Waterborne coatings binders

The types of surface moieties stabilizing the latex also are important. The binders used in waterborne coatings are not the hard-sphere, model polymer colloids used in adsorption studies. They are soft (low glass transition temperature), deformable moieties that are stabilized by grafted polymer fragments [e.g., (hydroxyethyl)cellulose (16) or poly(vinyl alcohol)] or by terpolymerized acid monomers extended from the surface of the colloid (IT). Such stabilizers produce a far less hydrophobic surface than is generally depicted in colloid texts. This situation is particularly true if the composition of the latex is predominately methacrylate or vinyl acetate, as they are in most U.S. commercial products. 

Progress in Organic Coatings 35, No.1-4, Aug.1999, p.235-46 OIL-ACRYLIC HYBRID LATEXES AS BINDERS FOR WATERBORNE COATINGS... 

The carrier is the vehicle in the uncured paint that carries the binder, the pigments, and the additives. It exists only in the uncured state. Carriers are liquids in the case of solvent-borne and waterborne coatings, and gases in the case of powder coatings. 

To work in a coating formulation, whether solvent-borne or waterborne, a pigment must be well dispersed, coated by a binder during cure, and in the proper ratio to the binder. The last point is the same for solvent-borne and waterborne formulations however, the first two require consideration in waterborne coatings. 

For environmental reasons, waterborne coatings are being used increasingly. The binder may be either dispersed or dissolved in the water phase. Dispersion coatings show lower gloss and less good adherence than the dissolved types such as alkyds, ureum and melamine, phenol, and acrylic-type coatings. 

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. 

Paints are often classified by the type of binder they include. The most common classifications (with percent of total coatings used m 1985) are Latexes (31%) waterborne (10%) noil-aqueous dispersions (2%) solvent-borne (55%) and one hundred percent sohds coatings (2%) A small volume of paint is made with silane binders. 

The increasing importance of environmental considerations places new requirements on paint resins and has broadened the range of paint systems. Paints are now required that have a low solvent content (medium-solids, high-solids coatings) or are solvent-free (powder coatings), that can be adjusted by dilution with water (waterborne paints), and that are thermoplastic or capable of undergoing cross-linking. All of these properties must be obtained via the polymer structure of the binders. Important parameters are described below. 

As a result of the particulate nature of the binders only a low gloss and, in some cases, only limited corrosion protection can be obtained. Waterborne paints based on dispersions can be applied by spraying, however they are of only limited use for electrostatic coating and dipping applications due to their rapid drying properties. 

For many years, paints used to coat cans contained considerable amounts of volatile organic solvents. Waterborne can coatings were developed to reduce solvent emissions and are used worldwide. Binders used in waterborne can coatings are modified epoxy resins (see Section 2.10). Acidic acrylate chains are grafted onto an epoxy molecule. After partially neutralizing with amines, the resins can be dispersed in water. 

Uses Crosslinking agent, hand builder adding durability and resilience to fabrics (cellulosics, synthetics) adds durability to fluorochem. and water repellent finishes crosslinking agent for hydroxyl-contg. emulsion polymers for top coat systems, waterborne wood finishes, nonwoven binders... 

Uses Binder insolubilizer tor paper and board coatings, nonwoven tab-rics deposit controi agent in wet-end paper processes str. additive tor alkaiine-sized paper component of waterborne inks, overprint varnishes, adhesives textiie, ieather, and paper water-repeiient formuiations antimicrobial treatment for textiles and timber coaguiant in mfg. of syn. leather cloth metal pretreatment coatings precursor to zirconia in cata-lyst systsms... 

Uses Abrasion resist, aid, toughener, flexibilizer, hardener, gloss aid in water-based coatings (automotive OEM, refinish, primers, basecoats, topcoats), adhesives for wood/plastic/metal substrates, inks binder in waterborne inks, bonding and laminating applies. 

Chem. Descrip. Waterborne polyurethane emulsion Uses Softener, hand modifier providing high flexibility in pad dyeing of nylon, polyester, rayon, cotton, and blends provides shrinkage control to wool, rayon, silks, dty-clean-only fabric flexible binder for pigment printing, plastics, paper, leather. Aims dear coat for leather, metals, and wood modifier tor other polymers... 

Chem. Descrip. Waterborne aliphatic urethane polymer emulsion Uses Urethane for metal primers, topcoats, floor coatings, etc. binder for pigmented and clear coat systems for wood, metal, concrete, other substrates... 

Chem. Descrip. Aliphatic waterborne PU Uses Thixotropic coating for syn. fabrics binder for thread and braid Features Firm contains heat reactive crosslinker Properties Dens. 8.7 Ib/gal vise. 50,000-70,000 cps (72 F) pH 9.5-10 100% tens. mod. 1200 psi tens. str. 3500 psi elong. 325% 37 2% solids... 

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