Two-component polyurethanes

Cure analysis of thermoset thin films by ETIR emission has also been reported [500]. FTIES was used to smdy cure monitoring of aerospace epoxy resins and prepregs and provides a rapid method for prepreg quality acceptance [501]. Also curing of commercial polyurethane two-component paints has been carried out by FUR emission [493]. 

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

For other recreational surfaces, such as mnning tracks, the installation techniques are quite different. Most are poured-in-place. An interlocking tile technique may be employed for tennis courts. In all cases, adequate provision for weathering and water drainage is essential. In general, the resiHent surfaces are installed over a hard base (see Fig. 4) that contains the necessary curbs to provide the finished level. Outdoors, asphalt is the most common base, and indoors, concrete. A poured-in-place polyurethane surface (14) is mixed on-site and cast from at least two components, an isocyanate and a filled... 

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. 

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. 

The first urethane reaction in Fig. 1 is used in two major ways in adhesives. In one case, a two-component adhesive usually employs a polyol and polyisocyanate with catalyst. This can react at room temperature to form the polyurethane. The second use of this reaction is to make an isocyanate-terminated prepolymer. Reacting a stoichiometric excess of isocyanate with polyol can produce an isocyanate-terminated prepolymer. A prepolymer is often made with an NCO/OH ratio of 2.0, as shown below, but the isocyanate ratio can range from 1.4 to over 8.0, depending upon the application ... 

Two-component waterborne urethane dispersions are similar to the one-component PUD s in that a polyurethane dispersion comprises one of the two components. The second component is usually a crosslinker from the following classes of materials (a) polyisocyanates, (b) aziridines, (c) polycarbodiimides, and (d) epoxies. Many of the crosslinkers are not inherently water-soluble or water-dispersible. Therefore, they must be modified with surface active agents themselves, so as to become emulsifiable in water. 

The basic RIM process is illustrated in Fig. 4.47. A range of plastics lend themselves to the type of fast polymerisation reaction which is required in this process - polyesters, epoxies, nylons and vinyl monomers. However, by far the most commonly used material is polyurethane. The components A and B are an isocyanate and a polyol and these are kept circulating in their separate systems until an injection shot is required. At this point the two reactants are brought together in the mixing head and injected into the mould. 

Where fumes or deposits which act as anti-oxidants are present, no orthodox paint which dries by oxidation can give satisfactory service. Instead, a coating which dries either by evaporation (e.g. a selected chlorinated rubber paint), or by a cross-linking reaction (e.g. a catalysed epoxy or two-component polyurethane paint) must be used. 

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. 

Scheme 4.23 Two-component water-borne polyurethane by the prepolymer method.

Example 9. Two-Component Waterborne Polyurethane Coating. This example utilizes the PUD from Example 8 in a two-component, waterborne coating formulation. An HDI-based, water-dispersible isocyanate is also prepared. 

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... 

Fig. 2 demonstrates the light stability of a high-solid lacquer based on two-component polyurethane. The loss of gloss was measured as a function of the irradiation time in a QUV instrument (Q-Panel Company, Cleveland Ohio). The figure also shows that a particularly good... 

Figure 2. Light stability of a high-solids, one-coat silver metallic paint based on a two component polyurethane. Test criterion gloss retention QUV irradiation. (HALS) Bis-(2,2,6,6-tetramethyl-piperidinyl-4)sebacate (UVA) 2-(2 -hydroxy-3, 5 -di-tert-amylphenyl) benzotriazole.

A two component polyurethane formulation was stored In the field In separate 208 liter (55 gal) vessels of 0.95 cm wall thickness and under a 0.35 to 0.9 MN/m (50-100 psl) over pressure. Upon demand the components are mixed and discharged to form a rigid foam re-... 

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. 

The addition polymerization reaction of dihydroxy compounds with diisocyanates sets in on mixing the two components and gentle warming. Under proper conditions, linear polyurethanes with molecular weights up to about 15,000 can be obtained. As in the case of polyamides and polyesters, the softening point of the aliphatic polyurethanes depends on the number of carbon atoms between the urethane groups. 

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. 

Most polyurethanes are different from other elastomers in that they are cast. Two components are mixed together. One component is a prepolymer which consists of two major chemical structures. One... 

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