On the application of decorative UV screen printing ink

In recent years, with the development of UV inks and UV curing technologies, decorative UV screen printing inks have become more and more widely used in packaging printing. After printing with decorative UV screen printing ink, some special artistic effects can be produced, which can play a decorative and beautifying role on the printed matter.

Commonly used decorative UV screen printing ink

Commonly used decorative UV screen printing inks are as follows.

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 produced on the surface of the printed matter makes the printed matter have a suspended three-dimensional sense. It is rich, luxurious and unique. It is unique in packaging printing Especially cigarettes and wine boxes are widely used. Generally, there are frosted inks with different thicknesses to choose from.

2.UV screen printing wrinkle ink

UV screen printing wrinkle ink is usually printed on gold and silver cardboard with high gloss. The printed product is first irradiated with weak UV light to completely cure the surface layer of the ink, and the interior is semi-cured. The surface UV ink is uneven due to curing shrinkage Look like lines. Then, by irradiating with strong UV light, the whole UV ink (outside and inside) is cured, and the surface effect with metal thumping or wrinkling can be achieved. Wrinkle printing is elegant and noble, and has a very good decorative effect. It is often used in the printing of cigarette cases, wine boxes, gift boxes, cosmetic boxes, 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. During printing, the ink blisters. This kind of bubbles gather together. The irregular continuous accumulation and the bubble-free smooth part form a coral-like texture. , Can also be said to form a three-dimensional coral-like texture instantly.

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, it is irradiated with strong UV light to cure all the UV ink (outside and inside) to produce the ice effect. Generally, inks with different sizes of ice effect are available.

5.UV screen printing refractive ink

UV screen printing refraction ink is suitable for printing on various types of gold, silver cardboard and mirror paper with specially made screens. After UV light irradiation, the ink film has obvious refraction effect.

6. UV screen printing crystal grain ink

A block agent is added to the UV screen printing crystal grain ink. Because the surface curing speed is different from the internal curing speed, a crystal grain is formed, which is mainly used for the decoration process of the crystal grain on the glass and metal surfaces.

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 when printing.

1. Wire mesh

The UV inks for different purposes have different screen meshes for printing due to different printing requirements. Generally, the higher the fineness of the printed matter, the higher the screen mesh required to be selected. When printing mesh adjustment products, the ratio of the number of screen meshes to the number of screens is generally greater than 4.2.

For the printing of decorative UV inks, the screen mesh number should be selected according to the requirements of specific inks. If UV screen printing imitation metal etching ink is used for printing, the screen mesh number should be matched with the thickness of the sand mold of the ink. If the sand mold is coarse and the particle size is large, the screen mesh with a lower mesh number should be selected. The larger pore size can cause the ink to leak to the substrate through the screen, otherwise, it will leave part of the screen on the screen, resulting in a thinner sand on the printed matter. And, as the printing progresses, the viscosity of the ink on the screen gradually increases, and the ink particles continue to accumulate. If the sand mold is fine and the particle size is small, you can choose a higher mesh screen. Generally, the screen mesh is between 150 and 250 mesh / inch. .

When printing with UV screen printing wrinkle ink, the screen mesh number can be selected according to the wrinkle size to be achieved. The higher the screen mesh number, the smaller the wrinkle, and vice versa. Generally, the screen mesh is between 120 and 200 mesh / inch. When using UV screen printing coral ink, the situation is similar to UV screen printing wrinkle ink. The number of screen meshes can be selected according to the size of the coral ripples to be achieved. The higher the screen mesh number, the smaller the coral ripples, and vice versa The bigger. For UV screen printing ice flower ink, the selected screen mesh number should match the ice flower size.

2. Net distance

When printing, the distance between the screen and the substrate (that is, the screen distance) also has a great influence on the printing effect. The mesh pitch is too small, the imprinted edges are not clear, and the effect of decorative ink printing is not obvious; the mesh pitch is too large, it will have a certain impact on the printing accuracy, and even tear the screen. Therefore, the screen pitch should be appropriate when printing.

3. Scraper angle

The angle of the squeegee is related to the amount of ink output during printing. The angle of the squeegee is large, the amount of ink output is small, the ink color of the printed matter is light, and the effect of the decorative ink after printing is not obvious; It will cause serious spreading of ink, and printing precision will be affected to a certain extent. Therefore, the squeegee angle should be appropriate when printing.

4. Printing pressure

Printing pressure also has an effect on the ink output during printing. The printing pressure is small, the ink output is small, the ink color of the printed product is light, and the effect of the decorative ink after printing is not obvious; too much printing pressure, too much ink output will cause The ink spreads badly, even tearing the screen. Therefore, the printing pressure should be appropriate.

5. Printing speed

The printing speed will also affect the ink output during printing. The printing speed is too fast, the ink output is small, and the ink color of the printed matter is light. In addition, the effect of decorative ink printing 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, if the printing speed is fast, a larger printing pressure and a smaller squeegee angle should be selected for printing, and the viscosity of the ink should not be too high.

6.UV curing light source

Because the curing of UV ink is dependent on the polymerization and crosslinking reaction after the photoinitiator absorbs the radiant energy of UV light, the choice of UV light source has a crucial influence on the curing speed of UV ink. The following factors should be considered when selecting a curing light source.

(1) The output spectrum of the light source should match the absorption spectrum of the photoinitiator as much as possible, so that the radiant energy of the light source can be used to the maximum to generate more free radicals, thereby increasing the curing speed of UV ink. Commonly used UV curing light sources are medium-pressure mercury lamps (including high-pressure mercury lamps in China), which mainly emit light of the following wavelengths: 405nm, 365-366nm, 312-313nm, 302-303nm, 297nm, 265nm, 254nm and 248nm.

(2) The efficiency of converting electrical energy into UV light energy should be high.

(3) The light intensity should be appropriate. If the intensity is too high, free radicals will be generated quickly. If the concentration is too high, the termination reaction will be accelerated, which will have an adverse effect on the cross-linking reaction. These will make the curing speed of UV ink too slow.

(4) Long service life. The UV lamp will gradually age, and the light intensity of the expired UV lamp will be reduced a lot, making the UV ink curing too slow.

(5) There should be a good lampshade spotlight. The quality of the lampshade has a great influence on the curing efficiency of UV ink. The same UV lamp, different lampshade, the curing efficiency of the ink can even differ by more than ten times

(6) The shape of the UV lamp is suitable, which can make the light shine on the printed matter evenly, and it is easy to install, cheap, safe and reliable. Generally, the tube lamp is used.

(7) Ozone will be generated in the air under the UV lamp, so there should be ventilation equipment.
The power density of medium-pressure mercury lamps for curing colored inks is generally 120W / cm. The power density of medium-pressure mercury lamps for curing colorless inks is 80W / cm. The lamp length can be from a few centimeters to 200cm and the diameter is 15 ~ 25cm. Due to the high temperature in the application, cooling is required, and the service life is generally about 1000 hours. A mercury lamp requires a ballast. The light intensity of the lamp is constant, the current and voltage can be adjusted, or high current and low voltage, or low current and high voltage.

After the mercury lamp is turned on, a preheating time is required to facilitate the evaporation of mercury. During the preheating 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 period of time, which will bring some inconvenience to the use. Nowadays, an electrodeless mercury lamp has been introduced on the market, which can be switched on and off instantaneously, and has a long life and great efficiency. The spectrum of the electrodeless mercury lamp used for UV curing is continuous, which is different from the medium pressure mercury lamp and can be used for the curing of thick films.

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