The use of solvent-based inks in advertising and other industries has become more common, but solvents in solvent-based inks are volatile and can contaminate the environment. In the printing process, the viscosity of the inks will increase as the volatilization of solvents increases. Causes the loss of fine dots and color distortion. At the same time, market competition also requires manufacturers to improve the printing accuracy. Save costs, strengthen labor protection and environmental protection. The UV-curable (uV) water-based ink, which is famous for its green and pollution-free, has the advantages of fast curing speed, small footprint of curing equipment, low energy consumption, good on-line stability, high efficiency, and no pollution. Therefore, the advertising ink is made of solvent-based ink. The move to uV curing inks and waterborne uV curing inks will be a trend in the coming years.
However, there are also some problems in the process of converting solvent-based inks to uV inks. Since uV inks do not volatilize after printing, under the same printing conditions, the ink thickness of the uV ink is the thickness of the solvent-based ink ink layer. 2x does not have any effect on monochrome printing but it is different for color printing. Especially in the third and fourth colors, especially the fourth color. After the ink is overprinted, the thickness of the ink layer is significantly increased, causing the surface of the substrate to be uneven. Under the pressure of the squeegee, the ink flows toward the low concave portion. The problem of hue distortion caused by the increase in the number of dots is caused by the increase in dot gain. Because there is no good solution. This hinders the conversion process of solvent-based inks to uV-cured inks.
In order to solve the above problem. NAZDAR (United States) developed and produced an advertising-specific uV screen printing ink - water-based HU000 series of UV inks, which can solve the problem of ordinary uV ink in the process of color overprint caused by the color of the image is difficult to restore the technology problem. The ink is favored by the advertising industry in the U.S. market. Its characteristics and process technology are briefly described below.
uV Curing ink characteristics
(1) The ink contains a certain amount of moisture and 5% of environmental protection solvents. Cured moisture evaporates. Ink thinning. and so. It has the advantages of thin ink layer after solvent ink drying. It also has the advantage that the curing of uV ink is quick and environmentally friendly.
(2) Suitable for modern printing equipment. For example, continuous production of automatic roller screen printing machine. Because the ink requires low curing energy. Can reduce the cost and reduce the thermal deformation of the substrate and overprint failure. At the same time, the surface of the ink is hard after curing. It has the characteristics of high density of dots, high sharpness of color, and no shadow on the periphery of dots. Especially four-color printing. Have a good network of sharpness, more suitable for indoor and outdoor advertising. Such as playing back advertising, before hitting advertising. (3) is a single component light-curable ink. Does not contain NVP or heavy metal contamination.
(4) High ink color density. Can be used as a varnish to change the printing effect.
To meet the requirements of outdoor advertising color rich features. Lisa up to four color advertising screen printing inks are available in two kinds of outlets magenta (blue. A kind of red). Two kinds of network yellow (a kind of green. A kind of red). There are also dot blue and dot black. Can be selected according to the color image color requirements. In order to achieve better visual effects.
uV Curing Ink Screen Printing Process
Substrate: Screen printing can be performed on synthetic paper (such as YUPO, etc.), PS, hard PVC, polyethylene materials, paper and card paper.
Scraper: Hardness HS70ï½žgo. .
Auxiliaries best use the same series of products. Such as Hu18O thinner Hu193 regulating paste, Hu34g thinning agent, HU350 spot oil. Curing: A medium pressure mercury lamp with a condenser cover is 200W/inch. The conveyor speed is about 20 meters per minute.
Printing techniques: HUO00 series printing inks have high color density, can be added to the dot gloss oil to reduce the color density if you need to adjust the viscosity and leveling. About 8% of Hu 193 conditioning cream or Hu18O thinner of about 2o/`0 can be added. However, the ink should be fully stirred before printing.
The ink must be fully stirred before printing. If the ink layer is not thin enough during the printing process, the dots can be increased in the first color. Hu34g thinning agent was added to the second color ink.
Each batch of ink should be tested for relevant properties before printing. The test was conducted 24 hours after the print was placed.
Screen making skills
(1) Under the same printing conditions. Because uV ink is thicker than solvent ink. The dot layer of the film should be adjusted before screen printing. And choose a higher mesh number of monofilament thin screens. Or choose uv) h ink special single-sided pressure mesh. Such as 14O ~ 15O head / cm monofilament polyester polyester mesh opening, stretching tension in more than 20N/cm. By controlling the thickness of the screen photosensitive layer or using yellow polyester mesh. Can also meet the requirements.
(2) Screen sensitized material: The screen is made of a solvent-sensitive photosensitive thin film or an indirect photosensitive film.
(3) When coated with photosensitive adhesive. The thickness of the photosensitive layer should be controlled at about 4m. Surface roughness (R) is less than 5m. Sharpens the sharpness of outlets.
(4) The main points of quality control in screen making:
1 In order to ensure that the screen is not lost when the screen is in use, before the screen is coated or pasted on the photographic film. The screen must be roughened and degreasing. The photosensitive adhesive and the screen firmly attached. Small outlets are not lost. Guarantee the depth of the color level transition naturally.
2 Screen printing screens of various colors are used to ensure consistent and uniform tension. After coating and sticking the photo-resist film, it must be completely dried before exposure. Otherwise in the development or printing, the small network is lost. The screen life is reduced; if the screen tension is not uniform. In addition to four-color printing is not allowed. It is also possible to generate moire and the like on the screen.
3 four-color printing screen production requires some skills. When exposed. The exposure time of the photosensitive layer must be controlled (the optimal exposure time is calculated using the exposure scale). In order to ensure that the high-profile network points on the screen (small outlets) through. Dark spot (small spot) is really attached to the screen
4 mesh screen edition development must be a combination of full development and partial development. Because the small screen on the screen is not easy to penetrate in the full display. If the small outlets have not yet come out. At this time, local water columns should be used to supplement small outlets and make small outlets transparent. Ensure that high-profile print points are not lost
5 on the screen after the development of the text. Control color separation film inspection. Make sure that you can double exposure the screen. To increase the life of the screen.
Reprinted from: Printing Technology
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