Application of thermosensitive color change powder in ink

1 selection of connecting material (resin) :
1.1 influence of viscosity and solid content of binder (resin) on color concentration and surface gloss:
The choice of resin in ink oil has a very important effect on the color concentration and surface gloss of temperature-varying ink, which is more significant for black ink. Because the content of pigment in the color changing ink is much higher than ordinary ink, if the resin modulation of ordinary ink color changing ink will lead to ink viscosity is too high and can not be used. Therefore, the ink can only reduce the amount of resin and increase the amount of solvent, in order to reduce the viscosity of the ink. As a result of this is: when the ink layer of printing products dry, due to the resin content is very small, not enough to fill the gap between pigments, making the surface of the ink layer uneven without luster, thus forming a diffuse reflection of light. So the ink layer apparent color concentration is low and high gray level. For black ink, it looks grey but not black. (if you cover the surface of the printing a layer of transparent varnish, you can obviously feel the blackness.) therefore, the modulation of temperature variable ink must use high solids and low viscosity (low polymerization or low molecular weight) of the resin, so as to achieve good results.
1.2 the relationship between the type of linker (resin) and its optical refractive index and the color concentration and post-bleaching transparency of the color-changing ink (coating)
Temperature-changing pigment is often used for printing “cover-display” patterns, the requirements of the surface of the printing ink layer in the hair color completely cover the lower layer of the pattern, after reaching the extinction temperature to be as transparent as possible, so that the lower layer of the pattern is clearly displayed. In this kind of use, if the resin selection is not appropriate, cover the ink layer after bleaching will produce a “white fog”, so that the lower layer pattern display is not clear. The basic reason is that the resin selected is not consistent with the optical refractive index of color-changing pigment microcapsule wall material. The numerous microcapsules scattered in the ink layer form a large number of optical refraction interface, like a piece of transparent glass after the formation of white opaque phenomenon. The proper choice of resin can greatly reduce this phenomenon of refraction in the color – changing ink layer, so that the color of the ink layer more transparent. Generally speaking, alkyd resin and acrylic resin have better transparency, while polyamide resin and nitrocellulose have the worst transparency.
2. Solvent selection and influence on color changing performance:
2.1 influence of photorefractive index of solvent on color concentration of color-changing inks (coatings) :
The optical refractive index of color-changing pigment microcapsules is between 1.50 and 1.54, and the color concentration of the ink is higher when the optical refractive index of the solvent is the same or similar, such as toluene, xylene and benzyl alcohol (the optical refractive index is 1.496, 1.493 and 1.540, respectively). Conversely, when the refractive index difference between the two, ink apparent color concentration is lower. Such as normal propyl alcohol (1.386), isopropyl alcohol (1.377), acetone (1.359), ethyl acetate (1.372), butyl acetate (1.394), ethylene glycol ether (1.392).
However, the solvent on the color of ink color concentration is temporary. After printing, this effect will gradually disappear as the solvent in the ink layer evaporates.
2.2 influence of solvent on pigment color changing properties:
Temperature-varying pigments have different tolerances to different solvents. Soaking in some solvents for 6 months will not affect the color changing properties, but other solvents can erode the surface of the microcapsule and penetrate into its interior within a few hours to a few weeks, making the color changing properties of the pigment fade or even completely disappear. Some of these discoloration properties can be partially recovered after the solvent evaporates, while others are completely unrecoverable. Generally speaking, solvents containing less than 3 carbon atoms are more destructive to the erosion of color-changing pigments, while solvents containing more than 6 carbon atoms have little effect on pigments. In addition, the erosion effect of solvent will be more obvious at higher temperature.
For the above reasons, in the deployment of ink and paint should take the following measures:
— use as little or no alcohol solvents as possible, and use other solvents instead. For example, cyclohexanone can be used instead of propanol.
— when it is necessary to use propanol and other solvents, ink (paint) should be used with, avoid storage.
Because the pigment is easy to disperse in the resin solution, so all the ink (coating) except pigment can be allocated well, before printing add the specified amount of pigment (pigment), stir evenly can be added to the ink bucket to start printing. Can also be in addition to propanol, isopropanol and other inks into the distribution of good (including color changing pigment), before the use of the first addition of the specified amount of the solvent, stir evenly after the start of printing. Pay attention to the amount of ink with not too much, with use, do not store.
Special note: the ink industry commonly used diluents/mixed solvents and some resin solutions may contain alcohol, acetone, propanol and other components that damage the performance of color-changing pigments. Even small amounts of harmful ingredients can have serious effects. Choose the appropriate ink oil and ink transfer method
Some blending oils contain chemical components such as phosphate ester or chlorine/bromine. Once a small amount of microcapsule pigment is damaged in the blending process, these substances will have irreversible color reaction with the damaged pigment, making the residual color significantly increased. Therefore should avoid the use of this ink oil.