The application of the hottest water-based ink and

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Application and precautions of water-based inks

1. Composition and characteristics of water-based inks

water based inks are made of water-soluble resins, advanced pigments, solvents and additives through composite processing and grinding. Water soluble resin mainly plays the role of connecting material in the ink, so that the pigment particles are evenly dispersed, so that the ink has a certain fluidity, and produces adhesion with the substrate material, so that the ink forms a uniform film after printing. The hue in the ink mainly depends on the pigment. The pigment is evenly distributed in the connecting material in the state of particles. The pigment particles can absorb, reflect, refract and transmit light, so they can show a certain color. Generally, pigments are required to have bright color, appropriate coloring power and hiding power, and high dispersion. In addition, it can also have different resistance according to the purpose of use. The function of solvent is to dissolve the resin, make the ink have a certain fluidity, transfer smoothly in the printing process, and adjust the viscosity and drying performance of the ink. The solvent of water-based ink is mainly water and a small amount of ethanol. Commonly used additives mainly include: pH stabilizer, slow drying agent, defoamer, diluent, etc

1) pH stabilizer

ph stabilizer is mainly used to adjust and control the pH value of water-based ink to stabilize it within the range of 8.0 ~ 9.5. At the same time, it can also adjust the viscosity of water-based ink and dilute the ink. Generally speaking, an appropriate amount of pH stabilizer should be added at regular intervals during the printing process to keep the water-based ink in good printing condition

2) slow drying agent

slow drying agent can inhibit and slow down the drying speed of water-based ink, prevent the ink from drying on the printing plate or roller, and reduce the incidence of printing failures such as blocking and pasting. However, the dosage of slow drying agent should be controlled well, which is generally controlled between 1% and 2% of the total ink volume. If the amount is too much and the ink is not completely dried, the printed matter will produce sticky dirt or peculiar smell

3) defoamer

the function of defoamer is to inhibit and eliminate the generation of bubbles. Generally speaking, when the viscosity of water-based ink is too high, the pH value is too low, or when the printing machine runs faster, it is easy to produce bubbles. If the amount of bubbles is relatively large, there will be white leakage and uneven ink color, which will inevitably affect the quality of printed matter. Generally, the addition amount is 1% - 2% of the total ink amount

4) diluent

is used to reduce the depth of color. The dosage is unlimited. Adding a large amount of diluent may cause the viscosity of ink to rise slightly. At this time, a small amount of diluent can be added at the same time for adjustment

the biggest feature of water-based oil blacksmithing first is that it reduces the emission of VOC (organic volatile matter) to the atmosphere, thus preventing air pollution, improving the printing environment, and greatly reducing fire hazards. Water based ink also has the characteristics of non-toxic, non corrosive, non irritating smell, good safety, convenient transportation and so on. Its high concentration, low dosage, low viscosity and good printing adaptability; Stable performance, good adhesion fastness, fast drying, excellent water resistance, alkali resistance and wear resistance after drying; Prints are full of imprints, bright colors and high gloss

the development and application of ink painting in China started late, but it has developed rapidly, especially in recent years. With the increasing demand for ink, the quality of domestic ink has also been improved. The shortcomings of traditional ink painting, such as slow drying, poor gloss, water intolerance, false printing, have been significantly improved. Under the condition that the price of imported ink is generally high, domestic ink with low price and good quality has gradually occupied the market

2. Application and control index of water-based ink

at present, the main application fields of water-based ink are flexographic printing and gravure printing. According to information, 95% of narrow flexo printing in the United States uses water-based ink, and 80% of paper gravure printing uses water-based ink. In China, it has also developed rapidly in recent years, but there is still a big gap compared with foreign countries

the control indicators that affect the printing quality of water-based ink include fineness, viscosity, drying speed and pH value

the fineness of water-based ink refers to the size of pigment particles in the ink and the uniformity of their dispersion in the binder. It is also a very important quality indicator. The fineness of the ink will not only have a certain impact on the coloring power and color equality of the ink, but also affect the rheology of the ink. The ink particles are too thick, which is easy to cause hairiness on the edge of the starting point, paste version and other defects; If the ink particles are too fine, the fluidity of the ink is too large, which will cause dot expansion and affect the printing quality

viscosity is the most important control index in the application of water-based ink, and it is a property that prevents fluid flow. Because viscosity directly affects the transferability and printing quality of ink, it is very important to control the viscosity of ink. In the printing process, the low viscosity of water-based ink will cause the disadvantages of light color, dot expansion, uneven ink transfer and so on; If the viscosity of water-based ink is too high, the transfer performance of ink is relatively poor, which is prone to dirty version, paste version and other disadvantages

flexographic water-based inks are generally used directly without dilution, and their viscosity can range from 30s to 45s/25 ℃. The viscosity of flexible version water-based ink can be lower. As long as an appropriate amount of stabilizer is added regularly, the viscosity change can be basically controlled. Gravure water-based inks are generally diluted with ethanol and water at a ratio of 1:1 diluent according to the traditional custom, and the viscosity is generally controlled at 15s ~ 25s/25 ℃

water based inks are usually alkaline (mainly maintained by amines). If the pH value of water-based inks is too high, it will affect the drying speed of inks; If the pH value is too low, the drying speed becomes faster, which is easy to cause the blocking of the printing plate and the corrugated roller, causing the dirty on the plate

the drying of ink is mainly volatile drying and osmotic drying. The drying performance of ink refers to the time required for the ink to dry after being transferred to the substrate, which is also one of the important indicators to measure the quality and performance of ink. Therefore, controlling the drying performance of ink is an important means to achieve good printing effect

the drying speed of water-based ink depends on the printing speed of the printing machine, the drying capacity of the drying equipment, the performance of the substrate material and the composition of the ink itself. If the ink dries too fast, it will dry and gradually accumulate on the printing plate and the embossing roller, and may block the embossing roller, resulting in the loss or damage of halftone points, and white leakage in the field part; If the drying speed of the ink is too slow, the performance characteristics of multi-color overprint are mainly reflected in the following: in some cases, the back will be sticky and dirty

in fact, the viscosity and pH value of the ink will also have a certain impact on the drying performance of the ink. For example, too high viscosity will reduce the drying speed of the ink, and too low pH value will make the ink dry too fast. Therefore, in the printing process, we should first adjust and control the viscosity and pH value of water-based ink, and then add an appropriate amount of fast drying agent or slow drying agent to the ink according to the actual printing speed to adjust the drying speed of water-based ink

4. Several problems that affect the quality of water-based ink and should be paid attention to

1) because water-based ink is a pure water-based system, it is not allowed to mix water-based ink with alcohol based ink or solvent based ink, or add organic solvents to the ink, so as to avoid printing quality problems if you do not know the connected COM port

2) ink should be stored indoors at room temperature of 5 ~ 50 ℃

3) when using, mix the ink in the bucket with a stirring rod, measure its viscosity and pour it into the ink tank. If the viscosity is too high or too low, it can be adjusted with diluent or thickener

4) generally, ink is suitable for high-speed printing. If the drying speed is too fast or the printing effect is poor during low-speed printing, a certain proportion of slow drying agent can be added

5) after printing, the remaining ink should be collected back into the corresponding original barrel or the cover of the ink tank should be tightly covered for next reuse. Be careful not to make the ink surface film, thicken or even dry due to the volatilization of water

6) the ink left on the printing equipment after printing can be washed away with clean water before it is completely dried, and the ink that cannot be washed with clean water can be cleaned with detergent

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