The Causes and Preventive Measures of Floating Color and Flower Blooming of Packaging Printing Inks

In the process of packaging and printing, the operator often spends a lot of time because of the floating color and hair-flowering of the printing ink film, and also greatly reduces the quality of printed products. This failure is mainly caused by the presence of multiple pigments or fillers in the printing ink. Due to the fact that the printing ink (film) ink (ink) floats in different colors and the pattern of hair growth is different, for this reason, the author tries to discuss the following points based on years of practice and discuss with the colleagues in the packaging and printing industry.
First, ink film floating color and hair flower expression form Floating color refers to the ink, once printed, the pigment in the wet ink film is horizontally layered separation. The concentration of one or more concentrations of a plurality of pigments in the JM film is a uniform distribution, but there is a clear difference from the color just produced from the ink factory or from the previous formulation.
Flowering refers to the uneven distribution of multiple colors in the ink film of a packaged and printed ink, which is usually a stripe or honeycomb. For this reason, people often understand the vertical separation of the pigment.
In addition to floating color or hair, the phenomenon of stripe-like bloom that can be seen on the surface of the ink film packaged and printed by the anilox roller after it is pumped or inked by the pump is called silk pattern.
1.1 The cause of floating color flowers. We know that in the packaging printing ink system, the composition containing two kinds of pigments or fillers may cause floating color and hair growth. The production process of the ink maker is improper or the improper operation of the packaging and printing operator also produces floating color and Hair flowers.
One is the effect of pigment settling and flocculation on floating color and hair growth. We have known in many years of practice that floating color and hair dyeing are caused by the uneven distribution of pigment on the surface of the ink film after printing (including uneven printing plates, uneven pressure, etc.). Although the reasons involved are many, the stability of pigment dispersion is very important. For example, in the ink system composed of a variety of pigments, the separation of the pigment-dispersed ink system is often caused by the excessive flocculation or sedimentation of a certain pigment, which is the reason why we often talk about floating color and flowering. Secondly, after observing the whole process of sedimentation of packaging printing ink, we learned that the role of particle size is more serious than density, and floating color is more serious, which is usually called the difference in pigment density. From the perspective of China's packaging and printing ink dispersion system, small-particle-size pigment particles absorb resins and solvents that are much larger than large pigment particles, and tend to show a decrease in density. Large-particle-size pigment particles increase in density and cause pigments. The sinking of the particles; while the pigment of the lower particle size floats and constitutes the floating color phenomenon of the printing ink. In this regard, people in the ink formulation design, for the slight control of flocculation in order to prevent the pigment floating flower was used as the focus of adjustment, although effective, but excessively serious flocculation, it will produce precipitation and cause floating color flowers The emergence of. For the sake of simplicity in production, after the 1990s, the effect of dispersants, especially coupling agents, in the ink system was very obvious. The purpose of the dispersants was to achieve the best adsorption state on the surface of the pigments. The purpose is to bridge the link between the binder and the pigment, so as to enhance the storage stability of the pigment and to prevent floating of the flower.
The second is the effect of solvents on floating color and hair growth. Ink expert Yang Haishu believes that the solvent solubility of the resin polymer and the rheology of the printing ink and the adaptability to the packaging printing process, especially the formation of ink film is very important. Therefore, in order to make full use of the solvent, generally use a variety of solvents (ie, mixed solvents) for compatibility, that is, the composition of the true solvent and the diluent. In the design of packaging printing ink formulations, the hydrogen bond between the solvent and the substrate should be similar (similar to the stickiness); the solubility of the solvent is similar to the solubility of the resin in the ink system (similar compatibility); the surface tension of the solvent and the resin in the ink system The surface tension is similar (nearly flat); the density of the solvent is similar to the density of the binder (resin) (similar stability); the gradient gap of the mixed solvent is similar (close and dry completely); the true solvent and diluent are needed to maintain the packaging printing ink Adapt the amount of printing. If we achieve the above six basic conditions, we will not cause the floating ink and the blooming of the printing ink film due to the solvent.
