Degradation principle of flexographic water-based ink
Date: Jun 03 2025 From: Star Color Views:
I. Introduction
Flexographic printing, characterized by high efficiency, flexibility, and suitability for various printing substrates, has become a critical technology in the packaging and printing industry. As a key consumable for flexographic printing, flexographic water-based inks have gained widespread application in recent years due to their unique environmental advantages. From food packaging to labels for daily necessities, flexographic water-based inks meet market demands for high-quality printing with their excellent printability and color expressiveness.
With the continuous enhancement of global environmental awareness and the tightening of environmental regulations, green printing has become an inevitable trend in the printing industry. International regulations such as RoHS (Restriction of Hazardous Substances) and REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals) strictly limit the use and emission of hazardous substances in printing inks. Against this backdrop, flexographic water-based inks have become a cornerstone of green printing due to their low pollution and low energy consumption, occupying a pivotal position under the framework of environmental regulations.
However, the environmental friendliness of flexographic water-based inks depends not only on the absence of harmful substances in their formulations but, more fundamentally, on their degradability after use. Understanding the degradation principles of flexographic water-based inks is of vital significance for promoting the development of green printing technologies, meeting increasingly strict environmental requirements, and achieving the sustainable development of the printing industry. This paper delves into the degradation mechanisms of flexographic water-based inks to provide theoretical support for technological innovation and applications in related fields.
II. Overview of the Composition and Structure of Flexographic Water-based Inks
The composition and structure of flexographic water-based inks determine their basic properties and degradability, primarily comprising the following components:
Water-based Resins: As the key film-forming substances in water-based inks, water-based resins form a continuous ink film after the ink dries, endowing the ink with excellent adhesion, wear resistance, and color performance. Common water-based resins include acrylic copolymers and PU dispersions. Acrylic copolymers offer good transparency, gloss, and weather resistance, with adjustable molecular structures and formulations to achieve diverse performance characteristics. PU dispersions, on the other hand, exhibit superior flexibility, wear resistance, and chemical resistance, suitable for printing scenarios with high-performance requirements.
Pigments: Pigments impart color to the ink and are crucial for transmitting printed graphic information. According to their chemical composition, pigments can be divided into inorganic pigments and organic pigments. Inorganic pigments typically have good covering power and light resistance, but some may contain harmful heavy metals. Organic pigments, meanwhile, offer vibrant colors and strong tinting strength.
Additives: Although used in small quantities, additives play a critical role in regulating the performance of water-based inks. Examples include dispersants, which promote the dispersion of pigments in the water-based system to prevent agglomeration and improve ink stability; defoamers, which eliminate bubbles generated during ink production and use to ensure print quality; and wetting agents, which reduce the surface tension of the ink to enhance its wettability and adhesion to the printing substrate.
Deionized Water: Deionized water serves as the primary solvent in flexographic water-based inks. Unlike solvent-based inks that use organic solvents as carriers, flexographic water-based inks rely on water, containing almost no volatile organic compounds (VOCs). This feature ensures minimal emission of harmful gases during printing, significantly reducing risks to the environment and human health.
III. Classification of Water-based Ink Degradation Mechanisms
1. Physical Degradation
Physical degradation refers to changes in flexographic water-based inks under the influence of external physical factors, primarily manifested as cracking and powdering of the ink film due to environmental factors such as ultraviolet (UV) light, temperature, and humidity. In outdoor exposure environments, UV radiation causes aging of the polymer materials in the ink film, gradually degrading the physical properties of the molecular chains and leading to surface cracking.
In long-term storage environments, fluctuations in temperature and humidity can also affect the ink film, causing its structure to loosen and eventually powder. It is important to note that physical degradation does not involve the breaking of molecular bonds but merely the physical fragmentation of the ink film. Therefore, physically degraded products still persist in the environment and require further chemical or biological degradation to achieve complete decomposition.
2. Chemical Degradation (Oxidation, Hydrolysis)
Chemical degradation primarily includes oxidation and hydrolysis, both of which lead to the breaking of polymer main chains. In the hydrolysis process, when the polymer main chains in water-based inks contain hydrolyzable chemical bonds such as ester bonds or amide bonds, these bonds will break in the presence of water. For example, the ester groups in acrylic polymers are prone to hydrolysis with water under certain humidity and temperature conditions, causing gradual chain breaking and a decrease in molecular weight.
Oxidative degradation occurs under the action of oxidizing agents. Water-based PU (polyurethane) is prone to oxidative degradation in alkaline environments or under enzymatic catalysis. Oxidizing agents attack unsaturated bonds or active hydrogen atoms in polymer chains, initiating free radical reactions that lead to chain scission and degradation. Chemical degradation alters the chemical structure of polymer materials in the ink, gradually breaking them down into smaller molecules and creating conditions for further degradation.
