The Analysis and Solution of the Phenomenon of Matte Paper Dropping after Printing

In the matte paper printing process, such a problem often occurs, that is, the drying performance is poor, the drying speed is slow, it is easy to "drop ink" during post-print processing, especially when printing solid black ink, it is more prominent, giving product quality, The production cycle has an impact. To this end, we look for reasons from the following aspects.

First, test the pH of the paper. Because the pH value of paper is one of the main factors affecting the drying of blots, acid paper has poor drying properties. After tracking and monitoring several commonly used matt papers, the pH value is between 7 and 8, which is neutral and alkaline, and is in the normal range. At the same time, the moisture content of the matt paper has also been tracked and monitored, and its value is between 8% and 9%, which is within the normal range.

Second, the pH value of the fountain solution was detected, and the pH value of the fountain solution was 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 requirements of water-ink balance, and the degree of ink emulsification is minimized.

Third, analyze the ink layer thickness. Although the black ink has a large amount of ink on the ground, it is not an overprint, and it is also "dropped" by gently rubbing in the high-profile part of the black ink, indicating that the thickness of the ink layer is not greatly affected.

Fourth, control the environmental temperature and humidity. Control the temperature at 25 ° C and the relative humidity at 65%. At the same time, the height of the delivery paper is also minimized, basically 200 to 300 sheets.

Fifth, choose a special ink specifically for matte paper printing, and also try to add a drier to the ink.

In response to the above factors that may affect the drying of the blot, corresponding measures are taken one by one, but the effect is not ideal, and the problem has not been fundamentally solved.

The author analyzes that the main reason for the poor drying of matt paper imprints is the particularity of matt paper itself and the particularity of black ink pigments.

Due to the low sizing degree, matt paper has a loose structure and rough surface, which makes it highly absorbent and the binder in the ink can be quickly absorbed. The pigments of yellow, magenta, and cyan inks are generally made of inorganic or organic pigments, while black inks use carbon black (elemental carbon) as the pigment. Carbon black has no drying effect. Generally, black ink is better than other color inks. Dry slowly. In addition, the adhesion between carbon black and the binder is lower than other inorganic or organic pigments, which causes the matte paper to absorb the binder in the ink too quickly, so that the carbon black floats on the surface of the paper.

The use of matt paper is becoming more and more widespread, and some printing companies use post-print varnish to alleviate this problem. This not only increases the cost and lengthens 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 requirements for the solid color of black ink on matte paper, and at the same time solve the problem of "dropping ink", the author made some attempts. First, yellow, magenta, and cyan inks were used as screen plates to obtain black with superimposed color ink The second is to use the toning method to mix black, magenta, and cyan ink in equal amounts to obtain black ink to avoid the "carbon black" in the black ink. Because the pigments in yellow, magenta, and cyan inks are basically inorganic pigments, their drying properties and adhesion are significantly better than carbon black.

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