High-precision and high-density printing conditions

For high-precision printing, the amount of information per unit area can be increased, reducing the presence of rose patches and moiré on the usual plates. In addition to the increase in the amount of work and the reduction of the image reproduction range, the printing quality far outweighs the conventional printing. In other words, research on high-grade printing technology has made it a standard for print quality in the all-digital era.

1 High-precision printing

1) Features of high-precision printing

In general, a printed matter having a resolution of 300 lpi or more is referred to as a high-definition printed matter.

The biggest difference between high-precision prints and ordinary prints is the difference in dot gain rates. For example, under the accuracy of 175 lpi, the 50% dot enlargement rate is about 15%; under the 600 lpi accuracy, the 50% dot enlargement rate is close to 30%. Therefore, it is a matter of course that the conditions for making high-precision plate-making separations should be adjusted. How to control the dot expansion on printing is also an important step in determining the printing quality. In addition, the length of the side of the 600 lpi highlight portion was only 6 μm with respect to the side length of 20 μm of the 175 lpi highlight portion. How to maintain the reproduction of 6μm dots, platemaking, color separation, and printing are all important.
2) High-precision printed plates

The commonly used printing plates can be divided into two types: water PS plates and anhydrous silicone plates. From the point of view of network expansion, since there is no watermark version is a plano-gravure version, the mechanical dots generated between the printing plate and the blanket are less expanded, the tone reproduction performance is excellent, and the adaptability to high-definition printing is good. However, there is still room for improvement in the development of small dots by developing a method of expanding and removing a silicone layer of an unexposed portion (positive pattern) using a solvent for development.

Since the PS version of water has a flat relief, the mechanical dot enlargement is more prominent, and under the influence of the influencing factors of the fountain solution on the emulsification properties of the ink, it will have an adverse effect on the reproduction of tone reproduction. However, the recent four-layer PS model has improved water storage performance, which can inhibit network expansion. Compared with the previous PS version, the reproduction performance has been improved.

As for exposure of the printing plate, it is necessary to pay attention to the reproduction of the highlight portion and reset the exposure amount. Compared with the usual situation, the exposure will be greatly reduced. Exposure is also prone to quality problems caused by dust and requires careful handling.

3) High-precision printing ink

The importance of controlling the dot enlargement rate of high-precision printing has been as described above. The enlargement of high-precision printing dots is also related to the ink used. Especially for water offsets, the following points are very important.

1 Emulsification performance improvement.

When the ink emulsification is severe, the dot deformation is severe, the dot enlargement rate increases, and the printing quality is significantly reduced. In the case of inks, the fountain solution should be properly absorbed and there should be no "blead" failure and the amount of excess water should be minimized. Such an ink is what we would expect. It is important to select the binder and pigment for the resin component that has the greatest influence on the ink emulsification properties.

2 Control the dot gain by increasing ink density and viscosity.

In order to control the dot enlargement from the ink composition, it is necessary to increase the proportion of the pigment and maintain the desired ink concentration with a thinner ink layer. It is also an effective method to increase the ink viscosity without affecting the ink transferability.

3 improve the printing gloss.

The thinner the ink layer, the poorer the flatness and the corresponding decrease in the printing gloss, which is the opposite of the above effect of increasing the ink density. Therefore, to improve the glossiness of printing, it is an important condition to select a resin with good pigment infiltration and a good dispersibility pigment.

4 High-precision printing conditions.

In order to stably perform high-precision printing production, it is necessary to minimize the dot expansion caused by the printing press and control the ink emulsification. One of the important issues is the adjustment of the printing pressure, the temperature and humidity of the equipment, and the fountain solution.

1 Press control.

Dot enlargement occurs mainly during the transfer of ink from the plate to the blanket. Therefore, the pressure between the printing plate and the blanket is too large, which will cause the dot enlargement rate to increase. It is advisable to minimize the pressure between the printing plate and the blanket without affecting the ink transferability. In addition, blankets with good compression properties should be selected.

2 temperature control.

When the temperature of the device is too high, the viscosity of the ink drops, resulting in an increase in dot gain and deterioration of the emulsification adaptability. Therefore, the temperature of the equipment should be kept constant by adjusting the cooling water. After the temperature rise of the waterless offset printing press, it is particularly prone to stickiness, which is an important factor affecting the quality.

3 fountain solution control.

When the amount of the ink is kept constant and the fountain solution is increased, the water content of the ink increases, and as a result, the ink viscosity and the ink transfer property (concentration) decrease.

In the case where the fountain solution is excessive, the ink thickness must be increased in order to keep the ink density constant. As a result, the dot enlargement rate increases.

Therefore, in order to control the over-expansion of outlets, the amount of water should be minimized as much as possible. In addition, in order to improve the emulsifying properties of the ink, it is also important to select the fountain solution that matches the ink used.

2 High-density printing

1) Characteristics of high-density printing

With respect to color printing with a highest density of 2.0 or more, the usual plate separation is to compress the density range in order to maintain the gradation reproduction of the dark tone portion. The density of the traditional color plates is: Black Edition 2.0 or so; Magenta Edition, Youth Edition 1.4 to 1.5; Yellow Edition 1.0 or so. High-density printing adjusts the color separation curve so that its density range is as close as possible to the color printing density range (2.0). This is a way to improve the sense of three-dimensional impression and thick impression.

2) High-density printing and printing plates

Through the implementation of high-density printing, the dot expansion on the printing press is measured, and the results are fed back to the plate making process setting tone curve. Of course, printing plates are required to reduce their dot gains. Therefore, in general, high-density printing plates and high-precision printing plates should have the same characteristics. Water PS version should use water-retention printing plate, no watermark version to increase the concentration of the ink and need to consider increasing the thickness of the silicone layer.

3) High density printing ink

Although the high-density printing can immediately obtain a thick impression, the disadvantage is that the dot density of the main portion of the halftone print becomes large, and the transferability of the ink after the multicolor portion becomes poor (overprinting is poor. ), produces a noticeable rough phenomenon. In particular, the thickening of the ink film promotes darkening of the ink. Therefore, in addition to having the same stable emulsifying properties as the high-precision printing ink and increasing its concentration, the ink used must satisfy the following points:

* Improve the ink's overprint performance

Although increasing the thickness of the ink film can improve the hiding rate of the ink in each solid portion, the ink transferability in the later-printed multicolor portion is deteriorated, and overprinting defects are likely to occur. Therefore, it is necessary to adjust the viscosity balance between the various inks without increasing the dot enlargement rate.

* Improve the vividness of the ink

The increase in the ink density makes the ink turbidity phenomenon prominent, especially the blue ink is particularly serious, and has an adverse effect on the color appearance of the complex color part. To eliminate turbidity as much as possible, it is necessary to change the hue of the ink.


Source: Print World

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