Liaoning Xinda Talc Group Co., Ltd. - Zheng Yi

Summary:

As an important coating filler, the particle size distribution of talc powder has a significant impact on the rheological properties, mechanical properties, optical characteristics, corrosion resistance, and construction process of coatings. This article systematically explores the mechanism and performance of talc powders with different particle sizes (coarse particle size>20 μ m, medium particle size 5-20 μ m, fine particle size 1-5 μ m, ultrafine/nanoscale<1 μ m) in coating systems. Research has shown that fine-grained talc powder significantly improves coating gloss, fineness, and anti settling properties, but may increase system viscosity and affect dispersion stability; Coarse particle size helps to reduce costs, improve extinction and anti sagging performance. Reasonable selection of talc powder particle size is the key to optimizing the comprehensive performance of coatings. Experimental data shows that the sedimentation rate of epoxy primer using 5 μ m talc powder is reduced by 60% compared to the 20 μ m sample, while the glossiness (60 °) is increased by 35%.

Keywords: * talcum powder; Particle size distribution; Coating performance; Rheological properties; Mechanical strength; Gloss; Settlement stability; workability

Introduction

Talc powder (3MgO · 4SiO ₂ · H ₂ O) is widely used in the coating industry as a functional filler due to its unique sheet-like structure, chemical inertness, low hardness, and oleophilicity. It not only effectively reduces costs, but also significantly improves the physical and mechanical properties, rheological properties, optical effects, and durability of coatings. With the continuous development of coating technology towards high performance, multifunctionality, and environmental friendliness, the fine control of fillers has become increasingly important. Among the many factors that affect the effectiveness of talc powder fillers, particle size and its distribution are the core parameters that determine their interaction with the resin matrix and the final coating performance. A deep understanding of the influence of talc powder particle size on the multidimensional performance of coatings is of great guiding significance for formula designers to accurately select materials, optimize performance, and solve practical production problems.

1、 Definition and typical role of particle size range

According to particle size, the application of talc powder in coatings can be roughly divided into the following categories:

2、 The influence mechanism and data of particle size on the performance of key coatings

1. Rheology and workability:

Viscosity and thixotropy: As the particle size decreases, the specific surface area increases sharply, and the number of interaction points with the resin increases, it usually leads to an increase in system viscosity. Ultra fine powder is prone to form a denser network structure, significantly improving low shear viscosity (beneficial for anti settling) and thixotropy (beneficial for anti sagging). For example, adding an equal amount (15% volume) of talc powder to the alcohol acid system can increase the Brookfield viscosity of samples with D50=3 μ m by 40-60% compared to samples with D50=15 μ m. But coarse particles provide a "skeleton" support in thick slurry systems and can also enhance anti sagging properties.

Settlement stability: Fine grained talc powder (especially<5 μ m) follows Stokes' law, and the settling velocity is proportional to the square of the particle size. Experimental results have shown that under the same formula and storage conditions, the 30 day settling volume ratio of epoxy primer prepared with D50=5 μ m talc powder is only 5%, while the settling volume ratio of the sample with D50=20 μ m is as high as 25%, with significant differences.

2. Optical performance:

Gloss and surface fineness: Particle size is the key factor affecting the surface smoothness and light reflection uniformity of coatings. Excessive particle size (close to or greater than the dry film thickness of the coating) can lead to uneven surfaces, causing diffuse reflection of light and significantly reducing gloss (60 ° gloss can be reduced by more than 20 units). Fine powder (D50<5 μ m) can fill micropores, forming a smoother surface, achieving high gloss (>85GU @ 60 °) and excellent hand feel. Research has shown that in acrylic topcoats, replacing talcum powder from D50=10 μ m to D50=2 μ m can increase the 60 ° gloss by about 35%.

Extinction: Coarse grained talc powder (>15 μ m) can act as extinction particles, and the portion protruding from the coating surface effectively scatters light, making it one of the choices for economical extinction fillers.

