Equipment verification becomes the core of rectification: Explore the process verification logic of vacuum drying ovens from the inspection by the drug regulatory authority
Recently, the enterprise was inspected by the National Medical Products Administration during the on - site production verification. The proportion of non - conforming items in the equipment verification process exceeded 60%. Among them, the lack of parameter verification and non - standard design of the scheme for the vacuum drying oven were the most prominent problems. This key equipment used for the pretreatment of silicone rubber raw materials has its process effectiveness directly determining the product quality, and it has also become a "tough nut to crack" in this rectification.
I. The technological mission of the vacuum drying oven: Solve the "incurable bubble disease" of silicone rubber
The core of producing silicone rubber products (such as medical seals and electronic encapsulation adhesives) is the mixing of two components. When the base rubber and the curing agent are stirred in proportion, high-speed shearing will bring in a large amount of air. Some condensation-type silicone rubbers will also release trace amounts of low-molecular substances (such as ethanol) due to the reaction. Under the dual effects, dense micro-bubbles of 10 - 100 μm are formed inside the raw materials. If these bubbles are not completely removed, two fatal problems will arise:
Appearance rejection: After the product is formed, "bulges" or internal cavities will appear on the surface. If it is used in scenarios with high appearance requirements such as medical catheters and electronic component encapsulation, it will be directly judged as unqualified.
Performance failure: Bubbles can disrupt the continuity of the molecular chains of silicone rubber, causing the tensile strength and tear strength to decrease by 20% - 50%. If it is used in sealing scenarios (such as infusion set interfaces and equipment waterproof rings), it will pose a leakage risk, seriously violating the mandatory requirements of GMP for product safety.
Therefore, the core function of the vacuum drying oven is to reduce the gas solubility through a negative pressure environment (Henry's law: the lower the pressure, the lower the solubility of gas in the liquid), allowing the bubbles to rapidly aggregate, rise, and burst for discharge. This step is a "critical juncture" before the molding of silicone rubber, and the effectiveness of its process parameters must be verified and confirmed.
II. Two major control parameters of the vacuum drying oven: Dual requirements for accuracy and logic
To achieve effective defoaming, the core control factors of the vacuum drying oven are "vacuum degree" and "vacuum pumping time". The synergistic effect of the two directly determines the defoaming effect. The following details need to be clarified:
1. Vacuum degree: Strict control from "range" to "stability"
The vacuum range of the equipment is 0 to -0.1 MPa (corresponding to an absolute pressure of 100 kPa to 0 kPa). It is equipped with a digital vacuum pressure gauge (with a graduation value of 0.01 MPa and an error ≤ ±0.002 MPa). The pumping rate is controlled by adjusting the opening of the intake valve of the vacuum pump, and it will finally stabilize within the range of the target vacuum ±0.005 MPa (for example, if the target is -0.08 MPa, the actual fluctuation needs to be controlled between -0.075 and -0.085 MPa). The key logic here is: the timing must be started after the vacuum is stable. If the timing starts before the vacuum reaches the target, it is equivalent to "ineffective vacuum pumping", and the bubbles cannot be fully discharged (for example, at a vacuum of -0.05 MPa, the air solubility only decreases by 50%, and the bubble discharge efficiency is low).
2. Vacuum pumping time: Specifications from the "timing starting point" to "accuracy"
Since the device is not integrated with an automatic timing function, this time a high-precision stopwatch (with an accuracy of 0.1 seconds) is used for manual timing. However, the timing trigger conditions need to be strictly defined: Only when the display value of the digital pressure gauge remains stable within the target vacuum range for 30 seconds (to confirm that there is no leakage in the device) should the stopwatch be started - to avoid the situation of "insufficient effective time" caused by vacuum fluctuations (for example, if the actual stable time is only 10 seconds but the timing is counted as 30 seconds, the defoaming effect will be more than 30% worse).
III. Design of the verification scheme: Replace "empirical judgment" with "data logic"
To verify the synergistic effect of vacuum degree and time, an orthogonal test scheme with two factors and three levels is designed in this study. The core logic is "controlling variables, reducing errors, and simulating reality". The specific details are as follows:
1. Basis for the selection of factor levels
The plan focuses on the two core parameters that affect the defoaming effect. The reason for setting three levels is to cover the "boundary values" and "commonly used values" of the process.
Vacuum degree: Select -0.06 MPa (low vacuum, simulating the extreme situation of equipment failure or incorrect parameter setting), -0.08 MPa (commonly used vacuum, the current process parameters of the enterprise), and -0.1 MPa (ultimate vacuum, the highest negative pressure that the equipment can reach) — The absolute pressure differences at the three - level are significant (40 kPa → 20 kPa → 0 kPa), which is sufficient to observe the changes in the defoaming effect.
