Cyanoacrylate adhesives applications

The diverse nature of the cyanoacrylate adhesives applications illustrates vividly that there is no truly typical application. The number of applications in which these adhesives are used is being expanded daily as technological improvements continue to broaden their capabilities. 

The largest application of methyl and ethyl cyanoacetale is the production of the cyanoacrylate adhesives widely used within the ear and electronic industries. 

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 well as for wire tacking and other applications 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 acrylics. Rather, the cyanoacrylate material is a thermoplastic, and thus, the adhesives typically have poor temperature resistance. 

Compact sealings They are given in a nonporous state and are compressible only to a minor degree. O-rings are to be mentioned as examples, which are producible at the point of application according to the required diameter by means of cyanoacrylate adhesives. 

With cyanoacrylate adhesives, the reactor used to convert the liquid monomer to the hard solid is the space between the parts being bonded. When conditions vary in this space, the performance of the adhesive will vary. Such parameters as temperature, humidity, space between the parts, and the type of surface being bonded can vary considerably in a given application. 

Repensek, W.G., Technology and Use of Cyanoacrylate Adhesives in Industrial Assembly Applications, American Fabricating Institute of Technology, Chicago, Sept. 1983. 

Repensek, W. G., Technolog Advances in Cyanoacrylate Adhesives for Industrial Applications, Society of Manufacturing Engineers, Dearborn, Mich., Nov. 1990. 

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. 

The most important step in the successful application of a cyanoacrylate adhesive is the application of a thin adhesive film between two well-mated surfaces. The thiimer the film is, the faster the rate of bond formation, and the higher the bond strength. Bond strength is dependent on proper surface preparation. 

Cyanoacrylates can be polymerized by free radical and ionic initiators (see Chain polymerization). In adhesive applications, ionic polymerization is by far the most important mode of chain growth. It is their marked susceptibility to initiation by anions and nucleophiles that is responsible for their usefulness as adhesives. The cyanoacrylate r-electron system is under the influence of two strongly electron-attracting groups. This results in a reduced electron density on the )8-carbon and enhanced susceptibility to nucleophilic attack (Scheme 2). 

Cyanoacrylate adhesives will bond a wide variety of substrates with the exception of polyolefins (unless pre-treated). Teflon and highly acidic surfaces. Porous substrates such as wood, paper and leather require the use of products containing accelerators. Formulations are now appearing that when used in conjunction with a so-called primer can give high bond strength on polyethylene and polypropylene. See Industrial applications of adhesives. 

Many lightweight non-metaUic components are bonded with Cyanoacrylate adhesives. Figure 2 shows some applications on a typical car body. 

Fig. 2. Some typical applications of cyanoacrylate adhesives in a car body...

Thermoplastic slmctural adhesives are less significant for the more-demanding applications however. Cyanoacrylate adhesives have gained considerable importance for applications at ambient temperatures and less severe environments, particularly on plastic substrates, mainly as a result of their very rapid cure speeds (seconds) and ease of application. 

Cyanoacrylate adhesives J GUTHRIE Anionic polymerization, additives, applications, advantages and disadvantages... 

A main application has been in vascular surgery. There have been reports on the direct closure or repairs of arterial lesions by the means of cyanoacrylates (Carton etal, 1961 Nathan et al, 1960 Casanova et al, 1987 Takenaka et al, 1992). Also, cyanoacrylates adhesives were used as an auxiliary after placing several stay sutures (Hosbein and Blumenstock 1964 Hafner et al., 1963 Tschopp 1975). Some complications were due to bleeding in the early stages (Carton et al, 1961). This bleedings were attributed by Takenaka et al (1992) to technical errors such as the insufficient application of adhesive or inadequate compression of the anastomotic part when pulling out the sutures. 

The cyanoacrylate adhesives sold today are quite similar to the first product, Eastman 910. This is due to the fact that changes in the structure of the monomer have dramatic effects on the adhesive properties, and because there are very few modifying monomers which will successfully coreact with the cyanoacrylates under normal application conditions. Also, the monomers with the best adhesive properties were discovered early in the development of cyanoacrylates. Finally, research toward improving the deficiencies of these products had a slow start owing to the early manufacturing problems. Beginning in the late 1970s, however, a number of adhesives with improved performance were introduced. 

While the bulk of any cyanoacrylate formulation consists of monomer, a large number of modifiers have been used to impart desired properties to the composition. These include stabilizers, inhibitors, thickeners, plasticizers, dyes or colorants, adhesion promoters, and others. Each of these classes of modifier will be dealt with in subsequent parts of this chapter. Because of the variety of modifiers, and the variety of applications for cyanoacrylates, a bewildering number of cyanoacrylate adhesives are now commercially available. These can be generally divided into the following classifications adhesives of different viscosities and cure rates, adhesives based on different monomers, adhesives for the bonding of metal, plastic, rubber, or wood, various types of improved performance adhesives, i.e., heat, moisture, or impact resistant, and adhesives for bonding low surface... 

Table XV. Typical Industrial Applications of Cyanoacrylate Adhesives...

The patent literature discloses that several speciality-type acrylate monomers, such as /3-hydroxyethyl acrylate,2-acrylyloxyethyl phenyl carbonate,vinyl acrylate,2,2,2-trifluoroethyl acrylate, N,N-dimethylaminoethyl acrylate,glycidyl acrylate,cyanoacrylates,and several diacrylates,have been copolymerized with MA. These copolymers were shown to exhibit properties which allowed the materials to be useful for polymeric emulsifiers, adhesives, " printing pastes,fire retardant textile coatings, and fibrous structural materials.Maleate and fumarate copolymers with acrylates also show possible utility in coatings, dispersants, adhesives, and other applications. Cyanoacrylate adhesives have much improved heat resistance... 

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