Operating steps of laboratory film coating machine
Laboratory coating machine is a precision instrument used to prepare uniform and controllable thickness coatings on substrates, which is widely used in R&D and quality inspection in coatings, inks, electronic materials and polymer films. Its core principle is to apply the sample to the surface of the substrate at a set speed and pressure through a precisely controlled scraper or coating stick. Standardized operation is the basis for obtaining reliable experimental results.
Preparation before operation
Before operation, it is necessary to ensure that the laboratory environment meets the requirements, usually controlled at 23±2°C and relative humidity of 50±5%. Operators should wear appropriate personal protective equipment. The main preparations are as follows:
First, check whether the parts of the coating machine are intact and clean, especially the coating knife edge should be free of defects and residues. Secondly, according to the experimental standard (e.g., GB/T 1727, ASTM D823) or research protocol, prepare the sample to be tested and the substrate of the appropriate size and material (e.g., glass plate, metal plate, polyester film). The sample should be thoroughly stirred well in advance and left to defoam. Finally, according to the target wet film thickness, the coating gap is calculated and set by formula. The common calculation formula is:
Wet film thickness ≈ (volume / (coating width × coating length)) × 1000
Among them, the thickness unit is micrometers (μm), the volume unit is milliliters (ml), and the length unit is millimeters (mm). This formula is suitable for ideal estimates of known sample solids and coating area, and the actual thickness is affected by the rheological properties of the sample.
Standard operating procedures
The standard operating process can be divided into three main stages: installation, coating, and cleaning, which need to be strictly implemented in order.
The first stage: installation and parameter setting。 The clean and dry substrate is flattened on the working platform of the film coating machine. Use a thickness gauge or feeler gauge to precisely adjust the gap between the applicator (e.g., scraper, wire rod) and the substrate to the target value. Pouring a sufficient, continuous amount of sample in front of the applicator. The coating speed is set according to the sample viscosity, and the typical speed range for medium and low viscosity samples is 5-50 mm/s.
The second stage: Perform the coating。 Start the applicator and the applicator scrapes over the sample at a constant speed to create a uniform wet film. The operation process should be smooth and non-stop. After the coating is completed, the coated substrate is immediately removed horizontally and cured or dried according to specified conditions (e.g., time, temperature and humidity).
The third stage: follow-up treatment。 Immediately after coating, clean the applicator and worktop with a suitable solvent (e.g., deionized water, ethanol, special cleaning agent) and a soft cloth to prevent sample curing residue. All components are homing and operating parameters and environmental conditions are recorded.
Common problems, cause analysis and treatment measures
During the coating process, problems such as uneven coating and defective coatings may be encountered. The following table lists common symptoms, possible causes, and treatment recommendations.
| FAQs | Possible causes and treatment measures |
| The coating has transverse streaks or uneven thickness | the coating knife edge is damaged or contaminated; The sample contains undispersed particles or bubbles. Treatment: Clean or replace the knife edge; Filter the sample or extend the defoaming time. |
| Coating edges are uneven or shrinkage | The surface of the substrate can be uneven or contaminated; The sample has poor wettability to the substrate. Treatment: Clean and possibly pre-treat the substrate; Adjust the surface tension of the sample or add a wetting agent. |
| The surface of the coating has pinholes or bubbles | Insufficient sample defoaming; The coating speed is too fast to get caught in the air. Treatment: Extend the defoaming time of the sample at rest; Reduce the coating speed appropriately. |
| The actual dry film thickness deviates greatly from the theoretical value | the coating gap is not set accurately; The sample solids content or solvent volatilization rate did not match the calculated assumptions. Treatment: Calibrate the coating gap; The solid content of the sample is measured and the influence of the environment on volatilization is considered. |
| The coating process has high resistance or poor scraping | the sample viscosity is too high; The coating gap is too small. Processing: Check whether the viscosity of the sample is within the applicable range of the instrument; Readjust to the appropriate clearance. |
Maintenance and calibration points
Regular maintenance and calibration are key to ensuring long-term stable operation and reproducible results of the coating machine. Routine maintenance mainly includes immediate cleaning after use. Regular maintenance is recommended to check the straightness and integrity of the coater knife edge every month, and check the smoothness of the transmission mechanism every quarter. The calibration work should be carried out according to the instrument manual or relevant work instructions, focusing on the consistency between the set value of the coating gap and the actual value, and the accuracy of the coating speed. Calibration intervals typically do not exceed 12 months, or at any time when there is a high frequency of use and there is doubt about the results. All maintenance and calibration activities should be documented.
Safety precautions
Safety must be paid attention to throughout the operation. Familiarize yourself with the material safety data sheet of the sample used, and handle volatile samples in a well-ventilated area. Use appropriate personal protective equipment when cleaning and avoid solvent contact with skin or inhalation. Make sure the instrument is well grounded and do not reach your hands or other objects when moving parts are running. In the event of sample leakage, it should be cleaned up immediately according to the chemical handling procedure.
References
GB/T 1727-1992, General preparation method of paint film.
ASTM D823-18， Standard Practices for Producing Films of Uniform Thickness of Paint, Varnish, and Related Products on Test Panels.
ISO 1514:2016， Paints and varnishes — Standard panels for testing.
General Technical Manual for Laboratory Coating Equipment.