Applications adhesives

Application of cyanoacrylates to the bonding surface is simple, for these are one-part, 100% reactive adhesives. The adhesive is applied as a drop or bead to one surface, then the other adherend is used to spread the adhesive in a thin film. Due to the volatility of the monomer and the fast cure, no more than three or four square inches of bondline should be open at one time. Enough adhesive should be applied to provide a slight fillet when the adherends are mated. This will ensure that the adherends are thoroughly wetted and that any air bubbles are removed. On impervious, well-fitted substrates, two drops (25 mg) of adhesive per square inch is sufficient coverage. Too much adhesive will create a weak bond, as the surface-initiated cure may not extend throughout a thick adhesive layer. Also, excessive adhesive can wash the initiators out of the bondline, causing a slow or incomplete cure. 

Once the adhesive is applied, any delay in mating the adherends can result in premature polymerization and a weak bond. After the adherends are mated, no further movement should occur, as the curing adhesive will be disturbed, and a weakened bond will be formed. Enough pressure should be used to closely mate the adherends, and this pressure should be maintained until handling strength has been achieved. This takes from two 

In many cases, there is no clear delimitation between application and mixing of the adhesives. In particular, in the case of adhesive systems with very short pot lives, mixing, dosing and application devices are often one single unit. Investing in such equipment is not only sensible for automation purposes, but also results in savings in adhesives since wrong batches or exceeded pot lives can be avoided. 

In addition, they contribute much to the quality of the bonded joint, which is not to be underestimated. 

In addition to surface preparation of the adherends described earlier, the production of adhesive-bonded parts involves (1) prefit, (2) adhesive application, (3) assembly, and (4) cure. 

Most structural film adhesives require a primer. Adhesive primers are usually spray-applied by air or airless spray systems. Roller or brush apphca-tion is sometimes used in small areas, or where spray equipment is not available. The primer coat must be air-dried and sometimes over-baked to remove solvents. The thickness of the prime coat will usually affect the adhesive bond strength and must be controlled and verified. This is usually accomplished by periodically certifying the primer applicator, and by monitoring primer thickness after drying.  

Film adhesives are applied by removing a paper or plastic separator/pro-tective film and laying the adhesive on the facing surface smoothly, taking 

The adhesive-coated detail parts are usually joined in a tool or holding fixture. Cleanliness and proper preparation of the tools should be verified. Time limits on the surface preparation, shop life of the adhesive, and remaining time during which the adhesive must be cured need verification at the point of assembly. 

Curing an adhesive in any joint is usually a time-temperature-pressure function. No matter how these three variables are controlled, the documentation-verification means are essentially the same. Controlling the length of cure time can be by manual or automatic timing devices. Verification is usually documented on a cure chart taken from a temperature and/or pressure recorder. Recording of pressure and temperature are made in the same maimer. 

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Latex Adhesive Applications. Polychloroprene latex adhesives have a long history of use in foil laminating adhesives, facing adhesives, and constmction mastics. Increasingly stringent restrictions on the emission of photoreactive solvents has heightened interest in latex compounds for broader apphcations, particularly contact bond adhesives. Table 10 makes a general comparison of solvent and latex contact bond adhesives (158). 

Surface prqiaiation of the joint area may be required to remove oxides, grease, moisture, etc. (prior to adhesive application) by mechanical, solvent, etching or degreasing processes to facilitate wetting. 

Access for adhesive application and/or process heat nessure is an important consideratiorL Awkward positions should be avoided and ideally processing should bepi ormed from above. 

Elevated temperatures are necessary for cure and the chemical resistance of the laminates is inferior to those from unmodified resins. Because of problems in handling, the polyamides have found only limited use with epoxy resins, mainly for coating and adhesive applications. 

The polysulphides are frequently used in casting mixes and to a less extent in coating, laminating and adhesive applications. Their value in casting and encapsulation lies mainly with their low curing shrinkage and flexibility in the cured state. Their tendency to corrode copper and the somewhat inferior electric insulation properties of the blends does lead to certain limitations. 

Titanium dioxide used for adhesive applications should contain an inorganic coating to control polarity, improve its ease of dispersion, and improve its weather resistance. The inorganic coating (zirconium dioxide, silica, alumina) is applied in the aqueous sluny by precipitation of one or more hydrated metal oxides and by neutralization of acidic and alkaline compounds. 

This chapter first reviews the general structures and properties of silicone polymers. It goes on to describe the crosslinking chemistry and the properties of the crosslinked networks. The promotion of both adhesive and cohesive strength is then discussed. The build up of adhesion and the loss of adhesive strength are explained in the light of the fundamental theories of adhesion. The final section of the chapter illustrates the use of silicones in various adhesion applications and leads to the design of specific adhesive and sealant products. 

