Causes and preventive measures of floating color a

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Causes and preventive measures of floating color and blooming of ink film in packaging and printing (Part 2)

Second, measures to prevent and remedy floating color and blooming

around the above-mentioned several manifestations of floating color and blooming of ink film, it is roughly analyzed and summarized. However, there is little literature on how to prevent and remedy the floating color of fait accompli. For this reason, the author describes each case according to the accumulated experience

the stability of packaging printing ink is the result of the interaction between components. For example, the polarity intensity 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 of the solvent is: toluene> dichloroethane> mixed solvent. Most people believe that various solvents only affect physical adsorption and will not affect chemical adsorption. At the same time, it is believed that the competitive adsorption of binders and surfactants on the surface of pigments has been proved to be correct by practice. This shows that competitive adsorption depends on the surface affinity of binders and surfactants with pigments and fillers. If the pigment or filler is hydrophilic, the material with higher polarity will be selected for adsorption in non-polar solvent. If it is hydrophobic, select substances with strong hydrophobicity for adsorption in polar solvents. The physical adsorption of surfactant will not affect the chemical adsorption of polymer, because the physical adsorption of surfactant on the surface of pigment and filler is not firm, and it is easy to be squeezed out of the surface of pigment by resin in solvent. Surfactants that form chemisorption with the surface of pigments cannot be squeezed out of the surface of pigments and fillers by resin polymers. The greater the adsorption saturation of surfactant on the surface, the greater the resistance of polymer adsorption. On the other hand, if the dispersion and grinding time during ink manufacturing is shorter, the ink will not be easily squeezed out of the pigment surface by the resin in the solvent during the manufacturing process or ink storage, but other phenomena may still occur, which needs to be proved by practice

in polar solvents, ultra-fine active calcium and alkyd resin can be adsorbed on the surface of iron blue and medium chrome yellow. This is because there are two active centers on the surface of the pigment, so the slightly acidic active calcium and alkyd resin can still be adsorbed on its surface, but its coverage rate is low, resulting in poor wetting and dispersion. When dispersed to 7.5 microns, the surface produces floating color; When dispersed to 12 microns, it will disappear. For example, after adding diluent in the printing process, floating color will appear again. Proper dispersant must be selected. Adding wetting dispersant can not only reduce the grinding time of pigments and fillers, but also save energy and improve work efficiency

in order to prevent ink floating and blooming, wetting dispersant should be introduced into the packaging printing ink system. Its purpose is nothing more than: (1) to increase the gloss of the ink film and improve the leveling of the ink film. It can greatly improve the fineness of pigments and fillers, ensure the storage stability of ink, prevent the generation of large flocculating particles, and improve the flatness of printing ink film; (2) Reducing the oil content of China's aviation aluminum alloy thick plate also depends on the viscosity of imported ink to improve the fluidity of ink. Under the same conditions, it can greatly improve the volume concentration of pigments and fillers, increase their fillability and reduce the material cost; (3) Improve the storage stability of packaging printing ink. The storage stability of packaging and printing inks depends entirely on the dispersion quality of pigments. Poor dispersion and precipitation will cause floating color, blooming and the decline of coloring power. Secondly, the rheology will also change, which is closely related to the proportion of resin (base material) and solvent and the dispersion performance of the resin. When the resin cannot achieve a good wetting and dispersion effect, it can only rely on the help of wetting and dispersing agents. If used properly, all wetting and dispersing agents have the function of solving the flexible packaging problems of medical devices and drugs, bottle caps, closures and primary experimental supplies. For example, domestic P 104s, lecithin, CP 88, TC series products, especially TM 27 and TM 200s with coupling bridge, are very effective for the packaging and printing ink of pseudoplastic fluid, with a general dosage of 0.13%; (4) Improve the coloring power and hiding power of pigments. It is known that the scattering degree of light and the hiding power of pigments tend to have a maximum value with the change of particle size. In printing inks, it is appropriate to have a small pigment viscosity. The simplest identification method is: A. take 0.1g of ink and drop it into the slot of the scraper fineness meter, hold the scraper for 90 degrees, and scrape it quickly from top to bottom. If the ink is interrupted or interrupted, it proves that the coloring force is less than 100%, that is, the printing suitability of the ink is poor or too poor. When printing on the machine, it is not the tail of the printed text, or it is easy to appear dry skin spots, etc. B. Take 0.1g of ink and drop it on the 65 195mm blueprint base paper. Hold the scraper for 25 degrees and scrape it off quickly from top to bottom (one breath). If the surface pigment of the blueprint paper cannot reach saturation, it is proved that its coloring power cannot meet the printing requirements, that is, the printing suitability is poor and it is easy to float and flower; (5) It can prevent floating color, sagging and sedimentation. Using a wetting dispersant that controls flocculation can prevent floating and blooming of multicolor or interchromatic inks and increase stability; (6) Improve the physical properties of ink film. Practice has proved that the best pigment dispersion can improve the absorption and reflection of ultraviolet light, increase the weatherability and chemical resistance of pigments, and thus improve the physicochemical properties of ink films; (7) Change the rheology of packaging printing ink. Practice has proved that using different wetting dispersants can sometimes get packaging and printing inks with low viscosity dispersion system close to Newtonian fluid, and pigment particles can be dispersed close to the state of primary particles (thinning the thickness of printing ink film), so as to obtain a stable and ideal dispersion system. For example, in inks with high pigment ratio and high oil absorption, which are easy to form thixotropic structure, reduce viscosity, improve flow and ensure high gloss leveling, but some wetting dispersants will make the dispersion system have pseudoplastic viscosity and thixotropic viscosity. After the ink system forms structural viscosity, the ink system will be in a stable state. This kind of anti sedimentation, anti sagging and anti floating color blooming is due to the dispersant color The filler controls the flocculation and is stabilized; (8) Save time and energy. Adding wetting dispersant can reduce the grinding time of pigments and fillers, save energy, and greatly improve production efficiency

