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Previous articles in this series have considered recent developments in the colouring and opacifying pigments which are added to all paints, and also in the protective pigments used in anticorrosive coatings for metals. Many paints also contain another component in their total pigmentation these being the extenders.

The object of this study was to compare the new grades Hydrocarb 90 and Omyalite 90 with the other grades of extenders used at present in a polyvinyl acetate paint for exterior use.

Whilst accepting the economic necessity for adding extenders to zinc rich paints, there are several problems which need careful consideration.

Lawrence Industries have announced their new distributorship for Fortrex micaceous extender for use in paint systems. This high brightness, plate‐like and fine particle size extender can be used in the production of a wide variety of paint systems giving improved mechanical strength, chemical resistance, better substrate adhesion, wash resistance, light fastness and resistance to chalking.

Lawrence Industries, Mitcham Industrial Estate, Streatham Road, Mitcham, Surrey CR4 2AP, market the Engelhard ASP range of aluminium silicates and the Reichard Coulston iron oxides — both from the USA. The latter have recently added 1475SS iron oxide to their range, which is recommended for top quality primers. It is a naturally occurring high iron content ore which has been thermally treated to improve its chemical properties and lower the water soluble salts content.

Titanate coupling agents have been described for the past decade. What they will do and how they are used has been summarised in an article by Monte, Sugerman, and Seeman [Modern Paint & Coatings, 67, July (1977) p. 27]. Thus the authors point out that the titanate coupling agents, which are basically organotitanium compounds whose structures are shown in the article, can make possible the formulation of metal oxides, pigments, and extenders into organic systems to produce coatings with improved physical properties, higher solids, and advantages from the points of view of manufacturing and application. In other words the organotitanium compound will couple a pigment or related material with the vehicle by forming chemical bonds. Thus, the authors propose that metal chromates may be replaced in corrosion‐resistant coatings with silica extenders if these silica extenders are coupled to the vehicle with an organopyrophosphatotitanate.

Titanium dioxide was introduced as a paint pigment during the late 1920's and thirties, and these early grades were anatase. Rutile grades appeared in the forties and early fifties, but without surface treatments.

Naintsch SE is an Austrian produced mineral extender with a high lamellar magnesium silicate content. Its industrial use is primarily based on its extreme whiteness and remarkable hiding power. These functional properties make Naintsch SE a unique extender for white coatings especially emulsions and roadmarking paints.

The effect of pigment filler and extender on the antifouling efficiency of six compositions containing organotin polymer is studied. The binder mixture is a blend containing a copolymer of tri‐n‐butyltin methacrylate and methylmeth acrylate (OTP) with 22% tin content, a vinyl copolymer with its external plasticizer and little amount of rosin. Cuprous oxide was added as a supplementary toxin with the OTP. Leaching rates of microamounts of copper and tin were determined for a period of nearly one year applying standard techniques. Painted plates were immersed in Suez Canal waters at Port‐Said for more than 36 months. Comparison between different fillers and extenders on the antifouling behaviour of painted surfaces is shown. Compositions containing cellite and china clay exhibited the maximum antifouling performance.