Solution to the problem of residual odor of large-area gold ink packs

Problems and Phenomenon

My company produces a large area of ​​gold ink shop bottom cigarette pack products: the old version of the white paper Jiapin red gold dragon, hard special red gold dragon, hard red gold dragon (Hong rainbow color Pu system), rich and noble and so on. Their printing features are: the main color is covered with a large area of ​​gold ink (or silver ink), then the special red is printed in the same area, and the final printing of water-based gloss oil.

At the beginning of the production of such cigarette packs, the problem of residual odor of the product was more serious and the pungent odor could be clearly smelled. In order to ensure that customers do not complain, at that time can only be taken to resolve the natural volatility, that is, products are not packaged after the completion of the production, under the conditions of ventilation to dry 2 to 3 days until the odor eliminated or reduced packaged delivery. However, in case of tight delivery or continuous rainy and wet weather, it is very troublesome.

Cause Analysis

In order to solve this problem, we start by looking for sources of odors and find out the reasons for this problem. First of all, we excluded the water-based gloss oil because the smell is mainly solvent odor, not ammonia smell; then, it excludes the influence of large-area red ink and other color inks, because there is no large area printed with them. There are no obvious odor residues in the printed cigarette products. In the end, we confirmed that the cause of the odor residue was gold ink.

So, why does Jinmo Printing cause such obvious odor retention? We also looked for the cause from the solvent used. The solvent we used was a mixed solvent of toluene and ester. After a special test, we found that the two solvents were completely volatile when used alone, and there was no obvious residue phenomenon. However, there is a clear solvent residue when used in combination. This is mainly due to the fact that the volatility of the mixed solvent is weaker than the volatility of the single solvent, and the more complex the composition of the mixed solvent is, the worse the volatilization performance is. Moreover, we also found that the residual odor on the cigarette pack is neither a single toluene smell nor an ester odor, but rather a mixture of various solvents. This also confirms that our analysis is correct.

However, we also found that the three-in-one solvent used in other color inks is more volatile than the two-in-one solvent used in gold ink. Why is this? Through careful analysis, we found the reason from the structure of gold ink, because the gold powder in gold ink looks like a powder, in fact it is a phosphorus sheet. After printing on paper, the solvent is enclosed in small metal sheets and paper. In the inter-resin, it is difficult to blow through the dry hot air, so the odor residue of the cigarette pack product caused by the large-area gold ink printing is serious.

At the same time, we also found that the gold bars themselves have obvious odors. After discussing with several ink manufacturers, we also found the reason. Gold powder is a mixture of several metal powders that are blended in a certain proportion and has no odor. However, in order to ensure safety, including transportation safety and safe use, a certain kind of mineral oil is used in particular to complex the gold powder together. Become a strip. This mineral oil has a distinct odor, and it is very stable and not volatile. And this kind of mineral oil must be added, but different manufacturers, different types of gold ink to add a difference. Since the amount of this mineral oil in the powder is the least, the odor is much smaller than that of the gold bar.

Solution

After finding the cause of the odor remaining, we have adopted the following comprehensive plan to deal with it.

1. Using gold powder, eliminate gold bars

Mineral oil odor is the main component of the residual odor, while the use of only a small amount of mineral oil in the gold powder, the odor residue is relatively small, so it should try to use gold powder, it is best not to use or less use of gold bars.

2. Replace toluene with benzene-free gold oil

This is not because of the large residual odor of toluene. On the contrary, the volatilization performance of toluene is quite good. Using benzene-free gold, we can use a single ester solvent instead of a poor solvent mixture.

3. Strengthen the drying process after the gold ink

In the printing process, we adopted the method of increasing the air volume and appropriately increasing the drying temperature for this group of gold inks, arranging the spare color group between gold and other spot colors, and turning on the hot air drying system of the empty color group. Make the solvent in the gold ink as volatile as possible. Because after printing spot colors and varnish on gold ink, the solvent will be enclosed in the inner layer and it will be very slow to evaporate. Therefore, it is very important that the solvent be completely evaporated before this time.

4. The choice of weather

For such cigarette pack products that require a large area of ​​gold ink to be deposited, printing should be arranged when the air humidity is lower as much as possible, because the higher the moisture content in the air, the less favorable the volatilization of the solvent and the odor residue.

Through comprehensive consideration of the above conditions and corresponding measures, the problem of residual odor in large-scale gold ink packs has been better resolved.

Reprinted from: Ke Yin Network