Protective Coatings HARRY BURRELL Interchemical Corp., Cincinnati, O h i o
I T SEEMS likely that a breakthrough has been made in the long search for satisfactory water-based industrial coatings. During 1958 two manufacturers introduced aqueous resin solutions which adequately wet steel and bake to hard, tough, marresistant films which rival melaminealkyd systems in color and gloss retention and resistance to water, salt spray, detergents, and solvents. These are true polymer solutions having typical viscosity and flow characteristics ; being solutions, they present no freczc-thaw problem. Unlike latexes or emulsions, their rheology is such that they present no unusual difficulties in roller coating or spray application and their water resistance and adhesion are outstanding. It is claimed that formulation is simpler than with latex bases because thickeners, stabilizers, bactericides, and wetting agents are not needed ; pigmentation must be carefully done, however, and normal precautions against rusting of iron containers must be observed. Great pressure has been put on paint manufacturers and their raw material suppliers in recent years to produce adequate water-thinned coatings to alleviate fire hazards and odor problems. Just how far these developments will go toward solving the many problems which arise remains to be seen, but a start has been made. Other companies have produced water-thinned alkyd emulsions for interior walls and architectural paints and also an emulsion of styrenated alkyd, as competition to latexes, but their usage appears to be small compared with the growing acrylic latex production and is, of course, dwarfed by the now gigantic butadiene-styrene and poly(vinyl acetate) tonnage. It was revealed that small amounts of solvent keep exterior poly(vinyl acetate) latex paints from peeling and blistering. New latex offerings included a uniform particle size ma-
terial with low foaming characteristics and others that give high gloss coatings. A product aimed at poly(vinyl acetate) economy with acrylic quality was a copolymer latex made from monomers of both types. Another interesting product is a spray-dried poly(vinyl acetate) emulsion which can be shipped without water and easily redispersed when needed. An inexpensive hydrocarbon resin emulsion was proposed as an extender in latex paints, and an emulsion of coal tar pitch is available as an anticorrosive coating. At least two suppliers offered emulsions of epoxy resins. N o n a q u e o u s Vehicles
Among the interesting new vehicles is a copolymer of styrene and allyl alcohol. This water-white resinous alcohol can be esterified with fatty acids or reacted with phenolics, amines, or isocyanates; it has unusual solubility for a styrene resin and is compatible with nitrocellulose. An acrylic copolymer especially designed to combine hardness with flexibility and exterior exposure resistance points up the increasing interest in acrylic automotive lacquers. Poly (vinyl stéarate) in bead form is an unusual
Spraying a water-based elimination of flammability
waxlike resin. Another copolymer resin of the styrenated alkyd type has the usual rapid drying speed and can be sanded about 2 hours after application. There are now seven suppliers of epoxy resins. The inevitable competition resulted in a substantial price reduction during the year, which will broaden the field of applications. New types of epoxies based on aliphatic polyols have low viscosity and better color retention than the bisphenol type. It is claimed that they accelerate the cure of the latter type and impart flexibility. Development of polyurethane coatings continued, but the principal outlet for diisocyanates continues to be in foams. Isocyanate-modified oils were manufactured, claiming the advantage of prereaction, thereby
coating directly into a hazard
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JANUARY 1959
53 A
I/EC ANNUAL REVIEW avoiding the handling of isocyanate at the point of application of the coating. A new low viscosity polyamide was introduced as a curing agent for epoxies and for chlorosulfonated polyethylene. A low-cost phenolic resin resistant to both acids and alkalies was suggested as especially useful in can coatings. A silicone intermediate is available in flake form for reaction with alkyds, phenolics, epoxies, and other resins to impart properties usually associated with silicones. O t h e r r a w materials include a butyl rubber-microcrystalline wax blend and water-soluble polyethylene oxide. Among the new chemical products of interest were beiizoguanamine, anhydroenneaheptitol, and sucrose acetate isobutyrate. 2,2'-Dihydroxy-4-methoxybenzophenone was suggested as a highly compatible ultraviolet light absorber. An interesting modification of di-^rt-butyl peroxide has this free radical generator adsorbed on a Molecular Sieve which releases the catalytic activity at 210° F. but remains stable at lower temperatures. Standard metal driers are now available in emulsion form for use in alkyd and similar emulsion systems. A complex q u a ternary a m m o n i u m compound can be incorporated in surface coatings to impart antistatic dust-repelling p r o p erties. New Pigments A line of quinacridone-based pigments was introduced, in which the shades vary from a brilliant red to an intense violet. These are wholly organic in nature and resem-
1958
ble the phthalocyanine family in lightfastness, heat and chemical stability, and resistance to bleeding. Tinting strength is high and properties are maintained in light tints. Another red is a b a r i u m lake with improved water, alkali, and bleed resistance. A red shade of phthalocyanine blue is also available. A plant was built for the decomposition of titanium tetrachloride to make a grade of titanium dioxide having improved wetting and dispersing characteristics, especially in water systems. Another grade contains iron, and although it has a tan color, it has better hiding than rutile. Lead chromate-coated silica was made for inexpensive rust-inhibitor paints. Barium metaborate was proposed as a zinc oxide replacement to retard mildew growth and chalking of paints containing titanium dioxide. Industrial Coatings Water-thinnable primers and top coats are now being m a d e which develop satisfactory water and corrosion resistance when baked. These carry more or less standard pigmentation. A rather unusual product is a water-soluble clear primer for polished or electrochemically treated metal surfaces; this coating helps tie down top coats but also protects metal objects against corrosion and fingerprints during handling without changing appearance of the metallic surface. An aqueous product is also available to spray on outdoor storage piles of loose or powdered materials to protect them from loss by wind or rain erosion and to reduce dust nuisance.
Wet film thickness gage has a range from 0.5 to 20 mils 56 A
INDUSTRIAL AND ENGINEERING CHEMISTRY
Interest has continued to grow in the thermosetting acrylic resintype finish. Unusual combinations of hardness, toughness, flexibility, and resistances are possible with these systems. Another innovation has been the resurfacing of concrete roads with epoxy or rubber latex formulations to reduce skidding a n d provide renewable wearing surfaces. O t h e r specialty coatings include polyethylene varnishes which improve gloss and reduce permeability, a skin coat for foamed polystyrene, temperature - indicating paints for warning of internal hot spots in processing equipment, aerosol packaged rust release compound or stencil ink, and an alkaliresistant primer for exterior cement or asbestos siding. Equipment Great interest was shown in 1958 in machines for mixing preselected colors, suitable for use in trade sales paint stores. Accurate color matches can be m a d e by setting machine dials to deliver predetermined amounts of tinting colors to stock base paints. H u m a n error is minimized and inventory is simplified. Several companies are making such machines at prices supposed to be within reach of hardware store paint departments. A novel spray gun has a button control, easily manipulated by the t h u m b , which changes the spray pattern from fan to cone shape. This allows controlled spraying of complicated objects having varied contours. Among the new items of laboratory equipment is a hollow square film applicator which can apply eight different film thicknesses, from 0.001 to 0.008 inch. A very simple and inexpensive wet film thickness gage has a range from 0.5 to 20 mils, while a magnetic dry film gage has a probe which allows measurements inside pipes or narrow cavities. From a business standpoint, the 1958 recession caused a drop in industrial sales during the first half of the year, with some gains during the second half. Trade sales, however, held steady, which is typical of the economic cycle because unemployed workers regularly do some long neglected painting. T h e paint industry sales as a whole are expected to be off about 5 % from 1957.
