Blocked reactive adhesive

Blocked reactive adhesives Adhesives in which the inter-reaction of the components is eliminated by mechanical (e.g., separated packing units, microencapsulation) or chemical measures (special formulations of resins, respectively, hardeners). 

Film adhesives have to be strictly delimitated from adhesive tapes and adhesive strips (Sections 5.6 and 5.7). Mainly blocked two-component reactive adhesives (Section 3.1.4) are used raw materials. For transport and storage (at low temperatures) they are applied to a - nonadhesive - substrate. Prior to processing they are removed and then applied between the adherends (compounding) and cured under pressure and heat (Sections 3.1.4, 3.2.2 and 4.1.2). Special film adhesives (e.g., phenolic resin nitrile rubber) are also activated by suitable solvents. 

Because high shear stress brings heat into an adhesive mixture, the viscosity of a reactive adhesive can increase considerably through a starting polymerization and, as a result, pipes and dozers can be blocked... 

These subgel prepolymers have been manufactured by industry for some time and used in two-component adhesives or coating materials. For one-component materials, storage below the actual Tg, whenever applicable, is the most efficient method for blocking the reactivities. This kind of blocking is used in powder coatings. 

Post-crosslinkable and substrate reactive polymers are widely used to Improve water and solvent resistance, strength, substrate adhesion and block resistance In binders, adhesives and coatings. The surprisingly rich chemistry of a new class of functional monomers (eg. 1 and 2) related to standard amide/aldehyde (amlnoplast) condensates, but which eliminate aldehyde emissions, was elucidated by monomeric model and mechanistic studies and discussed In the preceeding paper (1). Results with these monomers In copolymer systems are reported here. 

Many adhesives require special properties, for example, SBS polymers are often used for crosslinkable adhesives because the polybutadiene midblock is readily crosslinked by peroxides, UV light or electron-beam radiation. The vinyl content of the butadiene block of SBS polymers is often increased from the standard 8% to near 50% to make it more reactive to crosslinking. Star architectures are also used to reduce the number of crosslinks necessary to form a continuous network throughout the adhesive. For adhesives that require... 

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