How to determine the color sequence of plastic film flexo?

In the flexographic color printing, how to arrange the color sequence properly is an important task for process technicians. An important role of printing is to copy the manuscript artistically. This requires the printer to have a certain level of artistic appreciation and ability to grasp the changes in color. Misordering the color sequence may lead to color deviations, color mixing, and reverse printing failures in the printed matter. Scientific arrangement of the color sequence will make the color of the printed matter closer to the original, and even strengthen the atmosphere of certain colors, so that the printed matter is structured and the dots are clear. Accurate overprint, true color, natural, and coordinated.
First, the problem of the correct order of flexo printing should pay attention to

Printing color sequence refers to the sequence of color printing in multicolor printing. The color sequence is different, and its color rendering effect is also different.

In color printing in flexo printing, yellow (Y), magenta (M), cyan (C), and black (K) four-color plates are generally used, and superimposed in a certain order. Theoretically speaking, four-color printing can have 24 different types of printing colors, but in fact, due to the difference in printing color sequence, the color rendering of printed products is not the same. Reasonable printing color sequence will make the picture color closer to the original, and even strengthen the atmosphere of a certain color, adjust the level of the picture, soften the tone, and facilitate overprinting. Therefore, in the case of color printing, especially package printing, more than four colors or spot colors, and a full version, attention should be paid to the arrangement of printing color sequences.

In the determination of printing color sequence, it should be noted that, the flexographic printing color sequence and relief printing color sequence is basically the same, but do not use lithography color sequence. For the four-color screen version of the printed manuscript to analyze the pattern color, the commonly used color sequence is yellow, magenta, cyan, black. However, some people choose the color sequence of yellow, black, magenta, and blue. Because the water-based ink has high color density, strong hiding power, thick ink layer, bright color and low light transmittance. Four-color screen printing version of the color sequence can not be freely exchanged.

The color sequence printed in the flexographic printing is a variable, and there are many factors that affect the color sequence of the printing. Especially for the multicolor screen, the determination of the color sequence of the printing should fully consider various factors, according to the specific conditions and the printed products. The quality requirements are reasonably determined. In general, the following aspects should be emphasized when determining the color sequence of printing.

1. Color rendering and printability

Printing color sequence affects the color rendering effect. There is only one possibility when printing the first color, ie, the ink layer is directly printed on the surface of the printing material, and the color rendering effect is relatively stable. When the second color is printed, there are two possibilities. That is, some of the dots are directly transferred to the surface of the substrate, or some dots are printed on the dot of the first color (overprinting). In both cases, the color rendering effect will change. When the third color is printed, there are three possibilities. That is, some dots are directly printed on the surface of the substrate. Some dots are printed on the ink layer of the first or second dot. Some dots are printed on the first and second dots. Overprinted ink layer. If dots are printed directly on the substrate, dot gain may occur. If the dots are overprinted, the bottom layer of the ink will have three conditions: moderate dryness, insufficient drying, and excessive drying. In addition, defects such as dot gain or color cross-linking and vitrification will occur, which will cause difficulties in printing. Therefore, the greater the number of overprints, the more complex the problems that arise. For printability, due to ink overprinting will produce several possibilities, one is that the underlying ink is dry and moderate; the second is that the underlying ink is excessively dry, resulting in vitrification, the dot network shrinks after the new ink layer is printed, and even the underlying ink cannot be printed. , there is a printing failure.

2. The principle of color on the screen

In the high-profile part of the printed product, the dot arrangement is mostly in parallel, and the color sequence has little effect on the color mixing of the high-profile part. During the transition from high tone to intermediate tone to dark tone, the color rendering principle gradually increases, so that on the same screen, different color sequences cannot be reproduced in different parts. According to the law of color change, printing color sequence has little effect on high-profile color mixing, and has a great influence on dark tone.

3. Ink transparency

The ink has a certain hiding power. After the ink is overprinted on the ink that is printed first, it will affect the color rendering. Good ink with good transparency. After the two colors are superimposed, the color light of the ink layer below can pass through the ink layer (subtractive color mixing) to show the correct new color. In color inks, since the transparency and hiding power of each color ink have a certain difference, even if the same color plate is printed with a different color sequence, different color rendering effects will be obtained. For example, if the yellow ink used is clear yellow, then the order of the four inks transparency is: yellow> magenta> cyan> black. At this time, the ink with poor transparency should be printed first, and the ink with good transparency should be printed.

4. Characteristics of the screen

In general, the first printing with a small dot area, and the large printing with a large dot area, the printing plate of the main color on the screen can be printed after or printed. Operators should choose the color sequence of printing based on a thorough analysis of various factors.

