Poor Ink Adhesion? Find the Causes in These 4 Key Areas!

Ink adhesion failure (also known as poor adhesion or weak film bonding) refers to a phenomenon where the ink layer peels off or partially separates from the substrate surface when rubbed, crumpled, or pulled with transparent tape. Taking film materials as an example, poor ink adhesion can lead to ink transfer during film rewinding, causing backside contamination or color picking during overprinting. In severe cases, it may even result in the entire batch of finished products being scrapped—posing a significant risk to the quality of film labels.

There are many factors that affect ink adhesion, such as ink type, substrate material, printing process, and environmental temperature and humidity. A comprehensive analysis is required to identify the root cause. In this article, the author will explain the possible causes of poor ink adhesion from these four aspects, hoping to provide readers with useful insights.

1. Ink-Related Issues
01 Incorrect Ink Selection
Different types of ink are suitable for different film materials and product applications. If the ink is not compatible with the film or has poor affinity for it, adhesion issues are likely to occur. Therefore, before printing, it is essential to choose the appropriate ink based on the characteristics of the film material and the end-use requirements of the product. A one-size-fits-all approach should never be used.

02 Improper Ink Formulation
The ink formulation directly affects its adhesion performance—especially the selection of resin in the ink. An improper balance of components such as resin, pigment, and solvent may reduce the ink’s film-forming ability and internal cohesion, ultimately leading to reduced adhesion.

03 Improper Ink Storage
Improper storage of ink can also degrade its performance. Ink that has been stored for a long time often contains less resin. Using expired or aged ink may compromise its performance and, consequently, its adhesion to the film surface.

2. Substrate (Film Material)-Related Issues
01 Surface Tension of the Film
Commonly used films such as polyethylene (PE), polypropylene (PP), nylon, and polyester have very smooth surfaces with little natural affinity for ink, making it difficult for ink to adhere. Special treatments—such as corona treatment—are needed to alter the surface structure, increase roughness, and enhance polarity for better ink bonding. The adhesion of ink to the film surface is closely related to the surface tension of the substrate. If the surface tension of the film is lower than that of the ink, good adhesion cannot be achieved. Therefore, proper surface treatment is necessary before printing.

02 Poor Surface Cleanliness
Contaminants on the film surface, such as oil, dust, and other impurities, can hinder proper ink adhesion and reduce the bond strength between the ink and the film.

03 Additive Migration
Most printed films contain various additives such as anti-static agents, slip agents, anti-blocking agents, plasticizers, and UV stabilizers. When these additives migrate to the film surface, they form a barrier layer that weakens the adhesion between the ink and the base film, significantly reducing print durability.

04 Improper Storage Conditions
Unsuitable storage conditions, such as high humidity, can cause certain films (e.g., nylon, polyester) to absorb moisture easily. Moisture-laden films experience a decrease in surface tension, which can lead to poor ink adhesion. In addition, prolonged storage can degrade the surface properties of the film, further reducing ink adhesion.



3. Printing Process-Related Issues
During the printing process, problems such as ink emulsification due to moisture absorption, excessive ink layer thickness, and incomplete drying can all contribute to poor ink adhesion.

01 Ink Emulsification Due to Moisture Absorption
Ink emulsification occurs when ink disperses or coagulates under humid conditions or in contact with water. This reduces the adhesive and cohesive strength of the resin in the ink, thereby weakening its adhesion to the substrate.

02 Excessive Ink Layer Thickness
If the ink layer is too thick during printing, it may form an uneven coating on the film surface, resulting in a “false drying” effect that compromises ink adhesion.

03 Incomplete Ink Drying
Printing speed and the drying capacity of the equipment greatly influence the thoroughness of ink drying. High-speed printing may prevent the ink from fully drying on the film surface, causing it to peel off easily.

04 Insufficient Resin Content in Ink
Excessive dilution of ink reduces the resin content, which weakens the ink's overall adhesion and results in poor bonding performance.



4. Environmental Temperature and Humidity
01 Ambient Temperature
Temperature affects the molecular activity of the film material. Under higher temperatures, the viscosity of the ink decreases, the surface activity of the film increases, and the transfer and adhesion performance of the ink improves. Additionally, the leveling and wetting properties of the ink solvent are enhanced, allowing for better adhesion.

02 Ambient Humidity
Humidity also plays a role in ink adhesion. Excessively high humidity can form a moisture barrier on the film surface, and moisture entering the ink may cause resin emulsification. Unfavorable high-humidity environments can lead to a decline in ink adhesion.

Summary
The causes of poor ink adhesion involve multiple factors including ink properties, film material characteristics, printing processes, and environmental conditions. In actual printing operations, specific causes should be analyzed and addressed accordingly to improve ink adhesion on film surfaces. Some recommended measures include:

.Selecting inks that are compatible with the film material.
.Using high-quality inks to avoid adhesion issues at the source.
.Choosing solvents that match the ink and printing conditions to ensure good solubility, drying, and wetting performance.
.Performing surface treatments on the film in advance and checking the surface tension before printing.
.Strictly following warehouse management procedures for ink and film storage—controlling environmental temperature and humidity, maintaining cleanliness, and adhering to the first-in-first-out (FIFO) principle to avoid using expired materials.
By addressing these key areas, printers can significantly improve the adhesion performance of ink on film substrates and ensure high-quality label printing.

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