Composition characteristics and preparation of the

Composition, characteristics and preparation of gravure printing ink (II)

7 Mixed solvent. Refers to the solvent that mixes the above two or more solvents. The mixed solvent can not only dissolve the resin well, but also adjust the drying speed of the ink by changing its ratio. Our factory uses a mixed solvent of toluene, ethyl acetate and ethanol. In gravure printing ink, resin and solvent are both binder. The main use of binder is a large number of renewable resources, which will face the situation of no one recycling. The use is to bond pigments to the surface of substrate to form an ink film, so as to achieve the purpose of displaying images and words. The pigment is transferred to the print by the adhesion of the binder. Secondly, in printing, the connecting material also plays the role of protecting coloring, presenting gloss and protecting the substrate. If the connecting material is not properly prepared, not only can we not get prints with bright colors and excellent gloss, but also there will be a series of faults during printing, such as paste, dirt, scratches, not easy to dry, and even the connecting material is an important component of gravure printing ink

I. fluidity

fluidity is a comprehensive reflection of the relative density, viscosity, coagulability, yield value, thixotropy, ink length and other properties of gravure printing ink. In the printing process, the fluidity of gravure printing ink is required to be good. If the fluidity is not good, it is difficult to control the ink viscosity in the printing process. In the ink supply device, the ink delivery is not smooth, which may cause paste and uneven coating, resulting in the "orange peel" phenomenon of the ink film. The luster is not pleasing to the eye, etc. However, the ink should have a certain color concentration, and the pigment content should not be too low. However, when the pigment content in the ink reaches a certain level, it will become a plastic fluid with poor fluidity. In order to maintain good fluidity, pigments and binders should have good affinity. The connecting material should have appropriate viscosity, have appropriate wettability to the pigment, and minimize the thixotropy and yield value of the ink. Therefore, when preparing gravure printing ink, the ink should be free and smooth, fine and uniform, and have a certain cohesion

second, viscosity

viscosity is a measure of internal resistance that hinders the relative motion ability of molecules due to the mutual attraction between fluid molecules, that is, the new regulations on fluid flow require more standardized and strict internal resistance. Whether the viscosity of gravure printing ink is appropriate is the key to ensure its good transmission performance and get excellent prints. And viscosity can also determine the transfer rate of ink. If the viscosity is high, the transfer rate will decrease

the factors affecting the viscosity of gravure ink are as follows:

1 Viscosity of resin solution. Resin solution is a solution in which a certain amount of resin is dissolved in solvent. If the viscosity of this solution is small, the viscosity of the ink is also small; Otherwise, it is large

2. Matching of pigment and binder. If there is no condensation reaction between pigment and binder, the viscosity of the system is relatively small; Otherwise, it is large

3. Miscibility and miscibility of solvent and resin. If the solvent can dilute the dispersion resin in any proportion, the viscosity will decrease regularly with the increase of solvent content

when preparing gravure printing ink, the "use viscosity" (the actual viscosity of the ink in the printing process) of the ink should be controlled within the range of seconds/25 degrees

III. dryness

gravure printing ink is a volatile ink. The so-called volatilization refers to the process that the energy of liquid molecules escapes from the attraction between liquid molecules. Drying is a volatile process in which the solvent in the wet ink film escapes and changes from liquid to solid by using this property of liquid

after printing with gravure ink, the solvent in the ink layer is required to escape from the system in an instant to dry the print pattern at a faster speed before entering the next process. The drying speed has a decisive influence on the tone, accumulation and smell of prints. When drying too fast, after scraping and wiping the ink remaining in the gravure pit, at the moment of reaching the substrate, the solvent volatilizes too fast, and the viscosity increases, which affects the ink transfer, resulting in under inking in the high light part, poor ink dispersion in the dark part, and even paste. At the same time, peeling phenomenon will occur in color overlay printing; When the drying is too slow, although the transferability will not be a problem, the post process cannot be carried out, and overprint is also difficult

the drying speed of gravure printing ink mainly depends on the volatilization speed of ink solvent

the evaporation rate of solvent in gravure printing ink is not only related to the type of solvent used, but also related to the release of solvent by resin and pigment. Pure solvent volatilizes quickly, resin liquid volatilizes slowly, and it is even slower after adding pigment. Controlling the evaporation speed of gravure printing ink and formulating different drying speed indicators for different pigments are important conditions to ensure the smooth progress of printing

when preparing gravure printing ink, the main function of fatigue testing machine is to measure the fatigue performance of metal and its alloy materials under tensile, contraction or alternating tensile and compressive loads at room temperature. First determine the resin pigment, and then select the solvent, which is an important principle for preparing printing ink. The following factors are mainly considered:

1 The speed of the printing press

2. Type of substrate

3. The circulation path of ink is the circulation of ink bucket and ink tank, or others

4. Climatic conditions, generally normal drying requires temperature degrees, and the relative temperature is%. When printing below 20 degrees, the natural drying speed of ink should slow down, and the natural drying speed of ink above 30 degrees tends to accelerate; The low relative humidity of the air is conducive to the volatilization of the ink solvent, on the contrary, it hinders the volatilization of the solvent. In order to ensure the smooth progress of high-speed printing, the gravure press is generally equipped with a heating device to dry the ink film

5 food packaging is the field where film is most used Factors such as loose paper surface should also be considered

the prepared gravure printing ink should meet the following requirements:

1 Color. It should have bright hue, high saturation, and good transparency or opacity

2. Printability. It should have good leveling, transfer, adhesion and proper viscosity

3. Dryness. It should have a suitable drying speed to adapt to overprint, stacking and other operations

4. Resistance. It should have good flexibility, friction resistance, heat resistance, solvent resistance, processing resistance and other properties

according to the above introduction and the temperature and humidity conditions of the printing workshop, it is not difficult to prepare gravure printing ink that meets the requirements