Single-component adhesives

Commercial epoxy adhesives are composed primarily of an epoxy resin and a curing agent. Various additives and modifiers are added to the formulation to provide specific properties. Example trade names and suppliers of these ingredients are included in App. A. The curing agent may be incorporated into the resin to provide a single-component adhesive, or else it may be provided in a separate container to be mixed into the resin immediately prior to application. 

A significant amount of development is currently occurring relative to latent catalysts because of interest in their long shelf life, high reactivity, and single-component adhesive formulations. Present technologies involve absorption of acidic or basic catalysts in molecular sieves, formation of Lewis acid salts or other amine salts, microencapsulation of amines, and other novel segregation methods. 

To eliminate errors resulting from mixing or due to the exothermic reaction heat, so-called 1C adhesives were developed. These EP resins are only single-component adhesives in a procedural sense Chemically they are stiU two-component or multiple-component adhesives. These resins frequently contain additional catalysts that influence the course and kinetics of the reaction. 

Dimethacrylates are solvent-free, single-component adhesives with special properties. Since the transition from hquid to solid state in these adhesives is only possible in the absence of oxygen, i.e., under anaerobic conditions (anaerobes are bacteria that thrive in the absence of oxygen), they are called anaerobic adhesives. 

With single-component adhesives, the adhesive components are premixed in their final proportions. They are however chemically blocked. As long as they are not subjected to the specific conditions which activate the hardener, they will not bond. They require either high temperature or substances or media (light and humidity) from their surroundings to initiate the curing mechanism. The containers in which this type of adhesive is stored are carefully chosen to prevent any undesirable reaction. 

This rapidly developing group of materials, based on a variety of acrylic monomers, has viscosities which are fairly readily modified giving thin liquids, syrupy resins and thixotropic semi-solids. Some are truly single-component adhesives - the anaerobic versions (see Sections 5.1.2 and 5.1.12.1) - while others require some form of hardener. The hardener may be a surface primer or mixed directly into the adhesive. 

Polyurethane Adhesives. The search for formaldehyde-ffee binders resulted in a new generation of polyurethane-based glues for chipboard production. The usage of polyurethane based adhesives for assembly of wooden materials has also increased. These liquid polyurethane adhesives are single-component adhesives that harden by a chemical cross-linking reaction which is initiated by moisture in the material. The water... 

Smith has described in detail the practical advantages of carboxyl functional Neoprenes AF and AJ for making improved contact adhesives. The early room temperature bond strength of conventional neoprene contact adhesive is dependent on the crystallization rate of the polymer. Single component adhesive systems based on carboxyl functionality undergo crosslinking reactions with divalent... 

Single-component adhesives polyurethane 15-25°C (Cooling chamber/room temperature)... 

First, for normal reactive single-component adhesives, they are usually stored in large quantities after manufacture for a significant period of time, before they are filled into smaller quantities and delivered to the market. Hence, to eliminate any undesired chemical reactions during storage, low storage temperatures are essential. This group of adhesives includes cyanoacrylates and UV-sensitive epoxy resins. When stored at —20°C, in dark conditions, they have a minimum shelf life of approximately 2 years. 

Second, highly reactive single-component adhesives, such as catalyzed epoxy resins in the form of films, are viable at room temperature for only a few days. However, at —20°C, they can be stored for approximately 6 months. 

In single-component adhesives, all the raw materials are added in one component In two-part adhesives, the formulation is separated into two components. One part, usually called part A, contains the organic resins and the other part, called part B, contains the hardener and accelerator. 

Modified silanes (MS) are odourless, non-corrosive and do not contain isocyanates, solvents, silicones or PVC. They are normally available as single-component adhesive sealants (although two-part systems are also available) and require atmospheric moisture during the cure cycle. 

Reactive hot melts are single-component adhesives that are applied in the molten form (like conventional hot-melt adhesives) but have an additional secondary cure with atmospheric moisture to give a crosslinked polymer. Reactive hot melts will give... 

The curing of the single-component adhesive is important. Within the automotive industry curing is normally achieved at the same point in the process as the first paint coat is cured. Up to this stage of the production process the adhesive must remain in the correct position and be unaffected by any of the handling and fitting operations. 

Adhesive dispensing systems for applying single-component adhesives can be fed by either a pressure-feed container for light viscosity adhesives or ram-mounted dmm pumps for medium to heavy viscosity adhesives. Application can be manual or automatic. 

Anaerobic adhesives are single-component adhesives that are normally multifunctional acrylates or methacrylates for example, polyethylene glycol... 

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