[47] Although they increase cost of mortars and concrete when used as an additive, they enhance properties. Epoxy resins typically require a precise mix of two components which form a third chemical to get the stated properties. Use of blending, additives and fillers is often referred to as formulating. This "plastic tooling" replaces metal, wood and other traditional materials, and generally improves the efficiency and either lowers the overall cost or shortens the lead-time for many industrial processes. Novolaks are produced by reacting phenol with methanal (formaldehyde). The resins are low to medium viscosity at room temperature, which makes them easier to process than EPN or ECN resins. Reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer, often with favorable mechanical properties and high thermal and chemical resistance. Normal gelcoat formulated for use with polyester resins and vinylester resins does not adhere to epoxy surfaces, though epoxy adheres very well if applied to polyester resin surfaces. Insufficient heat during cure will result in a network with incomplete polymerisation, and thus reduced mechanical, chemical and heat resistance. Epoxies generally out-perform most other resin types in terms of mechanical properties and resistance to environmental degradation. Fusion Bonded Epoxy Powder Coatings (FBE) are extensively used for corrosion protection of steel pipes and fittings used in the oil and gas industry, potable water transmission pipelines (steel), and concrete reinforcing rebar. However, reactivity is rather low compared to other classes of epoxy resin, and high temperature curing using suitable accelerators is normally required. [34] In general, epoxies are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. [31] The applications include coatings, adhesives[32][33] and composite materials such as those using carbon fiber and fiberglass reinforcements (although polyester, vinyl ester, and other thermosetting resins are also used for glass-reinforced plastic). [4][5], The health risks associated with exposure to epoxy resin compounds include contact dermatitis and allergic reactions, as well as respiratory problems from breathing vapor and sanding dust, especially when not fully cured. Epoxy paints tend to deteriorate, known as "chalking out", due to UV exposure. Epoxy homopolymerisation is often used when there is a requirement for UV curing, since cationic UV catalysts may be employed (e.g. Important epoxy resins are produced from combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers. Hofer, Arnold; Schneider, Hildegard, and Siegenthaler, Nikolaus (1996) "Epoxy resin mixtures containing advancement catalysts". [46] By contrast, polyester resins can only bond using the first two of these, which greatly reduces their utility as adhesives and in marine repair. Epoxy is the family of basic components or cured end products of epoxy resins. [11] Devoe&Raynolds, which was active in the early days of the epoxy resin industry, was sold to Shell Chemical; the division involved in this work was eventually sold, and via a series of other corporate transactions is now part of Hexion Inc.[12]. The rate of cure of polyesters can therefore be controlled by the amount and type of catalyst as well as by the temperature. In the electronics industry epoxy resins are the primary resin used in overmolding integrated circuits, transistors and hybrid circuits, and making printed circuit boards. Most of the commercially used epoxy monomers are produced by the reaction of a compound with acidic hydroxy groups and epichlorohydrin. plant derived glycerol used to make epichlorohydrin). for chips on board ), LEDs, high-tension electrical insulators, paint brush manufacturing, fiber-reinforced plastic materials, and adhesives for structural[3] and other purposes. The epoxy curing reaction may be accelerated by addition of small quantities of accelerators. Temperature is sometimes increased in a step-wise fashion to control the rate of curing and prevent excessive heat build-up from the exothermic reaction. The technique is named "water shut-off treatment".[28]. This route of synthesis is known as the "taffy" process. [6][7][8], Condensation of epoxides and amines was first reported and patented by Paul Schlack of Germany in 1934. These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing. This class also displays lower viscosity at room temperature, but offers significantly higher temperature resistance than the aliphatic epoxy diluents. As with other classes of thermoset polymer materials, blending different grades of epoxy resin, as well as use of additives, plasticizers or fillers is common to achieve the desired processing or final properties, or to reduce cost. Epoxies are also used in producing fiber-reinforced or composite parts. Amine type hardeners will alter both the processing properties (viscosity, reactivity) and the final properties (mechanical, temperature and heat resistance) of the