Fine halftone screen printing analysis (2)

The particle size of the solids, especially the particles, should also be well controlled. The particles of the colorant are too large and may clog the mesh when the screen is opened. This changes the color density (lighten) of the printed image. In UV ink printing, especially if the screen used is flat on one side (on the side of the substrate). Because the ink may stay in the mesh.

The tendency of the ink to dissociate should also be well controlled. It will also change the density and color value of the image and cause the ink to adhere poorly to the printing material during the printing process.

Other variables that need to be controlled, such as color quality, should be controlled in two ways:

The first is the quality (purity) of the color material. The main color material contains other noise components as little as possible. It should be as transparent as possible to reduce the problem of “main colors”.

Second, adjust the density of the base color according to the copied image.

These densities are not pre-determined and should be adjusted between 0.95 and 1.35 depending on the image to be copied (if printed on some POP/POS boxes or posters at bus stops, or even higher).

Controlling these variables is not just a technical issue. It is more of a matter of artistic perception. It is largely an uncontrollable variable because the perception of images cannot be defined in scientific terms.

Also, make sure that the ink color is suitable for the material you want to print. Because the absorbability of printing materials will affect the color sequence of the printing and the color after printing (materials with higher hygroscopicity need to reduce the density of the ink, especially the color of the first printing, ie the main color).

The type of press usually determines the printing speed (for example, the speed of the cylinder press is faster than that of the plane printer, and the distance from the web is smaller), which also has a certain influence on the change of the chroma.

The use of prints is also a factor that requires the control of density. Obviously, the back-illuminated prints require a higher density of the main color, and at the same time, the coloring should be adjusted according to the “color temperature” of the light source. If there is an intermediate material between the printed material and the light source (usually the light is diffused), the color of the material and the intermediate material is also printed at high speed.

Other issues related to the use of prints, such as magnification (large size), give the impression that the space between enlarged dots is larger than the original size on small-size originals, making the final image appear lighter. This means that it is necessary to increase the density of the film, especially the density of the highlight area, and to change the density of the printing color.

The relative transparency of the basic colors should also be well controlled. If the transparency of one or several basic colors is not enough, the printer must first print a layer of opaque color (or opaque ink) on the surface of the printing material. However, this has the disadvantage of affecting the dominant color and affecting the visual quality of the image.

Regarding noise, no basic color other than yellow is absolutely pure. The completely pure basic color must be able to completely absorb its complementary color, and when the human eye receives it, it will only show its own color. Unfortunately, cyan contains a small amount of yellow and magenta, while magenta contains a small amount of cyan and more (sometimes as high as 60%) yellow. It is important to hire no pure magenta, even if the best choice is made, it should be corrected during the separation phase.

The color fastness (UV radiation in sunlight) is another variable that should be controlled. If you require prints (such as long-term outdoor advertising, etc.) to have this feature, it is also related to the problem of choosing the right product. The lightfastness of inks is usually classified into 1 (not lightfast) to 8 (good lightfastness). If the ink is required to be exposed to sunlight for more than two weeks, lightfastness grade 8 ink should be selected.

The sunscreen properties of inks are not related to the oily, watery, or UV inks of the ink. It is only related to the quality of the ink colorant.

In contrast, the physical (mechanical) and chemical strength (dry or polymeric) of an ink are absolutely related to its chemical composition. Due to the cross-linked polymerization of the UV system, UV inks have good mechanical strength and corrosion resistance and are resistant to rain, snow, sand, dust, pollution, and chemicals (solvents or gases). Selecting UV ink is a good way to control this variable.

If you do not use UV ink, what kind of slow drying agent should you use?

Most of the use of sunken type inks, and sometimes the use of water-based inks, must overcome the tendency of the ink to dry on screens. The key factor to control is the speed of the solvent or water.

The evaporation rate of ether is rated at level 1 (evaporation within 1 s). For most solvents, a good slow drying agent is benzyl alcohol (1800 times slower than ether evaporation).

For water-based inks, the addition of 5% ethylene glycol (or butyl acetate) can slow the dissociation between the ink and the screen due to the squeegee movement.

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