Green packaging and water-based ink

In recent years, many countries have added a lot of requirements and restrictions on packaging and printing in terms of hygiene and environmental protection, especially for food packaging and printing. With the continuous improvement of people's awareness of environmental protection, environmental protection has become the theme of development in the 21st century. The use of small pollution, less pollution, and even pollution-free water-based ink has become an inevitable requirement for the development of green packaging.

First, the composition and characteristics of water-based ink

Water-based inks are inks prepared from a combination of specific aqueous polymer resins, pigments, and water, and the addition of co-solvents via physical and chemical processes, referred to as ink. Water-based ink uses water as the solvent. After the ink is transferred to the substrate, the water evaporates into the environment or penetrates into the substrate. The ink dries with the evaporation of moisture. Water-based polymer resin is the most important component of water-based ink. It plays a role as a linking material in the ink. It allows the pigment to be uniformly dispersed, giving the ink a certain degree of fluidity and providing adhesion to the substrate material. The ink can be formed into a uniform ink layer after printing. At present, most of the research and development use of alkali-soluble resin, this type of resin can be dissolved in water, made of water-based link material, printing and drying into insoluble substances. The hue of the ink depends mainly on the pigment. The pigment is distributed uniformly in the binder in the state of particles. The pigment particles can absorb, reflect, refract, and transmit light, and thus can exhibit a certain color. General requirements Pigments have a bright color, suitable coloring power and hiding power, and a high degree of dispersion. In addition, depending on the purpose of use, it is also possible to select specific solvents that are resistant to different resistances. The role of the solvent is to dissolve the resin so that the ink has a certain degree of fluidity, and can be smoothly transferred during the printing process, and the viscosity and drying performance of the ink are adjusted. Auxiliaries have a great influence on ink performance and are an indispensable part of ink painting. Commonly used additives in inks are pH stabilizers, slow drying agents, defoamers, dilutants, and the like. Its features are as follows:

1. Environmental Characteristics: As a new type of packaging printing material, water-based ink has the biggest advantage that it does not contain volatile organic solvents. Its use reduces the amount of organic volatiles (VOC) and will not damage ink manufacturers and printing operations. The health of the person improves the quality of the environment and is therefore known as an eco-friendly ink. The biggest feature of water-based ink is no pollution to the environment, no impact on human health, not easy to burn, and good safety. It can not only reduce the residual toxicity of the printed surface, make the printing equipment clear and convenient, but also reduce the risk of fire due to static electricity and flammable solvents, so in this sense, water-based ink is a new type of "green" packaging printing materials .

2, printing characteristics: In addition to the advantages of environmental characteristics of aqueous ink, the printing characteristics are also better. The ink is stable, does not corrode plate material, has simple operation, low price, good adhesion after printing, strong water resistance, and quick drying (printing speed up to 150-200 m/min). In addition to gravure inks, water-based inks are also suitable for flexographic and screen printing applications with great potential for development. However, due to the high boiling point of water in the water-based ink, the heat of evaporation is large, the drying of the printed matter is slow, and the hot air drying device is required. In addition, the printed matter of some inks may also be hygroscopic and anti-adhesive due to the excessively high humidity, and the gloss of the printed matter is relatively poor.

Second, the application of water-based ink

From a printing point of view, water-based inks are not yet suitable for offset printing, and its main application areas are flexographic printing and gravure printing.

1. Application in the field of flexo printing: We know that most of the flexo and gravure products are packaged products, in which food packaging, tobacco packaging, children's toys and other hygienic conditions require strict proportions of packaging prints, therefore, There is an urgent need for new printed materials, and adaptive ink is undoubtedly one of the best choices. Under the impact of the “green revolution” set off in the world, flexo printing has developed rapidly. The main reason is that the vast majority of flexographic inks use water-based inks, have excellent environmental performance, and are in line with the development trend of modern packaging and printing. In the U.S., 95% of flexographic products use water-based inks. In Japan, 70% of flexographic plates are used for printing on corrugated cardboard, and 95% of them use water-based inks. In China, the proportion of flexo printing is increasing day by day.

2. Application in gravure printing: In the 1970s, water-based gravure printing inks were widely used in the printing of packaging papers and cardboard paperboards. Since paper printing has better evaporation drying and absorption drying, water-based inks are dried. The problem is better solved and popularized earlier. In the United States, 80% of gravure prints use water-based ink.

3. Applications in the field of screen printing: Countries that have already used water-based screen printing inks are Sweden, Germany and the United States. Since the 1980s, textiles, paper, PVC, PS, aluminum foils and metals have been developed on-line with light and matt water-based inks. 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. According to reports, screen-printed water-based inks have been applied to printing materials such as paper and plastics in China.

Third, the use of water-based ink should pay attention to the problem

In the use of water-based inks, there are often problems such as inaccurate hue, too fast or too slow drying, blurred outlines, difficulty in registration, ink bubbles, scumming, and detachment of prints. The main causes are the following:

1. PH value control: PH value is the key to the success or failure of water-based ink manufacturing and printability technology. When using aqueous inks, you need to precisely control the viscosity and pH. Its PH value 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 value 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 the water-based ink is mainly maintained by the amine compound. In the printing process, due to the continuous volatilization of the amine in the binder, 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 value is low, PH value stabilizer or a small amount of alkaline substance may be added; when the PH value is high, solvent or diluent may be added to polar 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. Relative humidity of 95% compared with 65%, drying time is almost 2 times more than the difference. 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 water-based ink oxidative polymerization and volatilization of solid ink film, the degree of ventilation in the printing shop and the stacking method of the prints will also affect the drying speed of the ink.

4. Printing materials: The PH value of the printing materials also has an influence on the drying and luster of water-based 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.

In short, due to the excellent environmental characteristics of water-based inks, developed countries and regions are currently working hard to develop and use water-based 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.

Source: Ink Information