3. Mechanical properties and shielding performance:

Enhancement and rigidity: The sheet-like structure of talc powder is the basis of its reinforcement effect. Small sheet-like particles have a larger diameter to thickness ratio and specific surface area, which can effectively bind with resins, hinder molecular chain movement, and disperse stress. The data shows that in epoxy anti-corrosion primer, using talcum powder with D50=3 μ m can increase the tensile strength of the coating by 15-25% and significantly improve the modulus compared to using talcum powder with D50=25 μ m.

Shielding (water resistance, corrosion resistance): Fine sheet-like talc powder can be arranged more parallel and oriented in the coating, forming a more tortuous penetration path, effectively blocking the diffusion of water vapor, oxygen, and ions, and enhancing the physical shielding and anti-corrosion ability of the coating. The salt spray test results show that the use of ultrafine talc powder (D50 ≈ 1 μ m) in the primer can reduce the corrosion propagation width at the scratch site by 30-50% compared to the use of medium particle size (D50 ≈ 10 μ m) primer.

4. Anti corrosion performance (especially in primer):

In addition to the physical shielding effect mentioned above, fine-grained talc powder can be more tightly packed around anti rust pigments (such as zinc phosphate), optimizing pigment stacking, increasing critical pigment volume concentration (CPVC), enhancing the synergistic shielding effect of the entire pigment filler system, and thus improving long-term anti-corrosion effect.

5. Process performance:

Dispersion: The smaller the particle size, the larger the specific surface area, the stronger the van der Waals forces between particles, the greater the tendency for agglomeration, and the higher the requirements for dispersion equipment (such as sand mills) and dispersants. Poor dispersion can lead to a decrease in the reading of fineness plates (such as Hegman fineness meters), affecting the final gloss and surface condition.

CPVC and Cost: Coarse particles typically have lower oil absorption, which helps to achieve higher CPVC, meaning that less resin base material can be used under the same volume filling, reducing formulation costs.

3、 Key considerations for application selection

Choosing the particle size of talc powder is not necessarily the finer the better, it requires a comprehensive consideration:

Coating functional requirements: Pursuing high gloss, delicate surface, and excellent shielding properties (such as topcoat and high-end anti-corrosion paint) → Preferred fine particle size (1-5 μ m) or even ultrafine powder; Focus on cost reduction, anti sagging, extinction or filling properties (such as primer, thick paste paint, architectural coatings) → Consider medium or coarse particle size.

Compatibility of resin system: For high viscosity resin systems, caution should be exercised when using ultrafine powders to prevent excessive viscosity; Low viscosity systems can better leverage the advantages of fine powders.

Dispersion ability and cost: The use of ultrafine powders requires the investment of more efficient dispersion equipment and suitable dispersants, which increases production costs.

Formula synergy effect: The particle size combination with other pigments and fillers (such as titanium dioxide, calcium carbonate, barium sulfate) is crucial to achieve the optimal stacking state and performance balance.

Conclusion

The particle size of talc powder is a powerful control lever in coating formulation design. From the cost-effectiveness and process friendliness brought by coarse particles to the high gloss, toughness, and excellent shielding provided by fine particles, talc powders of different particle sizes have their own advantages. Understanding the intrinsic mechanisms by which particle size affects rheology, optical properties, mechanical strength, corrosion resistance, and processability, and quantifying these effects through experimental data (such as significantly reducing settling rate, improving gloss and strength with fine powder), is the foundation for formulation designers to make precise material selection and performance optimization. The successful application lies in scientifically selecting the most suitable talc powder particle size and distribution based on the performance goals, resin characteristics, production process, and cost budget of specific coating products, in order to maximize their value and achieve the best balance of comprehensive coating performance. In the future, with the advancement of nanotechnology and surface modification technology, the application potential of ultrafine talc powder is expected to be further expanded in the field of higher performance and more intelligent coatings.