Adhesives hybrid

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... 

The early aerospace adhesives were primarily based on epoxy resin chemistry. However, unique applications requiring high temperatures and fatigue resistance have forced the development of epoxy-phenolic, epoxy-nitrile, epoxy-nylon, and epoxy-vinyl adhesives specifically for this industry. The aerospace industry has led in the development and utilization of these epoxy-hybrid adhesives. 

These blends can take a number of different forms. The added resin may be reacted with the epoxy resin, or it may be included as an unreacted modifier. The modifier may be blended into a continuous phase with the epoxy resin (epoxy alloys) or precipitated out as a discrete phase within the epoxy resin matrix (as is generally done in the case of toughening modifiers). Epoxy hybrid adhesives are often used as film (supported and unsupported) or tape because of the ease with which formulated systems can be dissolved into solvent and applied to a carrier or deposited as a freestanding film. Some systems, notably epoxyurethanes and epoxy-poly sulfides, can be employed as a liquid or paste formulation because of the low-viscosity characteristics of the components. 

TABLE 7.1 Common Epoxy Hybrid Adhesive Systems... 

TABLE 7. 2 Range of Bond Strengths (Measured at Room Temperature) of Various Hybrid Adhesives... 

Hybrid adhesive Tensile shear strength, psi T-peel strength, lb/in... 

The most common types of epoxy hybrid adhesives are... 

The first group, resins that are used primarily to toughen epoxy adhesive systems, is described in Chap. 8. This chapter focuses on the resinous modifiers that are used as alloy blends. Characteristics of commercially available epoxy alloy adhesives are presented in Table 7.1. Tensile shear and peel strengths that are typical of these hybrid adhesives are compared in Table 7.2. 

FIGURE 7.1 The effect of temperature on the tensile shear strength of modified epoxy-phenolic compared to other hybrid adhesives (substrate is aluminum).4... 

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... 

By adding nonepoxy flexibilizing resins to the formulation to create an epoxy-hybrid adhesive system... 

A good example of a flexible epoxy hybrid adhesive is the epoxy polysulfides. Figure 8.2 shows the improved impact resistance that can be realized by using increasing amounts of... 

Commercial silyl-epoxy hybrid adhesives have been developed by Collano AG. These are polymer alloys consisting of a matrix of silyl reactive polymers (elastic phase), which host domains of epoxy reactive polymers (hard domains). With a different choice of components, mixing ratios, and the size of respective domains, the overall properties of the bond line can be tailored for specific purposes. 

Epoxy dispersions also can easily be blended with other waterborne polymers to make modified latex adhesives. The resulting hybrid adhesive produces performance properties and application characteristics that are superior to those of the originating latex system. 

The substrate should then be washed in tap water and rinsed with distilled water. The final step in the process is an oven-dry of 10 min at 121 to 177°C.26 Several other surface preparation procedures for beryllium have been reported to have merit. Epoxy and epoxy hybrid adhesives have been found to provide high strengths on sulfuric acid-sodium dichromate etched beryllium.27... 

The control of bond line thickness is essential for high-power devices. A thin bond line is required since thickness is directly proportional to the junction-to-case thermal resistance, jc (see Chapter 2). Specially formulated solvent-based hybrid adhesives... 

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]. 

Bondline thickness. The control of bondline thickness is essential for high-power devices. A thin bondline is required since thickness is directly proportional to the junction-to-case thermal resistance, Qjq (see Ch. 2). Specially formulated solvent-based hybrid adhesives can produce uniform bondline thicknesses of one mil or less. Small hard spacers, acting as shims, added to paste adhesive formulations, have also been used to control thickness.The use ofpreforms instead of paste adhesives also assures reproducible thicknesses provided uniform pressure and temperature are applied during curing. 

Da Silva, L., Pirondi, A., Ochsner, A. (2011). Hybrid Adhesive Joints. (L. da Silva, A. Pirondi, A. Ochsner, Eds.). Heidelberg Springer. 

SikaBond -66 AT is a universal assembly adhesive for construction as it is a phthalate-free PUR-Hybrid adhesive with good bonding and compatibility to polystyrene insulation. An application is described in Section 6.8.8 entitled Bonding of Parquet/Timber Floors . Its mechanical properties are summarised in Fig. 82, along with those of Sikaflex -20. 

One-component Epoxy/PUR hybrid adhesive Combination and mixture of polyurethane and epoxy resin, where the epoxy group reacts with the latent hardener at high temperature... 

Frequently it is necessary to combine materials having quite dissimilar solubility parameters, and often differing in modulus as well. An important example, the manufacture of tires, is discussed in the chapter, Bonding Textiles to Rubber. Use is made of a hybrid adhesive, RFL, containing heat-resistant resorcinol-formaldehyde for good attachment primarily to the polar, high modulus fiber, plus an elastomer of moderate solubility parameter, butadiene-styrene-vinyl pyridine terpolymer latex, mainly for the rubber. 

Hybrid adhesives, comprised of a polymer adhesive and a synthetic cement, are also used in cartridge injection systems. These are generally fast-cure adhesives and may exhibit superior resistance to high temperatures. 

Hybrid anchors (not to be confused with hybrid adhesives as discussed in 4.3.2) combine the working principles of adhesive anchors with expansion or undercut mechanisms. Torque-controlled adhesive anchors (Figure 4.7) transfer tension loads via friction. Because of their ability to re-expand upon the application of tension loads, they are particularly suited for use in concrete that may crack over the anchor life, and may be used in a variety of applications where the flexibility of an adhesive anchor system is required. They are also less sensitive to hole cleaning procedures than ordinary adhesive anchors. Grouted undercut anchors, like standard undercut anchors, transfer tension loads via bearing. The grout improves the form-fit between the anchor and the concrete thereby reducing initial anchor movement under load. 

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. ... 

Abstract In this chapter, classification of adhesive and sealant materials is presented. For this purpose, various categories are considered depending on the polymer base (i.e., natural or synthetic), functionality in the polymer backbone (i.e., thermoplastic or thermoset), physical forms (i.e., one or multiple components, films), chemical families (i.e., epoxy, silicon), functional types (i.e., structural, hot melt, pressure sensitive, water-base, ultraviolet/ electron beam cured, conductive, etc.), and methods of application. The classification covers high-temperature adhesives, sealants, conductive adhesives, nanocomposite adhesives, primers, solvent-activated adhesives, water-activated adhesives, and hybrid adhesives. 

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