I. Basic knowledge of spectrum: ULTRAVIOLET rays are divided into three types according to different bands: UVC for those with a wavelength below 250 nm, UVB for those with a wavelength between 250 and 320 nm, and UVA for those with a wavelength between 320 and 380. The visible light range is 380-800 (nm) and the infrared light range is 900-1800 (nm).
Two, photochromic principle: the use of UVA energy to open the photosensitive molecular bonds, so that it from the low energy level to the high energy level. That is, from visible light to visible light, resulting in a change in color. When the uv exposure is lost or the temperature increases by more than 45℃, the photosensitive molecular bonds close, that is, to return to the original color.
Iii. Morphology and Application of MC Photosensitive Powder (Micro Capsule)
1. MC photosensitive powder is the core of microcapsule, and Malamine is the shell material to form 1-10um photochromic pigment, with a moisture content of less than 0.3% and a heat resistance of 280℃.
2. The basic colors of MC powder are MC#12 purple, MC13# sky blue, MC14 purple blue, MC16 yellow, MC17# orange and MC19 red. Good and stable discoloration. High fluidity, easy to evenly disperse, can be mixed with each other, and can also be used with other pigments, fluorescent pigments.
3, the use of the base material color and material is different. The lighter the use of less color, ink substrate water to PU and acrylic connector is better. Oily PLASTISOL linker is preferred. It is better to dye with SILICON connector.
4, screen printing screen is recommended for 80-150 mesh, can also use rotary printing, lithographic printing effect is poor.
Iv. Applications of photochromic products:
Standard usage concentration: Photosensitive microcapsule powder (MC powder) is used for plastic injection and extrusion of 0.5% W/W
Photochromic products can be used in many ways:
Coating: Suitable for all kinds of product surface coating, such as PMMA painting, ABS painting, PVC painting and water-based painting.
Ink: printing of various materials, such as fabric, paper, synthetic film, glass, etc.
Plastic products: suitable for injection and extrusion molding of various plastic materials, products have high color concentration photosensitive PE color masterbatch and photosensitive PMMA color masterbatch, photosensitive PS color masterbatch.
V. Factors affecting photochromic effect:
1. UVA ULTRAVIOLET light: Cannot be exposed to ultraviolet light for a long time.
2. Heat: Shock occurs easily above 45℃ and discoloration is lost.
3, with the product polarity has a great relationship. #12, #19 performed better in non-polar environments, and #14, #16 performed better in polar environments.
1. The base color of photosensitive products should not be too deep, but transparent or light color is generally preferred.
2. Base material selection: MI value greater than 25, bending elasticity coefficient must be less than 17,000; PH 5-7 is the most suitable material for acid and alkaline.
3, photochromic materials produced by UV light overexposure, acid, free radicals (singlet oxygen atoms) and humidity caused by the general recommendation to add UVB absorbent and antioxidants, in order to increase the light fatigue resistance.
4. Additives such as HALS, antioxidants, thermal stabilizers, UV absorbers and inhibitors used in photochromic materials can improve light fatigue, but the combination and selection of additives should depend on the medium used. Wrong combination formula will accelerate light fatigue instead.
5, photosensitive color materials do not contain substances harmful to human body, in line with the safety of toys and food packaging standards.