5. Measurement of the influence of printing color sequence on the color rendering effect

In color overprinting, the overprinting rate is generally used as a measure of the effect of the printing color sequence on the color rendering effect, that is, the overprinting ratio=[(the solid density of the 1st and 2nd color overprinting) and the first solid color density of the first color). Monochromatic solid ground density] × 100%. Obviously, different printing sequences have different overprinting rates, resulting in different printing effects. For spot color printing, the order of lightness and darkness is generally used, and the dark ink can be brightened after the overprint. For spot colors that are printed using a stacked-color method, the secondary colors are printed first, and the primary colors are printed afterwards.

Second, determine the color order of flexo printing

General principles

Since printing color sequence has a great influence on the printing effect, how should the color sequence of flexo printing be determined? In general, the following principles can be followed:

1. Arrange the color sequence according to the content and characteristics of the original

Printing is a means of designing layouts and texts, and the emotional components of each color are also different. Therefore, the arrangement of the color sequence must first consider the content and characteristics of the manuscript. Designers often have chosen the tone of layout color when designing graphic layouts. This tone represents the overall feeling of the overall tone and becomes the dominant color when printing. In terms of color, red, orange, and yellow are the warm colors; green and blue are the cool colors. Due to the hiding power of the ink, it is generally based on the warm tone of the first printed black, cyan, after the print magenta, yellow; to cool the first printing of the main red, after the cyan. For example, people want to see it mature.

The watermelon pods are red, and they do not want to see the purple and green color of the prints. Different color sequences have different color cast effects. Therefore, the color of the screen color needs to be enhanced, and it can be printed on the last color.

For ordinary color originals, the printing plate (such as black plate) with small dot area can be printed first, and the rule of printing plate with large dot area (such as yellow plate) can be used to determine the printing color sequence, ie pressing black → blue → The magenta → yellow sequence is printed.

2. Determine the color sequence according to the pros and cons of ink transparency

In general, the current ink transparency is best in yellow ink, followed by magenta ink and cyan ink, and the worst is black ink. Therefore, the printed color sequence is printed in black, then printed in blue or magenta, and finally in yellow.

3. Determine the color sequence according to the characteristics of the screen

The main color version of the screen should generally be placed on the last or second last printing, and other color versions are printed on the first or second color to facilitate the reproduction of the features of the screen. For example, a large-area landscape dominates the picture (cool tone as the keynote), with black, magenta, cyan, and yellow as the sequence. Arrange black prints first and use black to outline the outlines to facilitate overprinting of other colors. Transparent yellow last print, can be used to adjust the brightness of the entire screen to form a shiny, bright colors. People generally dominate the picture (warm tone) using black, cyan, magenta, and yellow sequences. The ink with poor transparency is printed first and will not cover other colors. After the magenta and yellow prints, the characters' faces are ruddy, with rich colors and vivid effects.

4. Determine the color sequence according to the features of the plate making process

Since the effect of the moire is to be minimized in the halftone printing, the angles of the screen lines of the adjacent two color groups at the time of printing differ by at least 30, which is favorable for preventing the defects such as color shift and moire. In addition, when printing on the mesh version and the field version, you can print the mesh version and print the ground version first.

5. Determine the color sequence according to the ink absorption properties of printing materials

When the ink absorbability of the printing material is large, the first color is printed with a high-tech ink first. For example, poor quality paper, considering its whiteness, low smoothness, fiber loose, poor ink absorption, easy to lose powder off hair, you can print yellow ink first, to make up for the above-mentioned defects of the paper. When printing at night, due to the recognition ability of human eyes, weak color ink with low lightness should not be arranged in the first color printing. The order of brightness of the ink is: white <yellow <orange <green <blue> <red <blue <violet.

6, arrange the color sequence according to the difficulty of overprinting

In the flexographic printing of paper, due to the objective defects such as paper deformation and stretching, the main colors of the printing products with higher printing requirements should be arranged in the adjacent two color groups for printing. Such as two-color machine, can be arranged in the same unit to complete a print, to avoid problems due to paper stretching. Large areas of the field can be arranged for post-printing to avoid problems such as smearing during the transfer of paper. Although objective defects such as plastic deformation and expansion are better than paper, it is also an objective reality. In addition, the monochromatic machine is superimposed on the second color after the first color is dry, and the multicolor machine is a process of “wet pressing wet”. Therefore, the degree of ink and the amount of ink under the ink should be controlled, that is, a large degree of arrangement is provided. The ink is printed first, and the ink with low viscosity is printed. This is crucial, otherwise it will cause adverse effects of reverse printing.

