How to Choose Defoamers for Water-Based Coatings and Inks?
During the production and application of water-based coatings and inks, air is often introduced due to
operations such as mixing, dispersion, and coating, or surfactants (such as dispersants and emulsifiers) in the
system stabilize the foam, leading to defects such as bubbles, pinholes, and craters, affecting the product's
appearance and performance. Choosing a defoamer requires considering factors such as system characteristics,
the cause of foam generation, performance requirements, and cost. The core principle is to "specifically eliminate
foam without affecting other properties." The following are specific selection points:
I. Clarifying System Characteristics and Foam Type: First, it is necessary to analyze the basic type of water-based
coating or ink (such as latex paint, ink, color paste, etc.), the stage of foam generation (production/grinding/application),
and foam stability (easily broken/stable foam), to select the appropriate type of defoamer.
1. System Type and Basic Components
Water-based latex paint/architectural coatings:
Using water as the medium, containing pigments and fillers (calcium carbonate, titanium dioxide, etc.), dispersants, thickeners,
preservatives, etc., foam is easily introduced during grinding/dispersion in production, and may also be generated during
application (roller coating/spraying) due to differences in surface tension. The defoamer needs to have both rapid defoaming
and long-lasting foam suppression, and have minimal impact on film gloss and adhesion.
Solvent-modified water-based coatings (such as epoxy water-based paint):
Containing a small amount of organic solvent (co-solvent/film-forming additive), the system has strong polarity, and the foam
may be more stable. A defoamer resistant to polar solvents should be selected (such as polyether or polyether-modified
polysiloxane types).
Water-based inks (letterpress/gravure/screen printing inks):
Containing resins, pigments, and solvents (alcohols/esters), high viscosity and fast drying characteristics are required during printing.
Foam can easily lead to pinholes, clogging of the printing plate, and other problems. A defoamer with low migration and that does
not affect printing properties (such as leveling and adhesion) should be selected. High-Viscosity Pigment Pastes/Masterbatches:
These have a high pigment concentration (>30%) and high system viscosity. During stirring and dispersion, the foam is viscous and
difficult to break. Therefore, a defoamer with high compatibility and high foam-inhibiting properties is required (such as
polyether-modified polysiloxane).
2. Foam Stability and Generation Stage
"Transient Foam" (e.g., rapidly generated during the initial stirring, easily broken after standing):
Mainly caused by air entrainment, a low-viscosity, easily dispersible defoamer can be selected (such as mineral oil or fatty
alcohol types) to quickly cover the foam surface.
"Stable Foam" (e.g., systems containing surfactants, where the foam is persistent and stable):
A defoamer with high activity and strong defoaming ability is needed, such as polyether types (which penetrate the foam film
and reduce surface tension) or polyether-modified polysiloxane types (which combine defoaming and foam inhibition).
II. Selection of Defoamer Type Based on Type and Performance
The chemical structure and mechanism of action of differenttypes of defoamers vary greatly, and must be matched to the system
characteristics to avoid "defoamer failure" or "side effects"
(such as cratering, fisheyes, and affecting gloss). 1. Silicone Defoamers (Polydimethylsiloxane)
Composition: The main chain is polydimethylsiloxane (Si-O bond, flexible, low surface energy), the lipophilic group is methyl, and
the hydrophobic-lipophilic balance (HLB) is low (1-3).
Performance Characteristics:
Fast defoaming speed: The surface energy of siloxane is extremely low (21 mN/m), allowing it to quickly penetrate the foam film
and cause the film to rupture;
Long foam inhibition time: It does not easily migrate in the system and can inhibit foam generation for a long time;
Disadvantages: Poor compatibility with polar systems (such as high pH, containing strong polar solvents), easily demulsified due to
"dehydration" or "electrolyte effects," leading to cratering and fisheyes; and may affect the weather resistance of the coating film
(especially for outdoor coatings, use with caution).
Application Scenarios:
Non-polar/weakly polar systems (such as solvent-based modified waterborne coatings and inks);
Low-viscosity waterborne systems (such as latex paints and varnishes);
Scenarios requiring high defoaming speed (such as rapid dispersion/grinding).
2. Polyether Defoamers
Composition: Ethylene oxide (EO), propylene oxide (PO) block copolymers (such as EO-PO block copolymers), containing ether bonds
(-O-), high hydrophilic-lipophilic balance (HLB) value (10-18), miscible with water.
Performance Characteristics:
Good compatibility: Completely miscible with waterborne systems, not prone to demulsification, no risk of cratering;
Strong foam inhibition: Diffuses quickly in water, continuously inhibiting foam;
Disadvantages: Slower defoaming speed (especially for stable foams), lower defoaming efficiency than organosilicon types when used alone.
Application Scenarios:
Highly polar systems (such as latex paints, waterborne color pastes, high-solids waterborne paints);
Scenarios requiring high compatibility and avoidance of cratering (such as coatings requiring high gloss);
Used alone or in combination with other additives (such as dispersants and thickeners) when compatibility with other additives is poor.
3. Polyether-modified Polysiloxane Defoamers (Most commonly used)
Composition: Polydimethylsiloxane main chain grafted with polyether chains (EO/PO blocks), combining the low surface energy
(defoaming) of siloxane and the high compatibility (water resistance, no cratering) of polyether.
Performance Characteristics:
Optimal overall performance: Fast defoaming speed (siloxane effect) + long foam inhibition time (polyether effect) + good compatibility
(no cratering);
Weather resistance: Superior to pure organosilicon types, suitable for outdoor coatings;
Wide range of applications: Applicable to almost all waterborne systems, especially high-viscosity, highly polar, and
pigment-containing systems. Applicable Scenarios:
Latex paint, water-based colorants, gravure/flexographic inks;
High-solids water-based coatings, leather/paper coatings;
Scenarios requiring simultaneous solutions for foam during production and application (e.g., defoaming during sanding,
foam suppression during application).
