Ink performance testing method

The ink management mainly realizes the control of the color quality parameters of the ink through the detection of the hue of the ink, the coloring power and the light fastness, and eliminates the color shift from the source.

The quality of the ink directly affects the correctness and stability of the color of the printed product. The water-based ink used in flexographic printing has the characteristics of low viscosity and small pollution. The ink management mainly realizes the control of the color quality parameters of the ink through the detection of the hue of the ink, the coloring power and the light fastness, and eliminates the color shift from the source. Ink detection and related data can be provided by the supplier, but can also be detected by the printing company itself.

1, ink hue, tinting strength detection

Hue, tinting power is the basic item of ink detection, they have a great influence on the color of the ink. Hue is a specific feature of the ink color, optically corresponding to a certain wavelength, frequency of light, such as: red, yellow, blue refers to the hue of the ink. Coloring power refers to the size of an ink that affects the color change of another ink. When spot color inks are blended, when the hue of one of the original inks changes, the color of the spot color inks that are picked up will change. For example, when the hue of the original ink is yellowish than before, the spot ink that is prepared will have the effect of increasing the yellow color; if the coloring power of the red original ink is strong, it will have the effect of increasing the red color. When this color deviation exceeds a certain range, visual inspection can be found, leading to customer complaints. Therefore, to ensure the correctness of the hue of the printing ink and the stability of the coloring power, it is very important to control the color of the printed matter.

2, hue detection

For newly provided inks, the viscosity of the newly provided ink is generally adjusted to the viscosity of the upper machine, the printing machine is used for proofing, the ink color sample is printed out in the field version, or the ink is dripped a few times on the pressure-developing color wheel. Drag with a certain pressure and speed on the surface of the substrate and display a ribbon as a color sample. Observe the effect of these proofs. If the ink layer is even and smooth, the coloring is good, there is a certain luster, the ink is thick, and the color is the same as the standard color card provided by the supplier (which can be provided by the ink factory), then the hue of the ink is shown. Meet the requirements. Finally, a certain amount of ink for the detection may be sealed and stored as a reference wet color sample for the next hue detection.

For inks that have been used, the viscosity of the ink can be adjusted to an appropriate value, and a good sample can be made with the color wheel, which is compared with the qualified color sample or standard color sample retained by the previous printing, and the color hue can be initially detected. Another method is to place the detected ink with the wet color sample of the ink that has passed the last test. Several drops of each color are separated by about 1 cm on the color wheel, and side by side.

At this point, two adjacent ribbons will be left on the printing paper. Comparison of these two ribbons can more accurately determine whether the hue is the same.

3, coloring power detection

The coloring power of ink is determined by using white ink as the reference color sample, and the strength of the coloring power is determined by the degree of influence of an ink on the white ink. The test of coloring power is to add the test ink and the standard color ink in a small beaker, stir and then make a version, and then compare and judge the color strength of the ink against the standard tinting strength color sample. The specific approach is as follows:

10g of the test ink and 100g of standard white ink are added into a small beaker, and the mixture is stirred and evenly patterned with a color wheel. The color sample produced is compared with the standard ink color strength card provided by the supplier. If the ink is light, the ink color Weak, if the ink is dark, it indicates 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 test ink or the standard white ink. Ink may be lighter to increase the weight of the ink to be measured. For example, add 2 g of the ink to be measured in a small beaker. Stir well and then use the color wheel to paint. If it is the same as the standard color, press (10+2):100= 10: x calculation, you can launch x = 100 × 10 ÷ 12 = 83.3 (g), indicating that the color ink color strength is only 83.3% of the standard color ink, it can be said that weak 16.7g.

Ink darkness can be added to the weight of white ink, if you add 10g standard white ink in a small beaker and the color version of the printing plate is the same as the standard color card, then press 10:(100+10)=10:x to push out the =110(g), The coloring power of the ink to be measured is 110% of the standard ink, and it can also be said that it is 10g.

The above x represents the weight of the white ink when a certain amount of white ink is added into a 10g of the test ink after meeting the standard tinting power color card. That is, the tinting strength is measured by the amount of white ink.

There is also a comparison method for the comparison of wet colors, that is, to measure the coloring power of the ink to be tested and the wet color of the ink that has passed the previous test to detect the wet color on the color wheel. Similar controls. This detection method eliminates the disadvantage of having a color shift between the wet color samples and the dry color samples and has a bad influence on the evaluation of the actual results. Since all of them are wet color samples and are adjacent to each other, the contrast colors are convenient and the accuracy is higher.

After finishing the tinting strength and hue detection, remember to keep the wet and dry color samples when testing. In particular, the wet and dry color samples of the standard ink must be sealed and properly marked to prepare for the next inspection. When used. Because spot colors require color stability, the hue of the ink is required to be correct, and the tinting strength is required to be stable. The general standard is: ±10% can be acceptable, ±±5% is acceptable, and must not be too high or too low.

4, the detection of ink viscosity

The viscosity of the liquid ink is relatively low, the fluidity is relatively good, and the method for detecting the viscosity is also very simple, and only one viscosity cup and one stopwatch can be used to complete the detection of the ink viscosity.

The specific operation method is: First, the ink is stirred evenly, then the viscous cup is immersed in the ink, and then the viscosity cup is raised at a uniform speed. When the viscous cup has just been pulled out of the ink surface, press the stopwatch to measure the outflow of the ink. When the ink has just stopped, stop the stopwatch immediately. At this time, the time value on the stopwatch represents the viscosity of the ink, the viscosity is high, and the number of seconds is large; the viscosity is low and the number of seconds is small. Because the temperature is different, the viscosity of the ink will also change, so the general detection temperature is fixed at 25 °C.

It is worth mentioning that there is no obvious correlation between the temperature and the color of the ink, but there will be some impact on the performance of the ink when printing on the machine.

5, ink light resistance detection

The lightfastness of an ink refers to a property of the ink that maintains a stable color after exposure to light. Lights with poor lightfastness fade after a period of light exposure. Some prints meet the requirements when printed in a printing factory, and color shifts occur after a period of time at the customer's place. The reason for this is mostly because of this.

Here is a rough method to detect the light resistance of inks: Divide the color samples after printing or patterning into two parts, one part is placed in sunlight for about 4 hours, the other part is placed in dark and dark place; or the color samples are folded in half. After being placed in the sun, a part of the printing surface is placed facing up, so that sunlight is irradiated, and a part of the printing surface is placed under the backlight. After 4 hours, the color deviation of the two color samples was checked. If there is a significant color shift, the ink has a poor light resistance.

When a printing company purchases ink, it should require the ink supplier to provide a product with accurate hue and stable coloring power, and a certain amount of safety stock should be kept.

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