The third is the effect of surface tension gradient on the floating color. For a long time, people have been ignoring the cause of the surface tension gradient on the ink film. It is not known that the solvent tension of the surface of the printing ink film on the packaging printing ink will cause the ink film to form eddy currents and cause a tension difference between the upper and lower surfaces of the printing ink film. . The surface of the wet ink film is heated or unevenly blown, resulting in a difference in surface tension, which may cause parallel movement (migration) of the ink film and generate a phenomenon of flowering.
Too much solubility of the solvent will cause the viscosity of the packaging printing ink to rapidly decrease, which will accelerate the settling speed of the pigment particles. As a result, the occurrence of color floating due to different particle diameters of the pigments creates conditions.
In addition, in the mixed solvent system, if the true solvent volatilizes too quickly, not only the surface tension difference but also the balance of the solvent volatilization gradient will be destroyed. As a result, the resin in the ink system also agglomerates the adsorbed pigment particles due to the reduction of the true solvent, thereby affecting the improvement of the flatness of the ink film surface. However, the slow evaporation of the solvent can cause the ink film to flow too long. As a result, the occurrence of eddy currents in the ink film is unavoidable, causing problems such as hair blooming, floating color, and sagging.
The fourth is the effect of the resin on the floating color in the ink system. The variety and variety of resins are different, and the ability to wet is not the same. For a plurality of pigment compatibility compositions, since various pigments have different adsorption capacities for resins (linking materials), non-wetting pigments are prone to condensation, which is also an important cause of floating color.
In the packaging printing ink system, when the molecular weight and molecular weight distribution of the resin are different, the size and distribution of polar reactive groups will not be the same, and the difference in these distributions will result in different wetting ability of the pigment. Second, various pigments have different adsorptive capacities for the binder (resin)—adsorption of thin pigments on the ink film layer tends to cause flocculation—floating dyeing. In the case of small-molecular-weight rosin or alkyd resin inks, due to its large polarity and strong adsorption force, the formed adsorption ink layer is thin, dispersion stability is poor, and flocculation occurs easily and color appears. From the theoretical point of view, when the packaging printing ink is flocculated, the concentration of the resin in the printing ink grinding process must be controlled according to the performance of different pigments and binders, and the polymer (bonding material) must be forcibly adsorbed on the The purpose of the pigment surface is to prevent a single pigment from flocculation failure.
Poor solubility of the polymer (resin binder) in the packaging printing ink system can also cause the disadvantages of floating coloration. In general, miscibility is poor when using several resins. Followed by the choice of solvent Solubility can not reach the critical value, that is, people often say that the poor mixing of the resin, coupled with the lack of affinity for the pigment is not enough, often dissolved in the volatile, it will appear floating color, hair. Even if the turbidity, floating color is eliminated under the effect of the solvent, it will appear in the solvent evaporation process. Because the volatilization of solvents and diluents destroys the balance of the resin binders, it is often said that the resin binders with poor compatibility will bring out the adsorbed pigments, resulting in the floating color of the ink ink film. Hair flowers and so on.
The fifth is the effect of packaging and printing conditions on the floating color. The dryness of water in the north of the Yellow River in China and the rainy and wet areas in the south of the Yangtze River will also result in the formation of floating color flowers after printing. Whether it is a dry environment or a high-humidity workshop (with the exception of workshops for temperature and humidity control), the evaporation of solvents, the decrease of the surface temperature of the ink film, and the condensation of moisture all cause the formation of eddy currents in the ink film of the packaging printing ink. Hydrophilic pigments on the surface absorb certain moisture, which in turn causes agglomeration and separation of the pigments. Once the moisture is brought into the ink layer and the hydrophilic pigment particles are bound, they often appear to be aggregated, settled and floated by bridging the non-intermolecular liquid. The occurrence of such failures is particularly evident in packaging printing inks that have a high rate of evaporation and hydrophilic solvents. This failure is often seen in water-based letterpress, water-based gravure, screen printing, plastic letterpress, plastic intaglio, and color inkjet inks.
