Epoxy resin dicyandiamide

Dicyandiamide (sometimes referred to as dicy ) or its derivatives are used in most commercial one-component epoxy adhesives. This curative is a white crystalline solid and is easy to incorporate into an epoxy formulation as a finely ground powder. When cured with epoxy resin, dicyandiamide provides an excellent set of performance properties. 

LaLiberle BR, Bomstein J, Sacher RE, Cure behaviour of an epoxy resin-dicyandiamide system accelerated by monuron, Ind Eng Chem Prod Res Dev, 22(2), 261-262, 1983. 

Cyanamide and its aromatic derivative, such as 4,4 -methylene bis(phenyl cyanamide), were reported to cure an epoxy resin at elevated temperatures.(4) It is also well known that the dimer of cyanamide (dicyandiamide) is the most important epoxy curing agent in one-package epoxy compounding.(5) Unfortunately, this dimer precipitates from the dispersion causing uneven mixing upon standing. 

Two-layered GRPs for copper clad laminates are obtained with one layer consisting of the three-component system (e.g. BPA/DC, BMI, brominated epoxide resin, Zn octoate and triethylenediamine in methylethylketone). The other layer has the usual epoxy matrix (brominated epoxide resin, dicyandiamide as a hardener and 2-ethyl-4-methylimidazole as curing accelerator) [119]. As similar two-layered laminate contains BPA/DC, BMI, epoxynovolak resin, Zn acetate and triethylenediamine in the first layer and BPA/DC only with the same catalysts in the second layer [120]. 

The most popular catalysts for epoxy resins are tertiary amines, tertiary amine salts, boron trifluoride complexes, imidazoles, and dicyandiamide. Many of these catalysts provide very long pot lives (months) at room temperatures and require elevated temperatures for reaction with the epoxy groups. These catalysts are often referred to as latent hardeners. 

Benzyldimethylamine (BDMA) is another tertiary amine that can be used as either a sole catalyst or an accelerator with other curing agents. It is used with DGEBA epoxy resins at 6 to 10 pph. The pot life is generally 1 to 4 h, and the cure will be complete in about 6 days at room temperature. When used by itself, BDMA can provide epoxy adhesive formulations with high-temperature resistance (Chap. 15). However, BDMA is mostly used as an accelerator for anhydride and dicyandiamide cured epoxy resins. 

Latent imidazole catalysts have also been developed to provide cure rates considerably faster than those of dicyandiamide cured epoxy resins.18 They also exhibit excellent adhesive characteristics and heat and chemical resistance. 

A unique feature of these imidazole catalysts is that they do not have the high exotherm that dicyandiamide produces when cured in epoxy resins. Thus, they do not char or burn when exposed to high cure temperatures for fast cure. This is an important factor for adhesives that are cured via induction or dielectric heating. These adhesive systems are also much safer to ship via ah freight than conventional dicyandiamide catalyzed epoxy formulations due to their low exotherm. 

Dicyandiamide (DICY) is a solid latent catalyst that reacts with both the epoxy terminal groups and the secondary hydroxyl groups. DICY has the advantage that it only reacts with the epoxy resins on heating beyond an activation temperature, and once the heat is removed, the reaction stops. It is widely used with epoxy resins where long shelf life (up to... 

Accelerators for dicyandiamide cured epoxy adhesive formulations include tertiary amines, modified aliphatic amines, imidiazoles, and substituted ureas. All except the substituted ureas can cure epoxy resins by themselves. All these materials provide good latency and excellent adhesive applications. 

Probably the most effective accelerator for dicyandiamide systems is the substituted ureas because of their synergistic contribution to the performance properties of the adhesive and their exceptionally good latency. It has been shown that adding 10 pph of a substituted urea to 10 pph of dicyandiamide will produce an adhesive system for liquid DGEBA epoxy resins that can cure in only 90 min at 110°C. Yet this adhesive will exhibit a shelf life of 3 to 6 weeks at room temperature. Cures can be achieved at temperature even down to 85°C if longer cure times are acceptable.10... 

The BF3-MEA complex offers a slightly faster rate of cure and a reduced shelf live in liquid epoxy systems when compared to unaccelerated dicyandiamide cured epoxy formulations. However, when used as a sole curing agent, BF3-MEA has not had the commercial success of dicyandiamide because of their lower bond strength and brittleness. The BF3-MEA complex compounds also hydrolyze in the presence of moisture, so that mixtures with epoxy resins must be stored in tightly closed containers to maintain shelf life. 

