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Reasons and solutions for poor adhesion of water-based ink

Date: Nov 11 2024  From: Star Color   

Water-based inks have become the preferred choice in many printing fields due to their environmental friendliness, non-toxicity, and low volatile organic compound (VOC) emissions. However, the issue of adhesion in water-based inks has always been a focus of attention in the industry, especially on non-absorbent substrates. If the ink fails to effectively adhere to the substrate during the printing process, it may lead to poor print quality and other issues. Therefore, understanding the causes and solutions to poor adhesion in water-based inks is crucial.

I. Common Causes of Poor Adhesion in Water-Based Inks

1. Improper Substrate Surface Treatment

The primary factor influencing ink adhesion is the surface properties of the substrate. If the substrate surface is smooth and untreated, it is difficult for the ink to achieve good physical and chemical bonding with the substrate. For example, untreated plastics, glossy paper, or smooth metal surfaces often result in poor ink adhesion, leading to peeling or bubbling.

2. Ink Formulation Issues

The formulation of water-based inks directly affects their adhesion. Inappropriate selection of binders (such as resins), unsuitable viscosity, or excessive drying times can all contribute to poor adhesion. The ink formulation needs to be precisely adjusted according to the characteristics of the printing medium; otherwise, adhesion instability may occur.

3. Unsuitable Humidity and Temperature

Ambient temperature and humidity have a significant impact on the adhesion of water-based inks. Excessively low temperatures or high humidity can slow down the drying speed of the ink, resulting in insufficient adhesion. Especially in humid or cold environments, moisture is difficult to quickly evaporate, and the ink cannot effectively cure and adhere to the substrate surface.

4. Grease or Contaminants on the Substrate

If the substrate surface contains grease, dust, or other contaminants, water-based inks will have difficulty achieving effective bonding with the substrate. Grease, silicone oil, or other lubricants are often used to improve the processing performance of the substrate, but these substances can form a "barrier" during printing, preventing the ink from bonding with the surface.

5. Excessively Fast or Slow Drying Speed

The drying speed of water-based inks affects adhesion. If the ink dries too quickly, it may form a thin film, causing the ink to adhere loosely to the substrate. Conversely, if it dries too slowly, issues such as stringing or poor adhesion may occur during the printing process.

6. Poor Compatibility Between Ink and Substrate

The adhesion of water-based inks also depends on their compatibility with the substrate. Different types of substrates (such as paper, plastics, metals, etc.) have different adsorbability for inks. If the composition of the ink differs significantly from the substrate, adhesion will be affected.

II. Strategies to Solve Poor Adhesion in Water-Based Inks

1. Substrate Surface Treatment

Effective surface treatment can significantly improve substrate adhesion. Common surface treatment methods include:

• Plasma Treatment: Altering the surface energy of the substrate through plasma discharge treatment to make it more hydrophilic and enhance ink adhesion.
• Flame Treatment: Using high-temperature flame to treat the substrate surface, increasing its roughness and improving ink adhesion.
• Applying an Underlying Adhesive: Coating a layer of adhesive on the substrate surface can increase ink adhesion, especially on plastic and metal surfaces.

2. Optimize Ink Formulation

   • Select Appropriate Binders: Using binders suitable for the substrate can significantly improve the adhesion of water-based inks. For example, choosing resins with high adhesion or adjusting the solid content of the ink according to different printing media.
   • Adjust Viscosity and Rheology: Adjust the viscosity of the ink according to the working conditions of the printing press and the characteristics of the substrate to ensure that the ink can be evenly distributed and fully penetrate the substrate surface.
   • Add Enhancers: Some enhancers (such as surfactants) can improve the wettability of the ink, allowing it to better cover the substrate surface and enhance adhesion.

3. Control Environmental Conditions

   • Humidity and Temperature Control: Ensure that the humidity and temperature in the printing environment are within the ideal range. Typically, a temperature of 20-25°C and humidity of 50-60% are optimal conditions. If the temperature is too low, heating equipment can be used to increase the drying speed of the ink; if the humidity is too high, dehumidification equipment can be used for regulation.
   • Drying Equipment Adjustment: Ensure that the drying equipment operates normally to avoid excessively fast or slow drying. If drying is too slow, the drying system can be optimized by increasing the temperature and airflow rate of the hot air.

4. Clean the Substrate Surface

Before printing, it is essential to ensure that the substrate surface is clean. Special cleaners can be used to remove surface grease, dust, and impurities, ensuring that the substrate surface is clean and无污染, so that the ink can better adhere to it.

5. Conduct Adhesion Tests

During production, adhesion tests should be conducted regularly. Common adhesion test methods include tape tests (applying transparent tape to the printed surface and quickly peeling it off to check for ink detachment) and tensile tests (testing the bonding strength between the ink and the substrate through mechanical tension). These tests can help adjust the ink formulation or optimize printing parameters.

6. Use Suitable Ink Types

Select appropriate types of water-based inks based on different substrates and application requirements. For example, choosing inks with high solid content can improve adhesion; for special substrates such as coated paper or irregular surfaces, use specially designed water-based inks.

The issue of poor adhesion in water-based inks is not uncommon in the printing industry, but it can be addressed through various measures such as optimizing ink formulations, adjusting printing processes, and improving substrate surface treatment levels. Only by deeply understanding the multiple factors affecting adhesion and adopting targeted solutions can we ensure that water-based inks exhibit excellent adhesion on various substrates, thereby enhancing the quality and production efficiency of the final printed products. In the future, with continuous innovation in water-based ink technology, adhesion control will become more precise, contributing to the sustainable development of the environmentally friendly printing industry.

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