Application of the most environmentally friendly w

The application of environment-friendly water-based inks and the problems that should be paid attention to

first, what is water-based inks

the so-called water-based inks are mainly processed scientifically with water as the solvent. Compared with other printing inks, water-based inks do not contain volatile toxic organic solvents, so in the printing process, the polishing damage layer is shallow, the health of brush operators has no adverse effects, and there is no pollution to the atmospheric environment and the print itself. As the ink is non flammable, it can also eliminate the hidden dangers of flammability and explosion in the printing workshop, which is conducive to safe production. Of course, the application scope of ink and ink is different now. Ink is mainly offset printing, while ink is mainly flexo printing and gravure printing. In developed countries such as Europe, America and Japan, ink has gradually replaced ink as a special ink for other printing methods except offset printing. Take the United States as an example, 95% of flexographic printing materials use ink, and 80% of gravure printing materials use ink

in addition to environmental protection, ink widely used abroad also has excellent performance: stable ink color, high brightness, strong coloring power, non-corrosive plate, strong adhesion after printing, adjustable drying speed, strong water resistance, four-color overprint and spot color printing, etc. 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. In the traditional sense, the shortcomings of ink painting, such as slow drying, poor gloss, water intolerance, and 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

II. Composition and characteristics of water-based inks

water based inks are made of water-soluble resins, advanced pigments, solvents and additives through scientific compound processing and grinding. Water soluble resin mainly plays the role of connecting material in the ink, which is to make the pigment particles evenly dispersed, make the ink have a certain fluidity, and provide the adhesion with the substrate material, so that the ink can form 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 realize the full clearing of 140 million tons of "ground bar steel", which can absorb, reflect, refract and transmit light, so it 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

the commonly used additives in water-based ink 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 make it stable 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 every certain time in 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 amount of slow drying agent should be controlled between 1% and 2% of the total ink volume. If the amount of slow drying agent 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

water based inks comply with the requirements of environmental protection. The products are non-toxic, non corrosive, non irritating odor, non combustible, non explosive, good safety, convenient transportation, high concentration, low dosage, low viscosity, good printing adaptability, stable performance, good adhesion fastness, fast drying, excellent water, alkali and abrasion resistance after drying; It is easy to adjust the operation before and after printing and during the printing process. After printing, the printed matter appears full of impressions, bright colors, high gloss, gorgeous and rich. The printed complex patterns can also reach a rich level, and can print bright and high gloss colors

III. application of water-based inks

the biggest feature of water-based inks is to reduce the emission of VOC (volatile matter) into the atmosphere, so as to prevent air pollution, improve the printing environment, and significantly reduce fire hazards. It can completely eliminate the harm of some toxic substances in solvent based ink to human body and the pollution of packaged goods, and improve the overall environmental quality. It is especially suitable for packaging and printing products with strict hygienic conditions such as food and drugs

the main application fields of water-based printing inks are flexible printing and gravure printing. According to information, 95% of narrow flexographic paper prints in the United States are printed with water-based ink, and 80% of gravure paper prints are printed with water-based ink. In recent years, China has also developed rapidly, but there is still a large gap between the application amount and that of foreign countries

whether the application of water-based ink is appropriate is an important factor affecting its printing quality. The control indicators of water-based ink include fineness, viscosity, drying speed and pH value

in flexographic printing, the transmission of water-based ink and the control of ink volume are undertaken by the wrinkle roller, so the fineness of the wrinkle roller must be selected according to the situation of the product. For field printing, the wrinkle roller with about 300 lines is generally selected, and the ink layer is relatively thick, while for printing 50 lines of fine-grained version, the wrinkle roller with 600 lines needs to be selected, and the number of lines of the wrinkle roller is generally four times the number of lines of the printed matter, so as to obtain better printing clarity and resolution

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 of ink and the quality of printed matter, 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; On the contrary, if the viscosity of water-based ink is too high, the transfer performance of ink is relatively poor, prone to dirty version, paste version and other disadvantages

flexographic water-based ink is generally used directly without dilution, and its viscosity range can be 30 "~ 45"/25 ℃ (coated with 4 \cup). The viscosity of flexographic water-based ink for cartons can be lower. As long as water stabilizer is added regularly, its viscosity change can be basically controlled. Gravure water-based ink is usually diluted with ethanol and water 1:1 diluent according to the traditional custom, and the viscosity is generally controlled at 15 "~ 25"/25 ℃

water based inks are usually alkaline (mainly maintained by amines). Generally, the pH value of water-based inks should be controlled between 8.0 and 9.5. 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 viscosity of the ink increases and the drying speed becomes faster, which is easy to cause the blocking of the printing plate and the wrinkle 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 flexo 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. The general principle of selecting the ink drying speed is that under the existing conditions of the printing machine, the ink should be able to be fully dried before the next printing color deck and before rewinding or stacking, but it cannot be dried on the printing plate. 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, there will be a printing smell, or in the case of multi-color overprint, it will cause the back to stick 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, if the viscosity is too high, the drying speed of the extended stretching space of the ink will be reduced, and if the pH value is too low, the ink will 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

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. If the ink particles are too thick, it is easy to cause hairiness on the edge of the starting point and paste plates. However, if the ink particles are too fine, the fluidity of the ink is too large, which will cause dot expansion, which is bound to affect the quality of the printed matter

IV. impact on the quality of water-based inks and several problems that should be paid attention to

1. Because water-based inks are pure water-based systems, do not mix water-based inks with alcohol based inks and solvent based inks, or add organic solvents to inks, so as to avoid printing quality problems

2. Ink should be stored indoors at room temperature of 5 ~ 50 ℃

3. When using, mix the ink in the barrel 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. Due to the volatilization of water in the printing process, the viscosity of ink will increase and the pH value will decrease. The pH value should be controlled between 8.5 and 9.5. If it is beyond this range, pH stabilizer can be used to adjust it to maintain the stability of viscosity and pH value

5. Generally, ink is very 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

6. 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

7. The ink remaining on the printing setting after printing can be washed with clean water before it is completely dried, and the ink that cannot be washed with clean water can be washed with detergent

how to use ink additives

the printability of ink is affected by objective conditions such as printing conditions, surface characteristics of substrate, ambient temperature and humidity, and the storage time of ink. Therefore, when using ink, it is necessary to use some additives to slightly adjust the ink to obtain the best printing effect

1. Color seed: used to deepen the color. The dosage is 0 ~ 30%, more than 30% will make the content of binder in ink too low, resulting in the decline of adhesion and wear resistance

2. Diluent: it is used to reduce the depth of color, and the dosage is unlimited. Adding a large amount of diluent may cause the viscosity of ink to rise slightly. At this time, it can