All packaging materials and labels can be printed with pearlescent gravure ink, but the surface of the substrate should be as smooth and flat as possible to optimize the alignment of the pigments. This is extremely important for obtaining the desired pearlescent effect. In gravure printing, the printing result is obtained by passing ink through the corrosion of the printing plate or the engraved ink port. Intaglio printing mainly uses low-viscosity liquid inks. According to the printing and post-press processing, the pearlescent pigments are suitable for most gravure printing solvent-based or water-based system inks. Choosing a highly transparent binder can prevent damage to the pearlescent effect. With color inks, it is necessary to mix well-dispersed transparent colorants with pearlescent pigments. Because pearlescent pigments only have an optical effect in a well-lighted ink layer, the amount of colorant should generally be within 3% of the finished ink. Hue that is too heavy will affect the pearlescent effect. Suitable rheology aids should also be used to improve the surface properties of pearlescent pigments in inks. When applied to solvent inks, the pigments are preferably pre-wet and dispersed. Twilight and embossing can increase the pearlescent effect.

Gravure inks are low-viscosity solvent-based or aqueous liquid inks, all of which are suitable for the preparation of pearlescent pigments. However, it should be noted that in the preparation of monochromatic and mixed pearlescent inks, the binder with higher transparency should be used. Since the pearl powder has a micron-sized particle size and therefore a large specific surface area, these indicate that pre-wetting of the pigment is required before formulating the pearlescent ink. Alkaline ink systems use alkaline reagents to adjust the pigment surface pH. The simplest method of pre-wetting is to add a suitable amount of ink carrier (such as water, alcohol, and diluent) into the pearl powder to make a paste. After being left for a period of time, it can be used together with the ink. In this process, it is necessary to pay attention to dust prevention. To achieve a good pearlescent printing effect, the relative density of pearlescent pigments should account for 15% to 25% of the finished ink. At present, the commonly used gravure printing ink formulas for pearlescent pigments are: Nitro varnish 55% to 65%, Ester (to prevent wear) 2% to 5%, Pearlescent pigment 10% to 20%, Butyl acetate 20% to 30%, Dibutyl phthalate (as a moisturizer, can be used for vinyl film printing) or phthalocyanine dioxin polyethylene wax mixture 1% to 3%. Pearlescent gravure plates are steel, copper, chrome or gravure nylon plates. The holes in the field version are larger and deeper, and the holes in the transitional version are smaller and shallower. The platen roller is immersed in the ink tank so that all plate holes fill the ink, and the excess ink is scraped by the squeegee. The ink is transferred to the substrate between the printing plate and the embossing roller (paper, plastic, etc.). In order to obtain a better pearlescent effect, the opening angle of the engraving is preferably 120 degrees, and it is preferable to use an etching plate. The engraving depth of the ink hole of the solvent ink should be controlled at 50 μm. For pearlescent pigments with particle sizes between 5 and 25 μm, 70-line/cm engraving parameters are generally used; for high-gloss pearlescent pigments with particle sizes between 10 and 60 μm, 60-line/cm or coarser engraving parameters are preferred.

In the preparation and use of gravure pearl ink, the following issues should be noted. First of all, pay attention to the use of pearl powder and pigment. The gravure printing mainly uses the low viscosity liquid ink, and the blending pearlescent pigment should choose the transparent material (resin) with higher transparency and the transparent diluting agent with better printability. In the preparation of color inks, according to different papers choose different color ink types. White card, white paper should use pigment type color material, PET composite paper should use dye type color material. Color and pearl powder can be mixed, generally not more than 20% of pearl powder. If the hue is too heavy, it will affect the pearlescent effect, because the pearlescent pigment can only have the special light interference function in the well-lighted ink layer. Excessive use of other colored pigments can result in the loss of large amounts of pearlescent light. The method for the preparation of the gravure pearl ink is generally as follows: dilute agent: color ink: pearlescent ink = 75:3:22, and the proportion of each can be added or reduced according to the desired effect. When preparing, first use diluting agent and color ink for deployment (note that the proportion should be weighed out), and deploy the sample to be slightly deeper than the required sample, then add the soaked pearl powder, evenly stir, and other pearl powder in the ink. It can be used after being evenly dispersed.

