Epoxy adhesives automotive applications

Direct bonding. In many high-volume production applications (i.e., the automotive and appliance industries), elaborate surface preparation of steel ad-herends is undesirable or impossible. Thus, there has been widespread interest in bonding directly to steel coil surfaces that contain various protective oils [55,56,113-116], Debski et al. proposed that epoxy adhesives, particularly those curing at high temperatures, could form suitable bonds to oily steel surfaces by two mechanisms (1) thermodynamic displacement of the oil from the steel surface, and (2) absorption of the oil into the bulk adhesives [55,56]. The relative importance of these two mechanisms depends on the polarity of the oil and the surface area/volume ratio of the adhesive (which can be affected by adherend surface roughness). 

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. 

Epoxy adhesives are chemical compounds used to join components by providing a bond between two surfaces. Epoxy adhesives were introduced commercially in 1946 and have wide applications in the automotive, industrial, and aerospace markets. Epoxies are probably the most versatile family of adhesives because they bond well to many substrates and can be easily modified to achieve widely varying properties. This modification usually takes the form of... 

Despite epoxy adhesives finding use in many fragmented markets, actual consumption in volume is surprisingly concentrated in a few specific end-use market segments. For example, automotive assembly applications account for nearly 50 percent of the total volume of epoxy adhesives consumed in the United States. The highest-value market areas include structural automotive, aircraft, and many specialty product assembly applications. These market areas are also expected to enjoy the highest growth rates. 

Talc is also often used as an extender in epoxy adhesives and sealants, but it also has flow control properties. Talc is used in higher-solids, high-viscosity applications such as caulking compounds, automotive putties, mastics, and sealants. Talc is a hydrophobic and organophilic material. 

As a family of curing agents for epoxy resins, the amidoamines are lower in viscosity than the polyamides. They exhibit very good adhesive properties due to their chemical structure and easy penetration. Amidoamine cured epoxy adhesives have shown very good properties on concrete and other porous substrates. They cure extremely well under humid conditions. In fact amidoamine cured epoxy formulations have been used to cure underwater in certain applications. A typical general-purpose room temperature curing epoxy-amidoamine system is described in Table 11.7. This adhesive is used as a general-purpose metal-to-metal adhesive and body solder in the automotive industry. 

Composite adhesives are being used for a growing number of applications outside the automotive industry as well. For example, Dow Formulated Systems recently developed a foam core system for wind blades that is bonded by epoxy adhesives. The new system offers long-term dynamic behavior and shear strength properties that deliver the excellent mechanical strength and fatigue resistance necessary to achieve blade durability. 

Thanks both to their good properties and mainly to their versatility, nowadays epoxy resins find application in the following major fields coatings, electrical and electronic insulation, adhesives and construction and as matrices for FRP automotive, nautical and aerospace applications. 

X-ray photoelectron spectroscopy also finds wide application in the study of adhesion phenomena [84] and may claim a history of defining loci of failure. Adhesion failure due to moulding compound additives (such as wax, polyoxyalkylene ethers and alkylsiloxanes) in epoxy-phenolics at chip surfaces in electronic devices was studied by XPS and SAM [85]. Hame treated PP compounds have been characterised by XPS and predictive information could be obtained on paint adhesion behaviour [86]. Results are highly relevant to automotive applications replacing other time-consuming paint tests. 

Extremely small components also benefit from the use of elastomeric adhesives. Common epoxy adhesives are rigid and concentrate the stress leading to device failure. However, elastomeric adhesives can be used to dissipate such stress and yield a more durable electronic device. This technology enables the development of inexpensive but durable electronic components, such as, cellular telephones, portable computers and automotive applications. For example, the computer command control module, which regulates the operation of modem automobiles, can survive the harsh conditions under the hood because it is encapsulated in elastomeric adhesives known as potting compounds. 

In order to eomplement their knowledge, the engineers who work with structural materials in automotive, aerospace, bonding of metals, plastics, and composites should also, of course, read the chapters Design and calculation of bonded parts , Physics and chemistry of adhesion , Surface preparation before bonding , Metal bonding , Bonding composites , and also Epoxy adhesives , Application equipment , etc. 

After reading some chapters on the various industries, the reader will need specific and detailed technical characteristics concerning the adhesives or sealants that they may consider for their own applications/end uses. For instance, those who wish to bond metal parts, those working in aircraft construction, automotive, and transportation, should read the chapters Epoxy adhesives , Engineering adhesives , and maybe also Heat stable adhesives . 

Several volumes will be published during 2005-2007 which contain chapters linked to the chapters in Volume 1, for instance Bonding metals , Bonding composites , Epoxy adhesives , Bonding in automotive , Structural adhesives , UV curing , Application equipment , and others. 

Fig. 20.1. Hand application o1 a two-part epoxy adhesive to a SMC sheet molding compound) automotive hood assembly. (Couftesy Lord Corp., Erie PA.)...

The major uses of BPA are in the production of polycarbonate resins (63%) and epoxy resins (27%). Polycarbonates have major outlets in automotive parts, compact discs, eyeglasses, and sheet and glazing applications, and have caused bisphenol A consumption to more than double during the past decade. Epoxy resins are two-component adhesives for very strong bonding. Miscellaneous uses include flame retardants (mostly tetrabromobisphenol A) and other polymer manufacture. Polycarbonate grade bisphenol A is >99% p,p isomer. The epoxy grade is 95% p,p. The p,p and o,p isomers can be separated by a combination of distillation and crystallization. 

For photochemical aging, it is well known that photooxidation affects only a thin superficial layer directly exposed to solar radiation - a few dozens of micrometers in the case of epoxies (Bellenger and Verdu, 1983). Thus the aging mode cannot control the material s lifetime in most cases (composites, adhesives), except for applications such as, for example, varnishes of automotive bodies (Bauer et ah, 1992). 

Highly cross-linked epoxy resins combine high strength stiffness thermal, chemical, and environmental stability adhesion low weight processability excellent creep resistance and favorable economics. These resins are widely applied as coatings, casting resins, structural adhesives, and matrix resins of advanced composite materials. The broad spectrum of applications ranges from the automotive and aerospace industries to corrosion protection and microelectronics. 

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