Improvement of water-based ink quality based on gravure printing machine structure

To solve the quality bottleneck of the film gravure aqueous ink, it is recommended to improve according to the structural characteristics of the gravure printing machine.

The problem of the adhesion of the water-based ink to the film is independent of the printing and transfer mechanism, and the binder of the aqueous ink is mainly selected according to the solubility characteristics. Water-based acrylic acid can be selected, or water-based polyurethane can be selected. At home and abroad, mutual modification of acrylic acid and polyurethane has been developed to adapt to various films. It is foreseeable that for the domestic water-based ink manufacturing industry, it is not very difficult to choose a suitable water-based resin. Furthermore, relatively mature film flexo-printing inks, no matter on OPP or PET, adhesion is no longer a big problem. If we refer to the resin system of flexographic inks, it is not impossible to use them in film gravure water-based inks.

In order to improve the adhesion of aqueous inks, the industry also achieves by controlling the pigment base ratio, so the particle size problem will also be considered as one of the factors to improve ink adhesion. In fact, the gravure process does not pay much attention to the particle size problem. Generally speaking, the fineness of the solvent-based gravure ink is controlled by 1/4 of the minimum aperture of the gravure cell. This classic data is for the gravure ink. It is also applicable. A serious problem is the stencil caused by the gravure aqueous ink, that is, the solubility of the aqueous ink matches the gravure short ink path. Flexo-printed inks have no problem with the filaments due to the long ink path of the flexo print. Even if there is a problem with the solubility, the ink path is long, and the thin line drawn on the anilox roller has been leveled by the ink itself before reaching the imprinting point. However, gravure cannot use the ink path to cover up such solubility defects, so solving the solubility defect is an urgent task of gravure aqueous ink.

The primary problem that causes the solubility fluctuation of the gravure aqueous ink is the fluctuation of the pH. The water-based resin is alkaline, and the pH is generally 8.5 to 9.5, and even more than 10.0. The basicity of the aqueous resin is related to its amination process, which is related to the process of dissolving the resin with an organic amine, ammonia or an inorganic base (NaOH or NaHCO3). The price of organic amines is relatively high, but the volatilization is slow. The aqueous resin dissolved with organic amines may have a change in pH at normal temperature, but the fluctuation is small. Ammonia water is cheap, but it evaporates quickly. Generally, it is water-based ink adjusted with ammonia water. It takes about 2 hours to measure the pH value and add stabilizer. The aqueous ink using the inorganic alkali process is substantially non-volatile, but has poor solubility.

The water-based inks we use nowadays use more ammonia water because of its good solubility and low price. However, due to the rapid evaporation of ammonia water and large fluctuations in pH, it is necessary to add stabilizers in time. In practice, the pH control level of the aqueous ink implemented in this way is as unstable as the sawtooth curve. To stabilize it, the pH measurement and stabilizer addition time must be shortened, and the frequency of pH determination and stabilizer addition must be increased. Therefore, foreign countries often use pH real-time control devices in water-based ink applications, which are measured at any time and added at any time to maintain the stability of aqueous ink performance.

This pH control method is also used in flexo-printed water-based inks, because flexo-printed inks have lower requirements for solubility, but they are certainly not used on gravure-based water-based inks, and solubility fluctuations must lead to knife filaments. Therefore, the use of an organic amine process for gravure aqueous inks will be preferred, as evidenced by the amination process of flexo-printed inks, even at slightly higher prices. Moreover, it is not realistic to require the operator of the gravure printing production line to pay attention to and adjust the fluctuation of the pH value of the aqueous ink from time to time, and the current production system has been unable to adapt to such work pressure.

The matching of the aqueous solution to the aqueous emulsion also affects the solubility of the aqueous ink, so the easiest way is to use a single resin. Water-based inks using only aqueous solutions have very few knives produced during the printing process, even less than the solvent-based inks. However, this aqueous ink does not solve the problem of adhesion of the ink on the film and the scratch resistance of the ink film. After the drying device of each color group of the gravure printing machine, there is generally a water-cooling roller for cooling the film, and the ink film surface of the film is directly wiped from the roller, and the ink film is easily scratched without a certain scratch resistance. Therefore, aqueous ink formulations typically have a certain amount of aqueous emulsion to enhance the hardness of the resin. However, if the aqueous solution and the aqueous emulsion are not properly selected, the hidden danger of solubility fluctuations will be buried.

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