CMCAB for Waterborne Coatings explored by British Society.At the November meeting of the British Society, a presentation on "Carboxymethyl Cellulose Noun 1. carboxymethyl cellulose - an acid derivative of cellulose cellulose - a polysaccharide that is the chief constituent of all plant tissues and fibers Acetate Butyrate butyrate /bu·ty·rate/ (bu´ti-rat) a salt, ester, or anionic form of butyric acid. bu·ty·rate n. A salt or ester of butyric acid. butyrate a salt of butyric acid. (CMCAB) in Waterborne Coatings" was given by Paul Swan, of Eastman (UK) Ltd. Due to changes in legislation, an increasing number of companies have tried to transfer technologies from solvent-based to water-based. Cellulose acetate butyrate (CAB) has been used for many years to improve the balance between flow, leveling, and antisag. It also contributes to faster touch dry and acts as an orientating o·ri·en·tate v. o·ri·en·tat·ed, o·ri·en·tat·ing, o·ri·en·tates v.tr. To orient: "He . . . agent for aluminum flake pigments. According to Mr. Swan, problems that are commonly associated with water-based coatings, especially in metallic basecoats, include slow drying, poor wetting, and corrosion of metallic flake pigments to give hydrogen gas expulsion. To improve slow drying, PU thickeners can be added, but these can contribute to increases in elasticity and can impede flow and leveling. Mr. Swan detailed the structure of a cellulose ether developed by his company. To prepare an aqueous dispersion of CMCAB, it must be dissolved in butyl butyl /bu·tyl/ (bu´t'l) a hydrocarbon radical, C4H9. bu·tyl n. A hydrocarbon radical, C4H9. butyl a hydrocarbon radical, C4H9. glycol glycol (glī`kōl), dihydric alcohol in which the two hydroxyl groups are bonded to different carbon atoms; the general formula for a glycol is (CH2)n(OH)2. or some other ester-miscible solvent blend, then water and amine amine (əmēn`, ăm`ēn): see under amino group. amine Any of a class of nitrogen-containing organic compounds derived, either in principle or in practice, from ammonia (NH3). should be added to neutralize approximately 10-15% of the acid groups. Below 15% solids the material will behave as Newtonian in nature. Above this level, the viscosity increases dramatically. Examples comparing solution viscosity as a function of time and shrinkage levels for metallic basecoats with and without CMCAB were provided. Also the experimental CMCAB formulation was compared against two commercial basecoats. Photographs showing the spray pattern of a coating based on CMCAB along with a conventional PU thickener thick·en tr. & intr.v. thick·ened, thick·en·ing, thick·ens 1. To make or become thick or thicker: Thicken the sauce with cornstarch. The crowd thickened near the doorway. 2. was shown to highlight differences in elasticity. The spray pattern gave a smoother film immediately after spraying. Further comparisons were made showing improved wetting characteristics and improved tints strengths in coatings based on CMCAB. Examples of water-based clearcoats with and without the product were shown regarding touch dry speed, distinctness of image gloss and hardness of coatings. In conclusion, the speaker said that in specific water-based formulations, CMCAB could be used to achieve the same effects as CAB does in solvent-based with simpler formulations than with other water-based technologies. --Zara Cunliffe, British Society Publicity Officer |
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