Curing agents, adhesive

Plasticizers and oils, curatives and accelerators may also be added. In solvent-borne adhesives, curing agents are generally packed separately. 

Doyle, Daryl J. (1989). A Review of Ultraviolet (UV) Radiation as an Adhesive Curing Agent. Society of Manufacturing Engineers Technical Paper AD89-534, Adhesives 89, September 12-14, 1989, Atlanta, Georgia. 

Adhesives consist of different raw materials. Organic monomers and polymers usually are the main part of a formulation and mostly contribute to the adhesive s mechanical and physical performance. In addition to the organic part of a formulation, other raw materials like inorganic mineral fillers or solvents are used. For reactive adhesives, curing agents and accelerators are added to the formulation to cross link the organic part of the formulation. 

The two-part epoxy adhesive, readily available in hardware stores or other consumer outlets, comes in two tubes. One tube contains the epoxy resin, the other contains an amine hardener. Common diamine room temperature epoxy curing agents are materials such as the polyamides, available under the trade name Versamid. These polyamides are the reaction products of dimer acids and aUphatic diamines such as diethylenetriamine [111-40-0] ... 

Phenolic Resins. Phenohc resins (qv) are formed by the reaction of phenol [108-95-2] C H O, and formaldehyde [50-00-0] CH2O. If basic conditions and an excess of formaldehyde are used, the result is a resole phenohc resin, which will cure by itself Hberating water. If an acid catalyst and an excess of phenol are used, the result is a novolac phenohc resin, which is not self-curing. Novolac phenohc resins are typically formulated to contain a curing agent which is most often a material known as hexamethylenetetraamine [100-97-0] C H22N4. Phenohc resin adhesives are found in film or solution... 

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

Formulation. Polysulftde-based sealants are formulated with appropriate ingredients to obtain the desired properties for a particular appHcation. A typical formulation contains Hquid polysulftde polymer, curing agent, cure accelerators (bases) or retarders (acids), fillers, plasticizers, thixotropes, and adhesion promoters. 

The outstanding performance characteristics of the resins are conveyed by the bisphenol A moiety (toughness, rigidity, and elevated temperature performance), the ether linkages (chemical resistance), and the hydroxyl and epoxy groups (adhesive properties and formulation latitude, or reactivity with a wide variety of chemical curing agents) (see also Phenolic resins). 

Rather similar are the 5.5-dimethylhydantoin derivatives shown in Figure 26.18 (b, e). These resins are said to eonfer improved weathering resistance but also exhibit higher water absorption. Another trifunctional material is p-glycidyl-oxy-A,A/-diglycidylaniline. This has been recommended for adhesive systems in conjunction with benzophenonetetracarboxylic acid dianhydride, which is a room temperature curing agent in this case. 

Some rubber base adhesives need vulcanization to produce adequate ultimate strength. The adhesion is mainly due to chemical interactions at the interface. Other rubber base adhesives (contact adhesives) do not necessarily need vulcanization but rather adequate formulation to produce adhesive joints, mainly with porous substrates. In this case, the mechanism of diffusion dominates their adhesion properties. Consequently, the properties of the elastomeric adhesives depend on both the variety of intrinsic properties in natural and synthetic elastomers, and the modifying additives which may be incorporated into the adhesive formulation (tackifiers, reinforcing resins, fillers, plasticizers, curing agents, etc.). 

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