Rubber toughened acrylic adhesive

Plate 15 The magnetic ferrites of this electric motor are bonded to the external case with a rubber toughened acrylic adhesive. This assembly technique avoids the problems of dimensions and distorted magnetic flux incurred when other methods are used. Material Permabond F241. 

The use of rubbers (low glass transition polymers) to toughen acrylic adhesives... 

Toughened acrylic adhesives are structural adhesives and comprise mono-functional methacrylate monomers containing a dissolved rubber polymer added as a toughener, cure... 

While both cyanoacrylate and toughened acrylic adhesives contain no solvents - all the liquid present is converted to solid - their common base material is an excellent solvent in its own right and so both function well on unprepared surfaces. Toughened acrylics are noteworthy in this respect, though the tolerance of the cyanoacrylates is partially limited because contamination may inhibit hardening. Nonetheless, the cyanoacrylates generally cope well with the unprepared surfaces of the small plastics, rubber and metal parts that they are usually used on. 

Urethanes have also been used to toughen vinyl-terminated acrylic adhesives for improved impact resistance. Thus rubber-toughened urethane acrylates [79,80], water-dispersible urethane acrylates [81], and high-temperature-performance urethane-acrylate structural adhesives have been reported [82]. Polyurethanes terminated with acrylic functionality are also used for anaerobic or radiation-cured adhesives with improved toughness [83]. 

Prane (11) reviews the field and concentrates on history citing pivotal patents related to acrylics (or reactive ) adhesives. These patents show that numerous materials have been utilized in toughening acrylic adhesivesr some nonreactive in the systems, others reacting in, while still others using combinations of each general type modifier. Thus, we find examples for polychloroprene, thermoplastic urethanes, urethane adducts, acrylic rubber, chlorosulfonated polyethylene in addition to buta-diene/acrylonitrile rubber (or its carboxylic version). 

Reactive acrylic adhesives generally consist of a solution of a toughening rubber (chlorosulphonated polyethylene) in a partly polymerized mixture of monomers this is mainly methylmethacrylate but ethane diol dimethacrylate is added as a cross-linking agent. The remaining monomer is polymerized in a free radical chain polymerization redox initiation involves an organic peroxide and a tertiary amine. Acrylic cements consist of a partly polymerized acrylic monomer containing an initiator. Cure is established by the thermal or UV decomposition of the initiator (see Radiation-cured adhesives). 

A toughened adhesive has small rubber-like particles dispersed throughout the adhesive which improves some of the properties. Toughened acrylics are relatively fast curing and offer high strength and toughness and have more flexibility than the common epoxies. 

Two-component acrylic adhesives were used for all rubber-to-composite bonding but this is now being replaced by rubber-toughened epoxy paste adhesives, whieh eure at ambient. 

Extremely versatile, these adhesives will readily bond almost any substrate with the exception of some rubber-based materials and the difficult thermoplastics such as polyethylene. Even the latter may respond well if the surface is correctly prepared before bonding. The toughened acrylics are very robust and will cope with demanding environments. 

Liquid organic rubbers with reactive functionality can be prepared by several methods. End-functional oligomers are preferred. Chains attached to the network at only one end do not contribute as much strength to the network as those attached at both ends [34], Urethane chemistry is a handy route to such molecules. A hydroxy-terminated oligomer (commonly a polyester or a polyether) can be reacted with excess diisocyanate, and then with a hydroxy methacrylate to form a reactive toughener [35]. The methacrylate ends undergo copolymerization with the rest of the acrylic monomers. The resulting adhesive is especially effective on poIy(vinyl chloride) shown in Scheme 2. 

The homopolymers, which are formed from alkyl cyanoacrylate monomers, are inherently brittle. For applications which require a toughened adhesive, rubbers or elastomers can be added to improve toughness, without a substantial loss of adhesion. The rubbers and elastomers which have been used for toughening, include ethylene/acrylate copolymers, acrylonitrile/butadiene/styrene (ABS) copolymers, and methacrylate/butadiene/styrene (MBS) copolymers. In general, the toughening agents are incorporated into the adhesive at 5-20 wt.% of the monomer. 

Their J-39 adhesives are room-temperature curable, second-generation acrylics (16). Methyl methacrylate is the monomer, and a nitrile rubber and Dow ABS resin are used as toughening agents. This family of adhesives have been used in automotive, machinery and aerospace structures. Their J-50 adhesives (17) are two-component, fast-cure acrylics. In addition, they also developed a special adhesive, J-15 structural adhesive, for hydroplanes. 

Toughening of anaerobics by using urethane methacrylate monomers or by incorporating rubbers has been moderately successful, to create (although expensive) structural adhesives. However, in contrast to other tough adhesives such as reactive acrylics and polyurethanes, they remain relatively brittle materials. 

Cyanoacrylate adhesive can be made from different acrylate monomers such as methyl, ethyl, butyl, isopropyl, and so on. These molecules differ in size and adhesives and exhibit different physical properties. Methyls are the smallest molecule and seem to work best on metal and rubber parts while ethyls work best on plastic parts. Many modifications can be made to the monomers to alter or improve their properties as adhesives. They can be toughened with rubber or formulated to have low odor, resistance to thermal cycling, or less sensitivity to surface conditions which tend to stabilize the adhesive and slow down the cure. ... 

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