Moisture Control in Soft Capsules

Generally, the moisture content of soft capsule shells should be maintained within the range of 8% to 12%. If the moisture level is too high, the finished capsule shells will become excessively soft and prone to mold growth; conversely, if the moisture level is too low, the shells will become brittle and susceptible to cracking, which is detrimental to storage and transportation. The primary factors influencing the drying efficacy of soft capsules are as follows:

① Environmental Temperature and Humidity
Changes in drying conditions significantly impact the drying rate of soft capsules. When the temperature of the drying environment is elevated, soft capsules dry more rapidly during the initial stages; however, during the later stages-as the surface of the capsule shell dries and hardens-internal moisture migration is impeded, resulting in a decline in the drying rate. Conversely, as environmental humidity decreases, the drying rate tends to accelerate. Under normal circumstances, environmental humidity should be maintained below 60%; otherwise, the capsules will be extremely difficult to dry.

② Drying Air Velocity
Increasing the air velocity within the drying environment enhances the rate of moisture transfer, thereby improving drying efficiency.

③ Drying Duration
Under conditions where environmental temperature and humidity are strictly controlled, the final moisture content of soft capsules is determined by the duration of the drying process. During the process investigation phase, samples of capsules dried for varying durations can be collected to determine the moisture content of the shells; a drying curve can then be plotted to establish the optimal drying endpoint.