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During the dispersion of a pigment in a given application medium, two main processes are taking place side by side. These are the wetting of the pigment surface by the binder components, and the actual dispersion process, i.e. the separation of agglomerates into primary particles or at least into smaller agglomerates by the application of mechanical energy.

Driers for Waterborne Alkyds ‐ A complete range of driers suitable for waterborne alkyd systems is now being marketed in the UK by Chemitrade.

A review of new and current products. Additive to improve levelling, slip and scratch resistance

Titanium dioxide has probably received more publicity in this last year than any other pigment used in the paint and allied industries. In a recent article, Antipov et al. in Lakokras. Mat. 1972, 4, pages 9–11, discuss a laboratory reactor that is suitable for the production of titanium dioxide by TiCl4 oxidation. The reactor has been used to investigate the temperature and residence time on the degree of dispersion and the crystalline structure of the pigment. The conditions prevailing were 700 to 1300°C, 0–20 sec. Experimental results are clearly presented using graphs.

Efficient particle size reduction or dispersions and wetting form a vital stage in an extensive range of production processes and, because it is frequently related to the quality of the final product, the consistency of performance of the machine over very long periods of continuous operation is of considerable importance.

A lamellar zinc pigment reacts in aqueous alkaline media (e.g. water‐borne paints) with the evolution of hydrogen. This corrosion reaction can be inhibited by certain surfactants. The most important structural part of the examined surfactants is the hydrophilic group; only anionic phosphate or phosphonate hydrophilic groups are effective corrosion inhibitors. Surfactants with carboxylate, sulfonate, amphoteric, cationic and non‐ionic hydrophilic groups are ineffective. There seems to be also an influence of the hydrophobic group of the surfactants because a partial ester of phosphoric acid with a fluorinated hydrophobic group was the most effective corrosion inhibitor in this study.

The term dispersion is used to refer to the process of incorporating a powder into a liquid medium so that the final product consists of fine particles distributed throughout the medium. The dispersion is termed ‘colloidal’ if at least one dimension of the particles is <1µ>1mµ. The term ‘sol’ is used for any colloidal system in which the dispersion medium is a liquid.

Our newly developed Cobra 251 V bead mill was presented to the public at the ACHEMA 79 Exhibition. Designed for the wetting and dispersion of printing inks, paints and other pasty products of average viscosities, it will supplement our line of three‐roll mills. This makes the Cobra 251 V an alternative to the present‐day annular chamber mills. Our new bead mill is characterized by its very high specific capacity, its maximum degree of automation, and its high efficiency at a given throughput rate and dispersion quality.

BYK‐Chemie GmbH are now making available for the UK paints and inks industries a range of silicone and polysiloxane additives for controlling surface defects. These include bad levelling, substrate wetting, cratering due to overspray or dust, airdraft sensitivity, Bénard cells, ghosting or telegraphing.

Water‐borne coatings Increasing use of water‐borne emulsion coatings for original equipment manufacturers (OEM) and product finishes is requiring greater efficiency in coalescing‐aid solvents, an Eastman Chemical Co. representative said at a recent Chicago Society for Coatings Technology meeting. Eastman's Ronald K. Litton said emulsions designed for OEM and industrial applications have higher glass transition temperatures than emulsions used in architectural paints. That requires higher levels of coalescing aid to achieve good film formation. As a result, coalescing‐aid efficiency with a given emulsion system is a key factor, both from environmental (lower‐volatile organic compound (VOC)) and economic standpoints. Several properties should be examined when a coalescing aid is selected for water‐borne emulsion industrial coatings. The formulator should consider the evaporation rate and solubility parameter of the coalescing aid, along with its distribution pattern in a specific emulsion system. Those properties are important in defining the efficiency of a coalescing aid in terms of its ability to lower the minimum film‐forming temperature (MFFT) of an emulsion system. The coalescing aids also must be hydrolytically stable to provide minimum loss of efficiency due to ageing, Litton said. He showed several charts designed to assist formulators in the selection of optimum coalescing aids for emulsion systems. At the same conference, James T.K. Woo of The Glidden Co. discussed the grafting of high‐molecular‐weight epoxy resins with styrene‐methacrylic acid monomers, producing a water‐reducible copolymer. Grafting takes place at the aliphatic carbons of the epoxy resin, according to carbon‐13 NMR spectroscopy. The study was a follow‐up to a paper presented 14 years ago. Woo said recent research indicates that five grafting “peaks” were identified on a 400 megacycle carbon‐13 nuclear magnetic resonance spectroscopy instrument. The paper provided several theoretical calculation on grafting. Three of the graft peaks resulted from grafting at the secondary methylene carbons ‐CH2‐ and two resulted from grafting at the tertiary carbon ‐CH‐. The ratio of grafting at ‐CH2‐ to ‐CH‐appears to be 2.7:1 — lower than the 4:1 ratio of protons present on the aliphatic carbons that are susceptible to hydrogen abstraction leading to grafting. That indicates that the tertiary hydrogen is somwhat more susceptible to grafting than the methylene hydrogens, he said.