4. Mineral Oil/Fatty Alcohol Defoamers
Composition: Mineral oil (white oil) or fatty alcohol (e.g., C12~C18 fatty alcohol), low surface energy (approximately 30 mN/m),
requires emulsifiers (such as Span/Tween) to form an emulsion for use.
Performance Characteristics:
Low cost: Price is only 1/3 to 1/2 of silicone-based defoamers;
Disadvantages: Poor compatibility (easily migrates to the coating surface), may cause craters and fisheyes, and has a short
defoaming time, requiring frequent addition.
Applicable Scenarios:
Basic water-based coatings (such as primers, putties);
Systems that are cost-sensitive and do not have high appearance requirements.
5. Other Types of Defoamers
Polydimethylsiloxane-polyether graft copolymer: Polyether is grafted onto the polysiloxane main chain, combining the advantages
of both, especially suitable for high-viscosity, high-solids systems (such as colorants).
Fluorine-containing defoamers: Lower surface energy (approximately 18 mN/m), but high cost (fluorine materials are expensive),
only used in high-end weather-resistant systems (such as fluorocarbon water-based paints).
III. Key Influencing Factors: System Parameters and Compatibility In addition to the type of defoamer, it is also necessary to consider
system parameters such as pH value, temperature, and other additives (dispersants, thickeners) to avoid defoamer "failure" or "side
effects". 1. pH Value and Temperature
pH Value:
Strongly acidic systems (pH<5): Avoid using polyether defoamers (ether bonds are easily hydrolyzed), prioritize
polyether-modified polysiloxanes (good acid resistance);
Strongly alkaline systems (pH>9): Polyethers (EO/PO block copolymers) are easily saponified (alkaline hydrolysis), fatty alcohols or
polysiloxane-polyether graft copolymers can be used (alkali resistance). Temperature:
High-temperature systems (>80℃, such as baking-type water-based paints): Silicone-based defoamers are prone to decomposition
at high temperatures (Si-O bond breakage), so temperature-resistant types (such as fluorosiloxanes) or polyether types (with good
thermal stability) should be selected;
Low-temperature systems (<5℃, such as coatings for winter construction): Mineral oils are prone to solidification, so products with
low pour points (such as isoalkane oils) should be selected.
2. Compatibility with other additives
Dispersants:
Dispersants (such as carboxylic acid/sulfonic acid anionic dispersants) may adsorb defoamers through electrostatic interaction,
leading to defoamer "failure".
Solution: Choose polyether-modified polysiloxane types (large steric hindrance, not easily adsorbed by dispersants) or fatty
alcohol types (requires emulsifiers to enhance dispersion).
Thickeners:
Alkali-swellable thickeners (ASE) and polyurethane thickeners (HEUR) are commonly used in water-based systems. In high-viscosity
systems, thickeners may encapsulate defoamers, reducing their effectiveness.
Solution: Choose self-emulsifying defoamers (such as polyether-modified polysiloxanes, which have hydrophilic groups and can
be dispersed in the thickened system).
Preservatives/Fungicides:
Preservatives containing formaldehyde-releasing agents (such as BIT) may damage the structure of polyether-based defoamers.
Defoamers resistant to chemical additives should be selected (such as fatty alcohol types or polysiloxane-polyether graft copolymers).
3. Impact on coating film performance
Gloss and Adhesion:
If silicone-based defoamers are used in excessive amounts or migrate to the coating surface, they may reduce gloss (especially
in high-gloss coatings/inks). The addition amount should be controlled (usually <0.5%, based on the total system);
Polyether-based defoamers have good compatibility and have little impact on gloss, making them suitable for high-gloss systems.
Water resistance/Weather resistance:
For outdoor coatings, pure silicone-based defoamers should be avoided (prone to oxidation under long-term UV exposure).
Polyether-modified polysiloxanes can be used (containing a small amount of polyether chains to improve weather resistance).
IV. Experimental Verification and Optimization of Defoamer Dosage: After selecting a defoamer, its effectiveness needs to be verified through small-scale testing. Key indicators include:
Defoaming speed: Observe the time it takes for the foam to disappear after stirring (usually required to break down foam within 5-10 minutes);
Foam inhibition time: Observe whether foam reappears after standing for 24 hours (no significant foam residue should be present);
Compatibility: Check whether there are craters or fisheyes on the coating surface (gloss can be measured using the "pendulum method,"
and compared with a blank sample; a difference of <5% is considered acceptable);
Dosage: Determine the optimal dosage through gradient testing (usually 0.1%~0.5%, based on the total system weight, to avoid excessive
amounts leading to craters).
Summary of Selection Steps:
Analyze the system: Clarify the type (latex paint/ink/color paste), pH value, temperature, pigment concentration, and other additives;
Identify the foaming problem: Transient foam/stable foam, need for defoaming/foam inhibition;
Select the defoamer type:
High compatibility/low gloss impact: Polyether or polyether-modified polysiloxane types (preferred);
Fast defoaming/long-lasting foam inhibition: Polyether-modified polysiloxane types (overall best);
Low cost/basic system: Mineral oil/fatty alcohol types;
High-end weather-resistant system: Fluorosiloxane or polysiloxane-polyether graft copolymer;
Small-scale testing (defoaming speed, foam inhibition time, coating performance), adjust the dosage to the optimum.
Through the above methods, defoamers for water-based coatings and inks can be selected specifically, balancing defoaming effect and
system stability, and avoiding foam defects affecting product quality.
