Ink color matching requirements and ink dispensing skills

In the actual screen printing, there are two kinds of color printing methods, one is dot printing, the other is spot color printing. Dot printing can print colorful and layered prints, but the colors are softer and generally used in the advertising industry. Spot color printing can print thick and bright color effects, and does not require color separation, but with multi-color overprinting, color spot color printing is achieved by spot color ink for spot color printing, so there are also no The small printing industry adopts spot color printing, but due to the ever-changing spot colors of printing, it is impossible and unnecessary for ink manufacturers to manufacture various hue inks, and often only a few basic color inks are produced. This is for printing companies. In this case, it is necessary to perform ink color matching to reproduce the original color. Here's an overview of the palette of inks.

First, the basic knowledge of color

1. The relationship between color and light. The physical basis of color light is light, and colors must exist in the presence of light. If there is no light, there will be no color, and it will be dark, so there is only light.

2. The three primary colors of light. In everyday life, the natural colors we can see are red, orange, yellow, green, cyan, blue, and purple. In the entire visible light, the longest wavelengths we most sensitive to are red, green, and blue, and orange. The three colors of yellow, blue and cyan only occupy a very narrow position between the three colors of red, green and blue. Actually, they are also obtained by mixing red, green, and blue light, and red, green, and blue light. However, it cannot be mixed with other shades. So we call red, green and blue the three primary colors of light.

3. Shade mixing.

(1) Concept: The blending of shades is an additive method (combined effect of two or more shades of light, called additive method.

(2) Mixing rules: The primary light is added by equal amounts.

Red light + green light = yellow light

Green light + blue light = blue light

Blu-ray + red light = magenta light

Chromatic light trichromatic and chromatic light coloration

If two colors of light are mixed in a certain proportion to become achromatic, the two colors of light complement each other.

Blue + Yellow = White

Green + Magenta = White Light

Red + blue = white light

That is, the complementary colors of red, green, and blue light are yellow, magenta, and cyan.

Chromatic light trichromatic and chromatic light coloration

4. Mix of pigments. The mixing of the colorant is a subtractive method, which reflects a phenomenon that a certain color is obtained by subtracting some color light from white light. When the pigment shows a certain color, it means that the color material is selective to certain color lights in the white light spectrum. Absorption, minus the results of some white light, such as: yellow, that is absorbed blue, purple, reflected red, green, red + green = yellow, that is, yellow.

Subtractive substances are divided into reflectors and transmissives. People can observe colors from the front of colored objects. They are called reflectors. The color behind them is called transmissive.

5. The three primary colors of pigments. According to the mixing rules of the colorants, each primary color of the colorant should reflect the color light of the two spectral regions, and the three primary colors of light, red, green, blue, and light, can be obtained by a mixture of three methods: magenta, yellow, and cyan. For the three primary colors of pigment, it is the basis for mixing other colors, which are consistent with the complementary colors of the three primary colors of light.

Second, the principle of color

1. The mixing of colors is a process of color reduction. The more colors are added, the more shades of color are subtracted, and the darker they appear. For this reason, it is preferable to use three primary colors or basic colors when matching colors. There are 1330 kinds of colors that can be allocated with the three primary colors. If you add black, you can get as many as 14640 kinds, that is, almost all colors can be adjusted. For example, the color on the PANTON color card. The mixing rules for the three primary colors of pigments are:

Magenta + yellow = red

Yellow + blue = green

Magenta + blue = blue

The primary colors are added together, and equal amounts of yellow, magenta, and green phases are added in black.

The mixing rule for the equal amount of inter-color and inter-color is:

Red + Green = Red Green (yellow grey)

Green + Blue = Green Blue (Cyan)

Blue + Red = Blue Red (red-gray)

2. In the color cards of various brands of ink, all are marked with the three primary colors, basic colors, and standard colors. When color matching, why use three primary colors or basic colors instead of standard colors? This is because the three primary colors and the basic colors are composed of a single pigment, and the standard colors are the basic colors. Each of the standard colors is derived from two or more pigments, and the colors formed by the standard colors cannot Satisfies the 3 attributes of the color. That is, the hue, brightness and purity are not as good as those of the three primary colors or the basic colors. The more gray and dark the color is, the older the color is, and the less vivid it is.

(1) Hue: It reflects the inherent color appearance of color, and is the main difference between color and color. That is, a certain wavelength of light represents a certain fixed hue. The hue is different, and the wavelength of the light wave is also different. The color measurement is represented by H.

(2) Brightness: Reflects lightness and darkness. There are two kinds of brightness for color, one is the degree of lightness and darkness between each color. This is due to the different wavelengths of light waves of different colors. After reflection, the degree of stimulation to the human eye depends on the tennis film. From the green to the entire visible spectrum, Yellow is the highest and lightness is high, so people are very sensitive to green, from orange to red, blue to purple, the brightness decreases; the other is the color of the same hue, the height is different, that is, they appear to be deep or dark due to different brightness. There are shallow, the more white, the greater the brightness.

(3) Purity (saturation): It reflects the degree of color close to natural color. The closer to natural color, the higher the purity, and vice versa. In the measurement of computer color separation, it is represented by C.

$Page break $

Third, the color steps

When you get a sample (sample), you should do it from the following steps:

1. According to the material of the substrate, determine which type of ink to use and then select the brand of ink.

2. According to the sample draft, first select the main color, the main color is selected, then see what color, that is, the secondary color.

