Screen printing ink performance testing, mainly 5 points!

May 24, 2021

The quality of ink directly affects the correctness and stability of the color of screen printing products. The water-based ink selected for flexographic screen printing has the characteristics of low viscosity and low pollution. The following is to share the ink management, which realizes the control of ink color quality parameters through five detection points. The content is for the reference of friends in the high quality packaging system.

Screen printing ink

Screen printing ink, also known as screen printing ink, usually refers to the ink used in screen printing. Like other types of ink, it is made by mixing and grinding with pigments, resins, solvents and additives. There are many kinds of screen printing inks, which can be printed according to different materials. This is also the special feature of screen printing process which is superior to other printing processes. Screen printing fastness generally depends on the selection of screen printing ink.

01Detection of ink hue and coloring power

Hue and coloring power are the basic items of ink detection, which have a great influence on the color of ink. Hue is the detailed characteristics of ink color, optically corresponding to a certain wavelength, frequency of light, such as: red, yellow, blue refers to the hue of ink. Coloring power refers to the extent to which one ink affects the color change of another ink. When distributing spot color ink, when the hue or appearance of one of the original ink changes, the color of the spot color ink will change.

For example, when the hue of the original ink is yellow, the spot color ink will have the effect of adding yellow; If the original red ink on the color power is too strong, there will be the role of adding red. When this kind of color deviation exceeds a certain scale, it can be found by visual inspection, resulting in customer complaints. Therefore, it is very important to ensure the correctness of the ink hue and the stability of the inking force for controlling the color of silk screen printing products.

02Detection of hue

For the new supply of ink, it is generally necessary to adjust its viscosity to the machine viscosity, use the screen printing machine proofing to screen out the color sample of the ink in the field version, or drop a few drops of the ink on the color developing wheel with the adjusted pressure, and drag the ink on the surface of the substrate with a certain pressure and speed to display a ribbon as the color sample. Observe the effect of these proofs, if the ink layer is smooth and uniform, the color is excellent, there is a certain luster, the ink color is thick and solid, the color is the same, the standard color card supplied by the supplier (which can be made and supplied by the ink factory) is basically the same, then clarify that the hue of the ink meets the requirements. Finally, a certain amount of ink for this test can be sealed and stored as the reference wet color sample for the next hue test.

For the used ink, the viscosity of the ink can be adjusted to the appropriate value, and the color sample can be made with the color developing wheel, which can be compared with the qualified color sample or standard color sample saved in the previous printing, so as to preliminarily detect whether the hue meets the requirements. Another way is to test the ink with the previous test of qualified ink wet color sample, in the development wheel about 25px away from each drop, side-by-side typesetting.

At this point in the master paper will leave two adjacent ribbons, the control of these two ribbons can be more accurate to determine whether the hue is the same.

03Detection of coloring power

The detection of ink coloring power is to use white ink as reference color sample, and judge the strength of a certain ink through its influence on white ink. The detection of color power is to take part in the ink to be tested and standard color ink in a small beaker, mix them evenly and then print the plate, and then compare and judge the strength of the ink according to the standard color sample. The details are as follows:

In a small beaker, take 10g of the ink to be tested and 100g of the standard white ink, mix them evenly, and then print the plate with the color developing wheel. Compare the color sample with the standard ink color card provided by the supplier. If the ink color is light, it indicates that the ink color is weak. If the ink color is deep, it indicates that the ink color is strong. If the ink color is basically common, it indicates that the ink color is qualified.

In addition, by adding the ink to be tested or regulating the component of white ink to detect the strength of color change. If the ink color is too light, the amount of the ink to be tested can be appropriately added. For example, add 2G of the ink to be tested in a small beaker, mix it evenly, and then use the color developing wheel to make the color sample. If it is the same as the standard color sample, then calculate according to (10 + 2) ∶ 100 = 10 ∶ x, and then x = 100 can be obtained × ten ÷ 12 = 83.3 (g), which indicates that the inking power of this color ink is only 83.3% of that of the standard color ink, or 16.7g.

If you add 10 g of standard white ink in a small beaker, the color sample of printing plate will be the same as the standard color card, and then the printing force of the ink to be tested will be 110% of the standard ink according to 10: (100 + 10) = 10 ∶ x = 110 (g).

The above X represents the amount of white ink in 10g ink to be tested after a certain amount of white ink meets the standard color card. In other words, the strength of the color is measured by the amount of white ink.

In addition, there is a wet color sample comparison method, that is to say, the wet color sample of the ink to be tested is the same as that of the qualified ink. The wet color sample is arranged side by side on the color developing wheel, and the wet color sample is compared after the color sample is made. This detection method eliminates the disadvantages of color deviation between wet color sample and dry color sample, which has adverse effect on the real result evaluation. Because they are all wet color samples and adjacent, the contrast color is convenient and the accuracy is higher.

After finishing the color power and hue test, remember to save the wet color sample and dry color sample, especially the standard ink wet color sample and dry color sample must be sealed and marked for the next test. Because spot color requires color stability, so the ink hue requirements are correct, color strength requirements adhere to stability, the general specification is: ± It is acceptable within 10% and is acceptable within 10% ± 5% or less is qualified, neither too high nor too low.

04Ink viscosity detection

Liquid ink viscosity is relatively low, liquidity is relatively good, viscosity detection method is also very simple, just a viscosity cup and a stopwatch can complete the detection of ink viscosity.

The detailed operation method is: first mix the ink evenly, then immerse the viscosity cup in the ink, and then put out the viscosity cup at a uniform speed. When the viscosity cup is just pulled out of the ink surface, press the stopwatch to watch the time and appreciate the outflow of the ink; Press the stop watch when the ink has just stopped. At this moment, the time value on the stopwatch represents the viscosity of the ink, high viscosity, large number of seconds; Low viscosity and few seconds. Because the temperature is different, the viscosity of the ink will change, so the general detection temperature is fixed at 25 ℃.

It is worth mentioning that there is no significant correlation between the concave convex temperature and the color of the ink, but it will have some impact on the performance of the ink when it is used in machine screen printing.

05Ink lightfastness test

Ink light resistance refers to the ink in the light to adhere to a stable color performance. Poor light fastness of ink through a period of light, will fade. Some silk screen products in the silk screen printing factory when the color meets the requirements, and through the use of customers for a period of time will produce color deviation phenomenon, most of the reasons lie in this.

This paper introduces a method to roughly test the Lightfastness of ink: divide the field color sample after screen printing or printing into two parts, one part is placed in the sunlight for about 4 hours, the other part is placed in the dark and dark place; Or fold the color sample in half and place it in the sunlight, part of the screen printing face up to let the sunlight shine, and part of the screen printing face down to backlight. After 4 hours, compared with the color deviation of these two parts of color samples, if there is a significant color deviation, the light fastness of the ink is not qualified

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