Prevention of color cast in prints

Color deviation: It refers to the difference in color when the printed product is compared with the original or the proof.

Prevention of color cast in the process technology should pay attention to two reasons. (1) Arrangement of plate-making cable angles. (2) Arrangement of printing color sequence.

A: Arrangement of screen angle in the process of color plate making

In the process of color plate-making, if the arrangement of the screen angle is not correct, it will affect the printing color effect, and when it is serious, it will also produce a moiré pattern.

The current four-color plate printing is based on the primary colors of yellow, magenta, and cyan, which represent the ever-changing colors of the picture. The black version only aggravates the dark tone and plays a role in the skeleton. From the perspective of color rendering performance, yellow, magenta, cyan, and black colors have the weakest visual sensitivity in yellow, followed by magenta, cyan, and black. Since the line of sight of a person is particularly sensitive to a dot at a 45° angle, the dot of 0 or 90 degrees feels worse, and for a dot angle of 15 or 75 degrees, the human eye feels normal.

In view of the above factors, the angle of the screen of each color version should be determined according to the main color tone of the original. Therefore, the main color plate of the original should generally be made 45°, 75°, and 90° in other colors.

For monochrome halftone prints, we should use 45-degree outlets. However, for multi-color halftone prints, the angles of the various editions must be staggered. The commonly used color screen angles are as follows:

1. For two-color printing, the main color version or the dark color version is used with a 45° screen angle, a sub-color version or a light color version with a 15° screen angle.

2. For three-color printing, the main color or dark version uses a 45° screen angle, and the other two versions use a 15° and 75° screen angle.

3, four-color printing, the main color version with a 45 ° screen angle, the yellow version with a 90 ° screen angle, the other two colors with 15 ° and 75 ° screen angle.

According to the screen main color arrangement network line angle has the following several kinds of situations:

(1) If the main color of the screen is a red warm tone, it can be set as: 45° for the magenta version, 15° for the black version, 75° for the cyan version, and 90° for the yellow version.

(2) If the main color of the picture is a cool cyan tone, then: 45° for cyan, 75° for black, 15° for magenta, and 90° for yellow.

(3) If the main colors of the picture are black Chinese paintings, then: Black Edition 45°, Youth Edition 75°, Magenta Edition 15°, Yellow Edition 90°.

In the normal printing situation, according to the above method to arrange the network line angle, and then correctly arrange the color sequence, can effectively prevent the printed products from color cast. Make the print colorful and clear.

Second: The arrangement of printing color sequence.

In color printing, no matter what type of ink is used, whether it is a monochrome machine or a multi-color machine, there will be a color sequence problem. Only by properly arranging the printing color sequence can it be beneficial to realize the gray balance, fully reproduce the original color and level, and achieve the desired printing effect.

In multi-color printing, the order in which a color separation plate is overprinted on a substrate in a certain color order is called a printing color sequence.

Printing color sequence is very important, and its main role is threefold:

(1) correct color cast

Yellow, magenta, and blue three-color printing inks, regardless of the brand, have a certain gray component, more or less some of the color cast. The whiteness of the paper we use, the accuracy of the press, and the operation of the process will also have some deficiencies. This will appear color cast. Choosing a reasonable printing sequence can compensate for these deficiencies to a certain extent and correct the color cast.

(2) Display colors correctly

The combination of the three primary inks in different proportions will show millions of new colors. Different print sequences show different color effects. If the same printing plate is used, the same operation process will overprint magenta on yellow, or yellow on magenta, and the color effect they present is not the same. In the four-color screen printing, the dots of the dark tone portion are overprinted on the halftone dots, and the dots of the high light tone portion are printed on the blank portion of the paper. The effect of the displayed color is different due to the difference of the ink covering and the ink layer thickness. .

In four-color printing, yellow, magenta, cyan, and black can be arranged in 24 different color orders. The kind of printing sequence is good and there are no specific regulations. Appropriate arrangements must be made according to specific circumstances.

(3) Reflect overprinting

If the selected print sequence does not match the performance of the ink, problems such as color mixing, ghosting, and poor printing may occur.

From this, it can be seen that choosing the correct printing color sequence is one of the important measures for guaranteeing normal printing and obtaining the best printing effect.

The choice of printing color sequence generally follows the following principles:

1, according to the brightness of the three primary colors arranged sequence: the brightness of the three primary colors reflected in the three primary colors of the ink on the spectrophotometric curve, the higher the reflectivity, the higher the brightness of the ink. Therefore, the brightness of three primary colors of ink is yellow> cyan> magenta> black. The small first printing, the bright printing.

