A wire rod applicator is a laboratory tool used to prepare uniform wet film coatings on flat substrates and is widely used in the sample preparation process in the coatings, inks, and printing industries. Its core principle is to transfer and control the thickness of the coated liquid as it rolls on the surface of the substrate through a wound wire with a specific diameter or a metal rod with carved grooves. The thickness of the coated wet film is mainly determined by the winding gap or groove depth of the wire rod, which is theoretically related to the wire rod diameter and the winding wire diameter. For the winding wire rod, the wet film thickness can be approximated by the formula:
h ≈ (D₁ - D₂) / 2
Among them, h is the thickness of the wet film, D₁ is the outer diameter of the winding steel wire, and D₂ is the diameter of the wire rod mandrel. In practical application, the final dry film thickness also needs to consider the volumetric solids of the coating.
Industry Applications
In the coatings industry, wire rod applicators are used to prepare samples for testing the adhesion, hardness, gloss and weather resistance of paint films. By selecting different types of wire rods, a series of coatings with gradient thicknesses can be quickly obtained to evaluate the performance of coatings at different film thicknesses.
In the field of inks, especially in the R&D and quality inspection of printing inks, wire stick applicators are used to simulate the printing process on standard paper or plastic film to prepare a uniform ink layer. This helps evaluate the ink's color, coverage, drying properties, and abrasion resistance. When operating, pay attention to the consistency of coating speed and pressure to ensure comparable results.
In printing material testing, wire stick applicators can be used to prepare functional coating samples such as varnishes, primers, or special effects layers to study their compatibility with substrates and subsequent printability.
Operational points
To ensure reproducibility of sample preparation, the operation follows a standardized process. First, the substrate should be clean, level, and fixed horizontally. An appropriate amount of sample is placed at one end of the substrate and pulled through a single time at a constant speed and pressure using a wire rod to form a uniform wet film. The coating speed is usually recommended between 100 mm and 300 mm per second, subject to relevant product standards.
Environmental conditions such as temperature and humidity can affect the rheology and drying process of the coating, which in turn affects the uniformity of film formation. The viscosity of the coating solution is a key parameter, too high viscosity may lead to uneven coating, too low may cause sagging. The sample is usually pre-adjusted to the specified viscosity range according to the standard method.
The cleaning and maintenance of the wire rod itself is also crucial. Thoroughly clean with a suitable solvent immediately after each use to avoid affecting the accuracy of subsequent application after the residue dries.
Wire rod model selection
The wire rods are usually identified by numbers, and different numbers correspond to different theoretical wet film thicknesses. When choosing, it should be calculated in combination with the thickness of the target dry film and the solid content of the coating. The following table lists some common wire rod models and their typical application film thickness ranges for reference:
| Common models of wire rods | Typical wet film thickness range (microns) |
| Low grade (e.g. 3-20) | 6-45 |
| Winning bid number (e.g. 30-80) | 65-180 |
| High grade (e.g. above 100) | 220-450 |
Note: The actual thickness is affected by the operation, material and substrate, and it is recommended to calibrate through pre-test.
The use of wire rod applicator is stipulated in a number of domestic and foreign standards. For example, in coating testing, general method standards involving paint film preparation are often referred to. These standards set guiding requirements for substrate handling, coating environment, operating techniques, and equipment calibration. In printing ink testing, the standards focus more on coating methods and evaluation procedures on specific substrates. Laboratories should prioritize adopting or referencing these recognized standards when establishing internal methodologies to ensure that test results are reliable and comparable within the industry.
As a cost-effective and efficient laboratory coating tool, wire rod applicators play an important role in the standardized preparation of coatings, inks, and printing samples. The key to its application success lies in a deep understanding of instrument principles, strict control of operating variables, and adherence to relevant standard methods. Specification use provides a reliable and consistent sample basis for subsequent material property evaluation.