Resins color migration

The dyes used in the ink sheet must satisfy various requirements (/) optimum color characteristics of the three primary colors (hue, color density, shape of absorption spectmm) (2) sensitivity, ie, sublimabiHty from ink sheet to acceptor sheet (3) fastness for light and migration and (4) compatibiHty with the resin in the ink sheet. With respect to these characteristics, a large number of anthraquinone dyes have been proposed particularly for magenta and cyan colors. Typical examples are given in Table 8 and Table 9. 

One of the first non-formaldehyde fluorescent dye carrier systems for polyolefins was based on the reaction of polyfunctional amines with polyfunctional carboxylic acids to form relatively short chain polyamides [5].These linear thermoplastic resins showed good solubility and friability making them suitable for the incorporation of dyes, which offered increased protection from thermal and UV degradation. This fluorescent resin showed a dramatic increase in color retention upwards of 288°C, even after a 10 minute hold period at this temperature. Due to its non-ide-alized polymeric nature, the polyamide chemistry suffered from preferential plating out or migration of polar oligomeric species not incorporated into the polymer chains. 

Three properties that contribute the most to migration are (1) incompatibility with the resin, (2) low melt point, and (3) low molecular weight. Examples of noncolorant additives that are prone to migrate are (1) lubricants/dispersants such as metal stearates and bis-stearamides, (2) mold release and slip agents, and (3) antistatic agents. All of these ingredients serve useful purposes in color formulations. If you exceed their solubility limit in the end-use resin, however, you risk blooming and its consequences. 

In the next step, a starting formulation of colorants, additives, and resin is developed. The computer generates formulas on the basis of a database of known spectral curves of colorants. The formulas are reviewed to ensure that colorants meet heat stability, weatherfastness, and migration and chemical resistance requirements, at a cost that is competitive. Lab samples are produced, evaluated, and submitted to the customer for approval. The customer can be internal or... 

The compounds used are semirigid and, in some cases, ABS blends. In the case of a straight PVC compound, 30-40 phr of a low-volatility phthalate or trimellitate plasticizer is used. From 15 to 20 phr calcium carbonate is supplemented with 1 phr titanium dioxide, 1-2 phr antimony trioxide for improved flame resistance, 2-3 phr ESO, colorants as required, and about 0.1 phr (or less) stearic acid. The stabilizers used are barium/zinc or calcium/zinc powders supplemented with mineral acid absorbers and also a source of perchlorate anion. The latter is active in scavenging amine catalysts migrating fiom the PUR layer, which rapidly discolor PVC. If need be, minor amounts of dispersion resin or of acryhc processing aid can be added to compounds such as the above to improve flowability. Although principally used in the United States for instrument panels, European and Japanese usage in arm and head rests has also been reported. 

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