Key to High Retention of Papermaking Color Pastes: Selection and Optimization of Carbon Black Dispersants

Introduction: Why is “Retention” the Core Challenge in Papermaking Color Pastes?

In papermaking color pastes, especially for carbon black applications, high retention is a key indicator of dispersant performance. If the dispersant is not properly selected, carbon black particles tend to be lost or flocculated in the pulp, not only causing uneven coloration and graying of the paper but also increasing production costs. Therefore, how to achieve efficient anchoring of carbon black onto fibers through proper dispersant selection is a core challenge for engineers.

Key Issues and Solutions for High Retention

Due to its high specific surface area and strong hydrophobicity, carbon black is extremely difficult to disperse and stabilize in waterborne systems. Conventional dispersants tend to destabilize in the papermaking wet-end environment (high shear, strong electrolytes), leading to reduced retention. To achieve high retention, the dispersant must possess:

1. Strong adsorptive anchoring capability: Strong adsorption onto the carbon black surface, resisting desorption.

2. Proper molecular structure: Provide steric hindrance or electrostatic repulsion to prevent re-agglomeration.

3. Compatibility with pulp fibers: Avoid conflicts with cationic additives (e.g., retention aids) that could cause destabilization.

#### Core Solution: Toynol® DS Series Polymeric Dispersants

Addressing the above pain points, Tianjin Hi-Perferal recommends Toynol® DS-195H and Toynol® DS-195L, high-performance waterborne dispersants specifically designed for difficult-to-disperse pigments such as carbon black. Both products are nonionic polymeric dispersants, with key advantages including:

• Strong anchoring and steric hindrance: The polymer chains form multi-point adsorption on the carbon black surface while providing robust steric hindrance, effectively preventing particle re-coarsening and flocculation after milling. This is distinctly different from conventional small-molecule dispersants, which are prone to desorption in the papermaking wet-end environment.
• Excellent viscosity reduction: Effectively reduces the viscosity of high-concentration carbon black pastes, facilitating the preparation of high-solids color pastes, thereby reducing dilution water usage and indirectly improving retention.
• Outstanding stability: DS-195H and DS-195L have solid contents of 39-44% and 38-42%, respectively. Their polymeric structure ensures stability over a wide pH and temperature range, adapting to the complex conditions of the papermaking process.

Application Recommendations and Formulation Tips

#### How to Optimize Color Paste Formulation for Improved Retention?

1. Dispersant dosage: It is recommended to first add Toynol® DS-195H into the grinding water at 15%-30% of the carbon black weight, adjust the pH to 8-9, then add carbon black and start grinding. A dose-response study should be conducted based on specific carbon black grades and target particle size.

2. Co-additives synergy:

• Wetting agent: During the grinding stage, Toynol® Superwet-320 (0.3%-0.5%) can be added to leverage its ultra-low surface tension (26.2 dyn/cm) for rapid wetting of carbon black, shortening grinding time.
• Defoamer: Stirring and grinding can generate micro-foam, affecting color paste stability and final paper coating quality. Toynol® Foamic 024 is recommended, a nonionic organic polymer defoamer free of silicone and mineral oil, at a dosage of 0.2%-0.5%, effectively eliminating micro-foam without causing paper shrinkage or defects, fully compatible with high-retention process requirements.

3. Compatibility with papermaking wet-end chemicals: Before adding the color paste to the pulp, it is advisable to conduct a small-scale test to verify compatibility with retention aids such as cationic polyacrylamide (CPAM). Since DS-195H is nonionic, it typically does not cause charge conflicts with cationic systems and offers excellent stability.

How to Validate the Effectiveness of High-Performance Dispersants?

We strongly recommend conducting systematic laboratory comparison tests. By comparing color pastes prepared under identical conditions with different dispersants, evaluate:

• Color strength: Measure K/S value or reflectance of the paper.
• Retention: Use a Dynamic Drainage Jar (DDJ) or ash method to determine the retention ratio of carbon black in the wet web.
• Particle size distribution: Use laser particle size analysis to track milling efficiency and storage stability.

Sample Request Process

Tianjin Hi-Perferal provides free test samples of Toynol® DS-195H, DS-195L, and other co-additives (e.g., Superwet-320, Foamic 024). Simply inform us of your specific process parameters (e.g., carbon black grade, target solids content, milling equipment), and we will customize a sampling plan along with preliminary recommended usage. Click “Contact Customer Service” or leave a message with your company information and testing requirements. We will arrange sample shipping promptly and provide full technical support to help you achieve the desired high retention performance.