With the continuous improvement of packaging requirements, packaging design and printing have become more diversified. In product packaging and printing, printing color is always the first focus that attracts people's attention. For example, the outer packaging of commodities in shopping malls has high transparency, giving people a shiny feeling. To this end, a variety of special inks have been developed and widely used in addition to pearlescent inks, etched metal inks, coral inks, fluorescent inks, ice inks, etc. The application of special inks not only strengthens the artistic effect of packaging, but also improves the persuasion of anti-counterfeiting. The application of transparent ink in packaging printing (mainly in the high-end flexible packaging in the field of flexible packaging, such as the food industry) also adds color to packaging printing and occupies a special position in packaging printing. Transparent ink is used for aluminum plating film or aluminum foil printing, the effect is more It is best for obvious visual effect. Now transparent ink has been widely used in the packaging and printing industry. It is specifically applied to high-end packaging such as flexible packaging in the food industry, carton packaging in the wine industry, and carton packaging in the tobacco industry. Let's talk about the application skills of transparent ink in packaging printing.
Characteristics of transparent ink
Transparent ink refers to an ink made by using all or most of the colorant with high-grade transparent pigments (dyes) as the main raw material, with high-grade transparent resin as the main raw material, and other types of additives through fine grinding. Its hiding power is very low and the transparency is extremely high. . Transparent ink can be divided into two types: surface printing transparent ink and inside printing (composite) transparent ink. Although both surface printing and internal printing transparent inks are of the same resin type, they should not be mixed. Especially, transparent inks of different brands produced by different manufacturers cannot be mixed to avoid failure and quality problems. Compared with other types of ink, transparent ink has the characteristics of high drilling, high transparency, high brightness, bright colors, firm adhesion and strong coloring power. In addition, in general, the leveling of transparent ink is better, and almost no problems such as knife line when printing. The fineness of the transparent ink is generally below 10 microns, so its hiding power and transferability are better than other inks, but the surface printing transparent ink is not as high temperature resistant as the internal printing transparent ink. In the design of packaging bags, there is generally no phenomenon of transparent ink at the position of the heat sealing knife. The surface printing transparent ink is generally resistant to high temperature around i2o0C. Of course, some ink manufacturers have produced more high temperature resistant transparent ink. The transparency of transparent ink is determined by pigments, binders and additives and the former plays a major role, the latter has little effect. In the case of inks made of several common resins such as poly (nitrogen vinegar), poly (phthalamide), and nitrided polypropylene, the transparency of poly (nitrogen vinegar) ink is relatively high. Generally speaking, the transparency of ink using dye as colorant is higher than that of ink using pigment as colorant. Sometimes due to the unimportant aspects of other aspects, some pigments will be mixed in the dye and the transparency of the ink will be reduced. The dyes used in transparent inks are completely soluble in organic solvents, so when the printed matter comes into contact with the adhesive for compounding. The solvent in the adhesive will more or less dissolve the transparent ink on the printed matter. Although increasing the compounding speed or improving the drill of the adhesive can alleviate this problem to a certain extent, it is not a fundamental solution. In addition, some pigments can be added to the dye to make transparent ink, which also improves the problem of dissolving transparent ink, but the transparency will be reduced. In response to this problem, some ink factories have developed transparent inks that are completely insoluble in alcohol-soluble colloidal agents, and have been well used in certain printing materials. Therefore, the development of transparent inks that are insoluble in vinegar-soluble adhesives is the fundamental solution to the problem.
In packaging and printing, the transparent ink is usually printed in combination with a composite aluminized film, but many products printed with a transparent ink often have a problem of poor peel strength when the aluminized film is composited. In fact, this is also a problem with other inks. For example, 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 printed with other inks. This process is rarely used, so the phenomenon of poor peel strength is rarely found. Because the transparency of the transparent ink is very high, the gloss of the aluminum film and the gloss of the ink are generally combined after printing, reflecting more vivid colors. Moreover, for products printed with transparent ink, the hue will be more obvious when viewed from different angles. The difference will be greater when viewed under different light sources. Therefore, when distributing transparent 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: Conversely, some inks have a hue after printing that is somewhat different from the standard sample, but the hue after compounding is closer to the standard sample. It is very difficult to adjust the hue of transparent ink, so it is very important to know the customer's process. The drying speed of the transparent ink is very slow. This is because the curing agent of the transparent ink contains low f (due to the higher color concentration of the dye than the pigment, so the amount does not need to be too much). The solvent contains high f, so the drying status needs to be controlled, otherwise it is easy to cause The residual solvent exceeds the standard and produces an odor. In severe cases, after compounding, the solvent will slowly penetrate and diffuse around to discolor other colors. Therefore, when printing such transparent inks, it is necessary to pay attention to the control of the solvent ratio and the printing speed. After printing, it is placed in a curing room at about 400 ° C for more than 10 hours.
