With the rapid development of the printing industry in our country and the continuous improvement of the living standards of packaging machinery, people are paying more and more attention to the perfection of printed products. Offset printing technology has also been widely adopted as a printing method with fast printing speed, good color reproduction and high economic efficiency. Offset printing is the use of oil-water insoluble principle, so that the ink and water coexist on the printing plate, and maintain balance between the state, in order to achieve the correct transfer of graphic and graphic printing, to obtain products that meet the printing quality standards. Therefore, the quality of printed products depends mainly on the printing process. This article will briefly describe the experience of improving the quality of printed products from the perspective of ink.
Correct arrangement of color sequence to prevent overprinting
The multicolor machine finishes the printing in a very short time. The ink printing method is wet and wet. Therefore, the basic principle of the color sequence arrangement in multicolor printing is that the viscosity of the ink should be reduced color by color. But even so, there is no guarantee of good overprinting of the ink. When the printer printed a kind of hand-held bag, it appeared that the posterior color group had magenta dots and the former color group had poor cyan overprint, and many red spotted spots appeared on the product. Despite repeated reductions in the viscosity of magenta ink, there was no noticeable effect. Finally, trying to reverse the order of cyan and magenta, the problem was finally solved.
The reason for the above failure lies in the fact that the cyan is on the ground. The ink thickness is a digital printing machine. The magenta is a light web and the ink is thin. When the magenta ink is printed on the wet, thick blue ink, the dots are not clean and easy to produce. With the increase in outlets, there was a spotted offset press that was very unfair. When the color order is reversed, magenta dots are directly printed on the printing materials, and they are very smooth and smooth. After the cyan field is overprinted, there is no problem. HP
Grasp the main tone to correct color shift
Commonly used four-color ink, often due to cost, price and other factors, rubber products, there is a certain degree of deviation in hue, such as yellowish reddish, magenta and yellowish, its overprinted color whether red or green, are partial dark type Design, grayscale, color is not bright enough. At this time, we must conduct targeted analysis of the product, seize the most important colors, select the best inkjet ink, and print the best results. This measure can also sometimes correct some color casts on the plate and achieve unexpected results. The author printed a type of four-color bankbook on a certain occasion. The main color of the cover was overprinted with 100% yellow and magenta ink. When the client signs on the machine, he thinks that the red color is somewhat dark, and it is necessary to achieve the vivid red-gold effect to die-cut the hot stamp indentation. This makes the printer very difficult, because if the re-plate, the time is too late, and increase the cost, so Think about solving ink issues. So digital printing, the author according to the formation of the color mechanism, the four-color ink used in the yellow to yellow, the red to red. As a result, the cover of the passbook has completely achieved a reddish effect, and the color is very vivid. The CTP is in China, but it has little effect on other minor patterns. Taking such measures is fast and economical.
Adjust ink stickiness to ensure overprint accuracy
When printing full-size large-volume ink products, the ink viscosity and printing pressure must not be too large. Otherwise, overprinting, paper curling, and other defects will occur, making it impossible to remove the paper from the blanket and print it digitally. After processing, normal transfer is completed, and the paper is thin, so it is difficult to overcome the excessive printing peeling tension, resulting in continuous tearing and peeling of the paper. On one occasion, a machine was printing a full-version branded beef sauce trademark printing process. The paper was 80g/m2 single-sided coated paper. Printing is always inaccurate, and the fourth-color group of blankets is constantly sticking and peeling. The captain of the aircraft suspects that there is a problem with tooth decay. Repeated cleaning and refueling of cavities cannot solve the problem. Later, after reviewing the situation, the printer went to the printers and took black ink, magenta ink, and yellow ink to dispense with an adhesive, and then reduced the printing pressure of each color group as much as possible, eventually eliminating the malfunction. This is because when the author took the ink de-bonding agent and measures to reduce the printing pressure, the peeling tension of the ink on the paper was greatly reduced, the paper would not be overprinted due to severe deformation, and the packaging was not safe and was no longer sticky. On blankets, production can proceed normally. Standards and certifications
Adjust ink balance to ensure print clarity
1. The ratio of wetting fluid
At present, the most commonly used wetting liquid in offset printing is alcohol wetting liquid, which is generally composed of 2% to 3% of fountain solution, 10% of isopropyl alcohol, and 87% to 88% of water. This ratio is also recommended by many equipment manufacturers and wetting fluid suppliers, and it is recommended not to change it easily. Because, once, the author of the company's company had a captain who believed that the excessive amount of fountain solution caused the ink to dry too slowly and the layout design changed its amount to 1%. As a result, the content of the fountain solution decreased, making the printing process Have to increase the amount of water, resulting in poor ink delivery, ink accumulation in the roller, emulsification equipment operation, its viscosity has dropped significantly, even more caused by the imprinted ink, rear ink color mixing, the rate of overprint and other failures . The blotting does not depend on the content of fountain solution, but it is more closely related to the nature of the paper, printing pressure, ink quality, ambient temperature and humidity and other factors, and must not be arbitrarily changed when the wetting fluid ratio is reasonable.
2. The dynamic balance of water volume and ink volume
In the printing process, there are many factors that affect the amount of water and the amount of ink. For example, layout area, paper type, environmental temperature and humidity, and printing speed, Huaguang Precision, will have a great impact on the amount of water and ink, so that the ink The equilibrium cannot be stabilized. In this changing situation, empirical judgment is very important. The author's method is to observe the paper in the printing process. If more than 3mm of ink is dirty on the surface, it means that the amount of water is slightly too small; if there is no other point on the ink, there is reflection of water. It shows that the amount of water is too large. This method is very reliable and easy to use under any environmental conditions.
In the printing process, the ink is transferred by the ink roller, emulsified by the wetting liquid, and transferred to the paper and printed by the blanket under the effect of the printing pressure. There are many factors of change, which may affect the effect of the ink. In operation, we must organically combine theory with practice and use it flexibly. After summarizing, the following aspects should draw attention.
(1) In winter and spring, where ink is stored, the temperature should be kept at about 20Â°C. Otherwise, the viscosity of the ink will vary greatly due to the change of temperature, and the ink cannot generally be used directly in winter.
(2) The ink in the ink fountain is easily crusted due to the oxidation of air, and it must be turned frequently to prevent the appearance of ink skin and ink residue on the print.
(3) When adjusting the spot color ink, the ink closest to the original color ink should be selected to adjust investment purchase, and the type of ink should be minimized. Otherwise it will increase the gray level of the ink and reduce the brightness of the ink and the vividness of the color. Koch report
(4) The addition of ink additives should be strictly controlled in mind. The addition of varnish, detackification, etc. must be targeted, and should not exceed 5%, otherwise it will cause oily, dirty version, color saturation, blotting, ink dry and other problems.