Adhesives waterborne systems

Almost all urethane materials are synthesized without the use of solvents or water as diluents or earners and are referred to as being 100% solids. This is true of all foams and elastomers. There are many products, however, which do utilize solvents or water, and these are known as solvent-borne and waterborne systems, respectively. In the past, many coatings, adhesives, and binders were formulated using a solvent to reduce viscosity and/or ease application. However, the use of volatile solvents has been dramatically curtailed in favor of more environmentally friendly water (see Section 4.1.3), and now there are many aqueous coatings, adhesives, and associated raw materials. Hydrophilic raw materials capable of being dispersed in water are called water reducible (or water dispersible), meaning they are sufficiently hydrophilic so as to be readily emulsified in water to form stable colloidal dispersions. 

Single-component epoxy adhesive formulations are the largest type of epoxy adhesives sold, with about 55 percent of the consumption, while two-component formulations account for another 44 percent of the volume. Radiation cure formulations represent the remainder of the market. Epoxy adhesives can also take many forms including solids, solvent-free liquids, solvent-borne systems, and waterborne systems. 

Formulation details are then presented in Chapters 11 through 14 for the various possible forms of epoxy adhesive systems room temperature and elevated-temperature curing liquids, pastes, and solids. The more or less unconventional forms of epoxy adhesives are also identified and discussed, since these are now achieving prominence in industry. These include uv and electron beam radiation curable, waterborne systems, and epoxy adhesives capable of curing via the indirect application of heat or energy. 

Uses Acrylic film-former in protective metal coatings, latex paints, ceramics, adhesives, textiles, cosmetics, paper, leather, floor polishes, chemir spedalties exc. dispersant, leveling, and binding chars. plasticizer for solv. or waterborne systems provides exc. pigment wetting Features Thermoplastic... 

Uses Provides adhesion, durability, heat sealability at low temps., exc. water and solv. resist, to waterborne systems process aid, mar resist, aid, adhesion promoter in can and coil coatings Features Usable pH 1+... 

Uses Antifoam for water-based coatings and adhesives, latex paints, acrylic emulsions, waterborne systems, esp. for formulations sensitive to silicone-caused surf, imperfections Features In-grind antifoam... 

Uses Coupling agent in polysulfide and PU caulks and sealants, and waterborne systems (latex coatings, adhesives, sealants)... 

In this paper/ we shall describe the development of adhesives during the last several years and the trends for further advances. In general/ traditionally used / solvent-borne systems (4) will be gradually replaced by waterborne systems/ hot-meltS/ nonvolatile solid (or liquid) systems/ two-part adhesiveS/ radiation-curable adhesiveS/ and powder and reactive liquid systems (Table 1). 

Hot-melt adhesives are currently one of the fastest growing segments of the industry (Fig. 14). No solvent discharge is the best answer to the pollution problem and, in comparison with the waterborne systems, hot-melts require less energy. From a capital investment standpoint, the installation of a hot-melt coater line does not require a large oven to remove water or solvent from the system. As a result, hot-melt adhesives have been widely used, e.g., the... 

As discussed in the Introduction, in addition to hot-melt adhesives, one of the most important forms of adhesives for the future is the waterborne system. In general, an advantage of the waterborne system is that it is free from the solvent-pollution problem. For this reason, we shall describe several new waterborne systems in detail acrylics, modified ethylene-vinyl acetate, polyurethanes, phenolics, epoxies, isocyanates, and tackifiers. Applications of these systems range from PSA s contact adhesives, and laminating adhesives to wood adhesives. 

The increasing amount of research in waterborne systems should some day overcome technological difficulties. Howeverr the change-over from some solvent-borne to waterborne systems has presented difficulties (107), for exampler poor coating quality, excessive foam, insufficient water resistance, and even some corrosion and clean-up problems. Despite the problems, some waterborne systems have already been adopted for the manufacture of PSA s, contact adhesives, laminating adhesives, and wood adhesives. However, few applications of the waterborne systems as structural adhesives, especially as aerospace structural adhesives have been found. 