Selection and application of transparent ink
The selection and application of transparent inks should be carried out according to the requirements of customers with different substrate characteristics. In summary, the main considerations are the following three aspects, and the reasonable selection of transparent inks.
1According to the printing material, choose the ink that suits it: if you print the surface-printed aluminum film, you must choose the surface-printed transparent ink: when you print the BOPP film and you need to compound the aluminum, you should choose the transparent ink (composite). Therefore, it can be said that the type of printing material determines the type of ink used. Even if it is the same type of film material, it is often different due to the variety and grade. Also note that when printing with transparent ink, a white underlay is generally not used under the color scheme, because white has a matting effect that will greatly reduce its use effect and value. Relatively speaking, the color scheme printed with transparent ink is 0.01 mm thinner than the place with white ink underlay.
2. Choose the suitable transparent ink according to the sample provided by the customer: the choice of transparent ink includes hue and color. To prepare a spot color transparent ink, you must consult the production supplier because the deployment of the transparent ink spot color is different from the general spot color ink. Its difficulty is significantly higher than that of opaque inks.
3. Choose the corresponding transparent ink according to the actual situation and application of the packaging: such as high temperature resistance, light resistance, penetration resistance and other parameters of the packaging print, these must be included in the selection consideration. In addition, transparent ink printing cannot achieve high brightness and vivid colors without materials such as aluminum plating film, aluminum foil paper, aluminum foil, etc. because the transparency of the transparent ink is extremely high, it will change if it is compounded with the aluminum coating film or printed directly on the above materials. In order to reveal the luster and color of metal, the effect of making yellow more yellow, green more green and red more red is better.
Nowadays, transparent inks have developed a variety of transparent golden, transparent yellow, transparent light blue. And if the transparent golden color is compounded on the aluminum coating film, it is golden glittering: because of its high transparency, transparent golden color is also often used in self-provision of gold, and it can also be lined with gold powder. According to the customer's requirements, you can choose to prepare such golden ink as gold powder, gold oil, and transparent golden gold in a ratio of 1: 3: 2, which not only shines, but also greatly enhances its adhesion. . At present, transparent inks are mainly used for printing brightly colored flowers and gift gold paper with color bars and ribbons. These packaging papers are made of transparent ink (red, yellow, green, blue, etc.) after printing with aluminum plating or with aluminum plating film for surface printing. It is a single adhesive film. After printing the transparent ink, the inner layer is made of aluminum coated film to make a flexible packaging bag or a small inner bag made of aluminum coated film. This is a film with more than two layers that has been widely used in the food industry. There are also high-grade packaging prints such as cartons, cartons, new year pictures, etc. after printing with transparent ink and aluminum plating and then re-coated on paper, which has the advantages of waterproof and moisture resistance. After printing with anti-counterfeiting materials, printing with transparent ink and then applying laser holographic film can not only improve the anti-counterfeiting effect, but also make the appearance colorful and radiant. In order to achieve the best results, it is not necessary to use transparent ink in the design, but only use transparent ink for partial printing, you can receive better results. Transparent inks are dry specialty inks. Due to their different formulations, the use method is also different from general inks.
The transparent ink must be fully stirred before printing. In the colder winter, it is not advisable to add too much thinner due to the low drilling degree. The drilling degree is generally controlled at 18-22 seconds. 3 mortar cups are appropriate. Then according to the depth of the printing plate Adjust the angle of the doctor blade and the pressure of the impression cylinder and the distance between the doctor blade and the impression point.
If the mismatch of the solvent ratio is not properly controlled or the process operation is wrong, it is very likely that many failures will occur, so every link cannot be sloppy.
Removal of common faults in transparent ink printing
In the process of flexible packaging printing, transparent ink is often used with aluminum coating or aluminum foil underlay to improve printing and visual effects. However, some quality phenomena often occur in the actual use process, such as pitting after printing of transparent ink, uneven ink spreading, etc. This greatly reduces its expected effect, so it is necessary to be familiar with the nature of transparent ink and printing characteristics, and analyze and exclude.
