Adhesives, applications types

The adhesives employed for in-line adhesive application are generally of two types (1) flexible, but non-pressure-sensitive adhesives based on blends of saturated stryenic block copolymers and wax and (2) pressure sensitives based... 

Specific substrates are described under each classification. Of course, adhesive applications are not limited to joints having only one type of substrate. Metal-to-plastic, aluminum-to-steel, metal-to-wood, glass-to-metal, and an infinite variety of other joint configurations are all possible. In these applications the nature of each substrate needs to be understood and considered in the overall selection of an adhesive formulation and bonding process. 

The single largest use for the phenol-formaldehyde resins is in adhesive applications for the production of plywood, chipboard, and particle board. The resin can comprise as much as one-third of the weight of the board, particularly of particle boards, which contributes to a total demand for phenolics in the U.S.A. of over half a million metric tonnes per year. They are also used as the matrix adhesives for the production of several types of grindstones. In combination with paper, woven cotton, glass fiber, etc., components, phenolics contribute to the production of engineering and decorative laminates in the form of rods, tubes, and sheets. The sheet products Arborite and Formica are familiar as the finished surfaces of furniture, bathroom, and kitchen counter tops and other areas where attractive patterns and water resistance are important characteristics. Molded products from phenolics are also important where heat or electrical resistance is required, such as saucepan and toaster handles, switches, and the printed circuit boards used in computers. Recent phenolics production in the U.S.A. has totaled over 500,000 metric tonnes per year, not including fillers [38]. 

The percentage of solids in the dispersion adhesives is 35-55%, in some cases as much as 70%, the rest is water, which after the adhesive application must either be completely evaporated (ventilation time) or diffuse into the joined parts (wood, textiles, concrete, foams, leather). The film formation temperature in types containing plasticizers and flexibilizing additives is lower than in types that are free of plasticizers. Additives, so-called high boilers (ethyl glycol, ethyl glycol acetate, ethylhexanol), are used to bring the film formation temperature down. 

A special form of application results when gases are absorbed by the molten mass (enter into solution) or are stirred into the melt (mechanical distribution). The material expands and foams after exiting from the nozzle. The densities are reduced by about 100% compared to the compact adhesives. This type of adhesive application... 

Reviews on this subject are significantly less than in previous years although this does not appear to be reflected in the proliferation of published papers. Two very comprehensive reviews have appeared on the subject of both uv and electron beam induced curing processes covering initiator types (radical and cationic), monomers and prepolymers. Two other reviews on similar themes have covered adhesive applications while others have covered... 

Adhesive/Supplier Type pm Surface Type Dispensing Application... 

Produced by a solution polymerization process, this material exhibited an ordered molecular structure with the styrene monomer located at the ends of the butadiene monomer chain. In addition, other monomers such as isoprene, ethylene, butylene, and others, could be added to the polymer chain, which further modified basic properties. These materials possess a continuous rubber phase for resilience and toughness, and a discontinuous plastic phase for solubility and thermoplasticity. A variety of different grades are also available for this type of SBR, with differences in molecular weight, differences in the types of monomers used, differences in structural configuration, and differences in the ratio of endblock to midblock. Both emulsion and solution polymerized grades of SBR are available as solvent-based and water-based adhesives and sealants. Block copolymers are extensively used for hot melt formulations and both water-based and solvent-based pressure sensitive adhesive applications. Today, SBR elastomers are the most popular elastomers used for the manufacture of adhesives and sealants. 

Adhesive/Supplier Type Bonding Conditions Application... 

The selection of mix ingredients may depend heavily on the type of adhesive application equipment used. The main types of equipment for plywood and LVL are roll coaters, spray systems, curtain coaters, and foam extruders. When foam extruders are used, animal blood and surfactants are usually added to the mill mix. For other application systems, resin producers typically supply the non-filler additives as part of the resin composition. 

During the course of this program, experimental studies were conducted to identify a number of polymer types in formulations which can be cured via radiation for adhesive applications. Performance studies were also made to determine endurance to exposures of various environmental conditions including moisture, solvents and high temperature aging. Data have been developed on a number of good candidate materials from both commercially available products and laboratory experimental... 

Figure 7.1 shows five types of stress found in adhesive joints. Any combination of these stresses may be encountered in an adhesive application. These stresses are described in the sections below. 

Care should be taken when applying adhesives. At the least, an air-filtering mask that is designed to provide protection from airborne particulates should be worn. Good ventilation is recommended for all adhesive applications. Ventilation hoods may be necessary for certain types of adhesives and building designs. 

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