Two-component Curing

Materials. The single films and multilayered materials examined are listed in Tables I and II, respectively. The adhesive (10thick) between any two layers was a two-component curing, epoxy—polyester adhesive, Adcote 503A, Morton Chemical Co. Pouches (11.5 X 17.8 cm) were made from the multilayered materials by heat sealing the sides and bottom under the optimum heat sealing conditions (3). 

Diol Two Component Cure. Amide/blocked aldehyde systems show high reactivity with 1,2 or 1,3 diols and give thermodynamically favored cyclic acetals. As mentioned above, even monomers which self-crosslink poorly because they cannot cycllze to the hemlamidal (I.e., 13, 14) will react efficiently to form crosslinked bis-cycloacetals H In the presence of a tetraol (or, to Impart organic solubility, a blocked tetraol, 15, Scheme 3). 

The two components cure without evolution of any by-products, little or no volume change occurs and the system is ideally suited for use in thick and variable thickness bondlines. Solventless and 100% solid systems are possible which cure at room temperature within a few minutes. Viscosity, curing rate and cure temperature requirements can be tailored to meet the user s needs. Application of the system is generally made by two-part metering and mixing equipment. 

Two component curing hot melts consist, for example, of (i) polyamide- -epoxy, or (ii) a polyol component -I- isocyanate. After the mixing of the two components, they possess only limited pot life. 

Poly isobutylene, PIB, is a homopolymer of high molecular weight. The butyl elastomers are copolymers of isobutylene with sufficient isoprene (0.5-2.5%) to permit crosslinking. Most butyl compositions are one-component, e.g., tapes or liquid gun-grade caulks. They may be modified with plasticizers such as polybutene, or tackifiers and fillers such as calcium carbonate and fibrous talc. Two-component, curing butyl sealants are also available. 

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. 

Silicone reliners are supplied as either a one-component system that cures in the presence of moisture or heat, or a two-component system containing base and catalyst. Both types adhere poody to denture base and carmot be polished satisfactorily. Some silicones support propagation of bacteria such as Candida albicans. Acrylic-based sifloxane monomers and resins have been proposed for overcoming these deficiencies (211). 

In 1975 Wacker-Chemie introduced silicones under the name of m-polymers. These are also room temperature curing liquid polymers which give rubbery materials on cross-linking and are available both as one- and two-component systems. Their particular feature is that they contain dispersions of copolymers such as those of styrene and n-butyl acrylate in the shape of rods or rice grains in the fluid silicone polymer. A small amount of the organic copolymer is also grafted onto the silicone backbone. 

The soft segments made from asymmetrical (amorphous) polyols are important for two-component structural adhesives and one-component moisture-curing adhesives. These materials are applied and usually cured at room temperature. 

The two-component urethane structural adhesives are among the most difficult to characterize, simply because of the widely varying properties that are possible. These adhesives may be rigid plastics similar in modulus to standard epoxy adhesives, with glass transition temperatures of the cured adhesive being approximately 60°C. 

Two-component systems consist of (1) polyol or polyamine, and (2) isocyanate. The hardening starts with the mixing of the two components. Due to the low viscosities of the two components, they can be used without addition of solvents. The mass ratio between the two components determines the properties of the bond line. Linear polyols and a lower surplus of isocyanates give flexible bond lines, whereas branched polyols and higher amounts of isocyanates lead to hard and brittle bond lines. The pot life of the two-component systems is determined by the reactivity of the two components, the temperature and the addition of catalysts. The pot life can vary between 0.5 and 24 h. The cure at room temperature is completed within 3 to 20 h. 

Moisture-curable urethane systems (one-pack) can be considered as two-component systems which use atmospheric moisture as the second component. One-pack urethane coatings can be produced that are similar in physical properties to the two-pack systems for almost all applications. These highly complex systems can have a great deal of flexibility. Claimed advantages are a one-pack system, rapid cure, even at low temperatures, excellent chemical and abrasion resistance and good flexibility. Although these systems have been available for some time in other countries of Europe, they are only recently beginning to be of interest in the UK. 

Exoxy resin paints are supplied as two components, a base and hardener, to be mixed at the time of application. Curing of the film to a tough, oil-. 

Few non.chemists know exactly what an epoxide is. but practically everyone has used an "epoxy glue for household repairs or an epoxy resin for a protective coating. Epoxy resins and adhesives generally consist of two components that are mixed just prior to use. One component is a liquid "prepolymer/ and the second is a "curing agent" that reacts with the prepolymer and causes it to solidify. 

The curing of two-component Isocyanate coatings appears to be strongly dependent on factors such as catalysis, temperature and relative humidity (8, 9),... 

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. 

Moreover curing is not always carried out at a high temperature also cold-curing resins are used (e.g. in two-component adhesives or in large ship decks). 

Otto Bayer produced PUs in the 1940 s by reacting diisocyanates, such as tolyl diisocyanate, with dihydric alcohols, such as ethylene glycol. In another experiment he added a diisocyanate to cure synthetic rubber (SR) containing hydroxyl groups. The rubber was cured (vulcanized), but it stuck to the mold. Variations of products from these two experiments are now used as two-component adhesives for bonding footwear and automotive plastic parts. 

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