Microencapsulation of dyes

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... 

Uses Capacitors transformers mfg. of plasticizers, hydraulic fluids, lubricants, surf, coatings, inks, sealants, adhesives pesticide extenders microencapsulation of dyes for carbonless duplicating paper ingred. in lacquers, paints, varnishes waterproofing compds. vacuum pump fluids air compressors... 

Studies on the microencapsulation of dyes using CO2 as detailed above are carried out with PS microspheres prepared by dispersion polymerization. These sterically stabilized (with PVP) PS particles retain their original size and shape after the incorporation of dye. When PS microspheres are prepared by surfactant-free emulsion... 

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. 

Similar approaches can be used in the microfluidic synthesis of Janus particles where two compartments are formed within the particle that have different compositions. In this case immiscible monomers are passed along microfluidic channels in parallel streams and then subsequently polymerized. This approach allows precise control over the volumetric fraction of each monomer by controlling the relative flow rates of the two monomer streams [3]. Polymerization is usually by UV irradiation, and the surfaces of each compartment of the Janus particles can be subsequently functionalized or used for immobilization of biomolecules. They can also be loaded with dyes or other small molecules to act as colorimetric indicators or in microencapsulation of drugs [3]. 

Scheme 11.4 Schematic representation of the mechanism of colour change in a microencapsulated leuco dye thermochromic system.

Thermochromic components are usually microencapsulated in order to limit undesirable influences of the environment. Thermochromic dyes are highly sensible to light, solvents and high temperatures. The wash durability of microencapsulated thermochromic dyes has been reported to be up to 20 washes [53]. 

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. 

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). 

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. 

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

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