3. Biodegradation
Biodegradation refers to the process by which polymer chains in flexographic water-based inks are broken down by microorganisms and ultimately converted into carbon dioxide, water, and biomass. This process is closely related to the presence of "biodegradable groups" in the ink, such as polyester, starch-modified, or natural resin components, which can be recognized and utilized by microorganisms. Enzymes secreted by microorganisms specifically act on these biodegradable groups, gradually breaking down polymer chains into small molecular fragments, which are then further metabolized into carbon dioxide, water, and biomass.
The rate of biodegradation is influenced by multiple factors, with environmental pH, temperature, and microbial populations playing key roles. Optimal pH and temperature provide favorable conditions for microbial growth and metabolism, thereby accelerating biodegradation. Different microbial populations have varying abilities to degrade specific biodegradable groups, so the composition and activity of microbial communities directly affect the efficiency of biodegradation.
IV. Key Factors Influencing the Degradability of Water-based Inks
1. Resin Structure
The structure of resins is one of the core factors influencing the degradability of flexographic water-based inks. If resin molecular structures contain hydrolyzable or biologically recognizable chemical bonds (e.g., ester or amide bonds), the resins are more prone to degradation under suitable environmental conditions. For example, water-based acrylic resins with a high content of ester groups are susceptible to hydrolysis in humid environments, accelerating ink degradation. Biodegradable resins with special structures, meanwhile, can be recognized and utilized by microorganisms, enabling complete decomposition in natural environments. Conversely, resins lacking such degradable bonds or with overly stable molecular structures exhibit poor degradability.
2. Pigment Type
Pigment type also significantly affects the degradability of water-based inks. Inorganic pigments generally have high chemical stability and are difficult to degrade in natural environments. Some inorganic pigments may even contain heavy metals, which could be released into the environment during ink degradation, posing potential pollution risks. The degradability of organic pigments is more complex: some can undergo partial degradation under certain conditions, while others are highly resistant to degradation due to their structural specificity. Additionally, the dispersion state of pigments in the ink and whether they are coated by resins or other substances can influence degradability. Pigments tightly encapsulated within resin films have reduced contact with the external environment, increasing the difficulty of degradation.
3. Surface Tension and Film Formation
The surface tension and film-forming properties of inks affect their film formation on the printing substrate, thereby influencing degradability. Generally, thicker ink films reduce the contact area with the external environment, making it difficult for degradation factors (e.g., oxygen, water, and microorganisms) to penetrate into the film, thus increasing degradation difficulty. Surface tension also affects ink wettability and adhesion to the substrate. Improper surface tension may result in uneven ink films with voids or weak points, which could accelerate localized degradation but complicate the overall degradation process due to the non-uniform structure.
4. External Conditions
External conditions are critical factors influencing ink degradability, including temperature, pH, oxygen, light, humidity, and microbial communities. Elevated temperatures can accelerate chemical reactions and microbial metabolism, promoting both chemical and biological degradation. Optimal pH levels maintain microbial activity and influence the progression of certain chemical degradation reactions. Oxygen is essential for oxidative degradation, as adequate oxygen supply accelerates polymer oxidation. Ultraviolet light in sunlight can initiate polymer aging and degradation. Humidity provides the necessary conditions for hydrolysis and affects microbial growth. The types and quantities of microbial communities directly determine the rate and efficiency of biodegradation.
5. Crosslinking Degree
During the drying and film-forming process of water-based inks, crosslinking reactions may occur between resin molecules, forming three-dimensional network structures. Higher crosslinking degrees result in more stable resin films, restricting molecular chain movement and making it harder for molecular chains to break during degradation. Crosslinking points connect molecular chains, increasing structural complexity and stability, which hinders the contact between degradation factors (water, oxygen, microorganisms) and molecular chains, thereby reducing ink degradability.
Conclusion
Flexographic water-based inks have emerged as an ideal solution for green printing due to their low VOC emissions and water-based carrier, serving as a strategic product for the printing industry to meet future environmental regulations. Understanding their degradation principles is essential for technological innovation in ink formulation design, process optimization, and for enterprises to effectively communicate the environmental value of their products to customers, addressing market demands for sustainable packaging and green printing.
Starcolor is committed to developing truly degradable and sustainable water-based ink systems. Through continuous exploration and innovation, we aim to optimize ink composition, structure, and degradability, assisting the printing industry in achieving green transformation and contributing to its sustainable development. In the future, with stricter environmental requirements and technological advancements, research on the degradation principles of flexographic water-based inks will deepen, driving their broader and more profound applications in the green printing sector.
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