An oral film drying tunnel removes water or solvent from the coated film while helping the film reach its target properties without exposing the formulation to unnecessary thermal stress. A single temperature set point may not provide optimal conditions throughout the tunnel, because the film changes as drying progresses. Multi-zone control allows different sections of the tunnel to operate under different conditions. Aligned Machinery’s casting machines include controlled drying configurations, with the ZM-160 specifying a temperature range from room temperature to 100 C with +/-3 C tolerance.
The drying profile, and what each zone is for
- First zone – controlled evaporation. The wet film contains a higher amount of liquid at the beginning of the tunnel. The drying conditions can be adjusted to promote efficient evaporation while maintaining film quality and avoiding excessive surface drying.
- Middle zone – continued moisture removal. As the film becomes drier, moisture removal can become more dependent on diffusion and mass transfer within the film. Temperature and airflow can be adjusted according to the formulation and the required drying rate.
- Final zone – reaching the target condition. The later part of the tunnel brings the film closer to its target residual moisture and a condition suitable for subsequent handling, winding or further processing.
These stages are a simplified way to understand the drying profile. Actual drying behavior depends on the formulation, film thickness, solvent system, airflow, temperature, line speed and other process conditions.
Why heat-sensitive APIs may benefit from zone control
Reducing the temperature of the entire tunnel is one way to reduce thermal exposure, but it can also reduce the drying rate throughout the process. Multi-zone control provides another approach: drying conditions can be adjusted along the tunnel according to the changing moisture content of the film. Evaporation can also cause the temperature of a wet film to remain below the surrounding air temperature during part of the drying process. The actual temperature profile should still be developed based on the formulation and the thermal stability of the API.
Temperature control accuracy is an important equipment specification, but it does not by itself guarantee process reproducibility. Consistent results also depend on formulation, coating conditions, airflow, line speed, film thickness and other controlled process parameters.
Air, not only temperature
- Air velocity affects heat and mass transfer and can change the drying rate at a given temperature. It should therefore be considered as part of the drying process rather than treated as an independent setting.
- Air exchange helps remove evaporated moisture or solvent from the drying environment. The required air exchange depends on the formulation and drying system.
- Exhaust balance helps control the removal of moisture or solvent from the drying system while maintaining stable operating conditions around the web.
Research on ODF processing has identified drying temperature, air flow rate, drying time and wet film thickness as important process variables that can affect film quality attributes. This is why drying development should consider the combined effect of these parameters rather than temperature alone.
What to record
Depending on the process and control strategy, relevant records can include zone temperature set points and actual values, air flow or fan settings, line speed, drying time and residual moisture at the end of the drying process. Recording these parameters helps manufacturers understand how process changes affect the final film and supports consistent process control.
Equipment implications
Aligned Machinery was founded in 2004 and has more than 20 years of experience in pharmaceutical machinery manufacturing. The company has supplied equipment and production solutions to pharmaceutical companies in more than 100 countries and regions and has served more than 550 customers worldwide. Its product portfolio includes ODF production equipment and transdermal patch production equipment.
Aligned Machinery’s casting machines use controlled drying systems, with equipment specifications varying by model. For example, the ZM-160 Automatic Oral Thin Film Making Machine specifies built-in hot air drying and temperature control from room temperature to 100 C with +/-3 C tolerance. Other casting configurations use independent drying zones to allow the drying profile to be adjusted according to production requirements.
FAQ
Why does an ODF line use more than one drying zone?
Different parts of the drying tunnel can require different conditions as the film loses moisture. Multi-zone control allows the drying profile to be adjusted along the web rather than using one temperature set point throughout the tunnel.
How can multi-zone drying support heat-sensitive APIs?
Multi-zone control allows temperature conditions to be adjusted according to the drying requirements of the formulation. This can help balance moisture removal and thermal exposure, but the appropriate profile depends on the formulation, API stability and target residual moisture.
What temperature range and tolerance do Aligned Machinery casting machines provide?
The ZM-160 Automatic Oral Thin Film Making Machine specifies drying temperature control from room temperature to 100 C with a tolerance of +/-3 C. Other Aligned Machinery casting configurations have different specifications, so the applicable equipment model should be checked for the exact drying configuration.
Does air velocity affect ODF drying?
Yes. Air flow rate can affect drying behavior and film quality at a given temperature. It should therefore be considered together with temperature, line speed, formulation and other drying parameters when developing the process.
What should be recorded during ODF drying?
Depending on the process, relevant records can include zone temperature set points and actual values, air flow or fan settings, line speed, drying time and residual moisture. These data help relate process conditions to the target film properties.
References
[1] Aligned Machinery, “ZM-160 Automatic Oral Thin Film Making Machine.” https://www.odfsolution.com/zm-160-automatic-oral-thin-film-making-machine-product/
[2] Aligned Machinery, “ZM-340-2M Automatic Oral Thin Film Making Machine.” https://www.odfsolution.com/zm-340-2m-automatic-oral-thin-film-making-machine-product/
[3] Aligned Machinery, “Oral Disintegrating Films Line with Modular Design | ODF Production.” https://www.odfsolution.com/news/oral-disintegrating-films-line-with-modular-design-odf-production/
[4] Mazumder, S. et al., “Quality by Design approach for studying the impact of formulation and process variables on product quality of oral disintegrating films.” International Journal of Pharmaceutics, 2017. https://pubmed.ncbi.nlm.nih.gov/28549972/
Post time: Aug-27-2026