One of the questions: In the printing of gravure solvent-based inks, what is the cause of the dirty plate (the foggy appearance in the non-graphic part of the gravure plate roller)?
In gravure printing, the reason for the dirty version is the ink transfer by the doctor blade. Specifically, the ink in the non-graphic part is not scraped during the scraping process. The reason for the ink in the blank part is not clean. The main reason is the mechanical and ink components. problem.
Mechanical factors: The first reason is that the squeegee wears badly. During the normal use of the squeegee, it may eventually be worn. To solve this problem, you can check the direction of the doctor blade along the gravure cylinder to ensure that the doctor blade is evenly pressed against the gravure cylinder. At the same time, it is necessary to ensure that the squeegee itself has no wear points and dirty spots, which will affect the squeegee effect of the squeegee. If these problems occur, it is better to replace the doctor blade; the second reason, if the surface of the copper and chrome layer of the gravure cylinder is rough, it will also cause the doctor blade to scrape the ink, sometimes Changing the angle of the doctor blade can solve this problem. If the squeegee is faked or adjusted, the roughness on the gravure roller cannot be overcome, so the plate roller should be polished.
Ink composition factor: If there is a need to frequently replace the squeegee during the production process, it is likely that the ink in the ink has a strong abrasiveness, consider whether to change another ink. In addition, improper use of solvent in the ink or excessive use of solvent will cause flocculation of the colorant in the ink. Flocculation causes the colorant to remain under the doctor blade, resulting in a dirty plate or causing the doctor blade to wear.
The lubricating performance of the ink is also a reason for 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 pitch to the ink component to improve the ink scraping performance.
Question 2: Please explain the reason why the viscosity of the solvent-based liquid ink becomes larger and gels? What does the color material have to do with this problem?
In general, the phenomenon of increased viscosity of solvent-based liquid inks is due to insufficient adsorption of the resin on the surface of the toner particles. If the surface of the toner particle crystals does not completely adsorb the polymer resin, the surfaces of the toner particles that do not adsorb the resin will aggregate with each other to form flocculation.
From a technical point of view, not all the surface of the colorant is surrounded by resin. Adsorption does not exist in isolation, and it will cause the solvent to be adsorbed on the surface of the colorant particles. Although the solvent can sometimes wet the colorant, the solvent The dispersion cannot be in a stable position. Therefore, a solvent instead of a polymer resin surrounds and adsorbs on the surface of the toner particles. Over time, the surface of the pigment particles. Over time, the toner particles slowly flocculate, and the end result is that the fluidity of the ink changes.
Theoretically, to solve the problem of the solvent adsorbing the toner particles is to use a resin with a high affinity for the toner particles, so that the affinity of the solvent and the surface of the toner particles is lower than the affinity of the resin and the toner particles . Similarly, if the polymer resin has good solubility in the solvent mixing system, the probability of flocculation of the colorant particles can be reduced to a minimum, because the solvent / resin is better than the colorant / solvent combination.
Question three: How to improve the adhesion of nitrocellulose (NC) / polyurethane (PU) solvent-based 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 modify the nitrocellulose / polyurethane resin using polychloroolefins. The problem to be considered is the nitrocellulose / polyurethane resin formulation in the nitrocellulose / polyurethane solvent type gondola. ratio.
Obviously, nitrocellulose resin is hard and brittle and does not have enough plasticity, so solvent-based inks using nitrocellulose resin as a binder lack toughness and elasticity, and have poor adhesion. Adding polyurethane to the continuous material can effectively improve the plasticity of the nitrocellulose and the adhesion of the ink, and the cost of the ink also increases. Adding titanate (DOP, BBP, DBP) or benzoate can soften nitrocellulose, and the price is also cheaper. However, some titanates are limited to some food packaging and printing applications.
Question 4: How to measure the surface tension of gravure solvent ink? How does the surface tension of the ink affect the printability and composite strength?
If the surface tension of the ink needs to be measured in the work, then we can use a tensiometer to measure. However, this measurement method can only measure the static surface tension of the ink (the surface tension of the ink at rest). However, the ink will definitely receive dynamic forces on the printing press. Therefore, the real effective surface tension should be the surface tension measured in the presence of dynamic forces. Sometimes the dynamic surface tension is not easy to measure.
There is a bubble pressure tensiometer that measures surface tension under the action of dynamic forces, but these devices are relatively expensive and are generally not used in ink laboratories.
When printing with water based inks, surface tension is an important issue. This is because the surface tension of the water-based ink is higher than that of the substrate. In these water-based inks, some additives are often added to reduce the surface tension of the ink, so that the water-based ink can wet the substrate surface well.
For any particular water-based ink formulation, the most important role of surface tension 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 a variety of substrates. However, good wettability does not mean good adhesion, but only shows good print quality. The binding performance of the resin component in the ink and the surface of the substrate is the primary factor affecting the adhesion and compound strength of the ink. The composite strength is also related to the adhesion of the ink itself. The interweaving of the polymer resin in the ink and the physical interaction between the various raw materials in the ink are the basis for the ink to resist the peeling effect of the composite film, so the structure of the resin molecule (linear molecule or branched molecule) and molecular weight also increase the Tackiness, so the composite bond strength increases.
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