Acrylic engineering adhesives

M. Hauser, "Anaerobic and Modified Acrylic Engineering Adhesives Technological Innovations in Structural Bonding, Technology Conference (SPE), ADHESIVES FOR INDUSTRY, June 24-25, 1980, El Segundo, CA. 

Early acrylic engineering adhesives were quite simple in composition and thus service well to illustrate their basic technology. An example of such an adhesive is as follows ... 

Modified or second generation acrylic engineering adhesives are more complicated than those described above. In modified acrylic adhesives, polymerization between adherends leads to impact resistant plastics with adhesion to the adherends. The following formulation of Brigas and Muschiatti illustrates an early modified acrylic engineering adhesive ... 

Another formulation of Toback and O Connor employs hydroxypropyl methacrylate as the fluidizing reactive component of a modified acrylic engineering adhesive. A condensation product of three moles of hydroxy-ethyl methacrylate, three moles of toluene diisocyanate, and one mole of a polypropylene triol provides a rubber phase. 

The polymerization of the monomer in acrylic engineering adhesives can be initiated by electron beam or ultraviolet (UV) radiation, provided that the adherends or the fillers in the adhesives are not barriers to radiation. Acrylic monomers are generally more reactive to radiation than methacrylates. Electron beams generate free radicals directly in the adhesive, whereas UV curing requires a photosensitizer or photoinitiator to provide free radicals. 

Because of their reactivity, acrylic engineering adhesives are necessarily two-part adhesives. No special application equipment is required for the two-part surface activated type, which is also called the no-mix type. As mentioned earlier, it is only necessary to wipe the activator on to the surfaces before spreading the adhesive and mating the surfaces. 

Epoxy-based and two-part acrylic engineering adhesives generally bond well to phenolics and roughening the surface was found to be beneficial for the UV-curing acrylics (Table 3.3). 

A. G. Bachmann, Aerobic acrylic adhesives (new technology in acrylic adhesives), Society of Manufacturing Engineers, Adhesives 84 Conference, 1984. 

Uses Flame retardant, plasticizer for NBR elastomers, PVC (sheeting, coatings for apparel, upholstery, wall coverings, wire insulation, plasti-sols), PVAc adhesives, cellulosics, phenolic, PP, PS, acrylic, engineering resins, unsat. polyesters, alloys... 

Uses Monomer for large-volume resins and polymers, organic synthesis comonomer for thermosetting acrylic resins carboxylated comonomer for S/B-nItrlle latex engineering adhesives thickener for hair care prods. paints Ion-exchange membrane processing agent, binder for paper and textiles leather treatment adhesion promoter pharmaceutical ophthalmics... 

Uses Engineering adhesives monomer for hydrophilic polymer synthesis reactive comonomer for acrylic and S/B resins Manuf./Distrib. ABCR http //www.abcr.de-, Acros Org. http //www.acros.be Trade Name Synonyms Blemmer P [NOF http //WWW. nof. co.jp]... 

Engineering acrylic adhesives are two-part systems which, when mixed or activated, polymerise (cure) to form an impact-resistant plastic layer which is well adhered to the surfaces of the adherends. The activator for the curing process may be a chemical (either mixed with the adhesive or applied to the adherend surfaces prior to the adhesive), or, for some varieties, UV or electron-beam radiation. The toughened or modified engineering adhesives have been widely used since the 1980 s in vehicle construction, wood to metal bonding, aerospace applications, panels and computer equipment. 

Finally, acrylic chemistry is the basis for a number of 100% solids reactive engineering adhesives used in structural bonding applications, generally involving metal or plastic non-porous surfaces. 

Engineering adhesives are solventless, liquid, reactive, durable adhesives for bonding durable substrates. There are six recognized chemical types of engineering adhesives acrylic, anaerobic, cyanoacrylate, epoxy, silicone, and urethane. Strictly speaking, the first three in this list are varieties of acrylic, but only the first will be discussed here. There is, however, considerable overlap in the chemistry and properties of acrylic and anaerobic adhesives. Since considerable progress has been made in acrylic adhesives over the last two decades, those used in engineering applications are now referred to as modified acrylic adhesives. 

This guide provides a full explanation of the cure mechanisms and discusses the performance benefits for four types of engineering adhesives (cyanoacrylates, epoxies, two-part acrylics and UV curing adhesives). There are also chapters on joint design, dispensing systems, the surface preparation for difficult plastics and information on several Other adhesive technologies. 

Firstly is an epoxy-based material adhesive. Although some people use the term epoxy as a generic reference to aU high-performance engineering adhesives, it has a specific meaning within flie adhesive world. It is also different from other adhesive types, particularly the acrylic-based adhesives. 

The reluctance of acrylic monomers to polymerise in the presence of air has been made a virtue with the anaerobic acrylic adhesives. These are usually dimethacrylates such as tetramethylene glycol dimethacrylate. The monomers are supplied with a curing system comprising a peroxide and an amine as part of a one-part pack. When the adhesive is placed between mild steel surfaces air is excluded, which prevents air inhibition, and the iron present acts as a polymerisation promoter. The effectiveness as a promoter varies from one metal to another and it may be necessary to use a primer such as cobalt naphthenate. The anaerobic adhesives have been widely used for sealing nuts and bolts and for a variety of engineering purposes. Small tube containers are also available for domestic use. 

Acrylics, unsaturated polyesters and other monomer-based adhesives containing ethy-lenic unsaturation, cure by formation of free peroxide radicals formed with transition metal ion donators such as cobalt, iron, copper and nickel. In engineering applications the presence of transition metals on surfaces sees them act as initiators by forming the free peroxide radicals from the added peroxide compound(s). The base monomers usually contain inhibitors such as phenols or other materials classed as peroxide stabilisers to... 

Because many acrylic adhesives cure very rapidly with a significant exotherm, manufacturers generally recommend that quantities greater than a pint (ca. 0.47 L) should not be mixed at one time. As a consequence of the rapid exothermic cure of many acrylic adhesives, the use of dual component cartridges is often ideal. Most products can be purchased in ready-to-use cartridges. For large continuous operations, various automated types of meter-mix-and-dispense equipment are marketed by a number of engineering companies. 

In the future the various families of acrylic adhesives are expected to grow as more and more design engineers specify bonded parts and as specialty substrates continue to emerge that are bondable only with acrylic adhesives. The development of formulations with lower overall odor, 1-part systems, and hybrid types will also have a positive effect on overall growth. 

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