reduce adhesion. However they are sometimes used because they decrease cost and increase solution viscosity. Carbon black and titanium dioxide are also used to provide colour to the adhesives. Clays, calcium carbonate and silicates are also common fillers in rubber adhesive formulations. For water-borne adhesives, typically protective colloid, preservative, defoamers, wetting agents and emulsifiers are included in the formulations. 

The difference between plasticizers and tackifiers is somewhat arbitrary and the effect of this difference is described below in the section on Physical Properties. Plasticizers are typically lower in molecular weight and melting or softening point than are tackifiers. Hydrocarbon oils including aromatic, naphthenic, and paraffinic are commonly used with rubber-based adhesives. Phthalates, such as dioctyl phthalate or dibutyl phthalate, are more typically used in small amounts with acrylics. Since plasticizers are usually low molecular weight compounds, there is often more latitude in the chemical types that will be compatible with the base pol5mier because of the contribution from entropy of mixing. 

As with PSA, the phenolics are added primarily for increased cohesive strength and temperature resistance ([216], pp. 284-306). More phenolic is used in adhesives with higher strength requirements, e.g. for metal-metal bonding. Resins based on /j-/-butyl phenolics are most commonly selected ([216], pp. 284-306). They are usually present in the adhesive at 35-50 parts per 100 rubber (phr), with typical optima at 40-45 phr ([216], pp. 284-306). Significant deviation from this optimum may have drastic effects. 

According to Kinloch, the addition of 1-8 wt.% of nanosilica particles with an average diameter of around 20 nm to a typical rubber-toughened adhesive, based... 

---