Epoxy resins adhesive formulations

Several methods can be used by the formulator to improve the flexibility of room temperature curing epoxy resin adhesive formulations ... 

Fillers are incorporated in epoxy resin adhesive formulations to enhance or obtain specific desired properties and to reduce cost. The amount and type of filler used are determined by the specific properties desired. 

Pentaerythritol in rosin ester form is used in hot-melt adhesive formulations, especially ethylene—vinyl acetate (EVA) copolymers, as a tackifier. Polyethers of pentaerythritol or trim ethyl ol eth an e are also used in EVA and polyurethane adhesives, which exhibit excellent bond strength and water resistance. The adhesives maybe available as EVA melts or dispersions (90,91) or as thixotropic, one-package, curable polyurethanes (92). Pentaerythritol spko ortho esters have been used in epoxy resin adhesives (93). The EVA adhesives are especially suitable for cellulose (paper, etc) bonding. 

Formulators in the adhesives industry do not normally manufacture epoxy resins. Generally, formulators buy epoxy resins, modify them with other materials, do similar compounding to the curative, and then package the product as a complete adhesive system ready for the end user. There are many excellent textbooks6-8 available giving information about the preparation, chemistry, and use of epoxy resins in general applications. It is not the intention here to go into such detail but to focus only on epoxy adhesive systems. 

DGEBA is the most commonly used epoxy in adhesive formulations. Although they may range from very simple, low molecular weight, primarily aliphatic resins to more complex, multifunctional, primarily aromatic materials. A wide choice of curing agents is available, in common with other applications. Schmidt and... 

One-component epoxy resin adhesives are almost limited to industrial use (car manufacture, aircraft construction, electronics). Resin and hardener components are already mixed, due to special formulations, however, they are prevented from reacting with each other at room temperature and thus from curing (blocking, Section 3.1.4). 

In adhesive joints, for example with epoxy resin adhesives, internal stress in the adhesive layer may result from different coefficients of expansion in the glued materials, whereby their moduli of elasticity are important factors. The glass transition temperature, and thus the curing temperature, also play a role. The reaction shrinkage of the resin is another source of internal stress. Suitable formulations with added fillers, oligomers or copolymers are among the measures taken to reduce these influences. 

Uses Polyamide for curing epoxy resins to formulate coatings, adhesives, and sealants food pkg. adhesives, coatings Features Reacts with epoxy resin to form tough, resilient, chemical-resistant coating or adhesive mix ratio 50 pbw Uni-Rez 2125 to 100 pbw epoxy resin... 

Epoxy resins have been used in canvas picture conservation. An unfortunate use as a varnish caused problems in identification and removal (Keck and Feller, 1964). Epoxy resin adhesives have been used for sticking threads across tears in canvases and also as a filler (Berger and Russell, 1993). The formulations need to be of sufficiently high viscosity to prevent absorption into the canvas, but must be flexible enough to respond to movement in the fabric. 

Epoxy Sealant (Cabot, 1994) - Hydrophilic grades of fumed sihca are widely used as thickening agents for epoxy resin adhesives and sealants. They impart excellent initial viscosity and sag resistance. After shelf aging for several months, however, the epoxy systems lose part or all of their sag resistance. A simple two part epo sealant formulation to test the utihty of a series of mineral thixotropes is shown in Table 13. 

The outstanding performance characteristics of the resins are conveyed by the bisphenol A moiety (toughness, rigidity, and elevated temperature performance), the ether linkages (chemical resistance), and the hydroxyl and epoxy groups (adhesive properties and formulation latitude, or reactivity with a wide variety of chemical curing agents) (see also Phenolic resins). 

Flexibilized epoxy resins are important structural adhesives [69]. Liquid functionally terminated nitrile rubbers are excellent flexibilizing agents for epoxy resins. This liquid nitrile rubber can be reacted into the epoxy matrix if it contains carboxylated terminated functionalities or by adding an amine terminated rubber. The main effects produced by addition of liquid nitrile rubber in epoxy formulations is the increase in T-peel strength and in low-temperature lap shear strength, without reducing the elevated temperature lap shear. 

Adhesives based on hydrolysis resistant chemistry (i.e., adhesives D and E) show a high retention of initial properties after exposure to an aggressive corrosion environment and the failure occurs cohesively within the adhesive. The cure reactions of these adhesives involve the formation of hydrolysis resistant carbon-nitrogen bonds in reactions involving the free N-H functionality of the Versamid or Genamid hardener with the oxirane functionality of the epoxy resin that is present in the adhesive formulation ... 

Structural adhesives are formulated from epoxy resins, phenolic resins, acrylic monomers and resins, high temperature-resistant resins (e.g., polyimidcs), and urethanes. Structural adhesive resins arc often modified by elastomers. 

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