How to solve the problem of high solvent residue and high solvent residue

Solvent residues in flexible packaging have always been a major threat to food hygiene and safety. Nowadays, people's awareness of safety and hygiene has gradually improved. From the raw materials of food and its packaging, production process control to transportation, the state has been constantly improving and issuing relevant regulations. Cause excessive residual solvents in food packaging is very complex, especially in high-speed gravure printing machine, solvent residue control more difficult. The choice of ink, the purity of the solvent and the solvent ratio, the design of the oven into and out of the air, the matching of the printed substrate, the control of all aspects of the production site and the configuration of the relevant testing equipment require the attention of the flexible packaging enterprises.

Ink

The residual amount of solvent is closely related to the ink. Different types of inks or inks from different suppliers will have different solvent release properties, and the residual amount of solvent in the ink will be completely different.

When printing food packaging with high-speed gravure printing machine, in addition to avoiding the selection of ink containing benzene-dissolving resin and benzene-containing solvent, benzene-free ink should not be indirectly contaminated. Solvent residues of benzene-free inks (especially alcohol-soluble benzene-free inks and aqueous inks) have proven to be significantly lower than those of benzene-containing inks. The fastness and printability of the plastic film alcohol-soluble composite gravure ink are not as strong as the ketone and ester-free benzene-free inks, but from the viewpoint of safety, the use of alcohol-soluble benzene-free ketone-free inks and aqueous inks is the best choice.

Solvent

Solubility and volatility of the solvent are the key to determining the drying performance of the ink layer and an important factor affecting the quality of the printed product.

First of all, we should pay attention to the ratio of solvents. For example, a benzene-free ink standard solvent ratio is: ethyl acetate 40%, isopropanol 20%, n-propyl ester 40%, when the printing speed is 200m / min, the ink can be well dried; if printing When the speed reaches 300m/min and the drying time of the ink becomes shorter, the drying speed must be accelerated. At this time, the solvent ratio should be adjusted to: 70% ethyl acetate , 20% isopropanol , and 10% n-propyl ester .

In addition, although the proper mixing solvent can dissolve a specific polymer resin well, over time, the inconsistency of the volatilization rates of various solvents may destroy the original system of the mixed solvent and volatilize the solvent. Poor, leading to ink separation from the layer, so the ratio of the solvent can not be simply adjusted and the performance of the solvent (including solvent purity, water content, boiling point, etc.) is neglected. The use of the solvent is very particular. The printing speed of the gravure printing machine is different during production, the mesh size of the printing plate is different from the area of ​​the solid part and the depth of the cell is different, and the use and ratio of the solvent are also different. When selecting a solvent, it is required to use a mixed solvent as much as possible, and in combination with the process and equipment characteristics, try to avoid using an ultra-fast or too slow-drying solvent.

Oven drying conditions

Generally speaking, because the printing speed is fast, if the printing plate has a large area and the cell is deep, and the drying time of the oven is short, the drying is often incomplete, even if the drying temperature of the oven is set high. There will still be more solvent residues, and some will even cause quality problems such as dry and anti-stick on the ink surface. Therefore, adjusting the oven design and improving the oven environment will have a significant effect on reducing the amount of solvent remaining.