Talking about the floating color and hair flower of printing ink film

In normal packaging and printing, operators often spend a lot of time due to floating and coloring of printed inks, which 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. Occasionally, uneven pigment separation occurs, and after a batch of packaging printing processes, floating color or hair change, that is, pigment change, can be clearly observed from the surface of the ink film. This is a change in the color of the ink that has not yet dried. However, there are differences in the expressions of the floating color and the hair flower, and the operator mistakenly called the shrinkage hole. This is caused by the overdose of the defoamer in the ink-and-wash system, and is different from the former. For this reason, the author will try to discuss the following points based on years of practical application, so as to discuss with colleagues in the packaging and printing industry.
First, the ink film floating color and hair expression form Floating color refers to the ink is printed, the wet ink film in the horizontal direction of the layer of separation. This means that the concentration of one or more transitions of a plurality of pigments in the ink film is concentrated on the surface and has a uniform distribution. However, there is a clear difference between the color of the ink that has just been produced by the ink factory or the previous recipe.
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 growth, after the anilox roller is pumping ink or printing ink, the stripe-like phenomenon that can be seen on the surface of the packaging printing ink film is called silk pattern.
The reason for the occurrence of floating colors is that we know that all compositions containing amphoteric pigments or fillers in the packaging printing ink system may cause floating color and hair growth, improper production processes of ink manufacturers, or operations of packaging and printing operators. Inappropriately it will also produce floating color and hair.
1. The effect of pigment settling and flocculation on floating color bloom We have known in many years of practice that floating color hair dyeing is caused by uneven distribution of pigment on the surface of the ink film after packaging printing (including uneven printing plate and uneven pressure Wait). 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. Secondly, we learned from the whole process of sedimentation of packaging printing inks that the effect of particle size is greater 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 printing ink dispersion system, small particle size pigment particles absorb resins and solvents that are much larger than large pigment particles, and tend to exhibit lower density. Larger particle size pigment particles have higher density and cause pigment particles. The sinking; while the small particle size pigment floats to constitute the floating color phenomenon of the printing ink. In this regard, people have made adjustments to the ink formulation design for flocculation with slight control in order to prevent the floating of the pigment. Although there are effects, excessive flocculation will cause precipitation and result in floating color. appear. 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.
2. The effect of solvent on floating color is known as China's “ink star” Professor Yang Haijun believes: Solubility of solvent to resin polymer and the rheology of printing ink and adaptability to packaging printing process, especially ink The formation of the film is very important. This represents a common view of China's packaging and printing industry for half a century. In this regard, 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 diluent. In the packaging printing ink formula design, 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 ink system The surface tension of the resin is similar (similar to the flatness); the density of the solvent is similar to that of the binder (resin) (similar stability); the mixed solvent is as close as possible to the volatilized gradient gaps (close to dry thoroughly); the true solvent and the diluent must be kept in the package The printing ink needs to be adapted to the printing ratio. If we reach the above six basic conditions, we will not cause the floating color and hair growth of the printing ink film due to the solvent.
3. Effect of Surface Tension Gradient on the Floatation of Colored Float For a long time, people have neglected the cause of surface tension gradient on the formation of ink on the ink film. I wonder if the solvent on the surface of the packaging printing ink ink volatilizes and the upper and lower surfaces of the printing ink film The difference in tension is often caused by the formation of eddy currents in the ink film. The difference in surface tension caused by uneven heating or uneven blowing of the surface of the wet ink film will also cause the ink film to move in parallel (sweep) - the formation of flowers.
Too much solubility of the solvent will cause the viscosity of the packaging printing ink to drop rapidly, which will accelerate the settling velocity of the pigment particles. As a result, the sedimentation difference that occurs due to the difference in the particle diameter of the pigment, that is, the generation of eddy currents, may cause the floating color to appear. Created conditions.
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 precipitate with the absorbed pigment due to the reduction of the true solvent, and will also cause the pigment particles to agglomerate and affect the improvement of the surface flatness of the ink film, but the evaporation of the solvent is too slow. , Will cause the printing ink viscosity to rise slowly, thus causes the printing ink film to flow the time to be too long, as a result the ink membrane vortex appearance will inevitably occur - Hair flower, floating color and sag and so on.
