Discussion on Water-based Gravure Printing

In the past, there have been many waves of water-based impact around the gravure printing industry, but so far it has failed to gain rapid popularity. However, each impact gave more or less impetus to the watering of the gravure. From the failure experience of many large companies in the past to water-based experiments, many characteristics of water-based inks, including printability, have been gradually discovered, and the relationship between drying equipment, drying and speed, and the use of inks have been gradually resolved. The differences in the quality of printed matter, including the cost of operation including ink costs, the choice of the best printing plate and squeegee, and the use of used ink and cleaning agents, have made it clear that there is a difference between aqueous inks and oil inks. And, finally, the obstacles to economic accounting can be said to be a major cause of the failure to achieve rapid adoption of waterborne technology. This article will discuss the possibility of water-based gravure printing.

The status of gravure ink

In general, the package gravure is a special gravure, the use of oily ink accounts for more than 1/4 of the total ink. However, packaging gravure has a wide variety of substrates and uses, and it is difficult to control the water-based rate. Therefore, this paper evaluates the non-tolueneization rate and water-based rate from our shipments.

It can be seen from Table 1 that when the printing material is paper, the paper is adsorptive, and its water-based properties are progressing; the non-adsorbing printing material PVC wallpaper has just started due to the heating process (200° C.); non-adsorption Water-based plastic film has not made much progress. Obstacles also appear to be economic performance or ink performance problems caused by productivity.

That is, one of the core issues of water-based inks is the drying performance of inks. The solutions are:
1) Add ethanol to the solvent;
2) Make the plate mesh shallow (light plate);
3) Improve the performance of the drying device.

Composition of ink

Let us first analyze point 1). Originally, the so-called water-based ink is an ink whose solvent is water, and it is necessary to add ethanol (usually added in a few tens of percent) in consideration of the wettability or printability of the plastic film. Completely water-based inks (ethanol 4% or less) have good stability and are ideal environmentally-friendly inks, but the actual water-based inks used in the solvent consist of water and ethanol. So how big is the proportion of ethanol? Judging from the laws and regulations in Japan, there is no restriction on the discharge of solvents at this stage. The PRTR Act is mainly directed at regulations concerning the registration of chemicals, and the composition of water-based inks is not included in the scope of limitation, but according to various regulations established during the Showa era in Japan. The regulations, Chiba Prefecture and Tachibuki Prefecture have published guidelines on relevant measures, requiring the use of chemicals to be reported and restrictions on emissions. It contains the content of less than 30% of the solvent as a low-pollution material and does not need to be processed. Therefore, it is a consensus that the actual ink with a solvent content of 30% or less is defined as an aqueous ink in the industry. In particular, recently the “Tachikiko Prefectural Living Environmental Protection Regulations” has been formulated, which restricts the discharge of solvents. The details of the relevant rules are yet to be introduced in the future. The details are not yet clear.

From the aspect of firefighting law. For example, if the volatile component in ethanol is less than 5%, the fire safety law will classify it as a combustible material rather than a dangerous material. Basically, the problem is not significant. When the volatile component exceeds 5%, it is classified as the fourth major oil (2). Type (water-soluble), as a dangerous substance, the specified amount is 1000L.
In addition, in terms of pigments, in order to make the prints dry as quickly as possible, the pigment concentration of the aqueous ink should be adjusted to 1.3 to 1.5 times the pigment concentration of the general oil ink according to the requirements of the shallower version. However, white ink should be set according to the general oily ink concentration. The premise of the shallow version of white ink is its hiding power. Therefore, the white ink version must be deep or through repeated printing to achieve the requirements.

With the exception of individual components, water-based ink pigments are basically the same as those of oil-based inks, so the color reproduction is consistent with that of oil-based inks.

In ink resins, propylene and urethane resins are gradually being eliminated. The surface printing and heat-shrinkable film printing use acrylic resin, which is printed in such a manner that it has versatility. The urethane-based resin is mainly used. However, because these resins still have some problems, new resins should be used in combination with other resins or two-component resins.

In summary, the undiluted raw ink ethanol content should be below 4%; dilution solvent ethanol content should be below 60%; on the machine ink content should be below 30%. However, the current use of oily ink packaging cart manufacturers have not been subject to fire restrictions, the ink ratio is not strict.

Shallow version

Let us analyze the issue of the shallow version. Water-based ink contains water, so the drying time is prolonged, and thin lines and vulgarity become thicker. This is one of the printability failures caused by the decrease in the surface tension and deterioration of the drying performance. The solution to these problems is to simplify the issue. In order to balance the drying problem, it is necessary to ensure the realization of the shallow plate by increasing the concentration of the aqueous ink. If the test color curve can be made and applied, the effect of the oil ink plate can be reproduced. Recently, laser platemaking equipment was introduced to prototype 350 lpi precision and 12 m depth plates. However, for the platemaking system, due to its advantages and disadvantages (see Table 2), the method corresponding to the graphic type and print lot should be selected.

Drying device

Now analyze the drying device. The drying systems currently under discussion include infrared, far infrared, and electromagnetic wave drying systems.

From the present situation, the air volume of the dryer has a great influence on the drying speed. The existing printing press (air volume 30-40m3/min) can only be opened to about 50 m/min, if you want to open to more than 100 m/min, you must change the dryer.

The various uses of flexible packaging water-based inks are currently under discussion, but there are still some problems with the physical properties of water-based inks compared to the oil-based inks currently used. Table 3 Therefore, physical properties for use must be checked and matched. Especially in lamination processing, the use of water-based inks is related to adhesives, which should be noted.

When laminating is considered, in order to exhibit the characteristics of the water-based ink, the choice of adhesive must be studied from the viewpoint of desolvation. In this case, AC compounds, water-based drying, solvent-free adhesives, and the like have been investigated, but they cannot meet the requirements in terms of cost and physical properties. Must choose the best adhesive that can meet a variety of requirements.

Source: Print World