Epoxy systems: application areas

Tpo maximize the utility of crosslinked cycloaliphatic epoxy resins in some of the more critical application areas, improved toughness is required. Such improvements can often be made through modification with various flexibilizing agents, but as a rule this improvement is accompanied by a severe degradation of the strength and heat distortion temperature of the cured system. 

There are many applications for polymeric waterborne adhesives. These include packaging adhesives, pressure-sensitive tape, coatings for textiles, wood adhesives, and various industrial adhesives and coatings. The potential applications for waterborne epoxy adhesives are more limited due to their lack of tack and pressure-sensitive characteristics and the time it takes for the chemical reaction to complete cure. However, waterborne epoxy systems have found significant markets in niche areas. 

This review is intended to provide a survey of the chemistry in these areas, to discuss some applications for photosensitive epoxy systems and to show recent advances. A number of previous reviews are available i" which have described... 

By combining epoxies of different molecular weight, type and reactivity with a variety of different curing agents one has the possibility to formulate two-component systems for nearly any application in civil engineering or the building industry. Table 3.1 outlines the properties, products and application areas of epoxy systems. 

Table 3.1 Properties, products and application areas of epoxy systems...

Floors ana walls of structures are obvious areas where epoxy systems may be utilized to prevent deterioration from abrasion and chemical attack. Such systems are now to be found in original specifications. VTall surfaces may be coated viith epoxy systems based on solid resins dissolved in solvents and hardened with polyamines and/or polyamides. Porous surfaces, such as concrete blocks, are first prepared viith fillers to provide a smooth surface for application of coatings. 

One of the largest areas of use of nitrile rubber modified epoxy systems is in the printed circuit board area. A number of systems have been described that are composed of carboxyl-containing nitrile rubber such as Hycar 1072 mixed with epoxy resin. " The low molecular weight functionally terminated nitrile rubbers have also found significant application in this area. Other workers have found useful a system that combines a high molecular weight nitrile rubber with the liquid functionally terminated materials. Finally, other references describe the use of non carboxylated nitrile rubbers in circuit board applications. 2 ... 

A typical heat release rate curve for a neat epoxy system and the respective layered silicate nanocomposite, is shown in Fig. 2.12. Both peak and average heat release rate, as well as mass loss rates, are all significantly improved through the incorporation of the nanopartieles. In addition, no increase in specific extinction area (soot), CO yields or heat of combustion is noticeable. However, the mechanism of improved flame retardation is still not clear and no general agreement exists as to whether the intercalated or exfoliated structure leads to a better outcome. The reduced mass loss rate occurs only after the sample surface is partially covered with char. The major benefits of the use of layered silicates as a flame retardation additive is that the filler is more environmentally-friendly compared to the commonly used flame retardants and often improves other properties of the material at the same time. However, whilst the layered silicate strategy is not sufficient to meet the strict requirements for most of its application in the electrical and transportation industry, the use of layered silicates for improved flammability performance may allow the removal of a significant portion of conventional flame retardants. 

In recent years acetylene terminated resins (AT-resins) have shown promise in the area of high temperature applications and are possible replacements for state-of-the-art epoxy resin systems where humidity exposure is expected. Acetylene terminated resins have two important advantages over previously developed systems ... 

The applications of epoxy resins are not only used for adhesives but in the area of coatings used for appliances, automobiles, and cans. These resins have the added advantage of being solventless systems, which helps avoid air pollution... 

Since slower-curing epoxy adhesives systems flow over and wet high-energy surfaces very well, there is little chance for air to become trapped at the interface. As a result, mechanical abrasion is often recommended as a substrate surface treatment prior to application of the epoxy adhesive. The added surface area and the mechanical bonding provided by the additional peaks and valleys on the surface will enhance adhesive strength. If the adhesive does not wet the substrate surface well, such as in the case of epoxy resin on polyethylene, mechanical abrasion is not recommended since it will only encourage the probability of gas voids being trapped at the interface. 

Structural adhesives that are commonly used for composites are supplied in two basic forms semisolid B-stage film and thixotropic pastes. The film adhesives are cast or extruded onto carrier fabrics or films and partially cured to a semisolid. They can easily be handled, cut, and applied to the joint area. There is no need for mixing, metering, or dispensing of liquid components. In use, these adhesive systems are activated by heat and pressure. The semisolid B-stage film liquefies briefly on application of heat and then cures to an insoluble state. Epoxy, polyimides, epoxy-nylons, epoxy-phenolic, and nitrile-phenolic adhesives are available as B-stage film. 

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