According to practice, the control of pearl gravure printing speed has a great influence on the printing effect. A reasonable match between the ink viscosity and the printing speed is an important factor in achieving a good printing effect, and in terms of ink viscosity, adjusting the printing speed is easier.

Gravure substrates are varied, and for a good pearlescent effect, substrates with a smooth, flat surface should be used. Usually pearl printing substrates can be strong absorptive wallpaper, cardboard, or cardboard for packaging and labeling, coated paper or even plastic film.

In the printing process, pearlescent inks sometimes show deposition. The tank can be operated cyclically and stirred at low speed to keep the pearl powder flowing. At the same time, the ink is used to guide the ink to the ink tray for printing. The remaining pearl ink flows back to the ink tank through the pipe. This device can prevent precipitation of pearl powder and can keep the color stable.

In addition, the depth of engraving and the effect of printing are also greatly related. If anti-settling agent is added to prevent precipitation, the ink concentration will increase and the fluidity will decrease, failing to meet the printing requirements.

The operating methods and requirements for printing methods of pearlescent printing are basically the same as the traditional printing methods except that they are emphasized in the above printing processes. However, in order to fully display the pearlescent effect of the pearlescent ink, three basic principles can be mastered at the same time as the usual printing operation.

(1) Mix pearlescent ink and translucent printing ink. This method produces only one printing process, and the pearlescent effect appears at the same time as the color of the translucent ink. However, since the pearlescent effect of pearlescent ink is easily masked by the deep color of the translucent ink, it is only applicable to the lighter translucent ink color, and the pearlescent pigment is added at a ratio of 15% to 35%.

(2) The first layer is printed with pearlescent ink, and a layer of translucent ink is printed on the surface. This method can be applied to a deeper color effect, but the hiding power of the printed translucent ink color must not be too high, otherwise it will completely cover the pearl effect.

(3) The first layer uses ordinary ink to print the ink color and then prints a layer of pearlescent oil on the surface. This method will achieve a softer pearlescent effect. The pearlescent pigment in the pearlescent ink can be added to the transparent binder (such as varnish) in a proportion of 3% to 7%. However, the ink color of the first layer should be printed deeper, otherwise it will be lightened by the pearl ink layer of the surface layer.

In pearl ink gravure, the following issues should be noted:

(1) The corresponding model should be selected according to the size of the printed pattern area and the size of the printing plate. If the small version is printed on the big machine, not only is the ink set large, and the amount of ink is insufficient, causing poor ink transfer, and if the amount of ink is increased, it will cause problems such as stacking of ink, stencil printing, and block printing.

If these faults occur, you should consider adjusting the following factors. Such as: ink drying too fast, should adjust the appropriate drying speed. Impurities are mixed in and the surrounding environment is kept clean during printing. Improve printing speed and reduce dry time. Reduce the distance between the cutter and the pressure roller.

(2) The transfer roller used for pearlescent printing should be soft and elastic to facilitate the uniform coating and transfer of the pearlescent ink.

(3) The pressure required for printing in the field is large, and the lining should be soft. If a single print does not meet the requirements, it can be printed multiple times.

(4) In the preparation of pearlescent inks, the color of high hiding power such as titanium dioxide, sulfide pigments, and chromium salt pigments should not be added to prevent the pearlescent pigments from being covered and losing the pearlescent effect.

(5) If metallic pearlescent pigments are used instead of gold powder in multicolor printing, golden pearlescent ink can be placed in the first color sequence before printing other colors on it.

General pearl printing requires that the surface of the printing material should be as smooth and flat as possible so that the pigments can be aligned optimally to obtain the best pearlescent effect. However, for some composite papers, such as the printing of pearlescent inks on PET composite paper, due to the smoothness of the surface of the paper, the transfer rate of the pearlescent ink during the printing process is reduced, and the covering effect is also poor, and the printed hair reveals the paper color. Then in the process of arrangement to take into account the vacant color sequence, printing two pearl ink or base oil, so that pearlescent light effects will be more vivid. There is no empty color sequence, consider adding appropriate aluminum powder, white ink or transparent ink in the pearlescent ink, so that the pearlescent light effect is slightly lost, but increased the coverage rate.

Source: 21st Century Fine Chemicals Network

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