Overcoating fastness

Tests to determine the bleed fastness of a paint system - also called overpainting or overcoating fastness - are not subject to industrial standards. A commonly used technique involves overpainting a white paint film of defined thickness to a... 

P.Y.12 is a typical diarylide yellow pigment in that its prints are fast to clear lacquer overcoating, which is used to protect tin prints against scratching and scrubbing. They are also fast to sterilization (Sec. 1.6.2.3), which is one of the major requirements of an ink to be printed on food cans. 

The paint industry shows little interest in P.Y.12, since it is not sufficiently fast to overcoating for use in baking enamels. In air drying paints, lightfastness of P.Y.12 in white reduction (with 1 5 TiOz) only equals step 2 on the Blue Scale. 

P.Y.13 and its chemically modified derivatives, due to their higher solvent fastness compared to P.Y.12, are used in much greater volume in packaging gravure inks. P.Y.13 is also fast to protective clear lacquer overcoatings and may be sterilized and calandered. 

In the paint field P.Y.16 is primarily used in industrial finishes. The similarity to P.Y.l is limited to a likeness in shade but P.Y.16 is fast to overcoating and shows no tendency to bleed in baking enamels. Although its full shade lightfastness equals step 7-8 on the Blue Scale, types that are only slightly reduced with TiOz (1 5) reach only step 5. Only full shades provide good weatherfastness. 

P.R.146 is a suitable candidate for a variety of special applications. The list includes wood stains, in which it is frequently blended with yellow pigments, especially with P.Y.83, and also with black to afford shades of brown. The products are fast to overcoating and stable to nitro and acid catalyzed and polyester varnishes. Intense shades match step 5 on the Blue Scale for lightfastness. Other areas of application include office articles and artists colors, cleaning agents, paper mass coloration, laundry markers, etc. In connection with cosmetics, the pigment frequently lends color to soaps. 

P.R.164 is heat stable up to 200°C, which made it a suitable candidate for applications where good temperature resistance is required. At baking temperatures of 140 to 160°C and higher, the fastness to overcoating begins to decrease. 

P.R.170 is broad in scope. It is found in wood stains, including solvent-based stains it is blended with carbon black and yellows to produce a variety of interesting shades of brown. The colorations are fast to overcoating in these media and resist nitro and acid hardening varnishes and polyester coatings. Its lightfastness in these media equals step 7 on the Blue Scale. 

P.O.38 is broad in scope. The list of applications includes special media, such as wax crayons, artists colors, and wood stains, including those that are solvent based. The products are very lightfast (step 7 on the Blue Scale) and fast to overcoating. Blends of P.O.38 with yellow pigments, such as P.Y.83 or P.Y.120, or with carbon black produce useful shades of brown. 

P.R.48 2 is less commonly found in paints. In paints, like in other areas of application, the calcium salt performs like the barium lake. Both are, for instance, equally fast to overcoating. The list of suitable application areas for both pigments is the same. P.R.48 2 is also used in oven drying paints, nitro paints, and in similar systems. Besides, it is also found in emulsion paints. While barium and calcium salts exhibit equal lightfastness in full shades, there is a considerable difference in white reductions. Increasing amounts of Ti02 render P.R.48 2 much more sensitive to light than P.R.48 . 

P.R.66, a barium salt, is sold only in the USA. The pigment is also available as an aluminum oxide hydrate precipitate. Its shade is considered a brilliant medium red, which is somewhat yellower than that of the chemically related P.R.67. Commercial types of P.R.66 are very transparent. The pigment is highly sensitive to acid, alkali, and soap. Its fastness to organic solvents is poor, its fastness to overcoating as well. P.R.66 exhibits limited lightfastness. Its main application is in metal deco printing. 

Naphthol AS pigment series. Excellent fastness to solvents and chemicals is accompanied by good migration fastness. Benzimidazolone pigments do not bloom, and most of them show good and some even excellent bleed fastness and fastness to overcoating. All benzimidazolone pigments, with one exception (P.Y.151), are inert to alkali and acid. Most of them disperse easily in the common application media. 

P.Y.120 has less of an impact on the paint industry. In contrast to the similarly colored P.Y.97, P.Y.120 is fast to overcoating. Moreover, it exhibits noticeably higher durability. White reductions, reduced 1 1 to about 1 5, are approximately as durable as P.Y.151 systems. P.Y.120 is recommended for general industrial finishes, including automotive refinishes, and it is also suitable for use in architectural paints. P.Y.120 is completely fast to alkali. 

Coatings containing P.Y.151 are very lightfast and durable. Systems based on acrylic melamine resin, for instance, were exposed to the Florida climate for one year and then evaluated. 1 1 reductions with TiOz equalled step 5 on the Gray Scale for weatherfastness, while 1 3 Ti02 reductions matched step 4, and 1 35 reduced samples coincided with step 3-4. Comparative values for P.Y.154 and 175 are listed for the respective pigments. P.Y.151 is fast to overcoating up to 160°C. 

P.O.36 is completely fast to overcoating. Bleeding into a white overcoat is only observed at baking temperatures above 160°C. P.O.36 is heat stable up to 160°C. In dispersing the opaque type, it is important to avoid excessive shearing forces and to closely monitor the temperature, especially if agitated ball mills are used. Faulty temperature control may lead to a dull color. 

P.O.60 is heat stable up to 160°C. Baking temperatures in excess of this value will in some paint systems cause a decrease in fastness to overcoating. 

Moreover, P.Br.25 is used in a variety of specialty media, for instance in oil colors for artists and in water colors. It lends itself to solvent-based wood stains. The products are very lightfast (step 7) and fast to overcoating. 

The paint industry is interested in individual representatives of this class, such as P.Y.128. These are used to color high grade paints, such as automobile (O.E.M) finishes and automotive refinishes. Other types are used in general industrial paints. As a rule, the fastness of disazo condensation pigments to overcoating is good to excellent in some media. The pigments are also used in architectural paints, sometimes also in emulsion paints. 

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