Floating color and blooming of the hottest printin

Floating color and hairiness of printing ink film (I)

in normal packaging and printing, operators often suffer a lot from floating color and hairiness of printing ink film, which also greatly reduces the quality of their printed products. This failure is mainly caused by more than one pigment or filler in the printing ink system. Although uneven pigment separation occasionally occurs, floating color or blooming can be clearly observed from the surface of the ink (Graphic) film after the batch packaging and printing process, that is, pigment changes. This is the change of pigment in the wet printing picture and text (ink) ink film state. However, the manifestations of floating color and blooming are different, and the operator mistakenly calls it shrinkage, which is caused by the excessive defoamer in the ink system, which is different from the former. For this reason, the author tries to talk about the following points based on years of practical application, in order to discuss with colleagues in the packaging and printing industry

I. The manifestation of ink film floating color and blooming

floating color refers to the horizontal layered separation of pigments in the wet ink film once the ink is printed. This is the concentration of one or more transformations of various pigments in the ink film concentrated on the surface and showed a uniform distribution. But it is obviously different from the color just produced from the ink factory or the previous formula

and blooming refers to the uneven distribution of multiple colors in the ink film after packaging and printing, which is usually in the shape of stripes or honeycombs. For this reason, it is often understood as the separation of pigments in the vertical direction

in addition to floating color and hairiness, the Striped hairiness that can be seen on the surface of the ink film of packaging and printing after the Striped roller is pumped or sprayed with ink is called silk

we know the causes of floating color and blooming: in the packaging and printing ink system, all components containing amphoteric pigments or fillers may produce floating color and blooming. Improper production technology of ink manufacturers or improper operation of packaging and printing operators will also produce floating color and blooming

1 The influence of pigment sedimentation and flocculation on floating color blooming

we have known in many years of practice that floating color blooming is caused by the uneven distribution of pigments on the surface of the ink film after packaging and printing (including uneven printing plate, uneven pressure, etc.). Although there are many reasons for solving horizontal competition through company acquisition, the stability of pigment dispersion is very important. For example, in the ink system composed of a variety of pigment dispersion, the separation of pigment dispersion ink system is often caused by the excessive flocculation or sedimentation of a certain pigment, which is the reason we often talk about floating color blooming. Secondly, we know from the observation of the whole process of packaging and printing ink sedimentation that the effect of particle size is greater than that of density, and the floating color is more serious. It is usually caused by the density difference of pigment, strictly speaking, it is caused by the effect of particle size of pigment

in the printing ink dispersion system, the resin and solvent adsorbed by small particle size pigment particles are much larger than that of large pigment particles, which often shows that the density becomes smaller, and the larger the density of large particle size pigment particles will cause the subsidence of pigment particles; The floating phenomenon of printing ink is formed by the floating of small particle size pigments. In this regard, people have made adjustments in the ink formulation design, focusing on the slight control of flocculation to prevent pigment floating and blooming. Although it has an effect, excessive serious flocculation will produce sedimentation and lead to floating and blooming. In order to simplify production, after the 1990s, people introduced dispersants, especially coupling agents, into the ink system, and the effect was very obvious. The purpose of dispersants was to achieve the best adsorption state on the surface of pigments, and the purpose of coupling agents was to build a bridge between the binder and pigments, so as to enhance the storage stability of pigments and prevent floating color

2. The influence of solvent on floating color and blooming Professor Yang Haijiao, known as the "star of ink" in China, believes that the solubility of solvent to resin polymer, the rheology of printing ink pressing the clear key and the adaptability to packaging and printing process, especially the formation of ink film, are very important. This represents the common view of China's packaging and printing industry for half a century. In this regard, in order to give full play to the use of solvents, a variety of solvents (i.e. mixed solvents) are generally used for compatibility, that is, the matching composition of real solvents and diluents. When designing the formula of packaging printing ink, we should make the hydrogen bond between the solvent and the substrate close (close and sticky); The solubility of the solvent is similar to that of the resin in the ink system (similar miscibility); The surface tension of the solvent is similar to that of the resin in the ink system (nearly flat); The density of solvent is similar to that of binder (resin) (nearly stable); Try to pay attention to the similar gap of the volatilization gradient of the mixed solvent (close and dry thoroughly); The true solvent and diluent should keep the proportion and amount of printing ink needed for packaging and printing. If we meet the above six basic conditions, we will not cause the floating color and blooming of the ink film of the printing ink due to the solvent. (to be continued)