Epoxy Adhesive Markets

The inception of epoxy adhesives occurred almost simultaneously with the commercialization of epoxy resins. This is due to the fact that all the unique handling, application, and performance properties of epoxy resins are especially important when it comes to adhesive bonding. 

Epoxy adhesives have become the most recognizable structural adhesive type. They have found commercial success in demanding industries such as aerospace, automotive, building and construction, and electrical and electronic. Their ease of use has also encouraged their commercialization in the do-it-yourself markets, which has added to the exemplary reputation of epoxy adhesives. 

Adhesive markets represent only a small percentage of the total consumption of epoxy resins. However, epoxy adhesives provide significant value added, so that their prices and profit margins are generally higher than those for other adhesive types. Globahy in the year 2002, epoxy adhesives represented about 31 percent (or about 0.7 billion lb) of the total liquid epoxy demand (Fig. 1.2). The U.S. market is estimated to be just less than 200 million lb.10 

Epoxy adhesives represent a significant part of the overall structural adhesives market (about 1.8 bihion). The main competitors to epoxy adhesives are polyurethanes however, thermosetting acrylics and cyanoacrylate adhesives are also strong challengers in certain market segments. 

Single-component epoxy adhesive formulations are the largest type of epoxy adhesives sold, with about 55 percent of the consumption, while two-component formulations account for another 44 percent of the volume. Radiation cure formulations represent the remainder of the market. Epoxy adhesives can also take many forms including solids, solvent-free liquids, solvent-borne systems, and waterborne systems. 

---

Analysis of the epoxy adhesive markets is difficult because so many market segments fragment the industry and because it is difficult to confine manufacturers, distributors, and end users into specific categories. However, there are several organizations that periodically publish market reports on the adhesives industry including epoxy adhesives.14... 

The commercial possibiUties for epoxy resins were first recognized by DeTrey Emres in Switzerland and DeVoe and Raynolds in the United States (1,2). In 1936, DeTrey Emres produced a low melting bisphenol A-based epoxy resin that gave a thermoset composition with phthaUc anhydride. Apphcation of the hardened composition was foreseen in dental products, but initial attempts to market the resin were unsuccessful. The patents were hcensed to CIBA AG of Basel, Switzerland (now CIBA-GEIGY), and in 1946 the first epoxy adhesive was shown at the Swiss Industries Eair and samples of casting resin were offered to the electrical industry. 

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. 

Although the overall annual growth rate for epoxy adhesive is in the 3 to 5 percent range, certain regional markets, such as China, are expected to have an annual growth rate... 

Advances in epoxy adhesive technology have meant that an increasing number of assembly and repair problems can be resolved without the use of mechanical fasteners, welding, or other nonadhesive assembly processes. Several of the more important developing market segments for epoxy adhesives are described in the following sections. 

Cured concrete can be bonded to cured concrete, as in the installation of precast buttons to a highway surface. Steel bridge railings can also be bonded to the concrete surface of a bridge sidewalk. In the case of deteriorated concrete, the adhesive can be used to rebuild the structure to its former line and grade. Epoxy adhesives are also commonly used on other roadway materials, such as asphalt and brick however, the predominant application is concrete substrates. The most frequent combinations of substrates that are bonded with adhesives in this market segment are... 

These adhesives have found their way into several niche markets where their advantages, such as fast setting speed, are highly valued. They have not seen application in the more ordinary markets because of their materials and equipment cost. However, it is expected that these epoxy adhesive systems will grow at a faster annual rate than the average market as their advantages become more widely known. 

In 1995, U.S. consumption of radiation cured products was 77 million lb, valued at 450 million.1 Growth is forecast to average about 7 percent per year—a rate about twice that of conventional thermal cured products. Although radiation curable adhesives comprise a relatively small segment of the overall adhesive market (13 percent) and epoxy adhesives represent an even smaller component, epoxy systems are a fast-growing part of the market. 

The main sources of energy for curing epoxy adhesives by radiation are electron beam (EB) and ultraviolet light (uv). Both provide instantaneous curing of resins that polymerize from a liquid to a solid when irradiated. The uv systems account for approximately 85 percent of the market for radiant cured adhesives, EB systems account for about 10 percent, and the remainder are chiefly adhesives that can cure by exposure to both visible and infrared light. 

Epoxy acrylates are dominant oligomers in the radiation curable adhesives market. A bisphenol A epoxy resin is reacted with acrylic acid or methacrylate acid to provide unsaturated terminal reactive groups. The acrylic acid-epoxy reaction to make bisphenol A diacrylate destroys any free ingredients such as epichlorohydrin used to make the DGEBA epoxy starting raw material. 

