Analysis and troubleshooting of the key points of the smoke mark printing process
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At present, both producers and users are paying more and more attention to the outer packaging of products, and the market is increasingly demanding a variety of high-end packaging and personalized packaging. Under this trend, the field of packaging and printing is constantly developing new processes and materials to meet the needs of the packaging market. The smoke mark sanding printing process is one of the best.
1. Frosted printing
The matte printing is to print a transparent UV matte ink on a mirror-shiny substrate, which is UV-cured to form a rough surface such as frosted glass, and is mostly screen printed. Since the pattern obtained by this printing is very similar to the effect of corrosion after metal, and has a special rough feeling, it is also called imitation metal etching printing.
2. Tobacco mark matte printing printing substrate
Printing cigarettes generally use 250~300g/m2 gold, silver cardboard and vacuum aluminized paper, and the surface is required to be flat, with high smoothness, and can produce mirror metal effect after printing.
It is also possible to use a method of printing a color paste on a white cardboard, that is, using a coating device to print a gold or silver color paste on a cardboard, but it is required to have a high coloring power, a uniform coating color, a flat clothes, and a good gloss. Compared with composite gold and silver cardboard, the effect of coating gold and silver cardboard is slightly worse.
3. Matte ink
In the matte printing process, the matte effect is formed by the special properties of the UV matte ink. The frosted ink printed by the cigarette label is a colorless transparent one-component UV light curing ink with a particle size of 15~30μm. The printed product has obvious frosting effect, and the ink film is full and the stereoscopic effect is strong, which can improve the product. Grades are therefore used for packaging and printing of cigarette labels, wine labels, cosmetics, health products, etc.
Compared with traditional solvent-based inks, UV matte inks have distinct advantages: exquisite printing patterns, strong stereoscopic effect; no solvent, high solid content, low environmental pollution; fast curing, energy saving, high production efficiency; The film is resistant to friction, solvent and heat. The cigarette label printing mainly uses medium sand ink, its appearance is white translucent fluid, and the basic technical parameters are viscosity: 3.0±0.1Pa·s (25 ° C); specific gravity: 1.10g / cm3 (25 ° C); pH: 6.5 ~ 7.5; non-volatile components accounted for more than 99%; curing speed of less than 5 seconds (40 m / min, 80W / cm high pressure mercury lamp 3 support). The ink should be cured by a UV curing device. The mechanism is that the photosensitive resin in the ink binder absorbs energy in the ultraviolet rays and instantly forms a cured film. If natural light curing is used, it takes about 2 to 3 days.
4. Printing process points
(1) Printing press
In order to ensure registration accuracy, it is best to use an automatic screen printing device with a UV curing device for sanding printing. For example, the Japanese Sakurai off sheet-fed screen printing machine with UV curing channel has a printing speed of 800~3000 sheets/hour.
(2) Printing environment
Temperature: 25 ± 5 ° C; humidity: 45% ± 5%.
(3) Overprint standard
The plate image should be consistent with the first few colors to ensure accurate overprinting, and the overprint error should be ≤ 0.25mm.
(4) Printing color sequence
Tobacco label printing belongs to high-grade trademark printing. It not only requires rich colors, but also needs certain anti-counterfeiting functions. Therefore, it is often combined with multi-color printing and multiple printing methods. In the arrangement of the printing color sequence, the matte ink should be arranged in the last color printing. For example, if you print a cigarette with white, red, pattern hot stamping and matte effect, the general color sequence is to print white and red ink first, then hot stamping, and finally to print matte ink. Because the matte ink is colorless and transparent, it is printed on the surface of gold and silver cardboard, which can transmit the inherent metallic luster of the printing material to achieve the imitation metal etching printing effect. Moreover, the final printing of the matte ink can also reveal the color of the ink printed the previous time.
(5) curing method
Cured with a high pressure mercury lamp. The life of the lamp is generally 1500~2000 hours, which needs to be replaced frequently. The price of domestic lamps is about 1,000 yuan per piece; the price of imported lamps is about 3,000 to 4,000 yuan.
(6) Printing pressure
When printing matte inks, the squeegee pressure should be slightly larger than the normal color ink, and the pressure should be consistent.
(7) Printing speed
The particles of the matte ink are large, and the printing speed should be lower than that of other inks in order to allow the matte ink to penetrate the mesh sufficiently. Generally, the printing speed of other color inks is 2500±100 sheets/hour; the printing speed of the matte inks is generally 2300±100 sheets/hour.
(8) Screen requirements
Generally, an imported plain nylon mesh of about 300 mesh is selected, and the tension of the stretched net is uniform, and the deformation of the printing plate is strictly controlled in the printing process.
5. Common faults and solutions
(1) Reasons for poor metal texture: The diluent added to the ink is not suitable; the power of the UV lamp is insufficient; the quality of the substrate is poor.
Solution: Add the thinner matching with the matte ink before printing; the amount of the diluent is accurate and the stirring is sufficient. During the curing process, the power range of the light source should be selected according to the thickness of the ink layer and the speed of the light-solid machine. The power of the light source should be 0.08~0.4kW. In addition, it is also necessary to select a substrate with a high metallic luster, the surface can not be scratched, and has appropriate tensile strength and high temperature resistance.
(2) The rough surface of the cigarette mark is rough and the particle distribution is uneven
Cause: The printing pressure is inconsistent.
Solution: The length of the squeegee should be slightly larger than the width of the printed substrate. The cigarette marking can be selected from a right angle scraper, but the hardness of the squeegee should not be too high, and the hardness is generally HS65.
(3) The ink is dried on the screen
Cause: Natural light direct screen. Because natural light contains a large amount of ultraviolet light, it is easy to cause a curing reaction of the photosensitizer in the ink. The surface of the paper or the ink contains impurities.
Solution: Try to avoid direct printing of natural light; use paper with high surface strength; keep the printing environment clean.
(4) Print adhesion
Cause: The ink layer on the printed matter is not completely cured.
Solution: Improve the power of the light-solid machine lamp; reduce the tape speed of the light-solid machine; reduce the thickness of the ink layer on the premise of meeting the printing requirements.
(5) Sticky version
Cause: The paper is not positioned correctly, and the impression cylinder is not properly adjusted.
Solution: Calibrate the paper positioning system to adjust the position of the gripper to prevent the paper from rotating with the drum.
(6) Plate rupture
Cause: The printing pressure is too large and the tension of the stretcher is uneven.
Solution: Adjust the scraper pressure evenly; keep the tension of the stretcher even; choose the imported mesh.
(7) Image hair edge
Cause: The ink viscosity is too large.
Solution: Add appropriate diluent to adjust the viscosity of the ink; avoid ink drawing.