Applicability of transparent ink and aluminum film printing
In the current high-end packaging carton, in order to improve the effect of packaging printing, the surface brightness of the packaging box is often improved. One of the common methods is to use special paper, such as gold and silver cardboard, to print on this type of paper, in order to obtain For higher gloss, transparent ink is often used for printing. Next, the author discusses the printing suitability of transparent ink.
The characteristics of transparent ink: transparent ink is an ink made of all or most of the colorant made of dyes, its hiding power is very low, and its transparency is extremely high.
Hue: Because the transparency of the transparent ink is very high, it is generally compounded with aluminum film after printing, so that the gloss of the aluminum film and the gloss of the ink are combined to reflect a more vivid color. Moreover, for products printed with transparent ink, the hue will be more obvious when viewed from different angles, and the difference will be greater when viewed under different light sources. Therefore, when formulating this type of ink, we must understand what materials the customer compounded, in order to formulate the ink according to the same process, and observe the hue of the ink under a similar environment. For example, the hue of some inks before compounding is very close to the standard sample, but the hue after compounding may be very different; on the contrary, there are some inks that have a certain gap between the hue and the standard sample, but the hue after compounding is closer to the standard sample. The blending of hue of transparent ink is very laborious, so it is very important to know the customer's process.
Transparency: The transparency of transparent ink is determined by the dye (pigment) and the binder (including additives), and the former plays a major role, and the latter has little effect. For inks made of polyurethane, polyamide, chlorinated polypropylene and other common resins, polyurethane inks have higher transparency. In general, inks that use dyes as colorants have higher transparency than inks that use pigments as colorants. Sometimes due to other needs, some pigments will be mixed in the dye, and the transparency of the ink will be reduced.
Residual solvents and odors: Careful operators will find that the drying speed of transparent ink is significantly slower, because the solid content of transparent ink is low (due to the higher color density of the dye than the pigment, so the amount does not need to be too much), the solvent content is high Therefore, it is necessary to control the drying condition, otherwise it is easy to cause the residual solvent to exceed the standard and produce odor. In severe cases, the solvent will slowly penetrate and diffuse around after compounding, causing other colors to change color. Therefore, when using this type of transparent ink, it is necessary to pay attention to the control of the solvent ratio and printing speed. After printing, it is placed in a curing room at about 40 ° C for more than 10 hours.
Adhesive dissolves in transparent ink: the dye used in transparent ink is completely soluble in organic solvents, so when the printed product comes into contact with the compound adhesive, the solvent in the adhesive will remove the transparent ink on the printed product Dissolve more or less. Increasing the compounding speed or increasing the viscosity of the adhesive can alleviate this problem to a certain extent, but it is only a cure for the symptoms. In addition, if transparency is allowed to be reduced appropriately, some pigments can be added to the dye to make transparent ink, which also improves the dissolution of 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 used in certain printing materials. I believe that insoluble ester-soluble adhesives will also be developed in the future Transparent ink for adhesives.
Peel strength: The problem of poor peel strength often occurs when the products printed with transparent ink are compounded with aluminized film. Why is this happening? In fact, it is not just the transparent ink that has this problem. When printing with other inks, if the white ink substrate is not printed, the peel strength will also be poor after the composite aluminum coating (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, not all compound inks have this problem.
Common faults in printing
Agglomeration of transparent ink, the main reasons and solutions: This phenomenon generally occurs in low temperature conditions. In this case, the ink should be placed at 35 ℃ room temperature and heated. In short, the mismatch of solvent ratio, improper drilling control or process operation errors are very likely to cause many failures, so every link should not be sloppy. When printing with transparent ink, in order to obtain the desired effect, each link must be strictly checked, and the appropriate ink should be selected according to the actual situation of printing.
The main reasons and solutions for this phenomenon are:
1. The transparency of the ink itself is poor, and the ink with good transparency should be replaced.
2. Solvent volatilization is too fast during printing and the drilling degree is too low, you should select the appropriate slow-drying solvent as needed, check and improve the ink drilling.
3. Poor homogeneity of the aluminized layer, resulting in poor gloss, replace the aluminized film, and ensure that the surface is uniform and free of pinholes.
4. The angle of the squeegee is too large, and the plate hole should be adjusted. The angle of the squeegee should be controlled. The general angle should be controlled at about 35 degrees.
Careful observation of the flash effect will reveal pinholes on the surface, as if they were not printed. The main reasons and solutions for this failure are:
1. The surface of the embossed rubber roller is not delicate enough, or there are foreign objects such as dust, which makes the ink here not thick enough. Check whether the imprinted rubber roller is stuck with dirt, wipe the surface clean, check the quality of the rubber roller; replace the qualified rubber roller.
2. Plasticizers and lubricants contained in the film float to the surface, preventing the normal transfer and lubrication of the ink. Before printing, preheat the plastic film and other pre-press treatments, and perform film heating printing. If it still does not work, replace the appropriate plastic film.
3. Ink is too high, too dry, or lack of drilling agent caused ink transfer, poor wet adaptability. Should be properly reduced ink drill and use slow-drying solvent.
4. The printing pressure is too small. The printing pressure can be increased appropriately, and pay attention to control the printing pressure (generally around 4kg).
5. The problem of printing plate or embossed rubber roller (shown as pitting is more regular). Care should be taken to check whether the printing plate and the rubber roller are defective. If there is, the plate should be remade or replaced.
Principles of ink selection during printing
Consider the suitability of the material
If printing surface printing aluminized film, you must choose surface printing transparent ink, when printing BOPP film and compound aluminizing, you should choose inside printing transparent (composite) ink. Therefore, the type of printing material determines the type of ink used. Even the same kind of thin film materials are often different due to different varieties and grades. In addition, when printing with transparent ink, generally no white underlay is needed under the color scheme, because white has a matting effect, which greatly reduces its use effect and value. Relatively speaking, the color scheme printed with transparent ink is 0.01mm thinner than the place with white ink underlay.
Take the sample provided by the customer as an important basis: the choice of transparent ink includes hue and color. If you want to prepare a special color transparent ink, you must consult the production supplier. Because the allocation of transparent ink spot colors is different from ordinary spot inks, its difficulty is significantly higher than that of opaque ink spot colors.
Considering the actual situation and considering the selection object: according to the actual situation of the packaging and the use of the corresponding transparent ink, such as high temperature resistance, light resistance, penetration resistance and other parameters of the packaging printed matter, these must be included in the selection consideration. In addition, in order to obtain high brightness and bright colors in transparent ink printing, it is inseparable from materials such as aluminum plating film, aluminum foil paper, aluminum foil and so on. Because the transparency of the transparent ink is extremely high, it will change with the aluminized film or printed directly on the above materials to reveal the luster and color of the metal, making yellow more yellow, green more green, red more red, and the effect is better.
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