Ink film floating color and hair flower manifestations and causes

In normal packaging and printing, the operator often spends a lot of time due to floating and coloring of the printed ink film, and also greatly reduces the quality of printed products. This failure is mainly caused by the presence of more than one pigment or filler in the printing ink system. Despite the occasional uneven pigment separation, the color of the ink (picture text) can be clearly observed as floating color or hair dye—that is, pigment change—in the bulk packaging printing process. This is the change in the color of the ink film that has not yet been printed. However, the search for its floating color and hair flower shows different forms, and the operator mistakenly called the shrinkage hole, which is caused by the overdose of the ink-and-wash defoamer, and is different from the former.
Floating color refers to the horizontal separation of the plastic in the wet ink film as soon as the ink is printed. This is the concentration of one or more of the various pigments in the ink film is concentrated on the surface and has a uniform distribution. However, there are obvious differences between the color produced by the ink factory or the previous one.
In contrast, hair dyeing refers to the uneven distribution of a variety of 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 and hair, after the roller of the mesh group is pumped with ink or ink is printed, the phenomenon of stripe-like flowering that can be seen on the surface of the ink film packaged and printed is called silk pattern.
The reason for the occurrence of floating flowers is that we know that all compositions containing amphoteric plastics or fillers in the packaging and printing oil system may cause floating color and hair growth. The ink manufacturers may have improper production processes or the operations of packaging and printing operators. Inappropriately it will also produce floating color and hair.
One is the effect of pigment settling and flocculation on the floating color. It has been known from practice that floating color hair dyeing is caused by the uneven distribution of the pigment on the surface of the ink film after the package 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 an ink system in which a plurality of pigments are dispersed, 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. Benchmark We learned from the whole process of sedimentation of packaging printing ink that the effect of particle size is bigger than density, and the floating color is more serious, which is also caused by the density difference of pigments. Strictly speaking, it is caused by the particle size of pigments. of. From our country's packaging and printing ink dispersion system, the small particle size pigment particles absorb resin and the party class is much larger than the large pigment particles. It tends to show that the density becomes smaller, and the larger particle size of the pigment particles will increase the density of pigments. The sinking of the particles; while the floating of the small particle size constitutes the floating color phenomenon of the printing ink. In this regard, the ink formulation design has been used as a key point in the control of flocculation in order to prevent the floating of the pigment. Although it is effective, excessive flocculation may cause precipitation and cause the appearance of floating color. . For ease of production, after the 1990s, the effect of introducing dispersants, especially coupling agents, into the ink system was very significant. The purpose of the dispersant is to achieve the best adsorption state on the surface of the pigment. The purpose of the coupling agent is to bridge the link between the binder and the pigment, so as to increase the storage stability of the pigment and to prevent the flocculation of the floating color.
The second is the effect of the solvent on the floating color. Professor Yang Haiduo, known as China’s “ink star”, believes that the solubility of solvents in resin polymers, the rheology of printing inks, and the adaptability to packaging and printing processes, especially the formation of ink film, are very important. This represents a common view of China's packaging and printing industry for half a century. In this regard, for the full use of solvents, generally use a variety of solvents (ie, mixed solvents) for compatibility, that is, the composition of the true solvent and diluent. In the packaging printing ink formula design, the hydrogen bond between the solvent and the substrate should be similar (similar compatibility); the solubility of the solvent is similar to the solubility of the resin in the ink system (almost soluble); 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 that of the binder (resin); the solvent is used to make sure that the gaps in the volatilization gradients are similar (close to dryness); the true solvents and thinners must be kept The printing ink needs to be adapted to the printing ratio. If the above six basic conditions are achieved, it will not be the floating color and hair growth of the printing ink ink film.
The third is the effect of the surface tension gradient on the floating color. For a long time, people have been ignoring the causes of the surface tension gradient on the formation of ink on the ink film. We do not know that the solvent tension of the surface of the printing ink film on the packaging and printing ink will cause poor tension on the upper and lower surfaces of the printing ink film, which often causes the formation of the ink film vortex. flower. The difference in the surface tension caused by the unevenness of the surface of the wet ink film due to heat or uneven blowing further causes the ink film to move in parallel and cause hair growth.
