BYK-035 Mineral Oil Defoamer for Gloss/Semi-Gloss Emulsion Coatings is a mineral oil-based, silicone-free foam-control agent formulated for aqueous architectural and light industrial coatings. It is supplied as a water-free, pumpable liquid with a density below 0.90 g/cm³ at 20 °C; release density is measured according to ISO 2811-1:2016. The product contains mineral oil and dispersed hydrophobic solids and does not contain polysiloxane or silicone fluids, which lowers the risk of surface-tension-driven craters in high-gloss acrylic, styrene-acrylic, and vinyl acetate-ethylene binder packages. On production-scale lines with batch sizes from 1,000 L to 5,000 L, the material is metered at 0.1–0.5 % based on finished formulation. The most common addition pattern is split between the pigment grind and the letdown stage: approximately half the dose is dispersed under a high-speed dissolver at 4–6 m/s tip speed, and the remaining half is added under low-shear agitation after latex letdown. Because the defoamer is a dispersion rather than a molecular solution, it requires homogenization after storage. Phase separation on standing is not necessarily evidence of chemical degradation unless the liquid has been exposed to sustained temperatures above 40 °C. Published data for solventborne or radiation-curable systems is limited, and the product is not recommended for those applications.

How Does Mineral Oil Interfere with Foam Stabilization in High-Gloss Emulsion Films?

Foam in emulsion paint is stabilized primarily by surfactant adsorption at the gas–liquid interface. The surfactant layer creates a surface elasticity that resists drainage; electrostatic and steric forces between adjacent lamellae further prevent bubble coalescence. A mineral oil defoamer such as BYK-035 operates through a bridging–dewetting–rupture sequence. The dispersed mineral oil droplet enters the foam lamella, forms an oil lens, spreads along the air–liquid interface, and displaces the foam-stabilizing surfactant film. This displacement lowers local film elasticity and produces a surface tension gradient that thins the lamella until rupture occurs. In high-gloss binders with an average latex particle size below 0.2 µm, bubble entrapment is particularly damaging because final dry-film thickness is commonly between 20 µm and 50 µm; trapped microfoam does not level out during film shrinkage and appears as gloss loss or haze. A defoamer that is too incompatible may break foam but create craters, while one that is too compatible may remain in the bulk phase and fail to enter the foam lamellae. Mineral oil-based defoamers generally possess a lower spreading coefficient than polysiloxane defoamers, which provides a wider addition window in high-gloss systems where surface smoothness is measured according to ISO 2813:2014 and ASTM D523-14.

In laboratory evaluation, BYK-035 is drawn down on sealed Leneta charts and assessed for 20° and 60° gloss. A 60° gloss loss of not more than 2 units relative to a defoamer-free control is often used as an internal acceptance threshold for high-gloss colored bases. However, published data for this specific configuration is limited, and the threshold should be verified against the specific binder and coalescent package. Over-shearing of mineral oil defoamers in rotor-stator devices can reduce the dispersed droplet size below the optimum range, lowering defoaming efficiency because very small droplets fail to bridge foam lamellae efficiently.

The table represents qualitative industrial practice rather than universal rankings. Within gloss and semi-gloss decorative paints, the mineral oil-based, silicone-free class is usually selected when surface defect control is weighted above absolute defoaming speed.

In semi-gloss styrene-acrylic formulas with pigment volume concentration between 20 % and 35 %, BYK-035 is typically used at 0.2–0.4 % on total formulation. Lower levels may be sufficient for tinted bases with high oil absorption pigments, while higher levels are required when the formulation contains nonylphenol-free surfactants, high free-surfactant levels, or high-coalescent loads. The defoamer should not be added directly to the thickener solution. Associative thickeners of the hydrophobically modified ethylene oxide urethane type can interact with mineral oil droplets and reduce low-shear viscosity development; therefore the defoamer is preferably added before the final thickener charge. In 1,000 L to 5,000 L vessels, the letdown dose is post-added at 2–4 m/s tip speed over 2–5 minutes while the surface remains moving but not vortexed. This procedure reduces microfoam-related haze without generating a new oil-exudation layer. When the full dose is introduced under high shear during pigment dispersion, over-dispersion can occur and may reduce persistent defoaming after filling and storage.

Dosage requirements in high-gloss waterborne systems are not fixed by binder type alone. Pigment volume concentration, choice of dispersing agent, cosolvent partition, and the presence of low-foam wetting agents all shift the effective dose. Anionic dispersants with high hydrophile-lipophile balance tend to stabilize more foam, increasing the demand for defoamer, while some nonionic additives may compete with the mineral oil at the air–liquid interface and reduce efficacy. Similarly, coalescents that lower minimum film formation temperature can alter the evaporation profile and bubble release rate. A dosage ladder at 0.1 %, 0.2 %, and 0.3 % is therefore more reliable than a single mid-range supplier recommendation, particularly in tinted bases where colorant addition can increase surfactant load and generate additional foam after dosing.