1.2 In printing inks, the formation of insoluble colloidal particles leads to shrinkage, and sometimes it is often confused with floating colored hair dyes. We know that the surface active material changes its concentration during the process of forming a printing ink, and it exceeds its solubility to generate a small amount of immiscible droplets that cause shrinkage. For example, excessive addition of silicone oil or excessive viscosity, easy to produce shrinkage. The difference between shrinkage holes and floating colors is that irregular, spherical, small depressions are formed on the ink film, often centered on a drop or a small piece of impurities, and a ring shape is formed around the ring. From the point of view of the leveling of packaging printing inks, it is a special "point type" unevenness that arises on the surface of the printing ink film (its shape is divided into planes, craters, exposed bottoms, bubbles, dots, etc.). .
Second, to prevent and remedy the floating color of the flowers to take measures around the above ink ink film floating flower hair several forms of expression, a rough analysis and induction. But how can we prevent and remedy faits accomplis, and the relevant literature is very few. For this reason, the authors described each case according to accumulated experience.
The stability of the packaging printing ink is the result of the interaction between the various components. For example, the polarity of the solvent is different, and the adsorption on the surface of the active agent pigment is also different. For example, the order of the adsorption amount of octadecylamine in each component solvent is: toluene>dichloroethane>mixed solvent. Most people think that various solvents only affect physical adsorption without affecting chemical adsorption. At the same time, it is believed that the binder and the active agent will produce competitive adsorption on the surface of the pigment, which has been proved to be correct. This shows that the competitive adsorption depends on the size of the binder, the active agent and the color, and the surface affinity of the filler. If the pigment or filler is hydrophilic, the more polar substance is selected for adsorption in the non-polar solvent. If it is hydrophobic, in the polar solvent, the more hydrophobic substance is selected for adsorption. The physical adsorption of the surfactant does not affect the chemical adsorption of the polymer, because the physical adsorption of the surfactant on the surface of the pigment and the filler is not strong, and the solvent is easily extruded from the surface of the pigment by the resin. Surfactants that form chemisorption with the pigment surface cannot be extruded from the surface of the pigment filler by the resin polymer. The greater the adsorption saturation of the surfactant on the surface, the greater the resistance to polymer adsorption. On the other hand, if the dispersion grinding time during the ink production is slightly shorter, the ink is not easily expelled from the pigment surface by the resin in the solvent during the manufacturing process or when the ink is stored, but other phenomena may still occur. This remains to be proved in practice.
In polar solvents, ultrafine active calcium and alkyd resins can be adsorbed on the surfaces of Tiafranium and Chromium Yellow. This is because the pigment surface has two active centers and therefore it is slightly acidic active calcium and alkyd resin. Can still be adsorbed on the surface, but its coverage is low, resulting in poor wetting and dispersing properties, when dispersed to 7.5 microns, the surface will have a floating color; when dispersed to 1-2 microns will disappear . If a thinner is added during the printing process, the floating color reappears again. Must choose the appropriate dispersant, adding wetting dispersant can not only reduce the grinding time of the pigment and filler, but also save energy and improve work efficiency.
In order to prevent the floating color of the ink, wetting and dispersing agent should be introduced into the packaging printing ink system, its purpose is nothing more than: (1) increase the gloss of the ink film, improve the leveling of the ink film. It can greatly improve the fineness of the pigment and filler, ensure the storage stability of the ink, prevent the generation of large flocculation particles, and improve the flatness of the printing ink film; (2) reduce the viscosity of the ink and improve the fluidity of the ink. Under the same conditions, it can greatly increase the concentration of pigments and fillers, increase their filling properties and reduce the cost of materials; (3) Improve the storage stability of packaging printing inks. The storage stability of packaging printing inks depends entirely on the dispersion quality of the pigments. If the dispersion is not good and the precipitates are precipitated, the floating color, hair growth, and coloring power will be reduced. Secondly, the rheology also changes, and the reason is closely related to the ratio of the resin (base material) and the solvent and the dispersion performance of the resin. When the resin can not achieve a good wetting and dispersing effect, it can only be assisted by the wetting dispersant. If used properly, all wetting and dispersing agents have this function. Such as domestically produced P-104S, lecithin, CP-88, TC series products, especially the TM-27 and TM-200S with coupling bridging are very effective for pseudoplastic fluid packaging printing ink, and the general dosage is 0.1-3. %; (4) improve the color