Waterborne systems

Waterborne resin systems can be divided roughly into two classes - water soluble and water insoluble. A true water soluble resin is a solution of a single polymer molecule solubilised on its own, and completely surrounded by water. The water insoluble types are emulsions, these consist of a particle (or micelle - see Chapter II for full definition) consisting of a number of polymer molecules solubilised by a surface covering of hydrophilic molecules. Consider the continuous reduction in particle size from an emulsion particle to a single molecule. There is a zone of colloidal dispersion where the particle size is so small that it is invisible to the eye and the dispersion is clear. These colloidal dispersions are sometimes referred to as a hydrosol. 

In between insoluble and soluble waterborne systems are dispersions of water reducible resins. These are insoluble resins with sufficient acid or amine functionality so that when neutralised (either fully or partially) the resin can be dispersed in water and remain as a stable dispersion. Many people consider emulsions to be dispersions. So they are. As a general rule, the term dispersion will refer to solubilised dispersed systems. Emulsion will be used to refer to insoluble particles dispersed in water with, in most cases, monomers having been polymerised in the water. Emulsions are sometimes referred to as latices. 

In actual practice very few polymers form true solutions and so this chapto will cover polymer Aspersions and emulsions. Many resins are only soluble in a solvent/water mixture, others are dispersions of a water soluble resin in an emulsion, e.g. water soluble alkyd dispersed in m acrylic emulsion. 

Although there is a continuous progression of properties from water soluble resins, through colloidal dispersions, to aqueous emulsions, it is possible to tabulate tbe typical properties of each as in Table 7-1. 

TABLE 7-1 SOME PROPERTIES OF WATER SOLUBLE RESINS AND EMULSIONS 

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Owing to governmental regulations, considerable research has been expended to develop systems suitable for substitution of solvent-based systems, particularly for automobile and container appHcations. In the switch from solvent-based to waterborne systems, epoxies are successfully bridging the gap largely by adaptation of conventional resins. 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

Although waterborne systems were developed in the 1960s, the form of this chemistry that dominates the industry utilizes end-functional, high molecular weight base polymers dissolved in organic solvents. Work on solventless condensation systems continues, but has not yet become commonplace [45,47]. Solvent-borne condensation cure systems are convenient for their ease of pro-... 

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. 

Water-borne primer 43 50-75 10 min 2 h Single-component primer as base for complete waterborne system on steel... 

Today, a large and increasing proportion of the automotive OEM metallic basecoats in Europe and North America are already waterborne and refrnish basecoats are also available in waterborne versions. Other paint applications have followed and the significant growth of waterborne systems can easily be seen in the statistics of the paint associations. Also in printing inks, the use of waterborne inks is steadily growing. 

Silanes can be polymerized into the backbone of a polymer during its synthesis [6]. Emulsion polymerization of methacryloxyalkyl or vinyl functional organosilanes has been shown to be a particularly useful method of incorporating a crosslinking silane into a waterborne system. Subsequent to reaction of the methacryl or vinyl functionality, the alkoxy groups are left available either to react with a substrate or filler, or to crosslink upon film formation. 

These methods offer an opportunity to measure the phenomena that cause instability of silane-containing formulations, and are valuable to the continued understanding of the complex factors that should be considered when formulating with silanes in real-world waterborne systems. 

Emulsifiable epoxies of varying molecular weights, water-dUutable modified epoxies, and dispersions of standard resins represent promising developments for coating appKcations. Can coatings are an important waterborne resin application. Two-component waterborne systems are also finding use as architectural coatings. 

Amino resins are also employed in waterborne systems used in industrial coatings (e.g., automotive spray primers and basecoats, can and coil coatings). Stable coatings can be formulated with hexakis(methoxymethyl)melamine or partially methylated melamine resins. 

Waterborne systems based on resol-epoxy resin precondensates are already at an advanced development stage. Carboxyl groups are introduced into the preformed resols and made water soluble by salt formation with amines. These systems offer a significant saving in solvent compared with that of conventional high-solvent, high-viscosity products. 

Most of the pigments used in conventional paints and coatings are also suitable for waterborne systems. Some exceptions are lead chromates and molybdates, manganese lakes (Pigment Red 48 and 52), some perylenes (Pigment Red 223), benzim-idazolone yellow (Pigment Yellow 151), and isoindolines (Pigment Yellow 13a) which all have limited alkali resistance. 

Wheels are electrocoated engine blocks are coated with heat-resistant, usually waterborne materials. Other parts (e.g., steering equipment and shock absorbers) are painted with two-pack, one-coat epoxy systems that are usually solventborne use of waterborne systems is, however, increasing. 

Waterborne systems are formulated with pure acrylates and have a solvent content below 10%, preferably glycols. The gloss is between silk-matt and full gloss. 

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