The characteristics of transparent ink and the essentials in printing
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Transparent ink refers to an ink made of dyes in whole or in most of the coloring agent, which has low hiding power and high transparency. This article will talk about some of the things that should be noted during the use of transparent inks.
1. Hue
Due to the high transparency of the transparent ink, the aluminum-plated film is generally composited after printing, so that the gloss of the aluminum film and the gloss of the ink are combined to reflect a relatively bright color. Moreover, products printed with clear inks will have a more pronounced change in hue from different angles, and the difference will be greater under different light sources. Therefore, when formulating such inks, it is important to understand what materials the customer compoundes in order to formulate the inks in the same process and observe the hue of the inks in a similar environment. For example, some hue before ink compounding is very close to the standard, but the hue after compounding may be very different; on the contrary, some hue after ink printing has a certain gap with the standard, but the hue is closer to the standard after compounding. The color matching of clear inks is very laborious, so it is very important to know the customer's process.
2. Transparency
The transparency of the transparent ink is determined by the dye (pigment) and the binder (including the auxiliary), and the former plays a major role, and the latter has little effect. Polyurethane inks have higher transparency in inks made from common resins such as polyurethane, polyamide, and chlorinated polypropylene. In general, an ink having a dye as a colorant has a higher transparency than an ink having a pigment as a colorant. Sometimes, due to other needs, some pigments are also mixed in the dye, and the transparency of the ink is lowered.
3. Residual solvent and odor
Attentive operators will find that the drying speed of the clear ink is significantly slower because the solid content of the clear ink is low (because the dye has a higher color density than the pigment, so the amount does not need to be too much) and the solvent content is high, so it needs to be The drying condition is controlled, otherwise it is easy to cause residual solvent to exceed the standard and produce odor. In severe cases, the solvent will slowly permeate and spread around the composite, causing discoloration of other colors. Therefore, when printing such a transparent ink, it is necessary to pay attention to the control of the solvent ratio and the printing speed. After printing, it is aged in a curing chamber of about 40 ° C for more than 10 hours.
4. Adhesive dissolves in clear ink
The dye used in the clear ink is completely soluble in the organic solvent, so when the print comes into contact with the composite adhesive, the solvent in the adhesive dissolves the clear ink on the print more or less. Increasing the speed of compounding or increasing the viscosity of the adhesive can alleviate this problem to a certain extent, but it is only a temporary solution. In addition, if the transparency is allowed to be appropriately lowered, a part of the pigment may be added to the dye to produce a transparent ink, which also has a certain improvement in the problem of dissolution of the transparent ink. In addition, in response to the above problems, some ink factories have developed transparent inks that are completely insoluble in alcohol-soluble adhesives, and have been well applied in some printing materials. It is believed that insoluble ester-soluble rubbers will be developed in the future. Clear ink for adhesives.
5. Peel strength
The product after the transparent ink printing often has a problem of poor peel strength in the composite aluminized film. Why is this so? In fact, it is not only the problem of transparent ink. When printing with other inks, if the white ink substrate is not printed, the peeling strength will be poor after the composite aluminized film (especially VMCPP), but usually This process is rarely used when printing with other inks, so the phenomenon of poor peel strength is rarely found. Of course, it is not that all composite inks have this problem.
In addition to the above characteristics, the leveling of transparent inks is generally very good, and there is almost no problem of cutting lines during printing.