In addition to the excellent performance properties and the reduction of solvent carriers, waterborne epoxy adhesives were found to have processing advantages. They could be easily applied by conventional coating systems (spray, roller, etc.) they were less hazardous to workers due to lower dermatitis potential and inflammability ventilation equipment costs could be reduced and application equipment could be easily cleaned with soap and water. In many applications, these processing advantages became the primary market drivers for waterborne epoxy adhesives as alternatives to more conventional adhesives. 

There are many applications for polymeric waterborne adhesives. These include packaging adhesives, pressure-sensitive tape, coatings for textiles, wood adhesives, and various industrial adhesives and coatings. The potential applications for waterborne epoxy adhesives are more limited due to their lack of tack and pressure-sensitive characteristics and the time it takes for the chemical reaction to complete cure. However, waterborne epoxy systems have found significant markets in niche areas. 

Unfortunately there is not a lot of information to assist the formulator in the proper or optimal use of the tools and resources available. There are not many forums that provide instruction on the art of adhesive formulating. Only a few textbooks have concentrated on the subject. And even though epoxy adhesives are the workhorse of the industry and occupy the majority of the structural adhesives market, practical, concentrated information on epoxy adhesive formulation is noticeably absent. This book is an attempt to correct this situation. 

Epoxy adhesives command a large portion of the structural adhesives market. Many people are probably familiar with epoxy structural adhesives, as these are the typical two-part adhesives found in hardware stores and supermarkets. Epoxy adhesives owe their popularity with both the general public and industry to their ease of use, their relative safety, and their compatibility with many adherends (Fig. 14.3). The various chemical reactions involving the epoxy ring provide a fertile field for the development of a wide range of properties.29 Even a half century after the first epoxy patents were issued,30 new patents on epoxy adhesive technology continue to appear every month (Fig. 14.1.)... 

Poly sulfide rubber was first produced in 1929, and the liquid polymers were used in sealants and as flexibilizers for epoxy adhesives around 1950. In 1952 the polysulfide sealant was introduced to the construction industry [11, p. 74]. In the 1950s the first butyl rubber caulks appeared in the construction market [11. p. 108] and latex caulks [vinyl acrylic and poly(vinyl acetate)] appeared sometime after 1956. 

Early adhesives would just have contained the epoxy resin and hardener, and although strong bonds were obtained, particularly when subjected to shear stresses, they were inherently brittle, that is, they possessed very poor peel characteristics. A better understanding of their formulating potential has significantly changed this situation and, nowadays, unmodified epoxy adhesives have a relatively low market share of the business. 

Among the various structural adhesives commercially available today, epoxies are the most widely accepted and used. A recent market study showed that epoxy structural adhesives account for approximately 41% of all structural adhesives sold, and it is expected that they will maintain this market share over at least the next several years. Numerous references exist, both in the patent and journal literature, describing every facet of these adhesives. It is not the intention to review all of the available information. Rather, this chapter will concentrate on three main areas (1) A general description of epoxy adhesives (2) A discussion of commercially available raw materials, formulations, properties, and uses of epoxy adhesives (3) A review of developments in epoxy adhesives since 1979. Earlier work has been discussed in several reviews, and will not be covered in detail in this chapter. "... 

Epoxy adhesives are expected to grow at GDP (3-4%) over the next decade. Increased usage in the automotive and recreational markets, and replacement of mechanical fasteners help offset the slowdown in the aerospace industry (see also Adhesive Compositions). 

Polyimides became popular for die-bonding adhesives because they are cleaner (in terms of ionic contaminants) than equivalent epoxy products. The market at present, however, is dominated by high-purity epoxy adhesives. Polyimides are always applied from solvent solution and require higher curing temperatures than epoxies. They are stable to higher temperatures. Solvent-borne thermoplastics pastes (or cast-film preforms) have been used for some lower reliability die-attachment applications. 

Although epoxy adhesives represent a relatively small proportion of the total adhesives market, there are perhaps more varieties of formulations available from more sources than for any other adhesive class. For many years, they have dominated the high-performance adhesives market, but the desire for increased service temperatures has led to the development of new adhesives based on imide polymers (Polyimides and Bismaleimides). 

Specializing in the manufacture of adhesives, primers, varnishes and coatings based on water, epoxy, acrylic, and polyurethane, LORD Industrial Ltda.—a subsidiary of the North /tmerican LORD Corp.—began its activities in Sao Paulo, Brazil, in 1972. The following year, it transferred its productive unit to the industrial hub of Jundiai (Sao Paulo), where it remains today. Throughout this period, LORD has become a main producer in the Brazilian adhesive market, principally with regard to the fabrication of products with tow levels of heavy metals, primers for the treatment of metal surfaces and water-based adhesives. For further information, visit www tordta. com.br and www.lord.com. 

---