What is the cause of gravure printing in the gravure printing ink type printing (the appearance of fog in the non-graphic part of the gravure plate roller)?
In gravure printing, the cause of a dirty plate is that the ink blade conveys ink. Specifically, the non-graphic ink is not scraped during the scraping process. The reason why the blank portion is not clean is mainly due to mechanical and ink components. .
Mechanical factors:
For the first reason, the squeegee wears badly. During the normal use of the squeegee, it eventually wears out. To solve this problem, it is possible to check the direction of the squeegee along the gravure roll to ensure that the squeegee is evenly pressed against the gravure roll. At the same time, make sure that the squeegee itself is free of wear and dirt, which can affect the squeegee's squeegee effect. If these problems occur, it is best to replace the squeegee again;
The second reason is that if the surface of the copper plated layer and chrome plated layer of the gravure platen roller is rough, it will also cause the squeegee blade to scrape the ink uncleanly. Sometimes changing the angle of the squeegee can solve this problem. Fake or adjusted squeegee can not overcome the roughness of the gravure roll, so the plate roll should be polished.
Ink composition factors:
If there is a need to frequently change the squeegee during production, it is likely that the ink in the ink has a strong abrasive, consider whether it is for another ink. In addition, improper use of solvents or excessive use of solvents in the ink can result in flocculation of the colorant in the ink. The flocculation causes the toner to remain under the squeegee, causing a dirty plate or abrasion of the squeegee. Lubricity of the ink is also a cause of the dirty version. The lubricity of the ink is related to the resin in the ink composition. Some gravure ink manufacturers will add a small amount of dark asphalt to the ink components to improve the ink squeegee performance.
Second question: Please explain why the viscosity of solvent-based liquid inks increases and gelation occurs.
What is the relationship between pigments and this issue?
In general, the increase in viscosity of solvent-based liquid inks is due to insufficient adsorption of the resin on the surface of the pigment particles. If the surface of the pigment particle crystal does not completely adsorb the polymer resin, the surfaces of the pigment particles without the adsorption resin will aggregate with each other to form flocculation. From the technical point of view, the surface of the colorant is not completely surrounded by resin. Adsorption does not exist in isolation. It will cause the solvent to adsorb on the surface of the colorant particles. Although the solvent sometimes wets the colorant, the solvent does not affect the colorant. Dispersion cannot be in a stable position. Therefore, it appears that a solvent rather than a polymer resin surrounds the surface adsorbed on the toner particles. Over time, the surface of the pigment particles. Over time, the pigment particles slowly flocculate and the end result is a change in the fluidity of the ink.
Theoretically, the problem of solving the solvent-adsorption pigment particles is to use a resin having a high affinity with the pigment particles so that the affinity of the solvent with the surface of the pigment particles is lower than the affinity of the resin with the pigment particles. . Also, if the solubility of the polymer resin in the solvent mixing system is good, then the probability of flocculation of the toner particles can be minimized because the solvent/resin combination with the colorant/solvent is better.
Question 3: How to improve the adhesion of nitrocellulose (PU) solvent inks?
There are several different ways to solve this problem. First, you can add titanate or zirconium aluminate additives to the ink. These additives can synergize with the oxygen-containing groups on the surface of the substrate to improve the adhesion of the ink to the substrate. The second solution is to use polychlorinated olefins to modify the nitrocellulose/polyurethane resin. The issues to be considered are the nitrocellulose/polyurethane in the formulation of nitrocellulose/polyurethane solvent-vehicle ratio.
Obviously, the nitrocellulose resin is hard and brittle and does not have enough plasticity. Therefore, the solvent type ink using the nitrocellulose resin as the linking material lacks the toughness and elasticity, and the adhesion is poor. Adding polyurethane to the continuous material can effectively improve the plasticity of the nitrocellulose and improve the adhesion of the ink, and the cost of the ink is also increased. The addition of titanates (DOP, BBP, DBP) or benzoates can soften nitrocellulose and are cheaper. However, some titanates are limited to some food packaging printing applications.
Question four: How to measure the surface tension value of gravure solvent ink? How does the surface tension of the ink affect printability and composite strength?
If you need to measure the surface tension of the ink during work, then we can use a tensiometer to measure. However, this measurement method only measures the static surface tension of the ink (surface tension of the ink at rest). However, the ink will certainly receive dynamic forces on the press. Therefore, the really effective surface tension should be the surface tension measured in the presence of dynamic forces, and sometimes dynamic surface tension is not easily measured.
There is a foam pressure tensiometer that measures surface tension under dynamic forces, but these devices are expensive and generally not used in ink labs. When printing with aqueous inks, surface tension is an important issue. This is because the surface tension of aqueous ink is higher than the surface energy of the substrate. In these aqueous inks, it is often necessary to add some additives to reduce the surface tension of the ink, so that the aqueous ink can be well wetted on the surface of the substrate. For any particular aqueous ink formulation, the most important effect of surface tension on the surface is to affect the leveling of the ink on the surface of the substrate. The surface tension of solvent-based inks is generally low, so they can wet well on the surface of many substrates. However, good wettability does not mean good adhesion, but it just means that the printing quality is good. The combination of resin components in the ink and the surface of the substrate is the primary factor that affects the adhesion and composite strength of the ink. The composite strength is also related to the adhesion of the ink itself. The interweaving of macromolecular resin in the ink and the physical interaction between various raw materials in the ink are the basis for the ink resisting the exfoliation effect of the composite film, so the structure of the resin molecule (linear molecules or molecules containing branched chains) and the molecular weight will also increase the ink's Adhesion, so the composite bond strength increases.