Ink management mainly realizes the control of ink color quality parameters through the detection of ink hue, tinting strength and lightfastness, and eliminates color deviation from the source.
The quality of the ink directly affects the color accuracy and stability of the printed product. The water-based ink used in flexographic printing has the characteristics of low viscosity and little pollution. Ink management mainly realizes the control of ink color quality parameters through the detection of ink hue, tinting strength and lightfastness, and eliminates color deviation from the source. Ink testing and related information can be provided by the supplier, or can be tested by the printing company itself.
1. Ink hue and tinting strength detection
Hue and tinting strength are the basic items of ink detection, and they have a great influence on the color of the ink. Hue is a specific feature of ink color, optically corresponding to a certain wavelength and frequency of light, such as: red, yellow, blue refers to the hue of the ink. Coloring power refers to the size of one ink affecting the degree of color change of another ink. When mixing spot color ink, when the hue or color of one of the original inks changes, the color of the spot color ink will change. For example, when the color of the original ink is yellower than before, the prepared spot color ink will have the effect of increasing yellow; if the coloring power of the red original ink is strong, it will have the effect of increasing red. When this color deviation exceeds a certain range, it can be found by visual inspection, which leads to customer complaints. Therefore, it is very important to control the color of the printed matter to ensure the correctness of the hue of the printing ink and the stability of the coloring power.
2. Hue detection
For the newly provided ink, generally adjust its viscosity to the viscosity of the upper machine, use the printing machine to proof, print the color sample of this ink on the solid plate, or drop this ink on the pressure-adjusted color development wheel. Drag on the surface of the substrate with a certain pressure and speed to display a ribbon as a color sample. Observe the effect of these proofs. If the ink layer is even and smooth, with good coloration, a certain gloss, and the ink color is solid, the standard color card provided by the same supplier (which can be provided by the ink factory) is basically the same, it means the hue of the ink Meet the requirements. Finally, a certain amount of ink for this test can be sealed and stored as a reference wet color sample for the next hue test.
For the inks that have been used, adjust the viscosity of the ink to a suitable value, use the color wheel to make excellent samples, and compare it with the qualified color samples or standard color samples retained in the previous version to check whether the hue is consistent. Another method is to put the wet color samples of the tested ink and the inks that passed the previous test on the color wheel at a distance of about 1 cm, and arrange them side by side.
At this time, two adjacent color bands will be left on the plate-making paper, and the two color bands can be compared to accurately judge whether the hue is the same.
3. Color strength test
Ink coloring power detection uses white ink as a reference color swatch, and judges the strength of the coloring power by the degree of influence of an ink on the white ink. The test of coloring power is to add the ink to be tested and standard color ink in a small beaker, stir it evenly, and then make the plate, and then compare and judge the color strength of the ink against the standard coloring color sample. The specific practices are as follows:
Add 10g of ink to be tested and 100g of standard white ink to a small beaker. Stir it evenly and then use the color wheel to print the plate. The color sample is compared with the standard ink color strength color card provided by the supplier. If the color of the ink is light, it means that the ink is colored Weak, if the color of the ink is dark, it means that the coloring power of this ink is strong, if it is basically the same, it means that the coloring power is qualified.
In addition, the strength of the change in coloring power can be detected by increasing the weight of the ink to be tested or standard white ink. Lighter ink color can appropriately increase the weight of the ink to be tested. For example, add 2g of the ink to be tested in a small beaker, stir well, and use the color wheel to make a good sample. If it is the same as the standard color sample, press (10 + 2): 100 = 10: x calculation, it can be derived that x = 100 Ã— 10 Ã· 12 = 83.3 (g), indicating that the color strength of this color ink is only 83.3% of the standard color ink, it can also be said to be weak 16.7g.
If the ink color is too dark, the weight of the white ink can be added. If 10g of standard white ink is added to the small beaker and the color sample is the same as the standard color card, then 10: (100 + 10) = 10: x launch = 110 (g), It shows that the color strength of the ink to be tested is 110% of the standard ink, which can also be said to be 10g stronger.
The x above all represents the weight of the white ink when 10g of the ink to be tested is added to a certain amount of white ink to meet the standard coloring power color card, that is to say, the strength of the coloring power is measured by the amount of white ink.
In addition, there is a wet color sample comparison method, that is, the wet color sample of the color strength test of the ink to be tested and the wet color sample of the previously determined qualified color ink are arranged side by side on the color wheel. SAMPLE CONTROL. This detection method eliminates the disadvantage that there is a color shift between the wet color sample and the dry color sample, which has an adverse effect on the evaluation of the real result. Because they are all wet color samples and are close to each Other, the color comparison is convenient and the accuracy is higher.
After finishing the color strength and hue test, remember to keep the wet and dry color samples during the test, especially the wet and dry color samples of the standard ink must be sealed and stored and marked for the next test When used. Since spot colors require stable colors, the hue of inks is required to be correct, and the tinting strength is required to remain stable. The general standard is: acceptable within Â± 10%, qualified within Â± 5%, and neither high nor low.
4. Detection of ink viscosity
The viscosity of liquid ink is relatively low, and the fluidity is relatively good. The method of detecting viscosity is also very simple. Only one viscosity cup and one stopwatch can complete the detection of ink viscosity.
The specific operation method is: stir the ink evenly, then immerse the viscosity cup in the ink, and then lift the viscosity cup at a uniform speed. Press the stopwatch when the viscosity cup is just pulled out of the ink surface to watch the ink flow out; when the ink just has a cutoff point, press the stop stopwatch immediately. At this time, the time value on the stopwatch represents the viscosity of the ink. The viscosity is high and the seconds are large; the viscosity is low and the seconds are few. As the temperature is different, the viscosity of the ink will change accordingly, so the general detection temperature is fixed at 25 â„ƒ.
It is worth mentioning that there is no obvious correlation between the temperature and the color of the ink, but it will have some impact on the performance of the ink when it is printed on the machine.
5. Light resistance test of ink
The light resistance of the ink refers to a performance of the ink to maintain a stable color after seeing light. Ink with poor light resistance will fade after a period of light exposure. Some printed materials meet the requirements when printed in the printing house, and the color deviation phenomenon will occur after being used at the customer for a period of time. The reason is mostly due to this.
Here is a method to roughly check the lightfastness of ink: divide the solid color sample after printing or plate-making into two parts, one part is exposed to sunlight for about 4 hours, the other part is placed in a dark and dark place; or the color sample is folded in half After being placed in the sun, part of the printing face is placed upwards, let the sunlight shine, and part of the printing face is placed downwards in the backlight. After 4 hours, compare the color deviation of the two parts of the color sample. If there is a significant color deviation, the light resistance of this ink is unacceptable.
When purchasing printing inks, printing companies should require ink suppliers to provide products with accurate hue and stable coloring power, and a certain safety stock should be kept, so as not to break the material.
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