Failure analysis of gravure ink and cutter wire

Gravure water-based ink and wire fault analysis knife wire is one of the common quality faults that gravure process is difficult to avoid. Since the ink path of gravure printing is very short, the distance from the scraper to the impression point is generally not more than 1/4 of the circumference of the plate roller. If, for technological reasons, the position of the scraper is raised closer to the impression point, the distance will be shorter. The risk of this short ink path is that if there is a foreign body embedded in the scraper, it can not wait for the wettability of the ink itself to level the thin line pulled out of the foreign body, and the thin line must be transferred to the substrate material to form the knife wire.

1, solvent-based gravure ink gravure ink using solvent-based ink, can not avoid the reason for the knife wire, in addition to environmental factors caused by foreign bodies embedded into the scraper, the main reason is the solubility of the solvent used in the solvent-based ink fluctuations. Gravure mixed solvent is generally composed of 2 to 3 kinds of solvents, the core of its formula, first to ensure the solubility of the mixed solvent to the resin (solute). The solubility of resin consists of the principle of similar polarity, the principle of similar solubility parameters and the principle of solvation. A good mixed solvent formula will generally comply with these three principles. However, because the calculation of the solubility parameter of the mixed solvent is related to the volume parameter of the solvent, when the mixed solvent is volatilized for a period of time, the volume ratio of each solvent will change greatly, and the solubility parameter of the mixed solvent will also change greatly. As long as the fluctuation of the solubility parameter is controlled within ± (15% ~ 20%), the solubility of the resin is still guaranteed, but if this limit is exceeded, the dissolved resin may re-condense into larger particles, forming a solubility failure. Under such conditions, if the particle is embedded in the scraper, the tool wire failure is inevitable. Gravure production line to evaluate whether a new ink is easy to knife wire, the method used is often to let the plate roller idling for more than half an hour, and then re-printing, the intention is to wait for the solvent-based ink mixing ratio and volatilization ratio is seriously inconsistent, to assess the risk of ink particle agglomeration. This method is very scientific, but it is doubtful how many people are thinking from the theoretical point of view of the solubility of mixed solvents while adopting this method.

2, Water-based gravure ink Water-based gravure ink does not use mixed solvents, theoretically there is no risk of solubility fluctuations caused by mixing ratio and volatilization ratio inconsistency. However, the objective reality is that the knife wire is still unavoidable in water-based gravure ink printing. In fact, the reasons for the fluctuation of solubility of water-based gravure ink still exist: first, the change of alkaline substances in water-based gravure ink causes the change of pH value, which causes the change of solubility; The second is the matching of water-based solution and water-based emulsion in water-based gravure ink, whether the resin will be insoluble after mixing the two. The compatibility of solubility and dryness of water-based emulsion with color paste directly affects the solubility and dispersion of water-based ink. Some brands of water-based ink, the safe storage period is only 6 months, more than 6 months may produce precipitation, stratification, even after re-mixing is difficult to regenerate, in fact, this is the solubility problem, that is, the color paste with water-based emulsion problem. Water-based ink solubility problems, and the use of gravure transfer mechanism of water-based ink, will inevitably cause tool line failure. There is a phenomenon that is worth noting: if only water-based ink composed of water-based solution is used for gravure printing, the knife wire in the printing process will be greatly reduced. This phenomenon contradicts the fluctuation of water-based ink solubility caused by the mismatch between water-based solution and water-based emulsion. However, in the film gravure printing, the adhesion of the ink and the resistance of the ink film are inseparable from the water-based emulsion, so it is unrealistic not to add water-based emulsion in order to avoid the knife thread. Water-based ink must be added to the water-based emulsion, but the addition of water-based emulsion can not ensure the stability of solubility, which has caused the current water-based ink manufacturers embarrassment.