Cyanoacrylate, curing adhesive

Cyanoacrylate adhesives cure by anionic polymerization. This reaction is catalyzed by weak bases (such as water), so the adhesives are generally stabilized by the inclusion of a weak acid in the formulation. While adhesion of cyanoacrylates to bare metals and many polymers is excellent, bonding to polyolefins requires a surface modifying primer. Solutions of chlorinated polyolefin oligomers, fran-sition metal complexes, and organic bases such as tertiary amines can greatly enhance cyanoacrylate adhesion to these surfaces [72]. The solvent is a critical component of these primers, as solvent swelling of the surface facilitates inter-... 

Skin bonding. Finally, cyanoacrylate adhesives cure rapidly and form strong bonds on contact with human skin, so careful handling is necessary. 

Cyanoacrylate adhesives cure readily on most surfaces where there are traces of moisture present. The moisture neutralises the stabiliser to initiate curing within a few seconds. 

Cyanoacrylate adhesives (Super-Glues) are materials which rapidly polymerize at room temperature. The standard monomer for a cyanoacrylate adhesive is ethyl 2-cyanoacrylate [7085-85-0], which readily undergoes anionic polymerization. Very rapid cure of these materials has made them widely used in the electronics industry for speaker magnet mounting, as weU as for wire tacking and other apphcations requiring rapid assembly. Anionic polymerization of a cyanoacrylate adhesive is normally initiated by water. Therefore, atmospheric humidity or the surface moisture content must be at a certain level for polymerization to take place. These adhesives are not cross-linked as are the surface-activated acryhcs. Rather, the cyanoacrylate material is a thermoplastic, and thus, the adhesives typically have poor temperature resistance. 

Acrylic adhesives cure by a free radical chain growth mechanism. In contrast, epoxy and urethane adhesives cure by a step growth mechanism. This has a major impact on the cure kinetics, as well as the composition of the adhesive during cure ([9], pp. 6-9). Cyanoacrylate adhesives (such as Super Glue ) also cure by chain growth, but the mechanism is ionic with initiation by surface moisture. 

Cyanoacetic acid, 2 138, 139 and esters, 2 7 244-245 Cyanoacrylate adhesives, 2 539-540 Cyanoacrylate vapors, 22 102 Cyanobacteria, in nitrogen fixation, 2 7 302 Cyanobacterial associations, in nitrogen fixation, 27 299-300 Cyanocobalamin, 7 238 25 803-804 Cyanoethene. See Acrylonitrile (AN) l-Cyanoethyl-2-ethyl-4-methylimidazole (2EMZ-CN) curing catalyst, 20 17 2V-Cyanoethylated toluenediamines, 25 197... 

The adhesion was measured by fastening a lead anchor of known area (2,84 cm ) to the coating with a cyanoacrylate adhesive (Loctite 414) and after curing, pulling it off normal to the surface with a Dillon tensile tester. The force to remove the coating was divided by the area of attachment to convert it to a normalized tensile adhesion value. 

Presence of Water on Surfaces to be Bonded. Substances in the Earth s atmosphere adsorb water from it, the water in many instances being bound tenaciously to the surface. This provides the basis for curing of the cyanoacrylate adhesives, which takes place on contact with surfaces covered with such a water layer. 

Cyanoacrylate adhesive Quickly, within seconds curing reactive adhesives, with curing being initiated by moisture. 

Cyanoacrylates are one-part, highly polar thermoplastic polymers. The resin monomers cure in seconds when in contact with a weak base such as the moisture that is present on most surfaces. Many cyanoacrylate-adhesive formulations are commercially available, but not widely used in electronics assembly because of their poor resistance to solvents and moisture at elevated temperatures (>70 °C). Cyanoacrylates have relatively low impact and peel strengths and may be brittle unless toughened by the addition of elastomeric resins. 

The initiator that drives the polymerization or curing reaction of cyanoacrylate adhesives can be any of the chemicals that generate free radicals. Electromagnetic... 

Sterilization. All devices implanted in the body or that come into contact with body fluids or blood must be sterilized and be resistant to the sterilization conditions. Adhesive-bonded parts are not used in direct contact with the body fluids. They are generally part of an electronic module that is hermetically sealed or otherwise encapsulated or shielded. However, the sterilization conditions for the module must not degrade the internal adhesive-attached components. Some adhesives such as cyanoacrylates andUV-cured acrylics degrade at the elevated temperatures and high humidity... 

A common method of wire-tacking today is to use cyanoacrylate adhesive and primer. In this process, a drop of cyanoacrylate is placed on top of the wire to be tacked, followed by a drop of primer. The resulting wire-tack is usually serviceable in 5 - 15 seconds although several hours can be required for full cure. The usage of the wire tack, although limited by a lack of moisture, temperature and impact resistance, has been finding increasing application in the electrical industry. 

An electronics manufacturer attaches a plastic base to a 1-in. square ceramic circuit holder with a UV adhesive. Cure time is 10 seconds, which is about the same as the previously used cyanoacrylate. The lower cost, higher performance, and worker safety features justified the change in adhesive. 

Table 5.2 Typical Performance of Cured Loctite 380 Cyanoacrylate Adhesive ...

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