To counter energy-saving problems, low-temperature curing by radiation has gained acceptance. For a long-term solution of pollution problems, hot-melt adhesives and the waterborne systems are being increasingly used as a substitute for the solvent-borne adhesives. In the future, the waterborne systems could dominate the entire adhesive industry. 

The shear adhesion values at very high levels (70% or greater) vary between the two resins also, with the modified terpene being lower. Cost/effectiveness will often determine which resin is used. Table 4 illustrates the differences observed between a solvent-applied system and a waterborne system using natural rubber as the elastomer and an alpha-pinene resin of very narrow molecular weight distribution. The numbers in the first three columns were obtained for the waterborne system while those in the last three columns illustrate the values for the same resin with the same natural rubber which was milled to allow its dissolution. Here again, we see the differences primarily in shear adhesion which was pointed out earlier. 

Aquadex, Water-dispersed polyurethane VOC compliant coating system, Dexter Adhesive Coating Systems (IL) waterborne coatings, Dexter Automotive Specialty Coatings... 

A further interfacial factor can be the presence of non adsorbable or non desorbable contaminating films (as previously mentioned above) at the interface. Such materials can be oils, fatty acids, plasticisers from the rubber and metal processing oils from inadequately cleaned metal components. Some of these lubricants can be absorbed by the adhesive if it is solvent-based but in the case of the new waterborne rubber to metal systems this absorption cannot take place, for the systems are neither miscible or compatible with oils. These new waterborne systems have a critical tolerance level for surface contamination of the metal and if this is exceeded then wetting out of the metal by the adhesive will not, at the worst be possible, or at the best complete. 

Air floated and water-washed grades of kaolin are widely used in paper, packaging and construction adhesives based on starch, emulsion and latex based waterborne systems. They are also used in fabric adhesives, mastics and caulking compoimds. Calcined kaolin is used as a low moisture reinforcing agent in one or two part construction and automotive sealants based on butyl, methane and silicone elastomers. Calcined kaolin is less acidic and so can be used with precipitated calcium carbonate in polysulfide sealants. Typical loading of kaolin fillers are 5 to 25% in adhesives, 5 to 20 % in sealants, and 25 to 50 % in mastics. 

Uses Surfactant, lubricant for waterborne systems, adhesives, agric., chem. processing, coatings, fibers, household specialties, metal processing, mining, paper,... 

Table 3.6 gives the treatment values recommended for a number of plastics as a function of the adhesive coating system and the manufacturing processes. Note that, as discussed earlier in this section, waterborne adhesives universally require higher surface energy levels than solvent-based... 

Turner, S. Richard, 1 Two-component (2-K), nonsagging, polyurea structural adhesive, preparation of, 255-256 Two-component (2-K) systems, 238-241 Two-component (2-K) waterborne polyurethane coatings, 206 preparation of, 254-255 Two-shot cast elastomer, preparation of, 249-250... 

Water-based inks, 14 326 Water-based muds, 9 3-5 Water-based writing inks, 14 328 Water-borne adhesives, 25 475 Waterborne alkyds, 2 156-158 Waterborne automotive coatings, 10 448 Waterborne can coating system, 10 445-446... 

Dearborn, Mi., 26th-29th Oct. 1997, p.397-423 EPA AND FDA REGULATIONS AS FACTORS IN THE CONVERSION FROM SOLVENT TO WATERBORNE ADHESIVE SYSTEMS FOR FLEXIBLE PACKAGING Simmons R A Keller Heckman LLP (Adhesive Sealant Council)... 

This paper discusses how tightening environmental regulations in the USA are encouraging a shift from solvent-based to waterborne adhesives for use in flexible packaging applications. It also looks at how new adhesive systems have a relatively easy path to Food Drug Administration clearance for food packaging uses. 

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