Nitrile rubber resin-cured

Nitrile rubber is compatible with phenol-formaldehyde resins, resorcinol-formaldehyde resins, vinyl chloride resins, alkyd resins, coumarone-indene resins, chlorinated rubber, epoxies and other resins, forming compositions which can be cured providing excellent adhesives of high strength, high oil resistance and high resilience. On the other hand, NBR adhesives are compatible with polar adherends such as fibres, textiles, paper and wood. Specific formulations of NBR adhesives can be found in [12]. 

Elastomers, plastics, fabrics, wood and metals can be joined with themselves and with each other using nitrile rubber/epoxy resin blends cured with amines and/or acidic agents. Ethylene-propylene vulcanizates can also be joined using blends of carboxylated nitrile rubber, epoxy resin and a reactive metal filler (copper, nickel, cobalt). However, one of the largest areas of use of nitrile rubber modified epoxy systems is in the printed circuit board area [12]. 

Chlorinated rubber is also an effective bonding agent. It can be used for bonding neoprene, nitrile and natural rubbers to metals. Phenol formaldehyde resins have been used alone or in conjunction with chlorinated rubbers, but curing time is lengthy. 

Film adhesives have to be strictly delimitated from adhesive tapes and adhesive strips (Sections 5.6 and 5.7). Mainly blocked two-component reactive adhesives (Section 3.1.4) are used raw materials. For transport and storage (at low temperatures) they are applied to a - nonadhesive - substrate. Prior to processing they are removed and then applied between the adherends (compounding) and cured under pressure and heat (Sections 3.1.4, 3.2.2 and 4.1.2). Special film adhesives (e.g., phenolic resin nitrile rubber) are also activated by suitable solvents. 

Relevant systems are mbber-toughened epoxy resins, high-impact acrylic (PMMA particles in mbber matrix, obtained by radical polymerization of 80/20 MMA/EVAc mixture), polyimide/silica hybrid materials (obtained using the sol-gel method), and a very high strength ( 60 MPa) mbbers (obtained by peroxide cure of a hydrogenated nitrile rubber/ zinc dimethacrylate system) [Inoue, 1995]. 

Later, in 1974, amine reactive versions of the liquid nitrile polymers (ATBN) were issued, thereby offering another way to introduce rubbery segments into a cured epoxy resin network. References are cited which provide detailed discussions of nitrile rubber, carboxylic nitrile rubber and both carboxyl- and amine-terminated nitrile liquid polymers (1-4). Table I illustrates CTBN and ATBN products structurally. Table II provides properties for typical solid carboxylic nitrile elastomers. 

Small nitrile-rubber inclusions in epoxy resin electrical en-capsulants have been examined in both amine (29-31) and acid (32) epoxy cures, in filled and unfilled systems. The value of rubber inclusion in a boron trlfluorlde/amine complex epoxy cure has also been demonstrated (33), where elevated-temperature, high-humldlty testing showed electrical properties retention to be better than a comparable system cured with dodecenylsucclnic anhydride. Rubber benefits low-temperature properties specifically and thermocycling in general. It affects high temperature insulation properties negatively therefore, the amount of rubber incorporated must be judiciously chosen. 

Lewis and co-workers (42) developed improved powder coatings with nitrile rubber-modification of an appropriate epoxy base (solid resin admixture) cured with an imidazoline-accelerated modified phenolic type hardener. Model coatings ground to 55 pm particle size, electrostatically applied to metals, cured 10 170°C, gave excellent therraocycling results as well as retained resistance to solvent attack. Elastomer-modified epoxy powder coatings have been covered extensively by Gelbel, Romanchick and Sohn in Chapter 5 of this volume. 

Chiou and Bradley [81] conducted hydraulic burst and stress rupture tests on 1.28mm thick (58v/o 87/ 35/87° hoop filament wound) tubes made from E-glass fibre/Brunswick LRF-571 DGEBA epoxy resin. There were 6% voids in the laminate. A co-cured nitrile rubber liner was employed, partly to keep the inner surface dry and partly to ensure that pressure could still be maintained if the GRP cracked during the tests. The tests followed 6 months immersion in static simulated sea water (Aquarium Systems Instant Ocean, p = 1023 kgm, pH = 8.2). The tubes had a high (1.5%) moisture uptake, although some of this might have been free water in the voids, but saturation was not reached. 

Their J-39 adhesives are room-temperature curable, second-generation acrylics (16). Methyl methacrylate is the monomer, and a nitrile rubber and Dow ABS resin are used as toughening agents. This family of adhesives have been used in automotive, machinery and aerospace structures. Their J-50 adhesives (17) are two-component, fast-cure acrylics. In addition, they also developed a special adhesive, J-15 structural adhesive, for hydroplanes. 

Conversely, the brittleness of cured epoxy resins can be ameliorated by copolymeiizing with flexible curing agents. The two most popular types are carboxyl-terminated nitrile rubber and mercaptan-terminated polysnlflde rnbber oligomers (Fig. 3.35). 

Nitrile rubber is used to increase impact strength of epoxy resins. It is made as a low-molecular-weight liquid oligomer with carboxy end-groups (CTBN) and used as a curing agent for the epoxy resin. 

In another study by Cherian et UPA was modified by blending with functionalized rubbers such as ENR, hydroxyl-terminated natural rubber, and maleated nitrile rubber. The elastomers bearing reactive functional groups showed better compatibility with the resin and improved the toughness and impact resistance of the cured resin substantially, compared to unmodified elastomers. Maleated nitrile rubber (NBR) was far superior to all other... 

Laminating. Nitrile rubbers blended with various epoxy resins and activated by suitable amines and/or acidic agents have been employed to bond elastomers, plastics, fabrics, wood, and metals to themselves and each other. Normally good bond strength can be developed at or near room temperature. Any information must be adapted to the substrate being bonded but Table 26 gives a starting formulation. The triethylenetetramine is added as a 50% solution in methyl ethyl ketone just prior to use. Such a cement will cure in 4-24 hours at room temperature and less than 30 minutes at 150°F. 

An adhesive consisting of an epoxy resin, a medium high acrylonitrile rubber, and Pb, Cu, Ni, Pd or Co compound fillers was used to bond EPDM vulcanizates. Peel strengths of 22.5 kg/20 mm after a 1 hour at 100 C cure were obtained. Another adhesive composition involving a blend of carboxylated nitrile rubber, epoxy resin and a reactive metal filler has been described for bonding EPDM vulcanizates or EPDM rubber-nitrile or butyl rubber blends. 

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