Polyurethane adhesives metals

Polyurethane adhesives are used for bonding wood, plastics, metals and leather. They can bond rubber to rubber, metal, glass or synthetic fibres. 

Abstract— The use of organosilanes as adhesion promoters for surface coatings, adhesives and syntactic foams is described and reviewed in the light of published work. Data are presented on the beneficial effect of silanes, when used as pretreatment primers and additives, on the bond strength of two pack epoxide and polyurethane paints applied to aluminium and mild steel. It is shown that silanes when used as additives to structural epoxide and polyurethane adhesives are less effective than when used as pretreatment primers on metals but are highly effective on glass substrates. The compressive properties of glass microballoon/epoxide syntactic foams are shown to be markedly improved by the addition of silanes. 

Comparison of silanes as pretreatments and additives for a rigid polyurethane adhesive Butt tensile, grit-blasted metal, 2 wt% as pretreatment and additive... 

The most efficient intermediate layers are polyurethane adhesives or glues.175 In this case, the correct choice of molecular weight of the polyester and its ratio to diisocyanate is very important. The dependence of the adhesive strength on the molecular weight and the isocyanate-to-diol ratio is shown in Fig. 4.13. The best adhesion to metal is achieved when an intermediate layer based on low-molecular-weight polyester and at a ratio of NCO OH = 2.5 is used. 

The major synthetic adhesives used for bonding wood include urea, phenol, and melamine formaldehyde resorcinol formaldehyde, phenol resorcinol, and polyvinyl acetate emulsions. More recently one-component, moisture cured polyurethane adhesives have become popular for bonding wood. Natural adhesives such as casein and animal glues are also often used for general-purpose wood bonding. Epoxies have been used for certain specialized wood joining applications such as when wood is bonded to metal substrates. 

The directives apply to all materials used in the make up of electrical and electronic components and include paint, plastics, adhesives and rubbers, plastic parts, protective coating materials, epoxy adhesives, cyanoacrylate adhesives, polyurethane adhesives as well as complete computer motherboards. Computer and peripheral equipment are made up of different materials consisting of plastic, ferrous and non-ferrous metals, trace heavy metals, glass, foams, rubber, carbon powder and additives. Other non-metal materials posing environmental and health problems present in electrical and electronic products are beyond the scope of this book and will not be discussed here. The supportive components used in these products fall within the following ten product categories in the directive which are ... 

A list of metal catalysts associated with polyurethane adhesives will be discussed under polyurethane analysis. Some epoxy adhesives may contain metal salts that can act both as filler and catalyst. Some of these catalysts contain toxic metals that must be controlled and monitored for health and environmental requirements. 

Polyurethane adhesives employ metal catalysts as part of their functionality and the most popular are listed in Table 6.23. Catalysts such as the borate or phosphate salts of Sb, Ge, Mo and W are also widely used in polyurethanes containing a high concentration of... 

Ashing Methods for Metal Analysis of Polyurethane Adhesives... 

There are a range of metal catalyst/activators used in phenolic and polyurethane adhesives that can be monitored using ICP-OES. In the metal analysis study of phenolic adhesives, the salts Ca(S03H)2 and Cu(S03H)2 were formulated as listed in Table 6.21, with and without fillers. Several metal salts are employed in polyurethane adhesives for the reasons listed in Table 6.23. As part of the sample preparation study of these products metal salts were formulated into typical polyurethane products consisting of volatile and non-volatile metal salts, listed in Table 6.24, showing the metals of interest and the concentrations expected. 

The use of polyurethane as a binder has found two interesting applications foundry cores and woodchip particleboard. The foundry industry has recognized the value of polyurethane adhesive binders to bind sand foundry cores for metal casting. This application is increasing steadily. The use of isocyanate binders for woodchip particleboard is receiving significant attention. The... 

C. Wehlack, R. Kramer, W. Possart, Ageing of a polyurethane adhesive bulk versus ultrathin films on metals, Proc. poster pres., 7th European Adhesion Conference EURADH 2004, Freiburg im Breisgau, September 5-9, 2004. 

