Flexible packaging refers to packaging in which the shape of the container can change after filling or removing the contents. Various bags, boxes, covers, envelopes, etc. made of paper, aluminum foil, fibers, plastic films, and their composites belong to flexible packaging.

Substrate
For different substrates, suitable ink should be selected. For example, ordinary ink can be used for printing BOPP films, polyurethane ink can be selected for printing NY/PET films, and it is best to choose aluminum foil specific ink when printing on aluminum foil as the substrate.

The most basic condition for gravure printing is to allow the printing ink to adhere to the printing substrate, so the ink's wetting and polarity are important properties. In order to improve adhesion performance, it is also necessary to perform surface treatment on the printing substrate in advance (some inks are specifically suitable for substrate films treated with corona discharge). The adhesion of ink can have an impact on the processing and durability after printing, so it is important to pay close attention to it.

The type of substrate is the most important factor in determining the type of ink used. Even for the same species, there are often differences due to differences in variety and grade. Therefore, it is necessary to investigate the following points in detail as much as possible: the type of printing substrate (material composition), manufacturer, thickness, presence or absence of electrostatic inhibitors and other additives, presence or absence of pre-treatment, treatment methods, printing surface, etc.

Printing conditions
The printing conditions include printing speed, drying device (capacity) and position, condition of the printing plate drum, printing color number and printing sequence, temperature and humidity in the printing workshop, function of the preheater cooler (roller), etc. These conditions can directly affect the transfer rate and drying speed of ink, so the ink selected for printing should be suitable for the printing conditions.

The drying conditions include drying air temperature, air volume (wind speed), and drying device structure, which determine the drying efficiency. The speed of printing determines the length of drying time and the separation speed at the moment of ink transfer. The temperature, humidity, and preheating conditions in the printing workshop have a certain impact on the drying and layering of ink. The cooling roller must be able to cool the heat carried by the ink film when it leaves the outlet of the drying oven in a timely manner. In addition, for low-speed printing machines, the quality requirements for ink are relatively low. When using medium to high speed printing machines, it is necessary to choose medium to high grade ink. Some ink with poor quality has a lower transfer rate and is difficult to adapt to shallow versions.

Printing quality requirements
Color tone, brightness, and purity

Transparency and covering ability

Surface glossiness

Hierarchical effect

Overlay state

Surface printing or back printing (inner printing)

Is there any additional printing varnish available

Other special quality requirements

Ink produced by different manufacturers has different ink colors. There are differences in concentration, transparency, glossiness, and level expression, and the selected ink should meet the customer's requirements in terms of printing effect. When the printing effect is high, it is undoubtedly necessary to choose higher grade ink with targeted selection. After obtaining a standard sample with one ink for the first time, it is difficult to catch up with the standard sample with another ink. Due to the same reasons, the amount of ink used for plate making and sample making should be consistent with the actual printing ink used.

Post press processing conditions
Most plastic gravure printing products need to go through post-printing processing steps such as lamination, slitting, bag making, or hot stamping and polishing after printing to obtain the product. The processing conditions of this process must be judged to determine whether it is suitable for the performance of the ink, which is an important part of ensuring product quality. The compatibility with adhesives, composite strength, and heat resistance of heat sealing in composite processing are closely related to the type of ink (i.e. the resin in the binder), while the boiling resistance and distillation resistance of boiling sterilization are not only related to the type of ink, but also to the durability of the pigments used in the ink.