4. The effect of resin on the floating color in the ink system The variety and variety of resins, wetting ability is not the same. 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 packaging printing ink system, especially when the distribution of molecular weight and 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 ability to wet 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 the theoretical point of view, when the packaging printing ink flocculates, it is more necessary to control the concentration of the resin in the printing ink grinding process according to the performance of different pigments and binders, and to force the polymer (linker) to adsorb on the pigment. On the surface, its purpose is to prevent flocculation failure caused by a single production of pigment.
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. Secondly, the solubility of the selected solvent does not reach the critical value. That is, people often say that the resin and the resin are poorly mixed. In addition, the affinity for the pigment is not enough, and after the solution volatilizes, the floating color and hair will appear. flower. Even if the turbidity and floating color are eliminated under the influence of the solvent, it will already begin during the evaporation of the solvent. Because the volatilization of solvents and diluents destroys the balance between the resin binders, it is often said that poorly compatible resin binders will release the adsorbed pigments and cause the floating color of the ink film. Hair flowers and so on. 
5. The effect of packaging and printing conditions on the floating color of flowers The water-dry and dry areas in the north of the Yellow River in China and the wet areas in the south of the Yangtze River are also directly responsible for the formation of floating color flowers after printing. Whether it is a dry environment or a high-humidity workshop (except for temperature and humidity control workshops), we all know that the evaporation of solvents during the printing process, the decrease of the surface temperature of the ink film, the condensation of moisture, etc., can cause turbulence in the ink film of the packaging printing ink. The appearance of hydrophilic pigments that appear on the surface absorbs a certain level, which in turn causes the pigments to separate and separate. Since the moisture is once bound into the ink layer and the hydrophilic pigment particles are bound, they often undergo condensation and sedimentation due to the bridging effect of non-intermolecular liquids. - floating color. 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. The formation of insoluble colloidal particles in printing inks causes shrinkage, which is sometimes confused with floating colored hair dyes. It is known that the concentration of surface-active substances in the process of forming a printing ink changes beyond its solubility and generates a small amount of immiscible droplets, which may 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 circular edge 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.). ).
Second, to prevent and remedy the floating color hair flower measures have been described in the ink film floating around the color of the form of expression, a rough analysis of several forms of its analysis and induction. But how can we prevent and remedy faits accomplis, and there are very few published and published documents on the market. For this reason, according to the accumulated experience, the author will tell each case and hope that his colleagues will criticize and give instructions.
Packaging printing ink is ultimately a storage stability. The ink storage stability is in turn the result of the interaction between the components. For example, the polarity of the solvent is different, and the adsorption on the pigment surface of the active agent is also different. The order of the adsorption amount of octadecylamine in each component solvent is: toluene>dichloroethane>mixing Solvents. Most scientists in the scientific community believe that various solvents only affect physisorption without affecting chemisorption. At the same time, they believe that the competitive adsorption of binders and active agents on the surface of pigments 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 by the resin from the surface of the pigment. The chemisorption surfactant formed on the surface of the pigmented filler cannot be extruded from the pigment filler surface by the resin polymer. The greater the adsorption saturation of the surfactant in performance, the greater the resistance to polymer adsorption. On the other hand, if the disperse grinding time during ink production is slightly shorter, the ink will not be easily expelled from the pigment surface by the resin in the solvent during the manufacturing process or the ink storage, but other phenomena may still occur. , to be practiced.
The ultra-fine active calcium and alkyd resins in polar solvents can be adsorbed on the surface of iron blue and yellow chromium. This is because the pigment has two active centers on the surface, so it is slightly acidic active calcium and alkyd. The resin can still be adsorbed on the surface, but its hiding rate is low, resulting in poor wetting and dispersing properties. When dispersed to 7.5mm, the surface has a floating color; when dispersed to 1 to 2mm, it will be Disappeared. If a thinner is added during the printing process, the floating color reappears again. Must choose the appropriate dispersant, adding wetting dispersant not only can reduce the grinding time of the pigment and filler, but also can save energy without improving work efficiency.
In order to prevent the floating color of the ink, the wetting and dispersing agent is introduced into the packaging printing ink system. Its purpose is to:
(1) Increase the gloss of the ink film and improve the leveling of the ink film, which can greatly improve the fineness of the pigment filler.

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