In the current printing, in addition to the common four-color printing, there are six colors, eight colors, or even more colors of printing. Four-color printing Due to overprint and ink balance control problems, it is not easy to achieve an ideal copy of the bird's-eye view. Therefore, it is sometimes necessary to use some spot color printing. Spot color printing can print colors that are not normally printed by the four-color process or badly printed colors. Spot color printing can not only solve the problem of hue of the product, but also can meet the quality requirements of innovative design, and the balance of ink and water in printing is also relatively easy to grasp.
1 Analysis of the concept and characteristics of spot color printing
Spot color printing refers to a printing process that uses a specific color ink other than the yellow, magenta, cyan, and black color inks to copy the color of a document. Spot color inks are specific color inks that have been pre-configured by the printer or produced by the ink factory. Such as fluorescent yellow, pearl blue, metal gold silver ink and so on. For each spot color of a print, there is a special color plate correspondence at the time of printing. Although the color cannot be accurately represented on a computer, the color of the color on the paper can be seen through the standard color sample card. , such as Pantone color matching system to create a very detailed color sample card. Since spot color printing is not synthesized by four colors of CMYK, it is prepared in advance. Therefore, the use of spot colors can make the colors more accurate. Spot color printing has the following features:
1) Accuracy. Each spot color has its own fixed hue, so it can guarantee the accuracy of the color in the printing, thus largely solving the problem of color transfer accuracy.
2) "Field". Spot colors generally define colors in solid colors, regardless of how light they are. Of course, spot colors can also be screened to present any shades of spot colors.
3) Opacity. Spot color ink is an overlaying ink that is opaque and can be covered.
4) Wide color gamut. The color gamut in the spot color library is very wide, exceeding the RGB color gamut, not to mention the CMYK color space, so a large part of the color is not reproduced with the CMYK four-color printing ink.
2 The necessity of spot color printing
The vast majority of current color printing uses CMYK four-color inks for printing. However, in order to achieve certain special effects in packaging printing, spot color printing is often used.
1) In order to print on the printed matter some colors other than the color gamut of CMYK four-color printing ink. The color gamut of CMYK four-color printing inks is significantly less than the visible color gamut. The effect designed on the computer is often not reflected in the printed matter, so it is necessary to use spot color ink to print the hue specified by the customer, which is more used in packaging printing.
2) To make up for the lack of printing process. Due to the errors in various processes in the overall printing process, equipment maintenance, operating environment, human error, and mechanical wear and tear, it is difficult to achieve uniform results even at the time of printing. At this time, we can use the full-page spot color (ie, In fact, instead of dot printing, it is easier to obtain uniform large-area color patches. In addition, sometimes in order to be able to clearly represent fine texts, such as fine-grained mixed-color graphics or invert white lines, spot color processing is also often used to make fine lines perform well.
3) To solve several defects of CMYK four-color color printing. The density of four-color printing inks is only about 1.6, which can not reach such as photo density (2.0), reversal film density (2.8), etc. In addition, dots printed in highlights are incomplete or missing; moreover, because of the ink color Insufficient degree, turbidity is too high, can not show thick and bright colors, so that some inter-color or complex color looks dirty; there are special colors such as fluorescent color, metallic color can not be expressed with CMYK. In order to make up for these deficiencies of the CMYK four-color printing process, a spot color printing process must be adopted.
3 spot color ink deployment
There is a growing number of products that use spot color inks, and the quality of spot inks determines the quality of the final product. The deployment of spot color inks is to use computer or artificial means to reconcile one or two or more inks together and add certain auxiliary materials to meet the printing needs and color requirements. The ink preparation mainly includes two aspects. On the one hand, it refers to the adjustment of ink printability, including the adjustment of ink viscosity, adhesiveness, fluidity, and drying; on the other hand, it refers to the ink color deployment. The color of the ink must be dispensed with the standard light source D65 (if it is daylight, it can be done in a sunny north window). Spot color inks, especially demanding spot color inks, are basically formulated at the ink factory.
The deployment of spot color inks is based on the color of the original and is based on the principles of the three primary colors of the ink. The mixing of colors is a process of color reduction, and the more colors are added, the darker it appears. For this reason, it is preferable to use three primary colors or basic colors when matching colors. In the case that the hue meets the requirements, the type of ink used should be as small as possible, that is, a mixture of two colors can be used, and the third color ink should not be used because the color reduction method is The principle is that the more colors are used in color matching, the more black components are, and the less saturated and vivid the mixed colors are.