cured copolymer network. Due to the low dielectric constants and the absence of chlorine, cycloaliphatic epoxides are often used to encapsulate electronic systems, such as microchips or LEDs. Epoxy resins are excellent electrical insulators and protect electrical components from short circuiting, dust and moisture. Epoxy resins are used to bond copper foil to circuit board substrates, and are a component of the solder mask on many circuit boards. Epoxies are typically cured with stoichiometric or near-stoichiometric quantities of hardener to achieve the best physical properties. Cure temperature should typically attain the glass transition temperature (Tg) of the fully cured network in order to achieve maximum properties. As there is a general trend to renewable and "green" sources and greater use of biobased materials, research is ongoing in the epoxy arena too. Epoxy systems are used in industrial tooling applications to produce molds, master models, laminates, castings, fixtures, and other industrial production aids. Some (non-crosslinked) epoxy resins with very high molar mass are added to engineering thermoplastics, again to achieve flame retardant properties. The most common epoxy resins are based on reacting epichlorohydrin (ECH) with bisphenol A, resulting in a different chemical substance known as bisphenol A diglycidyl ether (commonly known as BADGE or DGEBA). Bisphenol F may undergo epoxy resin formation in a similar fashion to bisphenol A. The risk has been shown to be more pronounced in epoxy resins containing low molecular weight epoxy diluents. The epoxide functional group is also collectively called epoxy. Depending on the properties required, the ratio may be anything from 1:1 or over 10:1, but in usually they must be mixed exactly. Castan's work was licensed by Ciba, Ltd. of Switzerland, which went on to become one of the three major epoxy resin producers worldwide. The strength of epoxy adhesives is degraded at temperatures above 350F (177C).[42]. The majority of the epoxy systems sold are produced by these formulators and they comprise over 60% of the dollar value of the epoxy market. 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate). Reaction and subsequent crosslinking occur only after opening of the anhydride ring, e.g. Epoxy resins are polymeric or semi-polymeric materials or an oligomer, and as such rarely exist as pure substances, since variable chain length results from the polymerisation reaction used to produce them. [9] Claims of discovery of bisphenol-A-based epoxy resins include Pierre Castan[10] in 1943. One downside of high purity liquid grades is their tendency to form crystalline solids due to their highly regular structure, which then require melting to enable processing. In general, epoxy adhesives cured with heat will be more heat- and chemical-resistant than those cured at room temperature. The global market is made up of approximately 50100 manufacturers of basic or commodity epoxy resins and hardeners. Epoxy materials tend to harden somewhat more gradually, while polyester materials tend to harden quickly, particularly if a lot of catalyst is used. This process is commonly referred to as curing or gelation process. [41] They found that the molecular reason for epoxy yellowing was a thermo-oxidative evolution of carbonyl groups in the polymeric carboncarbon backbone via a nucleophilic radical attack. Allergic reaction is often visible in the form of dermatitis, particularly in areas where the exposure has been highest (commonly hands and forearms). While some epoxy resin/ hardener combinations will cure at ambient temperature, many require heat, with temperatures up to 150C (302F) being common, and up to 200C (392F) for some specialist systems. By contrast, polyester resins are usually made available in a 'promoted' form, such that the progress of previously-mixed resins from liquid to solid is already underway, albeit very slowly. Two part epoxy coatings were developed for heavy duty service on metal substrates and use less energy than heat-cured powder coatings. Epoxy resins yellow with time, even when not exposed to UV radiation. Overall reactivity potential for different hardeners can roughly be ordered; aliphatic amines > cycloaliphatic amines > aromatic amines, though aliphatic amines with steric hindrance near the amino groups may react as slowly as some of the aromatic amines. This coupled with high reactivity, plus high temperature resistance and mechanical properties of the resulting cured network makes them important materials for aerospace composite applications. Phenols can be compounds such as bisphenol A and novolak. Epoxy resins are also used for decorative flooring applications such as terrazzo flooring, chip flooring, and colored aggregate flooring. These systems provide a tough, protective coating with excellent hardness. Electric generators, connected via the drivetrain with the rotor blades, convert mechanical wind energy in usable electric