Thickeners in coatings

Anionic starches are obtained by reaction with phosphoric acid and alkali metal phosphates or by derivatization with carboxymethyl groups.30,31 This modification is primarily used to introduce amphoteric properties into cationic com starch for application on the wet end of the paper machine. Anionic starches with carboxymethyl substitution are used as thickeners in coating colors or as binders in coatings for specialty paper grades. Oxidized starches are inherently anionic but without thickening action. Potato starch already carries sufficient natural anionic charge to provide amphoteric properties after cationization.32... 

Special starch products have been developed for use as thickeners in coatings that are based on synthetic latex or resin binders. Starch-based thickeners can have associative properties when substituted with a hydrophobic reagent. They provide an alternative for cellulose-based thickeners, but their use is limited. 

In addition, this product has also been disclosed to USDA as a thickener in coatings and adhesives in contact with fresh foods ... 

MAJOR APPLICATIONS Lacquers for wood, plastic, and paper, varnishes, hot melts, adhesives, thickener in coatings and inks, tablet coatings and binding, encapsulation. 

Zinc steareate n Zn(OOCCi7H35)2. A white powder used as a lubricant and stabilizer in vinyl compounds. An insoluble zinc soap used to produce matteness, flatting or thickening in coatings. 

Finally, by way of illustration, we mention a polymer type currently receiving much attention. The polymer is referred to as hydrophobically modified ethoxylated urethane (HEUR), the reaction product of a PEG and a diisocyanate, end-capped with a long chain alcohol or amine. HEURs are already recognized as having much potential as associative thickeners in coating formulations. Their structure suggests they will show pronounced interaction with surfactants in solution and this is indeed the case. Here we refer to two recent studies. The first by Hulden (95) included surface tension studies of the polymer... 

Schwab EG. Advantages and disadvantages of associative thickeners in coatings performance. In Glass JE, ed. Water-Soluble Polymers Beauty with Performance. Adv Chem Ser 213. Washington, DC American Chemical Society, 1986 369-373. 

CS derivatives/salts have found limited use as detergents (25), antistatic coatings for photographic film (26), oil drilling fluids (25), thickeners in food, cosmetics, and pharmaceuticals (27). They have been recommended for use as cation exchangers (28,29). Also, sulfated polysaccharides have recendy shown interesting antiviral activity (30). 

Cellulose is also commercially modified by acetylation to produce a material suitable for X-ray and cine film. Commercially cellulose ethers are also prepared, such as methylcellulose. This material is water-soluble and gives a highly viscous solution at very low concentrations. Hence it is widely used as a thickener in latex paints and adhesives, in cosmetics and for coating pharmaceutical tablets. 

The specific nature of the interactions among hydrophobes would suggest that the associative thickeners will vary in performance with the different latices and components used in coatings formulations. This has been observed(29) in... 

POLYMERS, WATER-SOLUBLE. Any substance of high molecular weight which swells or dissolves in water at normal temperature. These fall into several groups, including natural, semisynthetic, and synthetic products. Their common property of water solubility makes them valuable for a wide variety of applications as thickeners, adhesives, coatings, fooe additives, textile sizing, etc. 

Use (1) Thickeners in paints, fabric coatings and backings, adhesives. (2) Warp size for synthetic fibers, cotton and rayon, modifier of starch sizes. 

Use Protective colloid, dispersing agent, thickener, binder, adhesive and size in coatings, detergents, emulsions, paper, textiles, leather, latex, rust preventive, foam stabilizer. 

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