Coatings, binders

The other main natural binder is protein that is prepared by extraction from soy meal (100). Casein [9000-71 -0] once a large-volume paper-coating binder, has markedly declined in use because of its high price and susceptibiHty to microbial attack. 

J. W. Ramp, Tappi Notes, 1990 Coating Binders Short Course, Tappi Piess, Adanta, Ga., 1990. 

Other apphcations for VP/VA copolymers are uses as water-soluble or remoistenable hot melt adhesives (140), pharmaceutical tablet coatings, binders, and controUed-release substrates. 

Hydroxyethylstarch is widely used with synthetic latexes in the surface sizing of paper and as a coating binder. For these uses, the hydroxyethylstarch is acid-thinned, oxidized, or dextrinized. Hydroxypropylstarch is used in foods to provide viscosity stabiHty and to ensure water-holding during low temperature storage. 

Liquid Crystalline Oligoester Diols as Thermoset Coatings Binders... 

The mesophases formed by liquid crystalline (LC) polymers are well known to impart strength, toughness, and thermal stability to plastics and fibers (1-5). While LC polymers have been widely studied, their potential utility as coatings binders seems to have been overlooked. Among the very few reports that may describe LC polymers in coatings are patents claiming that -hydroxybenzoic acid (PHBA), a monomer commonly used in LC polymers, enhances the properties of polyester powder coatings (6-9). 

In the field of coatings, however, crystal formation in the film is usually avoided few reports ( ) of LC polymers in coatings binders are known to the authors. 

The preceding chapter (7 ) described synthesis of model LC oligomeric diols and their incorporation into coatings binders of the baking enamel type. The enamels had far better hardness and impact resistance than control enamels made from amorphous or crystalline oligomeric diols. The model LC oligomers were synthesized by a Schotten-Bauman method that would be costly for large-scale production. 

Desirable fixative properties superior to PVP homopolymer can be specified by judicious selection of the amount of vinyl acetate. Hair sprays are limited in the molecular weight of the resin because if they are too hLgh the resulting viscosity of the formulation will result in a poor (coarse) spray pattern. Increasing the VP/VA ratio causes properties to increase in the direction shown by the arrows. Other applications for VP/VA copolymers are uses as water-soluble or remoistenable hot melt adhesives, pharmaceutical tablet coatings, binders, and controlled-release substrates. 

While it is possible to use TMOS in the sol-gel process or in coating binders, the by-product of the hydrolysis is methanol. The toxicity of methanol makes TMOS unsuitable, so it must be converted into TEOS before it can be used. The conversion is carried out by reacting TMOS with ethanol. The reaction is catalyzed by both acids and bases. Since acid catalysis is used in the industrial preparation, this is the reaction that we have concentrated on. 

The performance and quality of starch can be improved through chemical modification (see Chapter 17). Chemical modifications provide processed foods, such as frozen, instant, dehydrated, encapsulated and heat-and-serve products, the appropriate texture, quality and shelf life (see Chapter 21), and improved processing condition tolerance, such as improved heat, shear and acid stability. Modification also allows starches to be used in the paper industry (see Chapter 19) as wet-end additives, sizing agents, coating binders, and adhesives and as textile sizes. 

Dextrins are produced by dry heating (roasting) starch in the presence of an acid catalyst. They are produced in a range of viscosity and color specifications. Dextrins are primarily used as adhesives in paper conversion, such as laminating and envelope production. A low-viscosity dextrin is used in Europe as a total chlorine free (TCF) coating binder for application on TCF paper. 

A previous trend in the paper industry of limiting starch purchases to unmodified grades and effecting modification on-site in the paper mill has changed. The variance in products thus obtained was frequently wider than in products supplied by the starch manufacturer. As a result, there is now more preference to utilize modified starches with specific application properties. Growth in paper recycling should lead to an increased use of starch as a coating binder in place of synthetic materials. 

The converter will operate most efficiently when it supplies coating binder at the same rate as it is consumed. Problems may occur when the converter has to be shut off and flushed with water. Channel flow and vortices during the purge with water affect cleaning time and may make it necessary to sewer starch product. In another converter, a single pump is used to transport the starch through the retention vessel. Jet cookers of the venturi type are placed at the entrance to the vessel and at its exit.114 In an alternative design, a retention coil is used instead of a retention vessel.115... 

Starch can be enzymically converted in the presence of pigment. The conversion follows a similar time-temperature cycle as in neat starch conversion. The pigment will adsorb a portion of the enzyme adsorption can be minimized by the addition of sodium silicate to the mixture prior to the addition of the enzyme (Vanderbilt process). Even with silicate treatment, a higher quantity of enzyme will be required to reach a specific viscosity target. Other coating components, such as latex and lubricants, have to be added after the conversion. The Vanderbilt process is now rarely used for the preparation of coating binder. 

---