Gloss Retention and Surface Defect Thresholds in Semi-Gloss Latex Paints

For clear bases and low-pigment tint formulations, the maximum practical dosage of BYK-035 in high-gloss systems is 0.3 %; above 0.5 %, the risk of turbidity increases in low-viscosity emulsions. This behavior is measured by a 20° specular gloss test according to ISO 2813:2014 and by haze measurement according to ASTM E430-19 on cured films. In semi-gloss paints, a 60° gloss difference of not more than 2 units compared with the defoamer-free control is a common release criterion; however, the absolute gloss value depends on binder refractive index, pigment dispersion, and coalescent efficiency. Surface defects such as fisheyes and craters arise when the defoamer droplet spreads too rapidly at the wet-film surface. The spreading pressure of mineral oil is lower than that of many polydimethylsiloxane fluids, so the cratering tendency is reduced. However, the product remains an insoluble droplet phase; if it is added too quickly or with poor agitation, localized oil-rich zones can produce visible surface defects that cannot be removed by later mixing.

In plant trials with semi-gloss acrylic formulations, a split addition of 0.2 % during the grind and 0.1 % during letdown has been used to control both pigment dispersion foam and letdown-generated microfoam while maintaining a 60° gloss within 2 units of the control. This protocol is not universal; high-surfactant formulations may require the upper end of the dosage range, but exceeding 0.5 % raises haze risk in clear bases and low-PVC pastel shades. Published side-by-side data in all binder classes is limited, so laboratory ladder studies at 0.1 %, 0.2 %, and 0.3 % are required to establish the optimum for a specific formulation.

When Low-Shear Letdown Addition Replaces Grind-Stage Dosing for Viscosity-Sensitive Formulations

Grind-stage addition is appropriate when the mill base contains enough shear to distribute the defoamer before the binder concentration becomes high. In highly filled semi-gloss formulations with fast-dispersing pigments, a high-speed disperser at 5–8 m/s tip speed can over-disperse the mineral oil droplets. The reduced droplet size may not affect foam control immediately, but activity can decline after 24–48 hours of storage because small droplets are more readily solubilized or stabilized by surfactants. In these systems, the entire or partial defoamer dose is shifted to the letdown. The grind is cooled below 35 °C, the first portion of latex is added, and BYK-035 is introduced at 0.1–0.3 % under low-shear agitation using a propeller or sweep blade at 1–3 m/s tip speed for 10–15 minutes. The surface should show no visible oil speckling before thickeners are charged.

Production batch-to-batch variation in defoamer performance is often caused by inconsistent addition temperature or mixer speed rather than variation in the defoamer itself. A fixed protocol of homogenizing BYK-035, adding it slowly over 2–5 minutes, and using a variable-frequency drive to control impeller speed reduces this variation. If the coating contains associative thickeners, the defoamer is added before the final thickener solution to prevent local incompatibility that appears as wet-film grain or gloss nonuniformity. In high-throughput lines using in-line dosing, the injection point should be placed downstream of the main disperser but upstream of the final static mixer.

The product should be stored in closed containers at 5 °C to 35 °C. Freezing may cause phase separation; if freezing occurs, the material should be warmed to 20–25 °C and gently homogenized. Repeated freeze-thaw cycles can shift the dispersed droplet size distribution and are not recommended. In comparison with silicone-based defoamers, the mineral oil type generally shows lower gloss reduction and fewer fisheye defects but may require a higher addition level in high-surfactant formulations and may have lower persistence under prolonged low-shear storage. Compared with polyether-siloxane copolymer defoamers, which can be supplied as water-dispersible, lower-viscosity liquids, BYK-035 remains a particulate defoamer whose primary action is at the air–liquid surface rather than in the bulk liquid. This distinction matters in high-gloss formulations because bulk-active defoamers can interfere less with leveling but may not break surface microfoam quickly enough during fast drying. Published side-by-side data in high-gloss 100 % acrylic systems is limited; direct laboratory evaluation remains necessary. Formulation-level compliance must be assessed under REACH and RoHS, because the defoamer itself is not an article and is used in industrial architectural coating manufacture.

Comparative Performance Limits with Polysiloxane and Polyether-Modified Siloxane Defoamers

The principal operational difference between BYK-035 and polysiloxane defoamers is the spreading coefficient at the wet-film interface. Polysiloxane molecules spread rapidly and strongly, producing fast foam knockdown but also increasing the probability of surface tension gradients that create craters. In high-gloss acrylic and styrene-acrylic paints where distinctness of image is measured according to ASTM E430-19, polysiloxane defoamers are usually limited to the grind stage and to dosages below 0.3 %. BYK-035 can be split between grind and letdown because its lower spreading pressure reduces the risk of surface disruption. However, its defoaming speed may be slower, and it may not be the first choice in formulations that are filled immediately after high-speed mixing or in paints that are applied by airless spray where foam is generated rapidly.

Polyether-modified siloxane defoamers are often classified as molecular defoamers or deaerators. They can be incorporated with minimal effect on gloss and may be used in clear coatings, but their activity against high-surfactant macrofoam can be insufficient when used alone. BYK-035 differs in that it supplies a dispersed oil phase that must be uniformly distributed to avoid localized incompatibility. In a direct comparison in a semi-gloss vinyl acetate-ethylene paint, the mineral oil product is expected to require a higher addition level than a polysiloxane defoamer but to produce fewer visible surface defects. The selection between defoamer classes is therefore not governed by dosage alone; it is governed by the formulation’s tolerance for surface defects, required frost resistance, and the shear history available during production. Published data for this specific configuration is limited, and the formulator should evaluate at minimum three dosages in the final paint rather than extrapolating from a generic model system.