Coatings nonaqueous dispersion

Acryhc and methacryhc nonaqueous dispersions (NADs) are primarily utilized by the coatings industry to avoid certain difficulties associated with aqueous dispersion (emulsion) polymers. Water as a suspension medium has numerous practical advantages, but also some inherent difficulties a high heat of evaporation, a low boiling point, and an evaporation rate that depends on the prevailing humidity. Nonaqueous dispersions alleviate these problems, but introduce others such as flammabihty, increased cost, odor, and toxicity. 

Phenolic Dispersions. These systems are predominantly resin-in-water systems in which the resin exists as discrete particles. Particle size ranges from 0.1 to 2 p.m for stable dispersions and up to 100 p.m for dispersions requiring constant agitation. Some of the earliest nonaqueous dispersions were developed for coatings appHcations. These systems consist of an oil-modified phenoHc resin complexed with a metal oxide and a weak solvent. 

Recently, hot melt PSA systems have been introduced and radiation curable PSA systems are at the commercial development stage. High solids (50%-70% by wt.) nonaqueous dispersion acrylic PSA systems have also been reported(1). Unlike the hot melt and radiation cured systems which require new capital outlay in coating head and/or curing (drying) equipment, BFG has developed PSA systems, based on Hycar 2100R reactive acrylic liquid polymers and isocyanate terminated prepolymer, which can be processed at 80% solids (by wt.) with equipment presently used in the PSA industry, namely, the reverse roll and knife-over-roll coater. 

In this process, the monomer and iniliator are soluble in the continuous phase and the polymer particles, which precipitate as they are produced, are stabilized against coagulation by dispersants that comprise di fferent segments that are respectively soluble and insoluble in the continuous phase. Dispersion polymerizations have been used successfully as an alternative to solution polymerization of vinyl polymers for application as surface coatings. In that case the diluents are usually aliphatic hydrocarbons, and the process acronym is NAD [for nonaqueous dispersion]. 

Coatings are up to 60% NV, conforming to Rule 66, EPA, and other regulations. These include NAD (nonaqueous dispersions) and coatings containing approved chlorinated solvents. 

Solvent emission from paints can be reduced without lowering the molecular mass by using nonaqueous dispersions (NAD) (see Section 3.6). Acrylates have been described as binders for NADs, but apart from a low viscosity they offer few advantages over conventional coatings [2.50] and moreover must compete with high-solids paints and powder coatings [2.56]. 

Nonaqueous dispersion polymer microgels have also found application as the main film former for certain types of exterior architectural coating where they give long term maintenance of mechanical properties leading to improved exterior durability on wooden substrates [3.94a]. 

More generally, nonaqueous dispersions have been used as components of polishes [3.95], adhesives [3.96], [3.97], fiber coatings [3.98], textile impregnating agents [3.99], printing inks [3.100], [3.101], and electrophotographic toners [3.102], [3.103]. 

More recently, classification according to the paint or lacquer system has come to be preferred. Here, a distinction is made between solvent paints or lacquers (that is, those with organic solvents), low-solvent systems, water-soluble binders, aqueous dispersions, nonaqueous dispersions, and powder coatings. 

Nonaqueous Dispersion (NAD) The solvent analog of a latex the polymer is dispersed in a volatile organic liquid which is not a solvent for the polymer. NAD s have much higher solids than conventional high molecular weight solvent coatings. Like latices, the viscosity is independent of the molecular weight as opposed to solvent soluble resins. 

Table 27.6 lists types of coatings used in industrial and special purpose coatings by technology. Chemark-based forecasts show increased usage of all types of materials in 1996 except for conventional noncompliant coatings, lacquers, and nonaqueous dispersions. Overall, consumption of solvent-based materials is expected to decline from a 74 percent level in 1986 to 63 percent in 1996. This compares to an 85 percent level in 1975. 

By coating poly-a-olefins with a fatty acid wax as a partitioning agent and dispersing it in a long-chain alcohol, a nonagglomerating, nonaqueous suspension can be obtained [918]. 

So far, we have prepared and tested many kinds of colloids, mainly in nonaqueous suspensions with combinations of metals or alloys as a dispersed phase and organic liquids as the dispersion media, without the use of any dispersing agents these are listed in Table 9.4.1. We next give some examples of transmission electron micrographs of nanoparticles produced by an aerosol method. A sample for TEM measurement was obtained by dropping colloidal suspension onto a Cu mesh coated with an evaporated carbon film of 10 nm thickness. Many colloids were so unstable... 

In a nonaqueous copolymerization, fluorinated acyl peroxides are added that are soluble in the medium.43 A chain transfer agent may be added to control the molecular weight of the resin. The polymer is separated from the medium and converted into useful forms such as melt-extruded cubes for processes working with melt (e.g., extrusion, injection molding). The resins are also available as aqueous dispersions, molding powders, and fine powders for powder coating.44 45... 

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