Technical defects and remedies of printing inks (4)

Whitening:

Fault phenomenon;

Ink or varnish (also known as paint), which produces a frost-like ink film or a varnish film during drying or filming, is called whitening, often referred to as whitening. Usually produced in the solvent evaporation drying ink printing or coating production process, in the case of serious loss of light. There are also UV inks or UV varnish molecules that are photon-absorbed because they are solidified. Under certain temperature and ambient conditions, the molecular solvent (water) remaining in the film will still be released again, resulting in white frost fogging and whitening.

cause:

During the printing or finishing process, if the solvent remaining in the ink film or oil film is mixed with water, (1) the solvent quickly evaporates, causing the temperature of the surface layer of the ink film to drastically drop below the dew point of the ambient temperature, resulting in moisture condensation. Water is mixed in the ink; (2) In the high-temperature season ink printing or varnish coating, the moisture in the compressed air is completely separated and mixed into the ink film or the oil film; (3) The UV ink or the UV light oil is dry The film of wet (un-photon-absorbed molecules) has the opportunity to release residual solvent under certain conditions of environment, humidity and light, and will still be invaded by water molecules in the process of thinning, so the ink or varnish itself has The surface of the remaining water solvent or substrate is not dry. In the process of film formation, the ink of the packaging printing ink or the gloss oil film affects the transparency of the ink film or the oil film due to the precipitation of the polymer binder resin. When the true solvent and the dilution solvent are generally used as the mixed solvent, the strong solvent can evaporate quickly. An increase in the proportion of poor solvent left will cause the resin binder in the ink and varnish system to precipitate and whiten. Of course, the incorporation of moisture (including moisture in the substrate) can also reduce the solubility of the resin in the above two systems. Precipitation. The UV ink or UV light oil should not be completely absorbed due to the light intensity (excessive light intensity will make the UV ink decomposition, which we do not want to see).

Countermeasures:

Whitening is related to the relative humidity of the environment and substrates, solvents, and binders. Residual UV solvent molecules, should strictly control the following six factors to prevent the whitening of ink film and oil film. (1) Select appropriate substrates and solvents, and dilute solvents to control the volatilization rate and light intensity to prevent the surface temperature of the ink film from being too low and prevent the precipitation of the resin binder; (2) Strictly control the relative humidity of the environment <70 articles, When the humidity is high, moisture-proof agent can be added, also called anti-whitening agent, that is, slow-drying solvent. Usually mainly cyclohexanone, ethylene glycol, propylene glycol compounds, both with water, but also with organic solvents miscible. To promote the moisture evaporate together, but its amount should be strictly controlled; (3) improve the light energy is mainly UV ink, light oil curing light intensity; (4) the surface of the substrate to be dried, it is best to keep the temperature higher than the environment Temperature: (5) When the package is printed or even varnished, the thinner material must use dehydrating solvent to eliminate compressed air;
(6) Strictly compounding of the binder with the solvent system and the thinner to prevent the resin polymer ink, varnish production, storage, and even precipitation during printing and finishing.


Hunan Packaging Liu Jiaju