2. According to the transparency and hiding power of the three primary colors, the color sequence is arranged: the transparency and hiding power of the ink depend on the difference between the refractive index of the pigment and the binder. The ink with high hiding power has a greater influence on the color after the color stacking. As the overprinting of the printing ink, the correct color cannot be displayed and the good color mixing effect cannot be achieved. Therefore, the ink with poor transparency is printed first, and the transparency is strong.

3. According to the size of the dot area, the color sequence is arranged: In general, the area of ​​the dot area is small and the area of ​​the dot area is large.

4, according to the characteristics of the original arrangement of the color sequence: Each original has different characteristics, some warm colors, and some are cool colors. In color sequence arrangement, the color sequence mainly based on warm color is black, cyan, magenta and yellow; the color sequence mainly based on cold color is black, magenta, cyan and yellow. $Page break $

5, according to different arrangements of printing equipment color sequence

(1) Monochromatic machine color sequence: When the monocolor machine prints multicolor products, the ink transfer is wet stacking. When considering the color sequence, the ink viscosity can be placed in a secondary position.

In the case of better paper and ink quality, the general printing sequence is black, cyan, magenta, and yellow. When the paper quality is poor, the surface is rough, the tightness is low, and the ink absorption is strong, the color sequence may be yellow, magenta, cyan, and black. Due to the large area of ​​the yellow version, it can make up for paper defects. Make the printing effect better. In addition, the use of yellow, magenta, cyan, black sequence, is conducive to color change, easy to clean the ink roller, ink tank. Another reason why a monochrome offset press prints a yellow version is that human vision is insensitive to yellow dots, and even if a pale yellow color is printed, even if it is slightly overprinted, it is not easily visible to the naked eye. Facilitate the effect of four-color overprint.

(2) In the printing of the two-color machine, the second color and the third color are wet-overprinted. The printing of 1-2 colors and 3 to 4 colors is a wet and dry wet overprint. The printing color sequence of a two-color machine is alternately suitable for bright and dark colors. The large amount of ink is placed in the second color group. Therefore, the following are commonly used in printing. Printing color sequence: 1-2 color magenta-cyan or cyan-magenta; 3-4 color black-yellow or yellow-black, but also as needed. To emphasize a heavy color, such as green, it should be printed according to the magenta-yellow, cyan-black overprint color sequence, so as to obtain a better printing effect.

It is also possible to use black-yellow, magenta-cyan color sequences, which are easier to control.

(3) Four-color printing is wet and wet printing. To make the latter color ink transfer well to the ink layer of the previous color substrate, the adhesion of the ink should be reduced along the color sequence of the printing sequence. Otherwise, an inverse stacking will occur. Printing phenomenon. It is generally the first printing ink dark color sticky, the printing ink sticky bright color. The commonly used color sequence is black, cyan, magenta, yellow, or black, magenta, cyan, and yellow. While changing the color sequence, the viscosity of the ink should also be adjusted accordingly.

In four-color printing, yellow ink is printed in the last color, and there are three main advantages

(1) Since the yellow ink has good transparency, it is advantageous for the last color to inject enough light into the upper and lower ink layers to make the print more vivid.
(2) The yellow ink has a faster drying performance and a larger printing area. Putting the yellow ink on the last color not only prevents the crystallization caused by the rapid drying of the yellow ink, but also makes it possible to use it to print a large area, while also allowing (3) the yellow color to be arranged in the last color to facilitate the control of the yellow ink consumption. Always adjust the proofs.

6, according to the nature of the paper arranged color sequence: paper smoothness, whiteness, tightness and surface strength vary, flat, tight paper first dark, bright after printing; thick, loose paper, printed bright yellow Ink, dark after printing, because the yellow ink can cover off paper and powder and other paper defects.

7, according to the drying performance of the ink arrangement color sequence: Practice has proved that the yellow ink is nearly twice as fast as the magenta ink, the magenta ink is twice as fast as the black ink, and the black ink is the slowest. Slow drying inks should be printed first, and inks with fast drying properties should be printed. The monochromator protects the surface of the ink from crystallization, and is generally printed with yellow to facilitate rapid drying of the conjunctiva.

8, according to the flat network and the field arrangement color order: prints have flat screen and on the ground, in order to obtain good print quality, so that the ground printed flat, thick ink, colorful, generally flat printing network graphics, after printing the field.

9, according to the light and dark color arrangement: To make prints with a certain degree of gloss and add light-colored, the first printing dark color, after printing light color.

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