Plastic gravure printing is a common printing method. Due to the good color reproducibility, realism, strong stereoscopic effect, easy to carry and beautiful appearance of the finished bag, it is widely used in various flexible packaging, such as food packaging, medical packaging and other fields. In the printing process, no matter what printing method, whether it is multi-color or monochrome printing, the primary problem encountered before printing is the color matching of ink. No matter how bright the ink, if the operator does not understand some ink properties and color matching knowledge, the mixed ink can not achieve a satisfactory appearance and the level of quality that should be. The blending of ink colors is a vital part. Some large-scale enterprises also have special blenders. I have been engaged in the flexible packaging industry for many years. Now I have compiled the relevant opinions on the coloring process and I hope to help my colleagues.

1 color matching principle

Any color is represented by three characteristics of hue, brightness and saturation. The above three characteristics must be considered in the color matching process. In the ink color matching process, the ink type should be selected according to the actual printing process, the thickness of the ink layer, the printing substrate, and the like, and the gloss, hue, tinting strength, hiding power, etc. of the ink itself should be considered.

1 gloss. Gloss can be measured either by instrument or by naked eye. Usually in the color matching process, only the naked eye is observed. For special cases, it must be measured with an instrument, such as a chromatograph. Gloss is actually the ability of the ink printing sample to reflect light in the same direction after being irradiated with light. Its direct contrast to the printed appearance is a very important indicator. At the same time, when selecting the ink, it is necessary to distinguish whether the ink itself is a bright, semi-light or matte ink. It should also be considered whether the same type of ink is used. If the printing ink is ink-printed (chlorinated polypropylene resin type) or surface-printed (polyamide resin) ink, it must be blended with the same ink to avoid mixing errors and cause unnecessary loss.

2 hue. It is the basic feature of color and is used for qualitative differences. When color matching, the first thing to consider is whether the hue is consistent. The detection method is usually observed and compared by scraping.

The specific way to observe the hue is:

1 On a flat glass coloring platform, take a standard sample and the color sample at a distance of 1 to 2 cm.

2 Take the scraping paper and tile the glass stand, then take the coloring ink, scrape the sample with a glass rod and compare the results. (Figure 1) The comparison of the color sample results involves two important factors:

1 opacity. The degree to which the ink covers the background color, and the better the hiding power, the worse the transparency. Transparency High and Low Shadow II is directed towards the efficiency of ink color registration and the extent to which it is affected by the printed substrate. Generally, the dark ink hiding power is stronger than the light color. For example, the blue is lighter yellow, and the ink hiding power is good, and it is closely related to the ink itself. For example, the thickness factor is usually related to the thickness of the titanium dioxide particles, and the particles are thick and covered. The force is not good, the printing is easy to agglomerate; the particles are fine, the hiding power is good, the surface is even, smooth and delicate. White inks generally require a diameter of no more than 15 m, and other color inks may not exceed 1 2 la m.

2 tinting strength. A method of indicating the level of ink concentration. The measurement is to take a certain amount of color ink, mix with a certain amount of standard white ink, and compare with the standard, the intensity of the coloring power reflects the degree of mixed color of the ink. Through the color identification (scraping paper scratching experiment), the difference in gloss, hue and hiding power of the ink sample and the standard sample can be compared. The specific method is as follows: standard ink is placed in the upper left corner of the smear paper, and color ink is placed in the upper right corner. Make the scraper at a nearly vertical angle to the scratched paper, and lightly flatten the standard and color matching inks to be compared. After the ink surface is dry, under a certain light source, judge the difference in gloss between the two, and observe the appearance of the entire color ( figure 2). Black and color inks are usually white smear, while white inks are black smear. When observing color samples, it is best to compare them under indirect indoor light sources during the day, and should not be exposed to direct sunlight. It is recommended to use in the evening observation: “Color fluorescent tube and color temperature 5000~200. K. You can also use homemade mixed light source: 2 blue fluorescent tubes, 3 6500K400W fluorescent tubes, 6 100W tungsten lamps, and fix them in It can be used inside a special cover, which is mainly convenient for viewing color samples."