How to eliminate quality issues with film label flexographic printing? Eight key points to teach you how to do it!

For flexographic printing, the choice of substrate plays a crucial role in the printing quality and production efficiency of the final product. With the increasing demand for diversified product packaging in the market, more and more film materials are being applied in the printing of adhesive labels. Thin film adhesive materials are a type of polymer that imposes stricter requirements on flexographic printing compared to paper-based adhesive materials. Therefore, many quality issues often arise in actual production.
In this article, the author will analyze some common quality problems encountered in the flexographic printing process of thin film materials, identify possible causes, and provide solutions for industry colleagues to refer to.
01 Intermittent spots
Some film labels may have intermittent spots on the surface after flexographic printing, characterized by uneven ink distribution in the printed area, which is a common quality problem in flexographic printing. The key factor that may cause such problems is the mismatch in the selection of the mesh roller, where the number of mesh lines and ink load cannot transfer the appropriate amount of ink to the film material, resulting in the formation of intermittent spots. It may also be due to poor surface flatness of the thin film material, resulting in the formation of uneven solid patterns during printing.
For the solution to the intermittent spot problem, the first step is to check whether the mesh roller and plate cylinder are suitable for printing film materials, and to investigate whether there are dirt, wear, and other conditions. The mesh roller should also be replaced in a timely manner. Secondly, considering the material itself, contact the supplier to determine whether it is necessary to replace the film or optimize the tension control of the printing machine's roll paper to ensure stable and consistent ink transfer.
02 Branch expansion

Dot enlargement is a typical printing quality issue in flexographic printing. Usually, dot expansion occurs when ink is transferred from the printing plate cylinder to the substrate, and the ink diffuses after absorption, causing the dot to further expand, thereby affecting the details and color saturation of the film label. There may be three reasons for the expansion of film label dots: excessive pressure between the printing plate cylinder and the film material, strong ink flowability, and high number of mesh lines on the mesh roller.
To solve the problem of the expansion of film label dots, it is also necessary to determine the root cause of the problem. Firstly, check if the printing pressure of the flexographic printing machine is set too high and adjust the pressure setting of the plate cylinder in a timely manner. Secondly, the diffusion speed of high viscosity ink is slower than that of low viscosity ink, and adjusting the ink viscosity can better avoid the problem of dot expansion. Finally, if the dot expansion of the film label is caused by the high number of mesh lines on the mesh roller, it can be alleviated by reducing the number of mesh lines on the mesh roller. Although the reduction in mesh lines makes the graphic and textual presentation less delicate, it also meets the visual effect of the film label while relaxing the printing conditions.
03 Pinhole phenomenon
When small gaps appear in the solid color area of the film label, pinhole phenomenon occurs. The occurrence of pinholes may be caused by residual air between the ink and the film substrate or poor surface wettability of the film substrate. Especially thin film materials are more prone to static electricity compared to paper materials, which can adsorb dust in the air, leading to the occurrence of pinhole phenomenon. You can try using ink with better wetting properties, or installing anti-static devices and cleaning printing equipment and substrates in a timely manner, which can significantly improve pinhole phenomenon.
04 Stripe phenomenon

Some film labels may exhibit stripes or bands after flexographic printing, manifested as vertical, horizontal, or irregular lines, with quantities ranging from a few to multiple. The occurrence of such problems is usually due to scratches on the mesh roller or ink clumping, resulting in stripe phenomenon. In order to minimize the occurrence of scratches on the mesh roller and improve its service life, it is necessary to regularly perform deep cleaning on the mesh roller to avoid ink drying and impurity accumulation. At the same time, optimize ink properties by using appropriate solvents and slow drying agents to control ink drying speed and prevent ink clumping caused by too fast drying.
05 Ink adhesion is not firm and ink falls off
Due to the fact that film materials do not have ink absorption properties like paper materials, ink adhesion and ink loss often occur when printing film materials. For thin film materials with coatings on the surface, it is necessary to choose ink with properties that match it, otherwise the printed product will have ink drop problems. In addition, some printed materials have certain requirements for the thickness of the ink layer. In the case of a thick ink layer, if the ink is not completely dried, ink shedding may also occur.
For the printing ink of thin film labels, it is necessary to choose specialized ink for thin film materials and use matching varnish and additives, otherwise there will be printing quality problems where the ink does not match the substrate, resulting in ink layer peeling. Controlling the speed of ink drying is of utmost importance due to ink dropping caused by incomplete ink drying. A small amount of desiccant can be added to the ink to improve its drying speed. In addition, regular cleaning of the ink curing device and regular replacement of UV lamps are also key to ensuring complete curing of UV ink.

06 Fading or color shift
Thin film labels printed on the same device from the same supplier may sometimes experience color fading or color shift, which can significantly affect the consistency of branded products. What is the root cause of the obvious color difference problem? When encountering this problem, you can first use a magnifying glass to observe and carefully check whether there is any significant change in the dot size of this batch of products printed by the same equipment as the previous batch. If there is only a change in the dot size of one color, then it is necessary to consider the color shift caused by the aging of the flexographic printing plate or excessive printing pressure; If the size of multiple color dots changes, it is necessary to consider whether the problem lies in the different surface energies of the materials in different batches, resulting in uneven drying of the ink on the material surface.
07 Wrinkle of film material
The flexographic printing machine must strictly control and adjust the printing tension when printing film labels, and adjust the tension control accordingly for different types and widths of materials. Otherwise, wrinkling of the film may result in inaccurate overprinting and even deformation of the printed pattern. In addition, the different thermal expansion rates between thin film materials and ink can also cause such problems.
A precise tension control system is the key to solving this problem. The correct feeding and receiving tension must first ensure accurate overprinting of the film material, and maintain the material end face not tilted during the printing process. Apply tension evenly throughout the entire printing process and pay attention to the temperature and humidity settings of the production environment.
08 Changes in Characteristics of Thin Film Materials
With the acceleration of global sustainable green development, many innovative biodegradable and compostable film materials have emerged one after another. Their unique physical and chemical properties produce different effects in flexographic printing compared to traditional film materials. Different surface energy characteristics may have a certain impact on the wettability of the film material itself, which also brings new challenges to traditional flexographic printing.
This requires material suppliers to collaborate with label printing companies for in-depth research to understand the characteristics exhibited by these new thin film materials under specific printing conditions. By adjusting process parameters such as ink formula and ink drying method through experiments to meet the unique requirements of new films, the best printing quality of film flexographic printing is presented.
When using thin film materials for flexographic printing, due to the potential quality issues mentioned above, label printing companies need to operate with caution. Understanding the unique properties of thin film materials and pairing them with the correct combination of mesh rollers, printing plates, and ink is crucial. Through strict quality control and regular equipment maintenance, these common quality defects can be detected and corrected as early as possible, paving the way for high-quality and stable printing quality in flexographic printing.