Liquid epoxy resin

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

Epichlorohydrin and Bisphenol A-Derived Resins. Liquid epoxy resins maybe synthesized by a two-step reaction of an excess of epichl orohydrin to bisphenol A in the presence of an alkaline catalyst. The reaction consists initially in the formation of the dichi orohydrin of bisphenol A and further reaction by dehydrohalogenation of the intermediate product with a stoichiometric quantity of alkaH. 

Liquid epoxy resin based on the reaction product of epichlorohydrin and bisphenol A or bisphenol F mild to moderate irritants mild to moderate sensitizers low volatility, exposure unlikely unless heated, sprayed, or spread over large unventilated surface low toxicity... 

The products of the chemical degradation of PETP with triethylene tetramine and triethaneolamine can be used as epoxy resin hardeners, it is demonstrated. Products of PETP aminolysis with triethylene tetramine and aminoglycolysis with triethanolamine, were characterised using NMR and rheometric measurements. Characteristics of the crosslinking process for the system epoxy resin/ PETP/amine degradation product, and epoxy resin/TETA for comparison were investigated by DSC. Three classes of liquid epoxy resins based on bisphenol A, bisphenol F and epoxy novolak resins were used in the experiments. 16 refs. 

Figure 5. The effect of detector time constant on the GPC separation of a liquid epoxy resin. Column Perkin-Elmer/ PL gel 2.00 Angstrom. Eluent THE at 2.0 ml/min.

Eponite" 100. Shell Chemical Co trademark for a water-dispersible liquid epoxy resin used in textile industry to impart crease resistance, shrinkage, etc Ref CondChemDict(1961), 444-R... 

Advancement Process. In the advancement process, sometimes rel crred to as the fusion method, liquid epoxy resin (etude diglycitlyl ether nf htsphcnol A) is chain-extended with hisphenol A in the presence of a catalyst to yield higher polymerized products. The advancement process is more widely used in commercial practice. 

DER 331 (Dow) liquid epoxy resin cured as indicated, h, 70°C water, to lose adhesion... 

In the preparation of commercial DGEBPA, an excess of epichlorohydrin is used in order to minimize polymerization of the reactants to higher molecular-weight species. Nevertheless, the typical viscous final product usually contains ca 80% by weight of the monomeric (n = 0) DGEBPA as determined by gel-permeation chromatography (gpc). The manufacture of liquid epoxy resins in a batch process has been described in some detail (9). 

FIGURE 1.2 Global liquid epoxy resin production.11 2002 Total Liquid Epoxy Resin Demand 2.14 billion pounds 970 thousand metric tons 2.0 billion AGR 4—5%. (Source DPNA International Inc.)... 

The higher-MW semisolid (EEW of 225 to 280) and solid epoxy resins (EEW > 450) may be blended into lower-MW resins to improve flexibility and decrease reactivity. They also improve adhesion due to the higher concentration of hydroxyl groups along the molecular chain. Ten percent of a higher-MW epoxy resin blended into a conventional liquid epoxy resin (EEW of 190) can significantly improve flexibihty, but a reactive diluent frequently needs to be added to the formulation to counteract the increased viscosity caused by the addition. 

DGEBA liquid epoxy resin alone (e.g., EPON 828, Resolution Performance Products, LLC) 44-49... 

Aromatic Amine Eutectics. There are several curing agents available that consist of eutectics of various aromatic amines. These perform very much as MPDA and MDA do. However, the eutectics are liquids with viscosity of approximately 2000 cP at room temperature. They are readily miscible with liquid epoxy resins at room temperature. 

A PMDA dispersion is prepared by mixing finely powdered PMDA into liquid epoxy resins at room or slightly elevated temperature by stirring. No noticeable settling will occur in resins having an initial viscosity greater than 5000 cP. 

The BF3-MEA must be melted and dissolved in liquid epoxy resins. For small batches, the procedure is to heat the resin to 85°C and stir in the curing agent. For larger batches, about 3 parts by weight of the catalyst is stirred into about 5 parts by weight of the resin preheated to 50°C. This produces a smooth paste, which then may be added to the remainder of the resin heated to 85°C. Alternatively, the BF3-MEA can be dissolved in a solvent such as furfural alcohol, which will also dissolve the epoxy resin. 

DICY is used at about 5 to 7 pph of liquid epoxy resins and 3 to 4 pph for solid epoxy resins in adhesive formulations. It is generally ball-milled into the epoxy resin. DICY forms very stable mixtures with epoxy resins at room temperature because the catalyst is not soluble at low temperatures. However, on being exposed to temperatures greater than 140°C, the DICY becomes soluble in the epoxy resin, and cure progresses rapidly. 

FIGURE 6.3 Effect of various diluents on the viscosity of a standard DGEBA liquid epoxy resin.6... 

For adhesive systems, the liquid epoxy resins most widely used with LP-3 polymers are liquid unmodified and diluent-modified bisphenol A resins and liquid blends of bisphenol A and bisphenol F resins. Solid bisphenol A, multifunctional, and aliphatic diepoxy resins have also been used. Ratios of liquid polysulfide polymer to epoxy are in the range of 1 2 to 2 1. The effect of various degrees of polysulfide on cure properties of a DGEB A epoxy is shown in Table 7.7. An increase in elongation and impact strength is the result of increased amounts of the liquid polysulfide polymer. 

Suitable curatives for the polysulfide-epoxy reaction include liquid aliphatic amines, liquid aliphatic amine adducts, solid amine adducts, liquid cycloaliphatic amines, liquid amide-amines, liquid aromatic amines, polyamides, and tertiary amines. Primary and secondary amines are preferred for thermal stability and low-temperature performance. Not all amines are completely compatible with polysulfide resins. The incompatible amines may require a three-part adhesive system. The liquid polysulfides are generally added to the liquid epoxy resin component because of possible compatibility problems. Optimum elevated-temperature performance is obtained with either an elevated-temperature cure or a postcure. 

The solubility of the vinyl polymer in the epoxy resins will depend on the molecular weight and grade of vinyl used. Polyvinyl esters can be dissolved in liquid epoxy resins that are heated to about 100°C or in melted solid epoxy resins. However, most epoxy-vinyl blends are normally prepared via solvent solution. 

Comparative sag resistance properties of various commercial types of fumed silica are shown in Table 9.7. In most liquid epoxy resin systems, fumed silica is only employed at a 1 to 3 wt percent basis to provide thixotropic characteristics. 

Both pigments and dyes have been used successfully as colorants. With liquid epoxy resins, inorganic pigments seem to provide optimal properties. Organic pigments are generally less effective with epoxy resins. 

---