The Study On Preparation And Application Of Photochromic Microcapsules

Photochromic materials have extensive application prospect in printing, security, packaging, particularly the defense industry. The organic photochromic materials with sensitive color changing and bright color were susceptible to be affected by temperature, light, pH value, oxygen and other enviromental factors, which led to oxidation and deterioration and poor fatigue resistance. And these enviromental factors impact its application in the field of textile.In this paper, photochromic microcapsules were prepared via in-situ polymerization, and perchlorethylene solution of spiroozaxine, melamine resin, SDS, PVA were used as core materials, wall materials, emulsifier and dispersant. The effects of photochromic solution concentration on color changing property and formaldehyde/melamine molar ratio on surface morphology and intensity of microcapsule were studied. Moreover, the influencing surface morphology and size distribution of the photochromic microcapsules, such as mixing speed, emulsifying time, emulsifier and dispersant concentration and acidification timewere discussed in detail. The effects of volume ratio of wall materials/core materials and emulsifier equipment to sealing and color changing of photochromic microcapsule were argued. The properties of photochromic microcapsules were analyzed by Optical Microscope, Scanning Electron Microscopy, Thermal Gravimetric Analysis, Laser Particle Size Analyzer. The wall thickness of the photochromic microcapsule were calculated. The free formaldehyde content of the photochromic microcapsules were detected through acetylacetone method. The soaping fastness and resistance rubbing fastness of photochromic fabric were tested.The results had shown that the best effect of color changing was obtained when the photochromic solution concentration was 0.75wt%. When the molar ratio of formaldehyde to melamine is 3/1, the rate of emulsifier is 1000rpm, the emulsifier time is 40 min, the acidification time is 0.5h, the emulsifier concentration is 0.5wt%, the dispersant concentration is 0.2wt%, the volume ratio of wall materials to core materials is 4/1, the photochromic microcapsules showing purple irradiated under sunlight were obtained. And these microcapsules could rapid and reversible change color. The free formaldehyde detecting results had conformed that the free formaldehyde of microcapsules in this paper ranged the GB18401-2001 standard limit.The photochromic microcapsules prepared using high-speed emulsification machine were coated on the surface of knitting-needle fabric. The photochromic fabrics was gained and could be rapid reversible changing color under sunlight. And this fabric had better resistance soaping fastness and rubbing fastness.