Among all the low energy interactions, London dispersion forces are considered as the main contributors to the physical adsorption mechanism. They are ubiquitous and their range of interaction is in the order 2 molecular diameters. For this reason, this mechanism is always operative and effective only in the topmost surface layers of a material. It is this low level of adhesion energy combined with the viscoelastic properties of the silicone matrix that has been exploited in silicone release coatings and in silicone molds used to release 3-dimensional objects. However, most adhesive applications require much higher energies of adhesion and other mechanisms need to be involved. 

The adhesives employed for in-line adhesive application are generally of two types (1) flexible, but non-pressure-sensitive adhesives based on blends of saturated stryenic block copolymers and wax and (2) pressure sensitives based... 

A general description of the three major classes of MDI s and brief descriptions of adhesive applications are shown in Table 1. More recently, MDl has become the isocyanate of choice in adhesives, partly because MDI has a lower vapor pressure than TDI does (see pp. 296-297 in [18]). Isocyanates have been shown to cause an allergic reaction in a small percentage of the population. This reaction can manifest itself in the form of an asthmatic condition [19]. Before starting work with isocyanates, researchers are encouraged to read about the proper precautions to take, in order to work safely with these materials. Researchers should also check with their local health and environmental safety representatives [20]. 

Certain fillers are commonly added to protect the urethane backbone from oxidative degradation. Carbon black and titanium dioxide are commonly used in conjunction with antioxidants to protect polyether polyurethanes in exterior adhesive applications that may be exposed to oxygen and light (Fig. 12). 

The manufacturing instructions and formula for a typical commercial resole to be used in a plywood adhesive application are shown in Table 2. Such resin... 

Although the acrylate adhesives are readily available and studies have shown that they can produce reasonable bonding properties, they have the disadvantages of having high shrinkage, high fluid absorption, and low service temperatures. Acrylate adhesive applications would be limited. The development of EB-curable epoxy adhesives would have applications in the aerospace and automotive industry and potential wider uses. The most immediate application for these resin systems is composite repair of commercial and military aircraft. 

The aerospace field is a broad one and has a complex history. A comprehensive review of structural adhesive applications on currently flying aerospace vehicles alone could fill its own book. Hence this chapter will concentrate on the aerospace commercial transport industry and its use of adhesives in structural applications, both metallic and composite. Both primary structure, that is structure which carries primary flight loads and failure of which could result in loss of vehicle, and secondary structure will be considered. Structural adhesives use and practice in the military aircraft and launch vehicle/spacecraft fields as well as non-structural adhesives used on commercial aircraft will be touched on briefly as well. 

Long, R.L., Cryogenic adhesive application. Papers from the Structural Adhesive Bonding Conference Presented March 15-16, 1966, NASA Marshall Space Flight Center, Clearinghouse for Federal Scientific and Technical Information, 1966. 

The final section in this volume deals with applications of adhesion science. The applications described include methods by which durable adhesive bonds can be manufactured by the use of appropriate surface preparation (Davis and Venables) to unique methods for composite repair (Lopata et al.) Adhesive applications find their way into the generation of wood products (Dunky and Pizzi) and also find their way into the construction of commercial and military aircraft (Pate). The chapter by Spotnitz et al. shows that adhesion science finds its way into the life sciences in their discussion of tissue adhesives. 

About 8,000 metric tons of peroxides were consumed in 1972. This consumption was strongly stimulated by the rapid growth in reinforced plastics (Ref 23). The largest volume product is benzoyl peroxide which is used in polystyrene and polyester markets for such items as toys, automobiles, furniture, marine, transportation and mil requirements. Also, methyl ethyl ketone peroxide is used in large volumes to cure (as a catalyst) styrene-unsatur-ated polyester adhesive resins used in mil ammo adhesive applications, as well as in glass fiber reinforced plastic products such as boats, shower stalls, tub components, automobile bodies, sports equipment, etc. The monoperesters are growing slowly because of some substitution of the peroxydicarbonates and azo compds (Refs 8,9 23)... 

Barrett EW, Phelps MVB, Silva RJ, Gaumond RP, and Allcock HR. Patterning poly(organophospha-zenes) for selective cell adhesion applications. Biomacromolecules, 2005, 6, 1689-1697. 

Open-fronted extraction booths for spraying operations, or adhesive application operations. 

Adhesive applications, thermosetting epoxy resin based on N-cyanourea-terminated oligomer, 107... 

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