Definition
A leveler is a laboratory testing instrument used to evaluate the ability of liquid materials such as coatings, inks, adhesives, etc., to flow autonomously from an initial irregular state to a flat and smooth state and eliminate traces after coating. The instrument quantifies the leveling properties of materials by simulating actual construction conditions, providing key data support for product development, quality control, and process optimization.
Principle
The core working principle of a leveler is based on the combination of fluid mechanics and optical or mechanical measurement techniques. The instrument is typically equipped with a standard comb tooth scraper for preparing a set of parallel groove-like coatings with regular spacing on the test substrate. The instrument then continuously monitors the evolution of the trench over time through built-in sensors, such as laser displacement sensors or high-resolution cameras. The coating, driven by surface tension, gradually flows towards the bottom of the trench and attempts to fill the trench, with contour height changes following the fluid spreading model. The leveling parameters of the material can be calculated by recording the time it takes for the trench depth to decay to a specific ratio, or by directly analyzing the rate of change in the curvature of the profile.
The leveling process can be simplified to the flow behavior dominated by the viscosity and surface tension of the material, and its dynamics can be described by the simplified relationship: the flow rate is directly proportional to the surface tension and inversely proportional to the viscosity. The specific relationship can refer to the following forms:
v ∝ γ / η
where v represents the flow rate, γ represents surface tension, and η represents viscosity. The actual analysis should be carried out in combination with the specific coating geometry model.
Measurement method
The standard measurement methods of leveling are mainly based on relevant international and national standards, such as ASTM D4062, GB/T 1750, etc. The typical operation process is as follows: First, the sample to be tested is placed in a constant temperature and humidity environment for state adjustment. Using the scraper supplied with the leveler, scrape on the prepared test plate at a constant speed and pressure, forming a set of parallel stripes with a known initial depth and spacing. The timing and automatic monitoring system is then activated immediately. The instrument collects contour data for the striped area at set intervals. The data processing software calculates the degree of streak disappearance or the time it takes to reach a specified flatness based on a standard algorithm, and finally outputs the result in the form of leveling level, leveling time, or leveling index. The entire measurement process requires strict control of ambient temperature, humidity, and scraping parameters to ensure data repeatability and comparability.
Influencing factors
The leveling properties of materials are affected by a combination of factors. In terms of intrinsic characteristics of materials, viscosity is the key factor. When the viscosity is low, the flow is good, which is conducive to leveling, but may cause sagging. Surface tension affects the spreading and wetting ability of liquids. Thixotropy and shear thinning behavior determine the viscosity recovery rate of the material after the construction shear force stops, which directly affects the duration of leveling. If the volatilization rate of a solvent or diluent is too fast, it can quickly increase viscosity, potentially interrupting the leveling process. In terms of external conditions, the thickness of the construction film directly affects the flow path and the amount of material migration. The surface energy, roughness and temperature of the substrate affect the wetting and adhesion of the coating, thereby changing the flow boundary conditions. Ambient temperature and humidity act on the leveling process by affecting solvent volatilization and material reactivity.
Applications
The application of levelers is found in a wide range of industries and R&D areas involving liquid coating materials. In the coatings industry, it is used to evaluate the final appearance of architectural coatings, industrial coatings, automotive coatings, etc., and guide resin selection, additive addition, and formulation optimization. In the field of ink manufacturing, it is used to test the spreading performance of printing inks on substrates to ensure the uniformity and clarity of printed patterns. In the adhesive and sealant industry, it is used to analyze the self-leveling ability of the surface after construction, which is valuable for the appearance and sealing effect of encapsulation or caulking. In addition, levelers are also used as an important quality control tool in the research and development of cosmetics (e.g. nail polish), some coatings for the food industry, and electronic materials (e.g. conductive pastes).
Instrument selection considerations
When choosing a leveler, it is necessary to conduct a comprehensive evaluation based on specific testing needs and standard requirements. The primary consideration is whether the measurement principle and accuracy of the instrument meet the requirements of relevant industry standards. The measurement range should be adapted to the expected leveling time and viscosity range of the sample to be tested. The degree of automation is an important factor, and highly automated instruments can reduce human operation errors and improve testing efficiency. The instrument's software analysis capabilities should be robust and compliant with standard algorithms, providing clear and compliant data reports. The size and material of the sample stage must be compatible with common test substrates. The ability to integrate environmental control modules, such as temperature-controlled platforms, is necessary for testing that requires stringent environmental conditions. In addition, the reliability and ease of maintenance, as well as the supplier's technical support and service capabilities, should also be included in the evaluation.