In order to improve the printing and visual effect, transparent ink is often used in the process of flexible packaging printing. However, some quality problems often occur in the actual use process, such as pockmarks after printing and uneven ink spreading, which greatly reduces the expected effect. Therefore, it is necessary to be familiar with the nature and printing characteristics of transparent ink, and analyze and eliminate them.
1. The main reasons and solutions of "pitting" in transparent ink printing
This kind of fault is that after the printed product is padded with aluminum coating, the flash effect will come out. However, if you observe it carefully, you will find that the surface has needle hole shape, as if it is not printed. The main causes of this failure are as follows:
① Imprint cot surface is not fine enough, or there are dust and other foreign matters, causing the ink here is not thick enough. Check whether there is dirt on the embossing cots and wipe the surface clean; check the quality of the cots and replace the qualified cots.
② The plasticizer and lubricant contained in the film float to the surface, which hinders the normal transfer and lubrication of the ink. Before printing, it is necessary to preheat the plastic film and other pre printing treatment. If the film heating printing is not available, the appropriate plastic film should be replaced.
③ Ink viscosity is too high, drying too fast or lack of adhesion agent, resulting in ink transfer, poor wetting adaptability. Should be appropriate to reduce ink viscosity and use slow drying solvent.
④ The printing pressure is too low. The printing pressure can be properly increased and controlled (generally about 4kg).
⑤ If there is a problem with the plate or the embossing cot (the pitting is regular), the plate and the roller should be carefully checked for defects. If so, the plate should be made again or the cots should be replaced.
2. Main reasons and solutions of adhesion after printing transparent ink

In the rainy season of high temperature and high humidity, the plastic film after gravure printing is easy to adhere during the winding and placing. The transparent ink is stuck in blocks, and even can not be separated from the lower plastic film at the ink place, resulting in a large number of waste products. Printing adhesion is mostly caused by the ink sticky, environmental humidity is too high, pressure is too large. The main reasons are as follows. ① The ink itself has poor heat resistance. Greater viscosity is produced at high temperatures. Ink drying, with the naked eye can not see. After the printed articles are rolled up, the residual solvent is difficult to evaporate, and the resin in the ink can not be dried and solidified, resulting in serious adhesion of the finished product. If there is too much residual solvent in the ink, the finished product will have serious adhesion after winding up. Too much residual solvent will not only affect its firmness, but also be very harmful to food, making the packaging produce peculiar smell. ② Because the environment temperature is too high, it will cause ink softening, resulting in printing adhesion. At room temperature, many printing materials using transparent ink are normal in operation and use, but when printing at high temperature, the ink will soften and produce adhesion. Therefore, it is required that the ambient temperature for the operation and use of printed matter should not exceed 50 ℃, and it is better to control it below 45 ℃. In addition, take-up too tight, take-up tension is too large will also cause adhesion. The solution is to control the drying temperature and relax the tension, and the winding should not be too tight. ③ The ink and the substrate do not have a good adhesion, so that the ink on the substrate is not firmly bonded, easy to produce transfer after winding, resulting in adhesion. The solution is to choose the right ink. Control the quality of ink to adapt to the substrate. In addition, the substrate surface can be treated to improve its affinity to ink is also a way to reduce ink adhesion. Generally, the surface tension of BOPP should be greater than or equal to 38 dyne.

3. Main reasons and solutions of low gloss of printing transparent ink after aluminizing
The main reasons for this phenomenon are: ① the transparency of the ink itself is poor, should be replaced with good transparency of the ink. ② Printing solvent volatilization is too fast, viscosity is too low, should be selected according to the needs of slow drying solvent, check and improve the ink viscosity. ③ If the uniformity of the aluminum coating is poor, resulting in poor reflection, it is necessary to replace the aluminum coating and ensure that its surface is uniform and free of pinholes. ④ Scraping knife angle is too large, plate mesh shallow to adjust, good control of the blade angle, the general angle of 35 degrees is appropriate.
4. The main reasons and solutions for the caking of transparent ink
This phenomenon generally occurs in the case of low temperature. In this case, the ink should be placed at 35 ℃ room temperature. In order to prevent accidents, special personnel must also be assigned to guard.
In a word, the imbalance of solvent ratio, improper viscosity control or process operation error are likely to lead to many failures, so every link can not be careless. Therefore, when using transparent ink printing, in order to obtain the ideal effect, each link must be strictly controlled, and the appropriate ink should be selected according to the actual situation of printing.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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