7. Reference ink price arrangement color sequence

At present, domestic ink prices are the most expensive with magenta ink, followed by yellow ink and blue ink, and black ink is the lowest price. Therefore, in order to reduce the printing cost, on the premise of satisfying the printing quality requirements, the cheap black and blue ink are printed first, the high-priced magenta ink printing plate and the yellow ink printing plate are printed behind, thus saving costs.

8. Multi-color machine overprint color sequence

Since the printability is reduced from the first color printing to the last color printing, the dark color version can be printed in the first color, and the bright color version can be printed in the final printing.

Due to the characteristics of flexo ink and the influence of related factors, the above principles can be used to determine the color sequence of printing. However, due to different printing contents, equipment, substrates, and features to be expressed, the arrangement of printing color sequences is different. Not the same. In addition to the above general principles, the arrangement of printing color sequence should be properly considered from an artistic point of view. This can make the printed matter more artistically appealing and satisfy readers' needs.

According to people's experience from printing practice, the following two points can be considered in determining the printing color sequence: When printing in multi-color dots, the printing color sequence that can be considered is yellow → magenta → blue → black or yellow → black → product Red → blue; if it is a color block overprint, the large color block should be printed first, after the small color block printing.

Third, how to determine the color sequence of plastic film flexo printing

Reasonable determination of printing color sequence is an important process link in plastic film flexo printing. Since the printing ink for plastic film printing has the distinction between the printing ink and the printing ink, and the printing process of the printing on the surface and the printing on the inside is not the same, so the color sequence of the printing is also determined to be different. To sum up, the differences in the composition and operation of the surface printing ink and the printing ink mainly include the following aspects:

1. The difference between the link material

The linking material of table printing ink is mainly polyamide resin, which has good adhesion and good gloss, but it is not suitable under high temperature conditions, and the composite fastness is poor. Non-cooked printing inks are mainly made of chlorinated polypropylene, and nitrocellulose and vinyl chloride-vinyl acetate copolymer resins are also used abroad. The high temperature cooking steam printing ink binder material is polyurethane, adding a certain amount of hardener, two liquids, cross-linking reaction.

2. The difference between the choice of solvent

The solvent used for the surface printing ink is mainly xylene and isopropanol. In general, printing ink solvents are mainly toluene and ethyl acetate. The high temperature cooking ink is mainly based on ethyl ketone and ethyl acetate. The printing ink solvent is suitable for high-speed printing, the solvent has a relatively high volatility, and the residual solvent is particularly low.

3. The difference in wear resistance

Because the polyamide resin has good flexibility and large elasticity, the added auxiliaries improve the wear resistance and are more solid when colliding with foreign objects. The chlorinated polypropylene resin used for printing inks has particularly good rigidity and poor wear resistance. Because it is printed in India, the wear resistance requirements are correspondingly lower.

4. The difference between the use of accessories

Table printing ink and ink in the printing due to different links, its auxiliary additives and additives are not the same, table printing ink often add water-soluble malic ester, kiwi fruit acid ester, to improve adhesion, increase luster, increase viscosity. India inks are also added with various types of pigment dispersants, enhancers, defoamers and other additives.

5. The difference of printing process

The printing process in the printing process is the same as the general plate making process. However, when the plate is printed, the image on the printing plate is reversed. After printing, it is a positive image. The printed image is a positive image and the image is reversed after printing. The drying speed of the surface printing ink is slow, and the drying speed of the ink inside the printing is faster than that of the surface printing.

According to the differences in the composition and use of printing inks and printing inks, the general color sequence in plastic flexo printing is:

(1). Printing sequence of table printing process

The “printing” of plastic film is based on white ink as the laying background, which is used to set off the printing effect of other colors. It mainly has the following

Advantages. First, the plastic white ink has good affinity with PE and PP films, which can improve the adhesion of the ink layer of the printed product. Secondly, the white background is total reflection, which can make the color of the printed product more vivid. Third, the printing of the background color can increase the thickness of the ink layer of the printing product, so that the printing product layer is more abundant, and has a rich sense of embossed visual effect. Therefore, the printing color sequence of the plastic film printing process is generally determined as: white → yellow → magenta → blue → black.

(2). Print color sequence of printing process

In order to obtain the same visual effect as “table printing”, the printing color sequence of the Indian printing process should be the opposite of “table printing”, that is, the white ink background is placed on the final printing so that the white ink background can be seen from the front of the printing product. To set off the role of various colors. Therefore, the printing sequence of the Indian printing process should be: black → blue → magenta → yellow → white.