For high-precision printing, it can increase the amount of information per unit area and reduce the rose spots and moire patterns usually existing in plate making. High Precision and High Density Printing
In addition to increasing the workload and reducing the image reproduction range, it is much better than conventional printing in printing quality. In other words, through the research on high-grade printing technology, it has become the standard of printing quality in the all digital era.High Precision and High Density Printing
Generally, a print with a resolution of more than 300 LPI is called a high-precision print.
The biggest difference between high-precision printing and ordinary printing lies in the difference of dot expansion rate. For example, under the accuracy of 175 LPI, the dot expansion rate of 50% is about 15%; Under 600 LPI accuracy, the expansion rate of 50% dots is close to 30%. High Precision and High Density Printing
Therefore, it is natural to adjust the conditions for plate making and color separation of high-precision printing. How to control the dot expansion in printing is also an important link to determine its printing quality. High Precision and High Density Printing
In addition, relative to 175 LPI, the highlight dot 20 μ The side length of 600 LPI highlights is only 6 μ m。 How to keep 6 μ The reproduction of M small ideas, plate making, color separation and printing conditions are important.High Precision and High Density Printing
Commonly used printing plates can be divided into water PS version and anhydrous silicone rubber version. In terms of dot expansion, since the anhydrous printing plate is a flat intaglio plate, there is less mechanical dot expansion between the printing plate and the blanket, with excellent tone reproduction performance and good adaptability to high-precision printing.
However, there is still room for improvement in the development of small dots because the development adopts the method of expanding and removing the silica gel layer of the unexposed part (positive pattern) with solvent.High Precision and High Density Printing
Because the watery PS plate is a flat relief plate, the mechanical dot expansion is more prominent, and under the joint action of the influencing factors of the fountain solution on the emulsion characteristics of the ink, it will have an adverse impact on the tone reproduction. High Precision and High Density Printing
However, the recent 4-layer sand mesh PS version has improved its water storage performance, which can inhibit the expansion of network points. Compared with the previous PS version, the reproduction performance has been improved.High Precision and High Density Printing
In terms of plate exposure, we must pay attention to the reproduction of the highlight part and reset the exposure. Compared with the usual situation, the exposure will be greatly reduced. It is also easy to cause quality problems due to dust during exposure, which requires careful operation.High Precision and High Density Printing
The importance of controlling the dot expansion rate of high-precision printing has been described above. High precision printing dot expansion is also related to the ink used. Especially for water offset printing, the following points are very important.High Precision and High Density Printing
① Improvement of emulsifying properties.High Precision and High Density Printing
When the ink emulsification is serious, the dot deformation is serious, the dot expansion rate increases, and the printing quality decreases significantly.High Precision and High Density Printing
In terms of ink, we should properly absorb the fountain solution, avoid the “bleed” fault, and minimize the excess water. High Precision and High Density Printing
Such ink is what we expect. It is important to select the connecting materials and pigments of the resin components that have the greatest impact on the emulsifying characteristics of the ink.High Precision and High Density Printing
② Control dot expansion by increasing ink concentration and viscosity.High Precision and High Density Printing
In order to control the dot expansion from the ink composition, it is necessary to increase the proportion of pigment and maintain the required ink concentration with a thinner ink layer. It is also an effective method to improve the viscosity of ink without affecting the transferability of ink.High Precision and High Density Printing
③ Improve printing luster.High Precision and High Density Printing
The thinner the ink layer, the worse its flatness, and the corresponding reduction of printing gloss, which is just opposite to the effect of increasing ink concentration. High Precision and High Density Printing
Therefore, in order to improve the printing gloss, it is important to select resins with good pigment wettability and pigments with good dispersion.High Precision and High Density Printing
④ Printing conditions of high-precision prints.High Precision and High Density Printing
In order to stably carry out high-precision printing production, it is necessary to minimize the dot expansion caused by the printing press and control the ink emulsification. High Precision and High Density Printing
One of the important problems is to adjust the printing press, the temperature and humidity of the equipment and the fountain solution.High Precision and High Density Printing
① Imprint control.High Precision and High Density Printing
Dot expansion mainly occurs in the process of transferring ink from printing plate to blanket. Therefore, too much pressure between the printing plate and the blanket will increase the dot expansion rate.High Precision and High Density Printing
It is best to minimize the pressure between the printing plate and the blanket without affecting the ink transfer. In addition, rubber blanket with good compression performance shall be selected.High Precision and High Density Printing
② Temperature control.High Precision and High Density Printing
When the equipment temperature is too high, the ink viscosity decreases, resulting in the increase of dot expansion rate and poor emulsification suitability. Therefore, the equipment temperature shall be kept constant through the regulation of cooling water. High Precision and High Density Printing
Water free offset press is especially prone to sticky dirt after temperature rise, which has become an important factor affecting quality.High Precision and High Density Printing
③ Control of fountain solution.
When the amount of ink remains constant and the fountain solution increases, the water content of the ink will increase, resulting in the decrease of ink viscosity and ink transferability (concentration).High Precision and High Density Printing
When printing with too much fountain solution, in order to maintain a certain ink concentration, the ink thickness must be increased, resulting in an increase in the dot expansion rate.High Precision and High Density Printing
Therefore, in order to control the excessive expansion of the network, the water volume should be minimized as far as possible. High Precision and High Density Printing
In addition, in order to improve the emulsifying suitability of the ink, it is also important to select the fountain solution that matches the ink used.High Precision and High Density Printing
Compared with the color printing with the highest density above 2.0, in order to maintain the hierarchical reproduction of the dark part, the density range must be compressed. The density of traditional color plate making is about 2.0 for black plate; High Precision and High Density Printing
Magenta version and cyan version 1.4-1.5; The yellow version is about 1.0. High density printing adjusts the color separation curve to make its density range as close as possible to the density range of color printing (2.0). This is a method to improve the three-dimensional and thick feeling of printing.
Through the implementation of high-density printing, the dot expansion on the printing machine is measured, and the results are fed back to the plate making process to set the tone curve. For the printing plate, it is of course required to reduce its dot expansion rate. High Precision and High Density Printing
Therefore, in general, the printing plate for high-density printing and the printing plate for high-precision printing should have the same characteristics. High Precision and High Density Printing
The PS plate with water shall be a printing plate with good water storage performance. For the anhydrous printing plate, in order to improve the ink concentration, it is necessary to consider increasing the thickness of the silicone layer.
Although high-density printing can immediately obtain thick prints, the disadvantage is that the dot density of the main part of halftone prints becomes larger, In addition, the transferability of the ink printed after the multicolor part becomes poor (poor overprint), resulting in obvious roughness.
In particular, the thickening of the ink film promotes the turbidity and darkening of the ink. Therefore, in addition to having the same stable emulsification characteristics and increasing its concentration as the ink for high-precision printing, the ink used still needs to meet the following points:
Although increasing the thickness of the ink film can improve the coverage of the ink in each pure color part, the ink transfer in the recolor part becomes worse, which is easy to produce poor overprint. Therefore, it is necessary to adjust the viscosity balance between various inks without increasing the dot expansion rate.
The increase of ink density makes the ink turbidity become prominent, especially blue ink, which has an adverse impact on the color presentation of multicolor parts. In order to eliminate the turbidity factor as much as possible, it is necessary to change the hue of the ink.