Coatings, water-soluble binder

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. 

Soft distemper n. Usually based on whiting, lightly bound with glue, size or other water-soluble binder so that the coating will withstand dry rubbing without disturbance but can easily be removed by water washing. 

In addition to liquid anaerobics, threadlockers are supplied in a solid form that can be pre-applied to a fastener. In these systems, the anaerobic adhesives or a catalyst are microencapsulated in a thin shell. A typical water-based slurry for applying such a system to fasteners consists of a water-soluble binder or emulsion, a dispersed anaerobic adhesive, and separate microcapsules of a peroxide and a transition metal salt. The slurry is applied to fasteners by the customer or a converter and is dry to touch after removal of the water. This preapplied coating remains stable until a nut is applied to the fastener when the shearing action of engagement breaks the microcapsules and the adhesive cures, locking the fastener. 

A more workable photopolymer system was based on the chemistry of diazonium salts. The diazo salt or diazo resin can be coated from water along with a water soluble binder, such as poly (vinyl alcohol). Upon exposure the salt is photolyzed, probably forming a phenol or haloaro-matic. The neutral organic photoproducts dissolve much more slowly than do the ionic starting materials. 

Water-borne adhesives are preferred because of restrictions on the use of solvents. Low viscosity prepolymers are emulsified in water, followed by chain extension with water-soluble glycols or diamines. As cross-linker PMDI can be used, which has a shelf life of 5 to 6 h in water. Water-borne polyurethane coatings are used for vacuum forming of PVC sheeting to ABS shells in automotive interior door panels, for the lamination of ABS/PVC film to treated polypropylene foam for use in automotive instmment panels, as metal primers for steering wheels, in flexible packaging lamination, as shoe sole adhesive, and as tie coats for polyurethane-coated fabrics. PMDI is also used as a binder for reconstituted wood products and as a foundry core binder. 

Other apphcations for VP/VA copolymers are uses as water-soluble or remoistenable hot melt adhesives (140), pharmaceutical tablet coatings, binders, and controUed-release substrates. 

Barium metaborate [13701-59-2], BaO B203 H20, [5.78] and zinc borophos-phate [84012-98-6], ZnO x B2Oa-y P205-2H20, are colorless pigments. Their properties are listed in Table 44 their uses in various binders are listed in Table 39. They both have a relatively high water solubility. Barium metaborate is coated with silica to reduce this. 

The main applications for PVA are in textile sizing, adhesives, polymerization stabilizers, paper coating, poly(vinyl butyial), and PVA fibers. In terms of percentage, and omitting the production of PVA not isolated prior to conversion into poly(vinyl butyral), the principal applications are textile sizes, at 30% adhesives, including use as a protective colloid, at 25% fibers, at 15% paper sizes, at 15%, poly(vinyl butyral), at 10% and others, at 5%, which include water-soluble films, nonwoven fabric binders, thickeners, slow-release binders for fertilizer, photoprinting plates, sponges for cosmetic, and health care applications. 

Desirable fixative properties superior to PVP homopolymer can be specified by judicious selection of the amount of vinyl acetate. Hair sprays are limited in the molecular weight of the resin because if they are too hLgh the resulting viscosity of the formulation will result in a poor (coarse) spray pattern. Increasing the VP/VA ratio causes properties to increase in the direction shown by the arrows. Other applications for VP/VA copolymers are uses as water-soluble or remoistenable hot melt adhesives, pharmaceutical tablet coatings, binders, and controlled-release substrates. 

Hydroxy propyl methyl cellulose (HPMC).35 HPMC is a partly O-methylated and 0-(2-hydroxypropylated) cellulose available in several grades that vary in viscosity and extent of substitution. It is used widely in pharmaceutical formulations, especially in oral products, as a tablet binder, in film coating, and as controlled release matrix. Soluble in cold water, it forms a viscous colloidal solution. For a 2% aqueous solution (20°C), viscosity can range from 2.4 to 120,000 mPa-s. High-viscosity grades can be used to retard the release of water-soluble drugs from a matrix. 

---