Analysis of Ink Film Floating Color and Hair Blooming Problems in Packaging Printing

In the process of packaging and printing, operators often spend a lot of time due to the color and hair dyeing of the printed artwork, and also greatly reduce the quality of printed products. This failure is mainly caused by the printing ink containing various pigments or fillers in the morning. Due to the different appearances of floating color and hair growth in the printing ink film, the author will discuss the following points according to the practice for many years, and consult with colleagues in the packaging and printing industry.

First, ink film floating color and hair expression form
Floating color refers to the separation of the pigment in the wet ink film in the horizontal direction as soon as the ink is printed. One or more of the various pigments in the JM film are concentrated on the surface and have a uniform distribution, but there is a clear difference from the color just produced from the ink factory or from the previous recipe. 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 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.

1. 1 Causes of floating 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 for many years that floating color and hair dyeing are caused by uneven distribution of pigment on the surface of the ink film after packaging and printing. 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, which is generally called the difference in the density of pigments. Strictly speaking, it is due to the size of pigments. Caused by the role of the trail. From the perspective of China's packaging and printing ink dispersion system, the resin and solvent adsorbed by small-particle-size pigment particles are relatively much larger than large-size 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 small particle size pigments floated to constitute the floating color phenomenon of the printing ink. In this regard, the ink formulation design focuses on the slight control of flocculation to prevent the floating color of the pigment from being the focus of adjustment. , Although effective, but excessively serious flocculation, it will produce precipitation and cause the emergence of floating color flowers. For the sake of simplicity in production, after the 1990s, the effect of dispersants, especially coupling agents, in the ink system was very clear. The purpose of the dispersants was to achieve the best interstitial state on the surface of the pigments. The purpose is to bridging between the linking material and the pigment, so as to enhance the storage stability of the pigment and to prevent the floating color from blooming.

The second is the effect of solvents on floating color and hair growth. The ink expert Professor Yang Haiyan believes that solvent solubility in tree shive polymer and the rheology of printing ink, and the printing process, especially the formation of Momo is very important. Therefore, in order to make full use of the solvent, a multi-solvent is generally used for compatibility, ie, a true solvent and a diluent are combined. In the design of packaging printing ink formulations, the hydrogen bond between the solvent and the substrate should be similar; the solubility of the solvent is similar to the solubility of the resin in the ink system; the surface tension of the solvent is similar to the surface tension of the resin in the ink system; the density and the connection of the solvent The material density is similar; the gradient gap of the mixed solvent volatilization is similar; the true solvent and the diluent need to keep the dosage required for the packaging printing ink to adapt to the printing proportion. 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.

The third is the effect of surface tension gradient on the floating color. For a long time, people have neglected the cause of the surface tension gradient on the formation of ink on the ink film. We do not know that the surface tension of the printing ink film on the surface of the printing and printing ink is so poor that the tension of the upper and lower surfaces of the printing ink film is so poor that it often causes the ink film to form a vortex and flowers. . The surface of the wet ink film is affected by uneven blowing or uneven surface tension, which may cause the ink film to move in parallel and cause hair growth.

Too much solubility of the solvent will cause the viscosity of the packaging printing ink to drop rapidly, thereby accelerating the settling velocity of the pigment particles. As a result, due to the difference in the particle diameter of the pigment, the occurrence of a difference in the settlement, ie, eddy currents, will occur to the floating color. Created conditions.

In addition, in a mixed solvent system, if the true solvent volatilizes too quickly, not only surface tension will occur, but also the balance of the volatilization gradient of the solvent will be destroyed. As a result, the resin in the ink system is also precipitated with the absorbed pigment due to the reduction of the true solvent, resulting in hair growth. At the same time, it will also cause the pigment particles to agglomerate and affect the improvement of the flatness of the ink film surface. 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 eddy currents in the ink film is not unavoidable, causing problems such as 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 compositions, since the adsorption ability of various pigments to resins is not the same, non-wetting pigments are prone to condensation, which is also a major cause of floating color.

In packaging printing ink systems, when the molecular weight and molecular weight distribution of tree shrews are different, the size and distribution of polar reactive groups will not be the same, and the differences in these distributions will cause differences in the wetting ability of the pigments. Secondly, the adsorptive capacity of various pigments on the binder is not the same. A pigment that is thin on the ink film can easily flocculate and float. 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 layers are thin, have poor dispersion stability, and are prone to flocculation and float coloration. From a theoretical point of view, in the flocculation of packaging and printing inks, the concentration of the resin in the ink grinding process should be more specifically targeted for the performance of different pigments and binders, and the polymer polymer must be forced to adsorb on the surface of the pigment. Prevents the pigment from being single and causes flocculation failure.

Poor polymer solubility in the packaging printing ink system can also cause the disadvantages of floating coloration. In general, when using several kinds of resins, they are poorly interwoven. 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 the water in the north of the Yellow River in China and the long raining in the south of the Meiyu area can also cause floating color blooms after the printing of graphic arts. Whether studying in a high-humidity workshop, because the evaporation of solvents, the decrease of the surface temperature of the ink film, and the condensation of moisture during the printing process all lead to the formation of a vortex in the ink film of the packaging printing ink, the hydrophilic pigment on the surface absorbs certain moisture. As a result, agglomeration and separation of the pigment are caused. Once the water is brought into the ink layer and bound with the hydrophilic pigment particles, they tend to undergo aggregation and sedimentation and a floating color due to bridging of 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 type of failure is often seen in non-professional, water-based gravure, screen, plastic, 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 hair dyeing. 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 circular edge is formed around it. From the point of view of leveling of packaging printing inks, it is a special dot-like flow that is generated on the surface of the printing ink film.

(to be continued)