Water-Based Flexographic Ink Formulation

Date: Feb 17 2025 From: Star Color

The increasingly stringent environmental regulations have become a significant driving force behind the development of water-based flexographic inks. The EU's 1999/13/EC directive imposes strict limits on emissions of volatile organic compounds (VOCs). Traditional solvent-based inks, due to their high VOC emissions, can no longer meet environmental requirements. Water-based flexographic inks, which contain almost no VOCs, align with environmental protection concepts and have become the preferred choice for many printing enterprises.

Compared to traditional solvent-based inks, water-based flexographic inks are not only more environmentally friendly with lower VOC emissions but also reduce the risk of operators being exposed to harmful substances in terms of safety. In terms of cost, as water-based ink technology continues to advance and the market scale expands, production costs have gradually decreased, resulting in high cost-effectiveness. Regarding drying efficiency, although water-based inks were traditionally considered to have slower drying speeds, through reasonable formulation design and optimization of drying equipment, the drying efficiency of water-based flexographic inks has been significantly improved.

Core Components of Water-Based Flexographic Inks

Binder System
Acrylic Resins: Acrylic resins are commonly used in water-based flexographic inks. They possess good adhesion, enabling the ink to firmly adhere to the substrate surface. Additionally, they exhibit excellent film-forming properties, allowing the ink film layer to possess certain strength and flexibility.

Polyurethane Dispersions (PUDs): The incorporation of polyurethane dispersions can effectively enhance the water resistance of the ink. In printing applications with high water resistance requirements, such as food packaging and outdoor advertising, the use of polyurethane dispersions ensures that the ink maintains good performance in humid environments.

Selection Criteria: When selecting the binder system, its pH stability should be considered, generally maintained between 8.0-9.5, to ensure the stability of the ink during storage and use. Solids content is also an important indicator, typically ranging from 40-55%. An appropriate solids content ensures the ink's fluidity and drying performance.

Pigments and Dispersion Technology
Organic Pigments: Common organic pigments include Phthalo Blue and Benzidine Yellow. Organic pigments have bright colors and good coloring power, imparting rich colors to the ink.
Inorganic Pigments: TiO₂ and Carbon Black are frequently used inorganic pigments. TiO₂ is mainly used to improve the ink's opacity, providing printed materials with better whiteness and opacity. Carbon Black is used to provide black coloration, exhibiting good abrasion resistance and light resistance.

Dispersant Selection: To evenly disperse pigments in the ink, an appropriate dispersant must be selected. Non-ionic surfactants (such as Triton X-100) are commonly used dispersants. They reduce the surface tension between pigment particles, preventing pigment agglomeration and improving pigment dispersion stability.
Water-Based Flexographic Ink Formulation

Additives

Defoamers: Silicone-based defoamers (typically added at 0.1-0.3%) effectively eliminate bubbles in the ink, preventing them from affecting print quality during the printing process.
Leveling Agents: Polyether-modified silicone oils serve as leveling agents, improving the ink's leveling performance, enabling it to form a uniform film layer on the substrate surface and reducing ink surface defects.
Wetting Agents: Acetylene glycol derivatives (such as Surfynol 104) act as wetting agents, lowering the ink's surface tension and enhancing its wetting performance on the substrate, allowing the ink to better adhere to the substrate surface.
Biocides: Isothiazolinones (MIT/BIT) are biocides that inhibit microbial growth, preventing ink spoilage due to microbial contamination during storage.
Water as Solvent
Deionized Water Standards: Deionized water is the main solvent in water-based flexographic inks, and its quality significantly impacts the ink's performance. Generally, the conductivity of deionized water should be less than 50 μS/cm to ensure impurities in the water do not adversely affect the ink's performance.
Cosolvent Selection: To adjust the ink's drying speed, sometimes a small amount of cosolvent, such as ethanol or propylene glycol (typically added at <5%), may be required. The addition of cosolvents can accelerate the ink's drying speed to a certain extent, while also improving its fluidity and printability.

