The impact of PP film surface treatment technology on printing effect

Polypropylene film, as an important packaging material, is widely used in food, medicine and chemical industry. According to statistics, the global polypropylene film market size has exceeded $20 billion, packaging sector accounted for more than 60%. However, the printing quality of polypropylene film is limited by its surface characteristics, poor ink adhesion, insufficient printing fastness and other problems, resulting in printed products ink peeling, blurring and other problems, seriously affecting product packaging effect and market competitiveness. Therefore, it has become the key to improve the printing quality of polypropylene film to study the influence of surface treatment technology on printing effect and to develop efficient and environmentally friendly surface treatment method.
Surface Characteristics of PP Films and Their Influence on Printing
Non-polar Molecular Structure
Polypropylene films are composed of hydrocarbon chains and lack polar groups in the molecular chain, resulting in low surface energy ( (typically 29-31 mN/m), well below the surface energy required for printing materials such as inks and adhesives (≥ 40 mN/ m). This nonpolar property makes it difficult for ink molecules to disperse uniformly on the surface of polypropylene films, forming uniform ink layer that affect printing quality.
Low Surface Energy
Surface energy is an important index to measure the wettability of material surface. The low surface energy of polypropylene film means its surface tension is small, making it difficult for ink molecules to form a stable adsorption layer on its surface. This leads to low ink transfer and uneven ink layer thickness in the printing process, further affecting the color reproduction and clarity of printed matter.
Additive Migration
In the process of polypropylene film production, anti-slip agent, anti-static agent and stabilizer are often added to improve its processing and usage performance. These additives gradually migrate to the surface during the film formation process, forming a low molecular weight oil layer, further reducing the surface energy of the film formation, preventing direct contact between ink and film formation, and affecting the printing effect.
High Crystallinity
Polypropylene films high crystallinity and tightly arranged molecular chains. This makes it difficult for ink molecules to penetrate the film and form mechanical anchoring effects. In addition, the high crystallinity makes the film surface smooth, reducing the contact area of ink and film, further reducing the adhesion of ink.
Surface Treatment Technologies for PP Film and Their Impact on Printing Effects
Corona Treatment Technology
Corona treatment is the most widely used polypropylene film surface treatment. The idea is to use a high-voltage electric field to ionize the air, producing high-energy electrons and ion streams that bombard the film's surface, breaking molecular chains and forming polar groups such as hydroxyl and carboxyl groups, while also increasing surface roughness and improving surface energy.
Impact Mechanisms:
Improved surface energy: Corona treatment can increase the surface energy of polypropylene films from 29-31 mN/m to 38-40 mN/m, meeting ink the wetting requirements.
Increasing Surface Roughness: Corona treatment produces micro-and nano-scale rough structures on the surface of the film, increasing the contact area between ink and film and enhancing the mechanical anchoring effect.
Introduced polar groups: the polar groups produced by corona treatment can form hydrogen bonds or chemical bonds with ink molecules, enhancing the chemical bond between ink and film.
Practical applications:
A food packaging enterprise used corona treatment technology to treat BOPP film. After treatment, the surface tension the film reached more than 38 mN/m, greatly increasing the adhesion of the printing ink. The printed product passed the crosscutting test (adhesion rating 0) and increased abrasion resistance by 30%.
3.2 Plasma Treatment Technologies
Plasma treatment is an emerging surface treatment technology. It works by using high-frequency power supply to produce excited gases (such as air, oxygen and nitrogen) rich in high-energy electrons, free radicals, ions and plasma of excited molecules. The plasma is then used to physically bombard and chemically react on the surface of the film, resulting in cleaning, etching and activation.
Impact Mechanisms:
Cleaning and degreasing: Plasma effectively removes organic pollutants such as grease and mold release agents from film surfaces, providing a clean substrate for printing.
Surface etching: Plasma produces etching on the film surface at micro and nanometer scales, increasing surface roughness and enhancing the mechanical anchoring effect.
Chemical Activation: Plasma introduces polar groups such as hydroxyl, carboxyl and amino groups, which can significantly improve surface energy and enhance the chemical bond between ink and film.
Practical applications:
A vehicle interior decoration enterprise adopts atmospheric plasma cleaning device to treat PP instrument panel frame. After treatment, the surface tension of lacquer film increased to more than 60 mN/m, and the paint adhesion increased 2-5 times. The return to rework rate fell from 8% to below 0.3%, saving more than $1 million a year.
3.3 Chemical Treatment Technology
Chemical treatment is coating of a chemical treatment agent (such as PP treatment agent) on the surface of the film to improve the surface performance of the film and enhance the adhesion of ink. Polypropylene treatment agents usually contain polar groups and active components, which can react with the film surface to form chemical bonds and increase surface roughness.
Impact Mechanisms:
Polar groups: Polar groups in polypropylene treatment agent can form chemical bonds with the film surface and enhance the chemical bond between ink and film.
Increasing Surface Roughness: Polypropylene treatment agent on the surface of the film to form nanoparticles, increase surface roughness, enhance the mechanical anchoring effect, improve wetness: polypropylene treatment agent can reduce surface tension of the film, increase the wetness of ink, promote uniform dispersion of ink.
Practical applications:
A medical consumables enterprise uses polypropylene treatment agent to activate the surface of polypropylene infusion bags. After treatment, it can be printed directly with high precision label without adding primer, which simplifies the process. At the same time, the printed products have passed the tests resistance tests resistance and chemical resistance and meet the strict requirements of medical packaging.
Comprehensive Impact of Surface Treatment Technologies on Printing Effects
Printing Fastness
Surface treatment technology can improve the printing fastness of polypropylene films. Corona treatment, plasma treatment, and chemical treatment all enhance the abrasion, abrasion resistance, water resistance chemical resistance of printed matter by increasing surface energy, introducing polar groups, and increasing surface roughness surface roughness enhance chemical adhesion and mechanical anchoring effect between ink and film.
Color Reproduction
Surface treatment technology can improve the color reproduction of polypropylene film printing. These techniques improve surface energy and surface roughness, promote uniform dispersion of ink, reduce the thickness of uneven ink layer thickness, so as to improve the color saturation and clarity of printed matter.
Printing Efficiency
Surface treatment technology can improve the printing efficiency of PP films. Corona treatment and plasma treatment can be carried out in real time on the production line, and the processing speeds fast and does not affect the production rhythm. While chemical treatment requires additional coating step, it simplifies subsequent printing processes (e.g. eliminating the need for primer) and generally improves printing efficiency.
Conclusions and outlook
The surface characteristics of PP films have important influence on the printing effect. Non-polar molecular structure, low surface energy, additive migration and high crystallinity are the main causes of poor printing quality. Corona treatment, plasma treatment and chemical treatment can significantly improve the printing effect of polypropylene films by increasing surface energy, introducing polar groups, increasing surface surface roughness, increasing printing fastness, color reproduction and printing efficiency.
In the future, with the improvement of environmental requirements and printing technology, polypropylene film surface treatment technology will develop in the direction of high efficiency, environmental protection and intelligence. Atmospheric plasma cleaning technology is expected to become a mainstream surface treatment method with its advantages of atmospheric operation, modular design and intelligent control. Chemical treatment technology needs to develop more environmentally friendly and efficient treatment agents to meet the requirements of green printing. At the same time, the deep fusion of surface treatment technology and printing technology will further improve the quality of polypropylene film printing to meet the demand of the high-end packaging market.