With the continuous improvement of the packaging and decoration requirements, UV printing does not contain volatile solvents. Can be quickly cured on the surface of non-absorbing substrates, and the characteristics of high brightness and anti-friction properties of printed products have been more and more widely used. Especially in the cigarette bag decoration more applications. Nowadays, many high-grade cigarette packs are decorated with bright gold, silver cardboard or laser paper, and UV- offset printing layers with rich layers of continuous pattern are coated with UV varnish, and some are hollowed out for embossing due to paper and uV varnish. The brightness of the high, embossed part looks very eye-catching to achieve hot stamping, hot silver effect. After using this process the entire decor looks very good. Can easily attract the attention of consumers. In the whole printing process, the mastering of UV offset printing process is very important, it is also difficult, and it is also a problem that the product quality is easily problematic. How to improve the level of UV offset printing process in the production process and improve product quality? The following discussion based on the work experience of the author need to pay attention to and master several issues.
UV offset printing plate, roller and blanket requirements
Since uV offset printing inks contain active monomer diluents and photoinitiators, they can decompose the dots on ordinary adhesive I~OPS plates, which will make the printing plate's printing tolerance drop significantly. Therefore, uV offset printing must use a special uV offset printing PS plate. The reactive monomer diluent in uV offset inks impregnates ordinary offset rollers and blankets during the printing process. The result will cause two kinds of printing troubles: First, ink failure. Ordinary rubber rollers, especially new rubber rollers and rubber blankets, significantly reduce the active monomer diluent in the ink due to a large amount of absorption of the active monomer diluent. This directly destroys the fluidity of the ink and causes the ink to dry and have a low viscosity. Increase the normal ink in the ink film in the active monomer to reduce the ink polymerization cross-linking component will be insufficient when the uV lamp irradiation curing will cause the ink film curing is not complete Print product intolerance friction: The second is the rubber roller and blanket failure Reactive monomer diluents in UV offset inks can cause swelling of common rubber rollers and blankets. Short-term printing can cause swelling. The vitrification of the surface and the dirtiness of the prints prevent the printing from proceeding properly. As the printing time increases, the peeling or surface cracking will occur when the expansion is more serious. Therefore, the uV offset printing must also use a dedicated uV rubber roller and uV blanket or uV, or both. Used rubber rollers and blankets.
Determination of color sequence in UV offset printing
In the ordinary offset printing process. The color printing sequence of ink is mainly determined by the following aspects:
1. Machine type: monochrome, double or multicolor. This determines whether the ink in the printing process is wet or wet.
2. The content of the manuscript determines the main color of the screen and the number of layouts occupied by various colors.
3. The quality of the paper determines the thickness of the first color ink layer, the amount of paper deformation and the gloss of the print.
4. The difference in ink determines its color cast, gray scale, color efficiency, and the consistency of stickiness, transparency, and tinting strength.
In addition to the above factors, the determination of the color sequence of uV offset printing is mainly determined by the curing properties of the ink. The curing of ordinary offset printing inks is a combination of oxidized conjunctiva and osmotic curing, and the curing performance of each color ink is basically the same. The curing of UV offset inks is accomplished by uv light irradiation. Due to the different degree of absorption of uV light by different colors in the ink. Therefore, the degree of curing of different color inks is also different. From the penetrating power of uV light on the pigment. The magenta transmittance is 50% to 60%, the yellow transmittance is 20% to 30%, the cyan transmittance is 8% to 20%, and the black transmittance is 10% to 12%. The white ink reflects most of the uV rays and has a lower transmission rate. Because each color ink has different transmittance of uV light, the same power uV light is irradiated at the same time. Some inks cure, while others do not cure. Therefore, in the uV offset printing color sequence arrangement should mainly consider the ink curing problem. The inks that are not easily cured are printed first, so that they can be irradiated with uV light several times, and the easily curable inks are printed. That is, the printing color sequence is: white, black, green, yellow, and yellow, which is the end of printing. Preparation of ink can be more thoroughly cured.
