The Influence of Plastic Film Characteristics on the Adhesion of UV Flexographic Inks

Date: Feb 08 2025 From: Star Color

Plastic film is widely used in packaging printing due to its advantages of light weight, low cost, and good mechanical properties. It is also a very common printing material. UV flexographic ink is increasingly widely used in combination with plastic films due to its environmental friendliness, fast curing speed, and high printing quality. However, if the adhesion between ink and plastic film is poor, it can cause printed patterns to easily peel off and fade, seriously affecting product quality and aesthetics. Therefore, in-depth research on the influence of plastic film characteristics on UV flexographic ink adhesion is of great significance for optimizing printing processes and improving printing quality.

1. Overview of UV Flexographic Inks and Plastic Film Printing

Basic Principles of UV Flexographic Inks

UV flexographic inks primarily consist of resins, reactive diluents, pigments, photoinitiators, and additives. Under ultraviolet radiation, the photoinitiator absorbs photon energy and decomposes to produce radicals, initiating a polymerization reaction between the resin and reactive diluent. The ink rapidly transitions from a liquid to a solid state, firmly adhering to the surface of the substrate material.

Application of Plastic Films in the Printing Industry

Plastic films come in various types, such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyester (PET), and are widely used in printing scenarios such as food packaging, daily use labels, and industrial product packaging. Different types of plastic films vary in their printing adaptability due to their unique characteristics.
The Influence of Plastic Film Characteristics on the Adhesion of UV Flexographic Inks

2. Influence of Plastic Film Characteristics on the Adhesion of UV Flexographic Inks

2.1 Influence of Chemical Structure

2.1.1Non-polar Plastic Films

Non-polar plastic films, represented by PE and PP, have molecular chains primarily composed of carbon-carbon single bonds and carbon-hydrogen bonds, with symmetrical structures and extremely low surface polarity. This low polarity results in poor compatibility with polar UV flexographic inks, making it difficult for the ink to adhere to their surfaces. For example, when printing directly on PE film with ordinary UV flexographic ink, the ink has a large contact angle on the film surface, fails to spread evenly, and is prone to agglomeration and detachment.

2.1.2 Polar Plastic Films

Polar plastic films such as PVC and PET contain polar groups in their molecular chains, such as chlorine atoms in PVC and ester groups in PET, increasing the polarity of the molecules and enhancing their affinity with UV flexographic inks. However, PVC often contains additives such as plasticizers during processing, which may migrate to the film surface, reducing the surface polarity and interfering with the bonding between the ink and film, thereby affecting ink adhesion.

2.2 Influence of Crystallinity

2.2.1 High-crystallinity Plastic Films

High-crystallinity plastic films, such as isotactic polypropylene (iPP), have tightly packed and ordered molecular chains, smooth surfaces, and low porosity. This makes it difficult for ink molecules to penetrate into the film interior, allowing them to adhere only to the surface with weak adhesion. Experiments show that when UV flexographic ink is printed on iPP film and adhesion is tested with adhesive tape, the ink film is easily removed by the tape, indicating poor adhesion.

2.2.2 Low-crystallinity Plastic Films

Low-crystallinity plastic films, such as atactic polypropylene (aPP), have relatively loosely arranged molecular chains and more microscopic defects and pores on their surfaces, which facilitate ink penetration and mechanical anchoring. Ink molecules can enter the microscopic pores of the film, forming physical entanglements and thus enhancing adhesion. In aPP film printing, the adhesion effect of UV flexographic ink is significantly better than that on iPP film, with more securely printed patterns.

2.3 Influence of Surface Energy

The surface energy of plastic films determines the wettability and spreading performance of ink on their surfaces. Films with low surface energy make it difficult for ink to spread, resulting in a large contact angle and a small contact area between the ink and film, leading to poor adhesion. Surface treatment, such as corona treatment or plasma treatment, can increase the surface energy of plastic films. Corona treatment, for example, introduces polar groups such as carbonyl and carboxyl groups onto the film surface, increasing the surface energy and enabling better wettability and spreading of the ink, thereby enhancing adhesion. Research data shows that after corona treatment, the surface energy of PE film increases from about 30mN/m to 40-50mN/m, significantly enhancing the adhesion of UV flexographic ink on its surface.

2.4 Influence of Additives

2.4.1 Plasticizers

Adding plasticizers to plastic films such as PVC can improve their flexibility and plasticity. However, plasticizers easily migrate to the film surface, forming an isolating layer between the film and ink, impeding direct contact between them and reducing adhesion. For example, severe plasticizer migration in PVC film printing can lead to bubbling and detachment of the ink.

2.4.2 Slip Agents

Slip agents are commonly used to reduce the coefficient of friction between plastic films, facilitating their processing and use. However, excessive slip agents can migrate to the film surface, forming a low-surface-energy film that affects ink adhesion. When excessive slip agents are added to PE film, the adhesion of UV flexographic ink on its surface decreases significantly, and the wear resistance of the printed patterns deteriorates.
The Influence of Plastic Film Characteristics on the Adhesion of UV Flexographic Inks

The chemical structure, crystallinity, surface energy, and additives of plastic films have significant effects on the adhesion of UV flexographic inks. Through reasonable surface treatment of plastic films, optimization of ink formulations, and adjustment of printing processes, the ink adhesion can be effectively improved, enhancing printing quality.

Huizhou Zhongzhixing has made positive contributions to the research and improvement of UV flexographic ink printing on plastic films. In depth research on the relationship between the characteristics of various plastic films and ink adhesion has enhanced the compatibility between ink and films; At the same time, Zhongzhixing continuously optimizes printing process parameters and collaborates with equipment manufacturers to develop UV flexographic printing equipment that is compatible with different plastic film printing, greatly improving the printing quality and efficiency of UV flexographic ink on plastic films and promoting technological progress of UV flexographic ink in the field of plastic film printing.