Six-color printing process theory and description (a)

In the past 10 years, four-color overprinting has had a great impact on screen printing. Some complicated design software and new screen-making methods have emerged. Digital prepress technology and printing equipment have also been greatly improved and improved. Can accurately predict the quality of the product, the product's reproducible printing has also been guaranteed. However, due to the limitations of the four-color printing mode and the screen printing method itself, it is not possible to obtain a color that is completely consistent with the original.

In the past, colored silk screen four-color overprint was completed by a monochrome printer. Only one color can be printed at one time, and then the second color is printed after drying, until all four colors are completely printed. This makes the control of the color very difficult to grasp. In recent years, due to the application of multi-color printing presses, the consistency and accuracy of color have been greatly improved. Initially there were two- and four-color printers, and now there are five-color and six-color printing systems.

Here, we will introduce the six-color overprint scheme in two parts.

Insufficient four-color printing

 Four-color overprinting is an economically and technically acceptable model. It is a universally accepted printing method that can also reproduce almost all colors. However, there are many technical defects in four-color overprinting.

Although image reproduction technology has greatly improved in recent years, four-color reproduction is still a less stable process, and it needs to control too many factors. What's more, it produces moire and dot gains in printing, resulting in the final image being either too flat or too contrasting. In addition, with the four-color process, some visible colors cannot be duplicated.

Therefore, four-color printing is difficult to carry out consistent quality control. On a press, the color may shift several times, even to a point where it is completely different. This is due to many environmental and physical factors, the main factors are: squeegee edge wear, printer temperature changes, screen tension changes, ink performance inconsistent (pigment accumulation and viscosity and rheological properties change) and so on.

The degree of color reproduction depends on the range of color gamut that the ink can print. From this perspective, four-color printing is also very limited.

The advantages of six-color overprint

The expansion of traditional four-color overprinting to six-color overprinting is a subject worthy of close attention and careful consideration. The six-color overprinting process is based on the traditional four-color overprinting and is obtained by expanding the standard four-color unit. However, unlike the hexagonal spot color process, hexagonal spot colors are based on CMYK with orange and green colors, and the six-color overprints described here still contain only four CMYK colors.

There are no two new colors added to the six-color system, but instead of the standard cyan and magenta ones, they use their lighter and deeper series respectively. Six-color overprint is represented by CMYKLcLm, where C and M represent dark cyan and dark magenta, and Lc and Lm represent lighter colors of the two colors. There are also CMYKcm or CcMmYK.

 Note that these names do not indicate the order of the colors; they merely indicate the hue of the colors used in the printing. This use of two different ink densities is called double-domain or two-color replication. It is a change in the new color reproduction method called "n-channel", where n is the number of colors used in printing.

 There are several important advantages to using two-color extended overprint inks. The biggest advantage is that it greatly expands the scope of the color gamut. Epson and several other inkjet printers and ink manufacturers are using a process similar to this six-color overprint to develop inkjet printers in hopes of achieving more realistic image colors. Inkjet printing has become a more popular digital replacement for film processors, and the use of lower-range inkjet printers can produce extraordinary results.

 We can improve the appearance by adjusting the intensity and density of the colors used in printing. The appearance effect is enhanced because the use of two colors reduces the contrast between colors. For example, when we have a very bright magenta and print the upper detail with a darker magenta, under bright magenta it may lose the darker point and enhance the image. This method of achieving the overall image effect by printing halftone dots in the details is clearly continuous in tone. POP display and other large designs used for close-up look can get better results from this method.

 Using a six-color process, not only can the image clarity and resolution be improved, but also the smoothness of overtones is better. Some of the more difficult to obtain colors such as flesh, grilled food, water, sky, chrome, and similar metallic colors can all be obtained by adding light tones in two-tone printing.