Suitability of transparent ink for aluminum film surface printing
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In the current high-end packaging cartons, in order to improve the effect of packaging printing, it is often necessary to improve the surface brightness of the packaging box. A common practice is to use special papers, such as gold and silver cardboard, to print on such papers, in order to obtain For higher gloss, it is often necessary to use transparent ink for printing. Next, I will discuss the printability of transparent ink.
Transparent ink characteristics
The clear ink is an ink made entirely or mostly of a coloring agent, which has a low hiding power and an extremely high transparency.
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 is compounding 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 hue blending of clear inks is very laborious, so it is important to understand the customer's process.
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.
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 using 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. Adhesive dissolution of transparent 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.
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 happening? 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.
Common faults in printing
Transparent ink agglomeration
Main reasons and solutions: This phenomenon generally occurs when the temperature is low. In this case, the ink should be heated at room temperature of 35 ° C.
In short, solvent ratio imbalance, improper drill control or process operation errors are likely to lead to many failures, so each link can not be sloppy. When printing with transparent inks, in order to achieve the desired results, each link must be strictly controlled, and the appropriate ink should be selected according to the actual conditions of printing.
Gloss is not very high after 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. When the solvent evaporates too fast, the drilling degree is too low. The slow drying solvent should be selected according to the need to check and improve the ink drill.
3. The aluminum plating layer has poor homogeneity, resulting in poor anti-gloss. It is necessary to replace the aluminized film and ensure that the surface is uniform and there is no pinhole.
4. The angle of the squeegee is too large, the plate mesh should be adjusted shallowly, and the angle of the squeegee should be controlled. Generally, the angle should be controlled at about 35 degrees. Annoying "pitting" phenomenon
A closer look at the flash effect reveals that the surface has pinholes that appear to be unprinted. The main reasons and solutions for this failure are:
1. The surface of the embossing rubber roller is not delicate enough, or there is foreign matter such as dust, which causes the ink here to be not thick enough. Check the adhesive roller for dirt, wipe the surface clean, check the quality of the rubber roller, and replace the qualified rubber roller.
2. The plasticizer, lubricant, etc. contained in the film float on the surface, hindering the normal transfer and lubrication of the ink. Pre-press processing such as preheating of the offset film before printing, film heating printing, if not, replace the appropriate plastic film.
3. Ink drilling is too high, too fast drying or lack of drilling agent causes ink transfer and poor wet adaptability. The ink drill should be appropriately reduced and the solvent should be dried.
4. The printing pressure is too small. It is appropriate to increase the printing pressure and pay attention to controlling the printing pressure (generally around 4kg).
5. The problem of printing plates or embossing rollers (expressed as pitting is more regular). Care should be taken to check the plates and the embossing rollers for defects and, if so, re-plate or replace the rollers.
Principle of ink selection during printing
Consider the suitability of the material
For example, when printing a printed aluminum film, it is necessary to select a transparent ink for printing. When printing a BOPP film and a composite aluminum plating, a transparent (composite) ink should be used. Therefore, the type of substrate determines the type of ink used. Even the same type of film material tends to vary depending on the variety and grade. In addition, when printing with transparent ink, generally no white bottom is used under the color case, because white is used for matting, which greatly reduces the use effect and value. Relatively speaking, the color of the transparent ink printing is 0.01mm thinner than the place with the white ink bottom.
Taking the sample provided by the customer as the important basis
The choice of clear inks includes hue and color. For dispensing clear inks, you must consult your production supplier. Because the matching of the transparent ink spot color is different from the general spot color ink, the difficulty is obviously higher than that of the opaque ink.
Consider the actual situation and consider the choice of objects
According to the actual situation and use of the packaging, the corresponding transparent inks, such as high temperature resistance, light fastness and impermeability resistance, should be included in the selection considerations. In addition, transparent ink printing requires high-brightness and vivid colors, such as aluminized film or aluminum foil, aluminum foil and other materials. Because the transparency of the transparent ink is extremely high, it will change with the aluminized film or directly printed on the above materials to change the gloss and color of the metal, making the yellow yellow, green green, red and red, and the effect is better.