Selection guide for solvent-based and UV system dispersants for inorganic pigments: pain point analysis and adaptation solutions
In the formulation production of coatings and inks, the dispersion stability of inorganic pigments is the core link that affects the fineness, hue, storage state and curing effect of the finished product. Inorganic pigments include titanium dioxide, iron oxide, bismuth vanadate, ultramarine and other categories. These pigments have strong surface polarity and high density. In the two mainstream systems of solvent-based and UV solvent-free systems, the media environment is very different, and the corresponding dispersion and stability logic is also completely different. The solvent-based system relies on solvents and resins to build a spatially stable environment, while the UV system relies on acrylate monomers and oligomers to form a cross-linked system, and has special limitations in curing polymerization inhibition. The root cause of most formula fluctuations and abnormal production problems lies in the insufficient matching of dispersants, systems, and pigments. This article combines actual production scenarios to sort out the dispersant product characteristics, common production problems, targeted solutions, and adapted product models of the two major systems of inorganic pigments. It also introduces the company's technical strength and common questions and answers, providing a compliant and stable selection reference for formula debugging and mass production.
I. Core Product Features
These specialized dispersants are designed specifically for inorganic pigments. Given the high polarity and high density characteristic of inorganic pigments, the products are optimized for both solvent-borne and UV-curable systems, meeting the requirements of industrial-scale mass production.
For solvent-borne systems, the dispersants utilize strong anchoring groups—such as phosphate esters and carboxylic acids—paired with polyester solvating chains compatible with solvents of low-to-medium polarity (e.g., esters, ketones, aromatic hydrocarbons, alcohols, and ethers). This molecular structure ensures firm adsorption onto the hydroxyl-rich surfaces of inorganic pigments, resisting displacement by resins or solvents. During the grinding process, these dispersants rapidly wet pigment agglomerates, effectively breaking them down to their primary particle size. Furthermore, their well-balanced molecular weight allows for the formation of a uniform steric hindrance layer on the pigment surface. These dispersants are suitable for high-solids solvent-borne coatings and inks, offering broad compatibility with common resin systems—such as alkyds, polyesters, and acrylics—and meeting the general dispersion needs for a wide variety of inorganic pigments.
For UV-curable systems, the dispersants retain strong anchoring capabilities while incorporating polyacrylate solvating chains that are highly compatible with acrylate monomers and oligomers. The formulations are free from components like tertiary amines or phenols—which can inhibit polymerization—making them ideal for UV free-radical curing systems. Certain grades feature reactive double bonds that allow the dispersant to participate in the cross-linking network of the cured film. This prevents the migration or exudation of additives, ensuring both dispersion stability and excellent final film properties. These products are well-suited for various solvent-free curing applications, including UV coatings, UV inkjet inks, and UV pigment pastes.
In our experience, a truly effective dispersant for inorganic pigments does not rely on excessive dosage to maintain stability. Instead, it achieves performance through the precise matching of molecular structures—balancing grinding efficiency, system compatibility, and the stability of the finished product—to support the formulation and routine mass production of coatings and inks.
II. Common Core Issues in Formulation and Production
From the perspectives of formulation engineers (during development) and production supervisors (during mass production), the challenges associated with inorganic pigments in various systems tend to be concentrated and follow predictable patterns—most often stemming from the improper selection of dispersants or incorrect methods of their addition.
In solvent-borne systems, a frequent issue is excessively high viscosity during the grinding process. High-loading inorganic pigment systems create significant grinding resistance, which reduces equipment efficiency and makes it difficult to achieve the required fineness. In some cases, while a pigment dispersion may meet fineness specifications, the addition of let-down solvents or resins can trigger particle coarsening or localized flocculation. This results in slight color variations in the final paint film, which can be clearly detected via a "rub-up" (finger-rub) test. During storage, the high density of inorganic pigments often leads to stratification or hard settling at the bottom of containers; such sediment can become so compacted that simple stirring is insufficient to restore a uniform mixture, directly hindering subsequent application. Furthermore, in multi-pigment systems, differences in the adsorption characteristics of various inorganic pigments can cause uneven particle movement, leading to issues like "floating" or "flooding" (color separation), which compromises color consistency between production batches.
