Two-component polyurethane systems

Polyurethane adhesives are known for excellent adhesion, flexibihty, toughness, high cohesive strength, and fast cure rates. Polyurethane adhesives rely on the curing of multifunctional isocyanate-terrninated prepolymers with moisture or on the reaction with the substrate, eg, wood and ceUulosic fibers. Two-component adhesives consist of an isocyanate prepolymer, which is cured with low equivalent weight diols, polyols, diamines, or polyamines. Such systems can be used neat or as solution. The two components are kept separately before apphcation. Two-component polyurethane systems are also used as hot-melt adhesives. 

Aqueous two-component polyurethane systems for automotive topcoats are under development. Currently the automotive topcoats are made from solvent-based two-component or blocked one-component systems based on HDI trimer (Desmodur N) or IPDI trimer (Desmodur Z) or both in conjunction with an acrylic polyol. The polyurethane topcoats provide the vehicles with a tough and durable finish with excellent long-lasting glossy appearance ( wet look ) One-component aqueous dispersions are already used in electrodeposition primers and pigmented base coats. Soft-feel polyurethane coatings are increasingly used for instrument panels and seat covers. 

Two-component polyurethane systems have become very popular for many commercial applications, as they can offer products with low VOC content while maintaining high performance. Such polyurethane systems are increasingly used in industrial coating applications. 

The presence of any appreciable amount of moisture in solvents used in a two-component polyurethane system can react with isocyanate crosslinkers and thus impair crosslinking efficiency. Therefore, moisture content is one of the important properties of solvents such as ketones and esters, which are used in two-component polyurethane coatings. Moisture content is normally determined by the Karl-Fischer titration method. 

Covalently bonded substructures having compositions distinguishable from their surroundings are formed in multicomponent systems they are called chemical clusters. The adjective chemical defines covalency of bonds between units in the cluster. To be a part of a cluster, the units must have a common property. For example, hard clusters are composed of units yielding Tg domains. Hard chemical clusters are formed in three-component polyurethane systems composed of a macromolecular diol (soft component), a low-molecular-weight triol (hard component) and diisocyanate (hard component). Hard clusters consist of two hard... 

Polyurethane-acrylic coatings with interpenetrating polymer networks (IPNs) were synthesized from a two-component polyurethane (PU) and an unsaturated urethane-modified acrylic copolymer. The two-component PU was prepared from hydroxyethylacrylate-butylmethacrylate copolymer with or without reacting with c-caprolactonc and cured with an aliphatic polyisocyanate. The unsaturated acrylic copolymer was made from the same hydroxy-functional acrylic copolymer modified with isocyanatoethyl methacrylate. IPNs were prepared simultaneously from the two-polymer systems at various ratios. The IPNs were characterized by their mechanical properties and glass transition temperatures. 

Unless you have been employed in the automobile refmishing or other business where painters manually mix two-component polyurethane paint systems, it is unlikely that you will be exposed to large amounts of HDI. 

An acrylate-terminated polyurethane modified epoxy compound and a polyethylene polyamine homologue and fatty acid combination were formulated into a two-component adhesive system. The adhesive is useful for bonding various thermoplastic resins such as ABS, PC, PBT-PC blends, and PPO.22... 

OTHER COMMENTS useful in bonding rubber to rayon and nylon used in two-component polyurethane coating systems used for aircraft, tank trucks, and truck trailers also used to produce polyurethane lacquer coatings applied to certain automobile body components other uses are in production of thermoplastic polyurethane resins and spandex fibers. 

The second major classification of common polyurethane adhesives is the two-component system. Two-component polyurethane adhesives are widely used where fast cure speeds are critical, as on OEM (original equipment manufacturers) assembly lines that require quick fixture of parts, especially at ambient or low bake temperatures. Two-component urethanes are required in laminating applications where no substrate moisture is available or where moisture cannot penetrate through to the adhesive bond. Two-component urethanes are also useful where CO2 (generated by a one-component moisture cure) or a volatile blocking agent would interfere with the adhesive properties. 

The adhesive bonding of plastic assembly components such as instrument panels, spoilers, spare wheel boxes, roof parts, trim assembles, and fenders is generally with one- or two-component polyurethanes. Frequently, a primer is used as pretreatment to improve adhesion. Adhesive tape systems can provide good results for the bonding of dash panels, trim lines, insignia parts, and rear view mirrors, for example. 

Figure 2.63 Schematic representation of two-component polyurethane resin system...

Polyurethane foam is commonly used to fill the void inside a hollow part for strength or insulation. The foam density is typically in the range of 2-4 Ibs/ft. (0.03-0.06 g/cm ) and is often used to provide buoyancy in flotation devices or insulation for storage vessels. The urethane foam is created using a two-component liquid system that is metered into the part using a special mixing head and as the components react it rises to fill the void inside. 

Second in importance come high-gloss applications, where cardboard or paper is laminated to a film in order to obtain a particular optical effect shiny or matt, for instance. The third area contains a variety of applications, e.g. flat antennas, microcircuits, insulation materials, under the heading technical laminations. Most of the time, these laminations involve metal foils or plates. While food packaging and technical laminations rely mostly on reactive two-component adhesive systems - solvent-based or solvent-free, based on polyurethane chemistry (for some applications dispersions are also used they can be made up of polyurethanes, acrylics or natural raw materials like latex and casein) - high-gloss... 

The most important types of two-component adhesives are moisture-sensitive polyurethane, comprising polyol resin and isocyanate catalyst, and heat-sensitive epoxy, comprising bisphenol A or F resins and polyamine catalyst. Both single- and two-component adhesive systems are available in the market. Single-component reactive adhesives, which include cyanoacrylate and silicone, are also widely known, with the latter often being used as a sealant. 

The original resins that Bayer produced in 1937 by condensing aliphatic diisocyanates and diols were elastomers and foams. However, both one- and two-component polyurethane coatings are produced by heating phenol-capped isocyanates to remove the phenol and permit the isocyanate group to react with diols present in the coating system. 

The conventional polyisocyanurate may be prepared with a two-component system using standard polyurethane foaming equipment. It is usual to blend isocyanate and fluorocarbon to form one component whilst the activator or activator mixture form the second component. 

Most polyurethane formulations are two-component systems, meaning they are made from two basic constituents which are mixed together and react to form the final polymer. The two components are an isocyanate (or isocyanate blend) and a polyol (or polyol blend). The isocyanate is often referred to as the A side and the polyol the B side , although some use the opposite convention. 

Example 10. Two-Component, Nonsagging, Polyurea Structural Adhesive. This example is an all-urea formulation unusual for a 100% solids, hand-castable system. It is also a two-component, one-shot system designed to be nonsagging so that it may be applied to nonhorizontal surfaces without dripping or running. This and similar examples are described in U.S. Patent 5,654,085. See also Guether et al., presented at Polyurethanes Conference 2000, October 8—11, 2000 CRC Press Boca Raton, FL, 2000. 

Polyurethane elastomeric fibers, 205 Polyurethane elastomers, 201 Polyurethane foams, 20, 29, 202 preparation of, 251-252 Polyurethane formulations, one- and two-component system, 238-241... 

Turner, S. Richard, 1 Two-component (2-K), nonsagging, polyurea structural adhesive, preparation of, 255-256 Two-component (2-K) systems, 238-241 Two-component (2-K) waterborne polyurethane coatings, 206 preparation of, 254-255 Two-shot cast elastomer, preparation of, 249-250... 

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