How to deploy some problems with spot color inks
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Why do you need to use spot color inks in printing?
1 The exact aspect of the hue. Although in theory, any color can be achieved by using the three primary colors + black color subtractive method on the printed matter by dot overprinting, but in many cases, due to various printing factors, such as ink balance, Overprinting effects, overprinting accuracy, and some human factors make it difficult to achieve the desired color on print. In particular, the saturation of color, the accuracy of hue, and the thickness of ink color, the effect of many spot color inks is difficult to achieve through dot folding.
2 Cost and process arrangement. If a large amount of the same color is used in the design of the product, such as green, then we will often use the green color of the yellow and blue shades as the spot color for the process selection, so that we can print in the spot color, so that we can print in the printing work. One process can be omitted to achieve the goal of reducing costs.
3 Customer requirements. In fact, the key to the problem is the customer's own requirements. With the development of packaging and advertising, more and more customers will require the printing factory to print in the specified color when printing their own products. The typical ones are some enterprises. LOGO, personalized business cards, product advertisements, and cross-page patches for flyers.
What are the basic requirements for blending inks?
There are three basic requirements when formulating printing inks:
1. The hue of the ink is accurately matched;
2. The printing suitability of the ink is reasonable;
3. The ink quantity is accurately adjusted.
What are the requirements for the light source when dispensing ink?
Since the color development of the ink is formed by selective absorption and reflection of the illumination light, there is a certain requirement for the light source for illumination when color matching (or colorimetric). Usually the color matching is good during the day (especially for the purpose of advertising), the sunlight from the north can not be directly into the ink. If at night, a standard light source is used, the color temperature of the light source is high and the green component is heavy; the color temperature is low and the red component is increased.
In the ideal case of ink color matching, satisfactory results will be obtained when the Twilight and D light source (6500K), or ASTM standard light source (7400K) and tungsten light (2900K) are used together. Another important factor in addition to the color temperature of the source is illumination. Color printing uses 1000 lux as the appropriate illumination. The above standard lighting is achieved by two lamps with 40W fluorescent lamps at one meter.
What is the principle of the deployment of spot color inks?
The dispensing of the spot color ink is based on the original color sample and is formulated according to the principle of the three primary colors of the ink. The physical effect exhibited by the pigment of the ink is called the subtractive method, that is, when the pigment exhibits a certain color, it means that the pigment achieves selective absorption (subtraction of color light) for various colors in the white light spectrum.
The color change law of the three primary colors of the ink is as follows:
Magenta + yellow = red, magenta + blue = purple,
Green + yellow = green, product + green + yellow = black,
Therefore, the mixing of ink pigments is a weakening of light, which is a phenomenon of color reduction. The more pigments are mixed, the darker and nearly black the final color.
The principle of coloring of spot color inks is that ink pigments exhibit effects through the principle of color reduction. For example, when the yellow and blue inks are blended in the same amount, since the pigment in the printing ink is the main body of the ink color forming, the particles are very small, and the insoluble suspension having a diameter of 0.01 to 0.5 μm, we print the prepared ink on the paper and do Partially magnified, when white light is irradiated on the ink particles in three cases, when white light is irradiated on the yellow ink particles, it absorbs blue light and reflects red light and green light; when irradiated on the blue ink particles, it absorbs Red light, reflecting green light and blue light; illuminating on yellow and blue mixed particles, it absorbs red and blue light and reflects green light.
Due to the equal amount of yellow and blue ink, the two opportunities are equal, and the reflected light is as follows:
W-B-R=G;
W-B=G+R
w-R=B+G
The combined effect of reflected light is:
3W—(2B+2R)= 3G+R+B=w+2G
(white light is w, green light is G, blue light is B, red light is R)
So the color of the two inks blended is green. If the yellow ink and the blue ink are not equally blended, then the two conditions cannot be equalized, and the yellow ink makes the ink blended yellow, and the color is blue. After mastering the basic laws of color change of the three primary colors, you can cite the colors of various originals.
What is the color difference? What is the color difference allowed for ink blending?
The so-called color difference is the color difference between two colors. If this color difference is quantized, it is called the color difference. The method of calculating the color difference is different according to the color defined by different color spaces, but the calculation method has many similarities. If the color represented by the CIE1976 (L*a*b*) color space is used, the color difference formula is:
△Eab*=[(△L*)2+(△a*)2+(△b*)2]1/2
Where △Eab* indicates chromatic aberration
What is the role of understanding the calculation of color difference? The calculation of color difference is very important for the standardization of ink preparation. We can usually use the color density meter or colorimeter to qualitatively analyze the color and objectively describe the subjective color, which will be reduced in the process of color description and adjustment. Dependence on the human eye, more use of instruments to make color matching more accurate.