Vacuum pumping time: Select 30s (short time, simulating the operation when the production rhythm is tight), 45s (regular time), and 60s (long time, verifying whether excessive vacuum pumping will cause the loss of silicone rubber) - The time interval is 15 seconds. Compared with the reference time of 30 seconds, it is a 50% increase, which can effectively distinguish the difference in effects.
2. Three major measures for error control
To ensure the "repeatability" of the test results, three types of interfering variables need to be fixed:
Test materials: Select encapsulated titanium shell sections (with a volume 1.5 times that of conventional products) – the larger the volume, the greater the number of bubbles (an increase of approximately 40%), which can better simulate extreme conditions and verify the robustness of the scheme;
Operator: The operation should be carried out by skilled workers who have been engaged in silicone rubber pretreatment for more than 5 years to ensure that the filling amount (±5g) and stirring speed (300rpm ± 10rpm) are consistent each time and to avoid interference from human factors (for example, if the stirring speed is increased by 10%, the number of bubbles will increase by 20%).
Repeated experiments: Each level combination is repeated 3 times (for example, the combination of -0.06 MPa + 30 s is carried out in 3 batches), and the average value is taken as the result - Random errors are reduced through multiple repetitions (for example, the fluctuation of the number of bubbles in a single experiment is ±10%, and the fluctuation after averaging three times is ≤ ±5%).
3. Full-chain tracking of data records
Three types of data need to be recorded during the experiment to ensure the "traceability" of the results.
1. Result data: The number of bubbles in each batch of products (counted with a microscope with an accuracy of 0.01 mm, count the number of bubbles ≥ 0.1 mm, and take the average of 5 cross - sections) —— This is the core indicator for judging the defoaming effect.
2. Process data: Stable value of vacuum degree, actual timing (e.g., target is 30 seconds, actual is 29.8 seconds);
3. Environmental data: Laboratory temperature (23°C ± 2°C), humidity (50%RH ± 10%RH) —— Temperature will affect the viscosity of silicone rubber (when the temperature rises by 10°C, the viscosity drops by about 30%, and bubbles are easier to discharge). Humidity will affect the curing speed of condensation-type silicone rubber. The interference of these variables needs to be eliminated.
IV. Rationality of the plan and core questions to be confirmed
From the perspective of process logic and verification specifications, this plan has three "bonus points":
1. Focus on core factors: Directly target the two key parameters (vacuum degree and time) that affect the defoaming effect, avoiding the misunderstanding of "comprehensive coverage but unclear focus".
2. Control interfering variables: Ensure the "reliability" of test results by fixing materials, personnel, and the environment.
3. Data-driven analysis: It is planned to use analysis of variance (ANOVA) to quantify the influence degree of factors (for example, the contribution rate of vacuum degree to the number of bubbles is 60%, and that of time is 30%), rather than judging which is more important based on experience.
However, there are still two issues in the plan that need further confirmation:
Is the interval between factor levels sufficient?
The three levels of vacuum degree have an interval of 0.02 MPa, and the corresponding absolute pressure changes in a "halving" manner (40 kPa → 20 kPa → 0 kPa), with a relatively large relative difference. This is sufficient to observe the differences in the defoaming effect; a time interval of 15 seconds can also distinguish the effects. However, the following should be considered: Is it necessary to increase a lower vacuum degree (such as -0.04 MPa) or a longer time (such as 90 seconds) to verify the effect under the "extreme situation"? For example, can a vacuum degree of -0.04 MPa meet the defoaming requirements? Will 90 seconds lead to excessive volatilization of low - molecular substances in the silicone rubber (such as a loss rate exceeding 5%)?
Is there a missing key factor?
The current scheme does not include the viscosity of silicone rubber (the viscosity difference of base rubber in different batches may reach 10%) and the heating temperature of the drying oven (if heating is turned on, the temperature will accelerate the rise of bubbles). If there are viscosity fluctuations or heating requirements in the process, the verification of these factors needs to be supplemented to avoid "incomplete verification".
Conclusion: Thoughts on the Transition from "Problem Rectification" to "Process Upgrade"
The inspection by the drug regulatory authority is not "nit - picking", but rather forcing enterprises to shift from "experience - driven" to "data - driven". The validation plan for the vacuum drying oven, in essence, uses quantified parameters, controllable variables, and traceable data to prove that the equipment can stably produce products that meet the requirements. Subsequently, the effectiveness of the plan needs to be verified through experimental data. If it is found that the interval between factor levels is insufficient, it can be adjusted to four levels (for example, increasing the vacuum degree by - 0.05 MPa and the time by 75 seconds), or factors such as viscosity and temperature can be supplemented. Finally, an equipment validation document that is "repeatable, verifiable, and traceable" will be formed to completely resolve the non - conforming items in the inspection.
In short, the core of equipment verification is not to "go through the process", but to prove with scientific methods that "the equipment can do things correctly and stably" – this is also the underlying logic of the drug regulatory authority's inspection.