Adhesion to metals

Three techniques to bond rubber to metal and synthetic fibres using metallic coagents have been developed [25]. They are  

1) in the uncured rubber compound as an internal adhesion promoter, 

2) in a thin adhesive strip that functions as a tie layer upon curing, 

3) in a reactive dispersion that can be applied as a viscous liquid or paste to either the metal or rubber prior to curing. 

Although the metallic coagents are not adhesives by themselves, there are applications where these techniques may be applied to improve the adhesion of rubber to metals and synthetic fibres. 

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Aluminum complex greases, obtained by the reaction of aluminum isopropylate with a mixture of benzoic acid and fatty acids. These greases have a remarkable resistance to water, very good adhesion to metallic surfaces, good mechanical stability properties and resistance to temperature. They are less common than the first two types. 

Its advantages include impermeability to air, excellent adhesion to metal, and good resistance to oils, weathering, and low temperature. 

It possesses resistance to oils up to 120°C and excellent abrasion resistance and adhesion to metal. 

Silicone rubbers have excellent ozone and weathering resistance, good electrical properties, and good adhesion to metal. 

Fig. 10. A model of PVC lubrication mechanism showing (a) PVC adhesion to metal without lubricant (b) surface activity of calcium stearate (c) nonmetal releasing character of paraffin only and (d) synergy between calcium stearate and paraffin (62).

Adhesion to Metals. For interaction between coating and substrate to occur, it is necessary for the coating to wet the substrate (107). Somewhat oversimplified, the surface tension of the coating must be lower than the surface tension of the substrate. In the case of metal substrates, clean metal surfaces have very high surface tensions and any coating wets a clean metal substrate. 

There have been other approaches to obtaining rubber/metal adhesion besides primers or additives consisting of phenolics or epoxies plus halogenated elastomers. For example, carboxylated polymers (olefins and diolefins copolymerized with acrylic acid monomers) have shown excellent adhesion to metals. Very little carboxyl is necessary, and polymers with carboxyl contents as low as 0.1% show good adhesion when laminated to bare steel. When these materials possess... 

Acrylonitrile-butadiene rubber (also called nitrile or nitrile butadiene rubber) was commercially available in 1936 under the name Buna-N. It was obtained by emulsion polymerization of acrylonitrile and butadiene. During World War II, NBR was used to replace natural rubber. After World War II, NBR was still used due to its excellent properties, such as high oil and plasticizer resistance, excellent heat resistance, good adhesion to metallic substrates, and good compatibility with several compounding ingredients. 

NBR adhesives are characterized by high resistance to oils and plasticizers, excellent heat resistance and superior adhesion to metallic substrates. 

Chlorinated rubber is also used to promote the adhesion of solvent-borne CR adhesives to metals and plasticized PVC. Addition of a low molecular weight chlorinated rubber (containing about 65 wt% chlorine) improves the shear strength and creep resistance of polychloroprene adhesives [75] but a reduction in open time is also produced. A heat reactivation (process in which the surface of the adhesive film is raised to 90-100°C to destroy the crystallinity of the film and allowing diffusion to produce polymer chain interlocking more rapidly) restores tack to the polychloroprene adhesives. 

There are other initiator systems of lesser commercial importance. Cumene hydroperoxide is reported to cure acrylic adhesives in the presence of alkyl or pyridyl thioureas [105]. These initiators have been combined with a phosphated acrylate to promote adhesion to metal [106]. Thiourea-based initiators can be applied as a one-part on galvanized metal, where the metal surface provides the second part of the redox initiator [107]. 

Greases are also made from soaps of strontium, barium and aluminum. Of these, aluminum-based grease is the most widely used. It is insoluble in water and very adhesive to metal. Its widest application is in the lubrication of vehicle chassis. In industry, it is used for rolling-mill applications and for the lubrication of cams and other equipment subject to violent oscillation and vibration, where its adhesiveness is an asset. 

A characteristic of the group (a) of resins is that they air-dry solely by solvent evaporation and remain permanently solvent soluble. This fact, combined with the need to use strong solvents, makes brush application very difficult, but sprayed coats can be applied at intervals of one hour. A full vinyl system such as (o) possesses excellent chemical and water resistance. Many members of group (o) have very poor adhesion to metal, and have therefore been exploited as strip lacquers for temporary protection. Excellent adhesion is, however, obtained by initial application of an etching primer the best known of such primers comprises polyvinyl butyral, zinc tetroxy-chromate and phosphoric acid. 

Another application for polyelectrolyte materials is in the forming plastics with unusual physical properties with regard to adhesion. The incorporation of small amounts of organic acid materials into polyolefin structures results in materials that have excellent adhesion to metals, paper, glass, and a variety... 

EPM and EPDM are not oil resistant, and are swollen by aliphatic and aromatic hydrocarbons, and halogenated solvents. They have excellent electrical properties and stability to radiation. Their densities are the lowest of the synthetics, and they are capable of accepting large quantities of filler and oil. They exhibit poor tack, and even if tackifiers are added, it still is not ideal for building operations. Adhesion to metal, fabrics and other materials, can be difficult to accomplish. 

Copolymers of vinyl chloride with vinyl acetate and maleic anhydride are made more adhesive to metals through hydrolysis of the ester and anhydride units. 

These polar copolyr ers are more transparent and. as a result of the presence of the polar acrylic acid moiety, have better adhesion to metallic surfaces than ldpb. The commercial copolymer, which is usually 50% neutralized to salts of sodium or zinc, is stiff and strong because of ionic crosslinking at room temperature, but it is readily proccssible when heated. 

Because of the presence of polar pendant groups, the partially saponified vinyl acetate copolymer and copolymers of vinyl chloride, vinyl acetate, and maleic anhydride have better adhesion to metals than PVC. 

Title (Co)polycarbonates Having Improved Adhesion to Metals... 

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