An NBS color difference unit is approximately five times the human visual limit resolution. What is the range of color difference between ink blending colors to be a reasonable range? Generally, depending on the printing activity, there will be different standards, and it is also determined according to the quality requirements of the product, the accuracy of the measurement together, and the measurement conditions. It is generally considered reasonable to control the color difference within the range of 5 to 6 color difference units. range.
Why do you sometimes have a very accurate ink that will change color after printing?
There are many reasons for this discoloration. One is that the ink itself is chemically reacted due to mixing or printing, and thus causes discoloration. This requires us not only to have a certain understanding of the hue of the ink, but also to Ink pigments have a certain understanding to avoid such discoloration, such as gold light red ink should not be diluted or used with orange ink to prevent fading.
The other is that the color difference occurs due to the difference in the spectral structure of the light source during printing and the subsequent observation of the ink, which involves the problem of metamerism. The so-called metamerism phenomenon is that two objects have different spectral distributions, but under certain lighting conditions, it is possible for a particular standard observer to display the same color, ie, have the same tristimulus value. However, in a different lighting condition (such as the ordinary indoor light source used in the preparation, and the daylight source used in the sample), the metachromatic ink and the original may not match.
Does the printing condition affect the color matching?
The type of printing press or wet overprinting, the printing color sequence also affects the color rendering effect. For example, ink made of opaque pigment must be printed first.
The structure and distribution of the layout and text, the lines of the lines, the dots and the field, the distribution of the patterns is sparse and dense, and the ink should be formulated according to different situations. For example, the full-version layout should reduce the viscosity of the ink a little. If it is a dot and a line, the external oil or the "0" varnish should be added appropriately to increase the viscosity of the ink. On the other hand, it is also necessary to consider how much the blank portion of the picture and its distribution are related to the corresponding color ink in order to adapt to changing the density of the color ink.
Need to pay attention to those in the ink preparation process?
※ Everyone knows that the color of the ink to be used should be as small as possible if the color tone meets the requirements. That is, the mixed color of the two colors can be used to indicate that the ink of the third color is not used. Because according to the principle of color reduction, the more colors used in color matching, the more the ink components are, and the saturation will decrease after mixing.
※ The ink color of the ink sample or the scratched ink layer directly affects the color of the ink. Under normal circumstances, if the ink layer is thick and the brightness is low, the color is darker. Different printing methods, such as embossing or lithography, solid or mesh, wet overprint or dry overprint, the thickness of the ink layer is different, and the color is also different. It is necessary to estimate the hue of the print of the print to determine which hue of ink to use to adjust, and at the same time judge which color is dominant, as the base ink, and the other ink as the toner. When blending the spot color ink, it must be based on the basic ink, supplemented by the color ink, so that the amount of ink is not too much.
※ The ink color sample should be darker than the original color. Because the offset ink is mixed with the dampening solution and the ink is dried, the ink hue will become lighter. There is also a correct hue, ink depth (saturation), which can reduce the amount of ink, which is beneficial to the control of offset ink balance;
※ Consider the nature of the substrate paper, such as whiteness, absorbency, smoothness, etc. If the nature of the paper is far from the paper quality of the original, it is necessary to analyze the specific situation, such as Kodak Red, but there are secondary users. It is required to use the pink stencil paper to print the Kodak logo. If the original ink-based method of Kodak Red is used, the printed color effect will be dark and gray, and the whole hue will be far from the original color. We can directly use the red ink and The effect of printing on paper and color is similar to that of Kodak Red.
※ It is necessary to consider the environmental impact of the color sample, to avoid illusion of color, in the color discrimination should cover the surrounding color, single observation, so as not to cause color shift.
* When the ink layer is obtained by the extension method and the scraping method, the thickness of the ink layer that masters the spot color ink is substantially similar to the thickness of the ink layer of the original color sample.
How to control the amount of ink adjustment?
The basic principle of the amount of ink control is that the amount of ink to be adjusted should be slightly more than the actual amount of ink required at the time of printing. If the amount of ink transferred by the ink is too large, it will cause waste; if the amount of ink is less than the actual required amount, the hue of the second ink adjusted during the redeployment is difficult to achieve with the previous one. The hue is exactly the same, which affects the quality of the product. The following factors should be considered when determining the amount of ink in actual work:
1. The amount of printing;
2. Type and surface properties of the paper;
3. The size of the printed graphic image;
4. The amount of ink tinting strength and the size of the ink specific gravity:
5. Printing speed and printing pressure;
6. The temperature of the printing workshop;
7. The number of times the ink roller and blanket are cleaned in the middle of printing, the minimum ink amount for normal ink infusion, and the like.
The amount of ink adjustment is difficult to calculate with a specific formula and can only be estimated empirically. Generally, the comparison can be made by referring to the situation listed in the table below (the printed paper is a offset paper, ordinary screen printing).
Ink type yellow ink magenta or blue ink black ink
Number of inks (g) 500 500 500
Number of printing (Zhang) 1000～2000 2000～3000 3000～5000