Color retention

The polymer can be vulcanized to give a rubber with very good chemical (solvent) resistance, excellent resistance to aging and weathering, and good color retention in sunlight. 

M C roni nddoodles. Lecithin (0.25—5%) is used as a conditioning ageat and antioxidant, improves machining, counteracts disiategration and syneresis, and improves color retention. 

Toluhydroquinone and methyl / fX butyUiydroquinone provide improved resin color retention 2,5-di-/-butyIhydroquinone also moderates the cure rate of the resin. Quaternary ammonium compounds, such as benzyl trimethyl ammonium hydroxide, are effective stabilizers in combination with hydroquinones and also produce beneficial improvements in color when promoted with cobalt octoate. Copper naphthenate is an active stabilizer at levels of 10 ppm at higher levels (150 ppm) it infiuences the cure rate. Tertiary butylcatechol (TBC) is a popular stabilizer used by fabricators to adjust room temperature gelation characteristics. 

Maleic acid and fumaric acid can also be, and are often, incorporated in alkyd resins in the form of the Diels-Alder adduct of rosin. The adducts are tribasic acids which provide pendent carboxyl groups in the resin molecules, which can be saponified to give ionic, and, in turn, water-soluble characteristics to the resin. However, the resultant alkyds often have poorer color retention, toughness, gloss retention, and exterior durabiUty. 

Aniline is slightly corrosive to some metals. It attacks copper, brass, and other copper alloys, and use of these metals should be avoided in equipment that is used to handle aniline. For appHcations in which color retention is critical, the use of 400-series stainless steels is recommended. 

Golorfastness. A variety of test methods exist for determining the fastness, or color retention, properties of dyed fabric exposed to various conditions of weathering, laundering, or general exposure associated with the end use of the product. The AATCC Technical Manual should be consulted... 

Primers for Metal. If reasonably high performance is required ia the end product and unless cost is of paramount importance, a minimum of two coats, usually a primer and a top coat, should be appHed to metal. For highest performance, primer vehicles should provide good wet adhesion, be saponification resistant, and have low viscosity to permit penetration of the vehicle iato microsurface irregularities ia the substrate. Color, color retention, exterior durabiHty, and other such properties are generally not important ia primers. Resia systems such as those including bisphenol A epoxy resias which provide superior wet adhesion can thus be used ia spite of their poor exterior durabiHty. 

The paint is sensitive to moisture during storage and application but then becomes exceptionally water-resistant. Its best use is for exterior exposure in an aggressive environment but where the maximum gloss and color retention is required. It is preferable to apply the urethane as a finishing coat over epoxy undercoating and priming. 

Metal exposure is a critical factor in color retention of most azo dye formulations. However, improved coating techniques have made it possible to attain the desired shelf life of products colored with azo dyes. 

Paraffinic oils are the least efficient as processing additives but the resulting vulcanizates have good aging and color retention properties and give the best low temperature performance. 

Surface Modifications. Basic photopolymer chemistry is also being used for the surface modification of films, textiles fibers, and many other organic-based materials (104). Some of the novel applications of photopolymer technology to surface modification include the design of cell repellent treatments and in photografting of various chemical functionality onto the surface of materials to improve color retention, enhance the adhesion of antistatic chemicals or to improve staining resistance. 

The structural chemistry of alkyds has already been covered in Chapter 15, Section 7. Although there are over 400-500 varieties of such resins, they are all polyesters with carbon-carbon double bonds that can be cross-linked. They are very versatile in coatings, and their diverse properties can be matched for particular uses. They are the most widely used resins for protective coatings. Their best points can be summarized as follows (1) easy to apply (2) can have flat, semigloss, or high-gloss finish (3) useful for most surfaces except concrete or plaster (alkaline) (4) good color retention and (5) odorless (some of them). 

Poly(vinyl acetate) dispersions are more sensitive to hydrolysis but have good color retention and resistance to grease and oil. 

Because of the intended outdoor applications of ASA materials, improved weatherability and color retention performance are of importance. These properties can be enhanced by additives. 

Traditional ASA compositions and such with improved weatherability are shown in Table 12.6. The nylon 6,6 compounds are added as the color retention agent in place of the poly(ester)s of the conventional composition (30). 

G.J. Kogowski, H. Goerrissen, and G.E. McKee, Method of improving the weatherbility and color retention performance of styrene copolymer compositions, US Patent 6482 893, assigned to BASF Corporation (Mt. Olive, NJ), November 19,2002. 

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