Coating process in cardboard packaging (top)

It is often forgotten that most folding cartons are treated with aqueous coating or UV curing coating. In fact, most new presses are also equipped with coating devices. UV coatings are commonly used coatings due to their high gloss and chemical resistance. However, UV coatings are expensive compared to waterborne coatings and are difficult to use. The cost of waterborne coating materials accounts for only a small part of the printer's production costs, typically less than 3% of the total packaging cost. Even so, poor coating quality can lead to package degradation or customer claims. Although coating materials are relatively inexpensive, they can greatly affect other cost factors, including excessive downtime and operator hands-on interventions.
This article focuses on why it is necessary to coat the packaging, what is the quality of the job and the amount of coating, and the practical significance of controlling the viscosity of the coating.
Why is the subjective feelings of the person involved in coating the packaging? Consumers often associate product quality with packaging quality. The packaging customer is very concerned about the specific gloss or the specific coefficient of friction. These are important packaging surface features. Of course, because printers sell products to packaging customers, the needs of customers are what printers need. The printer must also deal with some production problems such as drying speed and ease of use. Since an offset ink takes several hours to cure, an aqueous coating is used to provide a fast drying protective seal. This will not damage the ink layer when handling the package surface, thereby shortening the printer's processing time. In addition, printers can also use large lifting devices to reduce handling costs. Sometimes a flip coating is used so that the second side can be printed quickly after printing on the first side. The above coating helps to reduce the amount of offset dusting. Offset dusting tends to give the surface of the package a feeling of dust accumulation.
The above coating is also applied on the soft-gravure printing carton, mainly to increase the important surface characteristics of the package.
Important surface properties and barrier properties The coating layer is the last layer of the packaging surface. The rough surface of the substrate clay coating should be coated with a relatively flat water-based coating. It has a great influence on the surface characteristics of the package. Water-based coatings can use different formulations according to the surface needs, so that the packaging surface has a certain degree of gloss, wear resistance, the required coefficient of friction, corrosion resistance and barrier properties.
The coating has a great influence on the surface gloss of the package. In order to better attract consumers, they often use higher gloss. The packaging gloss of high-quality products is also relatively high. For this reason, some packaging designers also use a lower gloss or matte packaging surface in order to better highlight their own product packaging. In addition to gloss, product packaging also requires a certain degree of friction and scratch resistance.
Friction coefficient is of great significance for die-cutting, gluing, and high-speed filling operations. Cardboard with a non-compliant friction coefficient cannot pass the filling or folding process smoothly.
Safe handling of filled packaging products at warehouses and retailers is also very important. This is especially true for beverage packaging cartons. The packaging box containing the product should neither be slid off the pile, nor should it be stacked together, even under hot and humid conditions. During the molding, filling, transportation and display process, the surface coating of the package has the functions of scratch resistance, water resistance and corrosion resistance. If the package contains a liquid product, the above characteristics are even more important.
For food packaging must comply with the appropriate management regulations. The US Food and Drug Administration (FDA) approved packaging coatings can block inks that do not meet hygienic requirements and prevent inks from directly contacting foods. Coatings that meet FDA standards are formulated with resins and emulsions that can be in direct contact with food. They are available to all paper materials and are suitable for all conditions (except for extended shelf life of cooked foods).
It should be noted that the paint does not fully control the surface characteristics of the package. Substrates and inks can also play a role.
The reason for emphasizing coating stability emphasizes coating stability has two important meanings. The first concerns the previously mentioned important packaging surface characteristics and the second is the processor's stability, ie, the coating on the press has a stable and repeatable characteristic.
The physical properties of the coating, like the viscosity, can change over time, causing problems with some printer operations. The press operator needs to stop to adjust the setting of the press or change the viscosity of the paint to maintain the best speed and avoid problems such as sticking. Coating stability should be considered from the following aspects:
● Has the paint changed during the same shift?
● Are different operators using different standards when working in different teams?
● Does the operator always get the same coating effect every time he or she processes the same job?
● Is the performance of the paint stable in different seasons (for example, winter and summer)? Does the paint supplier provide different formulations in winter and summer to adapt to seasonal changes?
● Do you also require different paint formulations to process the same batch of jobs due to different coating equipment designs? Is the appearance of the print job affected by all coating equipment? Does the packaging customer require the appearance of the packaging to remain consistent? Is the appearance of the packaging produced by different factories consistent?
Control Coating Amount The coating formulation should meet specific job requirements. However, in order to make the paint play its role, it is necessary to determine the appropriate coating speed. The so-called coating weight refers to the weight of the paint applied on the substrate per unit area (usually measured in grams per square meter, or pounds per thousand square feet). If the amount of coating is not stable, other aspects will not be stable.
There are also some problems with the operation. The amount of coating affects the drying speed of the coating. If the coating amount is too high, the sheets cannot be sufficiently dried before stacking, and they may stick together. Sometimes we see orange peel patterns. Conversely, if the coating amount is too low to cover the ink, sticking will occur. (To be continued)

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