Hybrids epoxy-urethane

These reactive hybrid epoxy-urethane adhesives were developed initially for bonding to oily cold-rolled steel, but they have given good results on other substrates as well. It is believed that the oil contaminant on the substrate is adsorbed into the uncured adhesive and acts as a plasticizer. Table 7.9 shows tensile shear values obtained after curing 20 min at 177°C on various untreated substrates. The epoxy-urethane adhesives resist hydrolysis and give useful bond strengths up to about 100°C. 

TABLE 7.9 Cured Tensile Shear Strength of Uncleaned Substrates Bonded with Epoxy-Urethane Hybrid System16... 

Some more recent examples of epoxy-urethane hybrids in one- and two-component structural adhesives are noted below. These have had success in the automotive industry where high impact strength, fatigue resistance, and high bond strength to a variety of substrates are valued characteristics. 

Another common method of flexibilizing epoxy adhesives is by blending the primary epoxy resin with other, more elastic polymers. Epoxy-nylon, epoxy-polysulfide, and to a certain extent epoxy-urethane hybrids use such a mechanism to provide flexibility. These flexibilizers are important additives for epoxy adhesives even though they may reduce certain... 

Several hybrid epoxy emulsions have been commercially prepared. An epoxy emulsion blended with waterborne aliphatic urethanes exhibited peel strength on aluminum of 10 lb/in—1.5 times greater than with the polyurethane itself. The optimum concentration of urethane in the final emulsion was about 50 percent by weight.13 Epoxy-phenolic dispersions have also been developed to provide waterborne adhesive systems with high glass transition temperature and chemical resistance. 

Another development has been reported by P.A. Lucas, W.E. Stamer and S.G. Musselman of Air Products and Chemicals Inc. (Lucas et al., 1994). An acrylate functional urethane flexibiliser has been used to modify epoxy resin, which optimises reactivity and is more compatible with epoxy. Urethane-acrylate flexibiliser offers very tough hybrid epoxy systems meeting the more demanding requirements of civil engineering applications. 

RTM is compatible with a variety of thermosetting polymers including polyester, vinyl ester, epoxy, phenolic, modified acrylic, and hybrid polyester-urethane. A convenient typical viscosity of thermoset precursors is in the range of 0.2-0.6 Pa s. The RTM process has the following advantages (i) emissions are lower than in open-mold processes such as spray-up or hand lay-up (ii) it can produce parts faster, as much as 5-20 times faster than open-mold techniques (iii) the mold surface can produce a high quality finish (iv) complex mold shapes can be achieved and... 

Chem. Descrip. Polyethylene wax CAS 9002-88-4 EINECS/ELINCS 200-815-3 Uses Surf, modifier, slip agenL scratch/abrasion resist, aid, processing aid for powd. coalings based on epoxy, hybrid, polyester urethane, acrylic Features Larger particle size Regulatory EDA 21 CFR 175.300 Lanco 1550 [Lubrizol]... 

Uses Pigment for water-based paints/coatings, industrial maintenance, marine, wood, plastic, coil, and protective coatings, office furniture finishes, DIY decorative and special effect paints, leather finishes Features High pigment loading forexc. color control compat. with water-based chemistries (acrylic, latex, epoxy, urethane, hybrid systems) contain no VOC s glycol-free... 

Secondary hydroxyl groups of the epoxy resin backbone may be reacted with polyisocyanates, aromatic as well as aliphatic, in two-component ambient curing systems that are commonly known as epoxy-urethane hybrid systems. This type of coating combines advantages of epoxy and polyurethane systems. 

Adhesives usually are classified as epoxy, urethane, or acrylic, based upon the chemistry used to bring about the olymerization of the liquid adhesive. However, the distinction among the various types of adhesives is not always clear, and many hybrid adhesives have been developed and marketed. The objective usually is to take advantage of the desirable mechanical properties or chemical resistance of one polymer while retaining the processing attributes of a different cure system. ... 

The distribution of powder coating sales by resin type for various geographical areas is given in Table 5. The polyester—epoxy hybrids account for 50% of the European market, yet have only market share <25% in the rest of the world. Similarly, the polyester urethanes, which account for only a small market share in Europe, find significant usage in the United States andjapan. AcryUcs hold a significant share only in the Japanese market. 

Blocked isocyanate prepolymers have been mixed with epoxy resins and cured with amines.18,19 These blocked prepolymers will initially react with the amines to form amine-terminated prepolymers that crosslink the epoxy resin. Urethane amines are also offered commercially for use with epoxy resins to develop hybrid adhesive systems.20... 

A novel concept for generating new multifunctional modifiers was developed [26], Hydroxyurethane modifiers (HUMs), which possess a wide range of hydrogen bonds, are embedded in an epoxy polymer network without a direct chemical interaction. Some new hybrid materials obtained by introducing hydroxyalkyl urethane into the polymer network structure, without any additional chemical reactions, are described in the following sections. 

More recent efforts have focused on developments that create true hybrids. For example, blocked isocyanate prepolymers have been mixed with epoxy resins and cured with amines [68-70]. These blocked prepolymers will react initially with the amines to form amine-terminated prepolymers that cross-link the epoxy resin. Several blocked isocyanates are commercially available. The DESMOCAP (Bayer) llA and 12A products are isocyanates (believed to be blocked with nonylphenol) used as flexibilizing agents for epoxy resins. ANCAREZ (trademark. Pacific Anchor, Inc.) 2150 is a blocked isocyanate epoxy blend used as an adhesion promoter for vinyl plastisols. A one-package, heat-cured hybrid adhesive was reported consisting of isophorone diisocyanate, epoxy resin, and a dispersed solid curative based on the salt of ethylenediamine and bisphenol A [71]. Urethane amines are offered commercially that can be used with epoxy resins to develop hybrid adhesive systems [72]. 

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. 

Uses Surf, modifier, slip agent, matting agent, mar resist, aid, abrasion resist, aid for semigloss powd. coatings, urethanes, epoxies, hybrids, polyesters... 

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