Production challenges in UV-curable systems are more specialized—a point often overlooked by those new to formulation. Conventional dispersants designed for solvent-borne systems may undergo chain-segment coiling or lose their steric stabilization effect when used in UV systems, leading to significant settling even during short-term storage. Certain unsuitable dispersants can also interfere with the photo-curing reaction, slowing down the cure rate and leaving the paint film surface tacky or uncured—failing to meet application standards. Even if the target fineness is achieved during grinding, the particle size may gradually increase during storage, indicating poor system stability. Additionally, if an incompatible dispersant is added in excess, the residual free additive can remain within the cured film, impairing adhesion and water resistance. Over time, this may cause issues such as slight color bleeding, or, in the case of white ink systems, yellowing.
III. Targeted Solutions
To address various production challenges related to the dispersion of inorganic pigments in solvent-borne and UV-curable systems, we have developed two specialized solutions—leveraging our expertise in additive molecular design and practical formulation implementation—to precisely meet the requirements of different production conditions.
For solvent-borne systems, our core strategy focuses on enhancing the stability of adsorption on the pigment surface to prevent desorption-induced flocculation and sedimentation. During formulation development, we employ polymeric dispersants featuring phosphate ester anchoring groups. Through strong hydrogen bonding and acid-base interactions, these dispersants anchor firmly to the inorganic pigment surface, effectively preventing desorption and the subsequent coarsening of pigment particles during dilution. The dosage of the dispersant is adjusted based on the specific surface area of the pigment; for common pigments such as titanium dioxide or iron oxide, we conduct gradient testing—calculated as a percentage of the powder's mass—to determine the optimal dosage range. This avoids issues such as flocculation (due to insufficient dosage) or poor compatibility (due to excessive dosage). In multi-pigment systems, we utilize versatile inorganic-grade dispersants to balance the adsorption characteristics across different pigments, thereby mitigating issues like pigment flooding and floating. For mass production and storage, we incorporate mild thixotropic agents that are compatible with the system. These create a gentle internal structure that slows the sedimentation of high-density pigments, ensuring that any settled material remains loose and can be easily redispersed through simple stirring.
For UV-curable systems, the core strategy balances dispersion stability with curing compatibility. We exclusively use UV-grade dispersants that feature acrylate-solvating chains and minimal polymerization inhibition. These are fully compatible with solvent-free acrylate systems, allowing the polymer chains to extend effectively and create a stable steric barrier, which prevents pigment paste sedimentation and particle coarsening. For high-end applications requiring superior weather resistance and migration resistance, we employ reactive dispersants containing double bonds; these become integrated into the cross-linked polymer matrix during curing, completely eliminating issues related to additive migration or the degradation of film performance. During formulation optimization, we also conduct curing energy gradient tests to align with the specific parameters of the production line, ensuring the coating film cures thoroughly and preventing defects such as surface tackiness or incomplete drying. At the same time, the dosage of the dispersant is strictly controlled; the optimal amount is determined through saturation adsorption testing to minimize the impact of free additives on the performance of the paint film.
IV. Specialized Product Offerings
In line with the aforementioned solutions, we have introduced two core dispersants specifically designed for inorganic pigment systems—one for solvent-based applications and the other for UV-curable systems—both of which are ready for immediate integration into mass-production formulations.
RK-4012, a dispersant tailored for solvent-based inorganic pigment systems, utilizes phosphate ester groups as anchoring sites and polyester chains for solvation. It is compatible with a wide range of solvent systems—including xylene, butyl acetate, ketones, and glycol ethers—as well as alkyd, polyester, and acrylic resins. Offering exceptional wetting efficiency, it shortens pigment grinding times, effectively reduces the viscosity of pigment pastes, and boosts production efficiency. It also mitigates issues such as settling and pigment floating (color separation) in systems containing titanium dioxide or iron oxides, making it ideal for industrial coatings, anti-corrosion paints, and solvent-based pigment pastes.
