Microencapsulated dyes

Other significant uses of PCBs included heat exchangers and hydraulic fluids. Prior to controls PCBs were also used in adhesives, coatings, plasticizers and inks for microencapsulating dyes for carbonless duplicating paper as extenders in pesticide formulations and catalyst carriers in olefin polymerizations to impart hydrophobicity to materials and surfaces in bactericide formulations (combined with insecticides), and in immersion oil for microscopes. Mixed with chloronaphthalenes, PCBs were also used in wire and cable insulation in the mine and shipbuilding industries (ref. 80, p. 455). 

The development of early encapsulation technology and preparation of microcapsules dates back to 1950s when Green and coworkers produced microencapsulated dyes by complex coacervation of gelatin and gum Arabic, for the manufacture of carbonless copying paper. The technologies developed for carbonless copy paper have led to the development of various microcapsule products in later years. 

Carbonless Copy Paper. In carbonless copy paper, also referred to as pressure-sensitive record sheet, an acid-sensitive dye precursor, such as crystal violet lactone or /V-hen2oy11eucomethy1ene blue, is microencapsulated with a high boiling solvent or oil within a cross-linked gelatin (76,83,84) or in synthetic mononuclear microcapsules. Microcapsules that have a starch binder are coated onto the back of the top sheet. This is referred to as a coated-back (CB) sheet. The sheet intended to receive the image is treated on the front (coated-front (CF)) with an acid. When the top sheet is mechanically impacted, the dye capsules mpture and the dye solution is transferred to the receiving sheet where the acid developer activates the dye. 

Another important apphcation for 4-/ f2 -octylphenol is ia the production of phenoHc resias. Novolak resias based oa 4-/ f2 -octylpheaol are widely used ia the tire iadustry as tackifiers. The tackiaess of these resias biads the many parts of an automobile tire prior to final vulcanization. A specialty use for novolak resias based oa 4-/ f2 -octylpheaol is the productioa of a ziacated resia, which is formulated as a dispersioa ia water and coated onto paper ia combination with eacapsulated leuco dyes to yield carbonless copy paper (see Microencapsulation). Pressure from writing bursts the encapsulated leuco dye, which is converted from its colorless form to its colored form by the ncated resin (53). Novolak resias based oa 4-/ f2 -octylpheaol are also used ia the productioa of specialty printing inks. 

Pressure-sensitive recording materials are obtained by dissolving a triphenylmethane leuco dye in a solvent composed of paraffin oils. The microcapsules are formed from a water-soluble106 or water-dispersible material.107,108 Leuco dyes dissolved in sunflower oil are microencapsulated in a solution containing a melamine-HCHO precondensate and coated on the back side of a paper sheet. Contact of the microcapsule-coated sheet with an acid-coated receptor sheet allows the color formation to occur. 

Uses of Composite Particles. Composite particles are of substantial commercial importance because they provide new property balances for tougher plastics, films, nd coatings. They are used to combine in a cost-effective manner functional groups or high performance components which are expensive with low-cost components and they provide opportunities to vary the optical properties of coatings. Microencapsulation interests are diverse, ranging from pharmaceuticals to dyes and toners and to magnetic particles. 

Insulation for electrical wires, cables, and condensers Microencapsulation of dyes for carbonless duplicating papers Paint additives, ink dyes, plasticizers Protective coats for low flammable woods... 

Figure 1. Schematic representation of the microencapsulated imaging system A-microcapsule internal phase, B-transparent shell, C-substrate, D-dye developer layer.

Luo, Y., Chen, S., 2011. Effect of microencapsulation on dyeing behaviors of disperse dyes without auxiliary solubilization. Journal of Apphed Polymer Science 120 (1), 484—491. 

The most popular method of pigments encapsulation is spray-drying. Many papers present information about microencapsulation by spray-drying, and this method is most frequently used to protect pigments obtained from vegetables, fruits, flowers, and plants, for example, black carrot, curcumin, beetroot, or roselle. Application of natural polymers as shell to protect beetroot color increased the half-life of spray dried dye about three times, whilst pink color was stabile for about 8 weeks. In case of red roselle pigments stabilization, after microencapsulation, it was acceptable to extend the storage time under different water activities up to 4 months. ... 

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