Application of decorative UV screen printing ink
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In recent years, with the development of UV ink and UV curing technology, decorative UV screen printing inks have become more and more widely used in packaging printing. After printing with decorative UV screen printing ink, it can produce some special artistic effects, which can decorate and beautify the printed matter.
Common decorative UV screen printing ink
The commonly used decorative UV screen printing inks are mainly the following.
1.UV screen printing imitation metal etching ink
UV screen printing imitation metal etching ink is usually printed on gold and silver cardboard with high gloss. The matte effect on the surface of the printed matter makes the printed matter have a three-dimensional sense of suspension, rich and luxurious, unique and unique in packaging printing. Especially in cigarette cases and wine boxes, the application is very extensive. Scrub inks with different thicknesses are generally available.
2.UV screen printing wrinkle ink
UV screen printing wrinkle ink is usually printed on gold and silver cardboard with high gloss. The printed matter is first exposed to weak UV light, so that the surface layer of the ink is completely cured, and the interior is semi-cured. The surface UV ink is cured due to curing shrinkage. The pattern of the pattern. Then, by irradiating with strong UV light to cure the entire UV ink (outside and inside), a surface effect with metal beating or wrinkles can be achieved. Wrinkle printing is elegant and noble, and has a good decorative effect. It is often used in cigarette boxes, wine boxes, gift boxes, cosmetic boxes, and calendars, books, etc.
3.UV screen printing coral ink
UV screen printing coral ink is usually printed on gold and silver cardboard with high gloss. When printing, the ink is foamed. The bubbles gather together, and the irregular continuous accumulation and the bubble-free smooth part form a coral-like texture. It can also be said that a coral-like texture with a three-dimensional effect is formed instantaneously.
4.UV screen printing ice ink
UV screen printing ice ink is usually printed on gold and silver cardboard with high gloss. The printed matter is first irradiated with weak UV light to cure the surface of the ink, and the interior is semi-cured. Then, by irradiating with strong UV light, all of the UV inks are cured (external and internal) to produce an ice-flower effect, and generally an ink having an effect of different sizes of ice is available.
5.UV screen printing refractive ink
UV screen printing refractive ink is suitable for printing on various types of gold, silver cardboard and mirror paper by special-made screen. After UV light irradiation, the ink film has obvious refractive effect.
6.UV screen printing crystal grain ink
The UV screen printing crystal grain ink is added with agglomerating agent, and the surface curing speed is different from the internal curing speed, thereby forming a crystal grain, which is mainly used for the decoration process of the crystal grain on the glass surface and the metal surface.
Decorative UV screen printing ink printing process
In order to ensure the printing quality of decorative UV screen printing inks, the following process factors should be noted during printing.
1. Mesh number
UV inks for different applications have different mesh sizes for printing because of different printing requirements. In general, the higher the fineness of the print, the higher the mesh size required to be selected. When printing a mesh product, the ratio of the mesh size to the number of screen lines is generally required to be greater than 4.2.
For the printing of decorative UV inks, the mesh number should be selected according to the requirements of the specific ink. If UV screen printing imitation metal etching ink is used for printing, the mesh size should be matched with the thickness of the ink sand type. If the sand type is coarse and the grain size is large, the mesh with a lower mesh number should be selected. The larger aperture allows the ink to be printed on the substrate through the screen. Otherwise, some of the residue will remain on the screen, causing the sand on the print to be thin. Moreover, as the printing progresses, the viscosity of the ink on the screen gradually increases, and the ink particles continuously accumulate. If the sand type is fine and the particle size is small, the mesh with a higher mesh number can be selected. Generally, the mesh size is 150-250 mesh/inch, and the higher the mesh size, the finer the printed sand. .
When printing with UV screen printing wrinkle ink, the mesh number can be selected according to the size of the wrinkles to be achieved. The higher the mesh size, the smaller the wrinkles, and vice versa. Typically, the mesh size is between 120 and 200 mesh/inch. When printing with UV screen printing coral ink, the situation is similar to UV screen printing wrinkle ink. The mesh size can be selected according to the size of the coral corrugation to be achieved. The higher the mesh size, the smaller the coral ripple, otherwise The bigger. For UV screen printing ice inks, the selected mesh size should match the size of the ice.
