Fluorescent ink characteristics and application in screen printing (2)

Second, the screen printing of fluorescent ink

In order to improve the printing effect of fluorescent inks, fluorescent inks are best printed on papers with high whiteness and substrates such as vinyl films, which can be printed by various methods such as plain printing, gravure printing, flexo printing, screen printing, etc. Fluorescent ink prints are brightly colored and glittering, and the concentration of fluorescent ink pigments can be appropriately increased. However, it is more important to ensure that the printed ink film is as thick as possible. This will make the fluorescent effect better and make up for the fluorescent ink. Poor resistance. On the other hand, screen printing has the feature of thick ink film, which is very suitable for fluorescent ink printing. With the development of screen printing technology and equipment, the use effect of fluorescent ink can be fully utilized in the field of screen printing. Therefore, screen printing has become an ideal printing method for fluorescent ink in recent years. The screen printed fluorescent ink prints can form a uniform ink film layer, which is required for good gloss, stability and weatherability. Since the particle size of the photoluminescent pigment in the fluorescent ink is coarser than that of the conventional pigment, the fluorescent ink generally uses a lower mesh (usually 80 to 150 mesh) screen in screen printing, and is only used for comparison. Rough printing. However, with the continuous emergence of new fluorescent ink products, the particle size of their pigments has become finer and finer screen printing products have now been fully printed. The rheological characteristics of most fluorescent inks are pseudo-plastic flow, and the viscosity is small. This characteristic determines that the printing process is very different from the printing process of ordinary inks. In screen printing, the tension of the screen is high, and an appropriate squeegee is selected to increase the thickness of the ink layer, thereby improving the luminescent effect of the ink. Since the inorganic fluorescent substance emits light from the crystal, if the pressure is too high, the crystal will be broken and the luminous brightness will be reduced. Therefore, in addition to stickiness, connection material, and drying property, the printing pressure should be paid attention to during screen printing. The adjustment can not make the printing pressure too large and affect the printing effect. In fluorescent ink printing, pay attention to the following questions. (1) Prior to the use of fluorescent inks, it is necessary to thoroughly clean the printing plate and other related parts so as not to mix in with other colors. Of course, it is better to have special equipment. (2) When the color of the fluorescent ink and the ordinary colored ink is matched with the colorless red ink, the fluorescent effect is the best. Colorless red-printed blue ink or colorless blue-printed red ink has poor fluorescence. Different shades of background have a greater influence on fluorescence brightness, and the deeper the ink background, the worse the fluorescent effect. In addition, it should be noted that fluorescent inks cannot be mixed with a large number of ordinary colored inks, and they should not be mixed with ordinary inks as much as possible, otherwise they will lose their fluorescent effect. (3) Since fluorescent inks are poor in light fastness, they are not suitable for use in prints used outdoors for a long time. In addition, when the substrate is a transparent object, it is better to print a layer of white ink before printing fluorescent ink, which can improve the fluorescence effect. The desiccant should not be used in fluorescent inks. It is best not to add a varnish or bright oil with good transparency. (4) In order to improve the printing effect, the printing color sequence should be reasonably arranged. When the paper is printed, the fluorescent ink is generally used as the final color printing, otherwise it will be covered by other inks and affect the luminescent effect. When printing with clear plastic, the situation is different. External fluorescent ink is the last color; when printing, the first color. When the fluorescent ink is used for the background color, if the same color is used for printing, the color saturation can be improved and the light resistance can also be improved. (5) The fluorescent ink is not absolutely colorless or absolutely imprinted. On pure white paper, even if a fully transparent, five-colored varnish is printed, the difference in refraction and reflectance of paper and varnish may cause visual differences, resulting in differences in the brightness of the oil and the surface of the paper. Colorless fluorescent ink can only reduce the footprint or basic invisibility when the pattern or text is changed to a color line, a paper with good absorption (such as invoice special paper, etc.), and a place where the background color can cover the fluorescent ink trace. (6) Pay attention to the factors that affect the fluorescence brightness. Such as paper, should choose security paper or non-fluorescent brightener paper, so that the effect of fluorescence is better. When printed on plain paper (paper with fluorescent whitening agent), the fluorescent effect is significantly reduced. The more brightener the paper has, the weaker the fluorescent effect.

Therefore, when using plain paper, use paper with a low whitening agent as much as possible. In addition, the thinner the printed ink layer, the weaker the fluorescent effect; the thicker the ink layer, the stronger the fluorescent effect, but the more marked the same time. (7) Pay attention to controlling the printing pressure. Since the inorganic fluorescent material or the like emits light through the crystal, if the pressure is too high, the crystal will be broken, and the light emission brightness will be reduced. Therefore, relief printing is generally not used. In screen printing, gravure printing, etc., in addition to paying attention to its stickiness, linking materials, drying properties, but also pay attention to the adjustment of the printing pressure, should not make the printing pressure is too large, affecting the printing effect. (8) Control the printing speed. Since the fluorescent ink has a large fluidity and is relatively slow to dry, if the ink layer is thick, it is liable to cause the paste to spread due to the ink not being completely dried during rapid printing. Therefore, the printing speed cannot be too fast.

Finally, pay attention to the difference with phosphorescent inks. Phosphorescent inks differ from fluorescent inks in that the phosphorescent ink continues to glow after the end of the excitation, but its half-life is about a few milliseconds and cannot be seen with the naked eye. Phosphorescent inks are crystals in which phosphors are added to the ink. This type of material absorbs the light projected onto it under the excitation of ultraviolet light, and then emits it at a certain wavelength for a certain period of time. The emitted light and the body color are emitted. different. Phosphorescent ink color is a small amount of impurities such as zinc sulfide and cadmium, the link material is transparent, transparent to ultraviolet light, because the pigment is not resistant to acid, alkali, the resin used should be neutral. Phosphorescent inks can not be added desiccant, dry oil, etc., so as not to react with the pigment, affect the printing and light-emitting effect. Phosphorescence emits light in the dark after absorption of light, whereas fluorescence absorbs light in different colors and then emits light. That is, phosphorescence absorbs natural light or artificial light and emits light in a dark environment after the light is removed, and the fluorescent light must absorb light in the presence of light before it can emit light. Fluorescent inks can also emit light in the presence of "night light" or violet light. However, it does not glow in the dark and no light. The fluorescent ink not only shows its own color, but also has the ability to absorb light and change the light intensity so that the color it exhibits has a stronger light intensity, but the hue (or color) does not change. The phosphorescent color can be combined with the visible light hue, provided that the emission wavelength of the luminescent pigment does not match the absorption wavelength of the visible light pigment. This type of ink is particularly suitable for the rapid and reliable automatic detection of securities and the quality inspection during printing because of its excellent durability. The fluorescent ink used for anti-counterfeit packaging is best prepared by the user, because different formulations can obtain different fluorescence effects and are more difficult to copy. In addition, the combination of fluorescent ink and phosphorescent ink can also be combined with the characteristics of phosphorescent inks, and better anti-counterfeit effects will be obtained.