When the ink is formulated, the color sample is analyzed first. In the analysis of color samples, it is necessary to make clear as much as possible whether the original document is mainly printed on dot printing or on-site printing. If dot printing is the main method, the ink should be focused on the same color when the ink is blended; if the ink is mainly printed on the spot, the ink color can be focused on the same face color; if the two are combined, the ink color when the ink is blended is the same. The complexion must be taken into consideration.
4 What kind of product is suitable for spot color printing
For dark, large-area color patches, a four-color printing process may require the superposition of several colors of high-number dots, and the ink layer is too thick to be easily stained on the back. With spot color printing, only a single color printing process is required. The color is not easy to appear dirty on the back. With the four-color printing process, some parts of the graphic text may be synthesized by several colors; and using the spot color printing technology, the corresponding parts only print one color, which avoids the possibility of overprinting errors.
From the perspective of economic efficiency, it is mainly based on the use of spot color printing technology can not save the number of overprint. Because reducing the number of printing can not only save printing costs, but also can save the cost of prepress production.
If a product has both a color-graded picture and a large-area background, the color-graded picture part can be printed in four colors, and the large-area background color can be printed in spot colors. The advantage of this is that the four-color printing part can correctly restore the picture color by controlling the solid density, and the under color part can obtain the solid uniform effect of the ink color. This method is often used in the production of high-end packaging products and stamps.
5 spot color printing applications
Due to the characteristics of spot color printing itself, such as spot color printing solves the problem of color transfer accuracy, and its color gamut is larger than the color gamut of four-color printing, so spot color printing has been widely used in some printing. application.
1) When printing trademark packaging and promotional materials such as cigarettes, wine, cosmetics, pharmaceuticals, and daily necessities, spot color printing is often used to ensure that the hue of printed products is accurate and consistent.
2) In anti-counterfeiting printing, spot color inks can be used for printing, which has a certain anti-counterfeiting effect.
3) In the map printing, due to the process, in order to obtain the ideal color rendering effect, the characteristics (lots of spot colors, up to a dozen) must often be used in a large number of spot color printing.
4) In some special printing, spot color printing is often used to express its special effects.
6 Several Problems to Be Noted When Using Spot Color Printing
1) The unity of spot color names. In different software, the names may be different for the exact same two colors. For example, FreeHand named PANTONE 1F5 PANTONE 1F5CVC or PANTONE 1F5CVV and PageMaker named PANTONE 1F5CV. In this way, when FreeHand graphic objects are placed in PageMaker, the same color will have three names. When the color separation is output, three printing plates will be generated, causing output errors. Therefore, if the data file needs to be used in more than two kinds of software, before the integrated color separation output, it must be noted that the use name of the same spot color must be unified. The more common method is based on the name of the color in the distribution software, and the name of the same spot color is renamed as a unified name in the palette of various software.
2) Spot color screening angle. In general, spot colors are printed in the field and rarely used in dot processing. Therefore, the spot color screening is rarely mentioned. However, when using a light-colored screen, there are problems with spot-screen dots. If there is an overprint area between the spot color of the outlet and the color printed by other outlets, the issue of spot color screening must be considered.
3) Conversion of spot color to printing four colors. Many designers often use the colors in the spot color library to define colors and perform coloring when they do graphic design. In color separation, they are converted into CMYK printing four colors. At this time, pay attention to three points: 1 spot color gamut is larger than the four-color printing color gamut, in the conversion process, some spot colors can not be completely true, but will lose some color information; 2 must be in the output of the option "special "Color conversion to four colors" in the choice, otherwise it will lead to an output error; 3 CMYK color numerical ratio displayed next to the spot color number is not the proportion of printing CMYK four-color, that is, the proportion of four-color ink and can not print and reproduce The effect of the spot color (if you can use no spot color). Therefore, if printed at this ratio, the color of the product and the required spot color will have a significant difference in hue.
4) Spot color trapping processing. Since spot color printing is different from four-color printing (four-color printing inks generate mutual colors by overprinting each other, that is, the ink has transparency), a color is not generally generated by superposition of two spot colors. Intuitively, It will get a bad color effect (of course there are exceptions, such as design in the intentional use of spot color overprint processing to produce the required, superimposed blend of the third color, this third color is full, heavy and real, such as: The color yellow is embossed with the spot color modulated red, two colors superimposed to produce a steady deep red, often used as a book cover, etc.), so the definition of spot colors, generally do not use overprint (Overprint) method is used to let Keep away. In this way, when using spot colors, as long as there are other colors beside the spot color pattern, proper trapping should be considered to prevent the occurrence of defects on the white side.
Source: "Printing World" Author: Cao ago