Four-color printing process on a monochrome printing machine

For the obvious cost, quality and productivity reasons, most four-color printing is done on a multicolor press at a time. Completing four-color printing on a monochrome press can be a challenge. However, printing four-color products on a monochrome press also has certain advantages. For example, since the printing method is dry-stamping, and the double dot expansion caused by the blanket and the transfer roller is less, the ink superimposition effect is a clear advantage. However, due to obvious defects, the method of printing four-color printing products using a monochrome machine has not been recognized. The main disadvantages are as follows: When the relative humidity in the air changes, the paper size lacks stability. The completion of registration has brought a lot of obstacles. After many transmissions, more dust will accumulate and contaminate the blanket. Finally, the final result of the composite color cannot be seen between the two prints. Note: The ink overprint (wet overprint or dry overprint) mentioned here is the ability of an ink to transfer and adhere to another ink. Trapping refers to the amount of overlap between two adjacent colors so that the paper will not leak white when it cannot be fully registered. The ink sequence when performing four-color printing on a single-color or two-color machine One of the most significant concerns when printing in four colors on a monochrome or two-color printer is what ink sequence is used. For four-color products, there are 24 different possible combinations when deciding the order of printing colors. The printer needs to pick one of the best from these choices. If four-color printing is performed on a four-color printing press, the most common and recommended order of use is magenta, cyan, then yellow, and finally black; or the order of CMYK. This order can reduce the unnecessary color difference brought about in the multicolor superimposition. Chromatic aberration is the amount of unwanted contaminants that a monochromatic ink possesses from the superimposed second color ink. For example: When you superimpose 100% yellow blocks and magenta blocks, you want to get a red tone, but you don't. The actual result is an orange tone because the magenta ink usually contains about 50% of a mixture that crosses the yellow ink. By printing the yellow ink on the magenta ink, the yellow ink will mix with the underlying color during the wet-overprinting process, resulting in an overprint tone that is slightly yellower than ideal. Similarly, cyan ink also contains 25% magenta ink. This is why a 100% cyan and magenta superimposed color patch does not produce the desired blue color, but looks a little purple. The yellow ink is relatively clean and pure. When performing four-color printing on a two-color printing press, the color of the first printing process is very important. They are yellow and black. The contrast of yellow is very small and difficult to see alone. Use a blue filter to observe the yellow color on the white paper - for example KODAK Wratten #47 - to make the yellow three look black. In fact, the same filter is used for PMT (PMT) Drum Scanners or CCD (Charge Coupled) Platform Scanners and Densitometers. It is because yellow color is hard to see that yellow should be controlled by means of a reflection densitometer. Black does not affect the tone of a color, it only makes the color darker and dirtier. Adding black in CMY three-color printing only increases density to extend the dynamic range and establish contrast. Black is not only used to achieve gray balance in neutral grey. The gray balance is achieved through halftone dots on the screen. The magenta and yellow dots are smaller, while the blue dots are larger. The typical neutral gray balance consists of 65% blue dots and 50% magenta and yellow dots. By the way, no matter if black color is added to any color, the final result is to deepen the color. In turn, no matter how white color is added to any color, the color is eventually reduced. The color tone remains unchanged. Because the screening allows the white paper to be displayed and mixed with the color to make the color look lighter. To revert back to the problem of printing color sequence, to prevent any possible back side sticking problems, in the first printing process, first print yellow and then black. If any problem of back sticking due to ink film thickness due to plate coverage or incorrect ink stickiness occurs, yellow will stick to black and be ignored. It is recommended not to change the color sequence because this is overprinting yellow and black, causing the yellow to become dirty. In the second printing process, the two colors printed are very important magenta and cyan. Magenta and cyan bear the task of producing sub-tones, such as blue sky and water. The cyan in the second printing process also partially assumes the task of generating green grass and leaves when mixed with yellow. Magenta is also partly responsible for generating skin color and foods like bread and meat when it is mixed. When four-color printing is performed on a monochrome printing machine, the suggestion is simple to print black first. Don't use old information Some people still rely on outdated information to determine the order in which inks are printed, and raw materials like ink, paper, plates, ink rollers, and fountain solutions have been greatly improved, so time should change and progress. To change some operations. For example, yellow ink was not as transparent as the current yellow ink. Therefore, the yellow ink must be printed first. Now the situation has changed a lot. People usually choose such a sequence: First, print the color with the highest coverage of ink, until the color with the lowest coverage of the final printing ink, so that the ink can be overprinted better. Ink overprinting is a phenomenon that is affected by various different but related factors. Overprinting is due to the absorbency or resistance of the paper (compared to non-coated), the speed of the printing press (comparison of fast web with slower sheet-fed presses), residence time or between the units Distance, and the effects of ink viscosity, binder ratio (also called filler) and ink film thickness (IFT). An ink tension meter is one such device that can measure the viscosity of an ink. When discussing overprinting, these factors must be considered. In general, monochrome and dual-color printers have much smaller dot gains than multi-color printers. This is because many sources of outlet expansion are the shape of outlets being destroyed. Call this special dot gain double or ghost. When a circular dot or other shape dot is no longer symmetrical but stretched, ghosting can occur, just like an egg or a comet's tail. The double image occurs when an already printed dot is printed slightly on the next set of blankets. The next rotation cycle will be printed with a faint ghost next to the darker dot. Under the magnifying glass, the double image is most easily seen at the delicate high light dot. Of course, some color bars have visual indicators, such as the star index of the GATF or the concentric circles of the RIT. All of these visual indicators are very sensitive to ghosting and dot gain. If you encounter a large number of dot gains in multi-color printing, one solution is to drag a plate and see if dot gains are reduced. If this is the case, dot gain comes from the subsequent blanket contact. . The most modern sheet-fed presses printed products that were relatively sharp and tidy, with only 18% of the dots expanded. The sooner the colors are printed, the more often the dot gains, because the more times the color passes through the blanket, the larger the ghost and double shadow. Printers without rollers are more prone to dot gain. We previously mentioned that the disadvantage of printing on a single color press is that the final result of matching color cannot be seen during each printing process. If one of the colors is not printed correctly, the ink density is too dark or too bright, or if the dots are enlarged too much, there is nothing to be done. On multi-color printing presses, the transfer of paper is complete and it is very easy to evaluate the color and correct it. Do you consider a method of simulating the final color representation between two printing processes? If you buy or use a multi-layer overlay proofer, you can superimpose each individual color layer to predict what the color will look like when printing is complete. This practice is quite good. Since the final color result must be known after the final printing process is completed, the press operator must evaluate each intermediate color more with the aid of a densitometer. Some multicolor printer operators have now become too lazy to use densitometers because they can see the final composite image. For monochrome printers, reflective densitometers must be used to monitor and control the printing process as needed. This procedure constrains the work to some extent and can produce less color difference than the eye-visible color throughout the production process. Generally, the color density specifications for sheet-fed printing on coated paper are: 1.30 for magenta, 1.40 for magenta, 1.00 for yellow, and 1.80 for black. This is regular data. Each manufacturer needs to regulate them to meet specific conditions. Also, the conventional tolerance is 0.05 up and down no more than the target value.