1. The phenomenon of "pitting" occurs when printing with transparent ink
The main cause and solution of this problem is that after the printed product pad is coated with aluminum film, its flash effect will come out, but if you look closely, you will find that the surface has pinholes, which seem to be unprinted. The main reasons for this failure are:
â‘ The surface of the embossed rubber roller is not delicate enough, or there are foreign objects such as dust, which makes the ink not thick enough here. Check whether the imprinting rubber roller is stuck with dirt, and wipe the surface clean; check the quality of the rubber roller. Replace the qualified rubber roller.
â‘¡Plasticizers and lubricants contained in the film float to the surface and hinder the normal transfer and lubrication of the ink. Before printing, preheat the plastic film and other pre-press treatments. If the film heating printing is not enough, the appropriate plastic film should be replaced.
â‘¢Ink drilling is too high, drying too fast or lack of drilling agent causes poor transferability of ink transfer and wetting. Should reduce the ink drilling properly and use slow-thaw solvent.
â‘£ The printing pressure is too small. The printing pressure can be increased appropriately and the printing pressure can be controlled to control the printing pressure (generally around 4kg).
⑤ The problem of the printing plate or the impression rubber roller (showing that the pits are more regular) should be carefully checked for defects in the printing plate and the impression rubber roller. If there is any defect, the plate should be remade or replaced.
2. Blocking occurs after printing transparent ink
The main reason and solution: during the rainy season of high temperature and high humidity, the plastic film is prone to sticking during the gravure printing, and the rewinding of the dish. The transparent ink is stuck in blocks, and it cannot even be separated from the lower plastic film at the ink, so that Cause a lot of waste. The adhesion of the printed products is mostly caused by ink hair drilling, environmental humidity is too high, pressure is too high, etc., mainly caused by the following turbulence. â‘ The heat resistance of the ink itself is poor, resulting in greater drillability under high temperature conditions. When the ink is dry, it cannot be seen with the naked eye. After the printed matter is rolled up, the residual solvent is difficult to evaporate. The resin in the ink cannot be dried and solidified, which causes serious adhesion of the finished product. After the excessive residual solvent in the ink is rolled up, the final product will cause serious adhesion. Too much residual solvent will not only affect its firmness, but also be extremely detrimental to food, and cause odor in the packaged products. â‘¡Because the ambient temperature is too high, it will cause the ink to soften, which will cause the printed matter to stick. At room temperature, many printed products using transparent ink are normal in operation and use, but when printed at high temperature, the ink will soften and cause blocking. Therefore, it is required that the ambient temperature of the operation and use of the printed matter should not exceed 50 degrees Celsius, and it is better to be controlled below 45 degrees Celsius. In addition, too tight winding and excessive winding tension will also cause blocking. The solution is to control the printing drying temperature and relax the tension. The winding should not be too tight. â‘¢ The ink has no good adhesion to the substrate. The ink on the substrate is not firmly adhered, and it is easy to transfer and lead to adhesion after rewinding. The solution is to choose the ink correctly. Control the quality of the ink to adapt it to the substrate. In addition, the surface of the substrate can be treated to increase its affinity for the ink is also a method of reducing ink adhesion. Generally, the surface tension of BOPP should be 38 dynes.
3. The gloss is not high after printing transparent ink and aluminum compounding
The main reason and solution: The main reason for this phenomenon is: â‘ the transparency of the ink itself is poor, and the ink with good transparency should be replaced.
â‘¡During printing, the solvent volatilizes too fast and the drilling degree is too low. You should select a suitable slow-drying solvent according to your needs, check and improve the ink drilling degree. â‘¢The homogeneity of the aluminized layer is poor, causing poor gloss. Replace the aluminized film and ensure that its surface is uniform and free of pinholes. â‘£The angle of the squeegee is too large. The angle of the printing plate is shallow. The angle of the squeegee should be adjusted and controlled. Generally, the angle should be controlled at about 35 degrees.
4. Agglomeration of transparent ink
The main reason and solution: This phenomenon generally occurs when the temperature is low. In this case, the ink should be placed at 35 ℃ room temperature and heated. To prevent accidents, it must also be guarded by a designated person.
In short, the mismatch of solvent ratio, improper drilling control or process operation error, etc., are likely to cause many faults, so every link can not be sloppy. Therefore, when printing with transparent ink, each link must be strictly checked to obtain the desired effect, and the appropriate ink should be selected according to the actual situation of printing.
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