RK-4013A and RK-4013C are high-molecular-weight "super-dispersants" designed for inorganic pigments in UV-curable systems. Featuring acrylate-based solvation chains, they exhibit excellent compatibility with a variety of UV monomers and oligomers. These products are free of polymerization-inhibiting groups, ensuring they do not compromise UV-curing efficiency. They effectively address common challenges in UV pigment pastes, such as settling, re-agglomeration (coarsening), and poor storage stability. Their reactive structural design allows them to participate in the cross-linking of the paint film, thereby enhancing adhesion and water resistance. These dispersants are well-suited for high-end applications, including UV-curable coatings, UV-curable inkjet inks, and weather-resistant UV pigment pastes for outdoor use.
V. Company Profile
Dongguan Hongrui Chemical Co., Ltd. specializes in the R&D, production, and sales of additives for coatings, inks, and adhesives. With many years of deep expertise, the company focuses on core technical areas such as pigment wetting and dispersion, leveling and defoaming, and system stabilization. Equipped with comprehensive laboratories for formulation development and full-scale production lines, we provide customized additive solutions tailored to specific pigment systems and unique manufacturing conditions. By concentrating on specialized chemical additives and their practical application in end-use formulations, we continuously optimize our product portfolio to meet the production upgrade requirements across sectors including coatings, inks, and advanced materials. We are dedicated to providing stable, highly compatible additive products and technical support to formulation engineers and manufacturing enterprises alike.
VI. Core Strengths of the Company
The product and service advantages of Dongguan Hongrui Chemical Co., Ltd. are primarily reflected in three areas: formulation adaptability, stability in mass production, and technical implementation capability. Our product structure has been optimized through extensive testing under actual end-use operating conditions. By accounting for variations in the specific surface area of inorganic pigments and the polarity differences across diverse chemical systems, we achieve precise compatibility—effectively avoiding the poor compatibility and limited application scope often associated with generic additives. We maintain rigorous quality control throughout the production process, with standardized raw material ratios and synthesis protocols, ensuring consistent performance across every batch and preventing formulation fluctuations during mass production. Furthermore, our professional technical service team provides comprehensive support, including gradient testing for dispersant dosage, system compatibility assessments, and storage stability evaluations. We also offer one-on-one guidance for troubleshooting issues such as dispersion failures or curing anomalies encountered at the client’s site, helping businesses reduce the costs of trial and error while ensuring a stable, consistent mass production process.
VII. Frequently Asked Questions (FAQ)
1. Can general-purpose organic pigment dispersants be used to disperse inorganic pigments in solvent-borne systems?
It is not recommended. Dispersants designed for organic pigments typically feature a multi-anchor adsorption structure tailored to the surfaces of low-polarity organic pigments. When used with inorganic pigments, the adsorption strength is often insufficient; the dispersant may desorb during dilution or storage, leading to flocculation or pigment coarsening. As these cannot adequately stabilize inorganic pigments, it is preferable to use dispersants specifically designed for inorganic pigments, which typically utilize phosphate ester anchoring groups.
2. Why does slight settling still occur in UV-curable systems even when a specialized dispersant is used?
This is most likely because the dispersant dosage has not reached the point of saturated adsorption, or the pigment loading in the system is too high. Inorganic pigments have a relatively high density, and since solvent-free UV systems lack a solvent buffer, they are inherently more prone to settling. This can often be addressed by slightly adjusting the dispersant dosage or incorporating a small amount of a compatible thixotropic additive.
3. Does a higher dosage of dispersant always result in better system stability?
No. If the amount of dispersant exceeds the pigment's saturated adsorption capacity, the excess free dispersant will remain in the system. In solvent-borne systems, this can cause a loss of gloss in the paint film, while in UV-curable systems, it can negatively affect the curing process and film adhesion. For any system, the optimal dosage should be determined through gradient testing.
4. Should the choice of dispersant differ between coated titanium dioxide (TiO₂) and standard (uncoated) titanium dioxide?
Yes. Titanium dioxide treated with aluminum or silicon coatings exhibits changes in surface polarity and hydroxyl group content, which alters its adsorption characteristics. We recommend making minor adjustments to the dispersant dosage when using coated pigments to ensure consistent dispersion performance.