2. Net distance
When printing, the distance between the screen and the substrate (ie, the web distance) also has a great influence on the printing effect. The mesh distance is too small, the edge of the print is not clear, and the effect of the decorative ink after printing is not obvious; the mesh distance is too large, which will have a certain influence on the printing precision, and even tear the wire mesh. Therefore, the screen spacing should be appropriate when printing.
3. Scraper angle
The angle of the squeegee is related to the amount of ink discharged during printing. The squeegee angle is large, the amount of ink is small, the ink color of the printed matter is light, and the effect of the decorative ink after printing is not obvious; the angle of the squeegee is too small, and the amount of ink is too much. It will cause serious ink spreading and the printing fineness will be affected. Therefore, the angle of the squeegee should be appropriate when printing.
4. Printing pressure
The printing pressure also has an influence on the amount of ink discharged during printing. The printing pressure is small, the amount of ink is small, the ink color of the printed matter is light, and the effect of the decorative ink after printing is not obvious; the printing pressure is too large, and the amount of ink is too large, which may cause The ink spreads badly and even tears the screen. Therefore, the printing pressure should be appropriate.
5. Printing speed
The printing speed also affects the amount of ink discharged during printing. The printing speed is too fast, the amount of ink is small, and the ink color of the printed matter is light. In addition, the effect of printing the decorative ink is not obvious, so the printing speed cannot be too fast.
Of course, the above process conditions should also be matched with each other. For example, the printing speed is fast, and a large printing pressure, a small blade angle, etc. should be selected for printing, and the viscosity of the ink should not be too high.
6.UV curing light source
Since the curing of the UV ink is accomplished by the polymerization and crosslinking reaction of the photoinitiator after absorbing the radiant energy of the UV light, the choice of the UV source has a crucial influence on the curing speed of the UV ink. The following factors should be considered when selecting a curing light source.
(1) The output spectrum of the light source should be matched with the absorption spectrum of the photoinitiator as much as possible, so as to maximize the utilization of the radiant energy of the light source and generate more free radicals, thereby increasing the curing speed of the UV ink. A commonly used UV curing light source is a medium pressure mercury lamp (included in a high pressure mercury lamp in China) that emits light of the following wavelengths: 405 nm, 365-366 nm, 312-313 nm, 302-303 nm, 297 nm, 265 nm, 254 nm, and 248 nm.
(2) The efficiency of converting electrical energy into UV light energy should be high.
(3) The light intensity should be appropriate. If the strength is too high, the free radicals will be produced quickly. If the concentration is too high, the rate of termination of the reaction will increase, which will adversely affect the crosslinking reaction. If the intensity is too low, the rate of generating free radicals will be too slow, and the oxygen inhibition will be strong. These will make the UV ink cure too slowly.
(4) Long service life. The UV lamp will gradually age, and the UV lamp that has expired will have a much lower light intensity, making the UV ink cure too slowly.
(5) There should be a good lampshade to collect light. The quality of the lampshade has a great influence on the curing efficiency of the UV ink. The same UV lamp, the lampshade is different, and the curing efficiency of the ink can even differ by a factor of ten.
(6) The shape of the UV lamp is suitable for uniform illumination of the light on the printed matter, and is easy to install, cheap, safe and reliable, and generally uses a tubular lamp.
(7) Ventilation equipment should be provided because ozone is generated in the air under UV light.
The medium-pressure mercury lamp used for curing of colored inks generally has a power density of 120 W/cm, and the medium-pressure mercury lamp for colorless ink curing has a power density of 80 W/cm, a lamp length of several centimeters to 200 cm, and a diameter of 15 ~25cm. Since the temperature is high in the application and needs to be cooled, the service life is generally about 1000 hours. Mercury lamps require a ballast that has a constant light intensity, current and voltage regulation, or high current and low voltage, or low current and high voltage.
After the mercury lamp is turned on, it needs a warm-up time to facilitate the evaporation of mercury. During the warm-up of the mercury lamp, the expected UV light cannot be obtained. After the mercury lamp is turned off, it cannot be started again immediately, and it needs to be cooled for a while, which will bring some inconvenience to the use. Now, a non-polar mercury lamp has been introduced on the market, which can be switched on and off, and has a long life and high efficiency. The spectrum of the electrodeless mercury lamp used for UV curing is continuous, unlike the medium pressure mercury lamp, which can be used for the curing of thick films.