contrary to the eight functions mentioned above, if applied improperly, the resin binder will penetrate into the paper (even through the back), leaving the pigment alone on the surface and losing the gloss of the ink film

in molecules, anionic and cationic organic groups with basically the same size are called electrically neutral surfactants. It not only has good miscibility with all solvent based printing ink systems, but also has no side effects due to the use of wetting dispersants. In addition, there is also a polymer dispersant with super dispersing ability (consisting of a part of the polymerization chain with strong affinity to the solvent, and a part of the anchoring group with strong affinity to the particle surface, that is, in the dispersion system, the anchoring part polymerizes with the particle surface, binds firmly to the particle surface like an iron anchor, and its dispersed part extends in the solvent to form an anchoring adsorption layer)

although wetting dispersant can form a thick adsorption layer and generate external force, so that the pigment dispersion system is in a stable state, there are also some cases that can cause co flocculation between pigment particles to prevent excessive flocculation of a single pigment, so as to prevent floating color and blooming. Compared with other operation links in industrial and agricultural production, according to the experience of Hangzhou Yuhang Dibang fine chemicals factory and Yangzhou zhonglida ink company, the amount of remedy in the printing process should be increased by 10 times or even more to prevent any omission

in addition to the wetting dispersant mentioned above, which can make the pigment in a stable dispersion state or control flocculation under the dispersion state, next we will focus on the effect of leveling agent on floating color and blooming

according to nabede's eddy current theory, the purpose of adding leveling agent is to reduce the surface tension of the ink, prevent the packaging and printing ink from eddy current and causing blooming, make the surface smooth and flat, and achieve uniform color

among many leveling agents, silicone oil, silicone resin, acrylic copolymer, etc. We have known in practice that silicone oil can not solve the blooming of pigments. It can only turn the blooming into floating color, forming a surface with uniform hue and uniform hue, and can not solve the separation and flocculation of pigments

the organic matter in silicone oil and printing ink is immiscible. It condenses at the interface between air and ink film, so that the surface tension decreases, expands on the surface, forms a monolayer, and the radius of curvature becomes larger, which can expand to the whole surface. Therefore, it can form a better smooth surface state, and prevent eddy current from generating ink film. The surface of ink film forms a smooth, mirror like ink layer

the effect of polyacrylate leveling agent is roughly the same as that of silicone, but attention should be paid to the active group, thermal stability and dosage of silicone polymer, and some will bring obstacles to reprinting; Secondly, excessive use often has poor compatibility with the resin in the ink system, resulting in dry skin and shrinkage. Third, thixotropic tackifier will also make packaging printing ink have structural viscosity and improve the rheology of printing ink. The increase of ink viscosity often reduces the settling speed of pigments in the system and prevents the separation of pigments, so as to achieve the purpose of eliminating floating color and blooming. However, not all packaging and printing inks can use this kind of auxiliary agent. For example, it is not suitable to use the pump to circulate the ink, especially the spray printing ink products, because the addition of tackifier often directly affects the leveling of the ink after printing. Generally, the dosage should be determined after trial printing (or use the color developing wheel for proofing before printing), otherwise, the ink will flocculate

thickeners and thixotropic agents are widely used in packaging and printing inks because they can make the ink system produce structural viscosity, change the rheology of the ink and control the movement of the pigment

in addition, surface treatment or modification of pigments and fillers in advance is also a common method to prevent floating color and blooming, and the dosage is small

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