Laser particle size analyzer analyzes particle size distribution of paint pigments.

In the coatings industry, the particle size and distribution of pigments are key parameters that determine the optical properties, rheological properties and stability of coatings. Laser particle size analysis technology has become the core method of particle size characterization in this field due to its advantages of non-contact, high precision and fast statistics. Its rationale is based on the phenomenon of laser scattering by particles: when a monochromatic laser beam passes through a well-dispersed pigment suspension, the particles produce scattered light at a specific angle depending on their size. The volume size distribution of the particle group can be calculated by capturing the intensity of these scattered light and its angular distribution by multiple detectors, and mathematically inverting it based on the Mie scattering theory or Franchofer approximation theory.

Principles and data models

The core of data processing for laser particle size meters is to convert the distribution of scattered light energy into a particle size distribution. Particles are usually assumed to be spherical, fitted using a light scattering model. For pigment particles, their refractive index is a key input parameter. Volumetric frequency distribution D_vThe relationship between the instrumentally measured light intensity distribution I (θ) and the theoretical model F (D, θ, m) is fitted to find the most likely particle size distribution through iterative algorithms such as non-negative least squares methods.

Common characterization parameters include: D₁₀, D₅₀(median diameter), D₉₀, and span (Span), which is calculated as Span = (D₉₀ - D₁₀) / D₅₀。 The span value can be used to visually evaluate the width of the distribution.

Sample preparation

Reliable data is obtained if the sample is representative and well dispersed. Typical steps include: taking a sample from a batch of coatings and diluting them using a suitable dispersion medium such as deionized water or organic solvents; If necessary, dispersants are added and aggregates are destroyed by mechanical agitation or sonication. The dispersion process avoids excessive energy input leading to particle fragmentation. The uniform suspension is introduced into the instrument circulation cell, ensuring that the concentration is within the recommended shading rate range of the instrument to ensure the signal-to-noise ratio of the scattered signal.

Effect of particle size distribution on coating properties

The particle size distribution of pigments directly affects the final application performance of the coating. A narrower distribution usually helps improve coverage, tint strength, and gloss. while a wide distribution may affect the stability of the system, leading to settlement or flocculation. For example, in anti-corrosion coatings, the particle size-to-diameter-to-thickness ratio distribution of flake pigments (such as mica iron oxide) is crucial for forming a dense barrier layer. Analytical data provides quantitative basis for recipe optimization and process control.

Standard reference

In the actual analysis, attention should be paid to model selection (e.g., Mies' theory requires the complex refractive index of known particles and dispersed media), background subtraction and instrument calibration. Measurements should follow relevant standard methods, such as ISO 13320, which regulates the general process of laser diffraction. For specific coating systems, industry internal standards may have more detailed regulations on dispersion media and pretreatment. Repeated measurement and statistics are necessary to ensure the reproducibility of results.

Typical data

Through systematic analysis, laser particle size analyzers provide objective and quantitative data on pigment particle size distribution for coating R&D and quality control, which helps to understand the correlation between microstructure and macroscopic performance and promote product performance improvement.