Overview
Orally dissolving film is a film formulation molded by the coating process. During its preparation, the liquid mixture containing the film-forming material is evenly applied to the surface of the substrate through the coating machine, and then the solvent is removed through the drying process to form a solid film. The key to this process is to achieve uniform distribution and controlled drying of the coating solution on the substrate to obtain film products with uniform thickness and stable mechanical properties.
How it works:
The coating machine is usually composed of a coating head, a substrate conveying system, a drying unit and a winding device. The coating head applies a predetermined amount of coating solution to the moving substrate, controlling the wet film thickness through mechanisms such as scrapers or slits. The coating uniformity is affected by factors such as coating speed, coating gap, coating solution viscosity and surface tension. The drying unit mostly adopts hot air or infrared drying method with segmented temperature control, so that the solvent gradually volatilizes and avoids crusty or bubbles on the surface of the film.
The relationship between coating thickness (H) and coating liquid volume (V), coating width (W) and coating length (L) can be expressed as:
H = V / (W × L)
The volatilization rate of solvents during drying can be roughly described by the following relationship:
dm/dt = -k × A × (C_s - C_a)
dm/dt is the volatile mass of solvent per unit time, k is the mass transfer coefficient, A is the surface area, C_s is the surface solvent concentration, and C_a is the ambient solvent concentration.
Drying process control
The drying process is divided into two stages: constant speed drying and slow drying. In the constant speed stage, the solvent volatilizes freely from the surface of the film, and the drying rate is relatively stable. In the deceleration stage, the solvent needs to diffuse from the inside of the film to the surface, and the drying rate gradually decreases. Drying temperature, wind speed, humidity and film thickness all affect the drying efficiency and final product properties. Drying too quickly can lead to surface defects, while too slow can cause component migration or crystallization.
Film performance evaluation
The dried and formed film undergoes a number of performance tests to ensure that it meets the application requirements. The main evaluation indicators included thickness uniformity, mechanical strength, disintegration time and content uniformity. These indicators are closely related to the coating process parameters and drying conditions.
| Thickness deviation | Less than 5% |
| Tensile strength | Greater than 2 megapascals |
| Disintegration time | within 30 seconds |
| Content uniformity | The relative standard deviation is less than three percent |
Process optimization direction
In order to improve the quality of the film, process optimization can be started from two aspects: coating solution formulation and process parameters. Adjusting the ratio of film-forming material to plasticizer can improve the flexibility of the film. Optimizing the solvent system can affect the drying behavior and final film structure. In terms of process parameters, the influence of coating speed, drying temperature and other variables on film properties is systematically studied through experimental design methods, which helps to determine a robust process window.
Summary
The coating and drying molding of oral dissolving film is a comprehensive process involving fluid mechanics, heat and mass transfer, and materials science. By precisely controlling the coating uniformity and drying kinetics, you can obtain a film product of consistent quality. Continuously focusing on the correlation between process parameters and film properties is positive for efficient and controllable production.
References
1. The overview of coating process refers to the description of the principle of coating machine in the review of film preparation technology.
2. The key points of drying process control section cites technical articles on drying kinetics of polymer solutions.
3. The film performance evaluation index is partly based on the quality requirements of the film preparation in the relevant industry standards.