Reasons for easy ink drop after printing

In the printing process of matt paper, there is often such a problem that the drying performance is poor, the drying speed is slow, and it is easy to “discard ink” during the post-press processing, especially when printing black ink in the field, to give product quality, The production cycle has had an impact. To this end, we look for reasons from the following aspects.

First, the pH of the paper is tested. Because the pH value of the paper is one of the main factors affecting the drying of the print, acidic paper is less dry. After monitoring several commonly used brands of matte paper, the pH value is between 7 and 8, which is a neutral partial alkali, both in the normal range. At the same time, the moisture content of matt paper was also monitored and monitored. The value ranged from 8% to 9%, which was within the normal range.

Secondly, the pH of the fountain solution is tested. The pH of the fountain solution is basically stable between 4.8 and 5.2. At the same time, the amount of water is strictly controlled. In the production process, the amount of water is continuously reduced, basically meeting the requirement of water-ink balance, and minimizing the degree of ink emulsification.

Third, analyze the ink thickness. Although the black ink actually has a large amount of ink, it is not overprinted, and the lightly rubbing in the high-profile part of black ink also “discards ink”, indicating that the thickness of the ink layer is not greatly affected.

Fourth, control the ambient temperature and humidity. The temperature was controlled at 25°C and the relative humidity was controlled at 65%. At the same time, the delivery height is also reduced to a minimum, basically 200 to 300 sheets.

Fifth, choose special inks that are specially suitable for printing on matt paper, and also try to add driers to the ink.

In view of the above factors that may affect the drying of blots, corresponding measures were taken one by one, but the results were not satisfactory and the problems were not solved fundamentally.

The main reasons for the poor drying of the matte paper imprints are the particularity of the matt paper itself and the particularity of the black ink pigment.

Due to the small degree of sizing, the matt paper has a loose structure and a rough surface, so its absorption is strong and the binder in the ink can be quickly absorbed. The yellow, magenta, and cyan pigments are generally made of inorganic or organic pigments, while the black ink uses carbon black (elemental carbon) as the pigment, and the carbon black is non-drying. In general, black ink is better than other color inks. Dry slowly. In addition, the adhesion of carbon black and the binder is lower than other inorganic or organic pigments. This causes the matte paper to absorb the binder in the ink too quickly and float the carbon black on the surface of the paper.

The use of matt paper is becoming more and more widespread. Some printing companies use post-printing oils to alleviate this problem. This will not only increase the cost, prolong the production cycle, but also the biggest hazard is to change the original characteristics of matt paper, and the color is also affected.

In order to meet the customer's requirement for black ink on the matte paper and solve the problem of “disappearing ink” at the same time, some people have made some attempts. One is to use yellow, magenta, and cyan inks as the network cable version to obtain color ink overlays. Black; second is the use of color method, the yellow, magenta, cyan ink mixed black ink to avoid the black ink in the "carbon black." Because pigments in yellow, magenta, and cyan are basically inorganic pigments, their drying properties and adhesion are significantly better than those of carbon black.