A Complete Analysis of Inkjet Printing on Plastic Packaging Bags

Water-based ink, also known as water-based ink. The fundamental difference between typical water-based ink and traditional solvent-based ink is that water (or water and a minimal amount of cosolvent—alcohol) replaces the organic solvent in solvent-based ink to formulate a water-based binder. This binder, combined with pigments (pigments or dyes) and specific additives, constitutes water-based ink. Today, Shunxingyuan Packaging, a professional flexible packaging manufacturer, will analyze water-based ink printing on plastic packaging bags for you.

I. Advantages of Water-Based Ink

Compared to traditional printing inks, the binder in water-based ink should only contain water and no volatile organic compounds. Therefore, compared to traditional solvent-based inks, water-based inks exhibit a series of advantages, which can be summarized as follows:

1. Good Environmental Protection

During printing, water-based ink only emits water vapor and no volatile organic compounds. The printing site and surrounding environment are not polluted by toxic and harmful organic solvents, resulting in superior environmental protection performance.

2. Excellent Hygiene and Safety

Water-based ink binders contain only water and no toxic or harmful organic solvents. In printed products, there are no residual organic solvents. Therefore, printed materials using water-based ink have better hygiene and safety compared to traditional solvent-based inks.

3. Improved Production Safety

Water-based ink binders contain only water and no flammable or explosive organic solvents. Warehouses and production workshops storing water-based ink will not experience fires or explosions due to the presence of flammable or explosive organic solvents.

4. Resource Saving

Unlike solvent-based inks, water-based ink printing only releases abundant and inexpensive water vapor into the atmosphere during the drying process, not the scarce industrial resource—organic solvents. Therefore, from the perspective of resource saving and promoting sustainable human development, using water-based ink printing instead of solvent-based ink printing is also very advantageous.

Typical Example:

A gravure printing machine with a width of 1m and a printing speed of 300m/min prints plastic film for 20 effective operating hours per day, printing 360,000 square meters of film; based on the average ink consumption of 7gsm for gravure printing (wet ink), 25,200g of ink is consumed, i.e., 2.52t; solvents are added during gravure printing to adjust the ink viscosity, with a conventional addition ratio of 1.5 to 2.0 times the ink (i.e., 1.5-2.0kg of solvent is added per kg of ink).

If we calculate according to the standards of better-managed enterprises (i.e., adding 1.5 times the amount of solvent to the ink), 3.78t of solvent is also needed during the printing process. Adding the solvent already present in the ink, which accounts for about 70% of the ink (1.764t), a single gravure printing machine emits 5.544t of solvent per day.

The large amount of solvent emissions not only wastes precious resources but also causes significant environmental harm. Experts and scholars believe it is one of the important causes of haze in China. Therefore, the Chinese government has implemented a mandatory charging policy for volatile organic matter emissions. In addition, for food and pharmaceutical packaging materials, if the organic solvent does not evaporate completely during printing, the residual organic solvent will reduce hygiene and safety, harming human health. Therefore, solvent-based ink printing does not conform to the concept of green packaging and is not conducive to sustainable human development. With the development of the packaging industry and increased production, this negative impact is also increasing.

II. Two Major Challenges of Water-Based Ink Printing

1. Facing the Problem of High Surface Tension of Water and Difficulty in Spreading on the Substrate

The spreading of ink on the substrate is the basis for achieving printing processing and ensuring printing quality. As we all know, water has a very high surface tension (as high as 70mN/m or more), and its wettability on low-surface-tension substrates such as plastic films (surface tension of around 40mN/m or lower) is very poor. The surface tension of the water-based ink system must be significantly reduced to facilitate the spreading of the ink on the substrate. This requires the use of specific additives to modify the water-based ink system, significantly reducing its surface tension to a level lower than that of the substrate, facilitating the spreading of the ink on the printing substrate, and creating conditions for obtaining exquisite printing effects.

The emergence of a large number of high-quality surfactants has created favorable conditions for water-based ink manufacturers to reduce the research work on water-based ink systems; the vast number of scientific and technological workers engaged in water-based ink research have conducted long-term and arduous work to find ways to reduce the surface tension of water-based ink, finally achieving fruitful results and effectively solving the problem of reducing the surface tension of the water-based ink system, laying a good foundation for exquisite water-based ink printing.

2. Facing the Problem of High Latent Heat of Vaporization of Water and Difficulty in Evaporation and Drying

Given the high latent heat of vaporization of water, there is a problem of how to improve the printing speed of water-based ink. In industrial production, production speed directly restricts production costs. Therefore, the high or low production speed is often a decisive factor in determining whether a process has market competitiveness.

Comparison of Boiling Points and Heats of Vaporization of Water and Some Organic Solvents

From the data in the table, it is not difficult to see that the latent heat of vaporization of water is significantly higher than that of organic solvents, 3 to 8 times that of alcohols, esters, and other organic solvents. Due to the high latent heat of vaporization of water, the drying of water-based ink is naturally much more difficult than that of solvent-based ink, posing a huge challenge to achieving high-speed printing.

Practice has shown that simply relying on water-based ink manufacturers to improve the ink formula to increase the drying speed of water-based ink has a very limited effect. The problem of improving the printing speed of water-based ink requires the concerted efforts of printing equipment, printing rollers, and printing enterprises. Although significant progress has been made in improving the printing speed of water-based ink, a lot of work still needs to be done to achieve ideal results.

III. Current Status of Water-Based Ink Development and Application

Starting in the 1960s and 70s, some forward-thinking individuals concerned with environmental protection and the conservation of material resources began to dedicate themselves to the research and development of water-based inks. After years of hard work, significant progress has been made in water-based ink printing: Many water-based ink research and production companies have reduced the VOC content of their inks to below 5%; some high-level water-based ink production units have even achieved VOC content below 1%, approaching zero; the content of benzene and heavy metals in water-based inks is close to zero, reaching undetectable levels. At the same time, water-based ink products have been successfully applied in the production of plastic flexible packaging.

Currently, in developed industrial countries, water-based ink printing for packaging products reportedly accounts for over 80% of printed packaging; in contrast, the application of water-based inks in China is still quite limited, especially water-based ink printing on plastic films, which is still in its infancy. The work of promoting water-based ink printing is a long and arduous task.

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