Latent curing agents such as dicyandiamide are dissolved into solvent solutions of solid epoxy resins. This is then followed by evaporation of the solvent. 

Dicyandiamide is a true latent catalyst for epoxy resin curing. It is also considered to be the workhorse of one-component adhesives due to its ease of use, excellent performance properties, long shelf stability, and low toxicity. In certain admixtures with DGEBA, it has demonstrated a room temperature storage life in excess of 4 years. Dicyandiamide is usually added to the solid epoxy resin in concentrations of about 3 to 6 pph. It melts at about 150°C. Cures can be conducted in the range of 120 to 175°C but are very slow at the lower temperatures. As a result, it is common practice to add accelerators such as benzyl-dimethylamine (BDMA) and mono- or dichlorophenyl substituted ureas to these systems. 

Solid epoxy resin Epoxy novolac resin Solvent Dicyandiamide BDMA 100 100 As required 16 2-4... 

Solid epoxy resin (40% solids) Epoxy novolac resin (85% solids) Dicyandiamide BDMA 212 37.5 12 2.0... 

Similar information is presented in Table 14.5 for starting adhesive formulations made from an epoxy resin emulsion and dicyandiamide latent curing agent. This adhesive has exceptionally good water resistance when cured. The adhesive was applied to the indicated substrates in a manner similar to that described above, and it was cured for 3 min at 65°C followed by 10 min at 175°C. 

It is made by dimerizing cyanamide in basic aqueous solution, and is a colorless solid melting at 208°C. Dicyandiamide is soluble in polar solvents, but at room temperature is insoluble in bisphenol A epoxy resins. It can be made into a very fine powder and milled into epoxy resins to form stable dispersions. Because the dicy is insoluble in the epoxy, the only possible reaction sites are at the particle surfaces. Although some reaction certainly occurs over a short time, the adhesives easily can have a useful shelf life of six months. On heating to about 150°C, the dicyandiamide becomes soluble in the epoxy resin, and the adhesive polymerizes rapidly. Cure can be accelerated by incorporation of tertiary aromatic amines or substituted ureas. 

Epoxy resins may be cured in the manner of polyadditions, i. e., homogeneously catalyzed by multifunctional amines and isocyanates, or cyclic anhydride, dicyan-diamide, or biguanide derivatives. On the other hand epoxy resins are also subject to homopolymerization. The catalysts represent Lewis bases, preferably tertiary amines, imidazoles, or ureas (the latter exclusively for the dicyandiamide curing)... 

Epoxy resin 80% NVM in organic solvent Dicyandiamide Organic Solvent Cure Accelerator... 

The first problem is a reactivity problem. Early attempts at preparing water based systems encountered very slow reactivity of the dicyandiamide with the epoxy resin. This caused very slow line speeds for the laminator. This problem has been resolved with ED24574 and the cure response of the system is equal to organic solvent based standards. 

Such TTT diagrams have also been useful in describing the cure of polyimide systems, as shown in Palmese (1987), which shows the TTT diagram of a polyamicacid/polyimide system. The TTT diagram of a polycyanurate system is developed by Simon (1993) on the basis of FT-IR, DSC and torsional braid measurements. Kim et al (1993) developed a TTT diagram for a thermoset-thermoplastic blend, specifically a tetrafunctional epoxy-resin/poly(ether sulfone)/dicyandiamide thermoset-thermoplastic blend (Figure 2.9). 

The matrix material for the laminates for this investigation was a typical flame retardant epoxy resin system used in PWB technology. The epoxy resin was a brominated diglycidyl ether of bisphenol-A cured with dicyandiamide and catalyzed by benzyl dimethylamine. 

The adhesive is manufactured in tape form by a hot-melt process. It is a tacky solid at room temperature. The integrity is maintained by using a finely woven glass fabric scrim as the carrier. This process is an excellent example of the compromises required in the technology of formulation. Some of the high-temperature performance that is expected from the phenolic resole is sacrificed for the improved bond strength and toughness afforded from the epoxy resin. The filler is added to make the thermal coefficient of expansion of the cured adhesive more metallic in nature. Dicyandiamide is the... 

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