Emulsion setting adhesion

Many of the emulsion- and solution-based adhesives, already described, can be cross-linked, and can therefore be termed Reaction setting adhesives. 

Individual reaction-setting adhesives do have disadvantages. For example, phenolic systems require high pressure during bonding. In general, reactive adhesives are more toxic than emulsion and hot melt adhesives, and they are often much more expensive than other types of adhesives. However, reactive adhesives offer a number of advantages that are essential in many applications. 

Harmful effects can occur because of inhalation of vapour or skin absorption. Solvent-based adhesives are probably the greatest potential problem as far as toxicity is concerned because their mode of operation involves the evaporation of large quantities of solvents. Some of the components of reaction-setting adhesives are highly toxic and very efficient ventilation is necessary. Molten polymers have very low vapour pressures. However, additives in hot melt adhesives and decomposition products may produce toxic vapours, especially if reservoirs of melt adhesives are used. Emulsion adhesives where the dispersion medium is water represent the safest group of adhesives from the toxicity viewpoint. 

Emulsion-based adhesives are adhesives that contain aqueous synthetic resin dispersions or emulsions or rubber latices as their principal raw material or active binder [41]. They are milky white, odorless hquids with solids contents of 40 - 60 %. In quantitative terms, emulsion-based adhesives are one of the most important groups of adhesives. They set by the release of water and the formation of a film fi om the emulsified or dispersed resin or rubber droplets. 

Case Making. In case making, when the covering material consists of textiles, plastics film, or paper, as in the backlining of books, hot animal glues are used because they set rapidly by gelatinization and rapidly bond the narrow overlap of the coating material around the board, even under the brief contact pressure normally applied in the machine. In special cases, also emulsion-based adhesives are also used. 

Cartons are sealed with emulsion-based or hot-melt adhesives, depending on the length of the pressure belt and the quality of the cardboard. On modern, fast-running machines with up to 120 cases to be closed per minute, hot-melt adhesives are preferably used, due to their fast setting. An interesting combination is the simultaneous use of emulsion-based and hot-melt adhesives. In this case, a spot appfication of hot-melt adhesive performs the function of the pressure unit or compression section, whereas the actual bonding function is performed by emulsion-based adhesives, generally applied in line form. 

In the case of emulsion-based adhesives, the loss of a relatively small amount of water will cause the inversion of the emulsion and rapid setting of the adhesive. This contrasts favorably to solution-based adhesives, both water and organic solvent types, which require that most of their solvent be lost to the atmosphere and/ or absorbed into the substrate before they become tacky enough to hold the substrate together. In fact, even more solvent must be lost... 

Poly(viayl acetate) emulsions or hot-melt adhesives are typically used to form the manufacturer s or glue lap joiat of the box. The main criteria for the adhesive is that it provide a strong and tough final bond and that it set up quickly enough to allow fast box production speeds. Production rates ia excess of 240 boxes per minute are not uncommon ia the iadustry. 

The viscosity of an adhesive directly influences its penetration into a substrate as the viscosity increases, the penetrating power decreases. It also determines the amount of mileage or spread that can be obtained. An optimum viscosity exists for each substrate and each set of machine conditions and must be achieved in order to manufacture an efficient adhesive. Poly(vinyl acetate) emulsions are frequently too low in viscosity to be metered efficiently or to perform well as adhesives by themselves. They must be bodied to working viscosities, eg, by adding thickeners. 

Plasticizers soften the film and increase the adhesion and the setting speed. The most common are phthalates, adipates and benzoates. The amount added can be in a broad range of 10-50%. They affect the swelling and softening of the PVAc emulsion particles, ensure film formation at room temperature, and the tack of the still wet adhesive. They also provide improved moisture resistance of the bond. Disadvantages are the lower resistance of the bond line against heat, possible migration of the plasticizers and enhanced cold flow. 

Insulants for pipework and curved pressure vessels can be obtained ready shaped, so that they fit tightly to the surface. All surfaces should be quite dry before the material is applied, even if the adhesive is a water-based emulsion, and the water or other solvent must be given ample time to dry or set before any outer wrapping is applied. 

The study of forces between deformable interfaces can be broken into two categories, the interactions between two sets of deformable interfaces (e.g., two oil drops in water), or a rigid particle and a single deformable interface. Study of the forces in these systems is motivated by the prevalence of both types of systems (drop-drop or drop-rigid particle) in industrial problems. For example, wetting and adhesion of oil emulsions in porous media are concerns in the petroleum industry for both liquid/liquid separations and oil recovery [1]. An understanding of the interaction forces between... 

An emulsion polymer-isocyanate adhesive, a crosslinked polyvinyl acetate adhesive, a resorcinol-formaldehyde adhesive, a phenol-resorcinol-formalde-hyde adhesive, and an acid-catalyzed phenolic-formaldehyde adhesive developed bonds of high shear strength and wood failure at all levels of acetylation in the dry condition. A neoprene contact bond adhesive and a moisture-curing polyurethane hot-melt adhesive performed as well on acetylated wood as untreated wood in tests of dry strength. Only a cold-setting resorcinol-formal-... 

Wood was soaked or impregnated with chemicals. After that they were set in a hot press and pressed at 160 iC/0.5-2MPa for 5-30min. [Heat-Pressed Treatment]. Comparison specimens were set in a hot oven and dried at 160 °C for 2-6hrs. [Heat-Dried Treatment]. Heat pressed material was put on top of each other or untreated material with emulsion polymer-isocyanate adhesives to make a laminated board. 

Uses Emulsion tor pkg. applies, requiring quick tack development and fast setting speeds suitable for food pkg. adhesives, coatings, paper/ paperboard... 

Uses Dispersant, wetting agent, emulsifier for pojymerization, emulsion paints, brush cleaners, wallp er removers, pigment preps., binder emulsions surfactant costabilizer to inc. mech. or salt stability of polymer disps. emulsifier for mfg. of o/w emulsions food pkg. adhesives, paper/paperboard emulsifier in mfg. of food-contact articles Regulatory FDA 21CFR 175.105,176.180,178.3400 BGA approved Properties Clear liq. dens. 1.022-1.026 g/cm (70 C) FILB 13.4 hyd. no. 84-91 set pt. 7 C doud pt. 60-65 C (1 g/99 cm water) nonionic 99% min. act. <0.5% water... 

Uses Wetting agent for polymer disps., mech. processes, aq. paints/ coatings, printing inks, emulsions, adhesives, difficult substrates e.g., plastic and metal surfs., cellophane and plastic films, aluminum foil, silicone-treated papers, glass, aq. overprint varnishes of offset prints Features Compat. in different polymer systems Properties Water-wh. clear liq. sol. in water vise. 50-150 mPa-s set pt. 

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