Guidelines for Selecting Wetting Agents for Water-based Coatings
The core function of a wetting agent is to regulate the high surface tension of water to an appropriate range by directional adsorption at interfaces, simultaneously achieving two key functions: one is the wetting of various substrate materials, and the other is the wetting of pigment and filler powders. In water-based coating systems, substrate wetting agents and pigment wetting agents are typically two types of additives with entirely different functional roles, and in most scenarios, a single additive cannot simultaneously address both requirements. The selection logic must follow the prioritization principle of "first anchoring the application scenario and substrate surface energy level characteristics, then matching the corresponding chemical structure type" to avoid functional mismatch.
I. Selection by Substrate (Key Focus)
1. For the wet grinding of inorganic powders and preparation of high concentration colorants in aqueous systems, anionic wetting agents are preferred as pre wetting components and synergistically combined with high molecular weight polyacrylic dispersants; This combination can quickly reduce the interfacial tension on the surface of inorganic powders, fully infiltrate the pores on the particle surface, and combine with the electrostatic resistance stabilization effect of dispersants to significantly reduce the viscosity of the grinding process system. At the same time, it ensures that the color paste is stored for a long time without anti coarsening or settling.
2. Glass substrate: Organic silicon or alkyne diol, with controlled addition to avoid fish eyes. Recommended models: RK-8014XD, RK-8026, RK-8065.
3.PP、Modified PP and plastic substrate: Polyether modified silicone wetting agent, pre verified for recoating and adhesion, recommended models: RK-8014XD, RK-8026, RK-8065.
4. For various types of conventional coating substrates such as wood, cement substrates, steel plates, and aluminum metals, diyne glycol wetting agent is selected as the core wetting component of the substrate. This type of additive can ensure rapid spreading and wetting of the substrate, eliminate coating shrinkage and dry spots, and naturally have low foam and anti foaming properties. It will not form a weak interface layer that is prone to residual silicone additives at the paint film interface, fully adapting to the requirements of multiple recoating processes and ensuring stable interlayer adhesion. Recommended models: RK-8030, RK-8014XD
II、Applicable characteristics of mainstream wetting agent types
1. Anionic wetting agent
The functional positioning is mainly based on the infiltration of pigment powder, suitable for feeding during the grinding stage, and works synergistically with dispersants to improve pigment dispersion efficiency. Its weakness lies in its high tendency to bubble, coupled with the relatively limited wetting ability of the substrate, so it is generally not suitable as the main wetting agent for the substrate of the topcoat system, and is mostly used for primers and water-based colorants.
2. Fatty alcohol polyoxyethylene ether (non-ionic alcohol ether)
High comprehensive cost-effectiveness and stable wetting performance; Its limitation is that it has a relatively high tendency to bubble (depending on the number and amount of EO added), and its water resistance is relatively weak - small molecule varieties are prone to free residue in the paint film when used in high amounts or without anchoring structures, becoming channels for water penetration and affecting the water resistance of the paint film. Commonly used as industrial primer and sealing primer, the topcoat system should be used with caution.
3. Organosilicon (polyether modified siloxane)
Having excellent surface tension reduction ability and dynamic wetting performance, it can effectively wet low surface energy substrates such as PP and ABS; Key attention should be paid to application risks: the compatibility window of this type of additive is relatively narrow, and improper use can easily induce shrinkage, poor recoating performance, interlayer adhesion degradation, and silicon migration pollution. Formula application must be verified through small-scale trials; The category can be divided into super wetting type and universal wetting leveling type. Representatives such as: Hongrui RK-8026, RK-8065
4. Non ionic alkyne diols (alkyne diol surfactants)
As a universal preferred category for water-based coatings, it combines low foaming tendency with excellent dynamic wetting performance, good recoating ability, and adaptability to substrates such as metals, engineering plastics, and wood. It is suitable for topcoats, varnishes, and water-based industrial coatings. Its limitation lies in the limited reduction of static surface tension, and insufficient spreading and wetting ability for untreated or oily low surface energy polyolefin substrates such as PP and PE.
Representative examples include: Hongrui RK-8014XD, RK-8030.
5. Fluorocarbon wetting agents
Has outstanding surface tension reduction efficiency and excellent resistance to chemical media; However, the cost of such additives is relatively high, and some products are subject to PFAS related environmental control constraints. They are generally not used in ordinary water-based coating systems and are only suitable for specific special working conditions.
III、Key selection assessment indicators
1. Compatibility: It is necessary to evaluate the compatibility of wetting agent with film forming resin (acrylic acid, polyurethane, epoxy lotion), dispersant, leveling agent and other components in the system, so as to avoid fog shadow, paint film gloss loss and other defects caused by unbalanced compatibility.
2. foam tendency: for spraying, high-pressure construction and other working conditions, low foam alkyne glycol wetting agent is preferred; Alcohol ether type wetting agent has a high foaming tendency, and the formulation needs to be matched with defoamer additives to coordinate the control of the foam level of the system.
3. Dynamic surface tension: High shear construction conditions such as spraying and high-speed coating should focus on the dynamic surface tension of the system rather than static surface tension; The high-speed film formation process is prone to surface defects such as pinholes and edge shrinkage. Dynamic wetting ability is a key consideration indicator for such scenarios, and additives need to effectively reduce dynamic surface tension. Recommended models: RK-8026, RK-8065.
4. Interlayer adhesion and recoating performance: This indicator is the main application risk point of organic silicon wetting agents, and overlay adaptation testing must be carried out during the formula validation stage.
5. Water resistance and salt spray resistance: Excessive addition of organic silicon additives and alcohol ether wetting agents can easily cause a decrease in the water resistance of the paint film. Outdoor application coatings need to focus on verifying this aspect.
6. Environmental requirements: VOC and APEO restrictions, priority given to water-based wood coatings and interior wall coatings without APEO models.
IV、Add and Common Misconceptions
-Addition amount: The conventional addition range is 0.1% -0.5% (based on the total mass of the formula). Organic silicon wetting agents have a narrow dosage window, and excessive use can easily induce shrinkage problems.
-Timing of addition: The substrate wetting agent is usually added in the later stage of the paint mixing process; The pigment wetting agent is added to the system synchronously with the dispersant during the sanding and dispersing stage.
-Misconception: Confusing wetting agents and leveling agents; Wetting agents mainly solve the problem of substrate spreading and wetting, while leveling agents focus on improving the leveling of paint films and eliminating brush mark defects.
V、Quick selection summary
Outdoor water-resistant and salt spray resistant system → Use silicone and alcohol ether wetting agents with caution.
Grinding of color paste, primer pigment → Anionic wetting agent,
Conventional water-based interior/exterior walls, water-based wood coatings → acetylene glycol low foaming wetting agent,
Difficult to wet plastic substrate, PP water-based paint → polyether modified silicone wetting agent (re coating verification is required),