Too much solubility of the solvent causes a sharp drop in the viscosity of the packaged printing ink, which accelerates the settling velocity of the pigment particles. The result is a difference in the settlement of the pigment particles, which is the generation of eddy currents, which in turn creates the conditions for the appearance of floating colours.
In addition, in the mixed solvent system, if the true solvent volatilizes too quickly, not only the surface tension difference but also the volatility gradient of the solvent will be destroyed. As a result, the resin in the ink system will also precipitate with adsorbed pigments due to the reduction of the true solvent, and it will also agglomerate the pigment particles to affect the improvement of the surface flatness of the ink film. However, the slow evaporation of the solvent will cause the viscosity of the printing ink to rise slowly, which will cause the printing ink film to flow for a long time. As a result, the occurrence of the eddy current of the ink film will inevitably occur - the blooming, floating color, and sagging.
The fourth is the effect of the resin on the floating color in the ink system. Resin floating color effect. There are many different kinds of resins. For multiple pigment combinations, the adsorptive capacity of the various pigments for the resin will not be the same. Unsaturated pigments are prone to condensation, which is also a major cause of floating color. .
In the printing ink system, especially when the distribution of the molecular weight and the molecular weight of the resin is different, the size and distribution of the polar active groups will not be the same. The difference in these distributions is caused by the difference in the wetting ability of the pigment. Secondly, the adsorptive capacity of various pigments on the binder (resin) will not be the same. The adsorption of thin pigments on the ink film will easily result in flocculation. In the case of small-molecular-weight rosin or alkyd resin inks, due to their large polarity and strong adsorptive power, the resulting adsorbed ink layer is thin, and the dispersion stability is poor, and flocculation and floating color are very likely to occur. From a 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 forced to adsorb on the The purpose of the paint surface is to prevent the paint from being single and cause flocculation failure.
The solubility of the polymer (resin binder) in the packaging printing ink system does not also cause floating of the flowers. In general, miscibility is poor when using a resin. Secondly, the solvent used cannot reach the critical value. That is to say, the poor resin and resin mixing performance of the speech, together with the insufficient affinity for the pigment, will often appear after the solution volatilizes. Even if the solvent eliminates turbidity and floating color, it will already begin during solvent evaporation. Because the volatilization of solvents and diluents destroys the balance of the resin binders, as is often the case: poorly compatible resin binders carry out the adsorption of pigments and cause the ink film to float. Color and hair and so on.
The fifth is the impact of floating flowers on the packaging and printing. 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 also directly result in the floating color of flowers after printing. Whether it is a dry environment or a high-humidity workshop (with the exception of workshops for temperature and humidity control), we all know that due to the evaporation of solvents during the printing process, the surface temperature of the ink film drops, the condensation of moisture, etc., can cause turbulence in the ink film of the packaging printing ink. Hydrophilic pigments that form on the surface absorb certain moisture, which in turn causes aggregation and separation of the pigments. As water is once bound into the ink layer and the hydrophilic pigment particles are bound, they often undergo condensation and sedimentation due to bridging of the non-intermolecular liquid. - floating color. The occurrence of such failures is particularly evident in packaging printing inks that have a rapid evaporation rate and are hydrophilic solvents.
This failure is often seen in water-based letterpress, water-based gravure, screen printing, plastic letterpress, and plastic intaglio printing inks.
In addition, the formation of insoluble colloidal particles in printing inks leads to shrinkage, and there is a tendency to mix them with floating-colored hair dyes. We know that the surface active material changes its concentration during the process of forming a printing ink, exceeding its solubility and generating a small amount of droplets that cannot be staged and causing shrinkage. For example, excessive addition of silicone oil or excessive viscosity, resulting in shrinkage. The difference between shrinkage holes and floating colors is that regular, spherical, small depressions are formed on the ink film, often centered on a drop or a small piece of impurities, and a circular rib is formed around it. From the point of view of the leveling property 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.). ). (Liu Jiaju) (From "China Packaging News and Printing Weekly")