2. Application in gravure printing
Water-based gravure printing inks were widely used in the printing of packaging paper and cardboard carton in the 1970s. Because paper printing has better evaporation and absorption drying, the problem of water-based ink drying is better solved and the popularity is also relatively low. Early in the United States, 80% of gravure prints use water-based inks. In addition, from an overall point of view, an important reason why water-based gravure inks are not popularized further is that the contradiction between the gravure printing speed and the print quality and the performance of the gravure dryer has not been resolved.
3, application in the field of screen printing
Countries that have used water-based screen printing inks in large quantities are Sweden, Germany and the United States. Since the 1980s, gloss and matt water-based inks have been developed internationally for printing on paper, paper, PVC, PS, aluminum foil, and metals. The development of screen printing in our country is very fast, and the progress in the development and popularization of screen printing water ink is slow. What is gratifying is that China has attracted people's attention in the research and development of screen printing inks. After several years of hard work, we have achieved some results. According to reports, screen-printed water-based inks have been applied to printing materials such as paper and plastics in China.
Fourth, the use of water-based ink
In the use of water-based inks, there are usually problems such as inaccurate hue, unstable viscosity, too fast or too slow drying, blurred outlines, difficulty in registering, ink bubbles, scumming, and imprinting. The main reasons are the following:
1, the pH value control
The pH is the key to the success or failure of water-based ink manufacturing and printability technologies. When using aqueous inks, you need to precisely control the viscosity and pH. Its pH should be controlled between 8.0 and 9.5. If the pH value of the water-based ink is too high, too strong alkaline will affect the drying speed of the ink, there will be back dirty, poor water resistance; if the pH is too low, alkali Too weak will cause the viscosity of the ink to increase, the drying speed will increase, and it will easily cause defects such as dirty plate, paste plate, and bubbles.
The pH value of water-based inks is mainly maintained by amines. During the printing process, due to the continuous volatilization of the amines in the binders, the pH value will drop, affecting the printing quality. In actual control, on the one hand, it is necessary to avoid the leakage of amines as much as possible, such as covering the upper cover of the ink tank; on the other hand, it is necessary to add stabilizers to the ink tank regularly and quantitatively. When the pH is low, a pH stabilizer or a small amount of a basic substance may be added. When the pH is high, a solvent or diluent may be added for dilution.
2. Control of temperature and humidity
The temperature and humidity of the printing shop are closely related to the drying and color of water-based ink printing products. The relative drying time is almost 2 times more than the relative humidity of 95% and 65%. At the same time, the dry humidity of the substrate itself will also directly affect the drying time of the printed matter.
3, ventilation degree and printing method
Since oxygen or air blowing is a factor that promotes the formation of aqueous inks by oxidative polymerization and volatilization of solid ink films, the degree of ventilation in the press room and the way the prints are stacked also affect the drying speed of the ink.
4, printing materials
The pH of the substrate also affects the drying and gloss of aqueous inks. Water-based inks are affected by the pH value of the printing paper when it is printed on the surface of the paper. When the acidity of the paper is high, the coupling agent acting as a driers in the water-based ink does not work, the alkali in the aqueous ink is neutralized, and the dryness is advanced; when the paper alkali is high, the water-based ink dries slowly and sometimes the water-based ink is limited. Completely resistant to water.
Fifth, the development of water-based ink
Due to the excellent environmental characteristics of water-based inks, developed countries and regions are currently working hard to develop and use aqueous inks to gradually replace solvent-based inks. The packaging printing with water-based printing as the main development object has become a trend in the world. From the point of view of the development trend of international packaging printing, water-based ink has developed from a single carton ink to various substrates and multi-color overprints.
In the United States and some European countries, the use of solvent-based inks containing benzene has been banned and green inks have been replaced. At present, 40% of U.S. plastic printing uses water-based inks. Other developed countries, such as Japan, Germany, France, etc., are also increasingly using water-based inks in plastic film printing. The United Kingdom has already banned the use of solvent-based inks to print films for food packaging.
In recent years, China has made some provisions for the packaging of food, and the status of water-based printing has been continuously improved in China. At present, China's water-based ink for flexible packaging ranks first among other printing inks with a consumption of 35%.