The development of polyurethane adhesives can be traced back more than 60 years to the pioneering efforts of Otto Bayer and co-workers. Bayer extended the chemistry of polyurethanes initiated in 1937 [1] into the realm of adhesives about 1940 [2] by combining polyester polyols with di- and polyisocyanates. He found that these products made excellent adhesives for bonding elastomers to fibers and metals. Early commercial applications included life rafts, vests, airplanes, tires, and tanks [3]. These early developments were soon eclipsed by a multitude of new applications, new technologies, and patents at an exponential rate. 

The furniture industry uses polyurethane adhesives to bond veneers of various composition to boardstock and metal substrates. Both waterborne and solvent-based adhesives are used. 

Polyurethane adhesives are typically more flexible than epoxies, with good shear and high peel strengths on metals and engineering thermoplastics. These types of adhesives are particularly well-suited for joining substrates with dissimilar coefficients of thermal expansion and for securing various types of inserts in composite panels. 

Various technologies have been applied to minimise the required downtime, but so far a valid solution has not been found. The adhesive force between polyurethane and metal (either aluminum or steel) requires a release agent to be sprayed onto the moulds every single cycle (or every few cycles) to enable easy removal of the part. In addition, various internal mould release technologies are available, but they do not apply to all formulations. 

Atomic spectroscopy (including atomic absorption spectrometry, atomic emission spectrometry, and atomic fluorescence spectrometry) is of use across the span of reactive adhesive technologies. For example, the cure of anaerobic adhesives on non-reactive surfaces is usually assisted by the use of an active metal-based primer. Similarly, the cross-linking of silicone adhesives is promoted by the use of organometallic salts of cobalt, tin, iron, lead, and platinum. In the case of polyurethane adhesives, the key condensation reactions are catalyzed by tin salts (e.g., dibutyl tin dilaurate and stannous octoate). 

Urethanes and isocyanates have found widespread use as adhesives, in both industrial and household environments. They can be used to bond a variety of substrates such as rubber, plastics, metals, wood, glass, and ceramics. Polyurethane adhesives display good hydrolytic stability and have... 

When using two-part urethane structural adhesives, priming of the substrates is often required in order to obtain optimum bond durability, particularly when bonding metals. Primers are generally developed for use with a particular combination of adhesive and adherends. There are various types of primers for polyurethane adhesives, including one-part heat cure epoxies, two-part heat and room temperature cure epoxies, and one-part urethanes. 

Improved adhesion of polyurethanes to metals has been claimed to be achieved by incorporating phosphoryl compounds or silane coupling... 

Polyurethane adhesives are commonly recommended for bonding Lexan resin to metal, glass, ceramics, fluorocarbons, and other plastics . These two-part adhesives are characterized by bonds which have excellent room temperature... 

Reactive polyurethane adhesives polyurethane prepolymers with terminal hydroxyl groups or terminal isocyanate groups. Uses plastics, metals, silicate-containing materials. 

Rigid polystyrene foam is used for the manufacture of composite sheets, for example, for containers and prefabricated building boards. The rigid foam is combined with metals, wood-based materials, asbestos, cement, and plastic sheets. Polyurethane adhesives are particularly effective in this field. 

Fluoropolymers. There are no known adhesives for fluoropolymers that give bonds of adequate strength without pretreatment. Simple, low-quality bonds can be obtained with contact adhesives. After chemical pretreatment, for example, with a solution of an alkali metal naphthalenide in THF, polyfluorocarbons can be bonded with high strength by using epoxy and polyurethane adhesives. 

When the AS 1160 resin is mixed with isocyanate, and cured for up to 24 h in dry (typically less than 15 % RH), a thixotropic polyurethane adhesive is formed. The adhesive is commercially used to bond metals, organic and inorganic materials, and is particularly useful for reducing the relative movement of components in multimaterial assemblies. The performance of the polyurethane adhesive requires the ultimate tensile strength (UTS) to be a minimum of 15 MPa when measured using butt tensile specimens by ASTM Test Method D2095. 

Reegen, S. L., and Ilkka, G. A., The Adhesion of Polyurethanes to Metals, Adhesion and Cohesion Symposium, General Motors Research Laboratory, Elsevier, 1962. 

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