High-grade ceramic decal paper fine screen printing technology (2)

The setting of the percentage of net printing decal paper bottom nets

In the decal paper printing, outlets play the role of restoring the color and tone of the original. The dots created by the drawing through the color separation screen are copied and made into thousands of high-grade flower papers. How can we ideally copy high quality paper that is close to the original or even exceeds the artistic quality of the original? One of the keys is the correct setting of the percentage of the dots of the various colors in the color separation mastering. The factors influencing the percentage setting of the ceramic screen printing decals on the bottom of the paper are the copy characteristics of the dots, the printing characteristics, the printing characteristics, and the screen printing process.

1. The role of outlets

The high-grade fine ceramic screen printing decals produced by the separation color-hanging plate making process not only have the bright and bright color of ordinary screen printing decals with solid color blocks and lines, but also have rich layers, delicate, soft and strong three-dimensional effects. Artistic effect. This artistic effect is attributed to the role of outlets. The size of AM sites is measured as a percentage of their area per unit area. Dots of different sizes, large and small, form a series of dark-to-light tone levels, and colorful hues form a beautiful picture. Due to copying, printing and printing, the tone and the order of the original document are reproduced by the dot pitches of 100 lines, 120 lines, and 133 lines per inch, so that rich colors on the manuscript can be reproduced and reproduced on the decal or even obtained. Art improvement. How can you ideally copy a decal applique that is close to the original or exceeds the original artwork? The base plate making is the basis for printing. First of all, it depends on the proper handling of the color base level in the color separation bottom plate making, that is, the correct setting of the percentage of the bottom halftone dot.

2. Determination of outlets

When a net-printing paper mill receives a copy of a paper that is to be copied into a floral paper, the process design must be performed according to the coloring effect of the ceramic paint according to the color on the original before the separation, and it is determined which of the several colors to reproduce. The color should be arranged with a percentage of the number of outlets, and so on. Then according to this setting, the color dot screen blanks of each color are produced by color separation screening.

However, in the series of processes from the bottom plate to the printed paper, the dots on the bottom plate have undergone multiple transfers of printing and printing. After each transfer, the percentage of outlets will change more or less. At the same time, screen printing uses a certain pressure to leak ink from the screen mesh to the substrate. The wire diameter of the screen and the opening degree of the screen affect the penetration of the ink, and the screen printing value of the screen is The scope makes special demands. Only by understanding these changes and special requirements, find out the rules, and master it, and use it to provide basis for setting the percentage of color separation bottom nets.

3. Network changes

In order to more intuitively understand the formation of dot images on the separation master, the photo separation process is described. Photo separation is achieved through screen blocking, separate shooting or copying. The screen consists of uniformly arranged black dots and transparent dots. Since the black point's point type is a kind of dark halo virtual darkness point at the center, at the same time, in the shooting process, the light beam passing through the aperture and the transparent point of the screen tends to be the strongest in the center of the aperture and the transparent point. The weaker the edge light that goes to the aperture and the clear point, the corresponding dot also constitutes the density where the center is darkest and the blackness of the edge portion is gradually reduced. This density condition increases the variable factors of the dot size in exposure and development, increases the activity, and increases the restrictions on the performance of the current photosensitive material and the conditions of exposure and development. When printing, the dots cannot be made dark to light. Transfer unchanged. During the process of copying from the original to the large version, the number of prints, dozens, or even hundreds of bottom designs must be copied together according to the maximum effective printing area of ​​the printing press. The dots on the bottom copy must go through the process of copying. Repeatedly copying many times, even if there are only slight changes in the dots at the time of copying, as the number of copying increases, this change is also shown. The ideal dot copy feature is a straight line, and the actual copy effect often shows a curve (as shown in the figure. 1).

The more curved the curve, the greater the change in dot area. The amount of change depends on various factors such as the photosensitive material used and the operating conditions at the time of copying.

The use of computer-controlled laser imagesetters has made it possible to control the variable factors in the copying of the dots, and the change in the dot area percentage has also been improved.

The area will also change when the screen is transferred. The ideal printing characteristics should be the percentage of the dot on the base plate and the percentage of the dots that are printed on the plate. In other words, the characteristic curve should show a 45° straight line. In fact, due to the inflection of the bottom dot type and the refraction generated when the printing light passes through the bottom plate, as well as the limitations of photopolymer performance and lighting conditions, there are changes in stretch and compression at the high and low ends of the dot percentage. High-end outlets are easy to expand, and low-end outlets are easy to reduce (Figure 2).

When printing dots are transferred, the ink is printed on the paper by pressure. Because the ink layer has a certain thickness, the ink also has a certain degree of fluidity, the dots will expand around, the percentage of dots is different, and the circumference of the dot is different. The actual area is enlarged. Not the same. In terms of outlet expansion rate, 50% of outlets have the longest circumference and the largest area of ​​expansion. In terms of visual effects, more than 50% of the outlets, the gaps between the dots and the dots, are small and slightly enlarged, giving a very clear impression. The actual printing characteristic curve in Figure 3 shows that with the increase of the percentage after printing, the expanded area gradually increases to 50%, and the area expands the most; after 50% of the dots, the expanded area gradually increases with the percentage. cut back. The dot gain rate varies depending on the printability of the ink and the operating conditions during printing. For 133-line fine dot printing, taking into account the coarse ceramic pigment particles, in order to enhance the printability of the ink, often use thin varnish, or slightly increase the proportion of some of the ink varnish, the ink will be thin, After the printing, the dot area has been expanded more than ever.

Since the variation of outlets in copying, drying, and printing varies according to specific conditions, it is necessary to use the technical means and operating conditions of the unit in order to grasp the rules of copying, printing, and printing at the time of printing. Through actual operation, repeated testing, find out the actual characteristics of the copy, drying, and printing of the unit, and understand the expansion and reduction of outlets at the time of transfer. When setting the size of the base screen, adjust the percentage of the base screen according to these variations to achieve the desired printing effect.

(to be continued)