Formulation Process: Step-by-Step Breakdown

Pre-dispersion Stage: In this stage, a high-speed mixer (operating at speeds generally between 1,500-2,000 rpm) is used to evenly disperse pigments in the aqueous carrier. This step aims to initially break up pigment agglomerates, dispersing pigment particles as much as possible to prepare for subsequent milling processes.
Milling Process: Milling further refines pigment particles. Common milling equipment includes three-roll mills and bead mills. Through milling, the pigment particle size is reduced to ≤5 μm, ensuring the ink has good fluidity and printing performance.
Binder Mixing: When mixing the binder with other components, the temperature should be controlled below 40°C to prevent gelation of the binder. Gelation can drastically increase the ink's viscosity, affecting its fluidity and printability.
pH Adjustment: Use ammonia water or AMP-95 and other alkaline substances to maintain the ink's pH between 8.5-9.2. The appropriate pH ensures the binder's stability and ink fluidity, while also preventing deterioration of the ink during storage and use.
Viscosity Control: Measure the ink's viscosity using a Brookfield viscometer, with a target value typically between 30-60 seconds (Zahn Cup #2). Adjust the ink's viscosity by adding diluents or thickeners to meet printing process requirements.

Key Performance Indicators

Adhesion Test: Use the ASTM D3359 standard to test the ink's adhesion, with 5B being the best rating, indicating the strongest adhesion between the ink and the substrate.
Abrasion Resistance: Test the ink's abrasion resistance using the Sutherland Rub Test, typically requiring the ink to withstand ≥50 friction cycles to ensure printed materials do not fade or wear due to friction during use.
Drying Speed: Test the ink's drying efficiency using infrared (IR) drying equipment, requiring the ink to dry within ≤3 seconds at 80°C to meet high-speed printing demands.
Chemical Resistance: Test the ink's chemical resistance through an ethanol wipe test, requiring no flaking of the ink surface after wiping to ensure printed materials maintain good performance when in contact with chemicals.

Common Formulation Issues and Solutions

Issue 1: Blurred Printing Halftones
Cause: Blurred printing halftones may result from high ink viscosity or uneven pigment dispersion. High viscosity reduces the ink's fluidity during printing, making it difficult to accurately transfer to the substrate. Uneven pigment dispersion leads to uneven pigment particle distribution, affecting the clarity of printed halftones.
Solution: Address this issue by adjusting the milling time to ensure pigments are fully dispersed and appropriately adjusting the proportion of leveling agents to improve the ink's fluidity, thereby enhancing the clarity of printed halftones.

Issue 2: Slow Drying
Cause: Slow ink drying can affect printing production efficiency and increase costs. It may result from insufficient drying accelerators in the ink formulation or inappropriate cosolvent selection.
Solution: Add 2-3% propylene glycol methyl ether (PM) as a cosolvent. PM has good volatility, accelerating the ink's drying speed with minimal impact on other ink properties.

Issue 3: Excessive Foam
Cause: Excessive foam in the ink can affect ink transfer and print quality, potentially due to inappropriate or insufficient defoamer selection.
Solution: Switch to polyether-modified polysiloxane defoamers, which offer better defoaming effectiveness and stability. Adjust the defoamer's addition amount based on actual conditions to effectively eliminate foam in the ink.

The formulation of water-based flexographic inks requires comprehensive consideration of various components, properties, and printing process requirements. Rational formulation design and process control enable water-based flexographic inks to exhibit excellent performance and meet sustainable printing needs.
Water-Based Flexographic Ink Formulation

Among numerous water-based flexographic ink products, Zhongzhixing water-based inks stand out for their exceptional quality. Zhongzhixing water-based inks have been carefully developed considering various needs and potential issues during the printing process, utilizing advanced technology and high-quality raw materials in production. Their resin system is meticulously formulated, ensuring good adhesion to various substrates while also exhibiting excellent film-forming properties and water resistance. High-quality printing results can be achieved on both paper and plastic films. In terms of pigment selection and dispersion technology, Zhongzhixing water-based inks use high-quality organic and inorganic pigments and precise dispersion processes to ensure even pigment dispersion, resulting in vibrant and lasting printed colors while effectively avoiding blurred printing halftones.

Choosing Zhongzhixing water-based inks means selecting a high-quality, efficient, and reliable printing solution. It not only delivers outstanding printing results but also supports enterprises in achieving sustainable development and enhancing market competitiveness.