energy, and rely on epoxies electrical insulation and high thermal resistance properties. Polyphenols, such as bisphenol A or novolacs can react with epoxy resins at elevated temperatures (130180C, 266356F), normally in the presence of a catalyst. Since many novolacs are solids, this class of hardeners is often employed for powder coatings. Significant advances in understanding yellowing of epoxies were achieved by Down first in 1984 (natural dark aging) [39] and later in 1986 (high-intensity light aging). Tertiary amines, carboxylic acids and alcohols (especially phenols) are effective accelerators. This means that conventional nucleophilic hardeners such as amines are hardly suitable for crosslinking. These high-performance adhesives are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, skis, snowboards, and other applications where high strength bonds are required. The secondary amine can further react with an epoxide to form a tertiary amine and an additional hydroxyl group. Halogenated epoxy resins are admixed for special properties, in particular brominated and fluorinated epoxy resins are used.[13]. Also aliphatic glycidyl epoxy resins usually have a low viscosity compared to aromatic epoxy resins. Some epoxies are cured by exposure to ultraviolet light. In 1946, Sylvan Greenlee, working for the Devoe&Raynolds Company, patented resin derived from bisphenol-A and epichlorohydrin. Epoxy resins are applied using the technology of resin dispensing. Epoxy adhesives are a major part of the class of adhesives called "structural adhesives" or "engineering adhesives" (that includes polyurethane, acrylic, cyanoacrylate, and other chemistries.) They are also sold in boat shops as repair resins for marine applications. Transformer and inductor hot spots are greatly reduced, giving the component a stable and longer life than unpotted product. In Europe, wind energy components account for the largest segment of epoxy applications, about 27% of the market.[44]. Polyester epoxies are used as powder coatings for washers, driers and other "white goods". [13], Epoxidized vegetable oils are formed by epoxidation of unsaturated fatty acids by reaction with peracids. Polyfunctional primary amines form an important class of epoxy hardeners. [37] Epoxy coatings have also been used in drinking water applications.[38]. These companies are known as "formulators". Epoxy resins made of (long-chain) polyols are also added to improve tensile strength and impact strength. This process is known as catalytic homopolymerisation. [48], In the aerospace industry, epoxy is used as a structural matrix material which is then reinforced by fiber. These resins typically have lower viscosity and a higher mean epoxy content per gram than bisphenol A resins, which (once cured) gives them increased chemical resistance. [60] Solid epoxy resins are generally safer than liquid epoxy resins, and many are classified non-hazardous materials. [27] However, good properties are obtained by reacting the linear epoxy resin with suitable curatives to form three-dimensional cross-linked thermoset structures. Glycidylamine epoxy resins are higher functionality epoxies which are formed when aromatic amines are reacted with epichlorohydrin. Ciba's epoxy business was spun off as Vantico in the late 1990s, which was subsequently sold in 2003 and became the Advanced Materials business unit of Huntsman Corporation of the United States. Until they are mixed the two elements are relatively inert, although the 'hardeners' tend to be more chemically active and should be protected from the atmosphere and moisture. [62] Safe disposal also needs considering but usually involves deliberate curing to produce solid rather than liquid waste. One particular risk associated with epoxy resins is sensitization. They are more expensive than polyester resins and vinyl ester resins, but usually produce stronger and more temperature-resistant thermoset polymer matrix composite parts. This obviated the problem of solvent retention under the film, which caused adhesion problems later on. First a hydroxy group reacts in a coupling reaction with epichlorohydrin, followed by dehydrohalogenation. Fluorinated epoxy resins have been investigated for some high performance applications, such as the fluorinated diglycidether 5-heptafluoropropyl-1,3-bis[2-(2,3-epoxypropoxy)hexafluoro-2-propyl]benzene. Metal cans and containers are often coated with epoxy to prevent rusting, especially for foods like tomatoes that are acidic. One-component products generally have shorter shelf-lives than standard 2-component systems, and products may require cooled storage and transport. Hardeners which show only low or limited reactivity at ambient temperature, but which react with epoxy resins at elevated temperature are referred to as latent hardeners. As a result, a typical formulator sells dozens or even thousands of formulationseach tailored to the requirements of a particular application or market.

Sitemap 24