Hybrid acrylic adhesives

Aromatic tertiary amines can also be used as part of the initiator system [58], Glycidyl methacrylate or methacrylic acid have been used to hybridize acrylic adhesives based on this cure chemistry with epoxies [59]. The epoxy functionality is reactive with the carboxylic acid groups on the monomer. 

Worldwide use and sales for acrylic adhesives of the types discussed here are difficult to determine, particularly since so many of the chemistries involved are nowadays hybrids of more than one type. Acrylics would, no doubt, not be considered the major chemical family of adhesives, when compared to epoxies and urethanes. Nevertheless, due to the need for the unique handling characteristics and performance properties achievable with acrylics, they maintain and will continue to maintain an important position among high performance structural adhesive types. 

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. 

However, the implementation of miniemulsion polymerization in industry is challenging because industry will only adopt this method provided that new and improved materials can be produced and that the technology required to mn the process is available at a reasonable cost. The former is tme because hybrid alkyd-actylic coatings and polyurethane-acrylic adhesives with... 

Hybrids of block copolymer rubbers and acrylics have also been used to increase the low-temperature impact resistance of the adhesive used for body-side molding attachment [127]. To further enhance performance, a new type of hybrid adhesive has been developed, which combines an adhesive polymer, like an... 

There are two approaches to forming urethane-acrylic hybrids. First, an acrylate terminated urethane oligomer can be used [147]. Alternatively, polyisocyanate and benzoyl peroxide can be combined in one side of the adhesive, and methacrylate monomers and urethane curatives (especially polyols) in the other [148]. 

However, newer adhesives systems having moderate temperature resistance have been developed with improved toughness but without sacrificing other properties. When cured, these structural adhesives have discrete elastomeric particles embedded in the matrix. The most common toughened hybrids using this concept are acrylic and epoxy systems. The elastomer is generally a amine- or carboxyl-terminated acrylonitrile butadiene copolymer (ATBN and CTBN). 

In this book I have confined discussion to those polymeric materials which are cured by chemical reaction and which have found widespread application in the construction industry. As such, the book covers materials based on epoxies, polyurethanes, silicones, polysulphides, alkyds and polyesters. In addition, there is a chapter on hybrid polymer systems and one on acrylics. It is true that acrylic emulsions are not strictly thermosetting polymer systems, but their widespread use and importance made their exclusion difficult. These materials find use as coatings, sealants, adhesives, grouts, flooring compounds, repair compounds and waterproofing agents. 

In one example, a UV aerobic acrylic replaced an epoxy adhesive in an aircraft application. Epoxy adhesives frequently have been used to bond through-hole hybrid eomponents onto PC boards. This prevents breaking of the fragile leads under common aircraft stresses sueh as temperature changes and vibration. 

Chem. Descrip. Acrylic urethane hybrid polymer Uses Urethane-aciylic for high-performance VOC-compliant industrial coatings and adhesives ind. dear coats, wood coatings, graphic arts polymers, textile and vinyl coatings, leather finishes, plastic coatings, film lamination... 

Features Acrylate, anhydride and carboxyl functionality good cure speed, exc. copper adhesion, good solv. and acid resist., exc. aq. development hybrid cure systems high acid no. for alkali strippability Properties APFIA 50-150 clear liq. sp.gr. 1.11-1.15 dens. 9.3-9.6 Ib/gal vise. 10,000-25,000 cps acid no. 130-160 flash pt. (PMCC) 115-120 F 70 2% resin content... 

The primary chemical classes from which adhesives are made include epoxies, acrylics, phenolics, urethanes, natural and synthetic elastomers, amino resins, silicones, polyesters, polyamides, aromatic polyheterocyclics, and the various natural products such as carbohydrates and their derivatives as well as plant- and animal-based proteins. Chemical class was once a relatively clean differentiator of adhesives, but so many adhesives now are hybrids, designed to take advantage of specific attributes of more than one chemical class or type of material. Hybridization can be accomplished by incorporating into an adhesive a nonreactive resin of a different chemical class adding another type of reactive monomer, oligomer,... 

It is common to add a few percent of an alkyd-surfactant blend to latex paints to improve adhesion to chalky surfaces and, in some cases, to improve adhesion to metals. It is important to use alkyds that are as resistant as possible to hydrolysis. Hybrid alkyd-acrylic latices have been prepared by dissolving an oxidizing alkyd in the monomers used in emulsion polymerization, yielding a latex with an alkyd grafted on the acrylic polymer (28,29). Nonyellowing waterborne alkyds based on rosin-fatty acid modified acrylic latices have been reported (30). 

The major advantages of these UV-curable hybrid systems lie in their superior combination of properties which can be tailor-made for a given application by adjusting the proportions of the two components. The IPN formed will exhibit the main features of the two polymer networks, for instance the toughness and scratch resistance of UV-cured acrylate polymers and the elastomeric character of the cross-linked polyurethane-vinyl ether, with the expected benefit regarding adhesion and impact resistance. 

A preaccelerated, flexible high performance laminating urethane acrylate hybrid resin, particularly suited to high deflection applications, with high impact resistant properties. Offers excellent adhesion to both glass and aramid fibres which benefits interlaminar shear properties. 

In hybrid coatings deposited on plastic substrates, the critical load for which failure occurred was found to pronouncedly decrease when the friction coefficient increased. Microwave oxygen plasma modification of polypropylene substrates was found to favor the adhesion more than wet-chemical modification (Blees, 2000). Hybrid sol-gel coatings deposited on brass were also found to be the best compromise in terms of tarnishing, corrosion and scratching resistance, when conpared to hard coatings (TiN, TiZrN or acrylic varnish) (Dumont, 2000). 

Lopez A, Degrandi E, Cretan C, Canetta E, Keddie JL, Asua JM. Waterborne polyurethane-acrylic hybrid nanoparticles by miniemulsion polymerization applications in pressure-sensitive adhesives. Langmuir 2011 27 3878-3888. 

The adhesives can have open times varying from a few seconds up to about 10 minutes to match application requirements. Improvements related to adhesives that have long open times and/or high green strength via the use of urethane diols or polyurethane-acrylic hybrid systems has been reported [42]. 

Patents [95-99] describe similar hybrid systems but which incorporate an aminosilane as the complexing agent for the organoborane and a silanol (OH functional silicone) in the other part of the adhesive. It is claimed that the simultaneous acrylic and silicone polymerisations gives adhesives with much better toughness. 

Other than the hydrocarbon elastomers and acrylics, and to a smaller degree silicones, little success commercially has attended efforts to utilize other polymers for PSAs. The patent literature describes a number of water solubles, suitably crosslinked, as the base ingredient for repulpable adhesives on paper backings used to splice rolls during papermaking operations. The patent literature also reveals efforts to utilize polyurethanes, polyurethane-acrylic hybrids, ionomers, and polyester block elastomers, among others, but only repulpable adhesives have reached the marketplace. Two systems that have achieved mentionable commercial success are described below. 

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