Definition
A laboratory rotary coater is an instrument used to prepare uniform films on the surface of a flat substrate. It diffuses the liquid material coated on the substrate and forms a controllable thickness of the coating through the centrifugal force generated by the high-speed rotation. The equipment is widely used in research and development in the fields of materials science, electronic engineering, optics, and chemical engineering.
How it works:
Rotary coating is based on a hydrodynamic process under the action of centrifugal force. During operation, an appropriate amount of liquid droplets are added to the center of the substrate, and then the substrate rotates at high speed. During rotation, the liquid is spread outward under centrifugal force, and the solvent volatilizes at the same time, eventually forming a uniform film. The film thickness is mainly affected by the rotation speed, acceleration, rotation time and liquid properties, and the relationship can be roughly described by empirical formulas:h = kω-α, among themhis the film thickness,ωis the angular velocity,kWithαis a parameter related to the properties of the liquid.
Measurement method
Coating thickness measurement is usually done using non-contact optical methods, such as ellipsometry or interferometry. Ellipsic polarization method calculates film thickness and refractive index by analyzing the phase and amplitude changes of polarized light reflected on the surface of the film. The interference law uses the interference fringe spacing generated by the reflection of light at the upper and lower interfaces of the film to calculate the thickness. For routine quality control, a step meter can also be used for contact measurement, but care must be taken to avoid damaging the soft film.
Influencing factors
The uniformity and thickness of the film are affected by multiple factors. The rotation parameters include initial acceleration, steady-state speed and rotation time; Acceleration affects the initial spreading behavior of the liquid, and the rotational speed and time together determine the final thickness. Liquid properties such as viscosity, surface tension and solvent volatilization rate have significant effects on the formation of the film layer. When viscosity is high, the rotational speed needs to be increased appropriately to obtain a uniform coating. Environmental conditions such as temperature and humidity may change the volatilization kinetics of solvents, which in turn affects the morphology of the film. The surface cleanliness and flatness of the substrate are also the prerequisites for ensuring the quality of the coating.
Applications:
In photovoltaic research, it is used to prepare photoabsorbing layers or electrode coatings for solar cells. In the field of electronics, it can be used for photoresist coating and insulation preparation of semiconductor wafers. In the manufacture of optical components, it is used to plate anti-reflective or filter films. In materials science research, it is often used to prepare polymer films and nanocomposite coatings. In addition, it is also widely used in flat panel display, sensor manufacturing, and surface treatment.
Key points of selection
Higher speed can help with thinner coatings and precision speed control. The acceleration adjustment function helps to optimize the spreading process of liquids of different viscosities. The chuck design should be compatible with a wide range of substrate sizes and shapes, and should provide reliable vacuum adsorption. The equipment should provide programmable operating modes that make it easy to save and recall process parameters. Safety features include splash guards, emergency stops, etc. For special environmental needs, models with integrated atmosphere control or heating modules can be considered. Ease of maintenance and technical support from the manufacturer are also considerations for long-term use.