Research on Dispersion Process of Aqueous Carbon Black Ink

By using a sand milling dispersion process, aqueous carbon black ink suitable for water-based inks was developed. An orthogonal experimental design was employed to optimize the dispersion process of aqueous carbon black ink, and the influence of ethylene glycol (EG) on carbon black dispersion was investigated. The results indicate that the optimal conditions for dispersion are a dispersant addition of 2.5%, a sand milling speed of 2,000 r/min, and a milling time of 120 minutes. When 10% EG was added, the resulting aqueous carbon black ink had a ζ-potential of -38.5 meV and an average particle size of 117.1 nm, which increased to 159.6 nm after 90 days of storage, indicating good storage stability and application performance.

The general manufacturing process for ink is similar to that for coatings. Selecting suitable and stable ink dispersions is crucial for improving the stability of the final ink product and enhancing its performance. However, carbon black pigment, due to its unique structure, small primary particle size, large specific surface area, and strong interparticle forces, does not disperse readily in water and tends to form gels during the milling process, making it one of the challenging pigments to disperse. Various methods, such as surfactant treatment, surface modification, and surface oxidation of carbon black, have been explored both domestically and internationally to develop water-based carbon black dispersions. However, unlike coatings, writing ink has higher requirements for pigment particle size, stability, and compatibility. Consequently, there are limited water-based ink dispersions available in the market suitable for neutral pens, posing a key technical challenge in the development of water-based inks for neutral pens.

In this experiment, considering the basics of water-based inks, an orthogonal experiment was conducted to analyze the influencing factors during the experiment and optimize the preparation process and product to create a fine aqueous carbon black ink suitable for water-based inks. The resulting ink is not only compatible with existing mature formulation processes but is also simple to produce and suitable for industrial-scale production.

Key Details:

1. Materials and Equipment:

• High-color carbon black (Grade 6): Shanghai Wujing Carbon Black Factory

• Triethanolamine: Analytically pure, Shanghai Lingfeng Chemical Reagent Co., Ltd.

• Ethylene glycol: Analytically pure, China National Pharmaceutical Group Chemical Reagent Co., Ltd.

• Dispersant: Self-prepared

• Instruments: Zetasizer 3000HS dynamic light scattering laser particle size and ζ-potential analyzer, JEM-2100F transmission electron microscope, SFJ-400C stirring, dispersing, and grinding multipurpose machine, MiniZeta laboratory pin-type grinding machine, writing and drawing instrument: Tianjin Ruihang Electric Machine and Appliance Co., Ltd.

2. Carbon Black Pretreatment:

• After grinding in a mortar, carbon black was dried at 105°C for 24 hours and then stored in a drying cabinet.

3. Preparation of Aqueous Carbon Black Ink:

• A self-made dispersant was dissolved in a mixed solvent of deionized water and ethylene glycol. The carbon black was added gradually while stirring. After high-speed dispersion for 30 minutes, the mixture was transferred to a sand mill.

4. Particle Size Distribution Measurement:

• The average particle size and size distribution of the ink were measured using a Zetasizer 3000HS dynamic light scattering laser particle size and ζ-potential analyzer.

5. ζ-Potential Measurement:

• The ζ-potential of the ink was measured using the same instrument as for particle size analysis.

6. Particle Distribution Morphology Observation:

• The diluted ink was observed using a transmission electron microscope (TEM) after being evenly shaken and dried on carbon support film.

7. Ink Application Performance Evaluation:

• The ink was formulated into writing ink, and its writing performance was tested using a writing and drawing instrument in accordance with QB/T2625—2003 requirements.

Results and Discussion:

1. Optimization of Dispersion Process:

• An orthogonal experimental design was used to study the influence of various factors on the dispersion of carbon black. The optimal conditions for dispersion were found to be a dispersant addition of 2.5%, a sand milling speed of 2,000 r/min, and a milling time of 120 minutes.

2. Impact of Ethylene Glycol (EG):

• EG was used as a co-solvent and dispersant aid in the ink formulation. The addition of EG improved ink dispersion by reducing surface tension and enhancing the wetting of carbon black particles. However, excessive EG addition led to reduced milling efficiency.

3. Performance of the Optimized Ink:

• The optimized ink had an average particle size of 117.4 nm with a narrow size distribution. The ζ-potential was -38.5 meV. The ink exhibited good storage stability, with only a slight increase in average particle size after 90 days of storage. TEM images confirmed the ink's good dispersion characteristics.

4. Application Performance:

• The ink was tested in a writing and drawing instrument, showing good performance with no agglomeration or precipitation.

This study highlights the successful development of an aqueous carbon black ink dispersion suitable for water-based ink applications, with the optimization of the dispersion process and the inclusion of EG as an effective co-solvent and dispersant aid. The resulting ink exhibited excellent performance and stability, making it suitable for use in neutral pens and potentially other applications. The study also introduced the use of an orthogonal experimental design to systematically investigate and optimize the ink formulation process.