How it works:
The vacuum heating integrated coating machine is a composite sample preparation equipment that integrates vacuum environment control, precision coating and programmed heating and curing functions. Its core working principle is to create and maintain a low-pressure environment in a closed coating chamber through a built-in vacuum pump system. Coating operations in this environment can effectively reduce the formation and residue of bubbles in the coating liquid film. After the coating is completed, the equipment can seamlessly switch to the heating and curing mode, and the sample is accurately heat treated through the program temperature control system, which promotes chemical reactions such as cross-linking and polycondensation to form a uniform and dense curing coating. The high degree of automation of the whole process reduces the variables caused by human operation, and significantly improves the repeatability and reliability of sample preparation.
Sample Preparation Challenge
The film formation process of high-temperature curing coatings, such as certain epoxy coatings, ceramic-based coatings, and some high-performance polymer coatings, is not a simple solvent volatilization, but relies on irreversible chemical cross-linking reactions that occur at specific high temperatures, typically between 120°C and 300°C. The main challenges faced by this type of coating in laboratory sample preparation include: the mixing coating slurry is prone to entrapment of tiny bubbles, which are difficult to escape under conventional atmospheric pressure conditions and eventually form defects in the curing film; Secondly, the curing process requires strict accuracy of temperature profiles, and the control of heating rate, constant temperature time, and cooling process directly affects the final properties of the coating, such as adhesion, hardness, and chemical resistance. Traditional separate coating and oven curing processes are difficult to achieve consistent and precise control of the environment and process.
Sample preparation process
The application of vacuum heating integrated coating machine runs through the core link of high-temperature curing coating sample preparation. First, short-term vacuum pretreatment of the substrate can be performed before coating to remove the adsorbed gases on the surface. Then, automatic scraping or spinning is carried out in a vacuum environment, which minimizes the entrapment of air bubbles. Once the coating is complete, the preset curing procedure can be started directly in the same chamber without transferring the sample. Devices typically allow the user to set multiple temperature profiles, such as from room temperature to target curing temperature T at a controlled ratec, and keep time t, the relationship of which can be approximated to describe the degree of curing α the relationship with time with the following formula: α = 1 - exp(-k tnwhere k is the reaction rate constant, which follows the Arrhenius equation with temperature, and n is the reaction series. This integrated process ensures that the entire process, from wet to cured dry, is in a controlled environment, greatly reducing the risk of sample contamination and damage.
Process parameters
In order to obtain the ideal coating sample that meets the test standards, the key process parameters of the vacuum-heated all-in-one coater need to be systematically optimized. The main variables include vacuum level, coating speed (or rotational speed), curing temperature profile. These parameters need to be adjusted according to the rheological properties, solids content and curing kinetics of the coating. For example, for high-viscosity coatings, higher vacuum levels and lower initial coating speeds may be required to eliminate air bubbles. The curing temperature profile is set directly based on the technical data provided by the coating supplier or by the curing exothermic peak measured by differential scanning calorimetry. By designing experiments and evaluating the optical microscope morphology, thickness uniformity, and adhesion of the coating, a stable process window can be established.
| Key process parameters | Implications and considerations |
| Vacuum level | To affect the bubble removal efficiency, it is necessary to balance the defoaming effect with the volatilization of low boiling point components. |
| Coating speed/thickness | It determines the uniformity of wet film thickness and affects the final coating thickness and appearance. |
| Rate of warming | Affect the internal stress and leveling of the coating, and too fast may lead to defects. |
| Curing temperature and time | It determines the degree of cross-linking reaction and directly affects the hardness, resistance and other properties of the coating. |
| Cooling procedure | Controlling the cooling rate reduces coating cracking or peeling caused by thermal stress. |
Application Benefits:
The application advantages of this device are reflected in many aspects. It improves the quality of sample preparation, resulting in fewer bubbles, high uniformity, and good data reproducibility. Process integration reduces sample transfer steps, increases productivity, and reduces human error. Programmable controls enable traceability and repeatability of processes in line with laboratory quality management practices. However, there are also certain limitations to its application. The initial input cost of the equipment is relatively high. For coatings that require extremely high curing temperatures, it is necessary to confirm the long-term temperature resistance of the equipment cavity material. In addition, the effective coating area of the equipment is usually designed for laboratory sample sizes and is not suitable for large-scale or special-shaped workpiece preparation.
Epilogue
Vacuum heating all-in-one coating machines provide an efficient and reliable solution for laboratory sample preparation of high-temperature curing coatings. By integrating vacuum defoaming and programmed heating and curing functions, it effectively copes with the key technical difficulties in the preparation of such coatings, and lays a solid foundation for accurate coating performance detection and evaluation in the future. With the continuous development of materials science, the demand for the functional integration of this equipment and the intelligent control of process parameters will also be further deepened.
References
Wang Jianguo, Li Hua. Coating Preparation Technical Manual. Beijing: Chemical Industry Press, 2018.
ASTM D823-18， Standard Practices for Producing Films of Uniform Thickness of Paint， Varnish， and Related Products on Test Panels.
ISO 15184:2020， Paints and varnishes — Determination of film thickness.
Coating Process Editorial Board. Coating Process (4th Edition). Beijing: Chemical Industry Press, 2009.