In addition. There are two complementary color inks available for printing black ink. To accelerate the curing of the ink. The author's company used this method when printing a cigarette. Has achieved very good results. The cigarette label (see real objects) is printed with a ribbed laser. The main color is a full version of red, and there is a place in the red pattern on the side that is empty. In the missing portion, white ink is used to make a bottom. A black bar code is printed on the white ink, and the white ink is printed as the first color. Black ink for the second color printing, found that ink curing is not complete, the bar code made virtual. We blended black ink for printing with red ink and blue ink. Then add a small amount of black ink: add a little red ink to the white ink (because the ambient color is red. The amount of red ink added in the white ink is appropriate. The effect on the hue is not visible to the naked eye). When printing with new modulation ink. White ink and black ink cure more thoroughly, and the printed bar code is full and clear.
Therefore, understanding the difference in UV offset printing ink preparation, properly arranging the printing color sequence, and scientifically using complementary colors to adjust the ink is an important method to improve the quality of the ink and ink balance in the UV offset printing UV offset printing process.
Realization of ink-water balance in uv offset printing
In the offset printing process. The balance of ink and water is very important. Is it properly controlled? Directly affect the quality of the product. Ordinary lithographic offset is the use of water is polar ink is non-polar. The principle of incompatibility between the two makes the ink and water maintain the balance relationship on the same plane to realize the transfer of image dots. Ink and water exist on the plate at the same time and must adapt to each other. No one side can exceed the limit range to force the other side to develop in the opposite direction. The purpose of maintaining ink and water balance is in the process of the mutual adaptation of ink and water. It is necessary to maintain the maximum amount of ink in the text, so that the ink is bright, the outlets are clear, full and full. Also keep the blank area clean and tidy. And in uV offset printing. Ink shows weak polarity. Substrate water absorption is also poor. So the ink is more easily emulsified. Water black balance is more difficult to achieve. Based on work experience. The author believes that in order to better realize the ink-water balance in the uV offset printing process, it is necessary to start from the following aspects:
1 Several parameters of fountain solution should be well controlled. The temperature is 4-9. C. PH value 5.5 ~ 6.3. Isopropyl alcohol concentration is about 15%. After these several parameters are controlled. Can reduce the amount of fountain solution, reduce ink emulsification.
2. Plate selection should be appropriate. It is best to use uS dedicated Ps version, printing plate should have a solid graphic and blank basis. The grits on the surface of the plate remain uniform and fine. Has a certain structural strength. Make ink and water have good adsorption.
3. The operating process should be standardized. The pressure between the roller, the ink roller, and the water roller should be controlled well. Mix the ink in the ink fountain frequently to keep the printing pressure stable. The speed of the machine is stable. Workshop temperature and humidity stability. In order to avoid changes in ink properties caused by emulsification.
4. To achieve a small ink thick water printing method. At the beginning of printing, the amount of ink, water should be small. Then gradually increase the amount of ink and water as needed, found that when the ink emulsification. Emulsified ink scraping clean. Add back eight The new ink is printed until it reaches the printing state where the thick ink is small. This is because the thick ink viscosity is great. That is, the cohesion of the ink increases. Correspondingly enhance the adhesion between the ink molecules. To improve the ink's water resistance, reducing the ratio of water in the ink. Reduces the emulsification value of the ink. In order to ensure that the printed product is brightly colored, the ink layer is thick, the outlets are clear and full.
In short. Uv offset printing process is more difficult to grasp, must be carefully observed in the work, a serious summary. And master some necessary basic theoretical knowledge. In the process of solving the problem, the theory and experience are combined, compared with the method for solving ordinary offset printing problems, to find commonalities and differences. The idea will be more open when it comes to solving process problems. The method will also be more appropriate, and will only print higher quality products.
Author: Ma sent Zhengzhou gold leaf printing limited liability company
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