3. Color Matching: Remove the main color after thorough mixing and then add the secondary color. In the addition of the secondary color, be careful, add a little bit more, and then use the same parameter when the color of the deployment is close to the sample. The mesh number, the same screen thickness as the photosensitive layer, and the same scratch hardness, etc.) were tested until it passed.

4 ink sample preparation process method points:

(1) Analyze the sample, determine the main color and sub-color (color head), select the ink with the percentage of a certain weight with the reference color (three primary colors).

(2) In the color matching process, the principles of light and dark (white, yellow, orange, red, purple, blue, cyan, green, and black) are used. In particular, colors with strong coloring power can only be added to quantitative 70% to 80%. When the hue is close, it should be added with care and accurately weighed. The main color is added in 100 g units and the secondary colors are weighed in 0.1 g accuracy.

(3) Toning is to adjust the main color first, when the main color is close, then adjust the second color, when it reaches 90% or so stop, proofing (must pay attention to uniform deployment, stirring full). The light color is generally a little deeper than the sample draft, while the dark color is the wet ink that is lighter than the sample draft because the light color is lighter than the wet ink, and the dark color is generally lighter after being dried.

(4) Record in detail the usage data, name, code number, etc. of each color ink.

(5) Comparison of viewing sample and manuscript: Note that printing of the same kind of process parameters on the same material as the sample (sampling) shall be performed in a dedicated color box or a standard box without direct light.

(6) Correct and compare and confirm.

(7) Magnify deployment.

Note: Different types of inks cannot be mixed. Spot color solvents must be used to adjust the viscosity.

5. Determination of color:

(1) Light source: The same color has different effects under different wavelengths of light, so it is recommended to use standard light sources when detecting colors. Standard light sources include D65, D50, and A.

(2) Computer detection system: Because different colors have different wavelengths, the computer detects the color according to the perceived wavelength. The general computer film is the CIELAB system. As shown in the following figure, the colors can be determined based on the measured L, A, B, and calculated. ΔE, we can know the color difference between the color and the standard color. However, L, A, and B can only measure the color, cannot measure the color saturation, and have an error of 17% to 30% with the actual color. If coupled with L, C, H systems, first set the saturation, and then measure the L, A, B values ​​and L, C, H values, this time, the deviation from the actual color is only 7% to 17% of the error, and then When ΔE is measured, there is only an error of 0 to 3%. Therefore, only a complete inspection system can measure high-quality colors.

(3) different light sources, measured L, A, B values ​​are different, different standards derived E is also different, and now there are two international standards, one is the British standard, namely CMC, which requires all colors E the same; one for the Swiss standard, different colors E different.

(4) When comparing colors, color is best used in grey, white in white, and black in matte black.

6. When the adjusted ink is printed, the color is influenced by screen printing, scratching, and printing materials. Therefore, when printing proofing, the color proofing parameters should be the same as the customer's requirements for the screen parameters and substrates.

Fourth, screen printing ink color problems

1. There is a difference between color cards and user-determined colors because currently used color cards and color matching systems are provided by the offset printing system. Therefore, when the printing parameters change during the screen printing process will cause color changes, fine-tuning processing is still required. The amount of ink applied affects the color of the ink. The ink ink is gradually increased in the order of plain printing, gravure printing, embossing, and silk screen printing, as shown in the following table. Therefore, the printing ink in the three-primary color screen printing is very badly printed because each variable in the screen printing process affects the ink layer. Thickness, which affects the color of the print.

Several printing methods of ink thickness and transfer rate

Printing method Average ink layer thickness (U) Transfer rate (%)

Plain printing 0.7 to 1.4 30 to 50

Gravure 1.0 30～50

Embossing 8.0 50～60

Silkscreen 6.0 to 100 90 to 100

2. The appearance of color

The appearance of the color is affected by the transmittance, reflectance, and foreign matter (that is, the two colors match well with the light source, while the other light source does not match the phenomenon), observation conditions, lighting, ink layer thickness, and ink The effects of variables such as opacity, overprint, and substrate properties.

3. Impact of substrates

Substrate surface finish, handling, ink absorption and surface color.

4. Ink thickness

Thickness of ink can cause color changes. Thickness of the ink is affected by the diameter of the screen mesh, stretching tension, type and thickness of the screen. In addition, the appearance and hardness of the squeegee, the pressure of the squeegee, the speed of the squeegee, the angle of the squeegee, the distance between the screens, and the thickness of the ink Different pressures, speeds, shapes, and types of presses have different ink thicknesses.

5. Changes in stencil tension and other factors cause changes in hue

6. Standardization of light sources and observation conditions

Observation room with a dedicated light source. With a spectrometer, it can be measured that each color has its own spectral curve.

7. Chromatic aberration: that is, different colors have different color differences, which can be measured by a spectrum detector. The color difference that can be distinguished by the human eye is 1 DE, the color difference of the sample output by the computer is 2 DE, the yellow color has 3 DE between it and the target color, and only 0.5 DE is acceptable between the gray and its target color.

8. When the ink containing 100% of color, the three primary colors have their own different meshes, and the specific parts of the highest color density of screen printing are: Yellow (Y) 200-240 mesh, Magenta (M) 200-240 mesh, Cyan (C) 180 to 200 mesh, because the three primary colors are not