Fastness to solvents

There is no precise definition for the frequently used term application fastness of a pigment. It usually refers to the behavior exhibited by a finished product used in accordance with the specifications. The term may thus refer to a print, a coated object, or a plastic product, and the list of features ranges from properties such as lightfastness and weatherfastness to migration fastness and fastness to solvents. In this context, there is a certain amount of emphasis on features which play a role in connection with packaging materials and packed articles. 

Publication gravure printing inks are commonly toluene-based in some countries, mixtures of toluene and aliphatic hydrocarbons were also used. Ready-made printing inks normally contain solvents in excess of 60% solvent and between 4 and 10% pigment. The solvent content makes it necessary to employ pigments with sufficient fastness to solvents i.e., pigments which do not recrystallize too much under the conditions of dispersion and processing. 

A variety of Naphthol AS pigments are polymorphous they display at least two crystal modifications. The list includes P.R.9,12, and 187. A wide variety of dia-zonium compounds and coupling components with different substitution patterns have been developed in order to alter the properties of the resulting Naphthol AS pigments. This is particularly true for parameters such as fastness to solvents, in... 

Table 17 lists a number of commercially available pigments, along with their chemical structures, in order to illustrate the different structural types of Naphthol AS pigments. Fastness to solvents and migration resistance improve from top to bottom, i.e., with increasing number of CONH groups in the molecule. The first example, a simple (3-naphthol pigment, is the skeleton from which all other species are derived. 

Compared to other members of its class, P.R.5 exhibits good fastness to solvents. 

P.R.184 is used especially in applications where P.R.57 1 fails the requirements for alkali, acid, or soap fastness, or where the pigment lake is not lightfast enough to satisfy the demand. Depending on the standard depth of shade, the lightfastness of P.R.184 exceeds that of P.R.57 1 by approximately one step on the Blue Scale. Excellent fastness to solvents makes P.R.184 a suitable candidate for letterpress... 

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 affords a medium yellow shade. The pigment powder shows good fastness to solvents, in which it is similar to other yellow pigments within this class. 

P.Y 213 was released most recently onto the market. This greenish yellow quinox-alinedione pigment combines outstanding weatherability and overspray resistance with an excellent fastness to solvents, acid and alkali. These properties render P.Y. 

Fastness to solvents The test is carried out on the pigment powder. A closed filter bag containing 0.5 g of the pigment is immersed in 20 ml of the test solvent for 24 hours. The colour change of the solvent is compared against a standard colour sdae according to DIN EN 20105-A03 (formerly DIN 54002)... 

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