Packaging and ink selection

Editor's note: In recent years, with the continuous improvement of productivity, printing machinery has increased its performance, quality, and functionality in printing inks in order to increase printing quality and increase printing speed. The purity, saturation, lower ink film thickness, improved adhesion and gloss, reduced energy consumption, and the use of non-polluting, easily recyclable materials have made high demands.
Printing inks for flexible packaging are process inks that are printed on "soft" packaging materials such as plastic films, woven bags, aluminum foils, and roll wrappers using a printing press. In accordance with the different types of printing plates, it can be divided into gravure inks, letterpress inks and flexographic inks; according to the different main ink components, it can be divided into solvent inks, alcohol-soluble inks and water-based inks; Can be divided into table printing ink and printing ink.
First, the requirements of flexible packaging ink The application of flexible packaging products is mainly people's daily lives, generally require multiple transportation and longer use of time, and with the increasing consumer aesthetic standards, the printing quality must also be increased. In the course of daily use, the ink should not fade or change color due to light; the adhesion should have a certain degree of fastness; it should not fall off under the flexing during the packaging process and friction under general conditions; it should be good in the printing process. The adaptability of the printing overprinting, the printing surface is not adhered to other surface layers in the roll shape; in terms of stability, it is required to be able to withstand the solvent in the adhesive and the components of the acid, alkali, and oil in the packaging during compounding, It must also be able to withstand the heat of post-processing; suitable for cold areas and frozen storage; there are also many other testing items on viscosity, volatility, fineness, and so on. The relevant content has national standards, so we will not repeat them here.
In the field of environmental protection, solving the problem of environmental pollution during the manufacture and use of ink is currently the most pressing issue. Many developed countries have formulated strict laws and regulations, established strong regulatory and monitoring agencies, and continuously researched and developed a variety of effective solutions, such as the use of environmentally friendly materials and the suppression and recovery of harmful pollutant emissions.
In the past, since plastic films were more difficult to adhere to, the binder used in the gravure printing ink was generally made of a chlorinated polymer, but in the production process, chlorinated polymers required the use of strong solvents (such as toluene and other aromatics). Solvents) to dissolve and adjust the viscosity, in the production process will cause harm to the health and safety of the workers, the residual solvent in the package will also have a toxic effect on the human body, and the chlorofluorocarbons that are emitted from the chlorinated polymer will be destroyed The ozone layer, therefore, has begun to limit its use in many developed countries.
In order to meet the requirements of environmental protection regulations, flexible packaging inks have developed new systems adapted to environmental protection requirements, such as water-based inks and alcohol-soluble inks, among which water-based inks are more environmentally friendly products, but due to the higher surface tension of water, Up to 72 dyne/cm, resulting in hard to wet the ink, dry slowly, according to the current state of the art, can not fully meet the standards of flexible packaging ink.
In addition, in order to enable water-based inks to be used in gravure printing machines, not only inks and resins require more advanced technology, but gravure printing equipment also needs improvement. For example, an etching roll having a groove of about 38 to 42 micrometers needs to be converted into a laser patterning roll having a groove depth of 24 to 28 micrometers. In addition, more effective and powerful drying equipment and the like are required. These require a large amount of investment. So far, flexible packaging water-based ink has not yet been widely used in Europe and the United States and other major countries. Since water-based inks are not yet a complete replacement for toluene inks, the ink industry has developed alcohol-soluble inks that are environmentally acceptable, using low-toxic alcohols such as ethanol removed from the VOCs list as a solvent to solve toluene-based ink health problems. The resulting damage and solvent residue affect the quality of packaged foods. In developed countries, alcohol-soluble inks have completely replaced benzene-based inks. It is foreseeable that in the near future, inks used in China's flexible packaging will also use alcohol-soluble inks in large quantities.
Second, the choice of flexible packaging ink Before choosing ink, we must first determine the type of printing ink substrate, even if the same type of material, it should also learn more about the material composition including the substrate, the manufacturer, grade, additive pretreatment process, etc. , and then select the appropriate ink type according to the above characteristics. When choosing inks, you should also pay attention to the following four factors:
1. Printing conditions. Including the speed of printing, the ability of drying equipment, the shape and number of printing plates, the number of printing colors and the printing sequence, and the temperature and humidity conditions of the printing shop. The drying of the ink is the most important part influencing the printing quality, and the drying speed is affected by various factors such as the printing machine and the environment, and is the main factor that causes the printing effect to be unstable and the printing quality defect.
2. Printing effect. Including printing color, hue saturation, transparency, gloss, surface printing or in India, with or without additional printed glossy surface. The printing effect has a direct relationship with the degree of dispersion of the pigment particles in the ink. When the pigment particles are reduced, the color intensity thereof will increase rapidly, that is, a better gloss and transparency can be achieved. In order to prevent the coagulation of organic pigments, it is necessary to add a suitable dispersant therein.
3. Processing conditions. Most prints become finished products after one processing. For this processing condition, it must be judged whether it is suitable for the characteristics of the ink, which is also an important link to ensure the quality of the product. Especially in the subsequent composite processes, the compatibility with the adhesive, the strength of the composite, the strength of the heat seal, etc. are closely related to the type of ink and the resin binder in the ink, and it is necessary to conduct an experiment and investigation in advance.
4. Use. Before printing, it is also necessary to understand the final use and the state of use of the product. Special attention must be paid to it. Such as the packaging of daily chemical products must have a certain resistance to acid and alkali, oil resistance of oily food packaging, low temperature resistance of frozen packaging, etc. For some special packaging that requires high temperature cooking, not only the binder resin of the ink must have high temperature resistance. The pigments in the ink also need good resistance to high temperature decomposition. For special requirements of packaging, full testing should be conducted after full consultation with the customer, otherwise it is easy to produce quality problems.